Multinary alloy electrodes for solid state batteries I. A phase diagram approach for the selection and storage properties determination of candidate electrode materials

NASA Astrophysics Data System (ADS)

Anani, A.; Huggins, R. A.

The desire to produce high specific energy rechargeable batteries has led to the investigation of ternary alloy systems for use as negative electrode components in lithium-based cells. The addition of a third component to a binary alloy electrode could result in a significant change in the thermodynamic and/or kinetic behavior of the electrode material, depending on the relevant phase diagram and the crystal structures of the phases present. The influence of ternary phase diagram characteristics upon the thermodynamic properties and specific energies of multi-component electrodes is discussed with lithiumsilicon-based systems as an illustration. It is shown that the electrode potentials (and thus specific energies of the ensuing cell) as well as the theoretical lithium capacities of electrodes based on these ternary alloy modifications can be significantly increased with respect to their present day binary counterpart.

Fine structure of Fe-Co-Ga and Fe-Cr-Ga alloys with low Ga content

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kleinerman, Nadezhda M., E-mail: kleinerman@imp.uran.ru; Serikov, Vadim V., E-mail: kleinerman@imp.uran.ru; Vershinin, Aleksandr V., E-mail: kleinerman@imp.uran.ru

2014-10-27

Investigation of Ga influence on the structure of Fe-Cr and Fe-Co alloys was performed with the use of {sup 57}Fe Mössbauer spectroscopy and X-ray diffraction methods. In the alloys of the Fe-Cr system, doping with Ga handicaps the decomposition of solid solutions, observed in the binary alloys, and increases its stability. In the alloys with Co, Ga also favors the uniformity of solid solutions. The analysis of Mössbauer experiments gives some grounds to conclude that if, owing to liquation, clusterization, or initial stages of phase separation, there exist regions enriched in iron, some amount of Ga atoms prefer to entermore » the nearest surroundings of iron atoms, thus forming binary Fe-Ga regions (or phases)« less

Phase-field crystal modeling of compositional domain formation in ultrathin films.

PubMed

Muralidharan, Srevatsan; Haataja, Mikko

2010-09-17

Bulk-immiscible binary systems often form stress-induced miscible alloy phases when deposited on a substrate. Both alloying and surface dislocation formation lead to the decrease of the elastic strain energy, and the competition between these two strain-relaxation mechanisms gives rise to the emergence of pseudomorphic compositional nanoscale domains, often coexisting with a partially coherent single phase. In this work, we develop a phase-field crystal model for compositional patterning in monolayer aggregates of binary metallic systems. We first demonstrate that the model naturally incorporates the competition between alloying and misfit dislocations, and quantify the effects of misfit and line tension on equilibrium domain size. Then, we quantitatively relate the parameters of the phase-field crystal model to a specific system, CoAg/Ru(0001), and demonstrate that the simulations capture experimentally observed morphologies.

An empirical relationship for homogenization in single-phase binary alloy systems

NASA Technical Reports Server (NTRS)

Unnam, J.; Tenney, D. R.; Stein, B. A.

1979-01-01

A semiempirical formula is developed for describing the extent of interaction between constituents in single-phase binary alloy systems with planar, cylindrical, or spherical interfaces. The formula contains two parameters that are functions of mean concentration and interface geometry of the couple. The empirical solution is simple, easy to use, and does not involve sequential calculations, thereby allowing quick estimation of the extent of interactions without lengthy calculations. Results obtained with this formula are in good agreement with those from a finite-difference analysis.

PLUTONIUM-CERIUM ALLOY

DOEpatents

Coffinberry, A.S.

1959-01-01

An alloy is presented for use as a reactor fuel. The binary alloy consists essentially of from about 5 to 90 atomic per cent cerium and the balance being plutonium. A complete phase diagram for the cerium--plutonium system is given.

Observing Tin-Lead Alloys by Scanning Electron Microscopy: A Physical Chemistry Experiment Investigating Macro-Level Behaviors and Micro-Level Structures

ERIC Educational Resources Information Center

Wang, Yue; Xu, Xinhua; Wu, Meifen; Hu, Huikang; Wang, Xiaogang

2015-01-01

Scanning electron microscopy (SEM) was introduced into undergraduate physical chemistry laboratory curriculum to help students observe the phase composition and morphology characteristics of tin-lead alloys and thus further their understanding of binary alloy phase diagrams. The students were captivated by this visual analysis method, which…

Processing, physical metallurgy and creep of NiAl + Ta and NiAl + Nb alloys. Ph.D. Thesis. Final Contractor Report

NASA Technical Reports Server (NTRS)

Pathare, Viren M.

1988-01-01

Powder processed NiAl + Ta alloys containing 1, 2, and 4.5 at percent tantalum and NiAl + Nb alloys containing 1 and 2 at percent niobium were developed for improved creep properties. In addition, a cast alloy with 5 at percent tantalum was also studied. Hot extrusion parameters for processing alloys with 1 and 2 at percent of tantalum or niobium were designed. The NiAl + 4.5 at percent Ta alloy could be vacuum hot pressed successfully, even though it could not be extruded. All the phases in the multiphase alloys were identified and the phase transformations studied. The Ni2AlTa in NiAl + 4.5 at percent Ta alloy transforms into a liquid phase above 1700 K. Solutionizing and annealing below this temperature gives rise to a uniform distribution of fine second phase precipitates. Compressive creep properties were evaluated at 1300 K using constant load and constant velocity tests. In the higher strain rate region single phase NiAl + 1 at percent Ta and NiAl + 1 at percent Nb alloys exhibit a stress exponent of 5 characteristic of climb controlled dislocation creep. In slower strain rate regime diffusional creep becomes important. The two phase alloys containing 2 to 5 at percent Ta and 2 at percent Nb show considerable improvement over binary NiAl and single phase alloys. Loose dislocation networks and tangles stabilized by the precipitates were found in the as crept microstructure. The cast alloy which has larger grains and a distribution of fine precipitates shows the maximum improvement over binary NiAl.

Formation of an amorphous phase and its crystallization in the immiscible Nb-Zr system by mechanical alloying

NASA Astrophysics Data System (ADS)

Al-Aqeeli, N.; Suryanarayana, C.; Hussein, M. A.

2013-10-01

Mechanical alloying of binary Nb-Zr powder mixtures was carried out to evaluate the formation of metastable phases in this immiscible system. The milled powders were characterized for their constitution and structure by X-ray diffraction and transmission electron microscopy methods. It was shown that an amorphous phase had formed on milling the binary powder mixture for about 10 h and that it had crystallized on subsequent milling up to 50-70 h, referred to as mechanical crystallization. Thermodynamic and structural arguments have been presented to explain the formation of the amorphous phase and its subsequent crystallization.

Nonergodicity in binary alloys

NASA Astrophysics Data System (ADS)

Son, Leonid; Sidorov, Valery; Popel, Pjotr; Shulgin, Dmitry

2015-09-01

For binary liquids with limited miscibility of the components, we provide the corrections to the equation of state which arise from the nonergogic diffusivity. It is shown that these corrections result in lowering of critical miscibility point. In some cases, it may result in a bifurcation of miscibility curve: the mixtures near 50% concentration which are homogeneous at the microscopic level, occur to be too stable to provide a quasi - eutectic triple point. These features provide a new look on the phase diagrams of some binary systems. In present work, we discuss Ga-Pb, Fe-Cu, and Cu-Zr alloys. Our investigation corresponds their complex behavior in liquid state to the shapes of their phase diagrams.

Defining a Materials Database for the Design of Copper Binary Alloy Catalysts for Electrochemical CO2 Conversion.

PubMed

Lee, Chan Woo; Yang, Ki Dong; Nam, Dae-Hyun; Jang, Jun Ho; Cho, Nam Heon; Im, Sang Won; Nam, Ki Tae

2018-01-24

While Cu electrodes are a versatile material in the electrochemical production of desired hydrocarbon fuels, Cu binary alloy electrodes are recently proposed to further tune reaction directionality and, more importantly, overcome the intrinsic limitation of scaling relations. Despite encouraging empirical demonstrations of various Cu-based metal alloy systems, the underlying principles of their outstanding performance are not fully addressed. In particular, possible phase segregation with concurrent composition changes, which is widely observed in the field of metallurgy, is not at all considered. Moreover, surface-exposed metals can easily form oxide species, which is another pivotal factor that determines overall catalytic properties. Here, the understanding of Cu binary alloy catalysts for CO 2 reduction and recent progress in this field are discussed. From the viewpoint of the thermodynamic stability of the alloy system and elemental mixing, possible microstructures and naturally generated surface oxide species are proposed. These basic principles of material science can help to predict and understand metal alloy structure and, moreover, act as an inspiration for the development of new binary alloy catalysts to further improve CO 2 conversion and, ultimately, achieve a carbon-neutral cycle. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

PLUTONIUM-THORIUM ALLOYS

DOEpatents

Schonfeld, F.W.

1959-09-15

New plutonium-base binary alloys useful as liquid reactor fuel are described. The alloys consist of 50 to 98 at.% thorium with the remainder plutonium. The stated advantages of these alloys over unalloyed plutonium for reactor fuel use are easy fabrication, phase stability, and the accompanying advantuge of providing a means for converting Th/sup 232/ into U/sup 233/.

Effect of concentration dependence of the diffusion coefficient on homogenization kinetics in multiphase binary alloy systems

NASA Technical Reports Server (NTRS)

Tenney, D. R.; Unnam, J.

1978-01-01

Diffusion calculations were performed to establish the conditions under which concentration dependence of the diffusion coefficient was important in single, two, and three phase binary alloy systems. Finite-difference solutions were obtained for each type of system using diffusion coefficient variations typical of those observed in real alloy systems. Solutions were also obtained using average diffusion coefficients determined by taking a logarithmic average of each diffusion coefficient variation considered. The constant diffusion coefficient solutions were used as reference in assessing diffusion coefficient variation effects. Calculations were performed for planar, cylindrical, and spherical geometries in order to compare the effect of diffusion coefficient variations with the effect of interface geometries. In most of the cases considered, the diffusion coefficient of the major-alloy phase was the key parameter that controlled the kinetics of interdiffusion.

Kinetic Monte Carlo Simulations of Rod Eutectics and the Surface Roughening Transition in Binary Alloys

NASA Technical Reports Server (NTRS)

Bentz, Daniel N.; Betush, William; Jackson, Kenneth A.

2003-01-01

In this paper we report on two related topics: Kinetic Monte Carlo simulations of the steady state growth of rod eutectics from the melt, and a study of the surface roughness of binary alloys. We have implemented a three dimensional kinetic Monte Carlo (kMC) simulation with diffusion by pair exchange only in the liquid phase. Entropies of fusion are first chosen to fit the surface roughness of the pure materials, and the bond energies are derived from the equilibrium phase diagram, by treating the solid and liquid as regular and ideal solutions respectively. A simple cubic lattice oriented in the {100} direction is used. Growth of the rods is initiated from columns of pure B material embedded in an A matrix, arranged in a close packed array with semi-periodic boundary conditions. The simulation cells typically have dimensions of 50 by 87 by 200 unit cells. Steady state growth is compliant with the Jackson-Hunt model. In the kMC simulations, using the spin-one Ising model, growth of each phase is faceted or nonfaceted phases depending on the entropy of fusion. There have been many studies of the surface roughening transition in single component systems, but none for binary alloy systems. The location of the surface roughening transition for the phases of a eutectic alloy determines whether the eutectic morphology will be regular or irregular. We have conducted a study of surface roughness on the spin-one Ising Model with diffusion using kMC. The surface roughness was found to scale with the melting temperature of the alloy as given by the liquidus line on the equilibrium phase diagram. The density of missing lateral bonds at the surface was used as a measure of surface roughness.

Criteria for predicting the formation of single-phase high-entropy alloys

DOE PAGES

Troparevsky, M Claudia; Morris, James R..; Kent, Paul R.; ...

2015-03-15

High entropy alloys constitute a new class of materials whose very existence poses fundamental questions. Originally thought to be stabilized by the large entropy of mixing, these alloys have attracted attention due to their potential applications, yet no model capable of robustly predicting which combinations of elements will form a single-phase currently exists. Here we propose a model that, through the use of high-throughput computation of the enthalpies of formation of binary compounds, is able to confirm all known high-entropy alloys while rejecting similar alloys that are known to form multiple phases. Despite the increasing entropy, our model predicts thatmore » the number of potential single-phase multicomponent alloys decreases with an increasing number of components: out of more than two million possible 7-component alloys considered, fewer than twenty single-phase alloys are likely.« less

GPU-accelerated phase-field simulation of dendritic solidification in a binary alloy

NASA Astrophysics Data System (ADS)

Yamanaka, Akinori; Aoki, Takayuki; Ogawa, Satoi; Takaki, Tomohiro

2011-03-01

The phase-field simulation for dendritic solidification of a binary alloy has been accelerated by using a graphic processing unit (GPU). To perform the phase-field simulation of the alloy solidification on GPU, a program code was developed with computer unified device architecture (CUDA). In this paper, the implementation technique of the phase-field model on GPU is presented. Also, we evaluated the acceleration performance of the three-dimensional solidification simulation by using a single NVIDIA TESLA C1060 GPU and the developed program code. The results showed that the GPU calculation for 5763 computational grids achieved the performance of 170 GFLOPS by utilizing the shared memory as a software-managed cache. Furthermore, it can be demonstrated that the computation with the GPU is 100 times faster than that with a single CPU core. From the obtained results, we confirmed the feasibility of realizing a real-time full three-dimensional phase-field simulation of microstructure evolution on a personal desktop computer.

Microstructure and physical properties of bismuth-lead-tin ternary eutectic alloy

NASA Astrophysics Data System (ADS)

Kamal, M.; Moharram, B. M.; Farag, H.; El-Bediwi, A.; Abosheiasha, H. F.

2006-07-01

Using different experimental techniques, microstructure, electrical resistivity, attenuation coefficient, and mechanical and thermal properties of the quenched Bi-Pb-Sn ternary eutectic alloy have been investigated. From the X-ray analysis, Bi3Pb7 and Bi-Sn meta-stable phases are detected, in addition to rhombohedral bismuth and Sn body-centered tetragonal phases. This study also compared the physical properties of the Bi-Sn-Pb ternary eutectic alloys with the base binary Bi-Sn and Bi-Pb eutectic alloys.

Prediction of A2 to B2 Phase Transition in the High Entropy Alloy Mo-Nb-Ta-W

NASA Astrophysics Data System (ADS)

Huhn, William; Widom, Michael

2014-03-01

In this talk we show that an effective Hamiltonian fit with first principles calculations predicts an order/disorder transition occurs in the high entropy alloy Mo-Nb-Ta-W. Using the Alloy Theoretic Automated Toolset, we find T=0K enthalpies of formation for all binaries containing Mo, Nb, Ta, and W, and in particular we find the stable structures for binaries at equiatomic concentrations are close in energy to the associated B2 structure, suggesting that at intermediate temperatures a B2 phase is stabilized in Mo-Nb-Ta-W. Our ``hybrid Monte Carlo/molecular dynamics'' results for the Mo-Nb-Ta-W system are analyzed to identify certain preferred chemical bonding types. A mean field free energy model incorporating nearest neighbor bonds will be presented, allowing us to predict the mechanism of the order/disorder transition. We find the temperature evolution of the system is driven by strong Mo-Ta bonding. Comparison of the free energy model and our MC/MD results suggest the existence of additional low-temperature phase transitions in the system likely ending with phase segregation into binary phases. We would like to thank DOD-DTRA for funding this research under contract number DTRA-11-1-0064.

Phase Segregation Behavior of Two-Dimensional Transition Metal Dichalcogenide Binary Alloys Induced by Dissimilar Substitution

DOE PAGES

Susarla, Sandhya; Kochat, Vidya; Kutana, Alex; ...

2017-08-15

Transition metal dichalcogenide (TMD) alloys form a broad class of two-dimensional (2D) layered materials with tunable bandgaps leading to interesting optoelectronic applications. In the bottom-up approach of building these atomically thin materials, atomic doping plays a crucial role. Here we demonstrate a single step CVD (chemical vapor deposition) growth procedure for obtaining binary alloys and heterostructures by tuning atomic composition. We show that a minute doping of tin during the growth phase of the Mo 1–xW xS 2 alloy system leads to formation of lateral and vertical heterostructure growth. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) imagingmore » and density functional theory (DFT) calculations also support the modified stacking and growth mechanism due to the nonisomorphous Sn substitution. Our experiments demonstrate the possibility of growing heterostructures of TMD alloys whose spectral responses can be desirably tuned for various optoelectronic applications.« less

Biocompatibility of austenite and martensite phases in NiTi-based alloys

NASA Astrophysics Data System (ADS)

Danilov, A.; Kapanen, A.; Kujala, S.; Saaranen, J.; Ryhänen, J.; Pramila, A.; Jämsä, T.; Tuukkanen, J.

2003-10-01

The effect of surface phase composition on the biocompatibility of NiTi-based shape memory alloys was studied. The biocompatibility characteristics of parent β-phase (austenite) in binary NiTi and of martensite in ternary NiTiCu alloys after similar surface mechanical treatment were compared. The martensitic phase as a result of surface mechanical treatment (strain-induced martensite) was shown to decrease the biocompatibility of material in comparison to fully austenite state. The cytotoxicity (amount of dead cells / 1000 cells) and cell attachent (paxillin count / frame) were found to be linear functions of structural stresses in austenite.

Prediction of novel alloy phases of Al with Sc or Ta

PubMed Central

Bilić, Ante; Gale, Julian D.; Gibson, Mark A.; Wilson, Nick; McGregor, Kathie

2015-01-01

Using the evolutionary optimization algorithm, as implemented in the USPEX crystal predictor program, and first principles total energy calculations, the compositional phase diagrams for Al-Sc and Al-Ta alloy systems at zero temperature and pressure have been calculated. In addition to the known binary intermetallic phases, new potentially stable alloys, AlSc3 and AlTa7, have been identified in the Al-poor region of the phase diagram. The dynamic and thermal stability of their lattices has been confirmed from the calculated vibrational normal mode spectra in the harmonic approximation. PMID:25950915

Phase Composition and Hardening of Castable Al - Ca - Ni - Sc Alloys Containing 0.3% Sc

NASA Astrophysics Data System (ADS)

Belov, N. A.; Naumova, E. A.; Bazlova, T. A.; Doroshenko, V. V.

2017-05-01

The phase composition of aluminum alloys of the Al - Ca - Ni - Sc system containing 0.3 wt.% Sc is studied. It is shown that the aluminum solid solution may be in equilibrium not only with binary phases (Al4Ca, Al3Sc and Al3Ni) but also with a ternary Al9NiCa compound. The temperature of attainment of maximum hardening due to precipitation of nanoparticles of phase Al3Sc is determined for all the alloys studied. Principal possibility of creation of castable alloys based on an (Al) + Al4Ca + Al9NiCa eutectic, the hardening heat treatment of which does not require quenching, is substantiated.

Nial and Nial-Based Composites Directionally Solidified by a Containerless Zone Process. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Joslin, Steven M.

1995-01-01

A containerless electromagnetically levitated zone (CELZ) process has been used to directionally solidify NiAl and NiAl-based composites. The CELZ processing results in single crystal NiAl (HP-NiAl) having higher purity than commercially pure NiAl grown by a modified Bridgman process (CP-NiAl). The mechanical properties, specifically fracture toughness and creep strength, of the HP-NiAl are superior to binary CP-NiAl and are used as a base-line for comparison with the composite materials subsequently studied. Two-phase composite materials (NiAl-based eutectic alloys) show improvement in room temperature fracture toughness and 1200 to 1400 K creep strength over that of binary HP-NiAl. Metallic phase reinforcements produce the greatest improvement in fracture toughness, while intermetallic reinforcement produces the largest improvement in high temperature strength. Three-phase eutectic alloys and composite materials were identified and directionally solidified with the intent to combine the improvements observed in the two-phase alloys into one alloy. The room temperature fracture toughness and high temperature strength (in air) serve as the basis for comparison between all of the alloys. Finally, the composite materials are discussed in terms of dominant fracture mechanism observed by fractography.

Martensitic transformation and phase diagram in ternary Co-V-Ga Heusler alloys

NASA Astrophysics Data System (ADS)

Xu, Xiao; Nagashima, Akihide; Nagasako, Makoto; Omori, Toshihiro; Kanomata, Takeshi; Kainuma, Ryosuke

2017-03-01

We report the martensitic transformation behavior in Co-V-Ga Heusler alloys. Thermoanalysis and thermomagnetization measurements were conducted to observe the martensitic transformation. By using a transmission electron microscope and an in situ X-ray diffractometer, martensitic transformation was found to occur from the L21 Heusler parent phase to the D022 martensite phase. Phase diagrams were determined for two pseudo-binary sections where martensitic transformation was detected. Magnetic properties, including the Curie temperatures and spontaneous magnetization of the parent phase, were also investigated. The magnetic properties showing behaviors different from those of NiMn-based alloys were found.

The surface-induced spatial-temporal structures in confined binary alloys

NASA Astrophysics Data System (ADS)

Krasnyuk, Igor B.; Taranets, Roman M.; Chugunova, Marina

2014-12-01

This paper examines surface-induced ordering in confined binary alloys. The hyperbolic initial boundary value problem (IBVP) is used to describe a scenario of spatiotemporal ordering in a disordered phase for concentration of one component of binary alloy and order parameter with non-linear dynamic boundary conditions. This hyperbolic model consists of two coupled second order differential equations for order parameter and concentration. It also takes into account effects of the “memory” on the ordering of atoms and their densities in the alloy. The boundary conditions characterize surface velocities of order parameter and concentration changing which is due to surface (super)cooling on walls confining the binary alloy. It is shown that for large times there are three classes of dynamic non-linear boundary conditions which lead to three different types of attractor’s elements for the IBVP. Namely, the elements of attractor are the limit periodic simple shock waves with fronts of “discontinuities” Γ. If Γ is finite, then the attractor contains spatiotemporal functions of relaxation type. If Γ is infinite and countable then we observe the functions of pre-turbulent type. If Γ is infinite and uncountable then we obtain the functions of turbulent type.

First principles study of surface stability and segregation of PdRuRh ternary metal alloy system

NASA Astrophysics Data System (ADS)

Aspera, Susan Meñez; Arevalo, Ryan Lacdao; Nakanishi, Hiroshi; Kasai, Hideaki

2018-05-01

The recognized importance on the studies of alloyed materials is due to the high possibility of forming designer materials that caters to different applications. In any reaction and application, the stability and configuration of the alloy combination are important. In this study, we analyzed the surface stability and segregation of ternary metal alloy system PdRuRh through first principles calculation using density functional theory (DFT). We considered the possibility of forming phases as observed in the binary combinations of elements, i.e., completely miscible, and separating phases. With that, the model we analyzed for the ternary metal alloy slabs considers forming complete atomic miscibility, segregation of each component, and segregation of one component with mixing of the two other. Our results show that for the ternary combination of Pd, Rh and Ru, the Pd atoms have high tendency to segregate at the surface, while due to the high tendency of Ru and Rh to mix, core formation of a mixed RuRh is possible. Also, we determined that the trend of stability in the binary alloy system is a good determinant of stability in the ternary alloy system.

The modelling of heat, mass and solute transport in solidification systems

NASA Technical Reports Server (NTRS)

Voller, V. R.; Brent, A. D.; Prakash, C.

1989-01-01

The aim of this paper is to explore the range of possible one-phase models of binary alloy solidification. Starting from a general two-phase description, based on the two-fluid model, three limiting cases are identified which result in one-phase models of binary systems. Each of these models can be readily implemented in standard single phase flow numerical codes. Differences between predictions from these models are examined. In particular, the effects of the models on the predicted macro-segregation patterns are evaluated.

Microstructure, Tensile Properties, and Corrosion Behavior of Die-Cast Mg-7Al-1Ca- xSn Alloys

NASA Astrophysics Data System (ADS)

Wang, Feng; Dong, Haikuo; Sun, Shijie; Wang, Zhi; Mao, Pingli; Liu, Zheng

2018-02-01

The microstructure, tensile properties, and corrosion behavior of die-cast Mg-7Al-1Ca- xSn ( x = 0, 0.5, 1.0, and 2.0 wt.%) alloys were studied using OM, SEM/EDS, tensile test, weight loss test, and electrochemical test. The experimental results showed that Sn addition effectively refined grains and intermetallic phases and increased the amount of intermetallic phases. Meanwhile, Sn addition to the alloys suppressed the formation of the (Mg,Al)2Ca phase and resulted in the formation of the ternary CaMgSn phase and the binary Mg2Sn phase. The Mg-7Al-1Ca-0.5Sn alloy exhibited best tensile properties at room temperature, while Mg-7Al-1Ca-1.0Sn alloy exhibited best tensile properties at elevated temperature. The corrosion resistance of studied alloys was improved by the Sn addition, and the Mg-7Al-1Ca-0.5Sn alloy presented the best corrosion resistance.

Phase-field model for isothermal phase transitions in binary alloys

NASA Technical Reports Server (NTRS)

Wheeler, A. A.; Boettinger, W. J.; Mcfadden, G. B.

1992-01-01

A new phase field model is described which models isothermal phase transitions between ideal binary alloy solution phases. Equations are developed for the temporal and spatial variation of the phase field, which describes the identity of the phase, and of the composition. An asymptotic analysis, as the gradient energy coefficient of the phase field becomes small, was conducted. From the analysis, it is shown that the model recovers classical sharp interface models of this situation when the interfacial layers are thin, and they show how to relate the parameters appearing in the phase field model to material and growth parameters in real systems. Further, three stages of temporal evolution are identified: the first corresponding to interfacial genesis which occurs very rapidly; the second to interfacial motion controlled by the local energy difference across the interface and diffusion; the last taking place on a long time scale in which curvature effects are important and which correspond to Ostwald ripening. The results of the numerical calculations are presented.

Structural, microstructural and thermal analysis of U-(6-x)Zr-xNb alloys (x = 0, 2, 4, 6)

NASA Astrophysics Data System (ADS)

Kaity, Santu; Banerjee, Joydipta; Parida, S. C.; Bhasin, Vivek

2018-06-01

Uranium-rich U-Zr-Nb alloy is considered as a good alternative fuel for fast reactors from the perspective of excellent dimensional stability and desired thermo-physical properties to achieve higher burnup. Detailed investigations related to the structural and microstructural characterization, thermal expansion, phase transformation, microhardness were carried out on U-6Zr, U-4Zr-2Nb, U-2Zr-4Nb and U-6Nb alloys (composition in wt%) where the total amount of alloying elements was restricted to 6 wt%. Structural, microstructural and thermal analysis studies revealed that these alloys undergo a series of transformations from high temperature bcc γ-phase to a variety of equilibrium and intermediate phases depending upon alloy composition, cooling rate and quenching. The structural analysis was carried out by Rietveld refinement. The data of U-Nb and U-Zr-Nb alloys have been highlighted and compared with binary U-Zr alloy.

An Undergraduate Experiment Using Differential Scanning Calorimetry: A Study of the Thermal Properties of a Binary Eutectic Alloy of Tin and Lead

ERIC Educational Resources Information Center

D'Amelia, Ronald P.; Clark, Daniel; Nirode, William

2012-01-01

An alloy is an intimate association of two or more metals, with or without a definite composition, which has metallic properties. Heterogeneous alloys, such as tin-lead (Sn/Pb) solders, consist of a mixture of crystalline phases with different compositions. A homogeneous alloy with a unique composition having the lowest possible melting point is…

Numerical Modeling of HgCdTe Solidification: Effects of Phase Diagram, Double-Diffusion Convection and Microgravity Level

NASA Technical Reports Server (NTRS)

Bune, Andris V.; Gillies, Donald C.; Lehoczky, Sandor L.

1997-01-01

Melt convection, along with species diffusion and segregation on the solidification interface are the primary factors responsible for species redistribution during HgCdTe crystal growth from the melt. As no direct information about convection velocity is available, numerical modeling is a logical approach to estimate convection. Furthermore influence of microgravity level, double-diffusion and material properties should be taken into account. In the present study, HgCdTe is considered as a binary alloy with melting temperature available from a phase diagram. The numerical model of convection and solidification of binary alloy is based on the general equations of heat and mass transfer in two-dimensional region. Mathematical modeling of binary alloy solidification is still a challenging numericial problem. A Rigorous mathematical approach to this problem is available only when convection is not considered at all. The proposed numerical model was developed using the finite element code FIDAP. In the present study, the numerical model is used to consider thermal, solutal convection and a double diffusion source of mass transport.

Effects of gravity reduction on phase equilibria. Part 1: Unary and binary isostructural solids

NASA Technical Reports Server (NTRS)

Larson, D. J., Jr.

1975-01-01

Analysis of the Skylab II M553 Experiment samples resulted in the hypothesis that the reduced gravity environment was altering the melting and solidification reactions. A theoretical study was conducted to define the conditions under which such alteration of phase relations is feasible, determine whether it is restricted to space processing, and, if so, ascertain which alloy systems or phase reactions are most likely to demonstrate such effects. Phase equilibria of unary and binary systems with a single solid phase (unary and isomorphous) were considered.

First-principles study of amorphous Ga4Sb6Te3 phase-change alloys

NASA Astrophysics Data System (ADS)

Bouzid, Assil; Gabardi, Silvia; Massobrio, Carlo; Boero, Mauro; Bernasconi, Marco

2015-05-01

First-principles molecular dynamics simulations within the density functional theory framework were performed to generate amorphous models of the Ga4Sb6Te3 phase change alloy by quenching from the melt. We find that Ga-Sb and Ga-Te are the most abundant bonds with only a minor amount of Sb-Te bonds participating to the alloy network. Ga and four-coordinated Sb atoms present a tetrahedral-like geometry, whereas three-coordinated Sb atoms are in a pyramidal configuration. The tetrahedral-like geometries are similar to those of the crystalline phase of the two binary compounds GaTe and GaSb. A sizable fraction of Sb-Sb bonds is also present, indicating a partial nanoscale segregation of Sb. Despite the fact that the composition Ga4Sb6Te3 lies on the pseudobinary Ga Sb -Sb2Te3 tie line, the amorphous network can be seen as a mixture of the two binary compounds GaTe and GaSb with intertwined elemental Sb.

High pressure study of Pu(0.92)Am(0.08) binary alloy.

PubMed

Klosek, V; Griveau, J C; Faure, P; Genestier, C; Baclet, N; Wastin, F

2008-07-09

The phase transitions (by means of x-ray diffraction) and electrical resistivity of a Pu(0.92)Am(0.08) binary alloy were determined under pressure (up to 2 GPa). The evolution of atomic volume with pressure gives detailed information concerning the degree of localization of 5f electronic states and their delocalization process. A quasi-linear V = f(P) dependence reflects subtle modifications of the electronic structure when P increases. The electrical resistivity measurements reveal the very high stability of the δ phase for pressures less than 0.7 GPa, since no martensitic-like transformation occurs at low temperature. Remarkable electronic behaviours have also been observed. Finally, resistivity curves have shown the temperature dependence of the phase transformations together with unexpected kinetic effects.

Phase-field-crystal study of solute trapping

NASA Astrophysics Data System (ADS)

Humadi, Harith; Hoyt, Jeffrey J.; Provatas, Nikolas

2013-02-01

In this study we have incorporated two time scales into the phase-field-crystal model of a binary alloy to explore different solute trapping properties as a function of crystal-melt interface velocity. With only diffusive dynamics, we demonstrate that the segregation coefficient, K as a function of velocity for a binary alloy is consistent with the model of Kaplan and Aziz where K approaches unity in the limit of infinite velocity. However, with the introduction of wavelike dynamics in both the density and concentration fields, the trapping follows the kinetics proposed by Sobolev [Phys. Lett. A10.1016/0375-9601(95)00084-G 199, 383 (1995)], where complete trapping occurs at a finite velocity.

Screening on binary Ti alloy with excellent mechanical property and castability for dental prosthesis application

PubMed Central

Li, H. F.; Qiu, K. J.; Yuan, W.; Zhou, F. Y.; Wang, B. L.; Li, L.; Zheng, Y. F.; Liu, Y. H.

2016-01-01

In the present study, the microstructure, mechanical property, castability, corrosion behavior and in vitro cytocompatibility of binary Ti–2X alloys with various alloying elements, including Ag, Bi, Ga, Ge, Hf, In, Mo, Nb, Sn and Zr, were systematically investigated, in order to assess their potential applications in dental field. The experimental results showed that all binary Ti‒2X alloys consisted entirely α–Ti phase. The tensile strength and microhardness of Ti were improved by adding alloying elements. The castability of Ti was significantly improved by separately adding 2 wt.% Bi, Ga, Hf, Mo, Nb, Sn and Zr. The corrosion resistance of Ti in both normal artificial saliva solution (AS) and extreme artificial saliva solution (ASFL, AS with 0.2 wt.% NaF and 0.3 wt.% lactic acid) has been improved by separately adding alloying elements. In addition, the extracts of studied Ti‒2X alloys produced no significant deleterious effect to both fibroblasts L929 cells and osteoblast-like MG63 cells, indicating a good in vitro cytocompatibility, at the same level as pure Ti. The combination of enhanced mechanical properties, castability, corrosion behavior, and in vitro cytocompatibility make the developed Ti‒2X alloys have great potential for future stomatological applications. PMID:27874034

Electrochemical synthesis of mesoporous Pt-Au binary alloys with tunable compositions for enhancement of electrochemical performance.

PubMed

Yamauchi, Yusuke; Tonegawa, Akihisa; Komatsu, Masaki; Wang, Hongjing; Wang, Liang; Nemoto, Yoshihiro; Suzuki, Norihiro; Kuroda, Kazuyuki

2012-03-21

Mesoporous Pt-Au binary alloys were electrochemically synthesized from lyotropic liquid crystals (LLCs) containing corresponding metal species. Two-dimensional exagonally ordered LLC templates were prepared on conductive substrates from diluted surfactant solutions including water, a nonionic surfactant, ethanol, and metal species by drop-coating. Electrochemical synthesis using such LLC templates enabled the preparation of ordered mesoporous Pt-Au binary alloys without phase segregation. The framework composition in the mesoporous Pt-Au alloy was controlled simply by changing the compositional ratios in the precursor solution. Mesoporous Pt-Au alloys with low Au content exhibited well-ordered 2D hexagonal mesostructures, reflecting those of the original templates. With increasing Au content, however, the mesostructural order gradually decreased, thereby reducing the electrochemically active surface area. Wide-angle X-ray diffraction profiles, X-ray photoelectron spectra, and elemental mapping showed that both Pt and Au were atomically distributed in the frameworks. The electrochemical stability of mesoporous Pt-Au alloys toward methanol oxidation was highly improved relative to that of nonporous Pt and mesoporous Pt films, suggesting that mesoporous Pt-Au alloy films are potentially applicable as electrocatalysts for direct methanol fuel cells. Also, mesoporous Pt-Au alloy electrodes showed a highly sensitive amperometric response for glucose molecules, which will be useful in next-generation enzyme-free glucose sensors.

Mashing up metals with carbothermal shock

NASA Astrophysics Data System (ADS)

Skrabalak, Sara E.

2018-03-01

Different materials and the capabilities they enabled have marked the ages of civilization. For example, the malleable copper alloys of the Bronze Age provided harder and more durable tools. Most exploration of new alloys has focused on random alloys, in which the alloying metal sites have no metal preference. In binary and ternary metal systems, dissimilar elements do not mix readily at high concentrations, which has limited alloying studies to intermetallics (ordered multimetallic phases) and random alloys, in which minor components are added to a principal element. In 2004, crystalline metal alloys consisting of five or more principal elements in equal or nearly equal amounts (1, 2) were reported that were stabilized by their high configurational entropy. Unlike most random alloys, the “high-entropy” alloys (3, 4) reside in the centers of their multidimensional phase diagrams (see the figure, right). On page 1489 of this issue, Yao et al. (5) present an innovative and general route to high-entropy alloys that can mix up to eight elements into single-phase, size-controlled nanoparticles (NPs).

First-principles screening of structural properties of intermetallic compounds on martensitic transformation

NASA Astrophysics Data System (ADS)

Lee, Joohwi; Ikeda, Yuji; Tanaka, Isao

2017-11-01

Martensitic transformation with good structural compatibility between parent and martensitic phases are required for shape memory alloys (SMAs) in terms of functional stability. In this study, first-principles-based materials screening is systematically performed to investigate the intermetallic compounds with the martensitic phases by focusing on energetic and dynamical stabilities as well as structural compatibility with the parent phase. The B2, D03, and L21 crystal structures are considered as the parent phases, and the 2H and 6M structures are considered as the martensitic phases. In total, 3384 binary and 3243 ternary alloys with stoichiometric composition ratios are investigated. It is found that 187 alloys survive after the screening. Some of the surviving alloys are constituted by the chemical elements already widely used in SMAs, but other various metallic elements are also found in the surviving alloys. The energetic stability of the surviving alloys is further analyzed by comparison with the data in Materials Project Database (MPD) to examine the alloys whose martensitic structures may cause further phase separation or transition to the other structures.

High-Strength Nanotwinned Al Alloys with 9R Phase.

PubMed

Li, Qiang; Xue, Sichuang; Wang, Jian; Shao, Shuai; Kwong, Anthony H; Giwa, Adenike; Fan, Zhe; Liu, Yue; Qi, Zhimin; Ding, Jie; Wang, Han; Greer, Julia R; Wang, Haiyan; Zhang, Xinghang

2018-03-01

Light-weight aluminum (Al) alloys have widespread applications. However, most Al alloys have inherently low mechanical strength. Nanotwins can induce high strength and ductility in metallic materials. Yet, introducing high-density growth twins into Al remains difficult due to its ultrahigh stacking-fault energy. In this study, it is shown that incorporating merely several atomic percent of Fe solutes into Al enables the formation of nanotwinned (nt) columnar grains with high-density 9R phase in Al(Fe) solid solutions. The nt Al-Fe alloy coatings reach a maximum hardness of ≈5.5 GPa, one of the strongest binary Al alloys ever created. In situ uniaxial compressions show that the nt Al-Fe alloys populated with 9R phase have flow stress exceeding 1.5 GPa, comparable to high-strength steels. Molecular dynamics simulations reveal that high strength and hardening ability of Al-Fe alloys arise mainly from the high-density 9R phase and nanoscale grain sizes. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Durable pd-based alloy and hydrogen generation membrane thereof

DOEpatents

Benn, Raymond C.; Opalka, Susanne M.; Vanderspurt, Thomas Henry

2010-02-02

A durable Pd-based alloy is used for a H.sub.2-selective membrane in a hydrogen generator, as in the fuel processor of a fuel cell plant. The Pd-based alloy includes Cu as a binary element, and further includes "X", where "X" comprises at least one metal from group "M" that is BCC and acts to stabilize the .beta. BCC phase for stability during operating temperatures. The metal from group "M" is selected from the group consisting of Fe, Cr, Nb, Ta, V, Mo, and W, with Nb and Ta being most preferred. "X" may further comprise at least one metal from a group "N" that is non-BCC, preferably FCC, that enhances other properties of the membrane, such as ductility. The metal from group "N" is selected from the group consisting of Ag, Au, Re, Ru, Rh, Y, Ce, Ni, Ir, Pt, Co, La and In. The at. % of Pd in the binary Pd--Cu alloy ranges from about 35 at. % to about 55 at. %, and the at. % of "X" in the higher order alloy, based on said binary alloy, is in the range of about 1 at. % to about 15 at. %. The metals are selected according to a novel process.

Superconducting compounds and alloys research

NASA Technical Reports Server (NTRS)

Otto, G.

1975-01-01

Resistivity measurements as a function of temperature were performed on alloys of the binary material system In sub(1-x) Bi sub x for x varying between 0 and 1. It was found that for all single-phase alloys (the pure elements, alpha-In, and the three intermetallic compounds) at temperatures sufficiently above the Debye-temperature, the resistivity p can be expressed as p = a sub o T(n), where a sub o and n are composition-dependent constants. The same exponential relationship can also be applied for the sub-system In-In2Bi, when the two phases are in compositional equilibrium. Superconductivity measurements on single and two-phase alloys can be explained with respect to the phase diagram. There occur three superconducting phases (alpha-In, In2Bi, and In5Bi3) with different transition temperatures in the alloying system. The magnitude of the transition temperatures for the various intermetallic phases of In-Bi is such that the disappearance or occurrence of a phase in two component alloys can be demonstrated easily by means of superconductivity measurements.

Binary Colloidal Alloy Test-5: Compete

NASA Technical Reports Server (NTRS)

Frisken, Barbara J.; Bailey, Arthur E.; Weitz, David A.

2008-01-01

The Binary Colloidal Alloy Test - 5: Compete (BCAT-5-Compete) investigation will photograph andomized colloidal samples onboard the International Space Station (ISS) to determine their resulting structure over time. The use of EarthKAM software and hardware will allow the scientists to capture the kinetics (evolution) of their samples, as well as the final equilibrium state of each sample. BCAT-5-Compete will utilize samples 6 - 8 in the BCAT-5 hardware to study the competition between phase separation and crystallization, which is important in the manufacture of plastics and other materials.

First-principles prediction of stabilities and instabilities of compounds and alloys in the ternary B-As-P system

NASA Astrophysics Data System (ADS)

Ektarawong, A.; Simak, S. I.; Alling, B.

2017-07-01

We examine the thermodynamic stability of compounds and alloys in the ternary B-As-P system theoretically using first-principles calculations. We demonstrate that the icosahedral B12As2 is the only stable compound in the binary B-As system, while the zinc-blende BAs is thermodynamically unstable with respect to B12As2 and the pure arsenic phase at 0 K, and increasingly so at higher temperature, suggesting that BAs may merely exist as a metastable phase. On the contrary, in the binary B-P system, both zinc-blende BP and icosahedral B12P2 are predicted to be stable. As for the binary As-P system, As1 -xPx disordered alloys are predicted at elevated temperature—for example, a disordered solid solution of up to ˜75 at.% As in black phosphorus as well as a small solubility of ˜1 at.% P in gray arsenic at T =750 K, together with the presence of miscibility gaps. The calculated large solubility of As in black phosphorus explains the experimental syntheses of black-phosphorus-type As1 -xPx alloys with tunable compositions, recently reported in the literature. We investigate the phase stabilities in the ternary B-As-P system and demonstrate a high tendency for a formation of alloys in the icosahedral B12(As1 -xPx )2 structure by intermixing of As and P atoms at the diatomic chain sites. The phase diagram displays noticeable mutual solubility of the icosahedral subpnictides in each other even at room temperature as well as a closure of a pseudobinary miscibility gap around 900 K. As for pseudobinary BAs1 -xPx alloys, only a tiny amount of BAs is predicted to be able to dissolve in BP to form the BAs1 -xPx disordered alloys at elevated temperature. For example, less than 5% of BAs can dissolve in BP at T =1000 K. The small solubility limit of BAs in BP is attributed to the thermodynamic instability of BAs with respect to B12As2 and As.

Structural Stabilities of β-Ti Alloys Studied Using a New Mo Equivalent Derived from [ β/( α + β)] Phase-Boundary Slopes

NASA Astrophysics Data System (ADS)

Wang, Qing; Dong, Chuang; Liaw, Peter K.

2015-08-01

Structural stabilities of β-Ti alloys are generally investigated by an empirical Mo equivalent, which quantifies the stability contribution of each alloying element, M, in comparison to that of the major β-Ti stabilizer, Mo. In the present work, a new Mo equivalent (Moeq)Q is proposed, which uses the slopes of the boundary lines between the β and ( α + β) phase zones in binary Ti-M phase diagrams. This (Moeq)Q reflects a simple fact that the β-Ti stability is enhanced, when the β phase zone is enlarged by a β-Ti stabilizer. It is expressed as (Moeq)Q = 1.0 Mo + 0.74 V + 1.01 W + 0.23 Nb + 0.30 Ta + 1.23 Fe + 1.10 Cr + 1.09 Cu + 1.67 Ni + 1.81 Co + 1.42 Mn + 0.38 Sn + 0.34 Zr + 0.99 Si - 0.57 Al (at. pct), where the equivalent coefficient of each element is the slope ratio of the [ β/( α + β)] boundary line of the binary Ti-M phase diagram to that of the Ti-Mo. This (Moeq)Q is shown to reliably characterize the critical stability limit of multi-component β-Ti alloys with low Young's moduli, where the critical lower limit for β stabilization is (Moeq)Q = 6.25 at. pct or 11.8 wt pct Mo.

Effect of boundary heat flux on columnar formation in binary alloys: A phase-field study

NASA Astrophysics Data System (ADS)

Du, Lifei; Zhang, Peng; Yang, Shaomei; Chen, Jie; Du, Huiling

2018-02-01

A non-isothermal phase-field model was employed to simulate the columnar formation during rapid solidification in binary Ni-Cu alloy. Heat flux at different boundaries was applied to investigate the temperature gradient effect on the morphology, concentration and temperature distributions during directional solidifications. With the heat flux input/extraction from boundaries, coupling with latent heat release and initial temperature gradient, temperature distributions are significantly changed, leading to solute diffusion changes during the phase-transition. Thus, irregular columnar structures are formed during the directional solidification, and the concentration distribution in solid columnar arms could also be changed due to the different growing speeds and temperature distributions at the solid-liquid interfaces. Therefore, applying specific heat conditions at the solidifying boundaries could be an efficient way to control the microstructure during solidifications.

Embedded atom method potential for studying mechanical properties of binary Cu–Au alloys

NASA Astrophysics Data System (ADS)

Gola, Adrien; Pastewka, Lars

2018-07-01

We present an embedded atom method (EAM) potential for the binary Cu–Au system. The unary phases are described by two well-tested unary EAM potentials for Cu and Au. We fitted the interaction between Cu and Au to experimental properties of the binary intermetallic phases Cu3Au, CuAu and CuAu3. Particular attention has been paid to reproducing stacking fault energies in order to obtain a potential suitable for studying deformation in this binary system. The resulting energies, lattice constant, elastic properties and melting points are in good agreement with available experimental data. We use nested sampling to show that our potential reproduces the phase boundaries between intermetallic phases and the disordered face-centered cubic solid solution. We benchmark our potential against four popular Cu–Au EAM parameterizations and density-functional theory calculations.

Effects of chemical alternation on damage accumulation in concentrated solid-solution alloys

DOE PAGES

Ullah, Mohammad W.; Xue, Haizhou; Velisa, Gihan; ...

2017-06-23

Single-phase concentrated solid-solution alloys (SP-CSAs) have recently gained unprecedented attention due to their promising properties. To understand effects of alloying elements on irradiation-induced defect production, recombination and evolution, an integrated study of ion irradiation, ion beam analysis and atomistic simulations are carried out on a unique set of model crystals with increasing chemical complexity, from pure Ni to Ni 80Fe 20, Ni 50Fe 50, and Ni 80Cr 20 binaries, and to a more complex Ni 40Fe 40Cr 20 alloy. Both experimental and simulation results suggest that the binary and ternary alloys exhibit higher radiation resistance than elemental Ni. The modelingmore » work predicts that Ni 40Fe 40Cr 20 has the best radiation tolerance, with the number of surviving Frenkel pairs being factors of 2.0 and 1.4 lower than pure Ni and the 80:20 binary alloys, respectively. While the reduced defect mobility in SP-CSAs is identified as a general mechanism leading to slower growth of large defect clusters, the effect of specific alloying elements on suppression of damage accumulation is clearly demonstrated. This work suggests that concentrated solid-solution provides an effective way to enhance radiation tolerance by creating elemental alternation at the atomic level. The demonstrated chemical effects on defect dynamics may inspire new design principles of radiation-tolerant structural alloys for advanced energy systems.« less

Contributions of phase and structural transformations in multicomponent Al-Mg alloys to the linear and nonlinear mechanisms of anelasticity

NASA Astrophysics Data System (ADS)

Golovin, I. S.; Bychkov, A. S.; Mikhailovskaya, A. V.; Dobatkin, S. V.

2014-02-01

The effects of the processes of severe plastic deformation (SPD), recrystallization, and precipitation of the β phase in multicomponent alloys of the Al-5Mg-Mn-Cr and Al-(4-5%)Mg-Mn-Zn-Sc systems on the mechanisms of grain-boundary relaxation and dislocation-induced microplasticity have been studied in some detail. To stabilize the ultrafine-grained structure and prevent grain growth, dispersed Al-transition-metal particles, such as Al3Zr, Al6Mn, Al7Cr, Al6(Mn,Cr), Al18Cr2Mg3 have been used. We have special interest in alloys with additions of scandium, which forms compounds of the Al3Sc type and favors the precipitation of finer particles compared to the aluminides of other transition metals. After SPD, Al-(4-5%)Mg-Mn-Zr-Sc alloys exhibit an enhanced recrystallization temperature. The general features of the dislocation and grain-boundary anelasticity that have been established for the binary Al-Mg alloys are retained; i.e., (1) the decrease in the dislocation density in the process of recrystallization of cold-worked alloys leads to the formation of a pseudo-peak in the curves of the temperature dependences of internal friction (TDIF) and to a decrease in the critical amplitude of deformation corresponding to the onset of dislocation motion in a stress field; (2) the precipitation of the β phase suppresses the grain-boundary relaxation; (3) the dissolution of the β phase, the passage of the magnesium atoms into the solid solution, and the precipitation of the β' phase upon heating hinder the motion of dislocations; (4) the coarsening of the highly dispersed particles containing Zr and Sc increases the dislocation mobility. The grain-boundary relaxation and dislocation-impurity interaction and their temperature dependences, as well as processes of the additional alloying of the binary alloys by Mn, Cr, Zr, and Sc, have been estimated quantitatively.

Formation of the Fe-Containing Intermetallic Compounds during Solidification of Al-5Mg-2Si-0.7Mn-1.1Fe Alloy

NASA Astrophysics Data System (ADS)

Que, Zhongping; Wang, Yun; Fan, Zhongyun

2018-06-01

Iron (Fe) is the most common and the most detrimental impurity element in Al alloys due to the formation of Fe-containing intermetallic compounds (IMCs), which are harmful to mechanical performance of the Al-alloy components. In this paper we investigate the formation of Fe-containing IMCs during solidification of an Al-5Mg-2Si-0.7Mn-1.1Fe alloy under varied solidification conditions. We found that the primary Fe-containing intermetallic compound (P-IMC) in the alloy is the BCC α-Al15(Fe,Mn)3Si2 phase and has a polyhedral morphology with {1 1 0} surface termination. The formation of the P-IMCs can be easily suppressed by increasing the melt superheat and/or cooling rate, suggesting that the nucleation of the α-Al15(Fe,Mn)3Si2 phase is difficult. In addition, we found that the IMCs with a Chinese script morphology is initiated on the {1 0 0} surfaces of the P-IMCs during the binary eutectic reaction with the α-Al phase. Both the binary and ternary eutectic IMCs are also identified as the BCC α-Al15(Fe,Mn)3Si2 phase. Furthermore, we found that the Fe content increases and the Mn content decreases in the Fe-containing intermetallic compounds with the decrease of the formation temperature, although the sum of the Fe and Mn contents in all of the IMCs is constant.

Solute effects on deformation and fracture of beta brass

NASA Technical Reports Server (NTRS)

Shea, M. M.; Stoloff, N. S.

1973-01-01

It is shown that the ductility of several ternary beta brass alloys in air and in several liquid metals can be related to the operative slip and grain boundary relaxation processes. Nickel and manganese were chosen as alloying elements because they are expected to respectively enhance and suppress cross slip in beta brass. Single-phase binary and ternary beta brass alloys were used in both polycrystalline and single crystal form.

Au-Ge MEAM potential fitted to the binary phase diagram

NASA Astrophysics Data System (ADS)

Wang, Yanming; Santana, Adriano; Cai, Wei

2017-02-01

We have developed a modified embedded atom method potential for the gold-germanium (Au-Ge) binary system that is fitted to the experimental binary phase diagram. The phase diagram is obtained from the common tangent construction of the free energy curves calculated by the adiabatic switching method. While maintaining the accuracy of the melting points of pure Au and Ge, this potential reproduces the eutectic temperature, eutectic composition and the solubility of Ge in solid Au, all in good agreement with the experimental values. To demonstrate the self-consistency of the potential, we performed benchmark molecular dynamics simulations of Ge crystal growth and etching in contact with a Au-Ge liquid alloy.

Microstructure and mechanical properties of a single crystal NiAl alloy with Zr or Hf rich G-phase precipitates

NASA Technical Reports Server (NTRS)

Locci, I. E.; Noebe, R. D.; Bowman, R. R.; Miner, R. V.; Nathal, M. V.; Darolia, R.

1991-01-01

The possibility of producing NiAl reinforced with the G-phase (Ni16X6Si7), where X is Zr or Hf, has been investigated. The microstructure of these NiAl alloys have been characterized in the as-cast and annealed conditions. The G-phases are present as fine cuboidal precipitates (10 to 40 nm) and have lattice parameters almost four times that of NiAl. They are coherent with the matrix and fairly resistant to coarsening during annealing heat treatments. Segregation and nonuniform precipitate distribution observed in as-cast materials were eliminated by homogenization at temperatures near 1600 K. Slow cooling from these temperatures resulted in large plate shaped precipitates, denuded zones, and a loss of coherency in some of the large particles. Faster cooling produced a homogeneous fine distribution of cuboidal G-phase particles in the matrix. Preliminary mechanical properties for the Zr-doped alloy are presented and compared to binary single crystal NiAl. The presence of these precipitates appears to have an important strengthening effect at temperatures not less than 1000 K compared to binary NiAl single crystals.

A phase field model for segregation and precipitation induced by irradiation in alloys

NASA Astrophysics Data System (ADS)

Badillo, A.; Bellon, P.; Averback, R. S.

2015-04-01

A phase field model is introduced to model the evolution of multicomponent alloys under irradiation, including radiation-induced segregation and precipitation. The thermodynamic and kinetic components of this model are derived using a mean-field model. The mobility coefficient and the contribution of chemical heterogeneity to free energy are rescaled by the cell size used in the phase field model, yielding microstructural evolutions that are independent of the cell size. A new treatment is proposed for point defect clusters, using a mixed discrete-continuous approach to capture the stochastic character of defect cluster production in displacement cascades, while retaining the efficient modeling of the fate of these clusters using diffusion equations. The model is tested on unary and binary alloy systems using two-dimensional simulations. In a unary system, the evolution of point defects under irradiation is studied in the presence of defect clusters, either pre-existing ones or those created by irradiation, and compared with rate theory calculations. Binary alloys with zero and positive heats of mixing are then studied to investigate the effect of point defect clustering on radiation-induced segregation and precipitation in undersaturated solid solutions. Lastly, irradiation conditions and alloy parameters leading to irradiation-induced homogeneous precipitation are investigated. The results are discussed in the context of experimental results reported for Ni-Si and Al-Zn undersaturated solid solutions subjected to irradiation.

Elastic modulus of phases in Ti–Mo alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Wei-dong; Liu, Yong, E-mail: yonliu11@aliyun.com; Wu, Hong

2015-08-15

In this work, a series of binary Ti–Mo alloys with the Mo contents ranging from 3.2 to 12 at.% were prepared using non-consumable arc melting. The microstructures were investigated by X-ray diffraction and transmission electron microscope, and the elastic modulus was evaluated by nanoindentation testing technique. The evolution of the volume fractions of ω phase was investigated using X-ray photoelectron spectroscopy. The results indicated that the phase constitution and elastic modulus of the Ti–Mo alloys are sensitive to the Mo content. Ti–3.2Mo and Ti–8Mo alloys containing only α and β phases, respectively, have a low elastic modulus. In contrast, Ti–4.5Mo,more » Ti–6Mo, Ti–7Mo alloys, with different contents of ω phase, have a high elastic modulus. A simple micromechanical model was used to calculate the elastic modulus of ω phase (E{sub ω}), which was determined to be 174.354 GPa. - Highlights: • Ti–Mo alloys with the Mo contents ranging from 3.2 to 12 at.% were investigated. • XPS was used to investigate the volume fractions of ω phase. • The elastic modulus of Ti–Mo alloys is sensitive to the Mo content. • The elastic modulus of ω phase was determined to be 174.354 GPa.« less

Ternary phase equilibria in transition metal-boron-carbon-silicon systems. Part I. Related binary systems, Volume III. Systems Mo-B and W-B. Technical documentary report, 1 November 1964-1 June 1965

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rudy, E.; Windisch.

1965-07-01

On the basis of X-ray, melting point, metallographic, and differential thermoanalytical studies on molybdenum-boron and tungsten-boron alloys, constitution diagrams for both binary systems are presented. In the high temperature regions, the newly established phase diagrams differ significantly from previously reported systems. The results are discussed and compared with available literature data.

Liquid-liquid phase separation and core-shell structure of ternary Al-In-Sn immiscible alloys

NASA Astrophysics Data System (ADS)

Zhao, Degang; Bo, Lin; Wang, Lin; Li, Shanshan

2018-04-01

In this study, the liquid-liquid phase separation of four kinds of ternary immiscible Al-In-Sn melts was investigated with resistivity and thermodynamics method. The nonlinear changes in ρ-T and DSC curves of Al-In-Sn immiscible alloys above monotectic reaction temperature revealed the occurrence of liquid-liquid phase separation of Al-In-Sn melts. The monotectic temperature, liquid phase separation temperature and immiscible gap of ternary Al-In-Sn alloys were lower than those of binary Al-In alloy. With the Al content decreasing, the immiscible gap of Al-In-Sn alloy decreased. The composition of Al80In10Sn10, Al70In15Sn15, Al60In20Sn20 and Al50In25Sn25 was located in the immiscible zone of Al-In-Sn system. Due to the differences of Stokes effect, Marangoni convection and immiscible gap, the solidification morphology of four kinds of Al-In-Sn monotectic alloy was different. The core–shell structure of Al-In-Sn monotectic alloy can form within a certain range of composition.

NUMERICAL ANALYSES FOR TREATING DIFFUSION IN SINGLE-, TWO-, AND THREE-PHASE BINARY ALLOY SYSTEMS

NASA Technical Reports Server (NTRS)

Tenney, D. R.

1994-01-01

This package consists of a series of three computer programs for treating one-dimensional transient diffusion problems in single and multiple phase binary alloy systems. An accurate understanding of the diffusion process is important in the development and production of binary alloys. Previous solutions of the diffusion equations were highly restricted in their scope and application. The finite-difference solutions developed for this package are applicable for planar, cylindrical, and spherical geometries with any diffusion-zone size and any continuous variation of the diffusion coefficient with concentration. Special techniques were included to account for differences in modal volumes, initiation and growth of an intermediate phase, disappearance of a phase, and the presence of an initial composition profile in the specimen. In each analysis, an effort was made to achieve good accuracy while minimizing computation time. The solutions to the diffusion equations for single-, two-, and threephase binary alloy systems are numerically calculated by the three programs NAD1, NAD2, and NAD3. NAD1 treats the diffusion between pure metals which belong to a single-phase system. Diffusion in this system is described by a one-dimensional Fick's second law and will result in a continuous composition variation. For computational purposes, Fick's second law is expressed as an explicit second-order finite difference equation. Finite difference calculations are made by choosing the grid spacing small enough to give convergent solutions of acceptable accuracy. NAD2 treats diffusion between pure metals which form a two-phase system. Diffusion in the twophase system is described by two partial differential equations (a Fick's second law for each phase) and an interface-flux-balance equation which describes the location of the interface. Actual interface motion is obtained by a mass conservation procedure. To account for changes in the thicknesses of the two phases as diffusion progresses, a variable grid technique developed by Murray and Landis is employed. These equations are expressed in finite difference form and solved numerically. Program NAD3 treats diffusion between pure metals which form a two-phase system with an intermediate third phase. Diffusion in the three-phase system is described by three partial differential expressions of Fick's second law and two interface-flux-balance equations. As with the two-phase case, a variable grid finite difference is used to numerically solve the diffusion equations. Computation time is minimized without sacrificing solution accuracy by treating the three-phase problem as a two-phase problem when the thickness of the intermediate phase is less than a preset value. Comparisons between these programs and other solutions have shown excellent agreement. The programs are written in FORTRAN IV for batch execution on the CDC 6600 with a central memory requirement of approximately 51K (octal) 60 bit words.

Effect of heat treatment on morphology evolution of Ti2Ni phase in Ti-Ni-Al-Zr alloy

NASA Astrophysics Data System (ADS)

Sheng, Liyuan; Yang, Yang; Xi, Tingfei

2018-03-01

The Ti6Al2Zr alloy with 15 wt.% Ni addition was prepared and then heat treated in the research. The microstructure of the alloy and evolution of Ti2Ni precipitate were investigated. The microstructure observations demonstrate that the Ni addition could promote the formation of eutectoid and eutectic structures in Ti-Al-Zr alloy. In the eutectoid structure, the ultrafine Ti2Ni fiber precipitates in the α-Ti matrix, but in the eutectic structure, the fine α-Ti phases precipitate in the Ti2Ni matrix. The heat treatment could change the morphology of Ti2Ni precipitates by thinning, fragmenting, merging and spherizing. In the alloy heat treated at and below 1073K, the coarsening of α-Ti precipitates in eutectic structure and Ti2Ni precipitates in eutectoid structure is the mainly characteristic. In the alloy heat treated above 1073K, the phase transformation of α to β phase is the main characteristic, which changes the morphology and amount of Ti2Ni phase by the solid solution of Ni. The phase transformation temperature of Ti-Ni-Al-Zr alloy is between 1073-1123K, which is increased compared with that of the Ti-Ni binary phase diagram.

Structure of dental gallium alloys.

PubMed

Herø, H; Simensen, C J; Jørgensen, R B

1996-07-01

The interest in gallium alloys as a replacement for amalgam has increased in recent years due to the risk of environmental pollution from amalgam. Alloy powders with compositions close to those for alloys of amalgam are mixed with a liquid gallium alloy. The mix is condensed into a prepared cavity in much the same way as for amalgam. The aim of the present work was to study the structure of: (1) two commercial alloy powders containing mainly silver, tin and copper, and (2) the phases formed by mixing these powders with a liquid alloy of gallium, indium and tin. One of the alloy powders contained 9 wt% palladium. Cross-sections of cylindrical specimens made by these gallium mixes were investigated by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Discrete grains of the following phases were found to be present in both gallium alloys: hexagonal Ag2Ga, tetragonal Cu(Pd)Ga2, cubic Ag9In4 and tetragonal beta-Sn. Indications of hexagonal or orthorhombic Ag2Sn were found in the remaining, unreacted alloy particles. In the palladium-containing alloy the X-ray reflections indicate a minor fraction of cubic Cu9Ga4 in addition to the Cu(Pd)Ga2 phase. Particles of beta-Sn are probably precipitated because Sn-Ga phases cannot be formed according to the binary phase diagram.

Thermoelastic martensitic transformations in ternary Ni50Mn50- z Ga z alloys

NASA Astrophysics Data System (ADS)

Belosludtseva, E. S.; Kuranova, N. N.; Marchenkova, E. B.; Popov, A. G.; Pushin, V. G.

2016-01-01

We have studied the effect of gallium alloying on the structure, phase composition, and physical properties of ternary alloys of the Ni50Mn50- z Ga z (0 ≤ z ≤ 25 at %) quasi-binary section in a broad temperature range. Dependences of the type of crystalline structure of the high-temperature austenite phase and martensite, as well as the critical temperatures of martensitic transformations on the alloy composition, are determined. A phase diagram of the structural and magnetic transformations is constructed. Concentration boundaries of the existence of tetragonal L10 (2 M) martensite and martensitic phases (10 M and 14 M) with complex multilayer crystalline lattices are found. It is established that the predominant martensite morphology is determined by the hierarchy of packets of thin coherent nano- and submicrocrystalline plates with habit planes close to {011} B2, pairwise twinned along one of 24 equivalent {011}<011> B2 twinning shear systems.

Determination of Thermodynamic Properties of Alkaline Earth-liquid Metal Alloys Using the Electromotive Force Technique

PubMed Central

Nigl, Thomas P.; Smith, Nathan D.; Lichtenstein, Timothy; Gesualdi, Jarrod; Kumar, Kuldeep; Kim, Hojong

2017-01-01

A novel electrochemical cell based on a CaF2 solid-state electrolyte has been developed to measure the electromotive force (emf) of binary alkaline earth-liquid metal alloys as functions of both composition and temperature in order to acquire thermodynamic data. The cell consists of a chemically stable solid-state CaF2-AF2 electrolyte (where A is the alkaline-earth element such as Ca, Sr, or Ba), with binary A-B alloy (where B is the liquid metal such as Bi or Sb) working electrodes, and a pure A metal reference electrode. Emf data are collected over a temperature range of 723 K to 1,123 K in 25 K increments for multiple alloy compositions per experiment and the results are analyzed to yield activity values, phase transition temperatures, and partial molar entropies/enthalpies for each composition. PMID:29155770

Prediction of Formation of Amorphous Alloys During Annealing of Ti-binary Alloys and Validation of the Same

DTIC Science & Technology

2009-11-22

The authors argued that the occurrence of the reversible step in the specific heat reflected “the freezing and unfreezing of some degree of freedom...of steel, the austenite phase is sometimes formed in a composition range where ferrite and liquid are the equilibrium phases. The formation of the...austenite is explained by the construction of a meta-stable extension of the (austenite+liquid) field into the ( ferrite +liquid) region. The

Metastable Polymeric Nitrogen From N2H2 Alloys

DTIC Science & Technology

2008-12-01

dioxide [Iota et al., 2oo7J and oxygen [MililZer and Hemley, 2006] and rich phase diagrams have been derived for each. However, the r~overy of the... oxygen , may lead to the stabilization of ordered extended molecular solid phases [Vos et aI., 1992; Loubeyre et a!., 1993; Somayazulu et al., 1996...and SlI7.hemechny, M.A., 2007: Structure of quench condensed nl·lz-Nl binary alloys: isotope effect, Low Temp. Phys. 33, 499 - 503. Goncharov, A.F

Nuclear fuel alloys or mixtures and method of making thereof

DOEpatents

Mariani, Robert Dominick; Porter, Douglas Lloyd

2016-04-05

Nuclear fuel alloys or mixtures and methods of making nuclear fuel mixtures are provided. Pseudo-binary actinide-M fuel mixtures form alloys and exhibit: body-centered cubic solid phases at low temperatures; high solidus temperatures; and/or minimal or no reaction or inter-diffusion with steel and other cladding materials. Methods described herein through metallurgical and thermodynamics advancements guide the selection of amounts of fuel mixture components by use of phase diagrams. Weight percentages for components of a metallic additive to an actinide fuel are selected in a solid phase region of an isothermal phase diagram taken at a temperature below an upper temperature limit for the resulting fuel mixture in reactor use. Fuel mixtures include uranium-molybdenum-tungsten, uranium-molybdenum-tantalum, molybdenum-titanium-zirconium, and uranium-molybdenum-titanium systems.

Liquid-liquid phase separation and solidification behavior of Al55Bi36Cu9 monotectic alloy with different cooling rates

NASA Astrophysics Data System (ADS)

Bo, Lin; Li, Shanshan; Wang, Lin; Wu, Di; Zuo, Min; Zhao, Degang

2018-03-01

The cooling rate has a significant effect on the solidification behavior and microstructure of monotectic alloy. In this study, different cooling rate was designed through casting in the copper mold with different bore diameters. The effects of different cooling rate on the solidification behavior of Al55Bi36Cu9 (at.%) immiscible alloy have been investigated. The liquid-liquid phase separation of Al55Bi36Cu9 immiscible alloy melt was investigated by resistivity test. The solidification microstructure and phase analysis of Al55Bi36Cu9 immiscible alloy were performed by the SEM and XRD, respectively. The results showed that the liquid-liquid phase separation occurred in the solidification of Al55Bi36Cu9 monotectic melt from 917 °C to 653 °C. The monotectic temperature, liquid phase separation temperature and immiscibility zone of Al55Bi36Cu9 monotectic alloy was lower than those of Al-Bi binary monotectic alloy. The solidification morphology of Al55Bi36Cu9 monotectic alloy was very sensitive to the cooling rate. The Al/Bi core-shell structure formed when Al55Bi36Cu9 melt was cast in the copper mold with a 8 mm bore diameter.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Pei; Fang, Z. Zak; Koopman, Mark

Hydrogen has been investigated for decades as a temporary alloying element to refine the microstructure of Ti-6Al-4V, and is now being used in a novel powder metallurgy method known as "hydrogen sintering and phase transformation". Pseudo-binary phase diagrams of (Ti-6Al-4V)-xH have been studied and developed, but are not well established due to methodological limitations. In this paper, in situ studies of phase transformations during hydrogenation and dehydrogenation of (Ti-6Al-4V)-xH alloys were conducted using high-energy synchrotron X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The eutectoid phase transformation of β ↔ α + δ was observed in themore » (Ti-6Al-4V)-xH alloy via in situ synchrotron XRD at 211 °C with a hydrogen concentration of 37.5 at.% (measured using TGA-DSC). The relationships of hydrogen composition to partial pressure and temperature were investigated in the temperature range 450-900°C. Based on these results, a partial pseudo-binary phase diagram of (Ti-6Al-4V)-xH is proposed for hydrogen compositions up to 60 at.% in the temperature range 100-900°C. Using the data collected in real time under controlled parameters of temperature, composition and hydrogen partial pressure, this work characterizes relevant phase transformations and microstructural evolution for practical titanium-hydrogen technologies of Ti-6Al-4V.« less

Fabrication of cobalt-nickel binary nanowires in a highly ordered alumina template via AC electrodeposition

PubMed Central

2013-01-01

Cobalt-nickel (Co-Ni) binary alloy nanowires of different compositions were co-deposited in the nanopores of highly ordered anodic aluminum oxide (AAO) templates from a single sulfate bath using alternating current (AC) electrodeposition. AC electrodeposition was accomplished without modifying or removing the barrier layer. Field emission scanning electron microscope was used to study the morphology of templates and alloy nanowires. Energy-dispersive X-ray analysis confirmed the deposition of Co-Ni alloy nanowires in the AAO templates. Average diameter of the alloy nanowires was approximately 40 nm which is equal to the diameter of nanopore. X-ray diffraction analysis showed that the alloy nanowires consisted of both hexagonal close-packed and face-centered cubic phases. Magnetic measurements showed that the easy x-axis of magnetization is parallel to the nanowires with coercivity of approximately 706 Oe. AC electrodeposition is very simple, fast, and is useful for the homogenous deposition of various secondary nanostuctured materials into the nanopores of AAO. PMID:23941234

Al and Mg Alloys for Aerospace Applications Using Rapid Solidification and Powder Metallurgy Processing.

DTIC Science & Technology

1986-11-14

5wt % Si was completely different from that of the alloy without silicon. The (X phase formed around the primary Mg2 Si crystals, and an irregular...content, and primary crystals in a binary Mg- 5wt % Si alloy did not exhibit this behavior. The surface of the rapidly solidified melt pools was rough and...Microhardness* of the laser treated alloys . Alloy As-cast Laser treated Mg- 5wt %Li 40.8 55.7 o, Mg- 5wt %Li- 5wt % Si 51.1 74.1 Mg-8wt%Li 42.8 71.2

An Investigation of the Effects of Metallurgical and/or Testing Variables on the Acoustic Emission from Crystalline Materials.

DTIC Science & Technology

1982-09-01

alloy , a number of minor phases have been reported (Thompson and Brooks, 1975). The precipitates expected after the heat treatments used in this study... precipitate or inclusion fracture, twin formation, martensite to create detectable acoustic emission. In alloy formation, dislocation motion, and... precipitate anticipated for each heat The nominal composition of 2219 is given in Table 2. It is treatment. essentially a binary aluminium- copper alloy

Calculation of Gallium-metal-Arsenic phase diagrams

NASA Technical Reports Server (NTRS)

Scofield, J. D.; Davison, J. E.; Ray, A. E.; Smith, S. R.

1991-01-01

Electrical contacts and metallization to GaAs solar cells must survive at high temperatures for several minutes under specific mission scenarios. The determination of which metallizations or alloy systems that are able to withstand extreme thermal excursions with minimum degradation to solar cell performance can be predicted by properly calculated temperature constitution phase diagrams. A method for calculating a ternary diagram and its three constituent binary phase diagrams is briefly outlined and ternary phase diagrams for three Ga-As-X alloy systems are presented. Free energy functions of the liquid and solid phase are approximated by the regular solution theory. Phase diagrams calculated using this method are presented for the Ga-As-Ge and Ga-As-Ag systems.

Analytical model of radiation-induced precipitation at the surface of dilute binary alloy

NASA Astrophysics Data System (ADS)

Pechenkin, V. A.; Stepanov, I. A.; Konobeev, Yu. V.

2002-12-01

Growth of precipitate layer at the foil surface of an undersaturated binary alloy under uniform irradiation is treated analytically. Analytical expressions for the layer growth rate, layer thickness limit and final component concentrations in the matrix are derived for coherent and incoherent precipitate-matrix interfaces. It is shown that the high temperature limit of radiation-induced precipitation is the same for both types of interfaces, whereas layer thickness limits are different. A parabolic law of the layer growth predicted for both types of interfaces is in agreement with experimental data on γ '-phase precipitation at the surface of Ni-Si dilute alloys under ion irradiation. Effect of sputtering on the precipitation rate and on the low temperature limit of precipitation under ion irradiation is discussed.

Structure-property relationship of cast Ti-Nb alloys.

PubMed

Lee, C M; Ju, C P; Chern Lin, J H

2002-04-01

The present work is a study of the microstructure, mechanical properties and corrosion behaviour of a series of binary Ti-Nb alloys with Nb contents up to 35 wt%, with emphasis placed on the structure-property relationship of the alloys. The results indicate that crystal structure and morphology of the Ti-Nb alloys are sensitive to the Nb content. The cast c.p. Ti has a hexagonal alpha phase with a lath type morphology. The alloys containing 15 wt% or less Nb are dominated by a hexagonal alpha' phase with an acicular, martensitic structure. When containing 17.5-25 wt% Nb, the alloys are primarily comprised of an orthorhombic alpha" phase. With 27.5 wt% Nb, metastable beta phase starts to be retained. With Nb contents higher than 30 wt%, the equi-axed beta phase is almost entirely retained. Small amounts of omega phase are detected in alloys containing 27.5 and 30 wt% Nb. Among all present alloys, Ti-10Nb and Ti-27.5Nb exhibit the highest strengths, while the alpha"-dominated (17.5 and 20Nb) and beta-dominated (> 30Nb) alloys have the lowest moduli. All Ti-Nb alloys show excellent corrosion resistance in Hank's solution at 37 degrees C. From the present data, the microhardness, bending strength and modulus of the various phases in Ti-Nb alloys are compared and tentatively summarized as follows: Microhardness: omega > alpha' > alpha" > beta > alpha (c.p. Ti) Bending strength: omega > alpha' > alpha" > beta > alpha (c.p. Ti) Bending modulus: omega > alpha (c.p. Ti) > alpha' > alpha" > beta

Kinetics and Equilibrium of Age-Induced Precipitation in Cu-4 At. Pct Ti Binary Alloy

NASA Astrophysics Data System (ADS)

Semboshi, Satoshi; Amano, Shintaro; Fu, Jie; Iwase, Akihiro; Takasugi, Takayuki

2017-03-01

Transformation kinetics and phase equilibrium of metastable and stable precipitates in age-hardenable Cu-4 at. pct Ti binary alloy have been investigated by monitoring the microstructural evolution during isothermal aging at temperatures between 693 K (420 °C) and 973 K (700 °C). The microstructure of the supersaturated solid solution evolves in four stages: compositional modulation due to spinodal decomposition, continuous precipitation of the needle-shaped metastable β'-Cu4Ti with a tetragonal structure, discontinuous precipitation of cellular components containing stable β-Cu4Ti lamellae with an orthorhombic structure, and eventually precipitation saturation at equilibrium. In specimens aged below 923 K (650 °C), the stable β-Cu4Ti phase is produced only due to the cellular reaction, whereas it can be also directly obtained from the intergranular needle-shaped β'-Cu4Ti precipitates in specimens aged at 973 K (700 °C). The precipitation kinetics and phase equilibrium observed for the specimens aged between 693 K (420 °C) and 973 K (700 °C) were characterized in accordance with a time-temperature-transformation (TTT) diagram and a Cu-Ti partial phase diagram, which were utilized to determine the alloy microstructure, strength, and electrical conductivity.

Numerical Study of Variation of Mechanical Properties of a Binary Aluminum Alloy with Respect to Its Grain Shapes †

PubMed Central

Sharifi, Hamid; Larouche, Daniel

2014-01-01

To study the variation of the mechanical behavior of binary aluminum copper alloys with respect to their microstructure, a numerical simulation of their granular structure was carried out. The microstructures are created by a repeated inclusion of some predefined basic grain shapes into a representative volume element until reaching a given volume percentage of the α-phase. Depending on the grain orientations, the coalescence of the grains can be performed. Different granular microstructures are created by using different basic grain shapes. Selecting a suitable set of basic grain shapes, the modeled microstructure exhibits a realistic aluminum alloy microstructure which can be adapted to a particular cooling condition. Our granular models are automatically converted to a finite element model. The effect of grain shapes and sizes on the variation of elastic modulus and plasticity of such a heterogeneous domain was investigated. Our results show that for a given α-phase fraction having different grain shapes and sizes, the elastic moduli and yield stresses are almost the same but the ultimate stress and elongation are more affected. Besides, we realized that the distribution of the θ phases inside the α phases is more important than the grain shape itself. PMID:28788607

Lattice misfits in four binary Ni-Base γ/γ1 alloys at ambient and elevated temperatures

NASA Astrophysics Data System (ADS)

Kamara, A. B.; Ardell, A. J.; Wagner, C. N. J.

1996-10-01

High-temperature X-ray diffractometry was used to determine the in situlattice parameters, a γ and a γ', and lattice misfits, δ = ( a γ', - a γ)/ a γ, of the matrix (γ) and dispersed γ'-type (Ni3X) phases in polycrystalline binary Ni-Al, Ni-Ga, Ni-Ge, and Ni-Si alloys as functions of temperature, up to about 680 °C. Concentrated alloys containing large volume fractions of the γ' phase (˜0.40 to 0.50) were aged at 700 °C to produce large, elastically unconstrained precipitates. The room-temperature misfits are 0.00474 (Ni-Al), 0.01005 (Ni-Ga), 0.00626 (Ni-Ge), and -0.00226 (Ni-Si), with an estimated error of ± 4 pct. The absolute values of the lattice constants of the γ and γ' phases, at compositions corresponding to thermodynamic equilibrium at about 700 °C, are in excellent agreement with data from the literature, with the exception of Ni3Ga, the lattice constant of which is much larger than expected. In Ni-Ge alloys, δ decreases to 0.00612 at 679 °C, and in Ni-Ga alloys, the decrease is to 0.0097. In Ni-Si and Ni-Al alloys, δ exhibits a stronger temperature dependence, changing to-0.00285 at 683 °C (Ni-Si) and to 0.00424 at 680 °C (Ni-Al). Since the times required to complete the high-temperature X-ray diffraction (XRD) scans were relatively short (2.5 hours at most), we believe that the changes in δ observed are attributable to differences between the thermal expansion coefficients of the γ and γ' phases, because the compositions of the phases in question reflect the equilibrium compositions at 700 δC. Empirical equations are presented that accurately describe the temperature dependences of a γ, a γ', and δ over the range of temperatures of this investigation.

Containerless processing of Nb-Ge alloys in a long drop tube

NASA Technical Reports Server (NTRS)

Bayuzick, R. J.

1982-01-01

The thirty-two meter drop tube at the Marshall Space Flight Center was used to study the effect of zero gravity containerless processing on the structure and properties of materials. The concept involves the suppression of heterogeneous nucleation of solid in liquid and, therefore, solidification accompanied by large degrees of undercooling. Under these conditions metastable phases can be formed or, at the very least, unique nonequilibrium microstructures (containing equilibrium phases) with unique properties can be produced. The drop tube solidification was applied to niobium base alloys with emphasis on the Nb-Ge binary system in an effort to produce metastable phases with high superconducting transition temperatures in bulk specimens. In the past, only lower Ge alloys (Nb-13 a/o, Nb-18 a/o, and Nb-22 a/o) could be undercooled. Higher Ge alloys (e.g., Nb-25 a/o Ge and Nb-27 a/o Ge) can now be undercooled on a routine basis.

Roman bronze artefacts from Thamusida (Morocco): Chemical and phase analyses

NASA Astrophysics Data System (ADS)

Gliozzo, E.; Kockelmann, W.; Bartoli, L.; Tykot, R. H.

2011-02-01

Twenty-six objects (1st to the 3rd century AD) found at the archaeological site of Thamusida (Morocco), which is a military settlement between the 1st and the 3rd century AD, have been investigated by means of portable X-ray fluorescence and time of flight-neutron diffraction. The combination of element-sensitive X-ray fluorescence and structure-sensitive neutron diffraction yields, in a totally non-destructive way, the necessary information to discriminate the copper alloy from corrosion and alteration layers. Results allowed dividing the repertory into five groups: (a) unalloyed copper, (b) binary alloys made of Cu and Sn, frequently leaded; (c) unleaded binary alloys made of Cu and Zn; (d) ternary alloys made of Cu, Sn and Zn, both leaded and unleaded; (e) quaternary alloys made of Cu, Sn, Zn and As. The choice of alloy is heterogeneous, mainly depending on availability and costs of raw and/or scrap materials and on technological constraints. Interestingly, the reconstruction obtained for Thamusida could either anticipate the important change in the Roman use of copper alloys generally referred as 'zinc decline', or more likely, indicate that brass never conspicuously entered the local metal-working activities of this military site.

Dependence of stress-induced omega transition and mechanical twinning on phase stability in metastable β Ti–V alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, X.L.; Li, L.; Mei, W.

2015-09-15

Tensile properties and deformation microstructures of a series of binary β Ti–16–22V alloys have been investigated. The results show that the plastic deformation mode changes from the plate-like stress-induced ω phase transformation with a special habit plane of (− 5052){sub ω}//(3 − 3 − 2){sub β} to (332)<113> type deformation twinning with increasing the content of vanadium in the β Ti–16–22 wt.% V alloys. The plate-like stress-induced ω phase has a special orientation relationship with the β phase matrix, i.e., [110]{sub β}//[− 12 − 10]{sub ω}, (3 − 3 − 2){sub β}//(− 5052){sub ω} and (− 55 − 4){sub β}//(30more » − 31){sub ω}. The alloys plastically deformed by stress-induced ω phase transformation exhibit relatively higher yield strength than those deformed via (332)<113> type deformation twinning. It can be concluded that the stability of β phase plays a significant role in plastic deformation mode, i.e., stress-induced ω phase transformation or (332)<113> type deformation twinning, which governs the mechanical property of the β Ti–16–22 wt.% V alloys. - Highlights: • Tensile properties and deformed microstructures of β Ti–16–22V alloys were studied. • Stress-induced ω phase transformation and (332)<113> twinning occur in the alloys. • Stability of β phase plays a significant role in plastic deformation mode. • Plastic deformation mode governs the mechanical property of the alloys.« less

Assessment of phase constitution on the Al-rich region of rapidly solidified Al-Co-Fe-Cr alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wolf, W., E-mail: witorw@gmail.com

The formation of quasicrystalline approximants in rapidly solidified Al-Co-Fe-Cr alloys was investigated. Alloys of atomic composition Al{sub 71}Co{sub 13}Fe{sub 8}Cr{sub 8}, Al{sub 77}Co{sub 11}Fe{sub 6}Cr{sub 6} and Al{sub 76}Co{sub 19}Fe{sub 4}Cr{sub 1} were produced using melt spinning and arc melting methods and their microstructural characterization was carried out by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Up to the present there is no consensus in the literature regarding the formation of quasicrystalline phase or quasicrystalline approximants in the Al{sub 71}Co{sub 13}Fe{sub 8}Cr{sub 8} alloy. This work presents, for the first time, a detailed structural characterization of selected alloysmore » in the Al-Co-Fe-Cr system close to the atomic composition Al{sub 71}Co{sub 13}Fe{sub 8}Cr{sub 8}. The results indicated the samples to be composed, mostly, by two intermetallic phases, which are quaternary extensions of Al{sub 5}Co{sub 2} and Al{sub 13}Co{sub 4} and are quasicrystalline approximants. Although the Al{sub 5}Co{sub 2} phase has already been reported in the Al{sub 71}Co{sub 13}Fe{sub 8}Cr{sub 8} alloy, the presence of the monoclinic Al{sub 13}Co{sub 4} is now identified for the first time in the as cast state. In the binary Al-Co system a quasicrystalline phase is known to form in a rapidly solidified alloy with composition close to the monoclinic and orthorhombic Al{sub 13}Co{sub 4} phases. This binary quasicrystalline phase presents an average valence electron per atom (e/a) between 1.7 and 1.9; thus, in addition to the Al{sub 71}Co{sub 13}Fe{sub 8}Cr{sub 8} alloy, the compositions Al{sub 77}Co{sub 11}Fe{sub 6}Cr{sub 6} and Al{sub 76}Co{sub 19}Fe{sub 4}Cr{sub 1} were chosen to be within the region of formation of the quaternary extension of the Al{sub 13}Co{sub 4} phase and also within the (e/a) of 1.7 to 1.9. However, no quasicrystalline phase is present in any of the studied alloys. The Al-Co-Fe-Cr system, around the compositions studied, is composed of quaternary extensions of Al-Co intermetallic phases, which present solubility of Fe and Cr at Co atomic sites. - Highlights: •The Al rich region of the AlCoFeCr system is studied concerning phase formation on rapidly solidified alloys. •The alloys were composed mostly by quaternary extensions of Al-Co intermetallic phases. •Al{sub 5}Co{sub 2} and Al{sub 13}Co{sub 4} were the major phases observed in the alloys and are approximants of a quasicrystalline phase. •No quasicrystalline phase was observed in the Al{sub 71}Co{sub 13}Fe{sub 8}Cr{sub 8} composition.« less

Investigation on microstructure characterization and property of rapidly solidified Mg-Zn-Ca-Ce-La alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou Tao, E-mail: tzhou1118@163.com; Chen Zhenhua, E-mail: chenzhenhua45@hotmail.com; Yang Mingbo, E-mail: yangmingbo@cqit.edu.cn

2012-01-15

Rapidly solidified (RS) Mg-Zn-Ca-Ce-La (wt.%) alloys have been produced via atomizing the alloy melt and subsequent splat-quenching on the water-cooled copper twin-rollers in the form of flakes. Microstructure characterization, phase compositions and thermal stability of the alloys have been systematically investigated. The results showed that with addition of RE (Ce and La) to the Mg-6Zn-5Ca alloy, the stable intermetallic compounds i.e. the Mg{sub x}Zn{sub y}RE{sub z} phase with a few Ca (about 3 at.%), shortened as the T Prime phase, were formed at the expense of the binary Mg-Zn and Ca{sub 2}Mg{sub 6}Zn{sub 3} phases, which was possibly beneficial tomore » the enhanced thermal stability of the alloy. In the Mg-6Zn-5Ca-3Ce-0.5La alloy, the composition of the T Prime phase in the grain interior was different from that at the grain boundaries, in which the segregation of the La elements was found, and the atomic percentage ratio of Zn to Ce in the T Prime phase within the grains was close to 2. Moreover, the stable Mg{sub 2}Ca phases were detected around the T Prime phases at the grain boundaries in the alloy. - Research Highlights: Black-Right-Pointing-Pointer The phase constitution of RS Mg-6Zn-5Ca alloy can be improved by RE additions. Black-Right-Pointing-Pointer In the Mg-Zn-Ca-Ce-La alloys, the Mg{sub x}Zn{sub y}RE{sub z} phase with a few Ca (T Prime phase) is formed. Black-Right-Pointing-Pointer The formation of the T Prime phase leads to the loss of the Mg-Zn and Ca{sub 2}Mg{sub 6}Zn{sub 3} phases. Black-Right-Pointing-Pointer The composition of the T Prime phase differs from the grain interior to the grain boundary.« less

Contribution to the aluminum-tin-zinc ternary system

NASA Astrophysics Data System (ADS)

Drápala, J.; Kostiuková, G.; Losertová, M.

2017-11-01

The Sn-Zn-Al alloys are one of significant candidates in the proposal of alternative lead-free solders for higher temperature soldering. This paper deals with the study of the aluminum-tin-zinc system. Twenty Sn-Zn-Al alloys together with six binary Sn-Zn alloys were prepared and studied experimentally. Alloys were prepared from pure Sn, Zn and Al (melting and cooling in a vacuum resistance furnace). The specimens were studied metallographically including the micro-hardness measurements, complete chemical analysis (ICP-AES, OES), X-ray micro-analysis of alloys by SEM and EDX in order to determine the composition and identification of individual phases. Significant temperatures and enthalpies of phase transformations were determined by DTA. After long-term annealing of selected alloys in vacuum followed by quenching the structural and chemical microanalyses of the present phases and their limit concentrations were carried out. The achieved results were compared with the thermodynamic modelling of the ternary Sn-Zn-Al system (computer programs THERMOCALC, MTDATA, PANDAT and databases CALPHAD, COST). Electrical resistivity, density, magnetic susceptibility and wettability of Sn-Zn-Al solders were measured as well.

Preferential site occupancy of alloying elements in TiAl-based phases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holec, David, E-mail: david.holec@unileoben.ac.at; Reddy, Rajeev K.; Klein, Thomas

2016-05-28

First principles calculations are used to study the preferential occupation of ternary alloying additions into the binary Ti-Al phases, namely, γ-TiAl, α{sub 2}-Ti{sub 3}Al, β{sub o}-TiAl, and B19-TiAl. While the early transition metals (TMs, group IVB, VB, and VIB elements) prefer to substitute for Ti atoms in the γ-, α{sub 2}-, and B19-phases, they preferentially occupy Al sites in the β{sub o}-TiAl. Si is, in this context, an anomaly, as it prefers to sit on the Al sublattice for all four phases. B and C are shown to prefer octahedral Ti-rich interstitial positions instead of substitutional incorporation. The site preferencemore » energy is linked with the alloying-induced changes of energy of formation, hence alloying-related (de)stabilisation of the phases. We further show that the phase-stabilisation effect of early TMs on β{sub o}-phase has a different origin depending on their valency. Finally, an extensive comparison of our predictions with available theoretical and experimental data (which is, however, limited mostly to the γ-phase) shows a consistent picture.« less

Application of Molecular Interaction Volume Model for Phase Equilibrium of Sn-Based Binary System in Vacuum Distillation

NASA Astrophysics Data System (ADS)

Kong, Lingxin; Yang, Bin; Xu, Baoqiang; Li, Yifu

2014-09-01

Based on the molecular interaction volume model (MIVM), the activities of components of Sn-Sb, Sb-Bi, Sn-Zn, Sn-Cu, and Sn-Ag alloys were predicted. The predicted values are in good agreement with the experimental data, which indicate that the MIVM is of better stability and reliability due to its good physical basis. A significant advantage of the MIVM lies in its ability to predict the thermodynamic properties of liquid alloys using only two parameters. The phase equilibria of Sn-Sb and Sn-Bi alloys were calculated based on the properties of pure components and the activity coefficients, which indicates that Sn-Sb and Sn-Bi alloys can be separated thoroughly by vacuum distillation. This study extends previous investigations and provides an effective and convenient model on which to base refining simulations for Sn-based alloys.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, L. L.; Wang, Y. D.; Ren, Y.

Microstructure evolution, mechanical behaviors of cold rolled Ti-Nb alloys with different Nb contents subjected to different heat treatments were investigated. Here, optical microstructure and phase compositions of Ti-Nb alloys were characterized using optical microscopy and X-ray diffractometre, while mechanical behaviors of Ti-Nb alloys were examined by using tension tests. Stress-induced martensitic transformation in a Ti-30. at%Nb binary alloy was in-situ explored by synchrotron-based high-energy X-ray diffraction (HE-XRD). The results obtained suggested that mechanical behavior of Ti-Nb alloys, especially Young's modulus was directly dependent on chemical compositions and heat treatment process. According to the results of HE-XRD, α"-V1 martensite generated priormore » to the formation of α"-V2 during loading and a partial reversible transformation from α"-V1 to β phase was detected while α"-V2 tranformed to β completely during unloading.« less

Chemical interactions and thermodynamic studies in aluminum alloy/molten salt systems

NASA Astrophysics Data System (ADS)

Narayanan, Ramesh

The recycling of aluminum and aluminum alloys such as Used Beverage Container (UBC) is done under a cover of molten salt flux based on (NaCl-KCl+fluorides). The reactions of aluminum alloys with molten salt fluxes have been investigated. Thermodynamic calculations are performed in the alloy/salt flux systems which allow quantitative predictions of the equilibrium compositions. There is preferential reaction of Mg in Al-Mg alloy with molten salt fluxes, especially those containing fluorides like NaF. An exchange reaction between Al-Mg alloy and molten salt flux has been demonstrated. Mg from the Al-Mg alloy transfers into the salt flux while Na from the salt flux transfers into the metal. Thermodynamic calculations indicated that the amount of Na in metal increases as the Mg content in alloy and/or NaF content in the reacting flux increases. This is an important point because small amounts of Na have a detrimental effect on the mechanical properties of the Al-Mg alloy. The reactions of Al alloys with molten salt fluxes result in the formation of bluish purple colored "streamers". It was established that the streamer is liquid alkali metal (Na and K in the case of NaCl-KCl-NaF systems) dissipating into the melt. The melts in which such streamers were observed are identified. The metal losses occurring due to reactions have been quantified, both by thermodynamic calculations and experimentally. A computer program has been developed to calculate ternary phase diagrams in molten salt systems from the constituting binary phase diagrams, based on a regular solution model. The extent of deviation of the binary systems from regular solution has been quantified. The systems investigated in which good agreement was found between the calculated and experimental phase diagrams included NaF-KF-LiF, NaCl-NaF-NaI and KNOsb3-TINOsb3-LiNOsb3. Furthermore, an insight has been provided on the interrelationship between the regular solution parameters and the topology of the phase diagram. The isotherms are flat (i.e. no skewness) when the regular solution parameters are zero. When the regular solution parameters are non-zero, the isotherms are skewed. A regular solution model is not adequate to accurately model the molten salt systems used in recycling like NaCl-KCl-LiF and NaCl-KCl-NaF.

Microstructural Characterization of Base Metal Alloys with Conductive Native Oxides for Electrical Contact Applications

NASA Astrophysics Data System (ADS)

Senturk, Bilge Seda

Metallic contacts are a ubiquitous method of connecting electrical and electronic components/systems. These contacts are usually fabricated from base metals because they are inexpensive, have high bulk electrical conductivities and exhibit excellent formability. Unfortunately, such base metals oxidize in air under ambient conditions, and the characteristics of the native oxide scales leads to contact resistances orders of magnitude higher than those for mating bare metal surface. This is a critical technological issue since the development of unacceptably high contact resistances over time is now by far the most common cause of failure in electrical/electronic devices and systems. To overcome these problems, several distinct approaches are developed for alloying base metals to promote the formation of self-healing inherently conductive native oxide scales. The objective of this dissertation study is to demonstrate the viability of these approaches through analyzing the data from Cu-9La (at%) and Fe-V binary alloy systems. The Cu-9 La alloy structure consists of eutectic colonies tens of microns in diameter wherein a rod-like Cu phase lies within a Cu6La matrix phase. The thin oxide scale formed on the Cu phase was found to be Cu2O as expected while the thicker oxide scale formed on the Cu6La phase was found to be a polycrystalline La-rich Cu2O. The enhanced electrical conductivity in the native oxide scale of the Cu-9La alloy arises from heavy n-type doping of the Cu2O lattice by La3+. The Fe-V alloy structures consist of a mixture of large elongated and equiaxed grains. A thin polycrystalline Fe3O4 oxide scale formed on all of the Fe-V alloys. The electrical conductivities of the oxide scales formed on the Fe-V alloys are higher than that formed on pure Fe. It is inferred that this enhanced conductivity arises from doping of the magnetite with V+4 which promotes electron-polaron hopping. Thus, it has been demonstrated that even in simple binary alloy systems one can obtain a dramatic reduction in the contact resistances of alloy oxidized surfaces as compared with those of the pure base metals.

Solidification of a binary alloy: Finite-element, single-domain simulation and new benchmark solutions

NASA Astrophysics Data System (ADS)

Le Bars, Michael; Worster, M. Grae

2006-07-01

A finite-element simulation of binary alloy solidification based on a single-domain formulation is presented and tested. Resolution of phase change is first checked by comparison with the analytical results of Worster [M.G. Worster, Solidification of an alloy from a cooled boundary, J. Fluid Mech. 167 (1986) 481-501] for purely diffusive solidification. Fluid dynamical processes without phase change are then tested by comparison with previous numerical studies of thermal convection in a pure fluid [G. de Vahl Davis, Natural convection of air in a square cavity: a bench mark numerical solution, Int. J. Numer. Meth. Fluids 3 (1983) 249-264; D.A. Mayne, A.S. Usmani, M. Crapper, h-adaptive finite element solution of high Rayleigh number thermally driven cavity problem, Int. J. Numer. Meth. Heat Fluid Flow 10 (2000) 598-615; D.C. Wan, B.S.V. Patnaik, G.W. Wei, A new benchmark quality solution for the buoyancy driven cavity by discrete singular convolution, Numer. Heat Transf. 40 (2001) 199-228], in a porous medium with a constant porosity [G. Lauriat, V. Prasad, Non-darcian effects on natural convection in a vertical porous enclosure, Int. J. Heat Mass Transf. 32 (1989) 2135-2148; P. Nithiarasu, K.N. Seetharamu, T. Sundararajan, Natural convective heat transfer in an enclosure filled with fluid saturated variable porosity medium, Int. J. Heat Mass Transf. 40 (1997) 3955-3967] and in a mixed liquid-porous medium with a spatially variable porosity [P. Nithiarasu, K.N. Seetharamu, T. Sundararajan, Natural convective heat transfer in an enclosure filled with fluid saturated variable porosity medium, Int. J. Heat Mass Transf. 40 (1997) 3955-3967; N. Zabaras, D. Samanta, A stabilized volume-averaging finite element method for flow in porous media and binary alloy solidification processes, Int. J. Numer. Meth. Eng. 60 (2004) 1103-1138]. Finally, new benchmark solutions for simultaneous flow through both fluid and porous domains and for convective solidification processes are presented, based on the similarity solutions in corner-flow geometries recently obtained by Le Bars and Worster [M. Le Bars, M.G. Worster, Interfacial conditions between a pure fluid and a porous medium: implications for binary alloy solidification, J. Fluid Mech. (in press)]. Good agreement is found for all tests, hence validating our physical and numerical methods. More generally, the computations presented here could now be considered as standard and reliable analytical benchmarks for numerical simulations, specifically and independently testing the different processes underlying binary alloy solidification.

First-principles studiesy of the order-disorder phase transition in FeCo using Wang-Landau Monte-Carlo method

NASA Astrophysics Data System (ADS)

Pei, Zongrui; Eisenbach, Markus; Stocks, G. Malcolm

Simulating order-disorder phase transitions in magnetic materials requires the accurate treatment of both the atomic and magnetic interactions, which span a vast configuration space. Using FeCo as a prototype system, we demonstrate that this can be addressed by combining the Locally Self-consistent Multiple Scattering (LSMS) method with the Wang-Landau (WL) Monte-Carlo algorithm. Fe-Co based materials are interesting magnetic materials but a reliable phase diagram of the binary Fe-Co system is still difficult to obtain. Using the combined WL-LSMS method we clarify the existence of the disordered A2 phase and predict the Curie temperature between it and the ordered B2 phase. The WL-LSMS method is readily applicable to the study of second-order phase transitions in other binary and multi-component alloys, thereby providing a means to the direct simulation of order-disorder phase transitions in complex alloys without need of intervening classical model Hamiltonians. We also demonstrate the capability of our method to guide the design of new magnetic materials. This research was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division and it used Oak Ridge Leadership Computing Facility resources at Oak Ridge National Laboratory.

Development of a Novel, Bicombinatorial Approach to Alloy Development, and Application to Rapid Screening of Creep Resistant Titanium Alloys

NASA Astrophysics Data System (ADS)

Martin, Brian

Combinatorial approaches have proven useful for rapid alloy fabrication and optimization. A new method of producing controlled isothermal gradients using the Gleeble Thermomechanical simulator has been developed, and demonstrated on the metastable beta-Ti alloy beta-21S, achieving a thermal gradient of 525-700 °C. This thermal gradient method has subsequently been coupled with existing combinatorial methods of producing composition gradients using the LENS(TM) additive manufacturing system, through the use of elemental blended powders. This has been demonstrated with a binary Ti-(0-15) wt% Cr build, which has subsequently been characterized with optical and electron microscopy, with special attention to the precipitate of TiCr2 Laves phases. The TiCr2 phase has been explored for its high temperature mechanical properties in a new oxidation resistant beta-Ti alloy, which serves as a demonstration of the new bicombinatorial methods developed as applied to a multicomponent alloy system.

Improved hydrogen absorption and desorption kinetics of magnesium-based alloy via addition of yttrium

NASA Astrophysics Data System (ADS)

Yang, Tai; Li, Qiang; Liu, Ning; Liang, Chunyong; Yin, Fuxing; Zhang, Yanghuan

2018-02-01

Yttrium (Y) is selected to modify the microstructure of magnesium (Mg) to improve the hydrogen storage performance. Thereby, binary alloys with the nominal compositions of Mg24Yx (x = 1-5) are fabricated by inexpensive casting technique. Their microstructure and phase transformation during hydriding and dehydriding process are characterized by using X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy analysis. The isothermal hydrogen absorption and desorption kinetics are also measured by a Sievert's-type apparatus at various temperatures. Typical multiphase structures of binary alloy can be clearly observed. All of these alloys can reversibly absorb and desorb large amount of hydrogen at proper temperatures. The addition of Y markedly promotes the hydrogen absorption kinetics. However, it results in a reduction of reversible hydrogen storage capacity. A maximum value of dehydrogenation rate is observed with the increase of Y content. The Mg24Y3 alloy has the optimal desorption kinetic performance, and it can desorb about 5.4 wt% of hydrogen at 380 °C within 12 min. Combining Johnson-Mehl-Avrami kinetic model and Arrhenius equation, the dehydrogenation activation energy of the alloys are evaluated. The Mg24Y3 alloy also has the lowest dehydrogenation activation energy (119 kJ mol-1).

Development of a Knowledge Base of Ti-Alloys From First-Principles and Thermodynamic Modeling

NASA Astrophysics Data System (ADS)

Marker, Cassie

An aging population with an active lifestyle requires the development of better load-bearing implants, which have high levels of biocompatibility and a low elastic modulus. Titanium alloys, in the body centered cubic phase, are great implant candidates, due to their mechanical properties and biocompatibility. The present work aims at investigating the thermodynamic and elastic properties of bcc Tialloys, using the integrated first-principles based on Density Functional Theory (DFT) and the CALculation of PHAse Diagrams (CALPHAD) method. The use of integrated first-principles calculations based on DFT and CALPHAD modeling has greatly reduced the need for trial and error metallurgy, which is ineffective and costly. The phase stability of Ti-alloys has been shown to greatly affect their elastic properties. Traditionally, CALPHAD modeling has been used to predict the equilibrium phase formation, but in the case of Ti-alloys, predicting the formation of two metastable phases o and alpha" is of great importance as these phases also drastically effect the elastic properties. To build a knowledge base of Ti-alloys, for biomedical load-bearing implants, the Ti-Mo-Nb-Sn-Ta-Zr system was studied because of the biocompatibility and the bcc stabilizing effects of some of the elements. With the focus on bcc Ti-rich alloys, a database of thermodynamic descriptions of each phase for the pure elements, binary and Ti-rich ternary alloys was developed in the present work. Previous thermodynamic descriptions for the pure elements were adopted from the widely used SGTE database for global compatibility. The previous binary and ternary models from the literature were evaluated for accuracy and new thermodynamic descriptions were developed when necessary. The models were evaluated using available experimental data, as well as the enthalpy of formation of the bcc phase obtained from first-principles calculations based on DFT. The thermodynamic descriptions were combined into a database ensuring that the sublattice models are compatible with each other. For subsystems, such as the Sn-Ta system, where no thermodynamic description had been evaluated and minimal experimental data was available, first-principles calculations based on DFT were used. The Sn-Ta system has two intermetallic phases, TaSn2 and Ta3Sn, with three solution phases: bcc, body centered tetragonal (bct) and diamond. First-principles calculations were completed on the intermetallic and solution phases. Special quasirandom structures (SQS) were used to obtain information about the solution phases across the entire composition range. The Debye-Gruneisen approach, as well as the quasiharmonic phonon method, were used to obtain the finite-temperature data. Results from the first-principles calculations and experiments were used to complete the thermodynamic description. The resulting phase diagram reproduced the first-principles calculations and experimental data accurately. In order to determine the effect of alloying on the elastic properties, first-principles calculations based on DFT were systematically done on the pure elements, five Ti-X binary systems and Ti-X-Y ternary systems (X ≠ Y = Mo, Nb, Sn, Ta Zr) in the bcc phase. The first-principles calculations predicted the single crystal elastic stiffness constants cij 's. Correspondingly, the polycrystalline aggregate properties were also estimated from the cij's, including bulk modulus B, shear modulus G and Young's modulus E. The calculated results showed good agreement with experimental results. The CALPHAD method was then adapted to assist in the database development of the elastic properties as a function of composition. On average, the database predicted the elastic properties of higher order Ti-alloys within 5 GPa of the experimental results. Finally, the formation of the metastable phases, o and alpha" was studied in the Ti-Ta and Ti-Nb systems. The formation energy of these phases, calculated from first-principles at 0 K, showed that the phases have similar formation energies to the bcc and hcp phases. Inelastic neutron scattering was completed on four different Ti-Nb compositions to study the entropy of the phases as well as the transformations occurring when the phases form and the phase fractions. Ongoing work is being done to use the experimental information to introduce thermodynamic descriptions for these two phases in the Ti-Nb system in order to be able to predict the formation and phase fractions. DFT based first-principles were used to predict the effect these phases have on the elastic properties and a rule of mixtures was used to determine the elastic properties of multi-phase alloys. The results were compared with experiments and showed that if the ongoing modeling can predict the phase fraction, the elastic database can accurately predict the elastic properties of the o and alpha" phases. This thesis provides a knowledge base of the thermodynamic and elastic properties of Ti-alloys from computational thermodynamics. The databases created will impact research activities on Ti-alloys and specifically efforts focused on Ti-alloys for biomedical applications.

Phase equilibrium modeling for high temperature metallization on GaAs solar cells

NASA Technical Reports Server (NTRS)

Chung, M. A.; Davison, J. E.; Smith, S. R.

1991-01-01

Recent trends in performance specifications and functional requirements have brought about the need for high temperature metallization technology to be developed for survivable DOD space systems and to enhance solar cell reliability. The temperature constitution phase diagrams of selected binary and ternary systems were reviewed to determine the temperature and type of phase transformation present in the alloy systems. Of paramount interest are the liquid-solid and solid-solid transformations. Data are being utilized to aid in the selection of electrical contact materials to gallium arsenide solar cells. Published data on the phase diagrams for binary systems is readily available. However, information for ternary systems is limited. A computer model is being developed which will enable the phase equilibrium predictions for ternary systems where experimental data is lacking.

Local melting in Al-Mg-Zn-alloys

NASA Astrophysics Data System (ADS)

Droenen, Per-Erik; Ryum, Nils

1994-03-01

The internal melting of several Al-Mg-Zn-alloys has been studied by rapid upquenching in a salt bath of specimens slowly cooled at a rate of 2 °C/h down to 375 °C. The melting reaction was studied metallographically in the light- and electron-scanning microscope, and local concentrations were measured in the microprobe. Local melting of both the equilibrium phases T and η was observed to occur. There were, however, essential differences between the melting kinetics for the two phases. While the T-phase particles melted spontaneously at temperatures at or above the invariant temperature, 489 °C, and after some period of time at lower temperatures, the η-phase particles either melted spontaneously at or above the invariant temperature, T - 475 °C, or dissolved into the matrix at temperatures below 475 °C. This difference in behavior can be accounted for if the α(Al)-η section is not a quasi-binary section. The industrial implications of the internal melting in these alloys are discussed and compared to the same reaction in the Al-Mg-Si alloys. A model is developed in the Appendix to quantify the different behaviors of these two classes of alloys.

Characterisation of phases in nanostructured, multilayered titanium alloys by analytical and high-resolution electron microscopy.

PubMed

Czyrska-Filemonowicz, A; Buffat, P A

2009-01-01

Surface processing of a Ti-6Al-4V alloy led to a complex multilayered microstructure containing several phases of the Ni-Ti-P-Al-O system, which improves the mechanical and tribological surface properties. The microstructure, chemical and phase compositions of the hard layer formed on the surface were investigated by LM, XRD, SEM as well as analytical/high-resolution TEM, STEM, EDS, electron diffraction and FIB. Phase identification based on electron diffraction, HRTEM and EDS microanalysis revealed the presence of several binary and ternary phases in the system Ti-Ni-P, sometimes with partial substitution of Ti by Al. However some phases, mainly nanoparticles, still remain not identified satisfactorily. Electron microscopy techniques used for identification of phases present in surface multilayers and some practical limits to their routine application are reminded here.

Plutonium Metallurgy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Freibert, Franz J.

2012-08-09

Due to its nuclear properties, Pu will remain a material of global interest well into the future. Processing, Structure, Properties and Performance remains a good framework for discussion of Pu materials science Self-irradiation and aging effects continue to be central in discussions of Pu metallurgy Pu in its elemental form is extremely unstable, but alloying helps to stabilize Pu; but, questions remain as to how and why this stabilization occurs. Which is true Pu-Ga binary phase diagram: US or Russian? Metallurgical issues such as solute coring, phase instability, crystallographic texture, etc. result in challenges to casting, processing, and properties modelingmore » and experiments. For Ga alloyed FCC stabilized Pu, temperature and pressure remain as variables impacting phase stability.« less

Hardness behavior of binary and ternary niobium alloys at 77 and 300 K

NASA Technical Reports Server (NTRS)

Stephens, J. R.; Witzke, W. R.

1974-01-01

The effects of alloy additions of zirconium, hafnium, molybdenum, tungsten, rhenium, ruthenium, osmium, rhodium, and iridium on the hardness of niobium was determined. Both binary and ternary alloys were investigated by means of hardness tests at 77 K and 300 K. Results showed that atomic size misfit plays a dominant role in controlling hardness of binary niobium alloys. Alloy softening, which occurred at dilute solute additions, is most likely due to an extrinsic mechanism involving interaction between solute elements and interstitial impurities.

Microstructure Analysis of Ti-xPt Alloys and the Effect of Pt Content on the Mechanical Properties and Corrosion Behavior of Ti Alloys

PubMed Central

Song, Ho-Jun; Han, Mi-Kyung; Jeong, Hyeon-Gyeong; Lee, Yong-Tai; Park, Yeong-Joon

2014-01-01

The microstructure, mechanical properties, and corrosion behavior of binary Ti-xPt alloys containing 5, 10, 15 and 20 wt% Pt were investigated in order to develop new Ti-based dental materials possessing superior properties than those of commercially pure titanium (cp-Ti). All of the Ti-xPt (x = 5, 10, 15, 20) alloys showed hexagonal α-Ti structure with cubic Ti3Pt intermetallic phase. The mechanical properties and corrosion behavior of Ti-xPt alloys were sensitive to the Pt content. The addition of Pt contributed to hardening of cp-Ti and to improving its oxidation resistance. Electrochemical results showed that the Ti-xPt alloys exhibited superior corrosion resistance than that of cp-Ti. PMID:28788660

Growth of normally-immiscible materials (NIMs), binary alloys, and metallic fibers by hyperbaric laser chemical vapor deposition

NASA Astrophysics Data System (ADS)

Maxwell, J. L.; Black, M. R.; Chavez, C. A.; Maskaly, K. R.; Espinoza, M.; Boman, M.; Landstrom, L.

2008-06-01

This work demonstrates that two or more elements of negligible solubility (and no known phase diagram) can be co-deposited in fiber form by hyperbaric-pressure laser chemical vapor deposition (HP-LCVD). For the first time, Hg-W alloys were grown as fibers from mixtures of tungsten hexafluoride, mercury vapor, and hydrogen. This new class of materials is termed normally-immiscible materials (NIMs), and includes not only immiscible materials, but also those elemental combinations that have liquid states at exclusive temperatures. This work also demonstrates that a wide variety of other binary and ternary alloys, intermetallics, and mixtures can be grown as fibers, e.g. silicon-tungsten, aluminum-silicon, boron-carbon-silicon, and titanium-carbon-nitride. In addition, pure metallic fibers of aluminum, titanium, and tungsten were deposited, demonstrating that materials of high thermal conductivity can indeed be grown in three-dimensions, provided sufficient vapor pressures are employed. A wide variety of fiber properties and microstructures resulted depending on process conditions; for example, single crystals, fine-grained alloys, and glassy metals could be deposited.

In Situ Synchrotron Radiation X-ray Diffraction Study on Phase and Oxide Growth during a High Temperature Cycle of a NiTi-20 at.% Zr High Temperature Shape Memory Alloy

NASA Astrophysics Data System (ADS)

Carl, Matthew; Van Doren, Brian; Young, Marcus L.

2018-03-01

Ternary additions to binary NiTi shape memory alloys are known to significantly affect the characteristic martensite-to-austenite phase transformation, i.e., decrease or increase transformation temperatures. High temperature shape memory alloys can be created by adding Au, Pt, Pd, Hf, or Zr to binary NiTi in appropriate amounts; however, the majority of these ternary additions are exceedingly expensive, unfortunately making them impractical for most commercial applications. Zr is the exception of the group, but it is often disregarded because of its poor workability and thermal stability. In an effort to find a temperature range that allows for the potential workability of NiTiZr alloys in normal atmosphere environments and to gain understanding as to the cause of failure during processing, a NiTi-20 at.% Zr was subjected to a thermal cycle ranging from RT to 1000 °C with short 15 min holds at select temperatures during both heating and cooling while simultaneously collecting high-energy synchrotron radiation X-ray diffraction measurements. This study provides valuable insight into the kinetics of precipitation and oxide formation and its relationship to processing. In addition, scanning electron microscopy was performed on five samples, each isothermally held to examine precipitation and oxide structure and growth.

In Situ Synchrotron Radiation X-ray Diffraction Study on Phase and Oxide Growth during a High Temperature Cycle of a NiTi-20 at.% Zr High Temperature Shape Memory Alloy

NASA Astrophysics Data System (ADS)

Carl, Matthew; Van Doren, Brian; Young, Marcus L.

2018-02-01

Ternary additions to binary NiTi shape memory alloys are known to significantly affect the characteristic martensite-to-austenite phase transformation, i.e., decrease or increase transformation temperatures. High temperature shape memory alloys can be created by adding Au, Pt, Pd, Hf, or Zr to binary NiTi in appropriate amounts; however, the majority of these ternary additions are exceedingly expensive, unfortunately making them impractical for most commercial applications. Zr is the exception of the group, but it is often disregarded because of its poor workability and thermal stability. In an effort to find a temperature range that allows for the potential workability of NiTiZr alloys in normal atmosphere environments and to gain understanding as to the cause of failure during processing, a NiTi-20 at.% Zr was subjected to a thermal cycle ranging from RT to 1000 °C with short 15 min holds at select temperatures during both heating and cooling while simultaneously collecting high-energy synchrotron radiation X-ray diffraction measurements. This study provides valuable insight into the kinetics of precipitation and oxide formation and its relationship to processing. In addition, scanning electron microscopy was performed on five samples, each isothermally held to examine precipitation and oxide structure and growth.

Interpreting the Combustion Process for High-Performance ZrNiSn Thermoelectric Materials.

PubMed

Hu, Tiezheng; Yang, Dongwang; Su, Xianli; Yan, Yonggao; You, Yonghui; Liu, Wei; Uher, Ctirad; Tang, Xinfeng

2018-01-10

The ZrNiSn alloy, a member of the half-Heusler family of thermoelectric materials, shows great potential for mid-to-high-temperature power generation applications due to its excellent thermoelectric properties, robust mechanical properties, and good thermal stability. The existing synthesis processes of half-Heusler alloys are, however, rather time and energy intensive. In this study, single-phase ZrNiSn bulk materials were prepared by self-propagating high-temperature synthesis (SHS) combined with spark plasma sintering (SPS) for the first time. The analysis of thermodynamic and kinetic processes shows that the SHS reaction in the ternary ZrNiSn alloy is different from the more usual binary systems. It consists of a series of SHS reactions and mass transfers triggered by the SHS fusion of the binary Ni-Sn system that eventually culminates in the formation of single-phase ternary ZrNiSn in a very short time, which reduced the synthesis period from few days to less than an hour. Moreover, the nonequilibrium feature induces Ni interstitials in the structure, which simultaneously enhances the electrical conductivity and decreases the thermal conductivity, which is favorable for thermoelectric properties. The maximum thermoelectric figure of merit ZT of the SHS + SPS-processed ZrNiSn 1-x Sb x alloy reached 0.7 at 870 K. This study opens a new avenue for the fast and low-cost fabrication of half-Heusler thermoelectric materials.

Magnetic response of a disordered binary ferromagnetic alloy to an oscillating magnetic field

NASA Astrophysics Data System (ADS)

Vatansever, Erol; Polat, Hamza

2015-08-01

By means of Monte Carlo simulation with local spin update Metropolis algorithm, we have elucidated non-equilibrium phase transition properties and stationary-state treatment of a disordered binary ferromagnetic alloy of the type ApB1-p on a square lattice. After a detailed analysis, we have found that the system shows many interesting and unusual thermal and magnetic behaviors, for instance, the locations of dynamic phase transition points change significantly depending upon amplitude and period of the external magnetic field as well as upon the active concentration of A-type components. Much effort has also been dedicated to clarify the hysteresis tools, such as coercivity, dynamic loop area as well as dynamic correlations between time dependent magnetizations and external time dependent applied field as a functions of period and amplitude of field as well as active concentration of A-type components, and outstanding physical findings have been reported in order to better understand the dynamic process underlying present system.

Microstructural development from interdiffusion and reaction between Usbnd Mo and AA6061 alloys annealed at 600° and 550 °C

NASA Astrophysics Data System (ADS)

Perez, E.; Keiser, D. D.; Sohn, Y. H.

2016-08-01

The U.S. Material Management and Minimization Reactor Conversion Program is developing low enrichment fuel systems encased in Al-alloy for use in research and test reactors. Monolithic fuel plates have local regions where the Usbnd Mo fuel plate may come into contact with the Al-alloy 6061 (AA6061) cladding. This results in the development of interdiffusion zones with complex microstructures with multiple phases. In this study, the microstructural development of diffusion couples, Usbnd 7 wt%Mo, Usbnd 10 wt%Mo, and Usbnd 12 wt%Mo vs. AA6061, annealed at 600 °C for 24 h and at 550 °C for 1, 5, and 20 h, were analyzed by scanning electron microscopy with x-ray energy dispersive spectroscopy. The microstructural development and kinetics were compared to diffusion couples Usbnd Mo vs. high purity Al and binary Alsbnd Si alloys. The diffusion couples developed complex interaction regions where phase development was influenced by the alloying additions of the AA6061.

Ab-initio study of liquid systems: Concentration dependence of electrical resistivity of binary liquid alloy Rb1-xCsx

NASA Astrophysics Data System (ADS)

Thakur, Anil; Sharma, Nalini; Chandel, Surjeet; Ahluwalia, P. K.

2013-02-01

The electrical resistivity (ρL) of Rb1-XCsX binary alloys has been made calculated using Troullier Martins ab-initio pseudopotentials. The present results of the electrical resistivity (ρL) of Rb1-XCsX binary alloys have been found in good agreement with the experimental results. These results suggest that ab-initio approach for calculating electrical resistivity is quite successful in explaining the electronic transport properties of binary Liquid alloys. Hence ab-initio pseudopotentials can be used instead of model pseudopotentials having problem of transferability.

Characterization of microstructural, mechanical and thermophysical properties of Th-52U alloy

NASA Astrophysics Data System (ADS)

Das, Santanu; Kaity, S.; Kumar, R.; Banerjee, J.; Roy, S. B.; Chaudhari, G. P.; Daniel, B. S. S.

2016-11-01

Th-52 wt.% U alloy has a microstructure featuring interspersed networks of uranium rich and thorium rich phases. Room temperature hardness of the alloy is more than twice that of unalloyed thorium. The alloy age hardens (550 °C) only slightly (peak hardness/hardness of solution heated and quenched = 1.05). Room temperature thermal conductivity (25.6 W m-1 °C-1) is close to that of uranium and most of the binary and ternary metallic alloy fuel materials. Average linear coefficient of thermal expansion (CTE) of Th-52 wt.% U alloy [11.2 × 10-06 °C-1 (27-290 °C) and 16.75 × 10-06 °C-1 (27-600 °C)] are comparable with that of many metallic alloy fuel candidates. Th-52 wt.% U alloy with non-age hardenable microstructure, appreciable thermal conductivity, moderate thermal expansion may find metallic fuel applications in nuclear reactors.

Binary titanium alloys as dental implant materials-a review.

PubMed

Liu, Xiaotian; Chen, Shuyang; Tsoi, James K H; Matinlinna, Jukka Pekka

2017-10-01

Titanium (Ti) has been used for long in dentistry and medicine for implant purpose. During the years, not only the commercially pure Ti but also some alloys such as binary and tertiary Ti alloys were used. The aim of this review is to describe and compare the current literature on binary Ti alloys, including Ti-Zr, Ti-In, Ti-Ag, Ti-Cu, Ti-Au, Ti-Pd, Ti-Nb, Ti-Mn, Ti-Mo, Ti-Cr, Ti-Co, Ti-Sn, Ti-Ge and Ti-Ga, in particular to mechanical, chemical and biological parameters related to implant application. Literature was searched using the PubMed and Web of Science databases, as well as google without limiting the year, but with principle key terms such as ' Ti alloy', 'binary Ti ', 'Ti-X' (with X is the alloy element), 'dental implant' and 'medical implant'. Only laboratory studies that intentionally for implant or biomedical applications were included. According to available literatures, we might conclude that most of the binary Ti alloys with alloying <20% elements of Zr, In, Ag, Cu, Au, Pd, Nb, Mn, Cr, Mo, Sn and Co have high potential as implant materials, due to good mechanical performance without compromising the biocompatibility and biological behaviour compare to cp-Ti.

Phase Equilibria of Sn-Co-Cu Ternary System

NASA Astrophysics Data System (ADS)

Chen, Yu-Kai; Hsu, Chia-Ming; Chen, Sinn-Wen; Chen, Chih-Ming; Huang, Yu-Chih

2012-10-01

Sn-Co-Cu ternary alloys are promising lead-free solders, and isothermal sections of Sn-Co-Cu phase equilibria are fundamentally important for the alloys' development and applications. Sn-Co-Cu ternary alloys were prepared and equilibrated at 523 K, 1073 K, and 1273 K (250 °C, 800 °C, and 1000 °C), and the equilibrium phases were experimentally determined. In addition to the terminal solid solutions and binary intermetallic compounds, a new ternary compound, Sn3Co2Cu8, was found. The solubilities of Cu in the α-CoSn3 and CoSn2 phases at 523 K (250 °C) are 4.2 and 1.6 at. pct, respectively, while the Cu solubility in the α-Co3Sn2 phase is as high as 20.0 at. pct. The Cu solubility increases with temperature and is around 30.0 at. pct in the β-Co3Sn2 at 1073 K (800 °C). The Co solubility in the η-Cu6Sn5 phase is also significant and is 15.5 at. pct at 523 K (250 °C).

Friction and wear of iron-base binary alloys in sliding contact with silicon carbide in vacuum

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1980-01-01

Multipass sliding friction experiments were conducted with various iron base binary alloys in contact with a single crystal silicon carbide surface in vacuum. Results indicate that the atomic size and concentration of alloy elements play important roles in controlling the transfer and friction properties of iron base binary alloys. Alloys having high solute concentration produce more transfer than do alloys having low solute concentration. The coefficient of friction during multipass sliding generally increases with an increase in the concentration of alloying element. The change of friction with succeeding passes after the initial pass also increases as the solute to iron, atomic radius ratio increases or decreases from unity.

High-field superconductivity in the Nb-Ti-Zr ternary system

NASA Astrophysics Data System (ADS)

Ralls, K. M.; Rose, R. M.; Wulff, J.

1980-06-01

Resistive critical current densities, critical fields, and normal-state electrical resistivities were obtained at 4.2 °K for 55 alloys in the Nb-Ti-Zr ternary alloy system, excepting Ti-Zr binary compositions. The resistive critical field as a function of ternary composition has a saddle point between the Nb-Ti and Nb-Zr binaries, so that ternary alloying in this system is not expected to result in higher critical fields than the binary alloys.

Investigating the Thermal and Phase Stability of Nanocrystalline Ni-W Produced by Electrodeposition, Sputtering, and Mechanical Alloying

NASA Astrophysics Data System (ADS)

Marvel, Christopher Jonathan

The development of nanocrystalline materials has been increasingly pursued over the last few decades. They have been shown to exhibit superior properties compared to their coarse-grain counterparts, and thus present a tremendous opportunity to revolutionize the performance of nanoscale devices or bulk structural materials. However, nanocrystalline materials are highly prone to grain growth, and if the nanocrystalline grains coarsen, the beneficial properties are lost. There is a strong effort to determine the most effective thermal stability mechanisms to avoid grain growth, but the physical nature of nanocrystalline grain growth is still unclear due to a lack of detailed understanding of nanocrystalline microstructures. Furthermore, the influence of contamination has scarcely been explored with advanced transmission electron microscopy techniques, nor has there been a direct comparison of alloys fabricated with different bulk processes. Therefore, this research has applied aberration-corrected scanning transmission electron microscopy to characterize nanocrystalline Ni-W on the atomic scale and elucidate the physical grain growth behavior. Three primary objectives were pursued: (1) explore the thermal stability mechanisms of nanocrystalline Ni-W, (2) evaluate the phase stability of Ni-W and link any findings to grain growth behavior, and (3) compare the influences of bulk fabrication processing, including electrodeposition, DC magnetron sputtering, and mechanical alloying, on the thermal stability and phase stability of Ni-W. Several thermal stability mechanisms were identified throughout the course of this research. First and foremost, W-segregation was scarcely observed to grain boundaries, and it is unclear if W-segregation improves thermal stability contrary to most reports in the 2 literature. Long-range Ni4W chemical ordering was observed in alloys with more than 20 at.% W, and it is likely Ni4W domains reduce grain boundary mobility. In addition, lattice diffusivity calculations conceptually suggested that increasing W alloying concentrations can decrease the grain growth rate. The strongest evidence of grain growth stagnation was via nanoscale oxide particle drag in highly contaminated electrodeposited alloys. Interestingly, W-segregation was also detected to the oxide phase boundaries and revealed a potential indirect mechanism of thermal stability. The phase stability of pure and contaminated Ni-W alloys was investigated with density functional theory. Primarily, the calculations suggested that the intermetallic phases NiW and NiW2 are thermodynamically unstable, meaning the binary phase diagram is incorrect, but the ternary carbides Ni 6W6C and Ni2W4C are stable. Several Ni-W binary and Ni-W-C ternary phase diagrams were constructed using a simplified CALPHAD approach to improve the understanding of Ni-W phase stability. Lastly, it was determined that the fabrication process greatly influences the impurity types and concentrations of the alloys, and therefore greatly dictate which thermal stability mechanisms are active. Mechanically alloyed samples were found to be the most resistant to grain growth. The findings of this research will hopefully guide future efforts to design more thermally stable nanocrystalline alloys. The link between phase stability and grain growth behavior of Ni-W was thoroughly discussed, as well as the dependence of bulk fabrication processing on the contamination found in the alloys. Ultimately, this research has greatly expanded the general understanding of nanocrystalline Ni-W microstructures, and it is likely that similar phenomena occur in other nanocrystalline systems.

Morphological instabilities of rapidly solidified binary alloys under weak flow

NASA Astrophysics Data System (ADS)

Kowal, Katarzyna; Davis, Stephen

2017-11-01

Additive manufacturing, or three-dimensional printing, offers promising advantages over existing manufacturing techniques. However, it is still subject to a range of undesirable effects. One of these involves the onset of flow resulting from sharp thermal gradients within the laser melt pool, affecting the morphological stability of the solidified alloys. We examine the linear stability of the interface of a rapidly solidifying binary alloy under weak boundary-layer flow by performing an asymptotic analysis for a singular perturbation problem that arises as a result of departures from the equilibrium phase diagram. Under no flow, the problem involves cellular and pulsatile instabilities, stabilised by surface tension and attachment kinetics. We find that travelling waves appear as a result of flow and we map out the effect of flow on two absolute stability boundaries as well as on the cells and solute bands that have been observed in experiments under no flow. This work is supported by the National Institute of Standards and Technology [Grant Number 70NANB14H012].

Investigation of High Temperature Ductility Losses in Alpha-Beta Titanium Alloys

DTIC Science & Technology

1988-04-01

Gleeble simulation of GTAW thermal _ cycles, Figure 1.1 (6). They found that Ti-6AI-4V (Ti-64), Ti-6A1-2Nb-lTa-0.8Mo (Ti-6211), and Ti-6AI suffered...or weak beta stabilizers depending on the other alloying elements present. Vanadium, molybdenum, tantalum, niobium, chromium , silicon, copper...elements. Chromium , - silicon, copper, manganese, cobalt, iron, and hydrogen are all eutectic formers. A schematic binary phase diagram of a 0 beta

Plasma Processing Systems for the Manufacture of Refractory Metals and their Alloys for Military Needs

DTIC Science & Technology

1978-10-09

melting point is around 4000*K. An exceedingly interesting feature of these solidification composites is the formation of fibrous MC type carbide ...the matrix could be refractory metal binary alloys with copper or uranium and the eutectic phase could be carbide of tungsten, * molybdenum, tantalum or...42 Accs -n or - *DTTI Tf Avn ! -7ll ’ i CrDi t , l’’*i,;. LIST OF FIGURES FIG. 1 Flow Diagram of Cemented Carbide Manufacture

Cellular-dendritic transition in directionally solidified binary alloys

NASA Technical Reports Server (NTRS)

Tewari, S. N.; Laxmanan, V.

1987-01-01

The microstructural development of binary alloys during directional solidification is studied. Cellular growth data for the Al-Cu and Pb-Sn binary alloy systems are analyzed in order evaluate the criteria of Kurz and Fisher (1981) and Trivedi (1984) for cellular-dendritic transition. It is observed that the experimental growth values do not correlate with the Kurz and Fisher or Trivedi data.

High-Throughput Study of Diffusion and Phase Transformation Kinetics of Magnesium-Based Systems for Automotive Cast Magnesium Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Alan A; Zhao, Ji-Cheng; Riggi, Adrienne

The objective of the proposed study is to establish a scientific foundation on kinetic modeling of diffusion, phase precipitation, and casting/solidification, in order to accelerate the design and optimization of cast magnesium (Mg) alloys for weight reduction of U.S. automotive fleet. The team has performed the following tasks: 1) study diffusion kinetics of various Mg-containing binary systems using high-throughput diffusion multiples to establish reliable diffusivity and mobility databases for the Mg-aluminum (Al)-zinc (Zn)-tin (Sn)-calcium (Ca)-strontium (Sr)-manganese (Mn) systems; 2) study the precipitation kinetics (nucleation, growth and coarsening) using both innovative dual-anneal diffusion multiples and cast model alloys to provide largemore » amounts of kinetic data (including interfacial energy) and microstructure atlases to enable implementation of the Kampmann-Wagner numerical model to simulate phase transformation kinetics of non-spherical/non-cuboidal precipitates in Mg alloys; 3) implement a micromodel to take into account back diffusion in the solid phase in order to predict microstructure and microsegregation in multicomponent Mg alloys during dendritic solidification especially under high pressure die-casting (HPDC) conditions; and, 4) widely disseminate the data, knowledge and information using the Materials Genome Initiative infrastructure (http://www.mgidata.org) as well as publications and digital data sharing to enable researchers to identify new pathways/routes to better cast Mg alloys.« less

Fabrication of biodegradable Zn-Al-Mg alloy: Mechanical properties, corrosion behavior, cytotoxicity and antibacterial activities.

PubMed

Bakhsheshi-Rad, H R; Hamzah, E; Low, H T; Kasiri-Asgarani, M; Farahany, S; Akbari, E; Cho, M H

2017-04-01

In this work, binary Zn-0.5Al and ternary Zn-0.5Al-xMg alloys with various Mg contents were investigated as biodegradable materials for implant applications. Compared with Zn-0.5Al (single phase), Zn-0.5Al-xMg alloys consisted of the α-Zn and Mg 2 (Zn, Al) 11 with a fine lamellar structure. The results also revealed that ternary Zn-Al-Mg alloys presented higher micro-hardness value, tensile strength and corrosion resistance compared to the binary Zn-Al alloy. In addition, the tensile strength and corrosion resistance increased with increasing the Mg content in ternary alloys. The immersion tests also indicated that the corrosion rates in the following order Zn-0.5Al-0.5Mg

Concentration dependence of electrical resistivity of binary liquid alloy HgZn: Ab-initio study

NASA Astrophysics Data System (ADS)

Sharma, Nalini; Thakur, Anil; Ahluwalia, P. K.

2013-06-01

The electrical resistivity of HgZn liquid alloy has been made calculated using Troullier and Martins ab-initio pseudopotential as a function of concentration. Hard sphere diameters of Hg and Zn are obtained through the inter-ionic pair potential have been used to calculate partial structure factors. Considering the liquid alloy to be a ternary mixture Ziman's formula for calculating the resistivity of binary liquid alloys, modified for complex formation, has been used. These results suggest that ab-initio approach for calculating electrical resistivity is quite successful in explaining the electronic transport properties of binary Liquid alloys.

Large-Grain Tin-Rich Perovskite Films for Efficient Solar Cells via Metal Alloying Technique.

PubMed

Tavakoli, Mohammad Mahdi; Zakeeruddin, Shaik Mohammed; Grätzel, Michael; Fan, Zhiyong

2018-03-01

Fast research progress on lead halide perovskite solar cells has been achieved in the past a few years. However, the presence of lead (Pb) in perovskite composition as a toxic element still remains a major issue for large-scale deployment. In this work, a novel and facile technique is presented to fabricate tin (Sn)-rich perovskite film using metal precursors and an alloying technique. Herein, the perovskite films are formed as a result of the reaction between Sn/Pb binary alloy metal precursors and methylammonium iodide (MAI) vapor in a chemical vapor deposition process carried out at 185 °C. It is found that in this approach the Pb/Sn precursors are first converted to (Pb/Sn)I 2 and further reaction with MAI vapor leads to the formation of perovskite films. By using Pb-Sn eutectic alloy, perovskite films with large grain sizes up to 5 µm can be grown directly from liquid phase metal. Consequently, using an alloying technique and this unique growth mechanism, a less-toxic and efficient perovskite solar cell with a power conversion efficiency (PCE) of 14.04% is demonstrated, while pure Sn and Pb perovskite solar cells prepared in this manner yield PCEs of 4.62% and 14.21%, respectively. It is found that this alloying technique can open up a new direction to further explore different alloy systems (binary or ternary alloys) with even lower melting point. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Cu-Li-Sn Phase Diagram: Isopleths, Liquidus Projection and Reaction Scheme

PubMed Central

Flandorfer, Hans

2016-01-01

The Cu-Li-Sn phase diagram was constructed based on XRD and DTA data of 60 different alloy compositions. Eight ternary phases and 14 binary solid phases form 44 invariant ternary reactions, which are illustrated by a Scheil-Schulz reaction scheme and a liquidus projection. Phase equilibria as a function of concentration and temperature are shown along nine isopleths. This report together with an earlier publication of our group provides for the first time comprehensive investigations of phase equilibria and respective phase diagrams. Most of the phase equilibria could be established based on our experimental results. Only in the Li-rich part where many binary and ternary compounds are present estimations had to be done which are all indicated by dashed lines. A stable ternary miscibility gap could be found which was predicted by modelling the liquid ternary phase in a recent work. The phase diagrams are a crucial input for material databases and thermodynamic optimizations regarding new anode materials for high-power Li-ion batteries. PMID:27788175

[Study on high temperature oxidation of Ni-Cr ceramic alloys. Effects of Cr and Mo].

PubMed

Mizutani, M

1990-03-01

The effects of Cr and Mo addition to Ni-Cr alloys on high temperature oxidation were investigated. The alloys were prepared with the composition of Cr ranging from 5 to 40 wt%. Also 2, 4 and 9 wt% of Mo was added to both Ni-5% Cr and Ni-20% Cr binary alloys. The alloys were heated at 800 degrees C, 900 degrees C and 1000 degrees C for 15 minutes in air, and the weight change after heat treatment was measured by electric automatic balance. The weight change during heating was measured by thermogravimetric measurement (TG). The products after heat treatment were characterized by X-ray diffraction and scanning electron microscopy (SEM). The results are summarized as follows: The Ni-Cr binary alloys were classified into three types of Cr ranging from 5 to 20 wt%, Cr 25% and Cr from 30 wt% to 40 wt% according to the weight gains with oxidation. In the case of the more than 25 wt% Cr content of the Ni-Cr binary alloys, the weight gain was extremely low and the heating temperature effects on the weight change were also small. X-ray diffraction study showed that NiO, NiCr2O4 and Cr2O3 formed on the surface of the Ni-Cr binary alloys whose composition of Cr ranged from 5 to 25 wt%, whereas NiO and NiCr2O4 rarely formed on the Ni-Cr binary alloys whose composition of Cr ranged from 30 to 40 wt%. This suggests that the formation of Cr2O3 prevents the formation of NiO on the alloy with a high Cr content. The weight gain of the Ni-Cr-Mo ternary alloys was smaller than that of the Ni-Cr binary alloys without Mo, and the temperature effects on the weight gain of the Ni-Cr-Mo ternary alloys were different for each Cr content. However, the effect of the amounts of Mo was small. NiO, NiCr2O4, Cr2O3 and MoO2 were identified by X-ray diffraction on the surface of the Ni-Cr-Mo ternary alloys. According to the SEM observation, it seems that NiO was formed at the outermost layer, both NiCr2O4 and Cr2O3 at the inside layer, and MoO2 at the innermost layer. The formation of both NiO and Cr2O3 on the Ni-Cr-Mo ternary alloys was restrained compared with that of the Ni-Cr binary alloys. However, the adhesion of oxides to the Ni-Cr-Mo ternary alloys was lower than that of the Ni-Cr binary alloys.

TERNARY ALLOY-CONTAINING PLUTONIUM

DOEpatents

Waber, J.T.

1960-02-23

Ternary alloys of uranium and plutonium containing as the third element either molybdenum or zirconium are reported. Such alloys are particularly useful as reactor fuels in fast breeder reactors. The alloy contains from 2 to 25 at.% of molybdenum or zirconium, the balance being a combination of uranium and plutonium in the ratio of from 1 to 9 atoms of uranlum for each atom of plutonium. These alloys are prepared by melting the constituent elements, treating them at an elevated temperature for homogenization, and cooling them to room temperature, the rate of cooling varying with the oomposition and the desired phase structure. The preferred embodiment contains 12 to 25 at.% of molybdenum and is treated by quenching to obtain a body centered cubic crystal structure. The most important advantage of these alloys over prior binary alloys of both plutonium and uranium is the lack of cracking during casting and their ready machinability.

Metastable phase in binary and ternary 12-carat gold alloys at low temperature

NASA Astrophysics Data System (ADS)

Lamiri, Imene; Abdelbaky, Mohammed S. M.; Hamana, Djamel; García-Granda, Santiago

2018-04-01

Low temperature phase transitions in 12-carat gold alloys have been investigated for binary Au-Cu and ternary Au-Cu-Ag compositions. The thermal analyses investigations using differential scanning calorimetry (DSC) and the dilatometry were performed in the 50–300 °C temperature range in order to detect the structural transformations. The thermal analyses were carried out on annealed samples at 700 °C for two hour followed by water quenching. They reveal an important new reaction for both used compositions and both thermal techniques confirm each other. This reaction has been assessed as pre-ordering reaction. SEM and STM imaging were performed on annealed samples at 700 °C for two hours and water quenched followed by a heating from room temperature up to the temperature of the new peaks obtained in the thermal study. The imaging reveals the relationship between the pre-ordering reaction and the surface aspect presented in the fact of dendrite precipitates. A series of SEM observation have been performed in order to follow the kinetic of the observed precipitates by the way of several series of heating up, from 140 to 220 °C for the binary composition and from 100 to 180 °C for the ternary composition. Furthermore, this study shows that the silver accelerates the ordering reaction.

Nanoalloying and phase transformations during thermal treatment of physical mixtures of Pd and Cu nanoparticles

PubMed Central

Mukundan, Vineetha; Yin, Jun; Joseph, Pharrah; Luo, Jin; Shan, Shiyao; Zakharov, Dmitri N; Zhong, Chuan-Jian; Malis, Oana

2014-01-01

Nanoscale alloying and phase transformations in physical mixtures of Pd and Cu ultrafine nanoparticles are investigated in real time with in situ synchrotron-based x-ray diffraction complemented by ex situ high-resolution transmission electron microscopy. The combination of metal–support interaction and reactive/non-reactive environment was found to determine the thermal evolution and ultimate structure of this binary system. At 300 °C, the nanoparticles supported on silica and carbon black intermix to form a chemically ordered CsCl-type (B2) alloy phase. The B2 phase transforms into a disordered fcc alloy at higher temperature (> 450 °C). The alloy nanoparticles supported on silica and carbon black are homogeneous in volume, but evidence was found of Pd surface enrichment. In sharp contrast, when supported on alumina, the two metals segregated at 300 °C to produce almost pure fcc Cu and Pd phases. Upon further annealing of the mixture on alumina above 600 °C, the two metals interdiffused, forming two distinct disordered alloys of compositions 30% and 90% Pd. The annealing atmosphere also plays a major role in the structural evolution of these bimetallic nanoparticles. The nanoparticles annealed in forming gas are larger than the nanoparticles annealing in helium due to reduction of the surface oxides that promotes coalescence and sintering. PMID:27877663

Structure and Properties of Titanium Tantalum Alloys for Biocompatibility

NASA Astrophysics Data System (ADS)

Huber, Daniel E.

In this thesis, the phase stability and elastic modulus of Ti-Ta simple binary alloys as well as alloys with small additions of ternary elements have been studied. The binary alloy from a nominal 8 to 28 wt.% Ta was first explored using a combinatorial approach. This approach included Laser Engineered Net Shape (LENSTM) processing of materials and subsequent characterization by instrumented indentation and site specific Transmission Electron Microscopy (TEM). The composition range of 15 to 75 wt.% Ta was further explored by more traditional methods that included vacuum arc melting high purity elements, X-Ray Diffraction (XRD) and modulus measurements made by ultrasonic methods. Beyond the simple binary, alloys with low levels of ternary elements, oxygen, aluminum, zirconium and small additions of rare earth oxides were investigated. The crystal structure with space group Cmcm was chosen for it applicability with P63/mmc and Im-3¯m sub group / super group symmetry. This provides a consistent crystal structure framework for the purpose of studying the alpha to beta transformation pathway and associated alpha' and alpha'' martensitic phases. In this case, the pathway is defined by both the lattice parameters and the value of the parameter "y", where the parameter "y" describes the atomic positions of the [002]alpha plane. It was found that the lattice parameter changes in the Ti-Ta binary alloys are similar to structures reported for compositions in the Ti-Nb system of similar atomic percentages. Although samples produced by the LENSTM; process and characterized by instrumented indentation demonstrated the correct trends in modulus behavior, absolute agreement was not seen with modulus values published in literature. Alloys of the binary Ti-Ta system produced from high purity materials do indeed show close agreement with literature where there exist two minima of modulus near the compositions of Ti-28Ta wt.% and Ti-68Ta wt.%. These two minima occur at the discreet boundary between alpha' / alpha'' and alpha'' / beta respectively. The role of oxygen as an alloying addition was studied as it relates to the stability of alpha' and alpha'' martensite, here it was found that oxygen will stabilize alpha' yet cause an increase in the Young's modulus. Rare earth additions to getter interstitial oxygen in the high purity materials show no further reduction in modulus. Conversely, additions of another alpha stabilizer, Al, proved to lower the alpha' stability, with one composition exhibiting a modulus as low as 53 GPa. Zirconium being a neutral element regarding alpha and beta stability slightly changed the structure and lattice parameter, while making a little or no difference in the observed modulus. Observations by TEM of quenched specimens indicate the rise in modulus observed between the two minima is not caused the appearance of o. Rather weak o reflections were observed in Ti-65Ta wt.% in the as arc-melted condition and on annealing for 450°C for 24 hours. Precipitates of o were not clearly identified by dark-field TEM imaging. High Resolution Scanning Transmission Electron Microscopy (HRSTEM) of the aged specimen indicated that o might exist as 3-5nm particles.

Determination of 200 °C Isothermal Section of Al-Ag-Ga Phase Diagram by Microanalysis, X-ray Diffraction, Hardness and Electrical Conductivity Measurements

NASA Astrophysics Data System (ADS)

Premović, Milena; Tomović, Milica; Minić, Duško; Manasijević, Dragan; Živković, Dragana; Ćosović, Vladan; Grković, Vladan; Đorđević, Aleksandar

2017-04-01

Ternary Al-Ag-Ga system at 200 °C was experimentally and thermodynamically assessed. Isothermal section was extrapolated using optimized thermodynamic parameters for constitutive binary systems. Microstructure and phase composition of the selected alloy samples were analyzed using light microscopy, scanning electron microscopy combined with energy-dispersive spectrometry and x-ray powder diffraction technique. The obtained experimental results were found to be in a close agreement with the predicted phase equilibria. Hardness and electrical conductivity of the alloy samples from four vertical sections Al-Ag80Ga20, Al-Ag60Ga40, Ag-Al80Ga20 and Ag-Al60Ga40 of the ternary Al-Ag-Ga system at 200 °C were experimentally determined using Brinell method and eddy current measurements. Additionally, hardness of the individual phases present in the microstructure of the studied alloy samples was determined using Vickers microhardness test. Based on experimentally obtained results, isolines of Brinell hardness and electrical conductivity were calculated for the alloys from isothermal section of the ternary Al-Ag-Ga system at 200 °C.

A combined APT and SANS investigation of α' phase precipitation in neutron-irradiated model FeCrAl alloys

DOE PAGES

Briggs, Samuel A.; Edmondson, Philip D.; Littrell, Kenneth C.; ...

2017-03-01

Here, FeCrAl alloys are currently under consideration for accident-tolerant fuel cladding applications in light water reactors owing to their superior high-temperature oxidation and corrosion resistance compared to the Zr-based alloys currently employed. However, their performance could be limited by precipitation of a Cr-rich α' phase that tends to embrittle high-Cr ferritic Fe-based alloys. In this study, four FeCrAl model alloys with 10–18 at.% Cr and 5.8–9.3 at.% Al were neutron-irradiated to nominal damage doses up to 7.0 displacements per atom at a target temperature of 320 °C. Small angle neutron scattering techniques were coupled with atom probe tomography to assessmore » the composition and morphology of the resulting α' precipitates. It was demonstrated that Al additions partially destabilize the α' phase, generally resulting in precipitates with lower Cr contents when compared with binary Fe-Cr systems. The precipitate morphology evolution with dose exhibited a transient coarsening regime akin to previously observed behavior in aged Fe-Cr alloys. Similar behavior to predictions of the LSW/UOKV models suggests that α' precipitation in irradiated FeCrAl is a diffusion-limited process with coarsening mechanisms similar to those in thermally aged high-Cr ferritic alloys.« less

Prediction of as-cast grain size of inoculated aluminum alloys melt solidified under non-isothermal conditions

NASA Astrophysics Data System (ADS)

Du, Qiang; Li, Yanjun

2015-06-01

In this paper, a multi-scale as-cast grain size prediction model is proposed to predict as-cast grain size of inoculated aluminum alloys melt solidified under non-isothermal condition, i.e., the existence of temperature gradient. Given melt composition, inoculation and heat extraction boundary conditions, the model is able to predict maximum nucleation undercooling, cooling curve, primary phase solidification path and final as-cast grain size of binary alloys. The proposed model has been applied to two Al-Mg alloys, and comparison with laboratory and industrial solidification experimental results have been carried out. The preliminary conclusion is that the proposed model is a promising suitable microscopic model used within the multi-scale casting simulation modelling framework.

A comparative study of the microstructures observed in statically cast and continuously cast Bi-In-Sn ternary eutectic alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sengupta, S.; Soda, H.; McLean, A.

2000-01-01

A ternary eutectic alloy with a composition of 57.2 pct Bi, 24.8 pct In, and 18 pct Sn was continuously cast into wire of 2 mm diameter with casting speeds of 14 and 79 mm/min using the Ohno Continuous Casting (OCC) process. The microstructures obtained were compared with those of statically cast specimens. Extensive segregation of massive Bi blocks, Bi complex structures, and tin-rich dendrites was found in specimens that were statically cast. Decomposition of {radical}Sn by a eutectoid reaction was confirmed based on microstructural evidence. Ternary eutectic alloy with a cooling rate of approximately 1 C/min formed a doublemore » binary eutectic. The double binary eutectic consisted of regions of BiIn and decomposed {radical}Sn in the form of a dendrite cell structure and regions of Bi and decomposed {radical}Sn in the form of a complex-regular cell. The Bi complex-regular cells, which are a ternary eutectic constituent, existed either along the boundaries of the BiIn-decomposed {radical}Sn dendrite cells or at the front of elongated dendrite cell structures. In the continuously cast wires, primary Sn dendrites coupled with a small Bi phase were uniformly distributed within the Bi-In alloy matrix. Neither massive Bi phase, Bi complex-regular cells, no BiIn eutectic dendrite cells were observed, resulting in a more uniform microstructure in contrast to the heavily segregated structures of the statically cast specimens.« less

Effects of alloying elements (Mn, Co, Al, W, Sn, B, C and S) on biodegradability and in vitro biocompatibility of pure iron.

PubMed

Liu, B; Zheng, Y F

2011-03-01

Pure iron was determined to be a valid candidate material for biodegradable metallic stents in recent animal tests; however, a much faster degradation rate in physiological environments was desired. C, Mn, Si, P, S, B, Cr, Ni, Pb, Mo, Al, Ti, Cu, Co, V and W are common alloying elements in industrial steels, with Cr, Ni, Mo, Cu, Ti, V and Si being acknowledged as beneficial in enhancing the corrosion resistance of iron. The purpose of the present work (using Fe-X binary alloy models) is to explore the effect of the remaining alloying elements (Mn, Co, Al, W, B, C and S) and one detrimental impurity element Sn on the biodegradability and biocompatibility of pure iron by scanning electron microscopy, X-ray diffraction, metallographic observation, tensile testing, microhardness testing, electrochemical testing, static (for 6 months) and dynamic (for 1 month with various dissolved oxygen concentrations) immersion testing, cytotoxicity testing, hemolysis and platelet adhesion testing. The results showed that the addition of all alloying elements except for Sn improved the mechanical properties of iron after rolling. Localized corrosion of Fe-X binary alloys was observed in both static and dynamic immersion tests. Except for the Fe-Mn alloy, which showed a significant decrease in corrosion rate, the other Fe-X binary alloy corrosion rates were close to that of pure iron. It was found that compared with pure iron all Fe-X binary alloys decreased the viability of the L929 cell line, none of experimental alloying elements significantly reduced the viability of vascular smooth muscle cells and all the elements except for Mn increased the viability of the ECV304 cell line. The hemolysis percentage of all Fe-X binary alloy models were less than 5%, and no sign of thrombogenicity was observed. In vitro corrosion and the biological behavior of these Fe-X binary alloys are discussed and a corresponding mechanism of corrosion of Fe-X binary alloys in Hank's solution proposed. As a concluding remark, Co, W, C and S are recommended as alloying elements for biodegradable iron-based biomaterials. Copyright © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Adhesion and friction of iron-base binary alloys in contact with silicon carbide in vacuum

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1980-01-01

Single pass sliding friction experiments were conducted with various iron base binary alloys (alloying elements were Ti, Cr, Mn, Ni, Rh, and W) in contact with a single crystal silicon carbide /0001/ surface in vacuum. Results indicate that atomic size and concentration of alloying elements play an important role in controlling adhesion and friction properties of iron base binary alloys. The coefficient of friction generally increases with an increase in solute concentration. The coefficient of friction increases linearly as the solute to iron atomic radius ratio increases or decreases from unity. The chemical activity of the alloying elements was also an important parameter in controlling adhesion and friction of alloys, as these latter properties are highly dependent upon the d bond character of the elements.

Surface tension estimation of high temperature melts of the binary alloys Ag-Au

NASA Astrophysics Data System (ADS)

Dogan, Ali; Arslan, Hüseyin

2017-11-01

Surface tension calculation of the binary alloys Ag-Au at the temperature of 1381 K, where Ag and Au have similar electronic structures and their atomic radii are comparable, are carried out in this study using several equations over entire composition range of Au. Apparently, the deviations from ideality of the bulk solutions, such as activities of Ag and Au are small and the maximum excess Gibbs free energy of mixing of the liquid phase is for instance -4500 J/mol at XAu = 0.5. Besides, the results obtained in Ag-Au alloys that at a constant temperature the surface tension increases with increasing composition while the surface tension decreases as the temperature increases for entire composition range of Au. Although data about surface tension of the Ag-Au alloy are limited, it was possible to make a comparison for the calculated results for the surface tension in this study with the available experimental data. Taken together, the average standard error analysis that especially the improved Guggenheim model in the other models gives the best agreement along with the experimental results at temperature 1383 K although almost all models are mutually in agreement with the other one.

Interfacial free energy controlling glass-forming ability of Cu-Zr alloys.

PubMed

Kang, Dong-Hee; Zhang, Hao; Yoo, Hanbyeol; Lee, Hyun Hwi; Lee, Sooheyong; Lee, Geun Woo; Lou, Hongbo; Wang, Xiaodong; Cao, Qingping; Zhang, Dongxian; Jiang, Jianzhong

2014-06-04

Glass is a freezing phase of a deeply supercooled liquid. Despite its simple definition, the origin of glass forming ability (GFA) is still ambiguous, even for binary Cu-Zr alloys. Here, we directly study the stability of the supercooled Cu-Zr liquids where we find that Cu64Zr36 at a supercooled temperature shows deeper undercoolability and longer persistence than other neighbouring compositions with an equivalent driving Gibbs free energy. This observation implies that the GFA of the Cu-Zr alloys is significantly affected by crystal-liquid interfacial free energy. In particular, the crystal-liquid interfacial free energy of Cu64Zr36 in our measurement was higher than that of other neighbouring liquids and, coincidently a molecular dynamics simulation reveals a larger glass-glass interfacial energy value at this composition, which reflects more distinct configuration difference between liquid and crystal phase. The present results demonstrate that the higher crystal-liquid interfacial free energy is a prerequisite of good GFA of the Cu-Zr alloys.

Microstructural development from interdiffusion and reaction between U–Mo and AA6061 alloys annealed at 600° and 550 °C

DOE PAGES

Perez, E.; Keiser, D. D.; Sohn, Y. H.

2016-05-10

The U.S. Material Management and Minimization Reactor Conversion Program is developing low enrichment fuel systems encased in Al-alloy for use in research and test reactors. Monolithic fuel plates have local regions where the Usingle bondMo fuel plate may come into contact with the Al-alloy 6061 (AA6061) cladding. This results in the development of interdiffusion zones with complex microstructures with multiple phases. In this study, the microstructural development of diffusion couples, U–7 wt%Mo, U–10 wt%Mo, and U–12 wt%Mo vs. AA6061, annealed at 600 °C for 24 h and at 550 °C for 1, 5, and 20 h, were analyzed by scanningmore » electron microscopy with x-ray energy dispersive spectroscopy. The microstructural development and kinetics were compared to diffusion couples U–Mo vs. high purity Al and binary Al–Si alloys. As a result, the diffusion couples developed complex interaction regions where phase development was influenced by the alloying additions of the AA6061.« less

Atom Probe Tomography Analysis of the Distribution of Rhenium in Nickel Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mottura, A.; Warnken, N; Miller, Michael K

2010-01-01

Atom probe tomography (APT) is used to characterise the distributions of rhenium in a binary Ni-Re alloy and the nickel-based single-crystal CMSX-4 superalloy. A purpose-built algorithm is developed to quantify the size distribution of solute clusters, and applied to the APT datasets to critique the hypothesis that rhenium is prone to the formation of clusters in these systems. No evidence is found to indicate that rhenium forms solute clusters above the level expected from random fluctuations. In CMSX-4, enrichment of Re is detected in the matrix phase close to the matrix/precipitate ({gamma}/{gamma}{prime}) phase boundaries. Phase field modelling indicates that thismore » is due to the migration of the {gamma}/{gamma}{prime} interface during cooling from the temperature of operation. Thus, neither clustering of rhenium nor interface enrichments can be the cause of the enhancement in high temperature mechanical properties conferred by rhenium alloying.« less

Precipitation-Strengthened, High-Temperature, High-Force Shape Memory Alloys

NASA Technical Reports Server (NTRS)

Noebe, Ronald D.; Draper, Susan L.; Nathal, Michael V.; Crombie, Edwin A.

2008-01-01

Shape memory alloys (SMAs) are an enabling component in the development of compact, lightweight, durable, high-force actuation systems particularly for use where hydraulics or electrical motors are not practical. However, commercial shape memory alloys based on NiTi are only suitable for applications near room temperature, due to their relatively low transformation temperatures, while many potential applications require higher temperature capability. Consequently, a family of (Ni,Pt)(sub 1-x)Ti(sub x) shape memory alloys with Ti concentrations ranging from about 15 to 25 at.% have been developed for applications in which there are requirements for SMA actuators to exert high forces at operating temperatures higher than those of conventional binary NiTi SMAs. These alloys can be heat treated in the range of 500 C to produce a series of fine precipitate phases that increase the strength of alloy while maintaining a high transformation temperature, even in Ti-lean compositions.

On Nb Silicide Based Alloys: Alloy Design and Selection.

PubMed

Tsakiropoulos, Panos

2018-05-18

The development of Nb-silicide based alloys is frustrated by the lack of composition-process-microstructure-property data for the new alloys, and by the shortage of and/or disagreement between thermodynamic data for key binary and ternary systems that are essential for designing (selecting) alloys to meet property goals. Recent publications have discussed the importance of the parameters δ (related to atomic size), Δχ (related to electronegativity) and valence electron concentration (VEC) (number of valence electrons per atom filled into the valence band) for the alloying behavior of Nb-silicide based alloys (J Alloys Compd 748 (2018) 569), their solid solutions (J Alloys Compd 708 (2017) 961), the tetragonal Nb₅Si₃ (Materials 11 (2018) 69), and hexagonal C14-NbCr₂ and cubic A15-Nb₃X phases (Materials 11 (2018) 395) and eutectics with Nb ss and Nb₅Si₃ (Materials 11 (2018) 592). The parameter values were calculated using actual compositions for alloys, their phases and eutectics. This paper is about the relationships that exist between the alloy parameters δ, Δχ and VEC, and creep rate and isothermal oxidation (weight gain) and the concentrations of solute elements in the alloys. Different approaches to alloy design (selection) that use property goals and these relationships for Nb-silicide based alloys are discussed and examples of selected alloy compositions and their predicted properties are given. The alloy design methodology, which has been called NICE (Niobium Intermetallic Composite Elaboration), enables one to design (select) new alloys and to predict their creep and oxidation properties and the macrosegregation of Si in cast alloys.

On Nb Silicide Based Alloys: Alloy Design and Selection

PubMed Central

Tsakiropoulos, Panos.

2018-01-01

The development of Nb-silicide based alloys is frustrated by the lack of composition-process-microstructure-property data for the new alloys, and by the shortage of and/or disagreement between thermodynamic data for key binary and ternary systems that are essential for designing (selecting) alloys to meet property goals. Recent publications have discussed the importance of the parameters δ (related to atomic size), Δχ (related to electronegativity) and valence electron concentration (VEC) (number of valence electrons per atom filled into the valence band) for the alloying behavior of Nb-silicide based alloys (J Alloys Compd 748 (2018) 569), their solid solutions (J Alloys Compd 708 (2017) 961), the tetragonal Nb5Si3 (Materials 11 (2018) 69), and hexagonal C14-NbCr2 and cubic A15-Nb3X phases (Materials 11 (2018) 395) and eutectics with Nbss and Nb5Si3 (Materials 11 (2018) 592). The parameter values were calculated using actual compositions for alloys, their phases and eutectics. This paper is about the relationships that exist between the alloy parameters δ, Δχ and VEC, and creep rate and isothermal oxidation (weight gain) and the concentrations of solute elements in the alloys. Different approaches to alloy design (selection) that use property goals and these relationships for Nb-silicide based alloys are discussed and examples of selected alloy compositions and their predicted properties are given. The alloy design methodology, which has been called NICE (Niobium Intermetallic Composite Elaboration), enables one to design (select) new alloys and to predict their creep and oxidation properties and the macrosegregation of Si in cast alloys. PMID:29783707

Alloy hardening and softening in binary molybdenum alloys as related to electron concentration

NASA Technical Reports Server (NTRS)

Stephens, J. R.; Witzke, W. R.

1972-01-01

An investigation was conducted to determine the effects of alloy additions of hafnium, tantalum, tungsten, rhenium, osmium, iridium, and platinum on hardness of molybdenum. Special emphasis was placed on alloy softening in these binary molybdenum alloys. Results showed that alloy softening was produced by those elements having an excess of s+d electrons compared to molybdenum, while those elements having an equal number or fewer s+d electrons that molybdenum failed to produce alloy softening. Alloy softening and alloy hardening can be correlated with the difference in number of s+d electrons of the solute element and molybdenum.

Binary titanium alloys as dental implant materials—a review

PubMed Central

Liu, Xiaotian; Chen, Shuyang; Matinlinna, Jukka Pekka

2017-01-01

Abstract Titanium (Ti) has been used for long in dentistry and medicine for implant purpose. During the years, not only the commercially pure Ti but also some alloys such as binary and tertiary Ti alloys were used. The aim of this review is to describe and compare the current literature on binary Ti alloys, including Ti–Zr, Ti–In, Ti–Ag, Ti–Cu, Ti–Au, Ti–Pd, Ti–Nb, Ti–Mn, Ti–Mo, Ti–Cr, Ti–Co, Ti–Sn, Ti–Ge and Ti–Ga, in particular to mechanical, chemical and biological parameters related to implant application. Literature was searched using the PubMed and Web of Science databases, as well as google without limiting the year, but with principle key terms such as ‘ Ti alloy’, ‘binary Ti ’, ‘Ti-X’ (with X is the alloy element), ‘dental implant’ and ‘medical implant’. Only laboratory studies that intentionally for implant or biomedical applications were included. According to available literatures, we might conclude that most of the binary Ti alloys with alloying <20% elements of Zr, In, Ag, Cu, Au, Pd, Nb, Mn, Cr, Mo, Sn and Co have high potential as implant materials, due to good mechanical performance without compromising the biocompatibility and biological behaviour compare to cp-Ti. PMID:29026646

Effect of deformation twin on toughness in magnesium binary alloys

NASA Astrophysics Data System (ADS)

Somekawa, Hidetoshi; Inoue, Tadanobu; Tsuzaki, Kaneaki

2015-08-01

The impact of alloying elements on toughness was investigated using eight kinds of Mg-0.3 at.% X (X = Al, Ag, Ca, Gd, Mn, Pb, Y and Zn) binary alloys with meso-grained structures. These binary alloys had an average grain size of approximately 20 μm. The fracture toughness and crack propagation behaviour were influenced by the alloying elements; the Mg-Ag and Mg-Pb alloys had the highest and the lowest toughness amongst the alloys, respectively, irrespective of presence in their ? type deformation twins. The twin boundaries affected the crack propagation behaviour in most of the alloys; in contrast, not only was the fracture related to the twin boundaries, but also the intergranular fracture occurred in the alloys that included rare earth elements. The influential factor for toughness in the meso- and the coarse-grained magnesium alloys, which readily formed deformation twins during plastic deformation, was not the change in lattice parameter with chemical composition, but the twin boundary segregation energy.

Grain Floatation During Equiaxed Solidification of an Al-Cu Alloy in a Side-Cooled Cavity: Part II—Numerical Studies

NASA Astrophysics Data System (ADS)

Kumar, Arvind; Walker, Mike J.; Sundarraj, Suresh; Dutta, Pradip

2011-08-01

In this article, a single-phase, one-domain macroscopic model is developed for studying binary alloy solidification with moving equiaxed solid phase, along with the associated transport phenomena. In this model, issues such as thermosolutal convection, motion of solid phase relative to liquid and viscosity variations of the solid-liquid mixture with solid fraction in the mobile zone are taken into account. Using the model, the associated transport phenomena during solidification of Al-Cu alloys in a rectangular cavity are predicted. The results for temperature variation, segregation patterns, and eutectic fraction distribution are compared with data from in-house experiments. The model predictions compare well with the experimental results. To highlight the influence of solid phase movement on convection and final macrosegregation, the results of the current model are also compared with those obtained from the conventional solidification model with stationary solid phase. By including the independent movement of the solid phase into the fluid transport model, better predictions of macrosegregation, microstructure, and even shrinkage locations were obtained. Mechanical property prediction models based on microstructure will benefit from the improved accuracy of this model.

Thermal Stability of Nanocrystalline Alloys by Solute Additions and A Thermodynamic Modeling

NASA Astrophysics Data System (ADS)

Saber, Mostafa

Nanocrystalline alloys show superior properties due to their exceptional microstructure. Thermal stability of these materials is a critical aspect. It is well known that grain boundaries in nanocrystalline microstructures cause a significant increase in the total free energy of the system. A driving force provided to reduce this excess free energy can cause grain growth. The presence of a solute addition within a nanocrystalline alloy can lead to the thermal stability. Kinetic and thermodynamic stabilization are the two basic mechanisms with which stability of a nanoscale grain size can be achieved at high temperatures. The basis of this thesis is to study the effect of solute addition on thermal stability of nanocrystalline alloys. The objective is to determine the effect of Zr addition on the thermal stability of mechanically alloyed nanocrysatillne Fe-Cr and Fe-Ni alloys. In Fe-Cr-Zr alloy system, nanoscale grain size stabilization was maintained up to 900 °C by adding 2 at% Zr. Kinetic pinning by intermetallic particles in the nanoscale range was identified as a primary mechanism of thermal stabilization. In addition to the grain size strengthening, intermetallic particles also contribute to strengthening mechanisms. The analysis of microhardness, XRD data, and measured grain sizes from TEM micrographs suggested that both thermodynamic and kinetic mechanisms are possible mechanisms. It was found that alpha → gamma phase transformation in Fe-Cr-Zr system does not influence the grain size stabilization. In the Fe-Ni-Zr alloy system, it was shown that the grain growth in Fe-8Ni-1Zr alloy is much less than that of pure Fe and Fe-8Ni alloy at elevated temperatures. The microstructure of the ternary Fe-8Ni-1Zr alloy remains in the nanoscale range up to 700 °C. Using an in-situ TEM study, it was determined that drastic grain growth occurs when the alpha → gamma phase transformation occurs. Accordingly, there can be a synergistic relationship between grain growth and alpha → gamma phase transformation in Fe-Ni-Zr alloys. In addition to the experimental study of thermal stabilization of nanocrystalline Fe-Cr-Zr or Fe-Ni-Zr alloys, the thesis presented here developed a new predictive model, applicable to strongly segregating solutes, for thermodynamic stabilization of binary alloys. This model can serve as a benchmark for selecting solute and evaluating the possible contribution of stabilization. Following a regular solution model, both the chemical and elastic strain energy contributions are combined to obtain the mixing enthalpy. The total Gibbs free energy of mixing is then minimized with respect to simultaneous variations in the grain boundary volume fraction and the solute concentration in the grain boundary and the grain interior. The Lagrange multiplier method was used to obtained numerical solutions. Application are given for the temperature dependence of the grain size and the grain boundary solute excess for selected binary system where experimental results imply that thermodynamic stabilization could be operative. This thesis also extends the binary model to a new model for thermodynamic stabilization of ternary nanocrystalline alloys. It is applicable to strongly segregating size-misfit solutes and uses input data available in the literature. In a same manner as the binary model, this model is based on a regular solution approach such that the chemical and elastic strain energy contributions are incorporated into the mixing enthalpy DeltaHmix, and the mixing entropy DeltaSmix is obtained using the ideal solution approximation. The Gibbs mixing free energy Delta Gmix is then minimized with respect to simultaneous variations in grain growth and solute segregation parameters. The Lagrange multiplier method is similarly used to obtain numerical solutions for the minimum Delta Gmix. The temperature dependence of the nanocrystalline grain size and interfacial solute excess can be obtained for selected ternary systems. As an example, model predictions are compared to experimental results for Fe-Cr-Zr and Fe-Ni-Zr alloy systems. Consistency between the experimental results and the present model predictions provide a more rigorous criterion for investigating thermal stabilization. However, other possible contributions for grain growth stabilization should still be considered.

Temperature dependent structural and dynamical properties of liquid Cu80Si20 binary alloy

NASA Astrophysics Data System (ADS)

Suthar, P. H.; Shah, A. K.; Gajjar, P. N.

2018-05-01

Ashcroft and Langreth binary structure factor have been used to study for pair correlation function and the study of dynamical variable: velocity auto correlation functions, power spectrum and mean square displacement calculated based on the static harmonic well approximation in liquid Cu80Si20 binary alloy at wide temperature range (1140K, 1175K, 1210K, 1250K, 1373K, 1473K.). The effective interaction for the binary alloy is computed by our well established local pseudopotential along with the exchange and correction functions Sarkar et al(S). The negative dip in velocity auto correlation decreases as the various temperature is increases. For power spectrum as temperature increases, the peak of power spectrum shifts toward lower ω. Good agreement with the experiment is observed for the pair correlation functions. Velocity auto correlation showing the transferability of the local pseudopotential used for metallic liquid environment in the case of copper based binary alloys.

Development of ultrafine Ti-Fe-Sn in-situ composite with enhanced plasticity

NASA Astrophysics Data System (ADS)

Mondal, B.; Samal, S.; Biswas, K.; Govind

2012-01-01

The present investigation is aimed at developing ultrafine eutectic/dendrite Ti-Fe-Sn in-situ composite with balanced combination of strength and plasticity. It also studies the microstructure evolution in the series of hypereutectic Ti-Fe-Sn ternary alloys. Sn concentration of these alloys has been varied from 0 - 10 atom% in the binary alloy (Ti71Fe29) keeping the Ti concentration fixed. These alloys have been prepared by arc melting under an Ar atmosphere on a water-cooled Cu hearth, which are subsequently suction cast in a split Cu-mold under an Ar atmosphere. Detailed X-ray diffraction (XRD) study shows the presence of TiFe, β-Ti, and Ti3Sn phases. The SEM micrographs reveal that the microstructures consist of fine scale eutectic matrix (β-Ti and TiFe) with primary dendrite phases (TiFe and/or Ti3Sn) depending on concentration of Sn. α -Ti forms as a eutectoid reaction product of β-Ti. The room temperature uniaxial compressive test reveals simultaneous improvement in the strength (1942 MPa) and plasticity (13.1 %) for Ti71Fe26Sn3 ternary alloy. The fracture surface indicates a ductile mode of fracture for the alloy.

Precipitation behavior of AlxCoCrFeNi high entropy alloys under ion irradiation

NASA Astrophysics Data System (ADS)

Yang, Tengfei; Xia, Songqin; Liu, Shi; Wang, Chenxu; Liu, Shaoshuai; Fang, Yuan; Zhang, Yong; Xue, Jianming; Yan, Sha; Wang, Yugang

2016-08-01

Materials performance is central to the satisfactory operation of current and future nuclear energy systems due to the severe irradiation environment in reactors. Searching for structural materials with excellent irradiation tolerance is crucial for developing the next generation nuclear reactors. Here, we report the irradiation responses of a novel multi-component alloy system, high entropy alloy (HEA) AlxCoCrFeNi (x = 0.1, 0.75 and 1.5), focusing on their precipitation behavior. It is found that the single phase system, Al0.1CoCrFeNi, exhibits a great phase stability against ion irradiation. No precipitate is observed even at the highest fluence. In contrast, numerous coherent precipitates are present in both multi-phase HEAs. Based on the irradiation-induced/enhanced precipitation theory, the excellent structural stability against precipitation of Al0.1CoCrFeNi is attributed to the high configurational entropy and low atomic diffusion, which reduces the thermodynamic driving force and kinetically restrains the formation of precipitate, respectively. For the multiphase HEAs, the phase separations and formation of ordered phases reduce the system configurational entropy, resulting in the similar precipitation behavior with corresponding binary or ternary conventional alloys. This study demonstrates the structural stability of single-phase HEAs under irradiation and provides important implications for searching for HEAs with higher irradiation tolerance.

Beyond Atomic Sizes and Hume-Rothery Rules: Understanding and Predicting High-Entropy Alloys

DOE PAGES

Troparevsky, M. Claudia; Morris, James R.; Daene, Markus; ...

2015-09-03

High-entropy alloys constitute a new class of materials that provide an excellent combination of strength, ductility, thermal stability, and oxidation resistance. Although they have attracted extensive attention due to their potential applications, little is known about why these compounds are stable or how to predict which combination of elements will form a single phase. Here, we present a review of the latest research done on these alloys focusing on the theoretical models devised during the last decade. We discuss semiempirical methods based on the Hume-Rothery rules and stability criteria based on enthalpies of mixing and size mismatch. To provide insightsmore » into the electronic and magnetic properties of high-entropy alloys, we show the results of first-principles calculations of the electronic structure of the disordered solid-solution phase based on both Korringa Kohn Rostoker coherent potential approximation and large supercell models of example face-centered cubic and body-centered cubic systems. Furthermore, we discuss in detail a model based on enthalpy considerations that can predict which elemental combinations are most likely to form a single-phase high-entropy alloy. The enthalpies are evaluated via first-principles high-throughput density functional theory calculations of the energies of formation of binary compounds, and therefore it requires no experimental or empirically derived input. Finally, the model correctly accounts for the specific combinations of metallic elements that are known to form single-phase alloys while rejecting similar combinations that have been tried and shown not to be single phase.« less

Equivalent crystal theory of alloys

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Ferrante, John

1991-01-01

Equivalent Crystal Theory (ECT) is a new, semi-empirical approach to calculating the energetics of a solid with defects. The theory has successfully reproduced surface energies in metals and semiconductors. The theory of binary alloys to date, both with first-principles and semi-empirical models, has not been very successful in predicting the energetics of alloys. This procedure is used to predict the heats of formation, cohesive energy, and lattice parameter of binary alloys of Cu, Ni, Al, Ag, Au, Pd, and Pt as functions of composition. The procedure accurately reproduces the heats of formation versus composition curves for a variety of binary alloys. The results are then compared with other approaches such as the embedded atom and lattice parameters of alloys from pure metal properties more accurately than Vegard's law is presented.

Alloy softening in binary molybdenum alloys

NASA Technical Reports Server (NTRS)

Stephens, J. R.; Witzke, W. R.

1972-01-01

An investigation was conducted to determine the effects of alloy additions of Hf, Ta, W, Re, Os, Ir, and Pt on the hardness of Mo. Special emphasis was placed on alloy softening in these binary Mo alloys. Results showed that alloy softening was produced by those elements having an excess of s+d electrons compared to Mo, while those elements having an equal number or fewer s+d electrons than Mo failed to produce alloy softening. Alloy softening and hardening can be correlated with the difference in number of s+d electrons of the solute element and Mo.

Microstructure Formations in the Two-Phase Region of the Binary Peritectic Organic System TRIS-NPG

NASA Technical Reports Server (NTRS)

Mogeritsch, Johann; Ludwig, Andreas

2012-01-01

In order to prepare for an onboard experiment on the International Space Station (ISS), systematic directional solidification experiments with transparent hypoperitectic alloys were carried out at different solidification rates around the critical velocity for morphological stability of both solid phases. The investigations were done in the peritectic region of the binary transparent organic TRIS-NPG system where the formation of layered structures is expected to occur. The transparent appearance of the liquid and solid phase enables real time observations of the dynamic of pattern formation during solidification. The investigations show that frequently occurring nucleation events govern the peritectic solidification morphology which occurs at the limit of morphological stability. As a consequence, banded structures lead to coupled growth even if the lateral growth is much faster compared to the growth in pulling direction.

Lattice parameters and relative stability of α″ phase in binary titanium alloys from first-principles calculations

NASA Astrophysics Data System (ADS)

Li, Chun-Xia; Luo, Hu-Bin; Hu, Qing-Miao; Yang, Rui; Yin, Fu-Xing; Umezawa, Osamu; Vitos, Levente

2013-04-01

The crystallographic structure and stability of the α″ phase relative to the α and β phases in Ti-x M (M=Ta, Nb, V, Mo) alloys are investigated by using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation. We show that, with increasing concentration of the alloying elements, the structure of the orthorhombic-α″ phase evolutes from the hcp-α to the bcc-β phase, i.e., the lattice parameters b/a and c/a as well as the basal shuffle y decreases from those corresponding to the α phase to those of the β phase. The compositional α/α″ and α″/β phase boundaries are determined by comparing the total energies of the phases. The predicted α/α″ phase boundaries are about 10.2, 10.5, 11.5, 4.5 at% for Ti-V, Ti-Nb, Ti-Ta, and Ti-Mo, respectively, in reasonable agreement with experiments. The α″/β phase boundaries are higher than the experimental values, possibly due to the absence of temperature effect in the first-principles calculations. Analyzing the electronic density of states, we propose that the stability of the α″ phase is controlled by the compromise between the strength of the covalent and metallic bonds.

Understanding the bond-energy, hardness, and adhesive force from the phase diagram via the electron work function

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Hao; Huang, Xiaochen; Li, Dongyang, E-mail: dongyang.li@ualberta.ca

2014-11-07

Properties of metallic materials are intrinsically determined by their electron behavior. However, relevant theoretical treatment involving quantum mechanics is complicated and difficult to be applied in materials design. Electron work function (EWF) has been demonstrated to be a simple but fundamental parameter which well correlates properties of materials with their electron behavior and could thus be used to predict material properties from the aspect of electron activities in a relatively easy manner. In this article, we propose a method to extract the electron work functions of binary solid solutions or alloys from their phase diagrams and use this simple approachmore » to predict their mechanical strength and surface properties, such as adhesion. Two alloys, Fe-Ni and Cu-Zn, are used as samples for the study. EWFs extracted from phase diagrams show same trends as experimentally observed ones, based on which hardness and surface adhesive force of the alloys are predicted. This new methodology provides an alternative approach to predict material properties based on the work function, which is extractable from the phase diagram. This work may also help maximize the power of phase diagram for materials design and development.« less

Elastic moduli of cast Ti-Au, Ti-Ag, and Ti-Cu alloys.

PubMed

Kikuchi, Masafumi; Takahashi, Masatoshi; Okuno, Osamu

2006-07-01

This study investigated the effect of alloying titanium with gold, silver, or copper on the elastic properties of the alloys. A series of binary titanium alloys was made with four concentrations of gold, silver, or copper (5, 10, 20, and 30 mass%) in an argon-arc melting furnace. The Young's moduli and Poisson's ratios of the alloy castings were determined with an ultrasonic-pulse method. The density of each alloy was previously measured by the Archimedes' principle. Results were analyzed using one-way ANOVA and the Scheffé's test. The densities of Ti-Au, Ti-Ag, and Ti-Cu alloys monotonically increased as the concentration of alloying elements increased. As the concentration of gold or silver increased to 20%, the Young's modulus significantly decreased, followed by a subsequent increase in value. As the concentration of copper increased, the Young's modulus monotonically increased. The Young's moduli of all the Ti-Cu alloys were significantly higher than that of the titanium. The density of all the experimental alloys was virtually independent of the alloy phases, while the Young's moduli and Poisson's ratios of the alloys were dependent. The addition of gold or silver slightly reduced the Young's modulus of the titanium when the alloy phase was single alpha. The increase in the Young's modulus of the Ti-Cu alloys is probably due to the precipitation of intermetallic compound Ti2Cu. Copper turned out to be a moderate stiffener that gains a Young's modulus of titanium up to 20% at the copper concentration of 30 mass%.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, S.; Schaffer, J. E.; Ren, Y.

Room temperature deformation of a Ni{sub 46.7}Ti{sub 42.8}Nb{sub 10.5} alloy was studied by in-situ synchrotron X-ray diffraction. Compared to binary NiTi alloy, the Nb dissolved in the matrix significantly increased the onset stress for Stress-Induced Martensite Transformation (SIMT). The secondary phase, effectively a Nb-nanowire dispersion in a NiTi-Nb matrix, increased the elastic stiffness of the bulk material, reduced the strain anisotropy in austenite families by load sharing during SIMT, and increased the stress hysteresis by resisting reverse phase transformation during unloading. The stress hysteresis can be controlled over a wide range by heat treatment through its influences on the residualmore » stress of the Nb-nanowire dispersion and the stability of the austenite.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, S.; Schaffer, J. E.; Ren, Y.

Room temperature deformation of a Ni46.7Ti42.8Nb10.5 alloy was studied by in-situ synchrotron X-ray diffraction. Compared to binary NiTi alloy, the Nb dissolved in the matrix significantly increased the onset stress for Stress-Induced Martensite Transformation (SIMT). The secondary phase, effectively a Nb-nanowire dispersion in a NiTi-Nb matrix, increased the elastic stiffness of the bulk material, reduced the strain anisotropy in austenite families by loading sharing during SIMT, and increased the stress hysteresis by resisting reverse phase transformation during unloading. The stress hysteresis can be controlled over a wide range by changing the heat treatment temperature through its influences on the residualmore » stress-strain state of the Nb-nanowire dispersion.« less

Heteroepitaxial growth of 3-5 semiconductor compounds by metal-organic chemical vapor deposition for device applications

NASA Technical Reports Server (NTRS)

Collis, Ward J.; Abul-Fadl, Ali

1988-01-01

The purpose of this research is to design, install and operate a metal-organic chemical vapor deposition system which is to be used for the epitaxial growth of 3-5 semiconductor binary compounds, and ternary and quaternary alloys. The long-term goal is to utilize this vapor phase deposition in conjunction with existing current controlled liquid phase epitaxy facilities to perform hybrid growth sequences for fabricating integrated optoelectronic devices.

Multi-GPU hybrid programming accelerated three-dimensional phase-field model in binary alloy

NASA Astrophysics Data System (ADS)

Zhu, Changsheng; Liu, Jieqiong; Zhu, Mingfang; Feng, Li

2018-03-01

In the process of dendritic growth simulation, the computational efficiency and the problem scales have extremely important influence on simulation efficiency of three-dimensional phase-field model. Thus, seeking for high performance calculation method to improve the computational efficiency and to expand the problem scales has a great significance to the research of microstructure of the material. A high performance calculation method based on MPI+CUDA hybrid programming model is introduced. Multi-GPU is used to implement quantitative numerical simulations of three-dimensional phase-field model in binary alloy under the condition of multi-physical processes coupling. The acceleration effect of different GPU nodes on different calculation scales is explored. On the foundation of multi-GPU calculation model that has been introduced, two optimization schemes, Non-blocking communication optimization and overlap of MPI and GPU computing optimization, are proposed. The results of two optimization schemes and basic multi-GPU model are compared. The calculation results show that the use of multi-GPU calculation model can improve the computational efficiency of three-dimensional phase-field obviously, which is 13 times to single GPU, and the problem scales have been expanded to 8193. The feasibility of two optimization schemes is shown, and the overlap of MPI and GPU computing optimization has better performance, which is 1.7 times to basic multi-GPU model, when 21 GPUs are used.

Microstructure–property relationships in a high-strength 51Ni–29Ti–20Hf shape memory alloy

DOE PAGES

Coughlin, D. R.; Casalena, L.; Yang, F.; ...

2015-09-18

NiTiHf alloys exhibit remarkable shape memory and pseudoelastic properties that are of fundamental interest to a growing number of industries. In this study, differential scanning calorimetry and isothermal compression tests have revealed that the 51Ni–29Ti–20Hf alloy has useful shape memory properties that include a wide range of transformation temperatures as well as highly stable pseudoelastic behavior. These properties are governed by short-term aging conditions, which may be tailored to control transformation temperatures while giving rise to exceptionally high austenite yield strengths which aid transformation stability. The yield strength of the austenite phase can reach 2.1 GPa by aging for 3hrsmore » at 500°C, while aging for 3hrs at 700°C produced an alloy with an austenite finish temperature (A f ) of 146°C. High-resolution scanning transmission electron microscopy has revealed a new precipitate phase, H-phase, under the homogenized and extruded condition and the aged 3 hrs at 500°C condition, but only the previously identified H-phase precipitate was observed after aging at temperatures of 600°C and 700°C for 3 hrs. Finally, dislocation analysis indicated that plastic deformation of the austenite phase occurred by <100> type slip, similar to that observed in binary NiTi.« less

Three-dimensional phase-field simulations of directional solidification

NASA Astrophysics Data System (ADS)

Plapp, Mathis

2007-05-01

The phase-field method has become the method of choice for simulating microstructural pattern formation during solidification. One of its main advantages is that time-dependent three-dimensional simulations become feasible, which makes it possible to address long-standing questions of pattern stability and pattern selection. Here, a brief introduction to the phase-field model and its implementation is given, and its capabilities are illustrated by examples taken from the directional solidification of binary alloys. In particular, the morphological stability of hexagonal cellular arrays and of eutectic lamellar patterns is investigated.

Electrical and Magnetic Properties of Binary Amorphous Transition Metal Alloys.

NASA Astrophysics Data System (ADS)

Liou, Sy-Hwang

The electrical, superconductive and magnetic properties of several binary transition metal amorphous and metastable crystalline alloys, Fe(,x)Ti(,100-x) (30 (LESSTHEQ) x (LESSTHEQ) 100), Fe(,x)Zr(,100-x) (20 (LESSTHEQ) x (LESSTHEQ) 93), Fe(,x)Hf(,100-x) (20 (LESSTHEQ) x (LESSTHEQ) 100), Fe(,x)Nb(,100 -x) (22 (LESSTHEQ) x (LESSTHEQ) 85), Ni(,x)Nb(,100-x) (20 (LESSTHEQ) x (LESSTHEQ) 80), Cu(,x)Nb(,100-x) (10 (LESSTHEQ) x (LESSTHEQ) 90) were studied over a wide composition range. Films were made using a magnetron sputtering system, and the structure of the films was investigated by energy dispersive x-ray diffraction. The composition region of each amorphous alloys system was determined and found in good agreement with a model proposed by Egami and Waseda. The magnetic properties and hyperfine interactions in the films were investigated using a conventional Mossbauer spectrometer and a ('57)Co in Rh matrix source. In all Fe-early transition metal binary alloys systems, Fe does not retain its moment in the low iron concentration region and the result is that the critical concentration for magnetic order (x(,c)) is much larger than anticipated from percolation considerations. A direct comparison between crystalline alloys and their amorphous counterparts of the same composition illustrate no clear correlation between crystalline and amorphous states. Pronounced discontinuities in the magnetic properties with variation in Fe content of all Fe-early transition metal alloys at phase boundaries separating amorphous and crystalline states have been observed. This is caused by the differences in the atomic arrangement and the electronic structure between crystalline and amorphous solids. The temperature dependence of resistivity, (rho)(T), of several binary amorphous alloys of Fe-TM (where TM = Ti, Zr, Hf, Nb etc.) has been studied from 2K to 300K. The Fe-poor (x < x(,c)) samples and the Fe-rich (x > x(,c)) samples have distinctive differences in (rho)(T) at low temperature (below 30K). All the magnetic samples show a logarithmic dependence at low temperature that can be described by Kondo scattering. In addition, there is a change in slope of (rho)(T) at a temperature close to the magnetic ordering temperature, indicating a contribution attributed to magnetic ordering. Several Nb-based amorphous alloys (Fe-Nb, Ni-Nb, Cu-Nb) have also been systematically studied. The effect of the magnetic species on superconductivity is investigated. The value of superconducting transition temperature (T(,s)) increases linearly with increasing Nb concentration. (Abstract shortened with permission of author.).

Nonergodicity of microfine binary systems

NASA Astrophysics Data System (ADS)

Son, L. D.; Sidorov, V. E.; Popel', P. S.; Shul'gin, D. B.

2016-02-01

The correction to the equation of state that is related to the nonergodicity of diffusion dynamics is discussed for a binary solid solution with a limited solubility. It is asserted that, apart from standard thermodynamic variables (temperature, volume, concentration), this correction should be taken into account in the form of the average local chemical potential fluctuations associated with microheterogeneity in order to plot a phase diagram. It is shown that a low value of this correction lowers the miscibility gap and that this gap splits when this correction increases. This situation is discussed for eutectic systems and Ga-Pb, Fe-Cu, and Cu-Zr alloys.

The effects of thermomechanical processing and annealing on the microstructural evolution and stress corrosion cracking of alloy 690

NASA Astrophysics Data System (ADS)

Miller, Cody A.

The effects of short-range order (SRO), long-range order (LRO), and plastic strain on the microstructure and stress corrosion cracking (SCC) susceptibility of Ni-Cr-Fe Alloy 690 have been investigated in detail. First, the presence of 1/3{422} and 1/2{311} diffuse intensities in B=[111] and B=[112] selected area diffraction patterns (SADPs), previously believed to indicate the presence of SRO, has been examined in Alloy 690, a Ni-Cr binary alloy, and a number of FCC materials in an effort to determine their source. It is shown that these intensities are not due to SRO, although their source remains somewhat unclear. However, an experiment was conducted that tracked the strong {111} reflections in a B=[112] SADP as the sample was tilted (19°) towards a B=[111] zone axis. Significantly, it was noted that the {111} intensities never fully disappear and that they fall in the 1/3{422} positions within the B=[111] SADP. This indicates that these diffuse intensities are related to reflections that lie in the first order Laue zone (FOLZ) when the zone is aligned along B=[111], although theoretical calculations indicate scattering from these planes into the zero order Laue zone used to form the SADP should not occur. Thus, while calculations are inconsistent with the behavior expected, the diffuse intensities observed in a number of high index zones are consistent with projections of higher order Laue zone reflections into the zero layer, suggesting that the theory is in need of reassessment. Second, the stability of the gamma'-Ni2Cr LRO phase present on the Ni-Cr phase diagram was examined in a Ni-55Cr binary alloy. The results indicate that the gamma'-Ni2Cr phase is indeed metastable, and that the two-phase gamma-Ni + alpha-Cr phase field extends all the way to room temperature. Likewise, the sluggish formation of the gamma'-Ni 2Cr phase appears to occur only over a narrow composition and temperature range. It is speculated that this important phase in more complex alloys is also metastable and its metastability should be considered in applications involving long-term, high temperature exposures. Third, the effects of thermomechanical processing and long-term aging on the microstructural evolution and SCC susceptibility of Alloy 690 were examined in detail. It is shown that cold working and subsequent aging have large impacts on the microstructures observed and on the mechanical properties, and it is these changes that are related to the differences in SCC behavior. Most importantly, it is shown that the very high work hardening in Alloy 690 leads to large increases in yield strength that appear to overshadow the more subtle variations in carbide distributions at grain boundaries and prior coherent twin boundaries, and that SCC initiation is difficult if not impossible under static loading conditions. Based on these observations, it is concluded that the long-term concerns by industry of SCC initiation in Alloy 690 in the thermally-treated condition can probably be ignored unless there are regions where the alloy has been significantly hardened mechanically and the material will undergo some type of dynamic loading.

Thermodynamic assessment and binary nucleation modeling of Sn-seeded InGaAs nanowires

NASA Astrophysics Data System (ADS)

Ghasemi, Masoomeh; Selleby, Malin; Johansson, Jonas

2017-11-01

We have performed a thermodynamic assessment of the As-Ga-In-Sn system based on the CALculation of PHAse Diagram (CALPHAD) method. This system is part of a comprehensive thermodynamic database that we are developing for nanowire materials. Specifically, the As-Ga-In-Sn can be used in modeling the growth of GaAs, InAs, and InxGa1-xAs nanowires assisted by Sn liquid seeds. In this work, the As-Sn binary, the As-Ga-Sn, As-In-Sn, and Ga-In-Sn ternary systems have been thermodynamically assessed using the CALPHAD method. We show the relevant phase diagrams and property diagrams. They all show good agreement with experimental data. Using our optimized description we have modeled the nucleation of InxGa1-xAs in the zinc blende phase from a Sn-based quaternary liquid alloy using binary nucleation modeling. We have linked the composition of the solid nucleus to the composition of the liquid phase. Eventually, we have predicted the critical size of the nucleus that forms from InAs and GaAs pairs under various conditions. We believe that our modeling can guide future experimental realization of Sn-seeded InxGa1-xAs nanowires.

Three-dimensional nanometer scale analyses of precipitate structures and local compositions in titanium aluminide engineering alloys

NASA Astrophysics Data System (ADS)

Gerstl, Stephan S. A.

Titanium aluminide (TiAl) alloys are among the fastest developing class of materials for use in high temperature structural applications. Their low density and high strength make them excellent candidates for both engine and airframe applications. Creep properties of TiAl alloys, however, have been a limiting factor in applying the material to a larger commercial market. In this research, nanometer scale compositional and structural analyses of several TiAl alloys, ranging from model Ti-Al-C ternary alloys to putative commercial alloys with 10 components are investigated utilizing three dimensional atom probe (3DAP) and transmission electron microscopies. Nanometer sized borides, silicides, and carbide precipitates are involved in strengthening TiAl alloys, however, chemical partitioning measurements reveal oxygen concentrations up to 14 at. % within the precipitate phases, resulting in the realization of oxycarbide formation contributing to the precipitation strengthening of TiAl alloys. The local compositions of lamellar microstructures and a variety of precipitates in the TiAl system, including boride, silicide, binary carbides, and intermetallic carbides are investigated. Chemical partitioning of the microalloying elements between the alpha2/gamma lamellar phases, and the precipitate/gamma-matrix phases are determined. Both W and Hf have been shown to exhibit a near interfacial excess of 0.26 and 0.35 atoms nm-2 respectively within ca. 7 nm of lamellar interfaces in a complex TiAl alloy. In the case of needle-shaped perovskite Ti3AlC carbide precipitates, periodic domain boundaries are observed 5.3+/-0.8 nm apart along their growth axis parallel to the TiAl[001] crystallographic direction with concomitant composition variations after 24 hrs. at 800°C.

Thermodynamic investigation of the effect of alkali metal impuries on the processing of aluminum and magnesium alloys

NASA Astrophysics Data System (ADS)

Zhang, Shengjun

2006-12-01

Aluminum and magnesium alloys are widely used in the automobile and aerospace industries as structural materials due to their light weight, high specific strength and good formability. However, they suffer from the poor hot rolling characteristics due to undesired impurities like calcium, potassium, lithium and sodium. They increase the hydrogen solubility in the melt and promote the formation of porosity in aluminum castings. During fabrication of aluminum alloys, they cause the hot-shortness and embrittlement due to cracking. They also led to "blue haze" corrosion which promotes the discoloration of aluminum under humid condition. The removal of these elements increases overall melt loss of aluminum alloys when aluminum products are remelted and recast. Na is one of the common impurities in the Al and Mg alloys. In industry, primary Al is produced by the Hall-Heroult process, through the electrolysis of the mixture of molten alumina and cryolite (Al2O3+Na 3AlF6), the latter being added to lower the melting point. Therefore, Al inevitably contains some Na (>0.002%) without further treatment. The Na content in Al is influenced by the thermodynamics and kinetics of the electrolysis. Similarly, in the electrolytic production and subsequent processing of Mg, Mg is commonly in contact with molten salt mixtures of NaCl and MgCl 2. Consequently, 2--20 wt. ppm Na is often found in Mg alloys. Besides originating from the industrial production process, Na can be introduced in laboratory experiments from alumina crucibles by the reaction between the molten Al-Mg alloys and the Na2O impurity in the alumina crucible. The trace element K plays a similar role in Al alloys although it is seldom discussed. No systematic theoretic research has been carried out to investigate the behavior of these impurities during the processing of aluminum alloys. The thermodynamic description of the Al-Ca-K-Li-Mg-Na system is needed to understand the effects of Ca, K, Li and Na on phase stability of aluminum and magnesium alloys. As the first step of the thermodynamic description of the high-order system, the constitutive-binary systems were modeled in the present work using the CALPHAD technique combined with first-principles calculations. Then, ternaries and higher order systems can be modeled. For ternary systems without experimental data, the thermodynamic description is extrapolated by combining three constitutive-binary systems. Alkali-metal induced high temperature embrittlement (HTE) and loss of ductility were investigated in Al-Li, Al-Mg and Mg-Li alloys. It was discovered that the alkali-metal-rich liquid-2 phase is the cause of HTE and the loss of ductility is proportional to the mole fraction of the liquid phase and the grain size. The calculated results are consistent with experimental observations in the literature and were used to determine HTE safe and sensitive zones, maximum and critical hot-rolling temperatures and the maximum allowable Na content in alloys, which can be used to industrial processing of Al and Mg alloys. The degree of HTE is proportional to the mole fraction of the liquid-2 phase and the grain size.

Properties and Potential of Two (ni,pt)ti Alloys for Use as High-temperature Actuator Materials

NASA Technical Reports Server (NTRS)

Noebe, Ronald; Gaydosh, Darrell; Padula, Santo, II.; Garg, Anita; Biles, Tiffany; Nathal, Michael

2005-01-01

The microstructure, transformation temperatures, basic tensile properties, shape memory behavior, and work output for two (Ni,Ti)Pt high-temperature shape memory alloys have been characterized. One was a Ni30Pt20Ti50 alloy (referred to as 20Pt) with transformation temperatures above 230 C and the other was a Ni20Pt30Ti50 alloy (30Pt) with transformation temperatures about 530 C. Both materials displayed shape memory behavior and were capable of 100% (no-load) strain recovery for strain levels up to their fracture limit (3-4%) when deformed at room temperature. For the 20Pt alloy, the tensile strength, modulus, and ductility dramatically increased when the material was tested just about the austenite finish (A(sub f)) temperature. For the 30Pt alloy, a similar change in yield behavior at temperatures above the A(sub f) was not observed. In this case the strength of the austentite phase was at best comparable and generally much weaker than the martensite phase. A ductility minimum was also observed just below the A(sub s) temperature in this alloy. As a result of these differences in tensile behavior, the two alloys performed completely different when thermally cycled under constant load. The 20Pt alloy behaved similar to conventional binary NiTi alloys with work output due to the martensite-to-austenite transformation initially increasing with applied stress. The maximum work output measured in the 20Pt alloy was nearly 9 J/cu cm and was limited by the tensile ductility of the material. In contrast, the martensite-to-austenite transformation in the 30Pt alloy was not capable of performing work against any bias load. The reason for this behavior was traced back to its basic mechanical properties, where the yield strength of the austenite phase was similar to or lower than that of the martensite phase, depending on temperature. Hence, the recovery or transformation strain for the 30Pt alloy under load was essentially zero, resulting in zero work output.

Mössbauer study of oxide films of Fe-, Sn-, Cr- doped zirconium alloys during corrosion in autoclave

NASA Astrophysics Data System (ADS)

Filippov, V. P.; Bateev, A. B.; Lauer, Yu. A.

2016-12-01

Mössbauer investigations were used to compare iron atom states in oxide films of binary Zr-Fe, ternary Zr-Fe-Cu and quaternary Zr-Fe-Cr-Sn alloys. Oxide films are received in an autoclave at a temperature of 350-360 °C and at pressure of 16.8 MPa. The corrosion process decomposes the intermetallic precipitates in alloys and forms metallic iron with inclusions of chromium atoms α-Fe(Cr), α-Fe(Cu), α-Fe 2O3 and Fe 3O4 compounds. Some iron ions are formed in divalent and in trivalent paramagnetic states. The additional doping influences on corrosion kinetics and concentration of iron compounds and phases formed in oxide films. It was shown the correlation between concentration of iron in different chemical states and corrosion resistance of alloys.

Phase Transformations and Formation of Ultra-Fine Microstructure During Hydrogen Sintering and Phase Transformation (HSPT) Processing of Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Sun, Pei; Fang, Zhigang Zak; Koopman, Mark; Xia, Yang; Paramore, James; Ravi Chandran, K. S.; Ren, Yang; Lu, Jun

2015-12-01

The hydrogen sintering and phase transformation (HSPT) process is a novel powder metallurgy method for producing Ti alloys, particularly the Ti-6Al-4V alloy, with ultra-fine microstructure in the as-sintered state. The ultra-fine microstructure is obtained as a direct result of the use of H2 gas during sintering. The refinement of the microstructure during HSPT is similar to that of thermal hydrogen processing (THP) of bulk Ti alloys. For both THP and HSPT of Ti-6Al-4V alloy, the mechanisms of the grain refinement depend on the phase equilibria and phase transformations in the presence of hydrogen, which are surprisingly still not well established to date and are still subjected to research and debate. In recent work by the present authors, a pseudo-binary phase diagram of (Ti-6Al-4V)-H has been determined by using in situ synchrotron XRD and TGA/DSC techniques. Aided by this phase diagram, the current paper focuses on the series of phase transformations during sintering and cooling of Ti-6Al-4V in a hydrogen atmosphere and the mechanisms for the formation of the ultra-fine microstructures obtained. Using experimental techniques, including in situ synchrotron XRD, SEM, EBSD, and TEM, the microstructural refinement was found to be the result of (1) the precipitation of ultra-fine α/α2 within coarse β grains during an isothermal hold at intermediate temperatures, and (2) the eutectoid transformation of β → α + δ at approximately 473 K (200 °C).

The development of binary Mg-Ca alloys for use as biodegradable materials within bone.

PubMed

Li, Zijian; Gu, Xunan; Lou, Siquan; Zheng, Yufeng

2008-04-01

Binary Mg-Ca alloys with various Ca contents were fabricated under different working conditions. X-ray diffraction (XRD) analysis and optical microscopy observations showed that Mg-xCa (x=1-3 wt%) alloys were composed of two phases, alpha (Mg) and Mg2Ca. The results of tensile tests and in vitro corrosion tests indicated that the mechanical properties could be adjusted by controlling the Ca content and processing treatment. The yield strength (YS), ultimate tensile strength (UTS) and elongation decreased with increasing Ca content. The UTS and elongation of as-cast Mg-1Ca alloy (71.38+/-3.01 MPa and 1.87+/-0.14%) were largely improved after hot rolling (166.7+/-3.01 MPa and 3+/-0.78%) and hot extrusion (239.63+/-7.21 MPa and 10.63+/-0.64%). The in vitro corrosion test in simulated body fluid (SBF) indicated that the microstructure and working history of Mg-xCa alloys strongly affected their corrosion behaviors. An increasing content of Mg2Ca phase led to a higher corrosion rate whereas hot rolling and hot extrusion could reduce it. The cytotoxicity evaluation using L-929 cells revealed that Mg-1Ca alloy did not induce toxicity to cells, and the viability of cells for Mg-1Ca alloy extraction medium was better than that of control. Moreover, Mg-1Ca alloy pins, with commercial pure Ti pins as control, were implanted into the left and right rabbit femoral shafts, respectively, and observed for 1, 2 and 3 months. High activity of osteoblast and osteocytes were observed around the Mg-1Ca alloy pins as shown by hematoxylin and eosin stained tissue sections. Radiographic examination revealed that the Mg-1Ca alloy pins gradually degraded in vivo within 90 days and the newly formed bone was clearly seen at month 3. Both the in vitro and in vivo corrosion suggested that a mixture of Mg(OH)2 and hydroxyapatite formed on the surface of Mg-1Ca alloy with the extension of immersion/implantation time. In addition, no significant difference (p>0.05) of serum magnesium was detected at different degradation stages. All these results revealed that Mg-1Ca alloy had the acceptable biocompatibility as a new kind of biodegradable implant material. Based on the above results, a solid alloy/liquid solution interface model was also proposed to interpret the biocorrosion process and the associated hydroxyapatite mineralization.

An Introduction to the BFS Method and Its Use to Model Binary NiAl Alloys

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Noebe, Ronald D.; Ferrante, J.; Amador, C.

1998-01-01

We introduce the Bozzolo-Ferrante-Smith (BFS) method for alloys as a computationally efficient tool for aiding in the process of alloy design. An intuitive description of the BFS method is provided, followed by a formal discussion of its implementation. The method is applied to the study of the defect structure of NiAl binary alloys. The groundwork is laid for a detailed progression to higher order NiAl-based alloys linking theoretical calculations and computer simulations based on the BFS method and experimental work validating each step of the alloy design process.

Alloy softening in binary iron solid solutions

NASA Technical Reports Server (NTRS)

Stephens, J. R.; Witzke, W. R.

1976-01-01

An investigation was conducted to determine softening and hardening behavior in 19 binary iron-alloy systems. Microhardness tests were conducted at four temperatures in the range 77 to 411 K. Alloy softening was exhibited by 17 of the 19 alloy systems. Alloy softening observed in 15 of the alloy systems was attributed to an intrinsic mechanism, believed to be lowering of the Peierls (lattice friction) stress. Softening and hardening rates could be correlated with the atomic radius ratio of solute to iron. Softening observed in two other systems was attributed to an extrinsic mechanism, believed to be associated with scavenging of interstitial impurities.

Evaluation of damage induced by high irradiation levels on α-Ni-Ni3Si eutectic structure

NASA Astrophysics Data System (ADS)

Camacho Olguin, Carlos Alberto; Garcia-Borquez, Arturo; González-Rodríguez, Carlos Alberto; Loran-Juanico, Jose Antonio; Cruz-Mejía, Hector

2015-06-01

Diluted alloys of the binary system Ni-Si have been used as target of beam of ions, electrons, neutrons and so on because in this kind of alloy occurs transformations order-disorder, when the temperature is raised. This fact has permitted to evaluate the phenomena associated with the damage induced by irradiation (DII). The results of these works have been employed to understand the behavior under irradiation of complex alloys and to evaluate the reliability of the results of mathematical simulation of the evolution of the DII. The interest in the alloy system Ni-Si has been reborn due to the necessity of developing materials, which have better resistance against the corrosion on more aggressive environments such as those generated on the nuclear power plants or those that exist out of the Earth's atmosphere. Now, a growing interest to use concentrated alloys of this binary system on diverse fields of the materials science has been taking place because up to determined concentration of silicon, a regular eutectic is formed, and this fact opens the possibility to develop lamellar composite material by directional solidification. However, nowadays, there is a lack of fundamental knowledge about the behavior of this type of lamellar structure under aggressive environments, like those mentioned before. Hence, the task of this work is to evaluate the effect that has the irradiation over the microstructure of the concentrated alloy Ni22at%Si. The dendritic region of the hypereutectic alloy consists of an intermetallic phase Ni3Si, whereas the interdendritic region is formed by the alternation of lamellas of solid solution α-Ni and intermetallic phase Ni3Si. Such kind of microstructure has the advantage to get information of the DII over different phases individually, and at the same time, about of the microstructure influence over the global damage in the alloy. The hypereutectic Ni22at%Si alloy was irradiated perpendicularly to its surface, with 3.66 MeV - Ni ions up to 380 dpa at 650°C in a Tandetron linear accelerator. The level of irradiation dose was chosen similar to the irradiation conditions of the next-generation nuclear reactors. The theoretical maximum depth of the DII (maximum depth of damage (MDD)) was calculated as 1.35 µm using the SRIM-2013 program; the laminar microstructure of the eutectic was simulated using the lattice parameters of the eutectic before irradiation. The experimental MDD was 1.47 µm, as determined through transmission electron microscope (TEM) images and the DII was characterized using µX-ray diffraction and TEM. The elimination of cubic phase of the intermetallic Ni3Si, the suppression of lamellae of the α-Ni phase, the generation of dislocation loops and lines, all of these changes generated by the irradiation are clear evidences that the DII was severe. Based on theoretical and experimental evidence, we propose that the amount of phases, alternate of lamellae with different chemical concentrations of silicon and lamellae spatial distribution have a direct relation with the severe evolution of the DII.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Briggs, Samuel A.; Edmondson, Philip D.; Littrell, Kenneth C.

Here, FeCrAl alloys are currently under consideration for accident-tolerant fuel cladding applications in light water reactors owing to their superior high-temperature oxidation and corrosion resistance compared to the Zr-based alloys currently employed. However, their performance could be limited by precipitation of a Cr-rich α' phase that tends to embrittle high-Cr ferritic Fe-based alloys. In this study, four FeCrAl model alloys with 10–18 at.% Cr and 5.8–9.3 at.% Al were neutron-irradiated to nominal damage doses up to 7.0 displacements per atom at a target temperature of 320 °C. Small angle neutron scattering techniques were coupled with atom probe tomography to assessmore » the composition and morphology of the resulting α' precipitates. It was demonstrated that Al additions partially destabilize the α' phase, generally resulting in precipitates with lower Cr contents when compared with binary Fe-Cr systems. The precipitate morphology evolution with dose exhibited a transient coarsening regime akin to previously observed behavior in aged Fe-Cr alloys. Similar behavior to predictions of the LSW/UOKV models suggests that α' precipitation in irradiated FeCrAl is a diffusion-limited process with coarsening mechanisms similar to those in thermally aged high-Cr ferritic alloys.« less

Friction and wear with a single-crystal abrasive grit of silicon carbide in contact with iron base binary alloys in oil: Effects of alloying element and its content

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1979-01-01

Sliding friction experiments were conducted with various iron-base binary alloys (alloying elements were Ti, Cr, Mn, Ni, Rh, and W) in contact with a rider of 0.025-millimeter-radius, single-crystal silicon carbide in mineral oil. Results indicate that atomic size and content of alloying element play a dominant role in controlling the abrasive-wear and -friction properties of iron-base binary alloys. The coefficient of friction and groove height (wear volume) general alloy decrease, and the contact pressure increases in solute content. There appears to be very good correlation of the solute to iron atomic radius ratio with the decreasing rate of coefficient of friction, the decreasing rate of groove height (wear volume), and the increasing rate of contact pressure with increasing solute content C. Those rates increase as the solute to iron atomic radius ratio increases from unity.

Phase stability in nanoscale material systems: extension from bulk phase diagrams

NASA Astrophysics Data System (ADS)

Bajaj, Saurabh; Haverty, Michael G.; Arróyave, Raymundo; Goddard Frsc, William A., III; Shankar, Sadasivan

2015-05-01

Phase diagrams of multi-component systems are critical for the development and engineering of material alloys for all technological applications. At nano dimensions, surfaces (and interfaces) play a significant role in changing equilibrium thermodynamics and phase stability. In this work, it is shown that these surfaces at small dimensions affect the relative equilibrium thermodynamics of the different phases. The CALPHAD approach for material surfaces (also termed ``nano-CALPHAD'') is employed to investigate these changes in three binary systems by calculating their phase diagrams at nano dimensions and comparing them with their bulk counterparts. The surface energy contribution, which is the dominant factor in causing these changes, is evaluated using the spherical particle approximation. It is first validated with the Au-Si system for which experimental data on phase stability of spherical nano-sized particles is available, and then extended to calculate phase diagrams of similarly sized particles of Ge-Si and Al-Cu. Additionally, the surface energies of the associated compounds are calculated using DFT, and integrated into the thermodynamic model of the respective binary systems. In this work we found changes in miscibilities, reaction compositions of about 5 at%, and solubility temperatures ranging from 100-200 K for particles of sizes 5 nm, indicating the importance of phase equilibrium analysis at nano dimensions.Phase diagrams of multi-component systems are critical for the development and engineering of material alloys for all technological applications. At nano dimensions, surfaces (and interfaces) play a significant role in changing equilibrium thermodynamics and phase stability. In this work, it is shown that these surfaces at small dimensions affect the relative equilibrium thermodynamics of the different phases. The CALPHAD approach for material surfaces (also termed ``nano-CALPHAD'') is employed to investigate these changes in three binary systems by calculating their phase diagrams at nano dimensions and comparing them with their bulk counterparts. The surface energy contribution, which is the dominant factor in causing these changes, is evaluated using the spherical particle approximation. It is first validated with the Au-Si system for which experimental data on phase stability of spherical nano-sized particles is available, and then extended to calculate phase diagrams of similarly sized particles of Ge-Si and Al-Cu. Additionally, the surface energies of the associated compounds are calculated using DFT, and integrated into the thermodynamic model of the respective binary systems. In this work we found changes in miscibilities, reaction compositions of about 5 at%, and solubility temperatures ranging from 100-200 K for particles of sizes 5 nm, indicating the importance of phase equilibrium analysis at nano dimensions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr01535a

Monte Carlo simulation of magnetic properties of mixed spin (3/2, 1) ferromagnetic and ferrimagnetic disordered binary alloys with amorphous structure

NASA Astrophysics Data System (ADS)

Motlagh, H. Nakhaei; Rezaei, G.

2018-01-01

Monte Carlo simulation is used to study the magnetic properties of mixed spin (3/2, 1) disordered binary alloys on simple cubic, hexagonal and amorphous magnetic ultra-thin films with 18 × 18 × 2 atoms. To this end, at the first approximation, the exchange coupling interaction between the spins is considered as a constant value and at the second one, the Ruderman-Kittel-Kasuya-Yosida (RKKY) model is used. Effects of concentration, structure, exchange interaction, single ion-anisotropy and the film size on the magnetic properties of disordered ferromagnetic and ferrimagnetic binary alloys are investigated. Our results indicate that the spontaneous magnetization and critical temperatures of rare earth-3d transition binary alloys are affected by these parameters. It is also found that in the ferrimagnetic state, the compensation temperature (Tcom) and the magnetic rearrangement temperature (TR) appear for some concentrations.

Disorder trapping by rapidly moving phase interface in an undercooled liquid

NASA Astrophysics Data System (ADS)

Galenko, Peter; Danilov, Denis; Nizovtseva, Irina; Reuther, Klemens; Rettenmayr, Markus

2017-08-01

Non-equilibrium phenomena such as the disappearance of solute drag, the origin of solute trapping and evolution of disorder trapping occur during fast transformations with originating metastable phases [D.M. Herlach, P.K. Galenko, D. Holland-Moritz, Metastable solids from undrercooled melts (Elsevier, Amsterdam, 2007)]. In the present work, a theoretical investigation of disorder trapping by a rapidly moving phase interface is presented. Using a model of fast phase transformations, a system of governing equations for the diffusion of atoms, and the evolution of both long-range order parameter and phase field variable is formulated. First numerical solutions are carried out for a congruently melting binary alloy system.

Role of alloying elements in adhesive transfer and friction of copper-base alloys

NASA Technical Reports Server (NTRS)

Buckley, D. H.

1978-01-01

Sliding friction experiments were conducted in a vacuum with binary-copper alloy riders sliding against a conventional bearing-steel surface with normal residual oxides present. The binary alloys contained 1 atomic percent of various alloying elements. Auger spectroscopy analysis was used to monitor the adhesive transfer of the copper alloys to the bearing-steel surface. A relation was found to exist between adhesive transfer and the reaction potential and free energy of formation of the alloying element in the copper. The more chemically active the element and the more stable its oxide, the greater was the adhesive transfer and wear of the copper alloy. Transfer occurred in all the alloys except copper-gold after relatively few (25) passes across the steel surface.

Statistical physics of multicomponent alloys using KKR-CPA

DOE PAGES

Khan, Suffian N.; Staunton, Julie B.; Stocks, George Malcolm

2016-02-16

We apply variational principles from statistical physics and the Landau theory of phase transitions to multicomponent alloys using the multiple-scattering theory of Korringa-Kohn-Rostoker (KKR) and the coherent potential approximation (CPA). This theory is a multicomponent generalization of the S( 2) theory of binary alloys developed by G. M. Stocks, J. B. Staunton, D. D. Johnson and others. It is highly relevant to the chemical phase stability of high-entropy alloys as it predicts the kind and size of finite-temperature chemical fluctuations. In doing so it includes effects of rearranging charge and other electronics due to changing site occupancies. When chemical fluctuationsmore » grow without bound an absolute instability occurs and a second-order order-disorder phase transition may be inferred. The S( 2) theory is predicated on the fluctuation-dissipation theorem; thus we derive the linear response of the CPA medium to perturbations in site-dependent chemical potentials in great detail. The theory lends itself to a natural interpretation in terms of competing effects: entropy driving disorder and favorable pair interactions driving atomic ordering. Moreover, to further clarify interpretation we present results for representative ternary alloys CuAgAu, NiPdPt, RhPdAg, and CoNiCu within a frozen charge (or band-only) approximation. These results include the so-called Onsager mean field correction that extends the temperature range for which the theory is valid.« less

Lithium-aluminum-iron electrode composition

DOEpatents

Kaun, Thomas D.

1979-01-01

A negative electrode composition is presented for use in a secondary electrochemical cell. The cell also includes an electrolyte with lithium ions such as a molten salt of alkali metal halides or alkaline earth metal halides that can be used in high-temperature cells. The cell's positive electrode contains a a chalcogen or a metal chalcogenide as the active electrode material. The negative electrode composition includes up to 50 atom percent lithium as the active electrode constituent in an alloy of aluminum-iron. Various binary and ternary intermetallic phases of lithium, aluminum and iron are formed. The lithium within the intermetallic phase of Al.sub.5 Fe.sub.2 exhibits increased activity over that of lithium within a lithium-aluminum alloy to provide an increased cell potential of up to about 0.25 volt.

Solid-liquid surface tensions of critical nuclei and nucleation barriers from a phase-field-crystal study of a model binary alloy using finite system sizes.

PubMed

Choudhary, Muhammad Ajmal; Kundin, Julia; Emmerich, Heike; Oettel, Martin

2014-08-01

Phase-field-crystal (PFC) modeling has emerged as a computationally efficient tool to address crystal growth phenomena on atomistic length and diffusive time scales. We use a two-dimensional phase-field-crystal model for a binary system based on Elder et al. [Phys. Rev. B 75, 064107 (2007)] to study critical nuclei and their liquid-solid phase boundaries, in particular the nucleus size dependence of the liquid-solid interface tension as well as of the nucleation barrier. Critical nuclei are stabilized in finite systems of various sizes, however, the extracted interface tension as function of the nucleus radius r is independent of system size. We suggest a phenomenological expression to describe the dependence of the extracted interface tension on the nucleus radius r for the liquid-solid system. Moreover, the numerical PFC results show that this dependency can not be fully described by the nonclassical Tolman formula.

The Effect of Impurities on the Processing of Aluminum Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zi-Kui Liu; Shengjun Zhang; Qingyou Han

2007-04-23

For this Aluminum Industry of the Future (IOF) project, the effect of impurities on the processing of aluminum alloys was systematically investigated. The work was carried out as a collaborative effort between the Pennsylvania State University and Oak Ridge National Laboratory. Industrial support was provided by ALCOA and ThermoCalc, Inc. The achievements described below were made. A method that combines first-principles calculation and calculation of phase diagrams (CALPHAD) was used to develop the multicomponent database Al-Ca-K-Li-Mg-Na. This method was extensively used in this project for the development of a thermodynamic database. The first-principles approach provided some thermodynamic property data thatmore » are not available in the open literature. These calculated results were used in the thermodynamic modeling as experimental data. Some of the thermodynamic property data are difficult, if not impossible, to measure. The method developed and used in this project allows the estimation of these data for thermodynamic database development. The multicomponent database Al-Ca-K-Li-Mg-Na was developed. Elements such as Ca, Li, Na, and K are impurities that strongly affect the formability and corrosion behavior of aluminum alloys. However, these impurity elements are not included in the commercial aluminum alloy database. The process of thermodynamic modeling began from Al-Na, Ca-Li, Li-Na, K-Na, and Li-K sub-binary systems. Then ternary and higher systems were extrapolated because of the lack of experimental information. Databases for five binary alloy systems and two ternary systems were developed. Along with other existing binary and ternary databases, the full database of the multicomponent Al-Ca-K-Li-Mg-Na system was completed in this project. The methodology in integrating with commercial or other aluminum alloy databases can be developed. The mechanism of sodium-induced high-temperature embrittlement (HTE) of Al-Mg is now understood. Using the thermodynamic database developed in this project, thermodynamic simulations were carried out to investigate the effect of sodium on the HTE of Al-Mg alloys. The simulation results indicated that the liquid miscibility gap resulting from the dissolved sodium in the molten material plays an important role in HTE. A liquid phase forms from the solid face-centered cubic (fcc) phase (most likely at grain boundaries) during cooling, resulting in the occurrence of HTE. Comparison of the thermodynamic simulation results with experimental measurements on the high-temperature ductility of an Al-5Mg-Na alloy shows that HTE occurs in the temperature range at which the liquid phase exists. Based on this fundamental understanding of the HTE mechanism during processing of aluminum alloy, an HTE sensitive zone and a hot-rolling safe zone of the Al-Mg-Na alloys are defined as functions of processing temperature and alloy composition. The tendency of HTE was evaluated based on thermodynamic simulations of the fraction of the intergranular sodium-rich liquid phase. Methods of avoiding HTE during rolling/extrusion of Al-Mg-based alloys were suggested. Energy and environmental benefits from the results of this project could occur through a number of avenues: (1) energy benefits accruing from reduced rejection rates of the aluminum sheet and bar, (2) reduced dross formation during the remelting of the aluminum rejects, and (3) reduced CO2 emission related to the energy savings. The sheet and extruded bar quantities produced in the United States during 2000 were 10,822 and 4,546 million pounds, respectively. It is assumed that 50% of the sheet and 10% of the bar will be affected by implementing the results of this project. With the current process, the rejection rate of sheet and bar is estimated at 5%. Assuming that at least half of the 5% rejection of sheet and bar will be eliminated by using the results of this project and that 4% of the aluminum will be lost through dross (Al2O3) during remelting of the rejects, the full-scale industrial implementation of the project results would lead to energy savings in excess of 6.2 trillion Btu/year and cost savings of $42.7 million by 2020.« less

Cohesive Relations for Surface Atoms in the Iron-Technetium Binary System

DOE PAGES

Taylor, Christopher D.

2011-01-01

Iron-technetium alloys are of relevance to the development of waste forms for disposition of radioactive technetium-99 obtained from spent nuclear fuel. Corrosion of candidate waste forms is a function of the local cohesive energy () of surface atoms. A theoretical model for calculating is developed. Density functional theory was used to construct a modified embedded atom (MEAM) potential for iron-technetium. Materials properties determined for the iron-technetium system were in good agreement with the literature. To explore the relationship between local structure and corrosion, MEAM simulations were performed on representative iron-technetium alloys and intermetallics. Technetium-rich phases have lower , suggesting thatmore » these phases will be more noble than iron-rich ones. Quantitative estimates of based on numbers of nearest neighbors alone can lead to errors up to 0.5 eV. Consequently, atomistic corrosion simulations for alloy systems should utilize physics-based models that consider not only neighbor counts, but also local compositions and atomic arrangements.« less

Electrical Transport Properties of Liquid Sn-Sb Binary Alloys

NASA Astrophysics Data System (ADS)

Thakore, B. Y.; Suthar, P. H.; Khambholja, S. G.; Jani, A. R.

2010-06-01

The study of electrical transport properties viz. electrical resistivity, thermo electrical power and thermal conductivity of liquid Sn-Sb binary alloys have been made by our well recognized single parametric model potential. In the present work, screening functions due to Hartree, Taylor, Ichimaru et al.. Farid et al.. and Sarkar et al.. have been employed to incorporate the exchange and correlation effects. The liquid alloy is studied as a function of its composition at temperature 823 K according to the Faber-Ziman model. Further, thermoelectric power and thermal conductivity have been predicted. The values of electrical resistivity of binary alloys computed with Ichimaru et al. and Farid et al.. screening function are in good agreement with the experimental data.

Enthalpies of a binary alloy during solidification

NASA Technical Reports Server (NTRS)

Poirier, D. R.; Nandapurkar, P.

1988-01-01

The purpose of the paper is to present a method of calculating the enthalpy of a dendritic alloy during solidification. The enthalpies of the dendritic solid and interdendritic liquid of alloys of the Pb-Sn system are evaluated, but the method could be applied to other binaries, as well. The enthalpies are consistent with a recent evaluation of the thermodynamics of Pb-Sn alloys and with the redistribution of solute in the same during dendritic solidification. Because of the heat of mixing in Pb-Sn alloys, the interdendritic liquid of hypoeutectic alloys (Pb-rich) of less than 50 wt pct Sn has enthalpies that increase as temperature decreases during solidification.

Electrical resistivity of Al-Cu liquid binary alloy

NASA Astrophysics Data System (ADS)

Thakor, P. P.; Patel, J. J.; Sonvane, Y. A.; Jani, A. R.

2013-06-01

Present paper deals with the electrical resistivity (ρ) of liquid Al-Cu binary alloy. To describe electron-ion interaction we have used our parameter free model potential along with Faber-Ziman formulation combined with Ashcroft-Langreth (AL) partial structure factor. To see the influence of exchange and correlation effect, Hartree, Taylor and Sarkar et al local field correlation functions are used. From present results, it is seen that good agreements between present results and experimental data have been achieved. Lastly we conclude that our model potential successfully produces the data of electrical resistivity (ρ) of liquid Al-Cu binary alloy.

Band gap characterization of ternary BBi1-xNx (0≤x≤1) alloys using modified Becke-Johnson (mBJ) potential

NASA Astrophysics Data System (ADS)

Yalcin, Battal G.

2015-04-01

The semi-local Becke-Johnson (BJ) exchange-correlation potential and its modified form proposed by Tran and Blaha have attracted a lot of interest recently because of the surprisingly accurate band gaps they can deliver for many semiconductors and insulators (e.g., sp semiconductors, noble-gas solids, and transition-metal oxides). The structural and electronic properties of ternary alloys BBi1-xNx (0≤x≤1) in zinc-blende phase have been reported in this study. The results of the studied binary compounds (BN and BBi) and ternary alloys BBi1-xNx structures are presented by means of density functional theory. The exchange and correlation effects are taken into account by using the generalized gradient approximation (GGA) functional of Wu and Cohen (WC) which is an improved form of the most popular Perdew-Burke-Ernzerhof (PBE). For electronic properties the modified Becke-Johnson (mBJ) potential, which is more accurate than standard semi-local LDA and PBE calculations, has been chosen. Geometric optimization has been implemented before the volume optimization calculations for all the studied alloys structure. The obtained equilibrium lattice constants of the studied binary compounds are in coincidence with experimental works. And, the variation of the lattice parameter of ternary alloys BBi1-xNx almost perfectly matches with Vegard's law. The spin-orbit interaction (SOI) has been also considered for structural and electronic calculations and the results are compared to those of non-SOI calculations.

Thermodynamic assessment of the Sn-Co lead-free solder system

NASA Astrophysics Data System (ADS)

Liu, Libin; Andersson, Cristina; Liu, Johan

2004-09-01

The Sn-Co-Cu eutectic alloy can be a less expensive alternative for the Sn-Ag-Cu alloy. In order to find the eutectic solder composition of the Sn-Co-Cu system, the Sn-Co binary system has been thoroughly assessed with the calculation of phase diagram (CALPHAD) method. The liquid phase, the FCC and HCP Co-rich solid solution, and the BCT Sn-rich solid solution have been described by the Redlich-Kister model. The Hillert-Jarl-Inden model has been used to describe the magnetic contributions to Gibbs energy in FCC and HCP. The CoSn2, CoSn, Co3Sn2_β, and Co3Sn2_α phases have been treated as stoichiometric phases. A series of thermodynamic parameters have been obtained. The calculated phase diagram and thermodynamic properties are in good agreement with the experimental data. The obtained thermodynamic data was used to extrapolate the ternary Sn-Co-Cu phase diagram. The composition of the Sn-rich eutectic point of the Sn-Co-Cu system was found to be 224°C, 0.4% Co, and 0.7% Cu.

Influence of chemical disorder on energy dissipation and defect evolution in concentrated solid solution alloys

PubMed Central

Zhang, Yanwen; Stocks, G. Malcolm; Jin, Ke; Lu, Chenyang; Bei, Hongbin; Sales, Brian C.; Wang, Lumin; Béland, Laurent K.; Stoller, Roger E.; Samolyuk, German D.; Caro, Magdalena; Caro, Alfredo; Weber, William J.

2015-01-01

A grand challenge in materials research is to understand complex electronic correlation and non-equilibrium atomic interactions, and how such intrinsic properties and dynamic processes affect energy transfer and defect evolution in irradiated materials. Here we report that chemical disorder, with an increasing number of principal elements and/or altered concentrations of specific elements, in single-phase concentrated solid solution alloys can lead to substantial reduction in electron mean free path and orders of magnitude decrease in electrical and thermal conductivity. The subsequently slow energy dissipation affects defect dynamics at the early stages, and consequentially may result in less deleterious defects. Suppressed damage accumulation with increasing chemical disorder from pure nickel to binary and to more complex quaternary solid solutions is observed. Understanding and controlling energy dissipation and defect dynamics by altering alloy complexity may pave the way for new design principles of radiation-tolerant structural alloys for energy applications. PMID:26507943

DOE Office of Scientific and Technical Information (OSTI.GOV)

Susarla, Sandhya; Kochat, Vidya; Kutana, Alex

Transition metal dichalcogenide (TMD) alloys form a broad class of two-dimensional (2D) layered materials with tunable bandgaps leading to interesting optoelectronic applications. In the bottom-up approach of building these atomically thin materials, atomic doping plays a crucial role. Here we demonstrate a single step CVD (chemical vapor deposition) growth procedure for obtaining binary alloys and heterostructures by tuning atomic composition. We show that a minute doping of tin during the growth phase of the Mo 1–xW xS 2 alloy system leads to formation of lateral and vertical heterostructure growth. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) imagingmore » and density functional theory (DFT) calculations also support the modified stacking and growth mechanism due to the nonisomorphous Sn substitution. Our experiments demonstrate the possibility of growing heterostructures of TMD alloys whose spectral responses can be desirably tuned for various optoelectronic applications.« less

Walker photographs BCAT-5 (Binary Colloidal Alloy Test-5) payload

NASA Image and Video Library

2010-10-19

ISS025-E-008239 (19 Oct. 2010) --- NASA astronaut Shannon Walker, Expedition 25 flight engineer, uses a digital still camera to photograph Binary Colloidal Alloy Test-5 (BCAT-5) experiment samples in the Kibo laboratory of the International Space Station.

Thermodynamics of Liquid Alkali Metals and Their Binary Alloys

NASA Astrophysics Data System (ADS)

Thakor, P. B.; Patel, Minal H.; Gajjar, P. N.; Jani, A. R.

2009-07-01

The theoretical investigation of thermodynamic properties like internal energy, entropy, Helmholtz free energy, heat of mixing (ΔE) and entropy of mixing (ΔS) of liquid alkali metals and their binary alloys are reported in the present paper. The effect of concentration on the thermodynamic properties of Ac1Bc2 alloy of the alkali-alkali elements is investigated and reported for the first time using our well established local pseudopotential. To investigate influence of exchange and correlation effects, we have used five different local field correction functions viz; Hartree(H), Taylor(T), Ichimaru and Utsumi(IU), Farid et al. (F) and Sarkar et al. (S). The increase of concentration C2, increases the internal energy and Helmholtz free energy of liquid alloy Ac1Bc2. The behavior of present computation is not showing any abnormality in the outcome and hence confirms the applicability of our model potential in explaining the thermodynamics of liquid binary alloys.

Adhesion, friction, and wear of binary alloys in contact with single-crystal silicon carbide

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1980-01-01

Sliding friction experiments, conducted with various iron base alloys (alloying elements are Ti, Cr, Mn, Ni, Rh and W) in contact with a single crystal silicon carbide /0001/ surface in vacuum are discussed. Results indicate atomic size misfit and concentration of alloying elements play a dominant role in controlling adhesion, friction, and wear properties of iron-base binary alloys. The controlling mechanism of the alloy properties is as an intrinsic effect involving the resistance to shear fracture of cohesive bonding in the alloy. The coefficient of friction generally increases with an increase in solute concentration. The coefficient of friction increases as the solute-to-iron atomic radius ratio increases or decreases from unity. Alloys having higher solute concentration produce more transfer to silicon carbide than do alloys having low solute concentrations. The chemical activity of the alloying element is also an important parameter in controlling adhesion and friction of alloys.

Preparation and some properties of Cu-Li alloys containing up to 20 at. % Li

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mendelsohn, M.; Krauss, A.R.; Gruen, D.M.

1985-01-01

Lithium strongly segregates to the surface of Cu-Li alloys, thus substantially lowering the Cu sputtering yield relative to pure Cu. Use of Cu-Li limiters or divertors in tokamaks can therefore be expected to be beneficial in limiting high-Z plasma impurity influx. A large scale (100-200g) method for the preparation of Cu-Li alloys is described. Analysis reveals that on solidification from the melt stratification occurs which leads to compositional inhomogeneity. The results are discussed in the light of the Cu-Li binary phase diagram and rationalized on the basis of large density differences between Cu and Cu-Li solid solutions. It is concludedmore » that obtaining homogeneous Cu-Li solid solutions is a nontrivial task.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Pei; Fang, Zhigang Zak; Koopman, Mark

The hydrogen sintering and phase transformation (HSPT) process is a novel powder metallurgy method for producing Ti alloys, particularly the Ti-6Al-4V alloy, with ultra-fine microstructure in the as-sintered state. The ultra-fine microstructure is obtained as a direct result of the use of H-2 gas during sintering. The refinement of the microstructure during HSPT is similar to that of thermal hydrogen processing (THP) of bulk Ti alloys. For both THP and HSPT of Ti-6Al-4V alloy, the mechanisms of the grain refinement depend on the phase equilibria and phase transformations in the presence of hydrogen, which are surprisingly still not well establishedmore » to date and are still subjected to research and debate. In recent work by the present authors, a pseudo-binary phase diagram of (Ti-6Al-4V)-H has been determined by using in situ synchrotron XRD and TGA/DSC techniques. Aided by this phase diagram, the current paper focuses on the series of phase transformations during sintering and cooling of Ti-6Al-4V in a hydrogen atmosphere and the mechanisms for the formation of the ultra-fine microstructures obtained. Using experimental techniques, including in situ synchrotron XRD, SEM, EBSD, and TEM, the microstructural refinement was found to be the result of (1) the precipitation of ultra-fine alpha/alpha(2) within coarse beta grains during an isothermal hold at intermediate temperatures, and (2) the eutectoid transformation of beta -> alpha + delta d at approximately 473 K (200 degrees C). (C) The Minerals, Metals & Materials Society and ASM International 2015« less

Development of binary and ternary titanium alloys for dental implants.

PubMed

Cordeiro, Jairo M; Beline, Thamara; Ribeiro, Ana Lúcia R; Rangel, Elidiane C; da Cruz, Nilson C; Landers, Richard; Faverani, Leonardo P; Vaz, Luís Geraldo; Fais, Laiza M G; Vicente, Fabio B; Grandini, Carlos R; Mathew, Mathew T; Sukotjo, Cortino; Barão, Valentim A R

2017-11-01

The aim of this study was to develop binary and ternary titanium (Ti) alloys containing zirconium (Zr) and niobium (Nb) and to characterize them in terms of microstructural, mechanical, chemical, electrochemical, and biological properties. The experimental alloys - (in wt%) Ti-5Zr, Ti-10Zr, Ti-35Nb-5Zr, and Ti-35Nb-10Zr - were fabricated from pure metals. Commercially pure titanium (cpTi) and Ti-6Al-4V were used as controls. Microstructural analysis was performed by means of X-ray diffraction and scanning electron microscopy. Vickers microhardness, elastic modulus, dispersive energy spectroscopy, X-ray excited photoelectron spectroscopy, atomic force microscopy, surface roughness, and surface free energy were evaluated. The electrochemical behavior analysis was conducted in a body fluid solution (pH 7.4). The albumin adsorption was measured by the bicinchoninic acid method. Data were evaluated through one-way ANOVA and the Tukey test (α=0.05). The alloying elements proved to modify the alloy microstructure and to enhance the mechanical properties, improving the hardness and decreasing the elastic modulus of the binary and ternary alloys, respectively. Ti-Zr alloys displayed greater electrochemical stability relative to that of controls, presenting higher polarization resistance and lower capacitance. The experimental alloys were not detrimental to albumin adsorption. The experimental alloys are suitable options for dental implant manufacturing, particularly the binary system, which showed a better combination of mechanical and electrochemical properties without the presence of toxic elements. Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Effects of Some Light Alloying Elements on the Oxidation Behavior of Fe and Ni-Cr Based Alloys During Air Plasma Spraying

NASA Astrophysics Data System (ADS)

Zeng, Zhensu; Kuroda, Seiji; Kawakita, Jin; Komatsu, Masayuki; Era, Hidenori

2010-01-01

The oxidation behavior of iron binary powders with addition of Si (1, 4 wt.%) and B (1, 3 wt.%) and that of a Ni-Cr based alloy powder with Si (4.3 wt.%), B (3.0 wt.%), and C (0.8 wt.%) additions during atmosphere plasma spray (APS) have been investigated. Analysis of the chemical composition and phases of oxides in the captured in-flight particles and deposited coatings was carried out. The results show that the addition of Si and B to iron effectively reduced the oxygen contents in the coatings, especially during the in-flight period at higher particles temperature. Ni-Cr based alloy powder with Si, B, and C additions reduced the oxidation of the base alloys significantly. Preferential oxidation and subsequent vaporization of Si, B, and C from the surface of the sprayed particles are believed to play a major role in controlling oxidation in the APS process.

Grain boundary selective oxidation and intergranular stress corrosion crack growth of high-purity nickel binary alloys in high-temperature hydrogenated water

DOE PAGES

Bruemmer, S. M.; Olszta, M. J.; Toloczko, M. B.; ...

2017-11-26

The effects of alloying elements in Ni-5at%X binary alloys on intergranular (IG) corrosion and stress corrosion cracking (SCC) have been assessed in 300–360 °C hydrogenated water at the Ni/NiO stability line. Alloys with Cr or Al additions exhibited grain boundary oxidation and IGSCC, while localized degradation was not observed for pure Ni, Ni-Cu or Ni-Fe alloys. Environment-enhanced crack growth was determined by comparing the response in water and N 2 gas. Lastly, results demonstrate that selective grain boundary oxidation of Cr and Al promoted IGSCC of these Ni alloys in hydrogenated water.

Grain boundary selective oxidation and intergranular stress corrosion crack growth of high-purity nickel binary alloys in high-temperature hydrogenated water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bruemmer, S. M.; Olszta, M. J.; Toloczko, M. B.

The effects of alloying elements in Ni-5at%X binary alloys on intergranular (IG) corrosion and stress corrosion cracking (SCC) have been assessed in 300–360 °C hydrogenated water at the Ni/NiO stability line. Alloys with Cr or Al additions exhibited grain boundary oxidation and IGSCC, while localized degradation was not observed for pure Ni, Ni-Cu or Ni-Fe alloys. Environment-enhanced crack growth was determined by comparing the response in water and N 2 gas. Lastly, results demonstrate that selective grain boundary oxidation of Cr and Al promoted IGSCC of these Ni alloys in hydrogenated water.

Grain boundary selective oxidation and intergranular stress corrosion crack growth of high-purity nickel binary alloys in high-temperature hydrogenated water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bruemmer, S. M.; Olszta, M. J.; Toloczko, M. B.

The effects of alloying elements in Ni-5at%X binary alloys on intergranular (IG) corrosion and stress corrosion cracking (SCC) have been assessed in 300-360°C hydrogenated water at the Ni/NiO stability line. Alloys with Cr or Al additions exhibited grain boundary oxidation and IGSCC, while localized degradation was not observed for pure Ni, Ni-Cu or Ni-Fe alloys. Environment-enhanced crack growth was determined by comparing the response in water and N2 gas. Results demonstrate that selective grain boundary oxidation of Cr and Al promoted IGSCC of these Ni alloys in hydrogenated water.

Extended vapor-liquid-solid growth of silicon carbide nanowires.

PubMed

Rajesh, John Anthuvan; Pandurangan, Arumugam

2014-04-01

We developed an alloy catalytic method to explain extended vapor-liquid-solid (VLS) growth of silicon carbide nanowires (SiC NWs) by a simple thermal evaporation of silicon and activated carbon mixture using lanthanum nickel (LaNi5) alloy as catalyst in a chemical vapor deposition process. The LaNi5 alloy binary phase diagram and the phase relationships in the La-Ni-Si ternary system were play a key role to determine the growth parameters in this VLS mechanism. Different reaction temperatures (1300, 1350 and 1400 degrees C) were applied to prove the established growth process by experimentally. Scanning electron microscopy and transmission electron microscopy studies show that the crystalline quality of the SiC NWs increases with the temperature at which they have been synthesized. La-Ni alloyed catalyst particles observed on the top of the SiC NWs confirms that the growth process follows this extended VLS mechanism. The X-ray diffraction and confocal Raman spectroscopy analyses demonstrate that the crystalline structure of the SiC NWs was zinc blende 3C-SiC. Optical property of the SiC NWs was investigated by photoluminescence technique at room temperature. Such a new alloy catalytic method may be extended to synthesis other one-dimensional nanostructures.

Low Pt content direct methanol fuel cell anode catalyst: nanophase PtRuNiZr

NASA Technical Reports Server (NTRS)

Whitacre, Jay F. (Inventor); Narayanan, Sekharipuram R. (Inventor)

2010-01-01

A method for the preparation of a metallic material having catalytic activity that includes synthesizing a material composition comprising a metal content with a lower Pt content than a binary alloy containing Pt but that displays at least a comparable catalytic activity on a per mole Pt basis as the binary alloy containing Pt; and evaluating a representative sample of the material composition to ensure that the material composition displays a property of at least a comparable catalytic activity on a per mole Pt basis as a representative binary alloy containing Pt. Furthermore, metallic compositions are disclosed that possess substantial resistance to corrosive acids.

High-pressure high-temperature stability of hcp-Ir xOs 1-x (x = 0.50 and 0.55) alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yusenko, Kirill V.; Bykova, Elena; Bykov, Maxim

2016-12-23

Hcp-Ir 0.55Os 0.45 and hcp-Ir 0.50Os 0.50 alloys were synthesised by thermal decomposition of single-source precursors in hydrogen atmosphere. Both alloys correspond to a miscibility gap in the Ir–Os binary phase diagram and therefore are metastable at ambient conditions. An in situ powder X-ray diffraction has been used for a monitoring a formation of hcp-Ir0.55Os0.45 alloy from (NH 4) 2[Ir 0.55Os 0.45Cl 6] precursor. A crystalline intermediate compound and nanodimentional metallic particles with a large concentration of defects has been found as key intermediates in the thermal decomposition process in hydrogen flow. High-temperature stability of titled hcp-structured alloys has beenmore » investigated upon compression up to 11 GPa using a multi-anvil press and up to 80 GPa using laser-heated diamond-anvil cells to obtain a phase separation into fcc + hcp mixture. Compressibility curves at room temperature as well as thermal expansion at ambient pressure and under compression up to 80 GPa were collected to obtain thermal expansion coefficients and bulk moduli. hcp-Ir 0.55Os 0.45 alloy shows bulk moduli B0 = 395 GPa. Thermal expansion coefficients were estimated as α = 1.6·10 -5 K -1 at ambient pressure and α = 0.3·10 -5 K -1 at 80 GPa. Obtained high-pressure high-temperature data allowed us to construct the first model for pressure-dependent Ir–Os phase diagram.« less

Primary arm spacing in chill block melt spun Ni-Mo alloys

NASA Technical Reports Server (NTRS)

Tewari, S. N.; Glasgow, T. K.

1986-01-01

Chill block melt spun ribbons of Ni-Mo binary alloys containing 8.0 to 41.8 wt % Mo have been prepared under carefully controlled processing conditions. The growth velocity has been determined as a function of distance from the quench surface from the observed ribbon thickness dependence on the melt puddle residence time. Primary arm spacings measured at the midribbon thickness locations show a dependence on growth velocity and alloy composition which is expected from dendritic growth models for binary alloys directionally solidified in a positive temperature gradient.

Primary arm spacing in chill block melt spun Ni-Mo alloys

NASA Technical Reports Server (NTRS)

Tewari, S. N.; Glasgow, T. K.

1987-01-01

Chill block melt spun ribbons of Ni-Mo binary alloys containing 8.0 to 41.8 wt pct Mo have been prepared under carefully controlled processing conditions. The growth velocity has been determined as a function of distance from the quench surface from the observed ribbon thickness dependence on the melt puddle residence time. Primary arm spacing measured at the midribbon thickness locations show a dependence on growth velocity and alloy composition which is expected from dendritic growth models for binary alloys directionally solidified in a positive temperature gradient.

Micromechanisms of Monotonic and Cyclic Subcritical Crack Growth in Advanced High Melting Point Low-Ductility Intermetallics

DTIC Science & Technology

1993-05-01

Advanced Structural Ceramics, MRS Symp. Proc., P. F. Becher et al . (eds.), MRS, Pittsburgh, PA (1986). 11) M. J. Reece, F. Guiu and M. F. R. Sammur...composites under study, listed in Table 2.1, were fabricated by phase blending -80 mesh y-TiAI (Ti-55 at.% Al , with small additions of Nb, Ta, C and 0...on phase transformations in the alloy system. In the case of the binary Nb- Al system, the peritectic reaction at 2060’C (Fig. 3.1), involving the

The kinetics of composite particle formation during mechanical alloying

NASA Technical Reports Server (NTRS)

Aikin, B. J. M.; Courtney, T. H.

1993-01-01

The kinetics of composite particle formation during attritor milling of insoluble binary elemental powders have been examined. The effects of processing conditions (i.e., mill power, temperature, and charge ratio) on these kinetics were studied. Particle size distributions and fractions of elemental and composite particles were determined as functions of milling time and processing conditions. This allowed the deduction of phenomenological rate constants describing the propensity for fracture and welding during processing. For the mill-operating conditions investigated, the number of particles in the mill generally decreased with milling time, indicating a greater tendency for particle welding than fracture. Moreover, a bimodal size distribution is often obtained as a result of preferential welding. Copper and chromium 'alloy' primarily by encapsulation of Cr particles within Cu. This form of alloying also occurs in Cu-Nb alloys processed at low mill power and/or for short milling times. For other conditions, however, Cu-Nb alloys develop a lamellar morphology characteristic of mechanically alloyed two-phase ductile metals. Increasing mill power or charge (ball-to-powder weight) ratio (CR) increases the rate of composite particle formation.

TA [B] Predicting Microstructure-Creep Resistance Correlation in High Temperature Alloys over Multiple Time Scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomar, Vikas

2017-03-06

DoE-NETL partnered with Purdue University to predict the creep and associated microstructure evolution of tungsten-based refractory alloys. Researchers use grain boundary (GB) diagrams, a new concept, to establish time-dependent creep resistance and associated microstructure evolution of grain boundaries/intergranular films GB/IGF controlled creep as a function of load, environment, and temperature. The goal was to conduct a systematic study that includes the development of a theoretical framework, multiscale modeling, and experimental validation using W-based body-centered-cubic alloys, doped/alloyed with one or two of the following elements: nickel, palladium, cobalt, iron, and copper—typical refractory alloys. Prior work has already established and validated amore » basic theory for W-based binary and ternary alloys; the study conducted under this project extended this proven work. Based on interface diagrams phase field models were developed to predict long term microstructural evolution. In order to validate the models nanoindentation creep data was used to elucidate the role played by the interface properties in predicting long term creep strength and microstructure evolution.« less

Half-Heusler Alloys as Promising Thermoelectric Materials

NASA Astrophysics Data System (ADS)

Page, Alexander A.

This thesis describes Ph.D. research on the half-Heusler class of thermoelectric materials. Half-Heusler alloys are a versatile class of materials that have been studied for use in photovoltaics, phase change memory, and thermoelectric power generation. With respect to thermoelectric power generation, new approaches were recently developed in order to improve the thermoelectric figure of merit, ZT, of half-Heusler alloys. Two of the strategies discussed in this work are adding excess Ni within MNiSn (M = Ti, Zr, or Hf) compounds to form full-Heusler nanostructures and using isoelectronic substitution of Ti, Zr, and Hf in MNiSn compounds to create microscale grain boundaries. This work uses computational simulations based on density functional theory, combined with the cluster expansion method, to predict the stable phases of pseudo-binary and pseudo-ternary composition systems. Statistical mechanics methods were used to calculate temperature-composition phase diagrams that relate the equilibrium phases. It is shown that full-Heusler nanostructures are predicted to remain stable even at high temperatures, and the microscale grain boundaries observed in (Ti,Zr,Hf)NiSn materials are found to be thermodynamically unstable at equilibrium. A new strategy of combining MNiSn materials with ZrNiPb has also recently emerged, and theoretical and experimental work show that a solid solution of the two materials is stable.

Theoretical investigation of the structural stabilities, optoelectronic properties and thermodynamic characteristics of GaPxSb1-x ternary alloys

NASA Astrophysics Data System (ADS)

Oumelaz, F.; Nemiri, O.; Boumaza, A.; Ghemid, S.; Meradji, H.; Bin Omran, S.; El Haj Hassan, F.; Rai, D. P.; Khenata, R.

2018-06-01

In this theoretical study, we have investigated the structural, phase transition, electronic, thermodynamic and optical properties of GaPxSb1-x ternary alloys. Our calculations are performed with the WIEN2k code based on density functional theory using the full-potential linearized augmented plane wave method. For the electron exchange-correlation potential, a generalized gradient approximation within Wu-Cohen scheme is considered. The recently developed Tran-Blaha modified Becke-Johnson potential has also been used to improve the underestimated band gap. The structural properties, including the lattice constants, the bulk moduli and their pressure derivatives are in very good agreement with the available experimental data and theoretical results. Several structural phase transitions were studied here to establish the stable structure and to predict the phase transition under hydrostatic pressure. The computed transition pressure (Pt) of the material of our interest from the zinc blende (B3) to the rock salt (B1) phase has been determined and found to agree well with the experimental and theoretical data. The calculated band structure shows that GaSb binary compound and the ternary alloys are direct band gap semiconductors. Optical parameters such as the dielectric constants and the refractive indices are calculated and analyzed. The thermodynamic results are also interpreted and analyzed.

Binary Colloidal Alloy Test-5: Aspheres

NASA Technical Reports Server (NTRS)

Chaikin, Paul M.; Hollingsworth, Andrew D.

2008-01-01

The Binary Colloidal Alloy Test - 5: Aspheres (BCAT-5-Aspheres) experiment photographs initially randomized colloidal samples (tiny nanoscale spheres suspended in liquid) in microgravity to determine their resulting structure over time. BCAT-5-Aspheres will study the properties of concentrated systems of small particles when they are identical, but not spherical in microgravity..

Influence of silicon on friction and wear of iron-cobalt alloys

NASA Technical Reports Server (NTRS)

Buckley, D. H.; Brainard, W. A.

1972-01-01

Sliding friction and wear experiments were conducted with ternary ordered alloys of iron and cobalt containing various amounts of silicon to 5 weight percent. The friction and wear of these alloys were compared to those for binary iron-cobalt alloys in the ordered and disordered states and to those for the conventionally used bearing material, 440-C. Environments in which experiments were conducted included air, argon, and 0.25percent stearic acid in hexadecane. Results indicate that a ternary iron - cobalt - 5-percent-silicon alloy exhibits lower friction and wear than the simple binary iron-cobalt alloy. It exhibits lower wear than 440-C in all three environments. Friction was lower for the alloy in argon than in air. Auger analysis of the surface of the ternary alloy indicated segregation of silicon at the surface as a result of sliding.

Experimental Determination of Impurity and Interdiffusion Coefficients in Seven Ti and Zr Binary Systems Using Diffusion Multiples

NASA Astrophysics Data System (ADS)

Chen, Zhangqi; Liu, Zi-Kui; Zhao, Ji-Cheng

2018-05-01

Diffusion coefficients of seven binary systems (Ti-Mo, Ti-Nb, Ti-Ta, Ti-Zr, Zr-Mo, Zr-Nb, and Zr-Ta) at 1200 °C, 1000 °C, and 800 °C were experimentally determined using three Ti-Mo-Nb-Ta-Zr diffusion multiples. Electron probe microanalysis (EPMA) was performed to collect concentration profiles at the binary diffusion regions. Forward simulation analysis (FSA) was then applied to extract both impurity and interdiffusion coefficients in Ti-rich and Zr-rich part of the bcc phase. Excellent agreements between our results and most of the literature data validate the high-throughput approach combining FSA with diffusion multiples to obtain a large amount of systematic diffusion data, which will help establish the diffusion (mobility) databases for the design and development of biomedical and structural Ti alloys.

Experimental Determination of Impurity and Interdiffusion Coefficients in Seven Ti and Zr Binary Systems Using Diffusion Multiples

NASA Astrophysics Data System (ADS)

Chen, Zhangqi; Liu, Zi-Kui; Zhao, Ji-Cheng

2018-07-01

Diffusion coefficients of seven binary systems (Ti-Mo, Ti-Nb, Ti-Ta, Ti-Zr, Zr-Mo, Zr-Nb, and Zr-Ta) at 1200 °C, 1000 °C, and 800 °C were experimentally determined using three Ti-Mo-Nb-Ta-Zr diffusion multiples. Electron probe microanalysis (EPMA) was performed to collect concentration profiles at the binary diffusion regions. Forward simulation analysis (FSA) was then applied to extract both impurity and interdiffusion coefficients in Ti-rich and Zr-rich part of the bcc phase. Excellent agreements between our results and most of the literature data validate the high-throughput approach combining FSA with diffusion multiples to obtain a large amount of systematic diffusion data, which will help establish the diffusion (mobility) databases for the design and development of biomedical and structural Ti alloys.

Approximate formula for recalescence in binary eutectic alloys

NASA Technical Reports Server (NTRS)

Ohsaka, K.; Trinh, E. H.

1993-01-01

Supercooling of a liquid prior to the nucleation of a solid and the subsequent rapid growth are necessary conditions for producing novel microstructures including metastable phases which are not formed by conventional solidification processes. Since containerless techniques, such as levitation and free fall of a sample, are capable of achieving a significant supercooling level of liquids, they are under consideration as possible techniques for material processing on earth and in space.

Influence of compositional complexity on interdiffusion in Ni-containing concentrated solid-solution alloys

DOE PAGES

Jin, Ke; Zhang, Chuan; Zhang, Fan; ...

2018-03-07

To investigate the compositional effects on thermal-diffusion kinetics in concentrated solid-solution alloys, interdiffusion in seven diffusion couples with alloys from binary to quinary is systematically studied. The alloys with higher compositional complexity exhibit in general lower diffusion coefficients against homologous temperature, however, an exception is found that diffusion in NiCoFeCrPd is faster than in NiCoFeCr and NiCoCr. While the derived diffusion parameters suggest that diffusion in medium and high entropy alloys is overall more retarded than in pure metals and binary alloys, they strongly depend on specific constituents. The comparative features are captured by computational thermodynamics approaches using a self-consistentmore » database.« less

Formation and magnetic properties of the L10 phase in bulk, powder and hot compacted Mn-Ga alloys

NASA Astrophysics Data System (ADS)

Mix, T.; Müller, K.-H.; Schultz, L.; Woodcock, T. G.

2015-10-01

The formation and stability of the L10 phase in Mn-Ga binary alloys with compositions in the range 50-75 at% Mn (in steps of 5 at%) has been studied. Of these, single-phase L10 structure was successfully produced in the 55, 60 and 65 at% Mn alloys by annealing the high temperature phases, which had been retained to room temperature following arc melting. Further annealing and thermal analysis were used to determine the phase transformation temperatures in the alloys and the results were used to guide further processing. The saturation magnetisation, Ms, and the anisotropy field, Ha, were determined in applied fields up to 14 T. For Mn55Ga45, μ0Ms=0.807 T and μ0Ha=4.4 T were observed. Mechanically milled Mn55Ga45 powder had coercivity of μ0Hc=0.393 T, which was a twentyfold increase compared to the bulk material but the magnetisation was reduced (cf. powder: μ0M5 T=0.576 T, bulk: μ0M5 T=0.780 T). Annealing the powder at 400 °C led to recovery of the magnetisation but reduced the coercivity, which was still 10 times as high as the bulk value. A degree of texture of 0.45 was achieved by magnetic alignment of the powder particles, leading to a remanence of 0.526 T. Furthermore, isotropic hot compacts of powders were produced with packing density from 83% to 99%, in which the improved coercivity of the powders was partially retained.

Examination of Multiphase (Zr,Ti)(V,Cr,Mn,Ni)2 Ni-MH Electrode Alloys: Part II. Solid-State Transformation of the Interdendritic B2 Phase

NASA Astrophysics Data System (ADS)

Bendersky, L. A.; Wang, K.; Boettinger, W. J.; Newbury, D. E.; Young, K.; Chao, B.

2010-08-01

Solidification microstructure of multicomponent (Zr,Ti)-Ni-(V,Cr,Mn,Co) alloys intended for use as negative electrodes in Ni-metal hydride (Ni-MH) batteries was studied in Part I of this series of articles. Part II of the series examines the complex internal structure of the interdendritic grains formed by solid-state transformation and believed to play an important role in the electrochemical charge/discharge characteristics of the overall alloy composition. By studying one alloy, Zr21Ti12.5V10Cr5.5Mn5.1Co5.0Ni40.2Al0.5Sn0.3, it is shown that the interdendritic grains solidify as a B2 (Ti,Zr)44(Ni,TM)56 phase, and then undergo transformation to Zr7Ni10-type, Zr9Ni11-type, and martensitic phases. The transformations obey orientation relationships between the high-temperature B2 phase and the low-temperature Zr-Ni-type intermetallics, and consequently lead to a multivariant structure. The major orientation relationship for the orthorhombic Zr7Ni10 type is [011]Zr7Ni10//[001]B2; (100)Zr7Ni10//(100)B2. The orientation relationship for the tetragonal Zr9Ni11 type is [001]Zr9Ni11//[001]B2; (130)Zr9Ni11//(100)B2. Binary Ni-Zr and ternary Ti-Ni-Zr phase diagrams were used to rationalize the formation of the observed domain structure.

Simulation studies of GST phase change alloys

NASA Astrophysics Data System (ADS)

Martyna, Glenn

2008-03-01

In order to help drive post-Moore's Law technology development, switching processes involving novel materials, in particular, GeSbTe (GST) alloys are being investigated for use in memory and eFuse applications. An anneal/quench thermal process crystallizes/amorphosizes a GST alloy which then has a low/high resistance and thereby forms a readable/writeable bit; for example, a ``one'' might be the low resistance, conducting crystalline state and a ``zero'' might be the high resistance, glassy state. There are many open questions about the precise nature of the structural transitions and the coupling to electronic structure changes. Computational and experimental studies of the effect of pressure on the GST materials were initiated in order to probe the physics behind the thermal switching process. A new pathway to reversible phase change involving pressure-induced structural metal insulator transitions was discovered. In a binary GS system, a room-temperature, direct, pressure-induced transformation from the high resistance amorphous phase to the low resistance crystalline phase was observed experimentally while the reverse process under tensile load was demonstrated via ab initio MD simulations performed on IBM's Blue Gene/L enabled by massively parallel software. Pressure induced transformations of the ternary material GST-225 (Ge2Sb2Te5) were, also, examined In the talk, the behavior of the two systems will be compared and insight into the nature of the phase change given.

A quantitative study of factors influencing lamellar eutectic morphology during solidification

NASA Technical Reports Server (NTRS)

Kaukler, W. F. S.

1981-01-01

The factors that influence the shape of the solid-liquid interface of a lamellar binary eutectic alloy are evaluated. Alloys of carbon tetrabromide and hexachloroethane which serve as a transparent analogue of lamellar metallic eutectics are used. The observed interface shapes are analyzed by computer-aided methods. The solid-liquid interfacial free energies of each of the individual phases comprising the eutectic system are measured as a function of composition using a 'grain boundary groove' technique. The solid-liquid interfacial free energy of the two phases are evaluated directly from the eutectic interface. The phase diagram for the system, the heat of fusion as a function of composition, and the density as a function of composition are measured. The shape of the eutectic interface is controlled mainly by the solid-liquid and solid-solid interfacial free energy relationships at the interface and by the temperature gradient present, rather than by interlamellar diffusion in the liquid at the interface, over the range of growth rates studied.

Real-time synchrotron x-ray observations of equiaxed solidification of aluminium alloys and implications for modelling

NASA Astrophysics Data System (ADS)

Prasad, A.; Liotti, E.; McDonald, S. D.; Nogita, K.; Yasuda, H.; Grant, P. S.; StJohn, D. H.

2015-06-01

Recently, in-situ observations were carried out by synchrotron X-ray radiography to observe the nucleation and growth in Al alloys during solidification. The nucleation and grain formation of a range of Al-Si and Al-Cu binary alloys were studied. When grain refiner was added to the alloys, the location of the nucleation events was readily observed. Once nucleation began it continued to occur in a wave of events with the movement of the temperature gradient across the field of view due to cooling. Other features observed were the settling of the primary phase grains in the Al-Si alloys and floating in the Al-Cu alloys, the effects of convection with marked fluctuation of the growth rate of the solid-liquid interface in the Al-Si alloys, and an absence of fragmentation. The microstructures are typical of those produced in the equiaxed zone of actual castings. These observations are compared with predictions arising from the Interdependence model. The results from this comparison have implications for further refinement of the model and simulation and modelling approaches in general. These implications will be discussed.

Retraction Note to: Ultra-High Strength and Ductile Lamellar-Structured Powder Metallurgy Binary Ti-Ta Alloys

NASA Astrophysics Data System (ADS)

Liu, Yong; Xu, Shenghang; Wang, Xin; Li, Kaiyang; Liu, Bin; Wu, Hong; Tang, Huiping

2018-05-01

The editors and authors have retracted the article, "Ultra-High Strength and Ductile Lamellar-Structured Powder Metallurgy Binary Ti-Ta Alloys" by Yong Liu, Shenghang Xu, Xin Wang, Kaiyang Li, Bin Liu, Hong Wu, and Huiping Tang (https://doi.org/10.1007/s11837-015-1801-1).

Calculation of the surface tension of liquid Ga-based alloys

NASA Astrophysics Data System (ADS)

Dogan, Ali; Arslan, Hüseyin

2018-05-01

As known, Eyring and his collaborators have applied the structure theory to the properties of binary liquid mixtures. In this work, the Eyring model has been extended to calculate the surface tension of liquid Ga-Bi, Ga-Sn and Ga-In binary alloys. It was found that the addition of Sn, In and Bi into Ga leads to significant decrease in the surface tension of the three Ga-based alloy systems, especially for that of Ga-Bi alloys. The calculated surface tension values of these alloys exhibit negative deviation from the corresponding ideal mixing isotherms. Moreover, a comparison between the calculated results and corresponding literature data indicates a good agreement.

Effects of surface poisons on the oxidation of binary alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hagan, P.S.; Polizzotti, R.S.; Luckman, G.

1985-10-01

A system of reaction-diffusion equations describing the oxidation of binary alloys in environments containing small amounts of surface poisons is analyzed. These poisons reduce the oxygen flux into the alloy, which causes the alloy to oxidize in two stages.During the initial stage, the oxidation reaction occurs in a stationary boundary layer at the alloy surface. Consequently, a thin zone containing a very high concentration of the metal oxide is created at the alloy surface. During the second stage, the oxidation reaction occurs in a moving boundary layer. This leads to a Stefan problem, which is analyzed by using asymptotic andmore » numerical techniques. By comparing the solutions to those of alloys in unpoisoned environments, it is concluded that surface poisons can lead to the formation of protective external oxide scales in alloys which would not normally form such scales. 11 references.« less

Miscibility of amorphous ZrO2-Al2O3 binary alloy

NASA Astrophysics Data System (ADS)

Zhao, C.; Richard, O.; Bender, H.; Caymax, M.; De Gendt, S.; Heyns, M.; Young, E.; Roebben, G.; Van Der Biest, O.; Haukka, S.

2002-04-01

Miscibility is a key factor for maintaining the homogeneity of the amorphous structure in a ZrO2-Al2O3 binary alloy high-k dielectric layer. In the present work, a ZrO2/Al2O3 laminate thin layer has been prepared by atomic layer chemical vapor deposition on a Si (100) wafer. This layer, with artificially induced inhomogeneity (lamination), enables one to study the change in homogeneity of the amorphous phase in the ZrO2/Al2O3 system during annealing. High temperature grazing incidence x-ray diffraction (HT-XRD) was used to investigate the change in intensity of the constructive interference peak of the x-ray beams which are reflected from the interfaces of ZrO2/Al2O3 laminae. The HT-XRD spectra show that the intensity of the peak decreases with an increase in the anneal temperature, and at 800 °C, the peak disappears. The same samples were annealed by a rapid thermal process (RTP) at temperatures between 700 and 1000 °C for 60 s. Room temperature XRD of the RTP annealed samples shows a similar decrease in peak intensity. Transmission electronic microscope images confirm that the laminate structure is destroyed by RTP anneals and, just below the crystallization onset temperature, a homogeneous amorphous ZrAlxOy phase forms. The results demonstrate that the two artificially separated phases, ZrO2 and Al2O3 laminae, tend to mix into a homogeneous amorphous phase before crystallization. This observation indicates that the thermal stability of ZrO2-Al2O3 amorphous phase is suitable for high-k applications.

FCRD Advanced Reactor (Transmutation) Fuels Handbook

DOE Office of Scientific and Technical Information (OSTI.GOV)

Janney, Dawn Elizabeth; Papesch, Cynthia Ann

2016-09-01

Transmutation of minor actinides such as Np, Am, and Cm in spent nuclear fuel is of international interest because of its potential for reducing the long-term health and safety hazards caused by the radioactivity of the spent fuel. One important approach to transmutation (currently being pursued by the DOE Fuel Cycle Research & Development Advanced Fuels Campaign) involves incorporating the minor actinides into U-Pu-Zr alloys, which can be used as fuel in fast reactors. U-Pu-Zr alloys are well suited for electrolytic refining, which leads to incorporation rare-earth fission products such as La, Ce, Pr, and Nd. It is, therefore, importantmore » to understand not only the properties of U-Pu-Zr alloys but also those of U-Pu-Zr alloys with concentrations of minor actinides (Np, Am) and rare-earth elements (La, Ce, Pr, and Nd) similar to those in reprocessed fuel. In addition to requiring extensive safety precautions, alloys containing U, Pu, and minor actinides (Np and Am) are difficult to study for numerous reasons, including their complex phase transformations, characteristically sluggish phasetransformation kinetics, tendency to produce experimental results that vary depending on the histories of individual samples, rapid oxidation, and sensitivity to contaminants such as oxygen in concentrations below a hundred parts per million. Although less toxic, rare-earth elements such as La, Ce, Pr, and Nd are also difficult to study for similar reasons. Many of the experimental measurements were made before 1980, and the level of documentation for experimental methods and results varies widely. It is, therefore, not surprising that little is known with certainty about U-Pu-Zr alloys, particularly those that also contain minor actinides and rare-earth elements. General acceptance of results commonly indicates that there is only a single measurement for a particular property. This handbook summarizes currently available information about U, Pu, Zr, Np, Am, La, Ce, Pr, and Nd and alloys of two or three of these elements. It contains information about phase diagrams and related information (including phases and phase transformations); heat capacity, entropy, and enthalpy; thermal expansion; and thermal conductivity and diffusivity. In addition to presenting information about materials properties, the handbook attempts to provide information about how well the property is known and how much variation exists between measurements. Although it includes some results from models, its primary focus is experimental data. The Handbook is organized in two sections: one with information about the U-Pu-Zr ternary and one with information about other elements and binary and vi ternary alloys in the U-Np-Pu-Am-La-Ce-Pr-Nd-Zr system. Within each section, information about elements is presented first, followed by information about binary alloys, then information about ternary alloys. The order in which the elements in each alloy are mentioned follows the order in the first sentence of this paragraph. Much of the information on the U-Pu-Zr system repeats information from the FCRD Transmutation Fuels Handbook 2015. Most of the other data has been published elsewhere (although scattered throughout numerous references, some quite obscure); however, some data from Idaho National Laboratory is presented here for the first time. As the FCRD programmatic mission evolves, future editions of this handbook will begin to include other advanced reactor fuel designs and compositions. Hence, the title of the handbook will transition to the Advanced Reactor Fuels Handbook.« less

Superior thermoelectric performance in PbTe-PbS pseudo-binary. Extremely low thermal conductivity and modulated carrier concentration

DOE PAGES

Wu, D.; Zhao, L. -D.; Tong, X.; ...

2015-05-19

Lead chalcogenides have exhibited their irreplaceable role as thermoelectric materials at the medium temperature range, owing to highly degenerate electronic bands and intrinsically low thermal conductivities. PbTe-PbS pseudo-binary has been paid extensive attentions due to the even lower thermal conductivity which originates largely from the coexistence of both alloying and phase-separated precipitations. To investigate the competition between alloying and phase separation and its pronounced effect on the thermoelectric performance in PbTe-PbS, we systematically studied Spark Plasma Sintered (SPSed), 3 at% Na- doped (PbTe) 1-x(PbS)x samples with x=10%, 15%, 20%, 25%, 30% and 35% by means of transmission electron microscopy (TEM)more » observations and theoretical calculations. Corresponding to the lowest lattice thermal conductivity as a result of the balance between point defect- and precipitates- scattering, the highest figure of merit ZT~2.3 was obtained at 923 K when PbS phase fraction x is at 20%. The consistently lower lattice thermal conductivities in SPSed samples compared with corresponding ingots, resulting from the powdering and follow-up consolidation processes, also contribute to the observed superior ZT. Notably, the onset of carrier concentration modulation ~600 K due to excessive Na’s diffusion and re-dissolution leads to the observed saturations of electrical transport properties, which is believed equally crucial to the outstanding thermoelectric performance of SPSed PbTe-PbS samples.« less

Phase diagram and polarization of stable phases of (Ga1- x In x )2O3

NASA Astrophysics Data System (ADS)

Maccioni, Maria Barbara; Fiorentini, Vincenzo

2016-04-01

The full phase diagram of (Ga1- x In x )2O3 is obtained theoretically. The phases competing for the ground state are monoclinic β (low x), hexagonal (x ˜ 0.5), and bixbyite (large x). Three disconnected mixing regions interlace with two distinct phase-separation regions, and at x ˜ 0.5, the coexistence of hexagonal and β alloys with phase-separated binary components is expected. We also explore the permanent polarization of the phases, but none of them are polar. On the other hand, we find that ɛ-Ga2O3, which was stabilized in recent experiments, is pyroelectric with a large polarization and piezoelectric coupling, and could be used to produce high-density electron gases at interfaces.

Solid state amorphization in the Al-Fe binary system during high energy milling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Urban, P., E-mail: purban@us.es; Montes, J. M.; Cintas, J.

2013-12-16

In the present study, mechanical alloying (MA) of Al75Fe25 elemental powders mixture was carried out in argon atmosphere, using a high energy attritor ball mill. The microstructure of the milled products at different stages of milling was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The results showed that the amorphous phase content increased by increasing the milling time, and after 50 hours the amorphization process became complete. Heating the samples resulted in the crystallization of the synthesized amorphous alloys and the appearance of the equilibrium intermetallic compounds Al{sub 5}Fe{submore » 2}.« less

New eutectic alloys and their heats of transformation

NASA Technical Reports Server (NTRS)

Farkas, D.; Birchenall, C. E.

1985-01-01

Eutectic compositions and congruently melting intermetallic compounds in binary and multicomponent systems among common elements such as Al, Ca, Cu, Mg, P, Si, and Zn may be useful for high temperature heat storage. In this work, heats of fusion of new multicomponent eutectics and intermetallic phases are reported, some of which are competitive with molten salts in heat storage density at high temperatures. The method used to determine unknown eutectic compositions combined results of differential thermal analysis, metallography, and microprobe analysis. The method allows determination of eutectic compositions in no more than three steps. The heats of fusion of the alloys were measured using commercial calorimeters, a differential thermal analyzer, and a differential scanning calorimeter.

In vitro investigation of NiTiW shape memory alloy as potential biomaterial with enhanced radiopacity.

PubMed

Li, Huafang; Cong, Ying; Zheng, Yufeng; Cui, Lishan

2016-03-01

In the present study, a novel kind of NiTiW shape memory alloy with chemical composition of Ni43.5Ti45.5W11 (at.%) has been successfully developed with excellent X-ray radiopacity by the introduction of pure W precipitates into the NiTi matrix phase. Its microstructure, X-ray radiopacity, mechanical properties, corrosion resistance in simulated body fluid, hemocompatibility and in vitro cytocompatibility were systematically investigated. The typical microstructural feature of NiTiW alloy at room temperature was tiny pure W particles randomly distributing in the NiTi matrix phase. The presence of W precipitates was found to result in enhanced radiopacity and microhardness of NiTiW alloy in comparison to that of NiTi binary alloy. NiTiW alloy exhibits excellent shape memory effect, and a maximum shape recovery ratio of about 30% was obtained with a total prestrain of 8% for the NiTiW alloy sample. In the electrochemical test, NiTiW alloy presented an excellent corrosion resistance in simulated body fluid, comparable to that of NiTi alloy. Hemocompatibility tests indicated that the NiTiW alloy has quite low hemolysis (lower than 0.5%) and the adherent platelet showed round shape without pseudopod. Besides, in vitro cell viability tests demonstrated that the cell viability is all above 90%, and the cells spread well on the NiTiW alloy, having polygon or spindle healthy morphology. The hemocompatibility tests, in vitro cell viability tests and morphology observation indicated that the NiTiW shape memory alloys have excellent biocompatibility. The excellent X-ray radiopacity makes the NiTiW alloys show obvious advantages in orthopedic, stomatological, neurological and cardiovascular domains where radiopacity is quite important factor in order to guarantee successful implantation. Copyright © 2015 Elsevier B.V. All rights reserved.

The use of computational thermodynamics for the determination of surface tension and Gibbs-Thomson coefficient of multicomponent alloys

NASA Astrophysics Data System (ADS)

Ferreira, D. J. S.; Bezerra, B. N.; Collyer, M. N.; Garcia, A.; Ferreira, I. L.

2018-04-01

The simulation of casting processes demands accurate information on the thermophysical properties of the alloy; however, such information is scarce in the literature for multicomponent alloys. Generally, metallic alloys applied in industry have more than three solute components. In the present study, a general solution of Butler's formulation for surface tension is presented for multicomponent alloys and is applied in quaternary Al-Cu-Si-Fe alloys, thus permitting the Gibbs-Thomson coefficient to be determined. Such coefficient is a determining factor to the reliability of predictions furnished by microstructure growth models and by numerical computations of solidification thermal parameters, which will depend on the thermophysical properties assumed in the calculations. The Gibbs-Thomson coefficient for ternary and quaternary alloys is seldom reported in the literature. A numerical model based on Powell's hybrid algorithm and a finite difference Jacobian approximation has been coupled to a Thermo-Calc TCAPI interface to assess the excess Gibbs energy of the liquid phase, permitting liquidus temperature, latent heat, alloy density, surface tension and Gibbs-Thomson coefficient for Al-Cu-Si-Fe hypoeutectic alloys to be calculated, as an example of calculation capabilities for multicomponent alloys of the proposed method. The computed results are compared with thermophysical properties of binary Al-Cu and ternary Al-Cu-Si alloys found in the literature and presented as a function of the Cu solute composition.

Improvements to the strength and corrosion resistance of aluminum-magnesium-manganese alloys of near-AA5083 chemistry

NASA Astrophysics Data System (ADS)

Carroll, Mark Christopher

Aluminum alloys of the 5000 series (AI-Mg-Mn) are extremely popular in a wide range of applications that call for a balance of moderately high strength, good corrosion resistance, and light weight, all at a moderate cost. One of the most popular 5000 series alloys is designated A1-5083, containing, in addition to aluminum, approximately 4 wt% magnesium and 0.7 wt% manganese. In order to increase the range of versatility of this particular alloy, a number of modifications have been examined that will potentially improve the strength and corrosion resistance characteristics while maintaining a chemical composition that is very close to the proven 5083 alloy. The strength of the 5083-based alloys under study are investigated with two goals in mind---to maximize the potential strength characteristics in a "standard" 5083 form through changes in minor processing parameters or through minor alloying additions. Increasing the standard alloy's potential is possible through improved efficiency of "preprocessing" heat treatments that maximize the homogeneous dispersion of secondary manganese-based particles. For the modified alloy study, additions of scandium and zirconium are shown to improve strength not only by forming secondary particles in the alloy, but also through substitutional solid solution strengthening, even when added at very small levels. Corrosion resistance of these 5083-based alloys is investigated once again through minor alloying additions; specifically zinc, copper, and silver. Zinc is particularly effective in that it changes the corrosion-susceptible binary aluminum-magnesium phase that would otherwise form on grain boundaries following exposure to moderately elevated temperatures for extended periods of time to a ternary aluminum-magnesium-zinc phase. This chemical composition of this ternary phase that forms following zinc additions can be further altered through minor additions of copper and silver. By determining threshold levels for these modifications while maintaining a chemical composition that is very near that of standard Al-5083, it can be shown that even minor modifications to processing and alloying parameters can have a favorable effect on the final bulk properties of the alloy. The increased range of strength and corrosion resistance of these lightly modified alloys make them more attractive in a broadened range of potential applications.

Rapid solidification of high-conductivity copper alloys. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Bloom, Theodore Atlas

1989-01-01

The main objective was to develop improved copper alloys of high strength and high thermal and electric conductivity. Chill block melt spinning was used to produce binary alloys of Cu-Cr and Cu-Zr, and ternary alloys of Cu-Cr-Ag. By quenching from the liquid state, up to 5 atomic percent of Cr and Zr were retained in metastable extended solid solution during the rapid solidification process. Eutectic solidification was avoided and the full strengthening benefits of the large volume fraction of precipitates were realized by subsequent aging treatment. The very low solid solubility of Cr and Zr in Cu result in a high conductivity Cu matrix strengthened by second phase precipitates. Tensile properties on as-cast and aged ribbons were measured at room and elevated temperatures. Precipitate coarsening of Cr in Cu was studied by changes in electrical resistance during aging. X-ray diffraction was used to measure the lattice parameter and the degree of supersaturation of the matrix. The microstructures were characterized by optical and electron microscopy.

Preliminary in situ and real-time study of directional solidification of metallic alloys by x-ray imaging techniques

NASA Astrophysics Data System (ADS)

Nguyen Thi, H.; Jamgotchian, H.; Gastaldi, J.; Härtwig, J.; Schenk, T.; Klein, H.; Billia, B.; Baruchel, J.; Dabo, Y.

2003-05-01

During directional solidification of a binary alloy, the solid-liquid interface exhibits a variety of patterns that are due to the Mullins-Sekerka instability and governed by the growth conditions. It is well known that properties of the grown material are largely controlled by the microstructures left in the solid during processing. Thus, a precise mastering of the solidification is essential to tailor products in a reproducible fashion to a specified quality. One major difficulty for this study is the real-time and in situ observation of the interface, especially for metallic alloys. A possibility is to use an intense and coherent third generation x-ray beam. By combining different x-ray imaging techniques (absorption/phase contrast radiography and diffraction topography), we have studied the directional melting and solidification of aluminium-based alloys. The preliminary results show the great potential of these techniques for the study of the coupling between stress effects and microstructure formation in solidification processing.

Surface tension modelling of liquid Cd-Sn-Zn alloys

NASA Astrophysics Data System (ADS)

Fima, Przemyslaw; Novakovic, Rada

2018-06-01

The thermodynamic model in conjunction with Butler equation and the geometric models were used for the surface tension calculation of Cd-Sn-Zn liquid alloys. Good agreement was found between the experimental data for limiting binaries and model calculations performed with Butler model. In the case of ternary alloys, the surface tension variation with Cd content is better reproduced in the case of alloys lying on vertical sections defined by high Sn to Zn molar fraction ratio. The calculated surface tension is in relatively good agreement with the available experimental data. In addition, the surface segregation of liquid ternary Cd-Sn-Zn and constituent binaries has also been calculated.

Laser-induced reversion of δ' precipitates in an Al-Li alloy: Study on temperature rise in pulsed laser atom probe.

PubMed

Khushaim, Muna; Gemma, Ryota; Al-Kassab, Talaat

2016-08-01

The influence of tuning the laser pulse energy during the analyses on the resulting microstructure in a specimen utilizing an ultra-fast laser assisted atom probe was demonstrated by a case study of a binary Al-Li alloy. The decomposition parameters, such as the size, number density, volume fraction, and composition of δ' precipitates, were carefully monitored after each analysis. A simple model was employed to estimate the corresponding specimen temperature for each value of the laser energy. The results indicated that the corresponding temperatures for the laser pulse energy in the range of 10 to 80 pJ are located inside the miscibility gap of the binary Al-Li phase diagram and fall into the metastable equilibrium field. In addition, the corresponding temperature for a laser pulse energy of 100 pJ was in fairly good agreement with reported range of  δ' solvus temperature, suggesting a result of reversion upon heating due to laser pulsing. Microsc. Res. Tech. 79:727-737, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Mechanical Characterisation and Biomechanical and Biological Behaviours of Ti-Zr Binary-Alloy Dental Implants

PubMed Central

Jiménez-Garrudo, Antonio; Gil-Mur, Francisco Javier; Manero, José María; Punset-Fuste, Miquel; Chávarri-Prado, David; Diéguez-Pereira, Markel; Monticelli, Francesca

2017-01-01

The objective of the study is to characterise the mechanical properties of Ti-15Zr binary alloy dental implants and to describe their biomechanical behaviour as well as their osseointegration capacity compared with the conventional Ti-6Al-4V (TAV) alloy implants. The mechanical properties of Ti-15Zr binary alloy were characterised using Roxolid© implants (Straumann, Basel, Switzerland) via ultrasound. Their biomechanical behaviour was described via finite element analysis. Their osseointegration capacity was compared via an in vivo study performed on 12 adult rabbits. Young's modulus of the Roxolid© implant was around 103 GPa, and the Poisson coefficient was around 0.33. There were no significant differences in terms of Von Mises stress values at the implant and bone level between both alloys. Regarding deformation, the highest value was observed for Ti-15Zr implant, and the lowest value was observed for the cortical bone surrounding TAV implant, with no deformation differences at the bone level between both alloys. Histological analysis of the implants inserted in rabbits demonstrated higher BIC percentage for Ti-15Zr implants at 3 and 6 weeks. Ti-15Zr alloy showed elastic properties and biomechanical behaviours similar to TAV alloy, although Ti-15Zr implant had a greater BIC percentage after 3 and 6 weeks of osseointegration. PMID:29318142

Microhardness variation and related microstructure in Al-Cu alloys prepared by HF induction melting and RF sputtering

NASA Astrophysics Data System (ADS)

Boukhris, N.; Lallouche, S.; Debili, M. Y.; Draissia, M.

2009-03-01

The materials under consideration are binary aluminium-copper alloys (10 at% to 90.3 at%Cu) produced by HF melting and RF magnetron sputtering. The resulting micro structures have been observed by standard metallographic techniques, X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. Vickers microhardness of bulk Al-Cu alloys reaches a maximum of 1800 MPa at 70.16 at%Cu. An unexpected metastable θ ' phase has been observed within aluminium grain in Al-37 at%Cu. The mechanical properties of a family of homogeneous Al{1-x}Cu{x} (0 < x < 0.92) thin films made by radiofrequency (13.56 MHz) cathodic magnetron sputtering from composite Al-Cu targets have been investigated. The as-deposited microstructures for all film compositions consisted of a mixture of the two expected face-centred-cubic (fcc) Al solid solution and tetragonal θ (Al{2}Cu) phases. The microhardness regularly increases and the grain size decreases both with copper concentration. This phenomenon of significant mechanical strengthening of aluminium by means of copper is essentially due to a combination between solid solution effects and grain size refinement. This paper reports some structural features of different Al-Cu alloys prepared by HF melting and RF magnetron on glass substrate sputtering.

Mg-Al-Ca In-Situ Composites with a Refined Eutectic Structure and Their Compressive Properties

NASA Astrophysics Data System (ADS)

Shi, Ling-Ling; Xu, Jian; Ma, Evan

2008-05-01

In a series of Mg x (Al2Ca)100- x (76 ≤ x ≤ 87) ternary alloys near the Mg-(Mg,Al)2Ca pseudo-binary eutectic point, different phases and morphologies based on ultrafine eutectic microstructure have been obtained by controlling the composition and changing the cooling rate via either induction melting or copper mold casting. For 81 ≤ x ≤ 87, the chill-cast alloys with ductile Mg dendrites embedded in an ultrafine [Mg + (Mg,Al)2Ca] eutectic matrix exhibit gradually increased fracture strength from 415 to 491 MPa with the decrease of Mg content. At x = 79, the Mg79Al14Ca7 alloy contains hard (Mg,Al)2Ca precipitates coexisting with ductile Mg dendrite, dispersed in the strong eutectic matrix. This alloy exhibits the highest compressive fracture strength (600 MPa), and the specific strength reaches 3.4 × 105 N·m·kg-1. The alloys all exhibit substantial plastic strain (5 to 6 pct). The attainment of such a combination of strength and plasticity is an interesting and useful step in improving the mechanical properties of lightweight Mg alloys.

A new strategy to design eutectic high-entropy alloys using simple mixture method

DOE PAGES

Jiang, Hui; Han, Kaiming; Gao, Xiaoxia; ...

2018-01-13

Eutectic high entropy alloys (EHEAs) hold promising industrial application potential, but how to design EHEA compositions remains challenging. In the present work, a simple and effective strategy by combining mixing enthalpy and constituent binary eutectic compositions was proposed to design EHEA compositions. This strategy was then applied to a series of (CoCrFeNi)M x (M = Nb, Ta, Zr, Hf) HEAs, leading to the discovery of new EHEAs, namely, CoCrFeNiNb 0.45, CoCrFeNiTa 0.4, CoCrFeNiZr 0.55 and CoCrFeNiHf 0.4. The microstructure of these new EHEAs comprised of FCC and Laves phases in the as-cast state. In conclusion, the experimental result shows thatmore » this new alloy design strategy can be used to locate new EHEAs effectively.« less

Electrical conductivity and phase diagram of binary alloys. 21: The system palladium-chromium

NASA Technical Reports Server (NTRS)

Grube, G.; Knabe, R.

1985-01-01

Pd-Cr alloys were investigated by thermal analysis, hardness measurements, X-ray analysis, microscopic examination of etched pieces, and temperature-resistance curves of the solid alloys. Only one compound, Pd2Cr3, m, 1389 deg, is formed. It possesses a cubic face centered lattice and forms with excess Pd a series of solid solutions with a minimum m.p. at 45 atoms% Pd. Hardness maximum appears at the Pd2Cr3 point. Pd2Cr3 forms no solid solutions with Cr but eutectic point appears at 25 atoms% Pd, m. 1320 deg. The sp. resistance of pure Cr in an atom of H, indicates no allotropic forms. Cr2O3 is solid in molten Cr. Pure Cr melts at 1890 plus or minus 10 deg but Cr contg. Cr2O3 starts to melt at 1770 to 1790 deg.

Stability of Cd 1–xZn xO yS 1–y Quaternary Alloys Assessed with First-Principles Calculations

DOE PAGES

Varley, Joel B.; He, Xiaoqing; Rockett, Angus; ...

2017-02-08

One route to decreasing the absorption in CdS buffer layers in Cu(In,Ga)Se 2 and Cu 2ZnSn(S,Se) 4 thin-film photovoltaics is by alloying. Here we use first-principles calculations based on hybrid functionals to assess the energetics and stability of quaternary Cd, Zn, O, and S (Cd 1–xZn xO yS 1–y) alloys within a regular solution model. Our results identify that full miscibility of most Cd 1–xZn xO yS 1–y compositions and even binaries like Zn(O,S) is outside typical photovoltaic processing conditions. Finally, the results suggest that the tendency for phase separation of the oxysulfides may drive the nucleation of other phasesmore » such as sulfates that have been increasingly observed in oxygenated CdS and ZnS.« less

Stability of Cd 1–xZn xO yS 1–y Quaternary Alloys Assessed with First-Principles Calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varley, Joel B.; He, Xiaoqing; Rockett, Angus

One route to decreasing the absorption in CdS buffer layers in Cu(In,Ga)Se 2 and Cu 2ZnSn(S,Se) 4 thin-film photovoltaics is by alloying. Here we use first-principles calculations based on hybrid functionals to assess the energetics and stability of quaternary Cd, Zn, O, and S (Cd 1–xZn xO yS 1–y) alloys within a regular solution model. Our results identify that full miscibility of most Cd 1–xZn xO yS 1–y compositions and even binaries like Zn(O,S) is outside typical photovoltaic processing conditions. Finally, the results suggest that the tendency for phase separation of the oxysulfides may drive the nucleation of other phasesmore » such as sulfates that have been increasingly observed in oxygenated CdS and ZnS.« less

A new strategy to design eutectic high-entropy alloys using simple mixture method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Hui; Han, Kaiming; Gao, Xiaoxia

Eutectic high entropy alloys (EHEAs) hold promising industrial application potential, but how to design EHEA compositions remains challenging. In the present work, a simple and effective strategy by combining mixing enthalpy and constituent binary eutectic compositions was proposed to design EHEA compositions. This strategy was then applied to a series of (CoCrFeNi)M x (M = Nb, Ta, Zr, Hf) HEAs, leading to the discovery of new EHEAs, namely, CoCrFeNiNb 0.45, CoCrFeNiTa 0.4, CoCrFeNiZr 0.55 and CoCrFeNiHf 0.4. The microstructure of these new EHEAs comprised of FCC and Laves phases in the as-cast state. In conclusion, the experimental result shows thatmore » this new alloy design strategy can be used to locate new EHEAs effectively.« less

Zn-Li alloy after extrusion and drawing: Structural, mechanical characterization, and biodegradation in abdominal aorta of rat.

PubMed

Zhao, Shan; Seitz, Jan-M; Eifler, Rainer; Maier, Hans J; Guillory, Roger J; Earley, Elisha J; Drelich, Adam; Goldman, Jeremy; Drelich, Jaroslaw W

2017-07-01

Zinc shows great promise as a bio-degradable metal. Our early in vivo investigations implanting pure zinc wires into the abdominal aorta of Sprague-Dawley rats revealed that metallic zinc does not promote restenotic responses and may suppress the activities of inflammatory and smooth muscle cells. However, the low tensile strength of zinc remains a major concern. A cast billet of the Zn-Li alloy was produced in a vacuum induction caster under argon atmosphere, followed by a wire drawing process. Two phases of the binary alloy identified by x-ray diffraction include the zinc phase and intermetallic LiZn 4 phase. Mechanical testing proved that incorporating 0.1wt% of Li into Zn increased its ultimate tensile strength from 116±13MPa (pure Zn) to 274±61MPa while the ductility was held at 17±7%. Implantation of 10mm Zn-Li wire segments into abdominal aorta of rats revealed an excellent biocompatibility of this material in the arterial environment. The biodegradation rate for Zn-Li was found to be about 0.008mm/yr and 0.045mm/yr at 2 and 12months, respectively. Copyright © 2017 Elsevier B.V. All rights reserved.

Nanostructured Platinum Alloys for Use as Catalyst Materials

NASA Technical Reports Server (NTRS)

Narayan, Sri R. (Inventor); Hays, Charles C. (Inventor)

2015-01-01

A series of binary and ternary Pt-alloys, that promote the important reactions for catalysis at an alloy surface; oxygen reduction, hydrogen oxidation, and hydrogen and oxygen evolution. The first two of these reactions are essential when applying the alloy for use in a PEMFC.

Nanostructured Platinum Alloys for Use as Catalyst Materials

NASA Technical Reports Server (NTRS)

Hays, Charles C. (Inventor); Narayan, Sri R. (Inventor)

2013-01-01

A series of binary and ternary Pt-alloys, that promote the important reactions for catalysis at an alloy surface; oxygen reduction, hydrogen oxidation, and hydrogen and oxygen evolution. The first two of these reactions are essential when applying the alloy for use in a PEMFC.

ZIRCONIUM ALLOY

DOEpatents

Wilhelm, H.A.; Ames, D.P.

1959-02-01

A binary zirconiuin--antimony alloy is presented which is corrosion resistant and hard containing from 0.07% to 1.6% by weight of Sb. The alloys have good corrosion resistance and are useful in building equipment for the chemical industry.

Stabilization mechanism of γ-Mg17Al12 and β-Mg2Al3 complex metallic alloys

NASA Astrophysics Data System (ADS)

Vrtnik, S.; Jazbec, S.; Jagodič, M.; Korelec, A.; Hosnar, L.; Jagličić, Z.; Jeglič, P.; Feuerbacher, M.; Mizutani, U.; Dolinšek, J.

2013-10-01

Large-unit-cell complex metallic alloys (CMAs) frequently achieve stability by lowering the kinetic energy of the electron system through formation of a pseudogap in the electronic density of states (DOS) across the Fermi energy ɛF. By employing experimental techniques that are sensitive to the electronic DOS in the vicinity of ɛF, we have studied the stabilization mechanism of two binary CMA phases from the Al-Mg system: the γ-Mg17Al12 phase with 58 atoms in the unit cell and the β-Mg2Al3 phase with 1178 atoms in the unit cell. Since the investigated alloys are free from transition metal elements, orbital hybridization effects must be small and we were able to test whether the alloys obey the Hume-Rothery stabilization mechanism, where a pseudogap in the DOS is produced by the Fermi surface-Brillouin zone interactions. The results have shown that the DOS of the γ-Mg17Al12 phase exhibits a pronounced pseudogap centered almost exactly at ɛF, which is compatible with the theoretical prediction that this phase is stabilized by the Hume-Rothery mechanism. The disordered cubic β-Mg2Al3 phase is most likely entropically stabilized at high temperatures, whereas at lower temperatures stability is achieved by undergoing a structural phase transition to more ordered rhombohedral β‧ phase at 214 ° C, where all atomic sites become fully occupied. No pseudogap in the vicinity of ɛF was detected for the β‧ phase on the energy scale of a few 100 meV as determined by the ‘thermal observation window’ of the Fermi-Dirac function, so that the Hume-Rothery stabilization mechanism is not confirmed for this compound. However, the existence of a much broader shallow pseudogap due to several critical reciprocal lattice vectors \\buildrel{\\rightharpoonup}\\over{G} that simultaneously satisfy the Hume-Rothery interference condition remains the most plausible stabilization mechanism of this phase. At Tc = 0.85 K, the β‧ phase undergoes a superconducting transition, which slightly increases the cohesive energy and may contribute to relative stability of this phase against competing neighboring phases.

The structural, electronic, magnetic and optical properties of the half-metallic binary alloys ZCl3 (Z=Be, Mg, Ca, Sr): A first-principles study

NASA Astrophysics Data System (ADS)

Song, Jun-Tao; Zhang, Jian-Min

2018-06-01

The investigations of the electronic and magnetic properties show the binary Heusler alloys ZCl3 (Z = Be, Mg, Ca, Sr) are half-metallic (HM) ferromagnets with an integer magnetic moment (Mt) of 1 μB /f.u.. The alloy BeCl3 is thermodynamic meta-stable, while other alloys are thermodynamic stable according to their cohesive energies and formation energies. Moreover, wide HM regions for alloys ZCl3 (Z = Be, Mg, Ca, Sr) show their HM characters are robust when the lattices are expanded or compressed under uniform and tetragonal strains. Finally, some optical properties are analyzed in detail, such as the dielectric function, the absorption coefficient, the refractive index and the extinction coefficient.

Autonomous Filling of Grain-Boundary Cavities during Creep Loading in Fe-Mo Alloys

NASA Astrophysics Data System (ADS)

Zhang, S.; Fang, H.; Gramsma, M. E.; Kwakernaak, C.; Sloof, W. G.; Tichelaar, F. D.; Kuzmina, M.; Herbig, M.; Raabe, D.; Brück, E.; van der Zwaag, S.; van Dijk, N. H.

2016-10-01

We have investigated the autonomous repair of creep damage by site-selective precipitation in a binary Fe-Mo alloy (6.2 wt pct Mo) during constant-stress creep tests at temperatures of 813 K, 823 K, and 838 K (540 °C, 550 °C, and 565 °C). Scanning electron microscopy studies on the morphology of the creep-failed samples reveal irregularly formed deposits that show a close spatial correlation with the creep cavities, indicating the filling of creep cavities at grain boundaries by precipitation of the Fe2Mo Laves phase. Complementary transmission electron microscopy and atom probe tomography have been used to characterize the precipitation mechanism and the segregation at grain boundaries in detail.

The friction and wear of metals and binary alloys in contact with an abrasive grit of single-crystal silicon carbide

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1979-01-01

Sliding friction experiments were conducted with various metals and iron-base binary alloys (alloying elements Ti, Cr, Mn, Ni, Rh and W) in contact with single crystal silicon carbide riders. Results indicate that the friction force in the plowing of metal and the groove height (corresponding to the wear volume of the groove) decrease linearly as the shear strength of the bulk metal increases. The coefficient of friction and groove height generally decrease, and the contact pressure increases with an increase in solute content of binary alloys. There appears to be very good correlation of the solute to iron atomic ratio with the decreasing rate of change of coefficient of friction, the decreasing rate of change of groove height and the increasing rate of change of contact pressure with increasing solute content. These rates of change increase as the solute to iron atomic radius ratio increases or decreases from unity.

First-principles study on the thermal expansion of Ni-X binary alloys based on the quasi-harmonic Debye model

NASA Astrophysics Data System (ADS)

Shin, Yongjin; Jung, Woo-Sang; Lee, Young-Su

2016-11-01

In this study, we use the quasi-harmonic Debye model to predict the coefficient of thermal expansion of Ni- X binary alloys. The method bridges between the macroscopic elastic behavior and thermodynamic properties of materials without an expensive calculation of the volume dependence of the phonon density of states. Furthermore, the Grüneisen parameter is derived from the volume dependence of the Debye temperature, which is calculated from the first-principles elastic stiffness constants. The experimental coefficient of thermal expansion (CTE) of pure nickel is well reproduced, especially in the low temperature region. Among the few alloying elements tested, Al is predicted to slightly decrease the CTE whereas Mo and W are more effective in reducing the CTE. For the cases of Ni-X binary alloy systems, where the variation in the CTE is relatively small, the method used here appears to perform better than certain other formulations that rely entirely on the energy vs. volume relationship.

Diffuse scattering measurements of static atomic displacements in crystalline binary solid solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ice, G.E.; Sparks, C.J.; Jiang, X.

1997-09-01

Diffuse x-ray scattering from crystalline solid solutions is sensitive to both local chemical order and local bond distances. In short-range ordered alloys, fluctuations of chemistry and bond distances break the long-range symmetry of the crystal within a local region and contribute to the total energy of the alloy. Recent use of tunable synchrotron radiation to change the x-ray scattering contrast between elements has greatly advanced the measurement of bond distances between the three kinds of atom pairs found in crystalline binary alloys. The estimated standard deviation on these recovered static displacements approaches {+-}0.001 {angstrom} (0.0001 nm) which is an ordermore » of magnitude more precise than obtained with EXAFS. In addition, both the radial and tangential displacements can be recovered to five near neighbors and beyond. These static displacement measurements provide new information which challenges the most advanced theoretical models of binary crystalline alloys. 29 refs., 8 figs., 2 tabs.« less

Normal evaporation of binary alloys

NASA Technical Reports Server (NTRS)

Li, C. H.

1972-01-01

In the study of normal evaporation, it is assumed that the evaporating alloy is homogeneous, that the vapor is instantly removed, and that the alloy follows Raoult's law. The differential equation of normal evaporation relating the evaporating time to the final solute concentration is given and solved for several important special cases. Uses of the derived equations are exemplified with a Ni-Al alloy and some binary iron alloys. The accuracy of the predicted results are checked by analyses of actual experimental data on Fe-Ni and Ni-Cr alloys evaporated at 1600 C, and also on the vacuum purification of beryllium. These analyses suggest that the normal evaporation equations presented here give satisfactory results that are accurate to within an order of magnitude of the correct values, even for some highly concentrated solutions. Limited diffusion and the resultant surface solute depletion or enrichment appear important in the extension of this normal evaporation approach.

Microstructures and Grain Refinement of Additive-Manufactured Ti- xW Alloys

NASA Astrophysics Data System (ADS)

Mendoza, Michael Y.; Samimi, Peyman; Brice, David A.; Martin, Brian W.; Rolchigo, Matt R.; LeSar, Richard; Collins, Peter C.

2017-07-01

It is necessary to better understand the composition-processing-microstructure relationships that exist for materials produced by additive manufacturing. To this end, Laser Engineered Net Shaping (LENS™), a type of additive manufacturing, was used to produce a compositionally graded titanium binary model alloy system (Ti- xW specimen (0 ≤ x ≤ 30 wt pct), so that relationships could be made between composition, processing, and the prior beta grain size. Importantly, the thermophysical properties of the Ti- xW, specifically its supercooling parameter ( P) and growth restriction factor ( Q), are such that grain refinement is expected and was observed. The systematic, combinatorial study of this binary system provides an opportunity to assess the mechanisms by which grain refinement occurs in Ti-based alloys in general, and for additive manufacturing in particular. The operating mechanisms that govern the relationship between composition and grain size are interpreted using a model originally developed for aluminum and magnesium alloys and subsequently applied for titanium alloys. The prior beta grain factor observed and the interpretations of their correlations indicate that tungsten is a good grain refiner and such models are valid to explain the grain-refinement process. By extension, other binary elements or higher order alloy systems with similar thermophysical properties should exhibit similar grain refinement.

Free Energy Defect Model for the Cu-In-Ga-Se Tetrahedral Lattice

NASA Astrophysics Data System (ADS)

Stanbery, B. J.

2003-03-01

The most efficient thin-film photovoltaic converters of solar insolation to electrical power have recently achieved conversion efficiencies exceeding 19%, and are based on light absorbing layers containing the binary alloy (CuInSe_2)_1-X(CuGaSe_2)X of the α phases of these ternary chalcopyrite compounds. A statistical quantum mechanical model of the thermodynamic equilibrium defect structure of the tetrahedral lattice of copper, indium, and selenium with composition in the domain between that of the stoichiometric CuIn_1-XGa_XSe2 alloy and the β phase Cu(In_1-XGa_X)_3Se5 composition is presented. Compositions more copper-deficient than the latter have been reported experimentally to result in a breakdown of the tetrahedral coordination characteristic of the chalcopyrite lattice. These computations are based on a cluster expansion algorithm that minimizes the total free energy of the system using the Gibbs-Duhem equation to compute quasichemical reaction equilibria between the neutral clusters, and explicitly incorporates Fermi-Dirac statistics to determine their ionization equilibria and consequent carrier concentrations in the conduction and valence bands. The results are consistent with recent experimental evidence that the stoichiometric CuIn_1-XGa_XSe2 composition segregates in equilibrium into a two-phase mixture of a copper-deficient quaternary Cu_1-γIn_1-XGa_XSe2 composition and the binary Cu_2-δSe compound. The model predicts that the hole majority carrier (p-type) can only be achieved in the equilibrium single-phase chalcopyrite lattice with compositions that correspond to Cu_1-γIn_1-XGa_XSe_2+ɛ with γ and ɛ >0. This predicted requirement for selenium enrichment compared to the stoichiometric CuIn_1-XGa_XSe2 alloy composition for the dominance of holes over electrons as the majority carrier type is consistent with experimental evidence, and is explained in terms of a transition of the dominant lattice defect from the selenium vacancy in the stoichiometric case to the copper vacancy defect in the selenium-enriched lattice. This result is of particular importance since all CuIn_1-XGa_XSe2 thin-film solar cells utilize p-type absorber films.

Soft Multifunctional Composites and Emulsions with Liquid Metals.

PubMed

Kazem, Navid; Hellebrekers, Tess; Majidi, Carmel

2017-07-01

Binary mixtures of liquid metal (LM) or low-melting-point alloy (LMPA) in an elastomeric or fluidic carrier medium can exhibit unique combinations of electrical, thermal, and mechanical properties. This emerging class of soft multifunctional composites have potential applications in wearable computing, bio-inspired robotics, and shape-programmable architectures. The dispersion phase can range from dilute droplets to connected networks that support electrical conductivity. In contrast to deterministically patterned LM microfluidics, LMPA- and LM-embedded elastomer (LMEE) composites are statistically homogenous and exhibit effective bulk properties. Eutectic Ga-In (EGaIn) and Ga-In-Sn (Galinstan) alloys are typically used due to their high conductivity, low viscosity, negligible nontoxicity, and ability to wet to nonmetallic materials. Because they are liquid-phase, these alloys can alter the electrical and thermal properties of the composite while preserving the mechanics of the surrounding medium. For composites with LMPA inclusions (e.g., Field's metal, Pb-based solder), mechanical rigidity can be actively tuned with external heating or electrical activation. This progress report, reviews recent experimental and theoretical studies of this emerging class of soft material architectures and identifies current technical challenges and opportunities for further advancement. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Directional solidification of a planar interface in the presence of a time-dependent electric current

NASA Technical Reports Server (NTRS)

Brush, L. N.; Coriell, S. R.; Mcfadden, G. B.

1990-01-01

Directional solidification of pure materials and binary alloys with a planar crystal-metal interface in the presence of a time-dependent electric current is considered. For a variety of time-dependent currents, the temperature fields and the interface velocity as functions of time are presented for indium antimonide and bismuth and for the binary alloys germanium-gallium and tin-bismuth. For the alloys, the solid composition is calculated as a function of position. Quantitative predictions are made of the effect of an electrical pulse on the solute distribution in the solidified material.

Effect of zone size on the convergence of exact solutions for diffusion in single phase systems with planar, cylindrical or spherical geometry

NASA Technical Reports Server (NTRS)

Unnam, J.; Tenney, D. R.

1981-01-01

Exact solutions for diffusion in single phase binary alloy systems with constant diffusion coefficient and zero-flux boundary condition have been evaluated to establish the optimum zone size of applicability. Planar, cylindrical and spherical interface geometry, and finite, singly infinite, and doubly infinite systems are treated. Two solutions are presented for each geometry, one well suited to short diffusion times, and one to long times. The effect of zone-size on the convergence of these solutions is discussed. A generalized form of the diffusion solution for doubly infinite systems is proposed.

Lithium-aluminum-magnesium electrode composition

DOEpatents

Melendres, Carlos A.; Siegel, Stanley

1978-01-01

A negative electrode composition is presented for use in a secondary, high-temperature electrochemical cell. The cell also includes a molten salt electrolyte of alkali metal halides or alkaline earth metal halides and a positive electrode including a chalcogen or a metal chalcogenide as the active electrode material. The negative electrode composition includes up to 50 atom percent lithium as the active electrode constituent and a magnesium-aluminum alloy as a structural matrix. Various binary and ternary intermetallic phases of lithium, magnesium, and aluminum are formed but the electrode composition in both its charged and discharged state remains substantially free of the alpha lithium-aluminum phase and exhibits good structural integrity.

Structure, mechanical properties, and grindability of dental Ti-Zr alloys.

PubMed

Ho, Wen-Fu; Chen, Wei-Kai; Wu, Shih-Ching; Hsu, Hsueh-Chuan

2008-10-01

Structure, mechanical properties and grindability of a series of binary Ti-Zr alloys with zirconium contents ranging from 10 to 40 wt% have been investigated. Commercially pure titanium (c.p. Ti) was used as a control. Experimental results indicated that the diffraction peaks of all the Ti-Zr alloys matched those for alpha Ti. No beta-phase peaks were found. The hardness of the Ti-Zr alloys increased as the Zr contents increased, and ranged from 266 HV (Ti-10Zr) to 350 HV (Ti-40Zr). As the concentration of zirconium in the alloys increased, the strength, elastic recovery angles and hardness increased. Moreover, the elastically recoverable angle of Ti-40Zr was higher than of c.p. Ti by as much as 550%. The grindability of each metal was found to be largely dependent on the grinding conditions. The Ti-40Zr alloy had a higher grinding rate and grinding ratio than c.p. Ti at low speed. The grinding rate of the Ti-40Zr alloy at 500 m/min was about 1.8 times larger than that of c.p. Ti, and the grinding ratio was about 1.6 times larger than that of c.p. Ti. Our research suggested that the Ti-40Zr alloy has better mechanical properties, excellent elastic recovery capability and improved grindability at low grinding speed. The Ti-40Zr alloy has a great potential for use as a dental machining alloy.

Precipitation Modeling in Nitriding in Fe-M Binary System

NASA Astrophysics Data System (ADS)

Tomio, Yusaku; Miyamoto, Goro; Furuhara, Tadashi

2016-10-01

Precipitation of fine alloy nitrides near the specimen surface results in significant surface hardening in nitriding of alloyed steels. In this study, a simulation model of alloy nitride precipitation during nitriding is developed for Fe-M binary system based upon the Kampmann-Wagner numerical model in order to predict variations in the distribution of precipitates with depth. The model can predict the number density, average radius, and volume fraction of alloy nitrides as a function of depth from the surface and nitriding time. By a comparison with the experimental observation in a nitrided Fe-Cr alloy, it was found that the model can predict successfully the observed particle distribution from the surface into depth when appropriate solubility of CrN, interfacial energy between CrN and α, and nitrogen flux at the surface are selected.

On the role of structure-dynamic relationship in determining the excess entropy of mixing and chemical ordering in binary square-well liquid alloys

NASA Astrophysics Data System (ADS)

Lalneihpuii, R.; Shrivastava, Ruchi; Mishra, Raj Kumar

2018-05-01

Using statistical mechanical model with square-well (SW) interatomic potential within the frame work of mean spherical approximation, we determine the composition dependent microscopic correlation functions, interdiffusion coefficients, surface tension and chemical ordering in Ag-Cu melts. Further Dzugutov universal scaling law of normalized diffusion is verified with SW potential in binary mixtures. We find that the excess entropy scaling law is valid for SW binary melts. The partial and total structure factors in the attractive and repulsive regions of the interacting potential are evaluated and then Fourier transformed to get partial and total radial distribution functions. A good agreement between theoretical and experimental values for total structure factor and the reduced radial distribution function are observed, which consolidates our model calculations. The well-known Bhatia-Thornton correlation functions are also computed for Ag-Cu melts. The concentration-concentration correlations in the long wavelength limit in liquid Ag-Cu alloys have been analytically derived through the long wavelength limit of partial correlation functions and apply it to demonstrate the chemical ordering and interdiffusion coefficients in binary liquid alloys. We also investigate the concentration dependent viscosity coefficients and surface tension using the computed diffusion data in these alloys. Our computed results for structure, transport and surface properties of liquid Ag-Cu alloys obtained with square-well interatomic interaction are fully consistent with their corresponding experimental values.

Structural characterization of multimetallic nanoparticles

NASA Astrophysics Data System (ADS)

Mukundan, Vineetha

Bimetallic and trimetallic alloy nanoparticles have enhanced catalytic activities due to their unique structural properties. Using in situ time-resolved synchrotron based x-ray diffraction, we investigated the structural properties of nanoscale catalysts undergoing various heat treatments. Thermal treatment brings about changes in particle size, morphology, dispersion of metals on support, alloying, surface electronic properties, etc. First, the mechanisms of coalescence and grain growth in PtNiCo nanoparticles supported on planar silica on silicon were examined in detail in the temperature range 400-900°C. The sintering process in PtNiCo nanoparticles was found to be accompanied by lattice contraction and L10 chemical ordering. The mass transport involved in sintering is attributed to grain boundary diffusion and its corresponding activation energy is estimated from the data analysis. Nanoscale alloying and phase transformations in physical mixtures of Pd and Cu ultrafine nanoparticles were also investigated in real time with in situ synchrotron based x-ray diffraction complemented by ex situ high-resolution transmission electron microscopy. PdCu nanoparticles are interesting because they are found to be more efficient as catalysts in ethanol oxidation reaction (EOR) than monometallic Pd catalysts. The combination of metal support interaction and reactive/non-reactive environment was found to determine the thermal evolution and ultimate structure of this binary system. The composition of the as prepared Pd:Cu mixture in this study was 34% Pd and 66% Cu. At 300°C, the nanoparticles supported on silica and carbon black intermix to form a chemically ordered CsCl-type (B2) alloy phase. The B2 phase transforms into a disordered fcc alloy at higher temperature (>450°C). The alloy nanoparticles supported on silica and carbon black are homogeneous in volume, but evidence was found of Pd surface enrichment. In sharp contrast, when supported on alumina, the two metals segregated at 300°C to produce almost pure fcc Cu and Pd phases. Upon further annealing of the mixture on alumina above 600°C, the two metals interdiffused, forming two distinct disordered alloys of compositions 30% and 90% Pd. The annealing atmosphere also plays a major role in the structural evolution of these bimetallic nanoparticles. The nanoparticles annealed in forming gas are larger than the nanoparticles annealed in helium due to reduction of the surface oxides that promotes coalescence and sintering. The nanoscale composition and structure of alloy catalysts affect heterogeneous catalysis. We also studied Pd:Cu nanoparticle mixtures of different compositions. In Pd:Cu of composition ratio 1:1, ordered B2 phase is formed during annealing at 450C. During the ramped annealing from 450°C to 750°C, the B2 phase transforms into two different alloys, one alloy rich in copper and the other rich in Pd. This structural evolution is different from that of Pd-Cu system in bulk. In the 3:1 composition, the B2 phase dominates in the isothermal anneal at 450C but a disordered alloy fcc phase is also formed. On annealing to 750°C, the disordered fcc phase grows at the expense of the B2 phase. These findings have important applications for the thermal activation of Pd-Cu nanocatalysts for EOR reactions.

A Study of Magnesium-Base Metallic Systems and Development of Principles for Creation of Corrosion-Resistant Magnesium Alloys

NASA Astrophysics Data System (ADS)

Mukhina, I. Yu.

2014-11-01

The effect of 26 alloying elements on the corrosion resistance of high-purity magnesium in a 0.5-n solution of sodium chloride and in a humid atmosphere (0.005 n) is studied. The Mg - Li, Mg - Ag, Mg - Zn, Mg - Cu, Mg - Gd, Mg - Al, Mg - Zr, Mg - Mn and other binary systems, which present interest as a base for commercial or perspective castable magnesium alloys, are studied. The characteristics of corrosion resistance of the binary alloys are analyzed in accordance with the group and period of the Mendeleev's periodic law. The roles of the electrochemical and volume factors and of the factor of the valence of the dissolved element are determined.

Molybdenum-titanium phase diagram evaluated from ab initio calculations

NASA Astrophysics Data System (ADS)

Barzilai, Shmuel; Toher, Cormac; Curtarolo, Stefano; Levy, Ohad

2017-07-01

The design of next generation β -type titanium implants requires detailed knowledge of the relevant stable and metastable phases at temperatures where metallurgical heat treatments can be performed. Recently, a standard specification for surgical implant applications was established for Mo-Ti alloys. However, the thermodynamic properties of this binary system are not well known and two conflicting descriptions of the β -phase stability have been presented in the literature. In this study, we use ab initio calculations to investigate the Mo-Ti phase diagram. These calculations predict that the β phase is stable over a wide concentration range, in qualitative agreement with one of the reported phase diagrams. In addition, they predict stoichiometric compounds, stable at temperatures below 300 ∘C , which have not yet been detected by experiments. The resulting solvus, which defines the transition to the β -phase solid solution, therefore occurs at lower temperatures and is more complex than previously anticipated.

Preparation and characterization of mechanically alloyed AB3-type based material LaMg2Ni5Al4 and its solid-gaz hydrogen storage reaction

NASA Astrophysics Data System (ADS)

Jaafar, Hassen; Aymard, Luc; Dachraoui, Walid; Demortière, Arnaud; Abdellaoui, Mohieddine

2018-04-01

We developed in the present paper the synthesis of a new AB3-type compound LaMg2Ni5Al4 by mechanical alloying (MA) process. ​​X-ray diffraction analysis (XRD) was used to determine the structural properties and the phase evolution of the powder mixtures. Two different synthesis pathways have been investigated. The first starting from elemental metals and the second from a mixture of two binary compounds LaNi5 (CaCu5-type structure, P6/mmm space group) and Al(Mg) solid solution (cubic Fm-3 m space group). The results show multiphase alloys which contain LaMg2Ni5Al4 main phase with hexagonal PuNi3-type structure (R-3 m space group). Rietveld analysis shows that using a planetary ball mill, we obtain a good yield of LaMg2Ni5Al4 compound after 5 h of mechanical alloying for both synthesis pathways. TEM analysis confirmed XRD results. SEM-EDX analysis of the final product was in agreement with the nominal chemical formula. A setup of possible solid-gaz hydrogenation reaction will be described so far at the end of this work. Electrochemical results demonstrate evidence on hydrogen absorption in the AB3 material and the discharge capacity was equal to 5.9 H/f.u.

A cellular automaton - finite volume method for the simulation of dendritic and eutectic growth in binary alloys using an adaptive mesh refinement

NASA Astrophysics Data System (ADS)

Dobravec, Tadej; Mavrič, Boštjan; Šarler, Božidar

2017-11-01

A two-dimensional model to simulate the dendritic and eutectic growth in binary alloys is developed. A cellular automaton method is adopted to track the movement of the solid-liquid interface. The diffusion equation is solved in the solid and liquid phases by using an explicit finite volume method. The computational domain is divided into square cells that can be hierarchically refined or coarsened using an adaptive mesh based on the quadtree algorithm. Such a mesh refines the regions of the domain near the solid-liquid interface, where the highest concentration gradients are observed. In the regions where the lowest concentration gradients are observed the cells are coarsened. The originality of the work is in the novel, adaptive approach to the efficient and accurate solution of the posed multiscale problem. The model is verified and assessed by comparison with the analytical results of the Lipton-Glicksman-Kurz model for the steady growth of a dendrite tip and the Jackson-Hunt model for regular eutectic growth. Several examples of typical microstructures are simulated and the features of the method as well as further developments are discussed.

Highly dispersed Pt-Ni nanoparticles on nitrogen-doped carbon nanotubes for application in direct methanol fuel cells.

PubMed

Jiang, Shujuan; Ma, Yanwen; Tao, Haisheng; Jian, Guoqiang; Wang, Xizhang; Fan, Yining; Zhu, Jianmin; Hu, Zheng

2010-06-01

Binary Pt-Ni alloyed nanoparticles supported on nitrogen-doped carbon nanotubes (NCNTs) have been facilely constructed without pre-modification by making use of the active sites in NCNTs due to the N-participation. So-obtained binary Pt-Ni alloyed nanoparticles have been highly dispersed on the outer surface of the support with the size of about 3-4 nm. The electrochemical properties of the catalysts for methanol oxidation have been systematically evaluated. Binary Pt-Ni alloyed composites with molar ratio (Pt:Ni) of 3:2 and 3:1 present enhanced electrocatalytic activities and improved tolerance to CO poisoning as well as the similar stability, in comparison with the commercial Pt/C catalyst and the monometallic Pt/NCNTs catalysts. These results imply that so-constructed nanocomposite catalysts have the potential for applications in direct methanol fuel cells.

Short-Range-Order for fcc-based Binary Alloys Revisited from Microscopic Geometry

NASA Astrophysics Data System (ADS)

Yuge, Koretaka

2018-04-01

Short-range order (SRO) in disordered alloys is typically interpreted as competition between chemical effect of negative (or positive) energy gain by mixing constituent elements and geometric effects comes from difference in effective atomic radius. Although we have a number of theoretical approaches to quantitatively estimate SRO at given temperatures, it is still unclear to systematically understand trends in SRO for binary alloys in terms of geometric character, e.g., effective atomic radius for constituents. Since chemical effect plays significant role on SRO, it has been believed that purely geometric character cannot capture the SRO trends. Despite these considerations, based on the density functional theory (DFT) calculations on fcc-based 28 equiatomic binary alloys, we find that while conventional Goldschmidt or DFT-based atomic radius for constituents have no significant correlation with SRO, atomic radius for specially selected structure, constructed purely from information about underlying lattice, can successfully capture the magnitude of SRO. These facts strongly indicate that purely geometric information of the system plays central role to determine characteristic disordered structure.

Ab initio simulations of molten Ni alloys

NASA Astrophysics Data System (ADS)

Woodward, Christopher; Asta, Mark; Trinkle, Dallas R.; Lill, James; Angioletti-Uberti, Stefano

2010-06-01

Convective instabilities responsible for misoriented grains in directionally solidified turbine airfoils are produced by variations in liquid-metal density with composition and temperature across the solidification zone. Here, fundamental properties of molten Ni-based alloys, required for modeling these instabilities, are calculated using ab initio molecular dynamics simulations. Equations of state are derived from constant number-volume-temperature ensembles at 1830 and 1750 K for elemental, binary (Ni-X, X=Al, W, Re, and Ta) and ternary (Ni-Al-X, X=W, Re, and Ta) Ni alloys. Calculated molar volumes agree to within 0.6%-1.8% of available measurements. Predictions are used to investigate the range of accuracy of a parameterization of molar volumes with composition and temperature based on measurements of binary alloys. Structural analysis reveals a pronounced tendency for icosahedral short-range order for Ni-W and Ni-Re alloys and the calculations provide estimates of diffusion rates and their dependence on compositions and temperature.

Interdiffusion behaviors in doped molybdenum uranium and aluminum or aluminum silicon dispersion fuels: Effects of the microstructure

NASA Astrophysics Data System (ADS)

Allenou, J.; Tougait, O.; Pasturel, M.; Iltis, X.; Charollais, F.; Anselmet, M. C.; Lemoine, P.

2011-09-01

Si addition to Al is considered as a promising route to reduce (U,Mo)-Al interaction kinetics, due to its accumulation in the interaction layer, yielding the formation of silicide phases. The (U,Mo) alloy microstructure, and especially its homogenization state, could play a role on this accumulation process. The addition of a third element in γ(U,Mo) could also influence diffusion mechanisms of Al and Si. These two parameters were studied by means of diffusion couple experiments by joining γU based alloys with Al and (Al,Si) alloy. Chemical elements X added into γ(U,Mo) were thoroughly chosen on the following criteria: (i) the potential solubility of the alloying element into the γ(U,Mo) matrix, (ii) its capability to form the ternary aluminides based on the CeCr 2Al 20 and Ho 6Mo 4Al 43 - types, and (iii) the feasibility to control the microstructure of the alloys. On this basis, a test matrix is defined. It concerns γ(U80,Mo15,X5) alloys (in at.%) with X = Y, Cu, Zr, Ti or Cr. These alloys were homogenized and coupled with Al or (Al,Si) alloy. Results evidenced, first, the importance of the state of homogenization of the γ(U,Mo) binary alloy on interaction processes with (Al,Si) alloy, and the benefit on the diffusion of Si through the interaction layer, as observed on the elementary concentration profiles, when the third element X has some solubility into γ(U,Mo) alloy.

Phase transformations at interfaces: Observations from atomistic modeling

DOE PAGES

Frolov, T.; Asta, M.; Mishin, Y.

2016-10-01

Here, we review the recent progress in theoretical understanding and atomistic computer simulations of phase transformations in materials interfaces, focusing on grain boundaries (GBs) in metallic systems. Recently developed simulation approaches enable the search and structural characterization of GB phases in single-component metals and binary alloys, calculation of thermodynamic properties of individual GB phases, and modeling of the effect of the GB phase transformations on GB kinetics. Atomistic simulations demonstrate that the GB transformations can be induced by varying the temperature, loading the GB with point defects, or varying the amount of solute segregation. The atomic-level understanding obtained from suchmore » simulations can provide input for further development of thermodynamics theories and continuous models of interface phase transformations while simultaneously serving as a testing ground for validation of theories and models. They can also help interpret and guide experimental work in this field.« less

Modeling of the Structure of Disordered Metallic Alloys and Its Transformation Under Thermal Forcing

NASA Astrophysics Data System (ADS)

Cress, Ryan Paul

The morphology of disordered binary metallic alloys is investigated. The structure of disordered binary metallic alloys is modeled as a randomly close packed (RCP) assembly of atoms. It was observed through a 2-D binary hard sphere experiment that RCP structure can be modeled as a mixture of nano-crystallites and glassy matter. We define the degree of crystallinity as the fraction of atoms contained in nano-crystallites in an RCP medium. Nano-crystallites by size in a crystallite size distribution were determined experimentally to define the morphology of the RCP medium. Both the degree of crystallinity and the crystallite size distribution have been found to be determined by the composition of a given binary mixture. A 2-D Monte Carlo simulation was developed in order to replicate the RCP structure observed in the experiment which is then extended to cases of arbitrary composition. Crystallites were assumed to be spherical with isotropic cross sections. The number of atoms in an individual crystallite in 2-D is simply transformed into the number of atoms in 3-D; we then obtain the crystallite size distribution in 3-D. This experiment accounts for the contribution from the repulsive core of the inter-atomic potential. The attractive part of the potential is recovered by constructing spherical nano-crystallites of a given radius from a crystalline specimen of each given alloy. A structural model of a disordered alloy is thus obtained. With the basic structure of the RCP medium defined, the response to heating would be in the form of changes to the crystallite size distribution. This was first investigated in a hard sphere mechanical oven experiment. The experimental setup consists of a 2-D cell which is driven by two independent stepper motors. The motors drive a binary RCP bed of spheres on a slightly tilted plane according to a chaotic algorithmm. The motors are driven at four different speed settings. The RCP medium was analyzed using a sequence of digital images taken of the beds. The bursts of images provide a Gaussian distribution of particle speeds in x and y directions thus giving rise to the notion of "temperature." This temperature scales with the motor speed settings. The measured average degree of crystallinity is found to decrease as the effective temperature was raised suggesting that nano-crystallites dissociate under thermal forcing. The evolution of a specimen's structure is calculated rigorously by means of the law of mass action formalism. A system of thermal dissociation reaction equations is written out for the set of nano-crystallites according to the 3-D crystallite size distribution. The equilibrium treatment is justified because the energy differences between metastable RCP structures fall within kT. Thermal dissociation of one surface atom at a time is assumed because the energy cost in dissociation of a surface atom on a nano-crystallite is significantly less than that of a multi atom cluster. The full set of reaction equations cover all possible dissociation steps, which may amount to several thousand for a disordered alloy specimen. The primary determining factor in each of these dissociation equations is the dissociation potential or the amount of attractive energy needed to remove a surface atom on a nano-crystallite of a given size. The attractive potential between atoms is calculated using a Lennard-Jones potential between a pair of atoms for which quantum chemistry calculations exist in the literature. All interactions impinged on the surface atom by all other atoms in a crystallite are summed. As the nano-crystallites dissociate due to heating, the structure of the alloy changes, and this leads to modifications of alloy's transport properties. The model is found to predict the melting temperature of various disordered binary alloys as well as refractory metals in good agreement with known data. The structure model for disordered binary alloys gives an excellent characterization of the alloy morphology. It therefore provides fruitful avenues for making predictions about how thermophysical properties of disordered binary alloys change as the alloy temperature is raised by heating.

Finite Element Multi-scale Modeling of Chemical Segregation in Steel Solidification Taking into Account the Transport of Equiaxed Grains

NASA Astrophysics Data System (ADS)

Nguyen, Thi-Thuy-My; Gandin, Charles-André; Combeau, Hervé; Založnik, Miha; Bellet, Michel

2018-02-01

The transport of solid crystals in the liquid pool during solidification of large ingots is known to have a significant effect on their final grain structure and macrosegregation. Numerical modeling of the associated physics is challenging since complex and strong interactions between heat and mass transfer at the microscopic and macroscopic scales must be taken into account. The paper presents a finite element multi-scale solidification model coupling nucleation, growth, and solute diffusion at the microscopic scale, represented by a single unique grain, while also including transport of the liquid and solid phases at the macroscopic scale of the ingots. The numerical resolution is based on a splitting method which sequentially describes the evolution and interaction of quantities into a transport and a growth stage. This splitting method reduces the non-linear complexity of the set of equations and is, for the first time, implemented using the finite element method. This is possible due to the introduction of an artificial diffusion in all conservation equations solved by the finite element method. Simulations with and without grain transport are compared to demonstrate the impact of solid phase transport on the solidification process as well as the formation of macrosegregation in a binary alloy (Sn-5 wt pct Pb). The model is also applied to the solidification of the binary alloy Fe-0.36 wt pct C in a domain representative of a 3.3-ton steel ingot.

Numerical model for dendritic solidification of binary alloys

NASA Technical Reports Server (NTRS)

Felicelli, S. D.; Heinrich, J. C.; Poirier, D. R.

1993-01-01

A finite element model capable of simulating solidification of binary alloys and the formation of freckles is presented. It uses a single system of equations to deal with the all-liquid region, the dendritic region, and the all-solid region. The dendritic region is treated as an anisotropic porous medium. The algorithm uses the bilinear isoparametric element, with a penalty function approximation and a Petrov-Galerkin formulation. Numerical simulations are shown in which an NH4Cl-H2O mixture and a Pb-Sn alloy melt are cooled. The solidification process is followed in time. Instabilities in the process can be clearly observed and the final compositions obtained.

Surface Segregation in Multicomponent Systems: Modeling of Surface Alloys and Alloy Surfaces

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Ferrante, John; Noebe, Ronald D.; Good, Brian; Honecy, Frank S.; Abel, Phillip

1999-01-01

The study of surface segregation, although of great technological importance, has been largely restricted to experimental work due to limitations associated with theoretical methods. However, recent improvements in both first-particle and semi-empirical methods are opening, the doors to an array of new possibilities for surface scientists. We apply one of these techniques, the Bozzolo, Ferrante and Smith (BFS) method for alloys, which is particularly suitable for complex systems, to several aspects of the computational modeling of surfaces and segregation, including alloy surface segregation, structure and composition of alloy surfaces, and the formation of surface alloys. We conclude with the study of complex NiAl-based binary, ternary and quaternary thin films (with Ti, Cr and Cu additions to NiAl). Differences and similarities between bulk and surface compositions are discussed, illustrated by the results of Monte Carlo simulations. For some binary and ternary cases, the theoretical predictions are compared to experimental results, highlighting the accuracy and value of this developing theoretical tool.

Determination of parameters of a new method for predicting alloy properties

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Ferrante, John

1992-01-01

Recently, a semiempirical method for alloys based on equivalent crystal theory was introduced. The method successfully predicts the concentration dependence of the heat of formation and lattice parameter of binary alloys. A study of the parameters of the method is presented, along with new results for (gamma)Fe-Pd and (gamma)Fe-Ni alloys.

Intrinsic properties and strengthening mechanism of monocrystalline Ni-containing ternary concentrated solid solutions

DOE PAGES

Jin, K.; Gao, Y. F.; Bei, H.

2017-04-07

Ternary single-phase concentrated solid solution alloys (SP-CSAs), so-called "medium entropy alloys", not only possess notable mechanical and physical properties but also form a model system linking the relatively simple binary alloys to the complex high entropy alloys. Our knowledge of their intrinsic properties is vital to understand the material behavior and to prompt future applications. To this end, three model alloys NiCoFe, NiCoCr, and NiFe-20Cr have been selected and grown as single crystals. We measured their elastic constants using an ultrasonic method, and several key materials properties, such as shear modulus, bulk modulus, elastic anisotropy, and Debye temperatures have beenmore » derived. Furthermore, nanoindentation tests have been performed on these three alloys together with Ni, NiCo and NiFe on their (100) surface, to investigate the strengthening mechanisms. NiCoCr has the highest hardness, NiFe, NiCoFe and NiFe-20Cr share a similar hardness that is apparently lower than NiCoCr; NiCo has the lowest hardness in the alloys, which is similar to elemental Ni. The Labusch-type solid solution model has been applied to interpret the nanoindentation data, with two approaches used to calculate the lattice mismatch. Finally, by adopting an interatomic spacing matrix method, the Labusch model can reasonably predict the hardening effects for the whole set of materials.« less

From chemistry to mechanics: bulk modulus evolution of Li-Si and Li-Sn alloys via the metallic electronegativity scale.

PubMed

Li, Keyan; Xie, Hui; Liu, Jun; Ma, Zengsheng; Zhou, Yichun; Xue, Dongfeng

2013-10-28

Toward engineering high performance anode alloys for Li-ion batteries, we proposed a useful method to quantitatively estimate the bulk modulus of binary alloys in terms of metallic electronegativity (EN), alloy composition and formula volume. On the basis of our proposed potential viewpoint, EN as a fundamental chemistry concept can be extended to be an important physical parameter to characterize the mechanical performance of Li-Si and Li-Sn alloys as anode materials for Li-ion batteries. The bulk modulus of binary alloys is linearly proportional to the combination of average metallic EN and atomic density of alloys. We calculated the bulk moduli of Li-Si and Li-Sn alloys with different Li concentrations, which can agree well with the reported data. The bulk modulus of Li-Si and Li-Sn alloys decreases with increasing Li concentration, leading to the elastic softening of the alloys, which is essentially caused by the decreased strength of constituent chemical bonds in alloys from the viewpoint of EN. This work provides a deep understanding of mechanical failure of Si and Sn anodes for Li-ion batteries, and permits the prediction of the composition dependent bulk modulus of various lithiated alloys on the basis of chemical formula, metallic EN and cell volume (or alloy density), with no structural details required.

Fundamental Understanding of the Intrinsic Ductility in Nickel-Base L12 Type Alloys.

DTIC Science & Technology

1987-05-12

COSATI CO0ES I L SUBJE CT TIE RMS (Conue an eo e eee it necessary and identify by blb .un bPe) . ". Eo GROUP SUB. G. Nickel Aluminide , Single...Ni3Al alloys, three series of alloys were formulated and produced as singl’e--crtals. The alloying additions selected include tantalum, tin and titanium ...been completed-for a tantalum and a titanium -containing alloy. Relative .. to the binary alloy, the alloying additions were found to significantly

Dealloying, Microstructure and the Corrosion/Protection of Cast Magnesium Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sieradzki, Karl; Aiello, Ashlee; McCue, Ian

The purpose of this project was to develop a greater understanding of micro-galvanic corrosion effects in cast magnesium alloys using both experimental and computational methods. Experimental accomplishments have been made in the following areas of interest: characterization, aqueous free-corrosion, atmospheric corrosion, ionic liquid dissolution, rate kinetics of oxide dissolution, and coating investigation. Commercial alloys (AZ91D, AM60, and AZ31B), binary-phase alloys (αMg-2at.%Al, αMg-5at.%Al, and Mg-8at.%Al), and component phases (Mg, Al, β-Mg, β-1%Zn, MnAl3) were obtained and characterized using energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Full immersion in aqueous chloride was used to characterize the corrosionmore » behavior of alloys. Rotating disc electrodes (RDEs) were used to observe accelerated long-term corrosion behavior. Al surface redistribution for freely corroded samples was analyzed using SEM, EDS, and lithium underpotential deposition (Li UPD). Atmospheric corrosion was observed using contact angle evolution, overnight pH monitoring, and surface pH evolution studies. Ionic liquid corrosion characterization was performed using linear sweep voltammetry and potentiostatic dissolution in 150° choline chloride-urea (cc-urea). Two surface coatings were investigated: (1) Li-carbonate and (2) cc-urea. Li-carbonate coatings were characterized using X-ray photoelectron spectroscopy (XPS), SEM, and aqueous free corrosion potential monitoring. Hydrophobic cc-urea coatings were characterized using contact angle measurements and electrochemical impedance spectroscopy. Oxide dissolution rate kinetics were studied using inductively coupled plasma mass spectroscopy (ICP-MS). Computational accomplishments have been made through the development of Kinetic Monte Carlo (KMC) simulations which model time- and composition-dependent effects on the microstructure due to spatial redistribution of alloying elements during corrosion.« less

Auger electron spectroscopy study of surface segregation in the binary alloys copper-1 atomic percent indium, copper-2 atomic percent tin, and iron-6.55 atomic percent silicon

NASA Technical Reports Server (NTRS)

Ferrante, J.

1973-01-01

Auger electron spectroscopy was used to examine surface segregation in the binary alloys copper-1 at. % indium, copper-2 at. % tin and iron-6.55 at. % silicon. The copper-tin and copper-indium alloys were single crystals oriented with the /111/ direction normal to the surface. An iron-6.5 at. % silicon alloy was studied (a single crystal oriented in the /100/ direction for study of a (100) surface). It was found that surface segregation occurred following sputtering in all cases. Only the iron-silicon single crystal alloy exhibited equilibrium segregation (i.e., reversibility of surface concentration with temperature) for which at present we have no explanation. McLean's analysis for equilibrium segregation at grain boundaries did not apply to the present results, despite the successful application to dilute copper-aluminum alloys. The relation of solute atomic size and solubility to surface segregation is discussed. Estimates of the depth of segregation in the copper-tin alloy indicate that it is of the order of a monolayer surface film.

Studies of Lubricating Materials in Vacuum

NASA Technical Reports Server (NTRS)

Buckley, D. H.; Johnson, R. L.; Swikert, M. A.

1964-01-01

Lubricating materials for use in a vacuum environment have been the subject of a series of experimental investigations. Evaporation properties were evaluated for solid polymeric compositions. Friction and wear studies explored the behavior during sliding contact for series of polymeric compositions, binary alloys containing soft film-forming phases, complex alloys with film-forming materials, and a burnished MoS2 film. Friction and wear experiments were conducted at 10(exp-9)mm Hg with a 3/16-inch-radius-hemisphere rider specimen sliding on the flat surface of a rotating 2-1/2-inch-diameter disk specimen with materials that had low rates of evaporation. The influence of fillers in polytetrafluoroethylene (PTFE) on decomposition during vacuum friction studies was determined with a mass spectrometer. A real advantage in reducing decomposition and improving friction wear properties is gained by adding fillers (e.g., copper) that improve thermal conductivity through the composite materials. A polyimide and an epoxy-MoS2 composition material were found to have better friction and wear properties than PTFE compositions. A series of alloys (cast binary as well as more complex alloys) that contained microinclusions of potential film-forming material was studied. These materials replaced the normal surface oxides as they were worn away on sliding contact. Iron sulfide, nickel oxide, and tin are typical film-forming materials employed and were demonstrated to be effective in inhibiting surface welding and reducing friction. A burnished MoS2 film applied to type 440-C stainless steel in argon with a rotating soft wire brush had good endurance properties but somewhat higher friction than commercially available bonded films. An oil film applied to the burnished MoS2 markedly reduced its endurance life.

Comparative study on the structure and electrochemical hydriding properties of MgTi, Mg 0.5Ni 0.5Ti and MgTi 0.5Ni 0.5 alloys prepared by high energy ball milling

NASA Astrophysics Data System (ADS)

Rousselot, Steeve; Guay, Daniel; Roué, Lionel

MgTi, Mg 0.5Ni 0.5Ti and MgTi 0.5Ni 0.5 alloys doped with 10 wt.% Pd were prepared by high energy ball milling and evaluated as hydrogen storage electrodes for Ni-MH batteries. X-ray diffraction analyses indicated that the Mg 0.5Ni 0.5Ti and MgTi 0.5Ni 0.5 alloys could be monophased or composed of a nanoscale mixture of MgTi + NiTi and MgTi + MgNi phases, respectively. Their hydrogen storage characteristics were investigated electrochemically in KOH electrolyte. No activation step was observed during the cycling of the Mg-Ti-Ni electrodes in contrast to that observed with the MgTi electrode. The highest hydrogen discharge capacity was obtained with the MgTi 0.5Ni 0.5 electrode (536 mAh g -1) compared to 401 and 475 mAh g -1 for the Mg 0.5Ni 0.5Ti and MgTi electrodes, respectively. The ternary Mg-Ti-Ni alloys showed a better cycle life with an average capacity decay rate per cycle lower than 1.5% compared to ∼7% for the binary MgTi electrode. The Mg-Ni-Ti electrodes also displayed a much higher discharge rate capability than the binary MgTi electrode, especially with the Mg 0.5Ni 0.5Ti electrode. The origin of this was established on the basis of the anodic polarization curves, where a substantial decrease of the concentration overpotential (reflecting a higher hydrogen diffusivity) was observed for the Mg 0.5Ni 0.5Ti electrode.

Rate dependent strengths of some solder joints

NASA Astrophysics Data System (ADS)

Williamson, D. M.; Field, J. E.; Palmer, S. J. P.; Siviour, C. R.

2007-08-01

The shear strengths of three lead-free solder joints have been measured over the range of loading rates 10-3 to ~105 mm min-1. Binary (SnAg), ternary (SnAgCu) and quaternary (Castin: SnAgCuSb) alloys have been compared to a conventional binary SnPb solder alloy. Results show that at loading rates from 10-3 to 102 mm min-1, all four materials exhibit a linear relationship between the shear strength and the loading rate when the data are plotted on a log-log plot. At the highest loading rate of 105 mm min-1, the strengths of the binary alloys were in agreement with extrapolations made from the lower loading rate data. In contrast, the strengths of the higher order alloys were found to be significantly lower than those predicted by extrapolation. This is explained by a change in failure mechanism on the part of the higher order alloys. Similar behaviour was found in measurements of the tensile strengths of solder joints using a novel high-rate loading tensile test. Optical and electron microscopy were used to examine the microstructures of interest in conjunction with energy dispersive x-ray analysis for elemental identification. The effect of artificial aging and reflow of the solder joints is also reported.

Electronic structure of alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ehrenreich, H.; Schwartz, L.M.

1976-01-01

The description of electronic properties of binary substitutional alloys within the single particle approximation is reviewed. Emphasis is placed on a didactic exposition of the equilibrium properties of the transport and magnetic properties of such alloys. Topics covered include: multiple scattering theory; the single band alloy; formal extensions of the theory; the alloy potential; realistic model state densities; the s-d model; and the muffin tin model. 43 figures, 3 tables, 151 references. (GHT)

Thermal activation mechanisms and Labusch-type strengthening analysis for a family of high-entropy and equiatomic solid-solution alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Zhenggang; Gao, Yanfei; Bei, Hongbin

To understand the underlying strengthening mechanisms, thermal activation processes are investigated from stress-strain measurements with varying temperatures and strain rates for a family of equiatomic quinary, quaternary, ternary, and binary, face-center-cubic-structured, single phase solid-solution alloys, which are all subsystems of the FeNiCoCrMn high-entropy alloy. Our analysis suggests that the Labusch-type solution strengthening mechanism, rather than the lattice friction (or lattice resistance), governs the deformation behavior in equiatomic alloys. First, upon excluding the Hall-Petch effects, the activation volumes for these alloys are found to range from 10 to 1000 times the cubic power of Burgers vector, which are much larger thanmore » that required for kink pairs (i.e., the thermal activation process for the lattice resistance mechanism in body-center-cubic-structured metals). Second, the Labusch-type analysis for an N-element alloy is conducted by treating M-elements (M < N) as an effective medium and summing the strengthening contributions from the rest of N-M elements as individual solute species. For all equiatomic alloys investigated, a qualitative agreement exists between the measured strengthening effect and the Labusch strengthening factor from arbitrary M to N elements based on the lattice and modulus mismatches. Furthermore, the Labusch strengthening factor provides a practical critique to understand and design such compositionally complex but structurally simple alloys.« less

Thermal activation mechanisms and Labusch-type strengthening analysis for a family of high-entropy and equiatomic solid-solution alloys

DOE PAGES

Wu, Zhenggang; Gao, Yanfei; Bei, Hongbin

2016-11-01

To understand the underlying strengthening mechanisms, thermal activation processes are investigated from stress-strain measurements with varying temperatures and strain rates for a family of equiatomic quinary, quaternary, ternary, and binary, face-center-cubic-structured, single phase solid-solution alloys, which are all subsystems of the FeNiCoCrMn high-entropy alloy. Our analysis suggests that the Labusch-type solution strengthening mechanism, rather than the lattice friction (or lattice resistance), governs the deformation behavior in equiatomic alloys. First, upon excluding the Hall-Petch effects, the activation volumes for these alloys are found to range from 10 to 1000 times the cubic power of Burgers vector, which are much larger thanmore » that required for kink pairs (i.e., the thermal activation process for the lattice resistance mechanism in body-center-cubic-structured metals). Second, the Labusch-type analysis for an N-element alloy is conducted by treating M-elements (M < N) as an effective medium and summing the strengthening contributions from the rest of N-M elements as individual solute species. For all equiatomic alloys investigated, a qualitative agreement exists between the measured strengthening effect and the Labusch strengthening factor from arbitrary M to N elements based on the lattice and modulus mismatches. Furthermore, the Labusch strengthening factor provides a practical critique to understand and design such compositionally complex but structurally simple alloys.« less

Research and Development on Titanium Alloys

DTIC Science & Technology

1949-10-31

EVALUATION OF EPERIMENTAL TITANIUM-BASE ALLOYS• 65 Binary Alloys of Titanium . . . . .. 65 Titanium-Silver Alloys. . . . . ..... ... 68 Mechanical Properties...using a technique in melting designed to give more uniform distribution of the alloying additions. NMATTWLL MOMORIAL INSTITUTE 4...tc Dr. Derge for analysis. BATTELLE MEMORIAL INSTITUTE -107- 2TABLE 28. OXYGEN STANDARDS FOR ANALYSIS Wt fSapl Pein Cen Designation Sample lielting, 1

Tunable synthesis and acetylation of dendrimer-entrapped or dendrimer-stabilized gold-silver alloy nanoparticles.

PubMed

Liu, Hui; Shen, Mingwu; Zhao, Jinglong; Guo, Rui; Cao, Xueyan; Zhang, Guixiang; Shi, Xiangyang

2012-06-01

In this study, amine-terminated generation 5 poly(amidoamine) dendrimers were used as templates or stabilizers to synthesize dendrimer-entrapped or dendrimer-stabilized Au-Ag alloy nanoparticles (NPs) with different gold atom/silver atom/dendrimer molar ratios with the assistance of sodium borohydride reduction chemistry. Following a one-step acetylation reaction to transform the dendrimer terminal amines to acetyl groups, a series of dendrimer-entrapped or dendrimer-stabilized Au-Ag alloy NPs with terminal acetyl groups were formed. The formed Au-Ag alloy NPs before and after acetylation reaction were characterized using different techniques. We showed that the optical property and the size of the bimetallic NPs were greatly affected by the metal composition. At the constant total metal atom/dendrimer molar ratio, the size of the alloy NPs decreased with the gold content. The formed Au-Ag alloy NPs were stable at different pH (pH 5-8) and temperature (4-50°C) conditions. X-ray absorption coefficient measurements showed that the attenuation of the binary NPs was dependent on both the gold content and the surface modification. With the increase of gold content in the binary NPs, their X-ray attenuation intensity was significantly enhanced. At a given metal composition, the X-ray attenuation intensity of the binary NPs was enhanced after acetylation. Cytotoxicity assays showed that after acetylation, the cytocompatibility of Au-Ag alloy NPs was significantly improved. With the controllable particle size and optical property, metal composition-dependent X-ray attenuation characteristics, and improved cytocompatibility after acetylation, these dendrimer-entrapped or dendrimer-stabilized Au-Ag alloy NPs should have a promising potential for CT imaging and other biomedical applications. Copyright © 2012 Elsevier B.V. All rights reserved.

Correction factors for on-line microprobe analysis of multielement alloy systems

NASA Technical Reports Server (NTRS)

Unnam, J.; Tenney, D. R.; Brewer, W. D.

1977-01-01

An on-line correction technique was developed for the conversion of electron probe X-ray intensities into concentrations of emitting elements. This technique consisted of off-line calculation and representation of binary interaction data which were read into an on-line minicomputer to calculate variable correction coefficients. These coefficients were used to correct the X-ray data without significantly increasing computer core requirements. The binary interaction data were obtained by running Colby's MAGIC 4 program in the reverse mode. The data for each binary interaction were represented by polynomial coefficients obtained by least-squares fitting a third-order polynomial. Polynomial coefficients were generated for most of the common binary interactions at different accelerating potentials and are included. Results are presented for the analyses of several alloy standards to demonstrate the applicability of this correction procedure.

Estimation of the Viscosities of Liquid Sn-Based Binary Lead-Free Solder Alloys

NASA Astrophysics Data System (ADS)

Wu, Min; Li, Jinquan

2018-01-01

The viscosity of a binary Sn-based lead-free solder alloy was calculated by combining the predicted model with the Miedema model. The viscosity factor was proposed and the relationship between the viscosity and surface tension was analyzed as well. The investigation result shows that the viscosity of Sn-based lead-free solders predicted from the predicted model shows excellent agreement with the reported values. The viscosity factor is determined by three physical parameters: atomic volume, electronic density, and electro-negativity. In addition, the apparent correlation between the surface tension and viscosity of the binary Sn-based Pb-free solder was obtained based on the predicted model.

Phase-field simulation of weld solidification microstructure in an Al Cu alloy

NASA Astrophysics Data System (ADS)

Farzadi, A.; Do-Quang, M.; Serajzadeh, S.; Kokabi, A. H.; Amberg, G.

2008-09-01

Since the mechanical properties and the integrity of the weld metal depend on the solidification behaviour and the resulting microstructural characteristics, understanding weld pool solidification is of importance to engineers and scientists. Thermal and fluid flow conditions affect the weld pool geometry and solidification parameters. During solidification of the weld pool, a columnar grain structure develops in the weld metal. Prediction of the formation of the microstructure during welding may be an important and supporting factor for technology optimization. Nowadays, increasing computing power allows direct simulations of the dendritic and cell morphology of columnar grains in the molten zone for specific temperature conditions. In this study, the solidification microstructures of the weld pool at different locations along the fusion boundary are simulated during gas tungsten arc welding of Al-3wt%Cu alloy using the phase-field model for the directional solidification of dilute binary alloys. A macroscopic heat transfer and fluid flow model was developed to assess the solidification parameters, notably the temperature gradient and solidification growth rate. The effect of the welding speed is investigated. Computer simulations of the solidification conditions and the formation of a cellular morphology during the directional solidification in gas tungsten arc welding are described. Moreover, the simulation results are compared with existing theoretical models and experimental findings.

Binary Colloidal Alloy Test-5: Three-Dimensional Melt

NASA Technical Reports Server (NTRS)

Yodh, Arjun G.

2008-01-01

Binary Colloidal Alloy Test - 5: Three-Dimensional Melt (BCAT-5-3DMelt) photographs initially randomized colloidal samples in microgravity to determine their resulting structure over time. BCAT-5-3D-Melt will allow the scientists to capture the kinetics (evolution) of their samples, as well as the final equilibrium state of each sample. BCAT-5-3D-Melt will look at the mechanisms of melting using three-dimensional temperature sensitive colloidal crystals. Results will help scientists develop fundamental physics concepts previously shadowed by the effects of gravity.

Self-assembly of metal nanostructures on binary alloy surfaces

PubMed Central

Duguet, T.; Han, Yong; Yuen, Chad; Jing, Dapeng; Ünal, Barış; Evans, J. W.; Thiel, P. A.

2011-01-01

Deposition of metals on binary alloy surfaces offers new possibilities for guiding the formation of functional metal nanostructures. This idea is explored with scanning tunneling microscopy studies and atomistic-level analysis and modeling of nonequilibrium island formation. For Au/NiAl(110), complex monolayer structures are found and compared with the simple fcc(110) bilayer structure recently observed for Ag/NiAl(110). We also consider a more complex codeposition system, (Ni + Al)/NiAl(110), which offers the opportunity for fundamental studies of self-growth of alloys including deviations for equilibrium ordering. A general multisite lattice-gas model framework enables analysis of structure selection and morphological evolution in these systems. PMID:21097706

The surface alloying effect of silicon in a binary NiTi-base alloy on the corrosion resistance and biocompatibility of the material

NASA Astrophysics Data System (ADS)

Psakhie, S. G.; Lotkov, A. I.; Meisner, L. L.; Meisner, S. N.; Matveeva, V. A.

2013-02-01

The corrosion resistance behavior and cytotoxicity of binary NiTi-base alloy specimens subjected to surface modification by silicon ion beams and the proliferative ability of mesenchymal stem cells of rat marrow on an ion-implanted surface of the alloy have been studied. The silicon ion beam processing of specimen surfaces is shown to bring about a nearly two-fold improvement in the corrosion resistance of the material to attack by aqueous solutions of NaCl (artificial body fluid) and human plasma and a drastic decrease in the nickel concentration after immersion of the specimens into the solutions for ˜3400 and ˜6000 h, respectively (for the artificial plasma solution, a nearly 20-fold decrease in the Ni concentration is observed.)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reeve, Kathlene N.; Holaday, John R.; Choquette, Stephanie M.

New electronics applications demanding enhanced performance and higher operating temperatures have led to continued research in the field of Pb-free solder designs and interconnect solutions. In this paper, recent advances in the microstructural design of Pb-free solders and interconnect systems were discussed by highlighting two topics: increasing β-Sn nucleation in Sn-based solders, and isothermally solidified interconnects using transient liquid phases. Issues in β-Sn nucleation in Sn-based solders were summarized in the context of Swenson’s 2007 review of the topic. Recent advancements in the areas of alloy composition manipulation, nucleating heterogeneities, and rapid solidification were discussed, and a proposal based onmore » a multi-faceted solidification approach involving the promotion of constitutional undercooling and nucleating heterogeneities was outlined for future research. The second half of the paper analyzed two different approaches to liquid phase diffusion bonding as a replacement for high-Pb solders, one based on the application of the pseudo-binary Cu-Ni-Sn ternary system, and the other on a proposed thermodynamic framework for identifying potential ternary alloys for liquid phase diffusion bonding. Furthermore, all of the concepts reviewed relied upon the fundamentals of thermodynamics, kinetics, and solidification, to which Jack Smith substantially contributed during his scientific career.« less

Biomimetic superhydrophobic surface of high adhesion fabricated with micronano binary structure on aluminum alloy.

PubMed

Liu, Yan; Liu, Jindan; Li, Shuyi; Liu, Jiaan; Han, Zhiwu; Ren, Luquan

2013-09-25

Triggered by the microstructure characteristics of the surfaces of typical plant leaves such as the petals of red roses, a biomimetic superhydrophobic surface with high adhesion is successfully fabricated on aluminum alloy. The essential procedure is that samples were processed by a laser, then immersed and etched in nitric acid and copper nitrate, and finally modified by DTS (CH3(CH2)11Si(OCH3)3). The obtained surfaces exhibit a binary structure consisting of microscale crater-like pits and nanoscale reticula. The superhydrophobicity can be simultaneously affected by the micronano binary structure and chemical composition of the surface. The contact angle of the superhydrophobic surface reaches up to 158.8 ± 2°. Especially, the surface with micronano binary structure is revealed to be an excellent adhesive property with petal-effect. Moreover, the superhydrophobic surfaces show excellent stability in aqueous solution with a large pH range and after being exposed long-term in air. In this way, the multifunctional biomimetic structural surface of the aluminum alloy is fabricated. Furthermore, the preparation technology in this article provides a new route for other metal materials.

Application of computational thermodynamics in the study of magnsium alloys and bulk metallic glasses

NASA Astrophysics Data System (ADS)

Cao, Hongbo

In this thesis, the application of the computational thermodynamics has been explored on two subjects, the study of magnesium alloys (Chapter 1-5) and bulk metallic glasses (BMGs) (Chapter 6-9). For the former case, a strategy of experiments coupled with the CALPHAD approach was employed to establish a thermodynamic description of the quaternary system Mg-Al-Ca-Sr focusing on the Mg-rich phase equilibria. Multicomponent Mg-rich alloys based on the MgAl-Ca-Sr system are one of the most promising candidates for the high temperature applications in the transportation industry. The Mg-Al-Ca-Sr quaternary consists of four ternaries and six binaries. Thermodynamic descriptions of all constituent binaries are available in the literature. Thermodynamic descriptions of the two key ternaries, Mg-Al-Sr and Mg-Al-Ca, were obtained by an efficient and reliable methodology, combining computational thermodynamics with key experiments. The obtained thermodynamic descriptions were validated by performing extensive comparisons between the calculations and experimental information. Thermodynamic descriptions of the other two ternaries, MgCa-Sr and Al-Ca-Sr, were obtained by extrapolation. For the later case, a computational thermodynamic strategy was formulated to obtain a minor but optimum amount of additional element into a base alloy to improve its glass forming ability (GFA). This was done through thermodynamically calculating the maximum liquidus depressions caused by various alloying addition (or replacement) schemes. The success of this approach has been examined in two multicomponent systems, Zr-based Zr-Cu-Ni-Al-Ti and Cu-rich Cu-Zr-Ti-Y. For both cases, experimental results showed conclusively that the GFA increases more than 100% from the base alloy to the one with minor but optimal elemental addition. Furthermore, a thermodynamic computational approach was employed to identify the compositions of Zr-Ti-Ni-Cu-Al alloys exhibiting low-lying liquidus surfaces, which tend to favor the BMG formation. Guided by these calculations, several series of new Zr-based alloys with excellent GFA were synthesized. The approach using the thermodynamically calculated liquidus temperatures was proved to be robust in locating BMGs and can be considered as a universal method to predict novel BMGs not only of scientific interest but also potential technological applications.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Structural Feature and Solute Trapping of Rapidly Grown Ni3Sn Intermetallic Compound

NASA Astrophysics Data System (ADS)

Qin, Hai-Yan; Wang, Wei-Li; Wei, Bing-Bo

2009-11-01

The rapid dendritic growth of primary Ni3Sn phase in undercooled Ni-30.9%Sn-5%Ge alloy is investigated by using the glass fluxing technique. The dendritic growth velocity of Ni3Sn compound is measured as a function of undercooling, and a velocity of 2.47 m/s is achieved at the maximum undercooling of 251 K (0.17TL). The addition of the Ge element reduces its growth velocity as compared with the binary Ni75Sn25 alloy. During rapid solidification, the Ni3Sn compound behaves like a normal solid solution and it displays a morphological transition of “coarse dendrite-equiaxed grain-vermicular structure" with the increase of undercooling. Significant solute trapping of Ge atoms occurs in the whole undercooling range.

Development of rapidly quenched nickel-based non-boron filler metals for brazing corrosion resistant steels

NASA Astrophysics Data System (ADS)

Ivannikov, A.; Kalin, B.; Suchkov, A.; Penyaz, M.; Yurlova, M.

2016-04-01

Corrosion-resistant steels are stably applied in modern rocket and nuclear technology. Creating of permanent joints of these steels is a difficult task that can be solved by means of welding or brazing. Recently, the use rapidly quenched boron-containing filler metals is perspective. However, the use of such alloys leads to the formation of brittle borides in brazing zone, which degrades the corrosion resistance and mechanical properties of the compounds. Therefore, the development of non-boron alloys for brazing stainless steels is important task. The study of binary systems Ni-Be and Ni-Si revealed the perspective of replacing boron in Ni-based filler metals by beryllium, so there was the objective of studying of phase equilibrium in the system Ni-Be-Si. The alloys of the Ni-Si-Be with different contents of Si and Be are considered in this paper. The presence of two low-melting components is revealed during of their studying by methods of metallography analysis and DTA. Microhardness is measured and X-ray diffraction analysis is conducted for a number of alloys of Ni-Si-Be. The compositions are developed on the basis of these data. Rapidly quenched brazing alloys can be prepared from these compositions, and they are suitable for high temperature brazing of steels.

Correlation between crystallographic anisotropy and dendritic orientation selection of binary magnesium alloys.

PubMed

Du, Jinglian; Guo, Zhipeng; Zhang, Ang; Yang, Manhong; Li, Mei; Xiong, Shoumei

2017-10-19

Both synchrotron X-ray tomography and EBSD characterization revealed that the preferred growth directions of magnesium alloy dendrite change as the type and amount of solute elements. Such growth behavior was further investigated by evaluating the orientation-dependent surface energy and the subsequent crystallographic anisotropy via ab-initio calculations based on density functional theory and hcp lattice structure. It was found that for most binary magnesium alloys, the preferred growth direction of the α-Mg dendrite in the basal plane is always [Formula: see text], and independent on either the type or concentration of the additional elements. In non-basal planes, however, the preferred growth direction is highly dependent on the solute concentration. In particular, for Mg-Al alloys, this direction changes from [Formula: see text] to [Formula: see text] as the Al-concentration increased, and for Mg-Zn alloys, this direction changes from [Formula: see text] to [Formula: see text] or [Formula: see text] as the Zn-content varied. Our results provide a better understanding on the dendritic orientation selection and morphology transition of magnesium alloys at the atomic level.

On the transformation behaviour, mechanical properties and biocompatibility of two niti-based shape memory alloys: NiTi42 and NiTi42Cu7.

PubMed

Es-Souni, M; Es-Souni, M; Brandies, H F

2001-08-01

The transformation behaviour, mechanical properties and cytotoxicity of a binary NiTi42 and a ternary NiTi42Cu7 alloy have been investigated. The transformation temperatures were determined via differential scanning calorimetry, the mechanical properties have been investigated in 3-point bending tests in the temperature range between 6 and 60 degrees C. The cytotoxicity tests were performed on both alloys in cultured epithelial cells from human gingiva. The cytotoxicity investigations included both MTT tests and morphological observations. It is shown that although the ternary alloy is characterised by a narrower hysteresis and superior mechanical properties, including fatigue resistance, its cytotoxicity is higher than that of the binary alloy. This is thought to arise from the release of copper ions in the medium, which upon atomic absorption spectroscopy measurements amount to approximately 2.8 microg cm(-2) for an incubation period of 7 days.

Synthesis and Mechanical Characterization of Binary and Ternary Intermetallic Alloys Based on Fe-Ti-Al by Resonant Ultrasound Vibrational Methods.

PubMed

Chanbi, Daoud; Ogam, Erick; Amara, Sif Eddine; Fellah, Z E A

2018-05-07

Precise but simple experimental and inverse methods allowing the recovery of mechanical material parameters are necessary for the exploration of materials with novel crystallographic structures and elastic properties, particularly for new materials and those existing only in theory. The alloys studied herein are of new atomic compositions. This paper reports an experimental study involving the synthesis and development of methods for the determination of the elastic properties of binary (Fe-Al, Fe-Ti and Ti-Al) and ternary (Fe-Ti-Al) intermetallic alloys with different concentrations of their individual constituents. The alloys studied were synthesized from high purity metals using an arc furnace with argon flow to ensure their uniformity and homogeneity. Precise but simple methods for the recovery of the elastic constants of the isotropic metals from resonant ultrasound vibration data were developed. These methods allowed the fine analysis of the relationships between the atomic concentration of a given constituent and the Young’s modulus or alloy density.

Fabrication of (Ba,K)Fe2As2 tapes by ex situ PIT process using Ag-Sn alloy single sheath

NASA Astrophysics Data System (ADS)

Togano, K.; Gao, Z.; Matsumoto, A.; Kikuchi, A.; Kumakura, H.

2017-01-01

Instead of ordinal pure Ag, Ag-based Sn binary alloys (up to 7.5 at%Sn) with higher mechanical strength are used for the sheath material of ex situ powder-in-tube (PIT)-processed (Ba,K)Fe2As2(Ba-122) tapes. We found that the use of the Ag-Sn alloy enhances the densification and texturing of the Ba-122 core, resulting in higher transport, J c. Moreover, the optimum heat treatment temperature for a high J c can be lowered by around 100 °C due to the higher packing density of the Ba-122 core prior to the final heat treatment. We also found that the smoothness of the interface between the sheath and Ba-122 core is significantly improved by using the Ag-Sn binary alloy sheaths. These results show that the Ag-Sn alloy is promising as a sheath material in PIT-processed Ba-122 superconducting wires.

Synthesis and Mechanical Characterization of Binary and Ternary Intermetallic Alloys Based on Fe-Ti-Al by Resonant Ultrasound Vibrational Methods

PubMed Central

Chanbi, Daoud; Amara, Sif Eddine; Fellah, Z. E. A.

2018-01-01

Precise but simple experimental and inverse methods allowing the recovery of mechanical material parameters are necessary for the exploration of materials with novel crystallographic structures and elastic properties, particularly for new materials and those existing only in theory. The alloys studied herein are of new atomic compositions. This paper reports an experimental study involving the synthesis and development of methods for the determination of the elastic properties of binary (Fe-Al, Fe-Ti and Ti-Al) and ternary (Fe-Ti-Al) intermetallic alloys with different concentrations of their individual constituents. The alloys studied were synthesized from high purity metals using an arc furnace with argon flow to ensure their uniformity and homogeneity. Precise but simple methods for the recovery of the elastic constants of the isotropic metals from resonant ultrasound vibration data were developed. These methods allowed the fine analysis of the relationships between the atomic concentration of a given constituent and the Young’s modulus or alloy density. PMID:29735946

Theoretical calculation of the melting curve of Cu-Zr binary alloys

DOE PAGES

Gunawardana, K. G.S.H.; Wilson, S. R.; Mendelev, M. I.; ...

2014-11-14

Helmholtz free energies of the dominant binary crystalline solids found in the Cu-Zr system at high temperatures close to the melting curve are calculated. This theoretical approach combines fundamental measure density functional theory (applied to the hard-sphere reference system) and a perturbative approach to include the attractive interactions. The studied crystalline solids are Cu(fcc), Cu 51Zr 14(β), CuZr(B 2), CuZr 2(C11b), Zr(hcp), and Zr(bcc). The calculated Helmholtz free energies of crystalline solids are in good agreement with results from molecular-dynamics (MD) simulations. Using the same perturbation approach, the liquid phase free energies are calculated as a function of composition andmore » temperature, from which the melting curve of the entire composition range of this system can be obtained. Phase diagrams are determined in this way for two leading embedded atom method potentials, and the results are compared with experimental data. Furthermore, theoretical melting temperatures are compared both with experimental values and with values obtained directly from MD simulations at several compositions.« less

The role of the electrolyte in the selective dissolution of metal alloys

NASA Astrophysics Data System (ADS)

Policastro, Steven A.

Dealloying plays an important role in several corrosion processes, including pitting corrosion through the formation of local cathodes from the selective dissolution of intermetallic particles and stress-corrosion cracking in which it is responsible for injecting cracks from the surface into the undealloyed bulk material. Additionally, directed dealloying in the laboratory to form nanoporous structures has been the subject of much recent study because of the unique structural properties that the porous layer provides. In order to better understand the physical reasons for dealloying as well as understand the parameters that influence the evolution of the microstructure, several models have been proposed. Current theoretical descriptions of dealloying have been very successful in explaining some features of selective dissolution but additional behaviors can be included into the model to improve understanding of the dealloying process. In the present work, the effects of electrolyte component interactions, temperature, alloy cohesive energies, and applied potential on the development of nanoporosity via the selective dissolution of the less-noble component from binary and ternary alloys are considered. Both a kinetic Monte-Carlo (KMC) model of the behavior of the metal atoms and the electrolyte ions at the metal-solution interface and a phase-yield model of ligament coarsening are developed. By adding these additional parameters into the KMC model, a rich set of behaviors is observed in the simulation results. From the simulation results, it is suggested that selectively dissolving a binary alloy in a very aggressive electrolyte that targeted the LN atoms could provide a porous microstructure that retained a higher concentration of the LN atoms in its ligaments and thus retain more of the mechanical properties of the bulk alloy. In addition, by adding even a small fraction of a third, noble component to form a ternary alloy the dissolution kinetics of the least noble component can be dramatically altered, providing a means of controlling dealloying depth. Some molecular dynamics calculations are used to justify the assumptions of metal atom motion in the KMC model. A recently developed parameter-space exploration technique, COERCE, is employed to optimize the process of obtaining meaningful parameter values from the KMC simulation.

Model many-body Stoner Hamiltonian for binary FeCr alloys

NASA Astrophysics Data System (ADS)

Nguyen-Manh, D.; Dudarev, S. L.

2009-09-01

We derive a model tight-binding many-body d -electron Stoner Hamiltonian for FeCr binary alloys and investigate the sensitivity of its mean-field solutions to the choice of hopping integrals and the Stoner exchange parameters. By applying the local charge-neutrality condition within a self-consistent treatment we show that the negative enthalpy-of-mixing anomaly characterizing the alloy in the low chromium concentration limit is due entirely to the presence of the on-site exchange Stoner terms and that the occurrence of this anomaly is not specifically related to the choice of hopping integrals describing conventional chemical bonding between atoms in the alloy. The Bain transformation pathway computed, using the proposed model Hamiltonian, for the Fe15Cr alloy configuration is in excellent agreement with ab initio total-energy calculations. Our investigation also shows how the parameters of a tight-binding many-body model Hamiltonian for a magnetic alloy can be derived from the comparison of its mean-field solutions with other, more accurate, mean-field approximations (e.g., density-functional calculations), hence stimulating the development of large-scale computational algorithms for modeling radiation damage effects in magnetic alloys and steels.

Atomistic Modeling of Diffusion and Phase Transformations in Metals and Alloys

NASA Astrophysics Data System (ADS)

Purja Pun, Ganga Prasad

Dissertation consists of multiple works. The first part is devoted to self-diffusion along dislocation cores in aluminum followed by the development of embedded atom method potentials for Co, NiAl, CoAl and CoNi systems. The last part focuses on martensitic phase transformation (MPT) in Ni xAl1--x and Al xCoyNi1-- x--y alloys. New calculation methods were developed to predict diffusion coefficients in metal as functions of temperature. Self-diffusion along screw and edge dislocations in aluminum was studied by molecular dynamic (MD) simulations. Three types of simulations were performed with and without (intrinsic) pre-existing vacancies and interstitials in the dislocation core. We found that the diffusion along the screw dislocation was dominated by the intrinsic mechanism, whereas the diffusion along the edge dislocation was dominated by the vacancy mechanism. The diffusion along the screw dislocation was found to be significantly faster than the diffusion along the edge dislocation, and the both diffusivities were in reasonable agreement with experimental data. The intrinsic diffusion mechanism can be associated with the formation of dynamic Frenkel pairs, possibly activated by thermal jogs and/or kinks. The simulations show that at high temperatures the dislocation core becomes an effective source/sink of point defects and the effect of pre-existing defects on the core diffusivity diminishes. First and the foremost ingredient needed in all atomistic computer simulations is the description of interaction between atoms. Interatomic potentials for Co, NiAl, CoAl and CoNi systems were developed within the Embedded Atom Method (EAM) formalism. The binary potentials were based on previously developed accurate potentials for pure Ni and pure Al and pure Co developed in this work. The binaries constitute a version of EAM potential of AlCoNi ternary system. The NiAl potential accurately reproduces a variety of physical properties of the B2-NiAl and L12--Ni3Al phases. The potential is expected to be especially suitable for simulations of hetero-phase interfaces and mechanical behavior of NiAl alloys. Apart from properties of the HCP Co, the new Co potential is accurate enough to reproduce several properties of the FCC Co which were not included in the potential fit. It shows good transferability property. The CoAl potential was fitted to the properties of B2-CoAl phase as in the NiAl fitting where as the NiCo potential was fitted to the ab initio formation energies of some imaginary phases and structures. Effect of chemical composition and uniaxial mechanical stresses was studied on the martensitic phase transformation in B2 type Ni-rich NiAl and AlCoNi alloys. The martensitic phase has a tetragonal crystal structure and can contain multiple twins arranged in domains and plates. The twinned martensites were always formed under the uniaxial compression where as the single variant martensites were the results of the uniaxial tension. The transformation was reversible and characterized by a significant temperature hysteresis. The magnitude of the hysteresis depends on the chemical composition and stress.

Formation of amorphous materials

DOEpatents

Johnson, William L.; Schwarz, Ricardo B.

1986-01-01

Metastable amorphous or fine crystalline materials are formed by solid state reactions by diffusion of a metallic component into a solid compound or by diffusion of a gas into an intermetallic compound. The invention can be practiced on layers of metals deposited on an amorphous substrate or by intermixing powders with nucleating seed granules. All that is required is that the diffusion of the first component into the second component be much faster than the self-diffusion of the first component. The method is practiced at a temperature below the temperature at which the amorphous phase transforms into one or more crystalline phases and near or below the temperature at which the ratio of the rate of diffusion of the first component to the rate of self-diffusion is at least 10.sup.4. This anomalous diffusion criteria is found in many binary, tertiary and higher ordered systems of alloys and appears to be found in all alloy systems that form amorphous materials by rapid quenching. The method of the invention can totally convert much larger dimensional materials to amorphous materials in practical periods of several hours or less.

First-principles-based kinetic Monte Carlo studies of diffusion of hydrogen in Ni–Al and Ni–Fe binary alloys

DOE PAGES

Tafen, De Nyago

2015-02-14

The diffusion of dilute hydrogen in fcc Ni–Al and Ni–Fe binary alloys was examined using kinetic Monte Carlo method with input kinetic parameters obtained from first-principles density functional theory. The simulation involves the implementation of computationally efficient energy barrier model that describes the configuration dependence of the hydrogen hopping. The predicted hydrogen diffusion coefficients in Ni and Ni 89.4Fe 10.6 are compared well with the available experimental data. In Ni–Al, the model predicts lower hydrogen diffusivity compared to that in Ni. Overall, diffusion prefactors and the effective activation energies of H in Ni–Fe and Ni–Al are concentration dependent of themore » alloying element. Furthermore, the changes in their values are the results of the short-range order (nearest-neighbor) effect on the interstitial diffusion of hydrogen in fcc Ni-based alloys.« less

Identification of the heat transfer coefficient in the two-dimensional model of binary alloy solidification

NASA Astrophysics Data System (ADS)

Hetmaniok, Edyta; Hristov, Jordan; Słota, Damian; Zielonka, Adam

2017-05-01

The paper presents the procedure for solving the inverse problem for the binary alloy solidification in a two-dimensional space. This is a continuation of some previous works of the authors investigating a similar problem but in the one-dimensional domain. Goal of the problem consists in identification of the heat transfer coefficient on boundary of the region and in reconstruction of the temperature distribution inside the considered region in case when the temperature measurements in selected points of the alloy are known. Mathematical model of the problem is based on the heat conduction equation with the substitute thermal capacity and with the liquidus and solidus temperatures varying in dependance on the concentration of the alloy component. For describing this concentration the Scheil model is used. Investigated procedure involves also the parallelized Ant Colony Optimization algorithm applied for minimizing a functional expressing the error of approximate solution.

Surface Segregation in Ternary Alloys

NASA Technical Reports Server (NTRS)

Good, Brian; Bozzolo, Guillermo H.; Abel, Phillip B.

2000-01-01

Surface segregation profiles of binary (Cu-Ni, Au-Ni, Cu-Au) and ternary (Cu-Au-Ni) alloys are determined via Monte Carlo-Metropolis computer simulations using the BFS method for alloys for the calculation of the energetics. The behavior of Cu or Au in Ni is contrasted with their behavior when both are present. The interaction between Cu and Au and its effect on the segregation profiles for Cu-Au-Ni alloys is discussed.

Ab Initio Simulations of Temperature Dependent Phase Stability and Martensitic Transitions in NiTi

NASA Technical Reports Server (NTRS)

Haskins, Justin B.; Thompson, Alexander E.; Lawson, John W.

2016-01-01

For NiTi based alloys, the shape memory effect is governed by a transition from a low-temperature martensite phase to a high-temperature austenite phase. Despite considerable experimental and computational work, basic questions regarding the stability of the phases and the martensitic phase transition remain unclear even for the simple case of binary, equiatomic NiTi. We perform ab initio molecular dynamics simulations to describe the temperature-dependent behavior of NiTi and resolve several of these outstanding issues. Structural correlation functions and finite temperature phonon spectra are evaluated to determine phase stability. In particular, we show that finite temperature, entropic effects stabilize the experimentally observed martensite (B19') and austenite (B2) phases while destabilizing the theoretically predicted (B33) phase. Free energy computations based on ab initio thermodynamic integration confirm these results and permit estimates of the transition temperature between the phases. In addition to the martensitic phase transition, we predict a new transition between the B33 and B19' phases. The role of defects in suppressing these phase transformations is discussed.

In vitro corrosion and biocompatibility of binary magnesium alloys.

PubMed

Gu, Xuenan; Zheng, Yufeng; Cheng, Yan; Zhong, Shengping; Xi, Tingfei

2009-02-01

As bioabsorbable materials, magnesium alloys are expected to be totally degraded in the body and their biocorrosion products not deleterious to the surrounding tissues. It's critical that the alloying elements are carefully selected in consideration of their cytotoxicity and hemocompatibility. In the present study, nine alloying elements Al, Ag, In, Mn, Si, Sn, Y, Zn and Zr were added into magnesium individually to fabricate binary Mg-1X (wt.%) alloys. Pure magnesium was used as control. Their mechanical properties, corrosion properties and in vitro biocompatibilities (cytotoxicity and hemocompatibility) were evaluated by SEM, XRD, tensile test, immersion test, electrochemical corrosion test, cell culture and platelet adhesion test. The results showed that the addition of alloying elements could influence the strength and corrosion resistance of Mg. The cytotoxicity tests indicated that Mg-1Al, Mg-1Sn and Mg-1Zn alloy extracts showed no significant reduced cell viability to fibroblasts (L-929 and NIH3T3) and osteoblasts (MC3T3-E1); Mg-1Al and Mg-1Zn alloy extracts indicated no negative effect on viabilities of blood vessel related cells, ECV304 and VSMC. It was found that hemolysis and the amount of adhered platelets decreased after alloying for all Mg-1X alloys as compared to the pure magnesium control. The relationship between the corrosion products and the in vitro biocompatibility had been discussed and the suitable alloying elements for the biomedical applications associated with bone and blood vessel had been proposed.

Compressive creep behavior of alloys based on B2 FeAl

NASA Technical Reports Server (NTRS)

Mantravadi, N.; Vedula, K.; Gaydosh, D.; Titran, R. H.

1986-01-01

Alloys based on FeAl are attractive alternate materials for environmental resistance at intermediate temperatures. Addition of small amounts of Nb, Hf, Ta, Mo, Zr, and B were shown to improve the compressive creep of this alloy at 1100 K. Boron, in particular, was found to have a synergistic effect along with Zr in providing properties substantially better than the binary alloy. This improvement seems to be related to the higher activation energy found for this alloy, suggesting a modification in the diffusion behavior due to the alloying additions.

Compressive creep behavior of alloys based on B2 FeAl

NASA Technical Reports Server (NTRS)

Mantravadi, N.; Vedula, K.; Gaydosh, D.; Titran, R. H.

1987-01-01

Alloys based on FeAl are attractive alternative materials for environmental resistance at intermediate temperatures. Addition of small amounts of Nb, Hf, Ta, Mo, Zr, and B were shown to improve the compressive creep of this alloy at 1100 K. Boron, in particular, was found to have a synergistic effect along with Zr in providing properties substantially better than the binary alloy. This improvement seems to be related to the higher activation energy found for this alloy, suggesting a modification in the diffusion behavior due to the alloying additions.

Atomistic modeling of grain boundary behavior under shear conditions in magnesium and magnesium-based binary alloys

NASA Astrophysics Data System (ADS)

Nahhas, M. K.; Groh, S.

2018-02-01

In this study, the structure, the energetic, and the strength of a { 10 1 bar 1 } < 11 2 bar 0 > symmetric tilt grain boundary in magnesium and magnesium binary alloys were analyzed in the framework of (semi-)empirical potentials. Following a systematic investigation of the transferability and accuracy of the interatomic potentials, atomistic calculations of the grain boundary energy, the grain boundary sliding energy, and the grain boundary strength were performed in pure magnesium and in binary MgX alloys (X = Al, Ca, Gd, Li, Sn, Y, Ag, Nd, and Pb). The data gained in this study were analyzed to identify the most critical material parameters controlling the strength of the grain boundary, and their consequence on atomic shuffling motions occurring at the grain boundary. From the methodology perspective, the role of in-plane and out-of plane relaxation on the grain boundary sliding energy curves was investigated. In pure magnesium, the results showed that in-plane relaxation is critical in activating b2{ 10 1 bar 1 } twinning dislocation resulting in grain boundary migration. In the alloy systems, however, grain boundary migration was disabled as a consequence of the pinning of the grain boundary by segregated elements. Finally, while the grain boundary energy, the shape of the grain boundary sliding energy curves, and the grain boundary sliding energy are critical parameters controlling the grain boundary strength in pure magnesium, only the grain boundary energy and the segregation energy of the alloying elements at the grain boundary were identified as critical material parameters in the alloys system.

How can we make stable linear monoatomic chains? Gold-cesium binary subnanowires as an example of a charge-transfer-driven approach to alloying.

PubMed

Choi, Young Cheol; Lee, Han Myoung; Kim, Woo Youn; Kwon, S K; Nautiyal, Tashi; Cheng, Da-Yong; Vishwanathan, K; Kim, Kwang S

2007-02-16

On the basis of first-principles calculations of clusters and one dimensional infinitely long subnanowires of the binary systems, we find that alkali-noble metal alloy wires show better linearity and stability than either pure alkali metal or noble metal wires. The enhanced alternating charge buildup on atoms by charge transfer helps the atoms line up straight. The cesium doped gold wires showing significant charge transfer from cesium to gold can be stabilized as linear or circular monoatomic chains.

Structural difference rule for amorphous alloy formation by ion mixing

NASA Technical Reports Server (NTRS)

Liu, B.-X.; Johnson, W. L.; Nicolet, M.A.; Lau, S. S.

1983-01-01

A rule is formulated which establishes a sufficient condition that an amorphous binary alloy will be formed by ion mixing of multilayered samples when the two constituent metals are of different crystalline structure, regardless of their atomic sizes and electronegativities. The rule is supported by the experimental results obtained on six selected binary metal systems, as well as by the previous data reported in the literature. The amorphization mechanism is discussed in terms of the competition between two different structures resulting in frustration of the crystallization process.

Experimental study of the Ca-Mg-Zn system using diffusion couples and key alloys

NASA Astrophysics Data System (ADS)

Zhang, Yi-Nan; Kevorkov, Dmytro; Bridier, Florent; Medraj, Mamoun

2011-03-01

Nine diffusion couples and 32 key samples were prepared to map the phase diagram of the Ca-Mg-Zn system. Phase relations and solubility limits were determined for binary and ternary compounds using scanning electron microscopy, electron probe microanalysis and x-ray diffraction (XRD). The crystal structure of the ternary compounds was studied by XRD and electron backscatter diffraction. Four ternary intermetallic (IM) compounds were identified in this system: Ca3MgxZn15-x (4.6<=x<=12 at 335 °C, IM1), Ca14.5Mg15.8Zn69.7 (IM2), Ca2Mg5Zn13 (IM3) and Ca1.5Mg55.3Zn43.2 (IM4). Three binary compounds were found to have extended solid solubility into ternary systems: CaZn11, CaZn13 and Mg2Ca form substitutional solid solutions where Mg substitutes for Zn atoms in the first two compounds, and Zn substitutes for both Ca and Mg atoms in Mg2Ca. The isothermal section of the Ca-Mg-Zn phase diagram at 335 °C was constructed on the basis of the obtained experimental results. The morphologies of the diffusion couples in the Ca-Mg-Zn phase diagram at 335 °C were studied. Depending on the terminal compositions of the diffusion couples, the two-phase regions in the diffusion zone have either a tooth-like morphology or contain a matrix phase with isolated and/or dendritic precipitates.

Thermodynamic assessment of Ag–Cu–In

DOE PAGES

Muzzillo, Christopher P.; Anderson, Tim

2018-01-16

The Ag-Cu-In thermodynamic material system is of interest for brazing alloys and chalcopyrite thin-film photovoltaics. To advance these applications, Ag-Cu-In was assessed and a Calphad model was developed. Binary Ag-Cu and Cu-In parameters were taken from previous assessments, while Ag-In was re-assessed. Structure-based models were employed for ..beta..-bcc(A2)-Ag 3In, ..gamma..-Ag 9In 4, and AgIn 2 to obtain good fit to enthalpy, phase boundary, and invariant reaction data for Ag-In. Ternary Ag-Cu-In parameters were optimized to achieve excellent fit to activity, enthalpy, and extensive phase equilibrium data. Relative to the previous Ag-Cu-In assessment, fit was improved while fewer parameters were used.

Thermodynamic assessment of Ag–Cu–In

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muzzillo, Christopher P.; Anderson, Tim

The Ag-Cu-In thermodynamic material system is of interest for brazing alloys and chalcopyrite thin-film photovoltaics. To advance these applications, Ag-Cu-In was assessed and a Calphad model was developed. Binary Ag-Cu and Cu-In parameters were taken from previous assessments, while Ag-In was re-assessed. Structure-based models were employed for ..beta..-bcc(A2)-Ag 3In, ..gamma..-Ag 9In 4, and AgIn 2 to obtain good fit to enthalpy, phase boundary, and invariant reaction data for Ag-In. Ternary Ag-Cu-In parameters were optimized to achieve excellent fit to activity, enthalpy, and extensive phase equilibrium data. Relative to the previous Ag-Cu-In assessment, fit was improved while fewer parameters were used.

Theoretical study of the density of states and magnetic properties of LaCoO3

NASA Astrophysics Data System (ADS)

Zhuang, Min; Zhang, Weiyi; Hu, Cheng; Ming, Naiben

1998-05-01

The density of states and magnetic properties of low-spin, high-spin, and mixing states of LaCoO3 have been studied within the unrestricted Hartree-Fock approximation. The real-space recursion method is adopted for computing the electronic structure of the disordered system. The paramagnetic high-spin state is dealt with using the usual binary alloy coherent potential approximation (CPA); an extended trinary alloy CPA approximation is developed to describe the mixing state. In agreement with experiments, our results show that the main features of the quasiparticle spectra in the mixing state are not a sensitive function of the high-spin component, but the spectrum does get broadened due to spin scattering. The increasing of the high-spin component also results in a pileup of the density of states at the Fermi energy which indicates an insulator to metal phase transition. Some limitations of the present approach are also discussed.

Viscosities of Fe Ni, Fe Co and Ni Co binary melts

NASA Astrophysics Data System (ADS)

Sato, Yuzuru; Sugisawa, Koji; Aoki, Daisuke; Yamamura, Tsutomu

2005-02-01

Viscosities of three binary molten alloys consisting of the iron group elements, Fe, Ni and Co, have been measured by using an oscillating cup viscometer over the entire composition range from liquidus temperatures up to 1600 °C with high precision and excellent reproducibility. The viscosities measured showed good Arrhenius linearity for all the compositions. The viscosities of Fe, Ni and Co as a function of temperature are as follows: \\eqalign{ & \\log \\eta={-}0.6074 + 2493/T\\qquad for\\quad Fe\\\\ & \\log \\eta={-}0.5695 + 2157/T\\qquad for\\quad Ni \\\\ & \\log \\eta={-}0.6620 + 2430/T\\qquad for\\quad Co.} The isothermal viscosities of Fe-Ni and Fe-Co binary melts increase monotonically with increasing Fe content. On the other hand, in Ni-Co binary melt, the isothermal viscosity decreases slightly and then increases with increasing Co. The activation energy of Fe-Co binary melt increased slightly on mixing, and those of Fe-Ni and Ni-Co melts decreased monotonically with increasing Ni content. The above behaviour is discussed based on the thermodynamic properties of the alloys.

Computer-Based Methods for Thermodynamic Analysis of Materials Processing.

DTIC Science & Technology

1983-11-30

metallic alloys (12,13), silicides (14),and oxynitride * . systems (15). - . 2. Thermochemical System Employed to Characterize Binary Ill-V Phase Diagrams The...reference to Figure I shows that the stable form of RbF is the sodium chloride S form. Table I shows that OGH -oS -RFRFLS-RFRFLM-12866-.381T J/g.at. (5...KF, BF=(I/3)8aF LF-(I/4)LaF3V PF-(113)PbF 2 S- Sodium Chloride Structures Stable form of NF, KE, RE and (;F L-Liquid, M-Stable form of ZF, KeStable form

Optical Studies of model binary miscibility gap system

NASA Technical Reports Server (NTRS)

Lacy, L. L.; Witherow, W. K.; Facemire, B. R.; Nishioka, G. M.

1982-01-01

In order to develop a better understanding of separation processes in binary miscibility gap metal alloys, model transparent fluid systems were studied. The system selected was diethylene glycol-ethyl salicylate which has convenient working temperatures (288 to 350 K), low toxicity, and is relatively easy to purify. The system is well characterized with respect to its phase diagram, density, surface and interfacial tensions, viscosity and other pertinent physical properties. Studies of migration of the dispersed phase in a thermal gradient were performed using conventional photomicroscopy. Velocities of the droplets of the dispersed phase were measured and compared to calculated rates which included both Stokes and thermal components. A holographic microscopy system was used to study growth, coalescence, and particle motions. Sequential holograms allowed determination of particle size distribution changes with respect to time and temperature. Holographic microscopy is capable of recording particle densities up to 10 to the 7th power particles/cu cm and is able to resolve particles of the order of 2 to 3 microns in diameter throughout the entire volume of the test cell. The reconstructed hologram produces a wavefront that is identical to the original wavefront as it existed when the hologram was made. The reconstructed wavefront is analyzed using a variety of conventional optical methods.

NEUTRON REACTOR FUEL ELEMENT UTILIZING ZIRCONIUM-BASE ALLOYS

DOEpatents

Saller, H.A.; Keeler, J.R.; Szumachowski, E.R.

1957-11-12

This patent relates to clad fuel elements for use in neutronic reactors and is drawn to such a fuel element which consists of a core of fissionable material, comprised of an alloy of zirconium and U/sup 235/ enriched uranium, encased in a jacket of a binary zirconium-tin alloy in which the tin content ranges between 1 and 15% by weight.

Magnetic susceptibilities of liquid Cr-Au, Mn-Au and Fe-Au alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohno, S.; Shimakura, H.; Tahara, S.

The magnetic susceptibility of liquid Cr-Au, Mn-Au, Fe-Au and Cu-Au alloys was investigated as a function of temperature and composition. Liquid Cr{sub 1-c}Au{sub c} with 0.5 ≤ c and Mn{sub 1-c}Au{sub c} with 0.3≤c obeyed the Curie-Weiss law with regard to their dependence of χ on temperature. The magnetic susceptibilities of liquid Fe-Au alloys also exhibited Curie-Weiss behavior with a reasonable value for the effective number of Bohr magneton. On the Au-rich side, the composition dependence of χ for liquid TM-Au (TM=Cr, Mn, Fe) alloys increased rapidly with increasing TM content, respectively. Additionally, the composition dependences of χ for liquidmore » Cr-Au, Mn-Au, and Fe-Au alloys had maxima at compositions of 50 at% Cr, 70 at% Mn, and 85 at% Fe, respectively. We compared the composition dependences of χ{sub 3d} due to 3d electrons for liquid binary TM-M (M=Au, Al, Si, Sb), and investigated the relationship between χ{sub 3d} and E{sub F} in liquid binary TM-M alloys at a composition of 50 at% TM.« less

A canonical stability-elasticity relationship verified for one million face-centred-cubic structures.

PubMed

Maisel, Sascha B; Höfler, Michaela; Müller, Stefan

2012-11-29

Any thermodynamically stable or metastable phase corresponds to a local minimum of a potentially very complicated energy landscape. But however complex the crystal might be, this energy landscape is of parabolic shape near its minima. Roughly speaking, the depth of this energy well with respect to some reference level determines the thermodynamic stability of the system, and the steepness of the parabola near its minimum determines the system's elastic properties. Although changing alloying elements and their concentrations in a given material to enhance certain properties dates back to the Bronze Age, the systematic search for desirable properties in metastable atomic configurations at a fixed stoichiometry is a very recent tool in materials design. Here we demonstrate, using first-principles studies of four binary alloy systems, that the elastic properties of face-centred-cubic intermetallic compounds obey certain rules. We reach two conclusions based on calculations on a huge subset of the face-centred-cubic configuration space. First, the stiffness and the heat of formation are negatively correlated with a nearly constant Spearman correlation for all concentrations. Second, the averaged stiffness of metastable configurations at a fixed concentration decays linearly with their distance to the ground-state line (the phase diagram of an alloy at zero Kelvin). We hope that our methods will help to simplify the quest for new materials with optimal properties from the vast configuration space available.

Static and vibrational properties of equiatomic Na-based binary alloys

NASA Astrophysics Data System (ADS)

Vora, Aditya M.

2007-09-01

The computations of the static and vibrational properties of four equiatomic Na-based binary alloys viz. Na0.5Li0.5, Na0.5K0.5, Na0.5Rb0.5 and Na0.5Cs0.5, to second order in local model potential is discussed in terms of real-space sum of Born von Karman central force constants. The local field correlation functions due to Hartree (H), Ichimaru Utsumi (IU) and Sarkar et al. (S) are used to investigate the influence of the screening effects on the aforesaid properties. Results for the lattice constants C11, C12, C44, C12 C44, C12/C44 and bulk modulus B obtained using the H-local field correction function have higher values in comparison with the results obtained for the same properties using IU- and S-local field correction functions. The results for the Shear modulus (C‧), deviation from Cauchy's relation, Poisson's ratio σ, Young modulus Y, propagation velocity of elastic waves, phonon dispersion curves and degree of anisotropy A are highly appreciable for the four equiatomic Na-based binary alloys.

Effect of Ni +-ION bombardment on nickel and binary nickel alloys

NASA Astrophysics Data System (ADS)

Roarty, K. B.; Sprague, J. A.; Johnson, R. A.; Smidt, F. A.

1981-03-01

Pure nickel and four binary nickel alloys have been subjected to high energy Ni ion bombardment at 675, 625 and 525°C. After irradiation, each specimen was studied by transmission electron microscopy. The pure nickel control was found to swell appreciably (1 to 5%) and the Ni-Al and the Ni-Ti samples were found to swell at all temperatures, but to a lesser degree (0.01 to 0.35%). The Ni-Mo contained a significant density of voids only at 525° C, while swelling was suppressed at all temperatures in the Ni-Si alloy. The dislocation structure progressed from loops to tangles as temperature increased in all materials except the Ni-Ti, in which there was an absence of loops at all temperatures. Dislocation densities decreased as temperature increased in all samples. These results do not correlate well with the relative behavior of the same alloys observed after neutron irradiation at 455°C. The differences between these two sets of data appear to be caused by different mechanisms controlling void nucleation in ion and neutron irradiation of these alloys.

Combinatorial assessment of the influence of composition and exposure time on the oxidation behavior and concurrent oxygeninduced phase transformations of binary Ti-x systems

NASA Astrophysics Data System (ADS)

Samimi, Peyman

The relatively low oxidation resistance and subsequent surface embrittlement have often limited the use of titanium alloys in elevated temperature structural applications. Although extensive effort is spent to investigate the high temperature oxidation performance of titanium alloys, the studies are often constrained to complex technical titanium alloys and neither the mechanisms associated with evolution of the oxide scale nor the effect of oxygen ingress on the microstructure of the base metal are well-understood. In addition lack of systematic oxidation studies across a wider domain of the alloy composition has complicated the determination of composition-mechanism-property relationships. Clearly, it would be ideal to assess the influence of composition and exposure time on the oxidation resistance, independent of experimental variabilities regarding time, temperature and atmosphere as the potential source of error. Such studies might also provide a series of metrics (e.g., hardness, scale, etc) that could be interpreted together and related to the alloy composition. In this thesis a novel combinatorial approach was adopted whereby a series of compositionally graded specimens, (Ti-xMo, Ti-xCr, Ti-xAl and Ti-xW) were prepared using Laser Engineered Net Shaping (LENS(TM)) technology and exposed to still-air at 650 °C. (Abstract shortened by ProQuest.).

Thermodynamic criteria for the removal of impurities from end-of-life magnesium alloys by evaporation and flux treatment

NASA Astrophysics Data System (ADS)

Hiraki, Takehito; Takeda, Osamu; Nakajima, Kenichi; Matsubae, Kazuyo; Nakamura, Shinichiro; Nagasaka, Tetsuya

2011-06-01

In this paper, the possibility of removing impurities during magnesium recycling with pyrometallurgical techniques has been evaluated by using a thermodynamic analysis. For 25 different elements that are likely to be contained in industrial magnesium alloys, the equilibrium distribution ratios between the metal, slag and gas phases in the magnesium remelting process were calculated assuming binary systems of magnesium and an impurity element. It was found that calcium, gadolinium, lithium, ytterbium and yttrium can be removed from the remelted end-of-life (EoL) magnesium products by oxidization. Calcium, cerium, gadolinium, lanthanum, lithium, plutonium, sodium, strontium and yttrium can be removed by chlorination with a salt flux. However, the other elements contained in magnesium alloy scrap are scarcely removed and this may contribute toward future contamination problems. The third technological option for the recycling of EoL magnesium products is magnesium recovery by a distillation process. Based on thermodynamic considerations, it is predicted that high-purity magnesium can be recovered through distillation because of its high vapor pressure, yet there is a limit on recoverability that depends on the equilibrium vapor pressure of the alloying elements and the large energy consumption. Therefore, the sustainable recycling of EoL magnesium products should be an important consideration in the design of advanced magnesium alloys or the development of new refining processes.

Thermodynamic criteria for the removal of impurities from end-of-life magnesium alloys by evaporation and flux treatment

PubMed Central

Hiraki, Takehito; Takeda, Osamu; Nakajima, Kenichi; Matsubae, Kazuyo; Nakamura, Shinichiro; Nagasaka, Tetsuya

2011-01-01

In this paper, the possibility of removing impurities during magnesium recycling with pyrometallurgical techniques has been evaluated by using a thermodynamic analysis. For 25 different elements that are likely to be contained in industrial magnesium alloys, the equilibrium distribution ratios between the metal, slag and gas phases in the magnesium remelting process were calculated assuming binary systems of magnesium and an impurity element. It was found that calcium, gadolinium, lithium, ytterbium and yttrium can be removed from the remelted end-of-life (EoL) magnesium products by oxidization. Calcium, cerium, gadolinium, lanthanum, lithium, plutonium, sodium, strontium and yttrium can be removed by chlorination with a salt flux. However, the other elements contained in magnesium alloy scrap are scarcely removed and this may contribute toward future contamination problems. The third technological option for the recycling of EoL magnesium products is magnesium recovery by a distillation process. Based on thermodynamic considerations, it is predicted that high-purity magnesium can be recovered through distillation because of its high vapor pressure, yet there is a limit on recoverability that depends on the equilibrium vapor pressure of the alloying elements and the large energy consumption. Therefore, the sustainable recycling of EoL magnesium products should be an important consideration in the design of advanced magnesium alloys or the development of new refining processes. PMID:27877407

Mössbauer and X-ray Diffraction Investigations of Sn-containing Binary and Ternary Electrodeposited Alloys from a Gluconate Bath

NASA Astrophysics Data System (ADS)

Kuzmann, E.; Stichleutner, S.; Doyle, O.; Chisholm, C. U.; El-Sharif, M.; Homonnay, Z.; Vértes, A.

2005-04-01

Constant current technique was applied to electrodeposit tin-containing coatings such as tin-cobalt (Sn-Co), tin-iron (Sn-Fe) and a novel tin-cobalt-iron (Sn-Co-Fe) from a gluconate bath. The effect of plating parameters (current density, deposition time at an electrolyte temperature of 60°C and pH=7.0) on phase composition, crystal structure and magnetic anisotropy of alloy deposits has been investigated mainly by 57Fe CEMS, 119Sn CEMS and transmission Mössbauer Spectroscopy as well as XRD. 57Fe and 119Sn CEM spectra and XRD reflect that the dominant phases of the deposits are orthorhombic Co3Sn2, tetragonal FeSn2 or amorphous Fe-Sn and amorphous Sn-Co-Fe in Sn-Co, Sn-Fe and Sn-Co-Fe coatings, respectively. Furthermore, the relative area of the 2nd and 5th lines of the sextets representing the magnetic iron containing phases decreases continuously with increasing current density in all Fe-containing deposits. At the same time, no essential change in the magnetic anisotropy can be found with the plating time. 119Sn spectra reveal the presence of small amount of β-Sn besides the main phases in Sn-Fe and in the Sn-Co coatings. Magnetically split 119Sn spectra reflecting transferred hyperfine field were observed in the case of Co-Sn-Fe coatings.

Advances in Pb-free solder microstructure control and interconnect design

DOE PAGES

Reeve, Kathlene N.; Holaday, John R.; Choquette, Stephanie M.; ...

2016-06-09

New electronics applications demanding enhanced performance and higher operating temperatures have led to continued research in the field of Pb-free solder designs and interconnect solutions. In this paper, recent advances in the microstructural design of Pb-free solders and interconnect systems were discussed by highlighting two topics: increasing β-Sn nucleation in Sn-based solders, and isothermally solidified interconnects using transient liquid phases. Issues in β-Sn nucleation in Sn-based solders were summarized in the context of Swenson’s 2007 review of the topic. Recent advancements in the areas of alloy composition manipulation, nucleating heterogeneities, and rapid solidification were discussed, and a proposal based onmore » a multi-faceted solidification approach involving the promotion of constitutional undercooling and nucleating heterogeneities was outlined for future research. The second half of the paper analyzed two different approaches to liquid phase diffusion bonding as a replacement for high-Pb solders, one based on the application of the pseudo-binary Cu-Ni-Sn ternary system, and the other on a proposed thermodynamic framework for identifying potential ternary alloys for liquid phase diffusion bonding. Furthermore, all of the concepts reviewed relied upon the fundamentals of thermodynamics, kinetics, and solidification, to which Jack Smith substantially contributed during his scientific career.« less

Selective Internal Oxidation and Severe Plastic Deformation of Multiphase Fe-Y Alloys

NASA Astrophysics Data System (ADS)

Kachur, Stephen J.

Oxide dispersion strengthened (ODS) alloys are known for their desirable mechanical properties and unique microstructures. These alloys are characterized by an even dispersion of oxide phase throughout a metallic matrix, and exhibit high strength and enhanced creep properties at elevated temperatures. This makes them ideal candidate materials for use in many structural applications, such as coal-fired power plants or in next generation nuclear reactors. Currently most often produced by mechanical alloying, a powder metallurgy based process that utilizes high energy ball milling, these alloys are difficult and costly to produce. One proposed method for forming ODS alloys without high-energy ball milling is to internally oxidize a bulk alloy before subjecting it to severe plastic deformation to induce an even oxide distribution. This work examines such a processing scheme with a focus on the internal oxidation behavior. Internal oxidation has been shown to occur orders of magnitude faster than expected in multi-phase alloys where a highly reactive oxidizable solute has negligible solubility and diffusivity in other, more-noble, phases. Commonly referred to as in situ oxidation, this accelerated oxidation process has potential for use in a processing scheme for ODS alloys. While in situ oxidation has been observed in many different alloy systems, a comprehensive study of alloy composition and microstructure has not been performed to describe the unusual oxidation rates. This work used Fe-Y binary alloys as model system to study effects of composition and microstructure. These alloys have been shown to exhibit in situ oxidation, and additionally, Y is typically introduced during mechanical alloying to form Y-rich oxides in Fe-based ODS alloys. Alloys with Y content between 1.5 and 15 wt% were prepared using a laboratory scale arc-melting furnace. These alloys were two phase mixtures of Fe and Fe17Y2. First, samples were oxidized between 600 and 800 °C for 2 to 72 hours, using a Rhines pack to maintain low oxygen partial pressures so that in situ oxidation could occur. Oxidation rates were accelerated when compared to traditional theory, and were not well described by a single parabolic rate constant throughout the duration of the experiment. While results agreed with Wagner theory that increased Y content should lead to decreased oxidation rates, this was attributed to a depletion of oxygen supply from the Rhines pack over time. Samples were also subjected to plastic deformation to observe how changes in microstructure influenced kinetics. Connectivity of the oxidizable phase was found to be critical to promoting the fastest rates of oxidation. Oxidation studies where then carried out using thermogravimetric analysis. A gaseous mixture of Ar-H2 was passed through a dew point control unit to vary oxidant partial pressure between 10-25 and 10-20 atm. Flow rate of the gas parallel to the sample surface was also altered. Canonical correlation analysis was then used to analyze and simplify the relationships between input and output variables. This analysis pointed to the importance of quantifying the relationship between the size of formed oxides and changes in oxidation kinetics over time. Where sustained parabolic kinetics were observed, oxides were small throughout the depth of internal oxidation. The effects of oxide size on penetration depth were then numerically modeled and incorporated into existing oxidation theory to show that the observed kinetics could be qualitatively described. After oxidation experiments, severe plastic deformation was applied to both oxidized and unoxidized microstructures using equal channel angular pressing. By manipulating pressing temperature and the number of passes, microstructures were altered to varying degrees of success. No oxide refinement was observed, but increasing temperatures and number of passes allowed for even dispersion of both oxides and Fe17Y2 intermetallic.

Microstructure and mechanical behavior of metal injection molded Ti-Nb binary alloys as biomedical material.

PubMed

Zhao, Dapeng; Chang, Keke; Ebel, Thomas; Qian, Ma; Willumeit, Regine; Yan, Ming; Pyczak, Florian

2013-12-01

The application of titanium (Ti) based biomedical materials which are widely used at present, such as commercially pure titanium (CP-Ti) and Ti-6Al-4V, are limited by the mismatch of Young's modulus between the implant and the bones, the high costs of products, and the difficulty of producing complex shapes of materials by conventional methods. Niobium (Nb) is a non-toxic element with strong β stabilizing effect in Ti alloys, which makes Ti-Nb based alloys attractive for implant application. Metal injection molding (MIM) is a cost-efficient near-net shape process. Thus, it attracts growing interest for the processing of Ti and Ti alloys as biomaterial. In this investigation, metal injection molding was applied to the fabrication of a series of Ti-Nb binary alloys with niobium content ranging from 10wt% to 22wt%, and CP-Ti for comparison. Specimens were characterized by melt extraction, optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). Titanium carbide formation was observed in all the as-sintered Ti-Nb binary alloys but not in the as-sintered CP-Ti. Selected area electron diffraction (SAED) patterns revealed that the carbides are Ti2C. It was found that with increasing niobium content from 0% to 22%, the porosity increased from about 1.6% to 5.8%, and the carbide area fraction increased from 0% to about 1.8% in the as-sintered samples. The effects of niobium content, porosity and titanium carbides on mechanical properties have been discussed. The as-sintered Ti-Nb specimens exhibited an excellent combination of high tensile strength and low Young's modulus, but relatively low ductility. © 2013 Elsevier Ltd. All rights reserved.

Electrochemical characteristics of bioresorbable binary MgCa alloys in Ringer's solution: Revealing the impact of local pH distributions during in-vitro dissolution.

PubMed

Mareci, D; Bolat, G; Izquierdo, J; Crimu, C; Munteanu, C; Antoniac, I; Souto, R M

2016-03-01

Biodegradable magnesium-calcium (MgCa) alloy is a very attractive biomaterial. Two MgCa alloys below the solid solubility of Ca were considered, as to solely investigate the effect of Ca content on the behavior of magnesium and the pH changes associated to metal dissolution. X-ray diffraction analysis and optical microscopy showed that both Mg-0.63Ca and Mg-0.89Ca alloys were solely composed of α(Mg) phase. Degradation characteristics and electrochemical characterization of MgCa alloys were investigated during exposure to Ringer's solution at 37 °C by electrochemical impedance spectroscopy and scanning electrochemical microscopy. The impedance behavior showed both capacitive and inductive features that are related to the alloy charge transfer reaction and the relaxation of the absorbed corrosion compounds, and can be described in terms of an equivalent circuit. Scanning electron microscopy (SEM) was employed to view the surface morphology of the MgCa samples after 1 week immersion in Ringer's solution showing extensive precipitation of corrosion products, whereas the substrate shows evidence of a non-uniform corrosion process. Energy dispersive analysis showed that the precipitates contained oxygen, calcium, magnesium and chlorine, and the Mg:Ca ratios were smaller than in the alloys. Scanning electrochemical microscopy (SECM) was used to visualize local pH changes associated to these physicochemical processes with high spatial resolution. The occurrence of pH variations in excess of 3 units between anodic and cathodic half-cell reactions was monitored in situ. Copyright © 2015 Elsevier B.V. All rights reserved.

Enhanced-wetting, boron-based liquid-metal ion source and method

DOEpatents

Bozack, Michael J.; Swanson, Lynwood W.; Bell, Anthony E.; Clark Jr., William M.; Utlaut, Mark W.; Storms, Edmund K.

1999-01-01

A binary, boron-based alloy as a source for field-emission-type, ion-beam generating devices, wherein boron predominates in the alloy, preferably with a presence of about 60 atomic percent. The other constituent in the alloy is selected from the group of elements consisting of nickel, palladium and platinum. Predominance of boron in these alloys, during operation, promotes combining of boron with trace impurities of carbon in the alloys to form B.sub.4 C and thus to promote wetting of an associated carbon support substrate.

Enhanced-wetting, boron-based liquid-metal ion source and method

DOEpatents

Bozack, M.J.; Swanson, L.W.; Bell, A.E.; Clark, W.M. Jr.; Utlaut, M.W.; Storms, E.K.

1999-02-16

A binary, boron-based alloy as a source for field-emission-type, ion-beam generating devices, wherein boron predominates in the alloy, preferably with a presence of about 60 atomic percent is disclosed. The other constituent in the alloy is selected from the group of elements consisting of nickel, palladium and platinum. Predominance of boron in these alloys, during operation, promotes combining of boron with trace impurities of carbon in the alloys to form B{sub 4}C and thus to promote wetting of an associated carbon support substrate. 1 fig.

Role of electron concentration in softening and hardening of ternary molybdenum alloys

NASA Technical Reports Server (NTRS)

Stephens, J. R.; Witzke, W. R.

1975-01-01

Effects of various combinations of hafnium, tantalum, rhenium, osmium, iridium, and platinum in ternary molybdenum alloys on alloy softening and hardening were determined. Hardness tests were conducted at four test temperatures over the temperature range 77 to 411 K. Results showed that hardness data for ternary molybdenum alloys could be correlated with anticipated results from binary data based upon expressions involving the number of s and d electrons contributed by the solute elements. The correlation indicated that electron concentration plays a dominant role in controlling the hardness of ternary molybdenum alloys.

Calculation of optical parameters for covalent binary alloys used in optical memories/solar cells: a modified approach

NASA Astrophysics Data System (ADS)

Bhatnagar, Promod K.; Gupta, Poonam; Singh, Laxman

2001-06-01

Chalcogenide based alloys find applications in a number of devices like optical memories, IR detectors, optical switches, photovoltaics, compound semiconductor heterosrtuctures etc. We have modified the Gurman's statistical thermodynamic model (STM) of binary covalent alloys. In the Gurman's model, entropy calculations are based on the number of structural units present. The need to modify this model arose due to the fact that it gives equal probability for all the tetrahedra present in the alloy. We have modified the Gurman's model by introducing the concept that the entropy is based on the bond arrangement rather than that on the structural units present. In the present work calculation based on this modification have been presented for optical properties, which find application in optical switching/memories, solar cells and other optical devices. It has been shown that the calculated optical parameters (for a typical case of GaxSe1-x) based on modified model are closer to the available experimental results. These parameters include refractive index, extinction coefficient, dielectric functions, optical band gap etc. GaxSe1-x has been found to be suitable for reversible optical memories also, where phase change (a yields c and vice versa) takes place at specified physical conditions. DTA/DSC studies also suggest the suitability of this material for optical switching/memory applications. We have also suggested possible use of GaxSe1-x (x = 0.4) in place of oxide layer in a Metal - Oxide - Semiconductor type solar cells. The new structure is Metal - Ga2Se3 - GaAs. The I-V characteristics and other parameters calculated for this structure are found to be much better than that for Si based solar cells. Maximum output power is obtained at the intermediate layer thickness approximately 40 angstroms for this typical solar cell.

Process for preparing schottky diode contacts with predetermined barrier heights

DOEpatents

Chang, Y. Austin; Jan, Chia-Hong; Chen, Chia-Ping

1996-01-01

A process is provided for producing a Schottky diode having a preselected barrier height .phi..sub.Bn. The substrate is preferably n-GaAs, the metallic contact is derived from a starting alloy of the Formula [.SIGMA.M.sub..delta. ](Al.sub.x Ga.sub.1-x) wherein: .SIGMA.M is a moiety which consists of at least one M, and when more than one M is present, each M is different, M is a Group VIII metal selected from the group consisting of nickel, cobalt, ruthenium, rhodium, indium and platinum, .delta. is a stoichiometric coefficient whose total value in any given .SIGMA.M moiety is 1, and x is a positive number between 0 and 1 (that is, x ranges from greater than 0 to less than 1). Also, the starting alloy is capable of forming with the substrate a two phase equilibrium reciprocal system of the binary alloy mixture [.SIGMA.M.sub..delta. ]Ga-[.SIGMA.M.sub..delta. ]Al-AlAs-GaAs. When members of an alloy subclass within this Formula are each preliminarily correlated with the barrier height .phi..sub.Bn of a contact producable therewith, then Schottky diodes of predetermined barrier heights are producable by sputtering and annealing. Further provided are the product Schottky diodes that are produced according to this process.

Novel Zn-based alloys for biodegradable stent applications: Design, development and in vitro degradation.

PubMed

Mostaed, E; Sikora-Jasinska, M; Mostaed, A; Loffredo, S; Demir, A G; Previtali, B; Mantovani, D; Beanland, R; Vedani, M

2016-07-01

The search for a degradable metal simultaneously showing mechanical properties equal or higher to that of stainless steel and uniform degradation is still an open challenge. Several magnesium-based alloys have been studied, but their degradation rate has proved to be too fast and rarely homogeneous. Fe-based alloys show appropriate mechanical properties but very low degradation rate. In the present work, four novel Zn-Mg and two Zn-Al binary alloys were investigated as potential biodegradable materials for stent applications. The alloys were developed by casting process and homogenized at 350°C for 48h followed by hot extrusion at 250°C. Tube extrusion was performed at 300°C to produce tubes with outer/inner diameter of 4/1.5mm as precursors for biodegradable stents. Corrosion tests were performed using Hanks׳ modified solution. Extruded alloys exhibited slightly superior corrosion resistance and slower degradation rate than those of their cast counterparts, but all had corrosion rates roughly half that of a standard purity Mg control. Hot extrusion of Zn-Mg alloys shifted the corrosion regime from localized pitting to more uniform erosion, mainly due to the refinement of second phase particles. Zn-0.5Mg is the most promising material for stent applications with a good combination of strength, ductility, strain hardening exponent and an appropriate rate of loss of mechanical integrity during degradation. An EBSD analysis in the vicinity of the laser cut Zn-0.5Mg tube found no grain coarsening or texture modification confirming that, after laser cutting, the grain size and texture orientation of the final stent remains unchanged. This work shows the potential for Zn alloys to be considered for stent applications. Copyright © 2016 Elsevier Ltd. All rights reserved.

A study of the diffusional behavior of a two-phase metal matrix composite exposed to a high temperature environment

NASA Technical Reports Server (NTRS)

Tenney, D. R.

1974-01-01

The progress of diffusion-controlled filament-matrix interaction in a metal matrix composite where the filaments and matrix comprise a two-phase binary alloy system was studied by mathematically modeling compositional changes resulting from prolonged elevated temperature exposure. The analysis treats a finite, diffusion-controlled, two-phase moving-interface problem by means of a variable-grid finite-difference technique. The Ni-W system was selected as an example system. Modeling was carried out for the 1000 to 1200 C temperature range for unidirectional composites containing from 6 to 40 volume percent tungsten filaments in a Ni matrix. The results are displayed to show both the change in filament diameter and matrix composition as a function of exposure time. Compositional profiles produced between first and second nearest neighbor filaments were calculated by superposition of finite-difference solutions of the diffusion equations.

Information storage and retrieval in a single levitating colloidal particle

NASA Astrophysics Data System (ADS)

Myers, Christopher J.; Celebrano, Michele; Krishnan, Madhavi

2015-10-01

The binary switch is a basic component of digital information. From phase-change alloys to nanomechanical beams, molecules and atoms, new strategies for controlled bistability hold great interest for emerging technologies. We present a generic methodology for precise and parallel spatiotemporal control of nanometre-scale matter in a fluid, and demonstrate the ability to attain digital functionalities such as switching, gating and data storage in a single colloid, with further implications for signal amplification and logic operations. This fluid-phase bit can be arrayed at high densities, manipulated by either electrical or optical fields, supports low-energy, high-speed operation and marks a first step toward ‘colloidal information’. The principle generalizes to any system where spatial perturbation of a particle elicits a differential response amenable to readout.

Information storage and retrieval in a single levitating colloidal particle.

PubMed

Myers, Christopher J; Celebrano, Michele; Krishnan, Madhavi

2015-10-01

The binary switch is a basic component of digital information. From phase-change alloys to nanomechanical beams, molecules and atoms, new strategies for controlled bistability hold great interest for emerging technologies. We present a generic methodology for precise and parallel spatiotemporal control of nanometre-scale matter in a fluid, and demonstrate the ability to attain digital functionalities such as switching, gating and data storage in a single colloid, with further implications for signal amplification and logic operations. This fluid-phase bit can be arrayed at high densities, manipulated by either electrical or optical fields, supports low-energy, high-speed operation and marks a first step toward 'colloidal information'. The principle generalizes to any system where spatial perturbation of a particle elicits a differential response amenable to readout.

Advanced hydrogen electrode for hydrogen-bromide battery

NASA Technical Reports Server (NTRS)

Kosek, Jack A.; Laconti, Anthony B.

1987-01-01

Binary platinum alloys are being developed as hydrogen electrocatalysts for use in a hydrogen bromide battery system. These alloys were varied in terms of alloy component mole ratio and heat treatment temperature. Electrocatalyst evaluation, performed in the absence and presence of bromide ion, includes floating half cell polarization studies, electrochemical surface area measurements, X ray diffraction analysis, scanning electron microscopy analysis and corrosion measurements. Results obtained to date indicate a platinum rich alloy has the best tolerance to bromide ion poisoning.

Thermal Conductivity of Ten Selected Binary Alloy Systems.

DTIC Science & Technology

1975-05-01

of Commercial Metals and Alloys. IL Aluminmnns," J. Appt. Pys., .1(3), 496-503, 1960. 58. Mikryukov , V . E . and Karagpyan, A. 0., "Thermal and...74, 1900. 136. Mikryukov , V . E ., "Thermal and Electrical Properties of Copper Alloys," Moscow Univ. Vest. Ser. Mat. Mekh. Astron. Fiz. Khim., 12(2... Mikryukov , V . E ., "Thermal and Electrical Properties of Copper Alloys, "Moscow Univ. Vest. Ser. Mat. Mekh. Astron. Fis. Ehim., 12(3), 57-64, 195?. 145

Cobalt-Free Permanent Magnet Alloys.

DTIC Science & Technology

1984-10-01

carbide co- UC CbC lumbium carbide M003 Uranium carbide - tho- UC 2 25ThC rium carbide ZrO2 MgO WOs Use of this Process for MnAlC As indicated in the...cobalt. Free World Cobal Consumption Estimated Breakdown by End Uses Magnetic alloys 20% Cemented carbides - 5% 30 SuPerolloy _ 15% Other steels and...would normally result in the formation of binary alloy of TbFe 2 and preventing the formation of amorphous alloy (Fe-B) contain- ing Tb. The

Modeling the elastic energy of alloys: Potential pitfalls of continuum treatments.

PubMed

Baskaran, Arvind; Ratsch, Christian; Smereka, Peter

2015-12-01

Some issues that arise when modeling elastic energy for binary alloys are discussed within the context of a Keating model and density-functional calculations. The Keating model is a simplified atomistic formulation based on modeling elastic interactions of a binary alloy with harmonic springs whose equilibrium length is species dependent. It is demonstrated that the continuum limit for the strain field are the usual equations of linear elasticity for alloys and that they correctly capture the coarse-grained behavior of the displacement field. In addition, it is established that Euler-Lagrange equation of the continuum limit of the elastic energy will yield the same strain field equation. This is the same energy functional that is often used to model elastic effects in binary alloys. However, a direct calculation of the elastic energy atomistic model reveals that the continuum expression for the elastic energy is both qualitatively and quantitatively incorrect. This is because it does not take atomistic scale compositional nonuniformity into account. Importantly, this result also shows that finely mixed alloys tend to have more elastic energy than segregated systems, which is the exact opposite of predictions made by some continuum theories. It is also shown that for strained thin films the traditionally used effective misfit for alloys systematically underestimate the strain energy. In some models, this drawback is handled by including an elastic contribution to the enthalpy of mixing, which is characterized in terms of the continuum concentration. The direct calculation of the atomistic model reveals that this approach suffers serious difficulties. It is demonstrated that elastic contribution to the enthalpy of mixing is nonisotropic and scale dependent. It is also shown that such effects are present in density-functional theory calculations for the Si-Ge system. This work demonstrates that it is critical to include the microscopic arrangements in any elastic model to achieve even qualitatively correct behavior.

Influence of grain boundaries on the distribution of components in binary alloys

NASA Astrophysics Data System (ADS)

L'vov, P. E.; Svetukhin, V. V.

2017-12-01

Based on the free-energy density functional method (the Cahn-Hilliard equation), a phenomenological model that describes the influence of grain boundaries on the distribution of components in binary alloys has been developed. The model is built on the assumption of the difference between the interaction parameters of solid solution components in the bulk and at the grain boundary. The difference scheme based on the spectral method is proposed to solve the Cahn-Hilliard equation with interaction parameters depending on coordinates. Depending on the ratio between the interaction parameters in the bulk and at the grain boundary, temperature, and alloy composition, the model can give rise to different types of distribution of a dissolved component, namely, either depletion or enrichment of the grain-boundary area, preferential grainboundary precipitation, competitive precipitation in the bulk and at the grain boundary, etc.

Modification of band gaps and optoelectronic properties of binary calcium chalcogenides by means of doping of magnesium atom(s) in rock-salt phase- a first principle based theoretical initiative

NASA Astrophysics Data System (ADS)

Debnath, Bimal; Sarkar, Utpal; Debbarma, Manish; Bhattacharjee, Rahul; Chattopadhyaya, Surya

2018-02-01

The band gaps and optoelectronic properties of binary calcium chalcogenide semiconductors have been modified theoretically by doping magnesium atom(s) into their respective rock-salt unit cells at some specific concentrations x = 0.0, 0.25, 0.50, 0.75 and 1.0 and confirmed such modifications by studying their structural, electronic and optical properties using DFT based FP-LAPW approach. The WC-GGA functional is used to calculate structural properties, while mBJ, B3LYP and WC-GGA are used for calculating electronic and optical properties. The concentration dependences of lattice parameter, bulk modulus and fundamental band gap for each alloy system exhibit nonlinearity. The atomic and orbital origin of different electronic states in the band structure of each compound are explored from its density of states (DOS). The microscopic origin of band gap bowing for each of the alloy systems is explored in terms of volume deformation, charge exchange and structural relaxation. The chemical bonds between the constituent atoms in each compound are found as ionic in nature. Optical properties of each specimen are calculated from its computed spectra of dielectric function, refractive index, extinction coefficient, normal incidence reflectivity, optical conductivity, optical absorption and energy loss function. Several calculated results have been compared with available experimental and other theoretical data.

Melting Experiments in the Fe-FeSi System at High Pressure

NASA Astrophysics Data System (ADS)

Ozawa, H.; Hirose, K.

2013-12-01

The principal light element in the Earth's core must reproduce the density jump at the inner core boundary (ICB). Silicon is thought to be a plausible light element in the core, and the melting phase relations in Fe-FeSi binary system at the ICB pressure are of great importance. Theoretical calculations on the Fe-FeSi binary system suggested that the difference in Si content between the outer core and the inner core would be too small to satisfy the observed density jump at the ICB [Alfè et al., 2002 EPSL], which requires other light elements in addition to silicon. Here we experimentally examined partitioning of silicon between liquid and solid iron up to 97 GPa. High pressure and temperature conditions were generated in a laser-heated diamond-anvil cell. Chemical compositions of co-existing quenched liquid and solid Fe-Si alloys were determined with a field-emission-type electron probe micro-analyzer. We used Fe-Si alloy containing 9 wt% Si as a starting material. Chemical analyses on the recovered samples from 39 and 49 GPa demonstrated the coexistence of quenched Si-depleted liquid and Si-enriched solid. In contrast, silicon partitions preferentially into liquid metal at 97 GPa, suggesting the starting composition (Fe-9wt% Si) lies on the iron-rich part of the eutectic. These results indicate the eutectic composition shifts toward FeSi between 49 and 97 GPa.

Effect of atomic disorder on the magnetic phase separation.

PubMed

Groshev, A G; Arzhnikov, A K

2018-05-10

The effect of disorder on the magnetic phase separation between the antiferromagnetic and incommensurate helical [Formula: see text] and [Formula: see text] phases is investigated. The study is based on the quasi-two-dimensional single-band Hubbard model in the presence of atomic disorder (the [Formula: see text] Anderson-Hubbard model). A model of binary alloy disorder is considered, in which the disorder is determined by the difference in energy between the host and impurity atomic levels at a fixed impurity concentration. The problem is solved within the theory of functional integration in static approximation. Magnetic phase diagrams are obtained as functions of the temperature, the number of electrons and impurity concentration with allowance for phase separation. It is shown that for the model parameters chosen, the disorder caused by impurities whose atomic-level energy is greater than that of the host atomic levels, leads to qualitative changes in the phase diagram of the impurity-free system. In the opposite case, only quantitative changes occur. The peculiarities of the effect of disorder on the phase separation regions of the quasi-two-dimensional Hubbard model are discussed.

Effect of atomic disorder on the magnetic phase separation

NASA Astrophysics Data System (ADS)

Groshev, A. G.; Arzhnikov, A. K.

2018-05-01

The effect of disorder on the magnetic phase separation between the antiferromagnetic and incommensurate helical and phases is investigated. The study is based on the quasi-two-dimensional single-band Hubbard model in the presence of atomic disorder (the Anderson–Hubbard model). A model of binary alloy disorder is considered, in which the disorder is determined by the difference in energy between the host and impurity atomic levels at a fixed impurity concentration. The problem is solved within the theory of functional integration in static approximation. Magnetic phase diagrams are obtained as functions of the temperature, the number of electrons and impurity concentration with allowance for phase separation. It is shown that for the model parameters chosen, the disorder caused by impurities whose atomic-level energy is greater than that of the host atomic levels, leads to qualitative changes in the phase diagram of the impurity-free system. In the opposite case, only quantitative changes occur. The peculiarities of the effect of disorder on the phase separation regions of the quasi-two-dimensional Hubbard model are discussed.

Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr.

PubMed

Li, H F; Xie, X H; Zheng, Y F; Cong, Y; Zhou, F Y; Qiu, K J; Wang, X; Chen, S H; Huang, L; Tian, L; Qin, L

2015-05-29

Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals.

Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr

PubMed Central

Li, H. F.; Xie, X. H.; Zheng, Y. F.; Cong, Y.; Zhou, F. Y.; Qiu, K. J.; Wang, X.; Chen, S. H.; Huang, L.; Tian, L.; Qin, L.

2015-01-01

Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals. PMID:26023878

Study of Plastic Deformation in Binary Aluminum Alloys by Internal-Friction Methods

NASA Technical Reports Server (NTRS)

Olson, E. C.; Maringer, R. E.; Marsh, L. L.; Manning, G. K.

1959-01-01

The damping capacity of several aluminum-copper alloys has been investigated during tensile elongation. This damping is shown to depend on strain rate, strain, temperature, alloy content, and heat treatment. A tentative hypothesis, based on the acceleration of solute atom diffusion by deformation-produced vacancies, is proposed to account for the observed behavior. Internal-friction maxima are observed in deformed aluminum and aluminum-copper alloys at -70 deg and -50 deg C. The peaks appear to be relatively insensitive to frequency and alloy content, but they disappear after annealing at temperatures nearing the recrystallization temperature.

Influence of alloying elements on friction and wear of copper

NASA Technical Reports Server (NTRS)

Buckley, D. H.

1972-01-01

The friction and wear characteristics were determined for copper binary alloys containing 10 atomic percent aluminum, silicon, indium, and tin. A ternary alloy containing 10 atomic percent aluminum and 5 atomic percent silicon was also examined. The effectiveness of each of the alloying elements aluminum and silicon were very effective in reducing friction. Silicon, however, also reduced wear appreciably. With lubrication, silicon, indium, and tin were all effective alloying elements in reducing friction and wear from values obtained for copper. Silicon was the most effective single element in reducing friction and wear in dry sliding and with lubrication.

Influence of the alloying effect on nickel K-shell fluorescence yield in Ni Si alloys

NASA Astrophysics Data System (ADS)

Kalayci, Y.; Agus, Y.; Ozgur, S.; Efe, N.; Zararsiz, A.; Arikan, P.; Mutlu, R. H.

2005-02-01

Alloying effects on the K-shell fluorescence yield ωK of nickel in Ni-Si binary alloy system have been studied by energy dispersive X-ray fluorescence. It is found that ωK increases from pure Ni to Ni 2Si and then decreases from Ni 2Si to NiSi. These results are discussed in terms of d-occupation number on the Ni site and it is concluded that electronic configuration as a result of p-d hybridization explain qualitatively the observed variation of ωK in Ni-Si alloys.

Decagonal quasicrystal and related crystalline phases in Mn-Ga alloys with 52 to 63 a/o Ga

NASA Astrophysics Data System (ADS)

Wu, J. S.; Kuo, K. H.

1997-03-01

A decagonal quasicrystal (DQC) and six related intermetallic phases with large unit cells have been found in binary Mn-Ga alloys with 52 to 63 at. pct Ga by means of transmission electron microscopy (TEM). As does the Al-Mn DQC, the Ga-Mn DQC also has a periodicity of 1.25 nm along its tenfold axis. However, its Mn content, determined by electron microprobe X-ray analysis (about 45 to 50 at. pct Mn), is much higher than that of the Al-Mn DQC (about 20 to 30 at. pct Mn). The compositions of the intermetallic phases are about 53, 56, 58, and 62 at. pct Ga, corresponding respectively to the unknown structures of MnGa (50.7 to 53.4 at. pct Ga), Mn5Ga6 (55 at pct Ga), Mn5Ga7 (57.9 at. pct Ga), and Mn3Ga5 (62.9 at. pct Ga) given in the binary Mn-Ga phase diagram ( Metals Hand-book, T.B. Massalski, J.L. Murray, L.H. Benneft, and H. Baker, eds., ASM, Metals Park, OH, 1986, vol. 2, p. 1144). Their lattice types have been determined by selected area electron diffraction. The ferromagnetic Mn3Ga5 is tetragonal, a=1.25 nm and c=2.50 nm; Mn5Ga7 is orthorhombic, a=4.57 nm, b=1.25 nm, and c=1.44 nm; Mn5Ga6 has two different but closely related orthorhombic unit cells, a=1.26 nm, b=1.25 nm, and c=1.48 nm as well as a=0.77 nm, b=1.25 nm, and c=2.36 nm; MnGa also has two different and related unit cells, one orthorhombic with a=2.04 nm, b=1.25 nm, and c=1.48 nm and the other monoclinic with a=2.59 nm, b=1.25 nm, c=1.15 nm, and β≈=110 deg. All these orthorhombic phases have b=1.25 nm, being the same as the periodicity along the tenfold axis of the Ga-Mn and Al-Mn DQCs. Moreover, all these six intermetallic phases give electron diffraction patterns displaying a pseudo-tenfold distribution of strong diffraction spots and are considered to be crystalline approximants of the Ga-Mn DQC.

Effect of solutes in binary columbium /Nb/ alloys on creep strength

NASA Technical Reports Server (NTRS)

Klein, M. J.; Metcalfe, A. G.

1973-01-01

The effect of seven different solutes in binary columbium (Nb) alloys on creep strength was determined from 1400 to 3400 F for solute concentrations to 20 at.%, using a new method of creep-strength measurement. The technique permits rapid determination of approximate creep strength over a large temperature span. All of the elements were found to increase the creep strength of columbium except tantalum. This element did not strengthen columbium until the concentration exceeded 10 at.%. Hafnium, zirconium, and vanadium strengthed columbium most at low temperatures and concentrations, whereas tungsten, molybdenum, and rhenium contributed more to creep strength at high temperatures and concentrations.

Thermodynamic assessments and inter-relationships between systems involving Al, Am, Ga, Pu, and U

NASA Astrophysics Data System (ADS)

Perron, A.; Turchi, P. E. A.; Landa, A.; Oudot, B.; Ravat, B.; Delaunay, F.

2016-12-01

A newly developed self-consistent CALPHAD thermodynamic database involving Al, Am, Ga, Pu, and U is presented. A first optimization of the slightly characterized Am-Al and completely unknown Am-Ga phase diagrams is proposed. To this end, phase diagram features as crystal structures, stoichiometric compounds, solubility limits, and melting temperatures have been studied along the U-Al → Pu-Al → Am-Al, and U-Ga → Pu-Ga → Am-Ga series, and the thermodynamic assessments involving Al and Ga alloying are compared. In addition, two distinct optimizations of the Pu-Al phase diagram are proposed to account for the low temperature and Pu-rich region controversy. The previously assessed thermodynamics of the other binary systems (Am-Pu, Am-U, Pu-U, and Al-Ga) is also included in the database and is briefly described in the present work. Finally, predictions on phase stability of ternary and quaternary systems of interest are reported to check the consistency of the database.

Numerical formulation for the prediction of solid/liquid change of a binary alloy

NASA Technical Reports Server (NTRS)

Schneider, G. E.; Tiwari, S. N.

1990-01-01

A computational model is presented for the prediction of solid/liquid phase change energy transport including the influence of free convection fluid flow in the liquid phase region. The computational model considers the velocity components of all non-liquid phase change material control volumes to be zero but fully solves the coupled mass-momentum problem within the liquid region. The thermal energy model includes the entire domain and uses an enthalpy like model and a recently developed method for handling the phase change interface nonlinearity. Convergence studies are performed and comparisons made with experimental data for two different problem specifications. The convergence studies indicate that grid independence was achieved and the comparison with experimental data indicates excellent quantitative prediction of the melt fraction evolution. Qualitative data is also provided in the form of velocity vector diagrams and isotherm plots for selected times in the evolution of both problems. The computational costs incurred are quite low by comparison with previous efforts on solving these problems.

Thermodynamic assessments and inter-relationships between systems involving Al, Am, Ga, Pu, and U

DOE PAGES

Perron, A.; Turchi, P. E. A.; Landa, A.; ...

2016-12-01

We present a newly developed self-consistent CALPHAD thermodynamic database involving Al, Am, Ga, Pu, and U. A first optimization of the slightly characterized Am-Al and completely unknown Am-Ga phase diagrams is proposed. To this end, phase diagram features as crystal structures, stoichiometric compounds, solubility limits, and melting temperatures have been studied along the U-Al → Pu-Al → Am-Al, and U-Ga → Pu-Ga → Am-Ga series, and the thermodynamic assessments involving Al and Ga alloying are compared. In addition, two distinct optimizations of the Pu-Al phase diagram are proposed to account for the low temperature and Pu-rich region controversy. We includedmore » the previously assessed thermodynamics of the other binary systems (Am-Pu, Am-U, Pu-U, and Al-Ga) in the database and is briefly described in the present work. In conclusion, predictions on phase stability of ternary and quaternary systems of interest are reported to check the consistency of the database.« less

Theoretical studies of aluminum and aluminide alloys using CALPHAD and first-principles approach

NASA Astrophysics Data System (ADS)

Jiang, Chao

Heat-treatable aluminum alloys have been widely used in the automobile and aerospace industries as structural materials due to their light weight and high strength. To study the age-hardening process in heat-treatable aluminum alloys, the Gibbs energies of the strengthening metastable phases, e.g. theta ' and theta″, are critical. However, those data are not included in the existing thermodynamic databases for aluminum alloys due to the semi-empirical nature of the CALPHAD approach. In the present study, the thermodynamics of the Al-Cu system, the pivotal age-hardening system, is remodeled using a combined CALPHAD and first-principles approach. The formation enthalpies and vibrational formation entropies of the stable and metastable phases in the Al-Cu system are provided by first-principles calculations. Special Quasirandom Structures (SQS's) are applied to model the substitutionally random fee and bee alloys. SQS's for binary bee alloys are developed and tested in the present study. Finally, a self-consistent thermodynamic description of the Al-Cu system including the two metastable theta″ and theta' phases is obtained. During welding of heat-treatable aluminum alloys, a detrimental phenomenon called constitutional liquation, i.e. the local eutectic melting of second-phase particles in a matrix at temperatures above the eutectic temperature but below the solidus of the alloy, may occur in the heat-affected zone (HAZ). In the present study, diffusion code DICTRA coupled with realistic thermodynamic and kinetic databases is used to simulate the constitutional liquation in the model Al-Cu system. The simulated results are in quantitative agreement with experiments. The critical heating rate to avoid constitutional liquation is also determined through computer simulations. Besides the heat-treatable aluminum alloys, intermetallic compounds based on transition metal aluminides, e.g. NiAl and FeAl, are also promising candidates for the next-generation of high-temperature structural materials for aerospace applications due to their high melting temperature and good oxidation resistance. Many important properties of B2 aluminides are governed by the existences of point defects. In the present study, Special Quasirandom Structures (SQS's) are developed to model non-stoichiometric B2 compounds containing large concentrations of constitutional point defects. The SQS's are then applied to study B2 NiAl. The first-principles SQS results provide formation enthalpies, equilibrium lattice parameters and elastic constants of B2 NiAl which agree satisfactorily with the existing experimental data in the literature. It is unambiguously shown that, at T = 0K and zero pressure, Ni vacancies and antisite Ni atoms are the energetically favorable point defects in Al-rich and Ni-rich B2 NiAl, respectively. Remarkably, it is predicted that high defect concentrations can lead to structural instability of B2 NiAl, which explains well the martensitic transformation observed in this compound at high Ni concentrations.

Oxidation behaviour of zirconium alloys and their precipitates - A mechanistic study

NASA Astrophysics Data System (ADS)

Proff, C.; Abolhassani, S.; Lemaignan, C.

2013-01-01

The precipitate oxidation behaviour of binary zirconium alloys containing 1 wt.% Fe, Ni, Cr or 0.6 wt.% Nb was characterised in TEM on FIB prepared transverse sections of the oxide and reported in previous studies [1,2]. In the present study the following alloys: Zr1%Cu, Zr0.5%Cu0.5%Mo and pure Zr are analysed to add to the available information. In all cases, the observed precipitate oxidation behaviour in the oxide close to the metal-oxide interface could be described either with delayed oxidation with respect to the matrix or simultaneous oxidation as the surrounding zirconium matrix. Attempt was made to explain these observations, with different parameters such as precipitate size and structure, composition and thermodynamic properties. It was concluded that the thermodynamics with the new approach presented could explain most precisely their behaviour, considering the precipitate stoichiometry and the free energy of oxidation of the constituting elements. The surface topography of the oxidised materials, as well as the microstructure of the oxide presenting microcracks have been examined. A systematic presence of microcracks above the precipitates exhibiting delayed oxidation has been found; the height of these crack calculated using the Pilling-Bedworth ratios of different phases present, can explain their origin. The protrusions at the surface in the case of materials containing large precipitates can be unambiguously correlated to the presence of these latter, and the height can be correlated to the Pilling-Bedworth ratios of the phases present as well as the diffusion of the alloying elements to the surface and their subsequent oxidation. This latter behaviour was much more considerable in the case of Fe and Cu with Fe showing systematically diffusion to the outer surface.

PHASE DIAGRAM FOR THE SYSTEM TITANIUM-TIN (in Russian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kornilov, I.I.; Nartova, T.T.

1960-03-01

Differential thermal analysis, microstructural analyses, and determinations of hardness values and electric resistance were used to construct a diagram of state for the binary system Ti-Sn up to the composition of the compound Ti/sub 3/Sn (from 0 to 25 at.% Sn). Analyses of the thermograms showed that all conversions proceeding with the absorption of heat could be detected on the heating curves. Tin lowers the temperature of conversion of titunium with 5.0 at.% tin first to a minimum at 860 tained C which then increases to 890 tained C at higher tin contents. A peritectoid reaction ( alpha / submore » 2/ were ob ore resistant t + ) takes place with a conversion temperature at 890 tained C. A HF-HNO/sub 3/-glycerin etch showed a single-phase homogeneous structure of an alpha -solid solution with alloys containing up to 9 at.% Q. The amount of a second -phase increases with increasing tin content until a single-phase structure of a -solid solution of the compound Ti/sub 3/Sn is noted with alloys containing 23 to 25 at.% Sn. Alloys containing 8 to 22.5 at.% Sn undergo a peritectoid reaction, at a temperature of 890 tained C as shown by thermal analyses and by microstructural analyses of samples quenched frorn above and below the conversion temperature. A study of the microstructure of quenched alloys showed that the solubility of tin in ore resistant t -titanium increases from 8 at.% Sn at 890 tained C to 10.5 at.% Sn at 1100 tained C. X-ray analyses of annealed samples of alloy showed only the lines of an alpha solid solution for 5, 8, 9 at.% Sn, a -solid solution for 23 at.% Sn (close to the composition Ti/sub 3/Sn), and an alpha and mixed phase for a 15 at.% Sn. Vickers hardness numbers were determined with a diamond pyramid at a loading of 10 kg. The hardness increases smoothly with increasing tin content to a maximum at the saturation solubility of the tin in the alpha - or ore resistant t -solid solution. The hardness decreases smoothly with the appearance of the -phase until it attains a minimum at the composition of the compound Ti/sub 3/Sn. The specific electric resistance increases with an increase of tin in the solid solution of alpha -titanium. The rate of increase of the specific electric resistance decreases markedly with the appearance of the -phase. The electric resistance of an alloy with 14.3 at.% Sn was studied as a function of temperature from room temperature to 1100 tained C in special vacuum equipment. A sharp drop in electric resistance a; 890 tained C confirmed the existence of a peritectoid reaction in the system Ti-Sn. (TTT)« less

Investigations on Laser Beam Welding of Different Dissimilar Joints of Steel and Aluminum Alloys for Automotive Lightweight Construction

NASA Astrophysics Data System (ADS)

Seffer, Oliver; Pfeifer, Ronny; Springer, André; Kaierle, Stefan

Due to the enormous potential of weight saving, and the consequential reduction of pollutant emissions, the use of hybrid components made of steel and aluminum alloys is increasing steadily, especially concerning automotive lightweight construction. However, thermal joining of steel and aluminum is still being researched, due to a limited solubility of the binary system of iron and aluminum causing the formation of hard and brittle intermetallic phases, which decrease the strength and the formability of the dissimilar seam. The presented results show the investigation of laser beam welding for joining different dissimilar hybrid components of the steel materials HX220LAD+Z100, 22MnB5+AS150 and 1.4301, as well as the aluminum alloy AA6016-T4 as a lap joint. Among other things, the influences of the energy per unit length, the material grade, the sheet thickness t, the weld type (lap weld, fillet weld) and the arrangement of the base materials in a lap joint (aluminum-sided irradiation, steel-sided irradiation) on the achievable strengths are analyzed. The characterization of the dissimilar joints includes tensile shear tests and metallographic analyses, depending on the energy per unit length.

MPS solidification model. Analysis and calculation of macrosegregation in a casting ingot

NASA Technical Reports Server (NTRS)

Poirier, D. R.; Maples, A. L.

1985-01-01

Work performed on several existing solidification models for which computer codes and documentation were developed is presented. The models describe the solidification of alloys in which there is a time varying zone of coexisting solid and liquid phases; i.e., the S/L zone. The primary purpose of the models is to calculate macrosegregation in a casting or ingot which results from flow of interdendritic liquid in this S/L zone during solidification. The flow, driven by solidification contractions and by gravity acting on density gradients in the interdendritic liquid, is modeled as flow through a porous medium. In Model 1, the steady state model, the heat flow characteristics are those of steady state solidification; i.e., the S/L zone is of constant width and it moves at a constant velocity relative to the mold. In Model 2, the unsteady state model, the width and rate of movement of the S/L zone are allowed to vary with time as it moves through the ingot. Each of these models exists in two versions. Models 1 and 2 are applicable to binary alloys; models 1M and 2M are applicable to multicomponent alloys.

Microstructure and Interfacial Reactions During Vacuum Brazing of Stainless Steel to Titanium Using Ag-28 pct Cu Alloy

NASA Astrophysics Data System (ADS)

Laik, A.; Shirzadi, A. A.; Sharma, G.; Tewari, R.; Jayakumar, T.; Dey, G. K.

2015-02-01

Microstructural evolution and interfacial reactions during vacuum brazing of grade-2 Ti and 304L-type stainless steel (SS) using eutectic alloy Ag-28 wt pct Cu were investigated. A thin Ni-depleted zone of -Fe(Cr, Ni) solid solution formed on the SS-side of the braze zone (BZ). Cu from the braze alloy, in combination with the dissolved Fe and Ti from the base materials, formed a layer of ternary compound , adjacent to Ti in the BZ. In addition, four binary intermetallic compounds, CuTi, CuTi, CuTi and CuTi formed as parallel contiguous layers in the BZ. The unreacted Ag solidified as islands within the layers of CuTi and CuTi. Formation of an amorphous phase at certain locations in the BZ could be revealed. The -Ti(Cu) layer, formed due to diffusion of Cu into Ti-based material, transformed to an -Ti + CuTi eutectoid with lamellar morphology. Tensile test showed that the brazed joints had strength of 112 MPa and failed at the BZ. The possible sequence of events that led to the final microstructure and the mode of failure of these joints were delineated.

Primary radiation damage of an FeCr alloy under pressure: Atomistic simulation

NASA Astrophysics Data System (ADS)

Tikhonchev, M. Yu.; Svetukhin, V. V.

2017-05-01

The primary radiation damage of a binary FeCr alloy deformed by applied mechanical loading is studied by an atomistic molecular dynamics simulation. Loading is simulated by specifying an applied pressure of 0.25, 1.0, and 2.5 GPa of both signs. Hydrostatic and uniaxial loading is considered along the [001], [111], [112], and [210] directions. The influence of loading on the energy of point defect formation and the threshold atomic displacement energy in single-component bcc iron is investigated. The 10-keV atomic displacement cascades in a "random" binary Fe-9 at % Cr alloy are simulated at an initial temperature of 300 K. The number of the point defects generated in a cascade is estimated, and the clustering of point defects and the spatial orientation of interstitial configurations are analyzed. Our results agree with the results of other researchers and supplement them.

Thermodynamic properties of calcium-bismuth alloys determined by emf measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, H; Boysen, DA; Bradwell, DJ

2012-01-15

The thermodynamic properties of Ca-Bi alloys were determined by electromotive force (emf) measurements to assess the suitability of Ca-Bi electrodes for electrochemical energy storage applications. Emf was measured at ambient pressure as a function of temperature between 723 K and 1173 K using a Ca(s)vertical bar CaF2(s)vertical bar Ca(in Bi) cell for twenty different Ca-Bi alloys spanning the entire range of composition from chi(Ca) = 0 to 1. Reported are the temperature-independent partial molar entropy and enthalpy of calcium for each Ca-Bi alloy. Also given are the measured activities of calcium, the excess partial molar Gibbs energy of bismuth estimatedmore » from the Gibbs-Duhem equation, and the integral change in Gibbs energy for each Ca-Bi alloy at 873 K, 973 K, and 1073 K. Calcium activities at 973 K were found to be nearly constant at a value a(Ca) = 1 x 10(-8) over the composition range chi(Ca) = 0.32-0.56, yielding an emf of similar to 0.77 V. Above chi(Ca) = 0.62 and coincident with Ca5Bi3 formation, the calcium activity approached unity. The Ca-Bi system was also characterized by differential scanning calorimetry over the entire range of composition. Based upon these data along with the emf measurements, a revised Ca-Bi binary phase diagram is proposed. (C) 2011 Elsevier Ltd. All rights reserved.« less

Acoustic emission from a solidifying aluminum-lithium alloy

NASA Technical Reports Server (NTRS)

Henkel, D. P.; Wood, J. D.

1992-01-01

Physical phenomena associated with the solidification of an AA2090 Al-Li alloy have been characterized by AE methods. Repeatable patterns of AE activity as a function of solidification time are recorded and explained for ultrahigh-purity (UHP) aluminum and an Al-4.7 wt pct Cu binary alloy, in addition to the AA2090 Al-Li alloy, by the complementary utilization of thermal, AE, and metallographic methods. One result shows that the solidification of UHP aluminum produces one discrete period of high AE activity as the last 10 percent of solid forms.

Plastic behavior of two-phase intermetallic compounds based on L1{sub 2}-type (Al,Cr){sub 3}Ti

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, J.Y.; Wee, D.M.; Oh, M.H.

Plastic behavior of two-phase intermetallic compounds based on L1{sub 2}-type (Al,Cr){sub 3}Ti was investigated using compression test at R.T. and 77K. L1{sub 2} single phase alloys and two-phase alloys consisting of mainly L1{sub 2} phase and a few or 20% (mole percent) second phases were selected from Al-Ti-Cr phase diagram. In general, compared with L1{sub 2} single phase, two-phase alloys consisting of 20% second phase showed relatively high yield strength and poor ductility. Among the alloys, however, Al-21Ti-23Cr alloy consisting of 20% Cr{sub 2}Al phase showed available ductility as well as high yield strength. Plastic behavior of L1{sub 2} singlemore » phase alloys and two-phase alloys consisting of a few Cr{sub 2}Al was also investigated. Homogenization of arc melted ingots substantially reduced the amount of second phases but introduced extensive pore. When Cr content increased in L1{sub 2} single phase alloys after the homogenization, the volume fraction of pores in the alloys decreased, and no residual porosity was observed in two-phase alloys consisting of a few% Cr{sub 2}Al phase. Environmental effect on the ductility of the alloys was investigated using compression test at different strain rates (1.2 {times} 10{sup {minus}4}/s and 1.2 {times} 10{sup {minus}2}/s). Environmental embrittlement was least significant in Al-25Ti-10Cr alloy consisting of L1{sub 2} single phase among the alloys tested in this study. However, based on the combined estimation of the pore formation, environmental embrittlement and ingot cast structure, it could be supposed that Al-21Ti-23Cr alloy consisting of 20% Cr{sub 2}Al as a second phase is expected to show the best tensile elongation behavior among the materials tested.« less

Thermodynamic analysis of binary Fe{sub 85}B{sub 15} to quinary Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1} alloys for primary crystallizations of α-Fe in nanocrystalline soft magnetic alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takeuchi, A., E-mail: takeuchi@imr.tohoku.ac.jp; Zhang, Y.; Takenaka, K.

2015-05-07

Fe-based Fe{sub 85}B{sub 15}, Fe{sub 84}B{sub 15}Cu{sub 1}, Fe{sub 82}Si{sub 2}B{sub 15}Cu{sub 1}, Fe{sub 85}Si{sub 2}B{sub 12}Cu{sub 1}, and Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1} (NANOMET{sup ®}) alloys were experimental and computational analyzed to clarify the features of NANOMET that exhibits high saturation magnetic flux density (B{sub s}) nearly 1.9 T and low core loss than conventional nanocrystalline soft magnetic alloys. The X-ray diffraction analysis for ribbon specimens produced experimentally by melt spinning from melts revealed that the samples were almost formed into an amorphous single phase. Then, the as-quenched samples were analyzed with differential scanning calorimeter (DSC) experimentally for exothermicmore » enthalpies of the primary and secondary crystallizations (ΔH{sub x1} and ΔH{sub x2}) and their crystallization temperatures (T{sub x1} and T{sub x2}), respectively. The ratio ΔH{sub x1}/ΔH{sub x2} measured by DSC experimentally tended to be extremely high for the Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1} alloy, and this tendency was reproduced by the analysis with commercial software, Thermo-Calc, with database for Fe-based alloys, TCFE7 for Gibbs free energy (G) assessments. The calculations exhibit that a volume fraction (V{sub f}) of α-Fe tends to increase from 0.56 for the Fe{sub 85}B{sub 15} to 0.75 for the Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1} alloy. The computational analysis of the alloys for G of α-Fe and amorphous phases (G{sub α-Fe} and G{sub amor}) shows that a relationship G{sub α-Fe} ∼ G{sub amor} holds for the Fe{sub 85}Si{sub 2}B{sub 12}Cu{sub 1}, whereas G{sub α-Fe} < G{sub amor} for the Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1} alloy at T{sub x1} and that an extremely high V{sub f} = 0.75 was achieved for the Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1} alloy by including 2.8 at. % Si and 4.5 at. % P into α-Fe. These computational results indicate that the Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1} alloy barely forms amorphous phase, which, in turn, leads to high V{sub f} and resultant high B{sub s}.« less

Dentritic morphology and microsegregation in directionally solidified superalloy, PWA-1480, single crystal: Effect of gravity; center director's discretionary fund report

NASA Technical Reports Server (NTRS)

Tewari, S. N.; Kumar, M. Vijaya; Lee, J. E.; Curreri, P. A.

1990-01-01

Primary dendrite spacings, secondary dendrite spacings, and microsegregation have been examined in PWA-1480 single crystal specimens which were directionally solidified during parabolic maneuvers on the KC-135 aircraft. Experimentally observed growth rate and thermal gradient dependence of primary dendrite spacings are in good agreement with predictions from dendrite growth models for binary alloys. Secondary dendrite coarsening kinetics show a reasonable fit with the predictions from an analytical model proposed by Kirkwood for a binary alloy. The partition coefficients of tantalum, titanium, and aluminum are observed to be less than unity, while that for tungsten and cobalt are greater than unity. This is qualitatively similar to the nickel base binaries. Microsegregation profiles experimentally observed for PWA-1480 superalloy show a good fit with Bower, Brody, and Flemings model developed for binary alloys. Transitions in gravity levels do not appear to affect primary dendrite spacings. A trend of decreased secondary arm spacings with transition from high gravity to the low gravity period was observed at a growth speed of 0.023 cm s(exp -1). However, definite conclusions can only be drawn by experiments at lower growth speeds which make it possible to examine the side-branch coarsening kinetics over a longer duration. Such experiments, not possible due to the insufficient low-gravity time of the KC-135, may be carried out in the low-gravity environment of space.

PROCESS FOR DISSOLVING BINARY URANIUM-ZIRCONIUM OR ZIRCONIUM-BASE ALLOYS

DOEpatents

Jonke, A.A.; Barghusen, J.J.; Levitz, N.M.

1962-08-14

A process of dissolving uranium-- zirconium and zircaloy alloys, e.g. jackets of fuel elements, with an anhydrous hydrogen fluoride containing from 10 to 32% by weight of hydrogen chloride at between 400 and 450 deg C., preferably while in contact with a fluidized inert powder, such as calcium fluoride is described. (AEC)

A new approximate sum rule for bulk alloy properties

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Ferrante, John

1991-01-01

A new, approximate sum rule is introduced for determining bulk properties of multicomponent systems, in terms of the pure components properties. This expression is applied for the study of lattice parameters, cohesive energies, and bulk moduli of binary alloys. The correct experimental trends (i.e., departure from average values) are predicted in all cases.

Modeling of Disordered Binary Alloys Under Thermal Forcing: Effect of Nanocrystallite Dissociation on Thermal Expansion of AuCu3

NASA Astrophysics Data System (ADS)

Kim, Y. W.; Cress, R. P.

2016-11-01

Disordered binary alloys are modeled as a randomly close-packed assembly of nanocrystallites intermixed with randomly positioned atoms, i.e., glassy-state matter. The nanocrystallite size distribution is measured in a simulated macroscopic medium in two dimensions. We have also defined, and measured, the degree of crystallinity as the probability of a particle being a member of nanocrystallites. Both the distribution function and the degree of crystallinity are found to be determined by alloy composition. When heated, the nanocrystallites become smaller in size due to increasing thermal fluctuation. We have modeled this phenomenon as a case of thermal dissociation by means of the law of mass action. The crystallite size distribution function is computed for AuCu3 as a function of temperature by solving some 12 000 coupled algebraic equations for the alloy. The results show that linear thermal expansion of the specimen has contributions from the temperature dependence of the degree of crystallinity, in addition to respective thermal expansions of the nanocrystallites and glassy-state matter.

Predicted trends of core-shell preferences for 132 late transition-metal binary-alloy nanoparticles.

PubMed

Wang, Lin-Lin; Johnson, Duane D

2009-10-07

Transition-metal alloyed nanoparticles with core-shell features (shell enrichment by one of the metals) are becoming ubiquitous, from (electro-)catalysis to biomedical applications, due to their size control, performance, biocompatibility, and cost. We investigate 132 binary-alloyed nanoparticle systems (groups 8 to 11 in the Periodic Table) using density functional theory (DFT) and systematically explore their segregation energies to determine core-shell preferences. We find that core-shell preferences are generally described by two independent factors: (1) cohesive energy (related to vapor pressure) and (2) atomic size (quantified by the Wigner-Seitz radius), and the interplay between them. These independent factors are shown to provide general trends for the surface segregation preference for atoms in nanoparticles, as well as semi-infinite surfaces, and give a simple correlation (a "design map") for the alloying and catalytic behavior. Finally, we provide a universal description of core-shell preference via tight-binding theory (band-energy differences) that (i) quantitatively reproduces the DFT segregation energies and (ii) confirms the electronic origins and correlations for core-shell behavior.

In Situ Study of Microstructure Evolution in Solidification of Hypereutectic Al-Si Alloys with Application of Thermal Analysis and Neutron Diffraction

NASA Astrophysics Data System (ADS)

Sediako, Dimitry G.; Kasprzak, Wojciech

2015-09-01

Understanding of the kinetics of solid-phase evolution in solidification of hypereutectic aluminum alloys is a key to control their as-cast microstructure and resultant mechanical properties, and in turn, to enhance the service characteristics of actual components. This study was performed to evaluate the solidification kinetics for three P-modified hypereutectic Al-19 pct Si alloys: namely, Al-Si binary alloy and with the subsequent addition of 2.8 pct Cu and 2.8 pct Cu + 0.7 pct Mg. Metallurgical evaluation included thermodynamic calculations of the solidification process using the FactSage™ 6.2 software package, as well as experimental thermal analysis, and in situ neutron diffraction. The study revealed kinetics of solid α-Al, solid Si, Al2Cu, and Mg2Si evolution, as well as the individual effects of Cu and Mg alloying additions on the solidification path of the Al-Si system. Various techniques applied in this study resulted in some discrepancies in the results. For example, the FactSage computations, in general, resulted in 281 K to 286 K (8 °C to 13 °C) higher Al-Si eutectic temperatures than the ones recorded in the thermal analysis, which are also ~278 K (~5 °C) higher than those observed in the in situ neutron diffraction. None of the techniques can provide a definite value for the solidus temperature, as this is affected by the chosen calculation path [283 K to 303 K (10 °C to 30 °C) higher for equilibrium solidification vs non-equilibrium] for the FactSage analysis; and further complicated by evolution of secondary Al-Cu and Mg-Si phases that commenced at the end of solidification. An explanation of the discrepancies observed and complications associated with every technique applied is offered in the paper.

Two-dimensional time-resolved X-ray diffraction study of liquid/solid fraction and solid particle size in Fe-C binary system with an electrostatic levitator furnace

NASA Astrophysics Data System (ADS)

Yonemura, M.; Okada, J.; Watanabe, Y.; Ishikawa, T.; Nanao, S.; Shobu, T.; Toyokawa, H.

2013-03-01

Liquid state provides functions such as matter transport or a reaction field and plays an important role in manufacturing processes such as refining, forging or welding. However, experimental procedures are significantly difficult for an observation of solidification process of iron and iron-based alloys in order to identify rapid transformations subjected to fast temperature evolution. Therefore, in order to study the solidification in iron and iron-based alloys, we considered a combination of high energy X-ray diffraction measurements and an electrostatic levitation method (ESL). In order to analyze the liquid/solid fraction, the solidification of melted spherical specimens was measured at a time resolution of 0.1 seconds during rapid cooling using the two-dimensional time-resolved X-ray diffraction. Furthermore, the observation of particle sizes and phase identification was performed on a trial basis using X-ray small angle scattering with X-ray diffraction.

Friction Stir Welding of Stainless Steel to Al Alloy: Effect of Thermal Condition on Weld Nugget Microstructure

NASA Astrophysics Data System (ADS)

Ghosh, M.; Gupta, R. K.; Husain, M. M.

2014-02-01

Joining of dissimilar materials is always a global challenge. Sometimes it is unavoidable to execute multifarious activities by a single component. In the present investigation, 6061 aluminum alloy and 304 stainless steel were joined by friction stir welding (FSW) at different tool rotational rates. Welded joints were characterized in optical and scanning electron microscopes. Reaction products in the stirring zone (SZ) were confirmed through X-ray diffraction. Joint strength was evaluated by tensile testing. It was found that the increment in average heat input and temperature at the weld nugget (WN) facilitated iron enrichment near the interface. Enhancement in the concentration of iron shifted the nature of intermetallics from the Fe2Al5 to Fe-rich end of the Fe-Al binary phase diagram. The peak microhardness and ultimate tensile strength were found to be maxima at the intermediate tool rotational rate, where Fe3Al and FeAl2 appeared along with Fe2Al5.

Low-gravity fluid dynamics and transport phenomena. Progress in Astronautics and Aeronautics. Vol. 130

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koster, J.N.; Sani, R.L.

1990-01-01

Various papers on low-gravity fluid dynamics and transport phenomena are presented. Individual topics addressed include: fluid management in low gravity, nucleate pool boiling in variable gravity, application of energy-stability theory to problems in crystal growth, thermosolutal convection in liquid HgCdTe near the liquidus temperature, capillary surfaces in microgravity, thermohydrodynamic instabilities and capillary flows, interfacial oscillators, effects of gravity jitter on typical fluid science experiments and on natural convection in a vertical cylinder. Also discussed are: double-diffusive convection and its effects under reduced gravity, segregation and convection in dendritic alloys, fluid flow and microstructure development, analysis of convective situations with themore » Soret effect, complex natural convection in low Prandtl number metals, separation physics, phase partitioning in reduced gravity, separation of binary alloys with miscibility gap in the melt, Ostwald ripening in liquids, particle cloud combustion in reduced gravity, opposed-flow flame spread with implications for combustion at microgravity.« less

Search for the elusive magnetic state of hexagonal iron: The antiferromagnetic Fe71Ru29 hcp alloy

NASA Astrophysics Data System (ADS)

Petrillo, C.; Postorino, P.; Orecchini, A.; Sacchetti, F.

2018-03-01

The magnetic states of iron and their dependence on crystal structure represent an important case study for the physics of magnetism and its role in fundamental and applied science, including geophysical sciences. hcp iron is the most elusive structure as it exists only at high pressure but, at the same time, it is expected to be stable up to very high temperature. Exploring the magnetic state of pure Fe at high pressure is difficult and no conclusive results have been obtained. Simple binary alloys where the hexagonal phase of Fe is stabilized, offer a more controllable alternative to investigate iron magnetism. We carried out a neutron diffraction experiment on hcp Fe71Ru29 disordered alloy as a function of temperature. Fe in the hexagonal lattice of this specific alloy results to be antiferromagnetically aligned with a rather complex structure and a small magnetic moment. The temperature dependence suggests a Néel temperature TN = 124 ± 10 K, a value consistent with the low magnetic moment of 1.04 ± 0.10 μB obtained from the diffraction data that also suggest a non-commensurate magnetic structure with magnetic moments probably aligned along the c axis. The present data provide evidence for magnetic ordering in hcp Fe and support the theoretical description of magnetism of pure Fe at high pressure.

Effects of Growth Rates and Compositions on Dendrite Arm Spacings in Directionally Solidified Al-Zn Alloys

NASA Astrophysics Data System (ADS)

Acer, Emine; Çadırlı, Emin; Erol, Harun; Kaya, Hasan; Gündüz, Mehmet

2017-12-01

Dendritic spacing can affect microsegregation profiles and also the formation of secondary phases within interdendritic regions, which influences the mechanical properties of cast structures. To understand dendritic spacings, it is important to understand the effects of growth rate and composition on primary dendrite arm spacing ( λ 1) and secondary dendrite arm spacing ( λ 2). In this study, aluminum alloys with concentrations of (1, 3, and 5 wt pct) Zn were directionally solidified upwards using a Bridgman-type directional solidification apparatus under a constant temperature gradient (10.3 K/mm), resulting in a wide range of growth rates (8.3-165.0 μm/s). Microstructural parameters, λ 1 and λ 2 were measured and expressed as functions of growth rate and composition using a linear regression analysis method. The values of λ 1 and λ 2 decreased with increasing growth rates. However, the values of λ 1 increased with increasing concentration of Zn in the Al-Zn alloy, but the values of λ 2 decreased systematically with an increased Zn concentration. In addition, a transition from a cellular to a dendritic structure was observed at a relatively low growth rate (16.5 μm/s) in this study of binary alloys. The experimental results were compared with predictive theoretical models as well as experimental works for dendritic spacing.

Phase diagram and structural evolution of tin/indium (Sn/In) nanosolder particles: from a non-equilibrium state to an equilibrium state.

PubMed

Shu, Yang; Ando, Teiichi; Yin, Qiyue; Zhou, Guangwen; Gu, Zhiyong

2017-08-31

A binary system of tin/indium (Sn/In) in the form of nanoparticles was investigated for phase transitions and structural evolution at different temperatures and compositions. The Sn/In nanosolder particles in the composition range of 24-72 wt% In were synthesized by a surfactant-assisted chemical reduction method under ambient conditions. The morphology and microstructure of the as-synthesized nanoparticles were analyzed by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and X-ray diffraction (XRD). HRTEM and SAED identified InSn 4 and In, with some Sn being detected by XRD, but no In 3 Sn was observed. The differential scanning calorimetry (DSC) thermographs of the as-synthesized nanoparticles exhibited an endothermic peak at around 116 °C, which is indicative of the metastable eutectic melting of InSn 4 and In. When the nanosolders were subjected to heat treatment at 50-225 °C, the equilibrium phase In 3 Sn appeared while Sn disappeared. The equilibrium state was effectively attained at 225 °C. A Tammann plot of the DSC data of the as-synthesized nanoparticles indicated that the metastable eutectic composition is about 62% In, while that of the DSC data of the 225 °C heat-treated nanoparticles yielded a eutectic composition of 54% In, which confirmed the attainment of the equilibrium state at 225 °C. The phase boundaries estimated from the DSC data of heat-treated Sn/In nanosolder particles matched well with those in the established Sn-In equilibrium phase diagram. The phase transition behavior of Sn/In nanosolders leads to a new understanding of binary alloy particles at the nanoscale, and provides important information for their low temperature soldering processing and applications.

Linear chirp phase perturbing approach for finding binary phased codes

NASA Astrophysics Data System (ADS)

Li, Bing C.

2017-05-01

Binary phased codes have many applications in communication and radar systems. These applications require binary phased codes to have low sidelobes in order to reduce interferences and false detection. Barker codes are the ones that satisfy these requirements and they have lowest maximum sidelobes. However, Barker codes have very limited code lengths (equal or less than 13) while many applications including low probability of intercept radar, and spread spectrum communication, require much higher code lengths. The conventional techniques of finding binary phased codes in literatures include exhaust search, neural network, and evolutionary methods, and they all require very expensive computation for large code lengths. Therefore these techniques are limited to find binary phased codes with small code lengths (less than 100). In this paper, by analyzing Barker code, linear chirp, and P3 phases, we propose a new approach to find binary codes. Experiments show that the proposed method is able to find long low sidelobe binary phased codes (code length >500) with reasonable computational cost.

Surface and cut-edge corrosion behavior of Zn-Mg-Al alloy-coated steel sheets as a function of the alloy coating microstructure

NASA Astrophysics Data System (ADS)

Oh, Min-Suk; Kim, Sang-Heon; Kim, Jong-Sang; Lee, Jae-Won; Shon, Je-Ha; Jin, Young-Sool

2016-01-01

The effects of Mg and Al content on the microstructure and corrosion resistance of hot-dip Zn-Mg-Al alloycoated steel sheets were investigated. Pure Zn and Zn-based alloy coatings containing Mg (0-5 wt%) and Al (0.2-55 wt%) were produced by a hot-dip galvanizing method. Mg and Al addition induced formation of intermetallic microstructures, like primary Zn, Zn/MgZn2 binary eutectic, dendric Zn/Al eutectoid, and Zn/Al/MgZn2/ternary eutectic structures in the coating layer. MgZn2-related structures (Zn/MgZn2, Zn/Al/MgZn2, MgZn2) played an important role in increasing the corrosion resistance of Zn-Mg-Al alloy-coated steel sheets. Zn-3%Mg-2.5%Al coating layer containing a large volume of lamellar-shaped Zn/MgZn2 binary eutectic structures showed the best cut-edge corrosion resistance. The analysis indicated that Mg dissolved from MgZn2 in the early stage of corrosion and migrated to the cathodic region of steel-exposed cut-edge area to form dense and ordered protective corrosion products, leading to prolonged cathodic protection of Zn-Mg-Al alloy-coated steel sheets.

Thermophysical property of undercooled liquid binary alloy composed of metallic and semiconductor elements

NASA Astrophysics Data System (ADS)

Wang, H. P.; Wei, B.

2009-02-01

The thermophysical properties of the liquid Ni-Si binary alloy system were investigated by the molecular dynamics method. The properties investigated include density, excessive volume, enthalpy, mixing enthalpy and specific heat at both superheated and undercooled states. It is found that the density decreases with an increase in the Si content, and so do the temperature coefficients. If the Si content is smaller than 30%, the density changes linearly with the temperature. If it is larger than 30%, the density is a quadratic function of the temperature. The simulated enthalpies of different composition alloys increase linearly with a rise in temperature. This indicates that the specific heats of Ni-Si alloys change little with temperature. The specific heat versus composition first decreases to a minimum value at 50% Si, then experiences a rise to a maximum value at 90% Si and finally falls again. According to the excessive volume and mixing enthalpy, it can be deduced that the Ni-Si alloy system seriously deviates from the ideal solution. Moreover, a comparison was also performed between the present results and the approximated values by the Neumann-Kopp rule. It reveals that this work provides reasonable data in a broad temperature range, especially for the metastable undercooled liquid state.

Critical evaluation and thermodynamic optimization of the Iron-Rare-Earth systems

NASA Astrophysics Data System (ADS)

Konar, Bikram

Rare-Earth elements by virtue of its typical magnetic, electronic and chemical properties are gaining importance in power, electronics, telecommunications and sustainable green technology related industries. The Magnets from RE-alloys are more powerful than conventional magnets which have more longevity and high temperature workability. The dis-equilibrium in the Rare-Earth element supply and demand has increased the importance of recycling and extraction of REE's from used permanent Magnets. However, lack of the thermodynamic data on RE alloys has made it difficult to design an effective extraction and recycling process. In this regard, Computational Thermodynamic calculations can serve as a cost effective and less time consuming tool to design a waste magnet recycling process. The most common RE permanent magnet is Nd magnet (Nd 2Fe14B). Various elements such as Dy, Tb, Pr, Cu, Co, Ni, etc. are also added to increase its magnetic and mechanical properties. In order to perform reliable thermodynamic calculations for the RE recycling process, accurate thermodynamic database for RE and related alloys are required. The thermodynamic database can be developed using the so-called CALPHAD method. The database development based on the CALPHAD method is essentially the critical evaluation and optimization of all available thermodynamic and phase diagram data. As a results, one set of self-consistent thermodynamic functions for all phases in the given system can be obtained, which can reproduce all reliable thermodynamic and phase diagram data. The database containing the optimized Gibbs energy functions can be used to calculate complex chemical reactions for any high temperature processes. Typically a Gibbs energy minimization routine, such as in FactSage software, can be used to obtain the accurate thermodynamic equilibrium in multicomponent systems. As part of a large thermodynamic database development for permanent magnet recycling and Mg alloy design, all thermodynamic and phase diagram data in the literature for the fourteen Fe-RE binary systems: Fe-La, Fe-Ce, Fe-Pr, Fe-Nd, Fe-Sm, Fe-Gd, Fe-Tb, Fe-Dy, Fe-Ho, Fe-Er, Fe-Tm, Fe-Lu, Fe-Sc and Fe-Y are critically evaluated and optimized to obtain thermodynamic model parameters. The model parameters can be used to calculate phase diagrams and Gibbs energies of all phases as functions of temperature and composition. This database can be incorporated with the present thermodynamic database in FactSage software to perform complex chemical reactions and phase diagram calculations for RE magnet recycling process.

High impact strength polymers having novel nano-structures produced via reactive extrusion

NASA Astrophysics Data System (ADS)

Tortorella, Nathan Fraser

A major focus of scientists and engineers over the last century has been to increase the impact strength and therefore reduce the brittleness of materials. By altering and adding energy absorption mechanisms, brittle failure can be averted. Isotactic polypropylene (PP) is the focus of this dissertation because it is an extremely low cost, high volume, versatile plastic but behaves in a brittle manner at or below room temperature or in a notched state. Early work on impact modification of polypropylene focused on blending energy-absorbing low density elastomers and rubbers. These binary blends all had a common problem---an increase in impact strength was paralleled by a significant decrease in both elastic modulus and yield stress. Reactive extrusion processing has allowed the in-situ compatibilization of isotactic polypropylene and metallocene-catalyzed ethylene-octene copolymers (EOCs). This process involves combining both the comonomer and vector fluid approaches to grafting polyolefins. Styrene monomer and a multifunctional acrylate monomer undergo peroxide-induced copolymerization and grafting in the presence of both PP and EOC. This results in a phase separated alloy with an impact strength over 13 times that of pure polypropylene and double that of the physical blend. There is also a significant improvement in stress-strain performance when comparing the alloys to physical blend counterparts. Many researchers have categorized the necessary components to toughening polypropylene as pertaining to the amorphous phase. The alloys described in this dissertation meet the criteria put forth by these researchers, namely low density, crystallinity, and modulus of the elastomer phase, sub-micron particle diameter, close inter-particle distance, and a high degree of entanglements of both the PP matrix phase and EOC minor phase. But many people neglect to study the crystalline state of impact modified PP in conjunction with the amorphous phase. This work shows that the typical 10-100 mum diameter spherulitic structures found in pure PP are not present in the alloys. In fact, the spherulites are less than a micron in diameter, are uniformly distributed throughout the sample, and crystallize at much higher temperatures. SEM images, when coupled with DSC and XRD, reveal the presence of a high number of small lamellar crystals composed of a unique highly dense cross-hatched structure. Thus, impact strength and stiffness can be simultaneously improved by controlling the size and cross-hatch density of the lamellar crystals and applying phase transformation toughening concepts.

Casting Characteristics of High Cerium Content Aluminum Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weiss, D; Rios, O R; Sims, Z C

This paper compares the castability of the near eutectic aluminum-cerium alloy system to the aluminum-silicon and aluminum-copper systems. The alloys are compared based on die filling capability, feeding characteristics and tendency to hot tear in both sand cast and permanent mold applications. The castability ranking of the binary Al–Ce systems is as good as the aluminum-silicon system with some deterioration as additional alloying elements are added. In alloy systems that use cerium in combination with common aluminum alloying elements such as silicon, magnesium and/or copper, the casting characteristics are generally better than the aluminum-copper system. In general, production systems formore » melting, de-gassing and other processing of aluminum-silicon or aluminum-copper alloys can be used without modification for conventional casting of aluminum-cerium alloys.« less

Alloying effects of Ni, Si, and S on the phase diagram and sound velocities of Fe under high pressures and high temperatures

NASA Astrophysics Data System (ADS)

Lin, J.; Fei, Y.; Sturhahn, W.; Zhao, J.; Mao, H.; Hemley, R.

2004-05-01

Iron-nickel is the most abundant constituent of the Earth's core. The amount of Ni in the core is about 5.5 wt%. Geophysical and cosmochemical studies suggest that the Earth's outer core also contains approximately 10% of light element(s) and a certain amount of light element(s) may be present in the inner core. Si and S are believed to be alloying light elements in the iron-rich planetary cores such as the Earth and Mars. Therefore, understanding the alloying effects of Ni, Si, and S on the phase diagram and physical properties of Fe under core conditions is crucial for geophysical and geochemical models of planetary interiors. The addition of Ni and Si does not appreciably change the compressibility of hcp-Fe under high pressures. Studies of the phase relations of Fe and Fe-Ni alloys indicate that Fe with up to 10 wt% Ni is likely to be in the hcp structure under inner core conditions. On the other hand, adding Si into Fe strongly stabilizes the bcc structure to much higher pressures and temperatures (Lin et al., 2002). We have also studied the sound velocities and magnetic properties of Fe0.92Ni0.08, Fe0.85Si0.15, and Fe3S alloys with nuclear resonant inelastic x-ray scattering and nuclear forward scattering up to 106 GPa, 70 GPa, and 57 GPa, respectively. The sound velocities of the alloys are obtained from the measured partial phonon density of states for 57Fe incorporated in the alloys. Addition of Ni slightly decreases the VP and VS of Fe under high pressures (Lin et al., 2003). Si or S alloyed with Fe increases the VP and VS under high pressures, which provides a better match to seismological data of the Earth's core. We note that the increase in the VP and VS of Fe0.85Si0.15 and Fe3S is mainly contributed from the density decrease of adding Si and S in iron. Time spectra of the nuclear forward scattering reveal that the most iron rich sulfide, Fe3S, undergoes a magnetic to non-magnetic transition at approximately 18 GPa from a low-pressure magnetically ordered state to a high-pressure non-magnetic ordered state. The magnetic transition significantly affects the elastic, thermodynamic, and vibrational properties of Fe3S. It is conceivable that the magnetic collapse of Fe3S may also affect the binary phase diagram of the iron-sulfur system, changing the solubility of sulfur in iron under higher pressures. Study of the non-magnetic phase is more relevant to understand the properties of the Fe3S under planetary core conditions where high pressures and high temperature ensure the non-magnetic ordering state, affecting the interpretation of the amount and properties of sulfur being in the planetary cores. If the Martian core is in the solid state containing 14.2 wt% sulfur, it is likely that the non-magnetic Fe3S phase is a dominant component and that our measured sound velocities of Fe3S can be used to understand the velocity profile in the Martian core.

The upper critical field of filamentary Nb3Sn conductors

NASA Astrophysics Data System (ADS)

Godeke, A.; Jewell, M. C.; Fischer, C. M.; Squitieri, A. A.; Lee, P. J.; Larbalestier, D. C.

2005-05-01

We have examined the upper critical field of a large and representative set of present multifilamentary Nb3Sn wires and one bulk sample over a temperature range from 1.4 K up to the zero-field critical temperature. Since all present wires use a solid-state diffusion reaction to form the A15 layers, inhomogeneities with respect to Sn content are inevitable, in contrast to some previously studied homogeneous samples. Our study emphasizes the effects that these inevitable inhomogeneities have on the field-temperature phase boundary. The property inhomogeneities are extracted from field-dependent resistive transitions which we find broaden with increasing inhomogeneity. The upper 90%-99% of the transitions clearly separates alloyed and binary wires but a pure, Cu-free binary bulk sample also exhibits a zero-temperature critical field that is comparable to the ternary wires. The highest μ0Hc2 detected in the ternary wires are remarkably constant: The highest zero-temperature upper critical fields and zero-field critical temperatures fall within 29.5±0.3 and 17.8±0.3K, respectively, independent of the wire layout. The complete field-temperature phase boundary can be described very well with the relatively simple Maki-DeGennes model using a two-parameter fit, independent of composition, strain state, sample layout, or applied critical state criterion.

Modelling of Surfaces. Part 2: Metallic Alloy Surfaces Using the BFS Method

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Ferrante, John; Kobistek, Robert J.

1994-01-01

Using BFS, a new semiempirical method for alloys, we study the surface structure of fcc ordered binary alloys. We concentrate on the calculation of surface energies and surface relaxations for the L1(sub 0) and L1(sub 2) ordered structures. Different terminations of the low-index faces are studied. Also, we present results for the interlayer relaxations for planes close to the surface, revealing different relaxations for atoms of different species producing a rippled surface layer.

The Role of Grain Boundary Chemistry and the Environment on Intergranular Fracture.

DTIC Science & Technology

1980-10-01

and alloys as well. Grain boundary segregation of phosphorus, for example, has been observed in thermally treated nickel-base alloys such as Inconel ...base alloys such as Inconel 600 and Hastelloy C-276. Hence, Ni-P binary glasses may be considered to be good structural and chemical analog of grain...p. 625 17. H.W. Pickering and M. Zamanzedeh: This Conference, Poster Session 18. B.J. Berkowitz, J.J. Burton, C.R. Helms and R.S. Polizzotti

Equiaxed and columnar dendrite growth simulation in Al-7Si- Mg ternary alloys using cellular automaton method

NASA Astrophysics Data System (ADS)

Chen, Rui; Xu, Qingyan; Liu, Baicheng

2015-06-01

In this paper, a modified cellular automaton (MCA) model allowing for the prediction of dendrite growth of Al-Si-Mg ternary alloys in two and three dimensions is presented. The growth kinetic of S/L interface is calculated based on the solute equilibrium approach. In order to describe the dendrite growth with arbitrarily crystallographic orientations, this model introduces a modified decentered octahedron algorithm for neighborhood tracking to eliminate the effect of mesh dependency on dendrite growth. The thermody namic and kinetic data needed for dendrite growth is obtained through coupling with Pandat software package in combination with thermodynamic/kinetic/equilibrium phase diagram calculation databases. The effect of interactions between various alloying elements on solute diffusion coefficient is considered in the model. This model has first been used to simulate Al-7Si (weight percent) binary dendrite growth followed by a validation using theoretical predictions. For ternary alloy, Al-7Si-0.5Mg dendrite simulation has been carried out and the effects of solute interactions on diffusion matrix as well as the differences of Si and Mg in solute distribution have been analyzed. For actual application, this model has been applied to simulate the equiaxed dendrite growth with various crystallographic orientations of Al-7Si-0.36Mg ternary alloy, and the predicted secondary dendrite arm spacing (SDAS) shows a reasonable agreement with the experimental ones. Furthermore, the columnar dendrite growth in directional solidification has also been simulated and the predicted primary dendrite arm spacing (PDAS) is in good agreement with experiments. The simulated results effectively demonstrate the abilities of the model in prediction of dendritic microstructure of Al-Si-Mg ternary alloy.

Theoretical calculations of structural, electronic, and elastic properties of CdSe1-x Te x : A first principles study

NASA Astrophysics Data System (ADS)

M, Shakil; Muhammad, Zafar; Shabbir, Ahmed; Muhammad Raza-ur-rehman, Hashmi; M, A. Choudhary; T, Iqbal

2016-07-01

The plane wave pseudo-potential method was used to investigate the structural, electronic, and elastic properties of CdSe1-x Te x in the zinc blende phase. It is observed that the electronic properties are improved considerably by using LDA+U as compared to the LDA approach. The calculated lattice constants and bulk moduli are also comparable to the experimental results. The cohesive energies for pure CdSe and CdTe binary and their mixed alloys are calculated. The second-order elastic constants are also calculated by the Lagrangian theory of elasticity. The elastic properties show that the studied material has a ductile nature.

Equilibrium distribution of rare earth elements between molten KCl-LiCl eutectic salt and liquid cadmium

NASA Astrophysics Data System (ADS)

Sakata, Masahiro; Kurata, Masaki; Hijikata, Takatoshi; Inoue, Tadashi

1991-11-01

Distribution experiments for several rare earth elements (La, Ce, Pr, Nd and Y) between molten KCl-LiCl eutectic salt and liquid Cd were carried out at 450, 500 and 600°C. The material balance of rare earth elements after reaching the equilibrium and their distribution and chemical states in a Cd sample frozen after the experiment were examined. The results suggested the formation of solid intermetallic compounds at the lower concentrations of rare earth metals dissolved in liquid Cd than those solubilities measured in the binary alloy system. The distribution coefficients of rare earth elements between two phases (mole fraction in the Cd phase divided by mole fraction in the salt phase) were determined at each temperature. These distribution coefficients were explained satisfactorily by using the activity coefficients of chlorides and metals in salt and Cd. Both the activity coefficients of metal and chloride caused a much smaller distribution coefficient of Y relative to those of other elements.

Influence of Dy in solid solution on the degradation behavior of binary Mg-Dy alloys in cell culture medium.

PubMed

Yang, Lei; Ma, Liangong; Huang, Yuanding; Feyerabend, Frank; Blawert, Carsten; Höche, Daniel; Willumeit-Römer, Regine; Zhang, Erlin; Kainer, Karl Ulrich; Hort, Norbert

2017-06-01

Rare earth element Dy is one of the promising alloying elements for magnesium alloy as biodegradable implants. To understand the effect of Dy in solid solution on the degradation of Mg-Dy alloys in simulated physiological conditions, the present work studied the microstructure and degradation behavior of Mg-Dy alloys in cell culture medium. It is found the corrosion resistance enhances with the increase of Dy content in solid solution in Mg. This can be attributed to the formation of a relatively more corrosion resistant Dy-enriched film which decreases the anodic dissolution of Mg. Copyright © 2017 Elsevier B.V. All rights reserved.

A computational study of diffusion in a glass-forming metallic liquid

DOE PAGES

Wang, T.; Zhang, F.; Yang, L.; ...

2015-06-09

In this study, liquid phase diffusion plays a critical role in phase transformations (e.g. glass transformation and devitrification) observed in marginal glass forming systems such as Al-Sm. Controlling transformation pathways in such cases requires a comprehensive description of diffusivity, including the associated composition and temperature dependencies. In our computational study, we examine atomic diffusion in Al-Sm liquids using ab initio molecular dynamics (AIMD) and determine the diffusivities of Al and Sm for selected alloy compositions. Non-Arrhenius diffusion behavior is observed in the undercooled liquids with an enhanced local structural ordering. Through assessment of our AIMD result, we construct a generalmore » formulation for Al-Sm liquid, involving a diffusion mobility database that includes composition and temperature dependence. A Volmer-Fulcher-Tammann (VFT) equation is adopted for describing the non-Arrhenius behavior observed in the undercooled liquid. Furthermore, the composition dependence of diffusivity is found quite strong, even for the Al-rich region contrary to the sole previous report on this binary system. The model is used in combination with the available thermodynamic database to predict specific diffusivities and compares well with reported experimental data for 0.6 at.% and 5.6 at.% Sm in Al-Sm alloys.« less

Viscosity and diffusivity in melts: from unary to multicomponent systems

NASA Astrophysics Data System (ADS)

Chen, Weimin; Zhang, Lijun; Du, Yong; Huang, Baiyun

2014-05-01

Viscosity and diffusivity, two important transport coefficients, are systematically investigated from unary melt to binary to multicomponent melts in the present work. By coupling with Kaptay's viscosity equation of pure liquid metals and effective radii of diffusion species, the Sutherland equation is modified by taking the size effect into account, and further derived into an Arrhenius formula for the convenient usage. Its reliability for predicting self-diffusivity and impurity diffusivity in unary liquids is then validated by comparing the calculated self-diffusivities and impurity diffusivities in liquid Al- and Fe-based alloys with the experimental and the assessed data. Moreover, the Kozlov model was chosen among various viscosity models as the most reliable one to reproduce the experimental viscosities in binary and multicomponent melts. Based on the reliable viscosities calculated from the Kozlov model, the modified Sutherland equation is utilized to predict the tracer diffusivities in binary and multicomponent melts, and validated in Al-Cu, Al-Ni and Al-Ce-Ni melts. Comprehensive comparisons between the calculated results and the literature data indicate that the experimental tracer diffusivities and the theoretical ones can be well reproduced by the present calculations. In addition, the vacancy-wind factor in binary liquid Al-Ni alloys with the increasing temperature is also discussed. What's more, the calculated inter-diffusivities in liquid Al-Cu, Al-Ni and Al-Ag-Cu alloys are also in excellent agreement with the measured and theoretical data. Comparisons between the simulated concentration profiles and the measured ones in Al-Cu, Al-Ce-Ni and Al-Ag-Cu melts are further used to validate the present calculation method.

Unraveling Recrystallization Mechanisms Governing Texture Development from Rare Earth Element Additions to Magnesium

NASA Astrophysics Data System (ADS)

Imandoust, Aidin

The origin of texture components associated with rare-earth (RE) element additions in wrought magnesium (Mg) alloys is a long-standing problem in magnesium technology. The objective of this research is to identify the mechanisms accountable for rare-earth texture during dynamic recrystallization (DRX). Towards this end, we designed binary Mg-Cerium and Mg-Gadolinium alloys along with complex alloy compositions containing zinc, yttrium and Mischmetal. Binary alloys along with pure Mg were designed to individually investigate their effects on texture evolutions, while complex compositions are designed to develop randomized texture, and be used in automotive and aerospace applications. We selected indirect extrusion to thermo-mechanically process our materials. Different extrusion ratios and speeds were designed to produce partially and fully recrystallized microstructures, allowing us to analyze DRX from its early stages to completion. X-ray diffraction, electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to conduct microstructure and texture analyses. Our analyses revealed that rare-earth elements in zinc-containing magnesium alloys promote discontinuous dynamic recrystallization at the grain boundaries. During nucleation, the effect of rare earth elements on orientation selection was explained by the concomitant actions of multiple Taylor axes in the same grain. Isotropic grain growth was observed due to rare earth elements segregating to grain boundaries, which lead to texture randomization. The nucleation in binary Mg-RE alloys took place by continuous formation of necklace structures. Stochastic relaxation of basal and non-basal dislocations into low-angle grain boundaries produced chains of embryos with nearly random orientations. Schmid factor analysis showed a lower net activation of dislocations in RE textured grains compared to ones on the other side of the stereographic triangle. Lower dislocation densities within RE grains favored their growth by setting the boundary migration direction toward grains with higher dislocation density, thereby decreasing the system energy. We investigated the influence of RE elements on extension twinning induced hardening. RE addition enhanced tensile twinning induced hardening significantly. EBSD analysis illustrated that tensile twins cross low angle grain boundaries in Mg-RE alloys, which produced large twins and facilitated transmutation of basal to prismatic dislocations. Higher activity of pyramidal II dislocations in Mg-RE alloys resulted in higher twinning induced hardening.

Gravity-induced anomalies in interphase spacing reported for binary eutectics.

PubMed

Smith, Reginald W

2002-10-01

It has been reasoned that desirable microstructural refinement in binary eutectics could result from freezing in reduced-gravity. It is recognized that the interphase spacing in a binary eutectic is controlled by solute transport and that, on Earth, buoyancy-driven convection may enhance this. Hence, it has been presumed that the interphase spacing ought to decrease when a eutectic alloy is frozen under conditions of much-reduced gravity, where such buoyancy effects would be largely absent. The result of such speculation has been that many workers have frozen various eutectics under reduced gravity and have reported that, although some eutectics became finer, others showed no change, and some even became coarser. This reported varied behavior will be reviewed in the light of long term studies by the author at Queen's University, including recent microgravity studies in which samples of two eutectic alloy systems, MnBi-Bi and MnSb-Sb, were frozen under very stable conditions and showed no change in interphase spacing.

Investigation and modeling of Al3(Sc, Zr) precipitation strengthening in the presence of enhanced supersaturation and within Al-Cu binary alloys

NASA Astrophysics Data System (ADS)

Deane, Kyle

Diffuse Al-Sc and Al-Zr alloys have been demonstrated in literature to be relatively coarsening resistant at higher temperatures when compared with commonly used precipitation strengthening alloys (e.g. 2000 series, 6000 series). However, because of a limited strengthening due to the low solubility of scandium and zirconium in aluminum, and owing to the scarcity and therefore sizeable price tag attached to scandium, little research has been done in the way of optimizing these alloys for commercial applications. With this in mind, this dissertation describes research which aims to tackle several important areas of Al-Sc-Zr research that have been yet unresolved. In Chapter 4, rapid solidification was utilized to enhance the achievable supersaturation of the alloy in an effort to increase the achievable precipitate strengthening. In Chapter 5, Additive Friction Stir processing (AFS), a novel method of mechanically combining materials without melting, was employed in an attempt to pass the benefits of supersaturation from melt spun ribbon into a more structurally useful bulk material. In Chapter 6, a Matlab program written to predict precipitate nucleation, growth, and coarsening with a modified Kampmann and Wagner Numerical (KWN) model, was used to predict heat treatment regimens for more efficient strengthening. Those predictions were then tested experimentally to test the validity of the results. And lastly, in Chapter 7, the effect of zirconium on Al-Cu secondary precipitates was studied in an attempt to increase their thermal stability, as much higher phase fractions of Al-Cu precipitates are achievable than Al-Zr precipitates.

AB INITIO STUDY OF STRUCTURAL, ELECTRONIC AND OPTICAL PROPERTIES OF MgxCd1-xX (X = S, Se, Te) ALLOYS

NASA Astrophysics Data System (ADS)

Noor, N. A.; Shaukat, A.

2012-12-01

This study describes structural, electronic and optical properties of MgxCd1-xX (X = S, Se, Te) alloys in the complete range 0≤x ≤1 of composition x in the zinc-blende (ZB) phase with the help of full-potential linearized augmented plane wave plus local orbitals (FP-LAPW+lo) method within density functional theory (DFT). In order to calculate total energy, generalized gradient approximation (Wu-Cohen GGA) has been applied, which is based on optimization energy. For electronic structure calculations, the corresponding potential is being optimized by Engel-Vosko GGA formalism. Our calculations reveal the nonlinear variation of lattice constant and bulk modulus with different concentration for the end binary and their ternary alloys, which slightly deviates from Vegard's law. The calculated band structures show a direct band gap for all three alloys with increasing order in the complete range of the compositional parameter x. In addition, we have discussed the disorder parameter (gap bowing) and concluded that the total band gap bowing is substantially influenced by the chemical (electronegativity) contribution. The calculated density of states (DOS) of these alloys is discussed in terms of contribution from various s-, p- and d-states of the constituent atoms and charge density distributions plots are analyzed. Optical properties have been presented in the form of the complex dielectric function ɛ(ω), refractive index n(ω) and extinction coefficient k(ω) as function of the incident photon energy, and the results have been compared with existing experimental data and other theoretical calculations.

Dry silver electromigration process for optical glass waveguide fabrication and fluxless bonding technology for photonics and MEMS packaging

NASA Astrophysics Data System (ADS)

Chuang, Ricky Wenkuei

2001-07-01

An effectively simple dry silver electromigration technology without the need of evaporating separate gold or aluminum film electrodes onto both sides of glass is reported to fabricate low-loss deep multimode planar and channel waveguides on BK7 and BF450 glass substrates. A relatively high electrical field ranging from 440 to 545 V/mm was applied to the glass to speed up the migration, while at the same time preventing silver ions that were driven into the glass from reducing into silver atom; a major contributor to waveguide loss. The deep planar and channel waveguides thus fabricated showed no discolors or cracks, of which the attenuation losses of less than 2dB/cm and 0.1dB/cm were later measured from channel waveguides constructed on the BK7 and BF450 glass substrates, respectively, using our 0.6328mum He-Ne laser edge-coupling setup. To complete the waveguide studies, the scanning electron microscope (SEM) equipped with energy-dispersive X-ray (EDX) detector was adopted to obtain the concentration profiles of silver and sodium ions distributed in a waveguiding region after the exchange. The EDX measurements acquired hereafter were then utilized along with the Gladstone-Dale relation altogether to deduce the refractive index profile; of which a nearly step-like profile was consistently deduced from every deep planar and channel waveguides fabricated. Finally, a numerical model utilizing the space charge approach was devised to explain the nonlinear current effect often observed during the actual waveguide fabrication. The simulation results have confirmed that the nonlinear current-versus-time profile obtained is mainly attributed to the inhomogeneous distribution of the electric field in the glass substrate due to a space charge region created by the separation between silver- and sodium-ion migration fronts as a result of their unequal mobilities; a phenomenon which is ultimately responsible for the eventual slow down in the ion exchange rate as monitored during the actual electromigration process. A fluxless oxidation-free bonding technology using multilayer composite solders based on the non eutectic binary alloys of indium-tin (In-Sn), silver-indium (Ag-In), gold-tin (Au-Sn), and bismuth-tin (Bi-Sn) has been established and studied to determine its applicability to photonics and MEMS packaging. The scanning acoustic microscopy (SAM) conducted on these solder samples has consistently shown that a nearly void-free joint fabricated from each non-eutectic binary alloy system can be reliably achieved. In addition, the scanning electron microscopy (SEM) equipped with the energy dispersive X-ray (EDX) detector was also performed on the cross section of each sample to determine its joint composition, especially of any sign of intermetallic compounds. These results will demonstrate that any intermetallic compound or phase present in a joint fabricated with a pre-determined multilayer composition based on a specific binary alloy system can be well understood and fully justified by correlating the experimental outcome with its respective binary phase diagram.

Magnetic, structural and magnetocaloric properties of Ni-Si and Ni-Al thermoseeds for self-controlled hyperthermia.

PubMed

Pandey, Sudip; Quetz, Abdiel; Aryal, Anil; Dubenko, Igor; Mazumdar, Dipanjan; Stadler, Shane; Ali, Naushad

2017-11-01

Self-controlled hyperthermia is a non-invasive technique used to kill or destroy cancer cells while preserving normal surrounding tissues. We have explored bulk magnetic Ni-Si and Ni-Al alloys as a potential thermoseeds. The structural, magnetic and magnetocaloric properties of the samples were investigated, including saturation magnetisation, Curie temperature (T C ), and magnetic and thermal hysteresis, using room temperature X-ray diffraction and magnetometry. The annealing time, temperature and the effects of homogenising the thermoseeds were studied to determine the functional hyperthermia applications. The bulk Ni-Si and Ni-Al binary alloys have Curie temperatures in the desired range, 316 K-319 K (43 °C-46 °C), which is suitable for magnetic hyperthermia applications. We have found that T C strictly follows a linear trend with doping concentration over a wide range of temperature. The magnetic ordering temperature and the magnetic properties can be controlled through substitution in these binary alloys.

Monosilicide-disilicide-silicon phase equilibria in the nickel-platinum-silicon and nickel-palladium-silicon systems

NASA Astrophysics Data System (ADS)

Loomans, M. E.; Chi, D. Z.; Chua, S. J.

2004-10-01

Bulk-phase equilibria in Ni-rich/Si-rich alloys of the Ni-Pt-Si and Ni-Pd-Si systems were investigated. Results suggest that a bulk monosilicide solid solution, containing up to at least 11 at. pct Pt, exists in the Ni-Pt-Si system. Monosilicides containing more than 11 at. pct Pt were not examined. Results from both ternary systems point convincingly to the existence of a NiSi+Si↔NiSi2 eutectoid reaction near 700 °C in the Ni-Si binary system; data from the Ni-Pt-Si system, which yield the more accurate determination of the eutectoid temperature, place it at roughly 710 °C. The Pt and Pd concentrations of monosilicide in equilibrium with disilicide and Si were measured using energy-dispersive spectrometry (EDS) and were found to increase with temperature.

Scheil-Gulliver Constituent Diagrams

NASA Astrophysics Data System (ADS)

Pelton, Arthur D.; Eriksson, Gunnar; Bale, Christopher W.

2017-06-01

During solidification of alloys, conditions often approach those of Scheil-Gulliver cooling in which it is assumed that solid phases, once precipitated, remain unchanged. That is, they no longer react with the liquid or with each other. In the case of equilibrium solidification, equilibrium phase diagrams provide a valuable means of visualizing the effects of composition changes upon the final microstructure. In the present study, we propose for the first time the concept of Scheil-Gulliver constituent diagrams which play the same role as that in the case of Scheil-Gulliver cooling. It is shown how these diagrams can be calculated and plotted by the currently available thermodynamic database computing systems that combine Gibbs energy minimization software with large databases of optimized thermodynamic properties of solutions and compounds. Examples calculated using the FactSage system are presented for the Al-Li and Al-Mg-Zn systems, and for the Au-Bi-Sb-Pb system and its binary and ternary subsystems.

Experimental and Computational Investigation of High Entropy Alloys for Elevated-Temperature Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liaw, Peter; Zhang, Fan; Zhang, Chuan

2016-07-30

To create and design novel structural materials with enhanced creep-resistance, fundamental studies have been conducted on high-entropy alloys (HEAs), using (1) thermodynamic calculations, (2) mechanical tests, (3) neutron diffraction, (4) characterization techniques, and (5) crystal-plasticity finite-element modeling (CPFEM), to explore future candidates for next-generation power plants. All the constituent binary and ternary systems of the Al-Cr-Cu-Fe-Mn-Ni and Al-Co-Cr-Fe-Ni systems were thermodynamically modeled within the whole composition range. Comparisons between the calculated phase diagrams and literature data are in good agreement. Seven types of HEAs were fabricated from Al-Cr-Cu-Fe-Mn-Ni and Al-Co-Cr-Fe-Ni systems. The Al xCrCuFeMnNi HEAs have disordered [face-centered cubic (FCC)more » + body-centered cubic (BCC)] crystal structures, not FCC or BCC single structure. Excessive alloying of the Al element results in the change of both microstructural and mechanical properties in Al xCoCrFeNi HEAs. There are mainly three structural features in Al xCoCrFeNi: (1) the morphology, (2) the volume fractions of the constitute phases, and (3) existing temperatures of all six phases. After homogenization, the Al 0.3CoCrFeNi material is a pure FCC solid solution. After aging at 700 °C for 500 hours, the optimal microstructure combinations, the FCC matrix, needle-like B2 phase within grains, and granular σ phase along grain boundary, is achieved for Al 0.3CoCrFeNi. The cold-rolling process is utilized to reduce the grain size of Al 0.1CoCrFeNi and Al 0.3CoCrFeNi. The chemical elemental partitioning of FCC, BCC, B2, and σphases at different temperatures, before and after mechanical tests, in Al-Cr-Cu-Fe-Mn-Ni and Al-Co-Cr-Fe-Ni systems are quantitatively characterized by both synchrotron X-ray diffraction, neutron diffraction with levitation, scanning electron microscopy (SEM), advanced atom probe tomography (APT), and transmission electron microscopy (TEM). In-situ neutron diffraction experiments were conducted to study the strengthening effect of B2 phase on tensile properties of Al 0.3CoCrFeNi HEAs directly. The results shows the creep behavior of Al 0.3CoCrFeNi is superior to conventional alloys, and the heat treatment introduces secondary B2 phase into the FCC matrix, which increase the yielding strength, decrease the ductility, diminish the serrated flow during compression tests at high temperatures. In summary, the outcomes of the development of the HEAs with creep resistance include: (1) Suitable candidates, for the application to boilers and steam and gas turbines at temperatures above 760 °C and a stress of 35 MPa. (2) Fundamental understanding on the precipitate stability and deformation mechanisms of both single-phase and precipitate-strengthened alloys at room and elevated temperatures, and (3) The demonstration of an integrated approach, coupling modeling [thermodynamic calculations and crystal-plasticity finite-element modeling (CPFEM)] and focused experiments, to identify HEAs that outperform conventional alloys for high-temperature applications, which will be applicable for the discovery and development of other high-temperature materials in the power-generating industry.« less

Silver-hafnium braze alloy

DOEpatents

Stephens, Jr., John J.; Hosking, F. Michael; Yost, Frederick G.

2003-12-16

A binary allow braze composition has been prepared and used in a bonded article of ceramic-ceramic and ceramic-metal materials. The braze composition comprises greater than approximately 95 wt % silver, greater than approximately 2 wt % hafnium and less than approximately 4.1 wt % hafnium, and less than approximately 0.2 wt % trace elements. The binary braze alloy is used to join a ceramic material to another ceramic material or a ceramic material, such as alumina, quartz, aluminum nitride, silicon nitride, silicon carbide, and mullite, to a metal material, such as iron-based metals, cobalt-based metals, nickel-based metals, molybdenum-based metals, tungsten-based metals, niobium-based metals, and tantalum-based metals. A hermetic bonded article is obtained with a strength greater than 10,000 psi.

Shape selection criterion for cellular array during constrained growth of binary alloys - Need for low gravity experiment

NASA Technical Reports Server (NTRS)

Tewari, Surendra N.; Trivedi, Rohit

1991-01-01

Development of steady-state periodic cellular array is one of the critical problems in the study of nonlinear pattern formation during directional solidification of binary alloys. The criterion which establishes the values of cell tip radius and spacing under given growth condition is not known. Theoretical models, such as marginal stability and microscopic solvability, have been developed for purely diffusive regime. However, the experimental conditions where cellular structures are stable are precisely the ones where the convection effects are predominant. Thus, the critical data for meaningful evaluation of cellular array growth models can only be obtained by partial directional solidification and quenching experiments carried out in the low gravity environment of space.

New Approaches to the Computer Simulation of Amorphous Alloys: A Review.

PubMed

Valladares, Ariel A; Díaz-Celaya, Juan A; Galván-Colín, Jonathan; Mejía-Mendoza, Luis M; Reyes-Retana, José A; Valladares, Renela M; Valladares, Alexander; Alvarez-Ramirez, Fernando; Qu, Dongdong; Shen, Jun

2011-04-13

In this work we review our new methods to computer generate amorphous atomic topologies of several binary alloys: SiH, SiN, CN; binary systems based on group IV elements like SiC; the GeSe 2 chalcogenide; aluminum-based systems: AlN and AlSi, and the CuZr amorphous alloy. We use an ab initio approach based on density functionals and computationally thermally-randomized periodically-continued cells with at least 108 atoms. The computational thermal process to generate the amorphous alloys is the undermelt-quench approach, or one of its variants, that consists in linearly heating the samples to just below their melting (or liquidus) temperatures, and then linearly cooling them afterwards. These processes are carried out from initial crystalline conditions using short and long time steps. We find that a step four-times the default time step is adequate for most of the simulations. Radial distribution functions (partial and total) are calculated and compared whenever possible with experimental results, and the agreement is very good. For some materials we report studies of the effect of the topological disorder on their electronic and vibrational densities of states and on their optical properties.

Estimation of the viscosities of liquid binary alloys

NASA Astrophysics Data System (ADS)

Wu, Min; Su, Xiang-Yu

2018-01-01

As one of the most important physical and chemical properties, viscosity plays a critical role in physics and materials as a key parameter to quantitatively understanding the fluid transport process and reaction kinetics in metallurgical process design. Experimental and theoretical studies on liquid metals are problematic. Today, there are many empirical and semi-empirical models available with which to evaluate the viscosity of liquid metals and alloys. However, the parameter of mixed energy in these models is not easily determined, and most predictive models have been poorly applied. In the present study, a new thermodynamic parameter Δ G is proposed to predict liquid alloy viscosity. The prediction equation depends on basic physical and thermodynamic parameters, namely density, melting temperature, absolute atomic mass, electro-negativity, electron density, molar volume, Pauling radius, and mixing enthalpy. Our results show that the liquid alloy viscosity predicted using the proposed model is closely in line with the experimental values. In addition, if the component radius difference is greater than 0.03 nm at a certain temperature, the atomic size factor has a significant effect on the interaction of the binary liquid metal atoms. The proposed thermodynamic parameter Δ G also facilitates the study of other physical properties of liquid metals.

New Approaches to the Computer Simulation of Amorphous Alloys: A Review

PubMed Central

Valladares, Ariel A.; Díaz-Celaya, Juan A.; Galván-Colín, Jonathan; Mejía-Mendoza, Luis M.; Reyes-Retana, José A.; Valladares, Renela M.; Valladares, Alexander; Alvarez-Ramirez, Fernando; Qu, Dongdong; Shen, Jun

2011-01-01

In this work we review our new methods to computer generate amorphous atomic topologies of several binary alloys: SiH, SiN, CN; binary systems based on group IV elements like SiC; the GeSe2 chalcogenide; aluminum-based systems: AlN and AlSi, and the CuZr amorphous alloy. We use an ab initio approach based on density functionals and computationally thermally-randomized periodically-continued cells with at least 108 atoms. The computational thermal process to generate the amorphous alloys is the undermelt-quench approach, or one of its variants, that consists in linearly heating the samples to just below their melting (or liquidus) temperatures, and then linearly cooling them afterwards. These processes are carried out from initial crystalline conditions using short and long time steps. We find that a step four-times the default time step is adequate for most of the simulations. Radial distribution functions (partial and total) are calculated and compared whenever possible with experimental results, and the agreement is very good. For some materials we report studies of the effect of the topological disorder on their electronic and vibrational densities of states and on their optical properties. PMID:28879948

Effect of Al content on structure and mechanical properties of the Al{sub x}CrNbTiVZr (x = 0; 0.25; 0.5; 1) high-entropy alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yurchenko, N.Yu.

2016-11-15

In present study, structure and mechanical properties of the Al{sub x}CrNbTiVZr (x = 0; 0.25; 0.5; 1) high-entropy alloys after arc melting and annealing at 1200 °C for 24 h are investigated. The CrNbTiVZr alloy is composed of body centered cubic (bcc) and C15 (face centered cubic) Laves phases while the Al{sub x}CrNbTiVZr (x = 0.25; 0.5; 1) alloys consist of bcc and two C14 (hexagonal close packed) Laves phases with different chemical compositions. Thermodynamic modeling predicts existence of two phases – bcc and C15 Laves phase and broadening of single bcc phase field due to Al addition. The densitymore » of the alloys decreases with the increase of Al content. The alloys are found to be extremely brittle at room temperature and 600 °C. The alloys have high strength at temperatures of 800–1000 °C. For example, yield strength at 800 °C increases from 440 MPa for the CrNbTiVZr alloy to 1250 MPa for the AlCrNbTiVZr alloy. The experimental phase composition of the Al{sub x}CrNbTiVZr alloys is compared with predicted equilibrium phases and the factors governing the transformation of C15 to C14 Laves phases due to Al addition to the CrNbTiVZr alloy analyzed. Specific properties of the alloys are compared with other high-entropy alloys and commercial Ni-based superalloys. - Highlights: •Al{sub x}CrNbTiVZr (x = 0; 0.25; 0.5; 1) alloys are arc melted and annealed at 1200 °C. •The CrNbTiVZr alloy has bcc and C15 Laves phases. •The Al-containing alloys are composed of bcc and two C14 Laves phases. •The alloys demonstrate high specific strength at temperatures of 800 °C and 1000 °C. •The strength of the alloys increases in proportion with increase of Al content.« less

Acceptable aluminum additions for minimal environmental effect in iron-aluminum alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sikka, V.K.; Viswanathan, S.; Vyas, S.

A systematic study of iron-aluminum alloys has shown that Fe-16 at. % Al alloys are not very sensitive to environmental embrittlement. The Fe-22 and -28 at. % Al alloys are sensitive to environmental embrittlement, and the effect can be reduced by the addition of chromium and through the control of grain size by additions of zirconium and carbon. The Fe-16 at. % Al binary, and alloys based on it, yielded over 20% room-temperature (RT) elongation even after high-temperature annealing treatments at 1100[degree]C. The best values for the Fe-22 and -28 at. % Al-base alloys after similar annealing treatments were 5more » and 10%, respectively. A multicomponent alloy, FAP, based on Fe- 16 at. % Al was designed, which gave an RT ductility of over 25%.« less

Acceptable aluminum additions for minimal environmental effect in iron-aluminum alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sikka, V.K.; Viswanathan, S.; Vyas, S.

A systematic study of iron-aluminum alloys has shown that Fe-16 at. % Al alloys are not very sensitive to environmental embrittlement. The Fe-22 and -28 at. % Al alloys are sensitive to environmental embrittlement, and the effect can be reduced by the addition of chromium and through the control of grain size by additions of zirconium and carbon. The Fe-16 at. % Al binary, and alloys based on it, yielded over 20% room-temperature (RT) elongation even after high-temperature annealing treatments at 1100{degree}C. The best values for the Fe-22 and -28 at. % Al-base alloys after similar annealing treatments were 5more » and 10%, respectively. A multicomponent alloy, FAP, based on Fe- 16 at. % Al was designed, which gave an RT ductility of over 25%.« less

Study on the Mg-Li-Zn ternary alloy system with improved mechanical properties, good degradation performance and different responses to cells.

PubMed

Liu, Yang; Wu, Yuanhao; Bian, Dong; Gao, Shuang; Leeflang, Sander; Guo, Hui; Zheng, Yufeng; Zhou, Jie

2017-10-15

Novel Mg-(3.5, 6.5wt%)Li-(0.5, 2, 4wt%)Zn ternary alloys were developed as new kinds of biodegradable metallic materials with potential for stent application. Their mechanical properties, degradation behavior, cytocompatibility and hemocompatibility were studied. These potential biomaterials showed higher ultimate tensile strength than previously reported binary Mg-Li alloys and ternary Mg-Li-X (X=Al, Y, Ce, Sc, Mn and Ag) alloys. Among the alloys studied, the Mg-3.5Li-2Zn and Mg-6.5Li-2Zn alloys exhibited comparable corrosion resistance in Hank's solution to pure magnesium and better corrosion resistance in a cell culture medium than pure magnesium. Corrosion products observed on the corroded surface were composed of Mg(OH) 2 , MgCO 3 and Ca-free Mg/P inorganics and Ca/P inorganics. In vitro cytotoxicity assay revealed different behaviors of Human Umbilical Vein Endothelial Cells (HUVECs) and Human Aorta Vascular Smooth Muscle Cells (VSMCs) to material extracts. HUVECs showed increasing nitric oxide (NO) release and tolerable toxicity, whereas VSMCs exhibited limited decreasing viability with time. Platelet adhesion, hemolysis and coagulation tests of these Mg-Li-Zn alloys showed different degrees of activation behavior, in which the hemolysis of the Mg-3.5Li-2Zn alloy was lower than 5%. These results indicated the potential of the Mg-Li-Zn alloys as good candidate materials for cardiovascular stent applications. Mg-Li alloys are promising as absorbable metallic biomaterials, which however have not received significant attention since the low strength, controversial corrosion performance and the doubts in Li toxicity. The Mg-Li-Zn alloy in the present study revealed much improved mechanical properties higher than most reported binary Mg-Li and ternary Mg-Li-X alloys, with superior corrosion resistance in cell culture media. Surprisingly, the addition of Li and Zn showed increased nitric oxide release. The present study indicates good potential of Mg-Li-Zn alloy as absorbable cardiovascular stent material. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Tailoring Morphology and Size of Microstructure and Tensile Properties of Sn-5.5 wt.%Sb-1 wt.%(Cu,Ag) Solder Alloys

NASA Astrophysics Data System (ADS)

Dias, Marcelino; Costa, Thiago A.; Soares, Thiago; Silva, Bismarck L.; Cheung, Noé; Spinelli, José E.; Garcia, Amauri

2018-02-01

Transient directional solidification experiments, and further optical and scanning electron microscopy analyses and tensile tests, allowed the dependence of tensile properties on the micromorphology and length scale of the dendritic/cellular matrix of ternary Sn-5.5Sb-1Ag and Sn-5.5Sb-1Cu alloys to be determined. Extensive ranges of cooling rates were obtained, which permitted specific values of cooling rate for each sample examined along the length of the casting to be attributed. Very broad microstructural length scales were revealed as well as the presence of either cells or dendrites for the Ag-containing alloy. Hereafter, microstructural spacing values such as the cellular spacing, λ c, and the primary dendritic spacing, λ 1, may be correlated with thermal solidification parameters, that is, the cooling rate and the growth rate. While, for the Cu-containing Sn-Sb alloy, the β-Sn matrix is characterized only by the presence of dendritic arrangements, the Ag-containing Sn-Sb alloy is shown to have high-velocity β-Sn cells associated with high cooling rate regions, i.e., positions closer to the bottom of the alloy casting, with the remaining positions being characterized by a complex growth of β-Sn dendrites. Minor additions of Cu and Ag increase both the yield and ultimate tensile strengths when compared with the corresponding values of the binary Sn-5.5Sb alloy, with a small reduction in ductility. This has been attributed to the homogeneous distribution of the Ag3Sn and Cu6Sn5 intermetallic particles related to smaller λ 1 characterizing the dendritic zones of the ternary Sn-Sb-(Cu,Ag) alloys. In addition, the Ag-modified Sn-Sb alloy exhibited an initial wetting angle consistent with that characterizing the binary Sn-5.5Sb alloy.

Phase-field simulations of velocity selection in rapidly solidified binary alloys

NASA Astrophysics Data System (ADS)

Fan, Jun; Greenwood, Michael; Haataja, Mikko; Provatas, Nikolas

2006-09-01

Time-dependent simulations of two-dimensional isothermal Ni-Cu dendrites are simulated using a phase-field model solved with a finite-difference adaptive mesh refinement technique. Dendrite tip velocity selection is examined and found to exhibit a transition between two markedly different regimes as undercooling is increased. At low undercooling, the dendrite tip growth rate is consistent with the kinetics of the classical Stefan problem, where the interface is assume to be in local equilibrium. At high undercooling, the growth velocity selected approaches a linear dependence on melt undercooling, consistent with the continuous growth kinetics of Aziz and with a one-dimensional steady-state phase-field asymptotic analysis of Ahmad [Phys. Rev. E 58, 3436 (1998)]. Our simulations are also consistent with other previously observed behaviors of dendritic growth as undercooling is increased. These include the transition of dendritic morphology to absolute stability and nonequilibrium solute partitioning. Our results show that phase-field models of solidification, which inherently contain a nonzero interface width, can be used to study the dynamics of complex solidification phenomena involving both equilibrium and nonequilibrium interface growth kinetics.

Direct Observation of Defect Range and Evolution in Ion-Irradiated Single Crystalline Ni and Ni Binary Alloys.

PubMed

Lu, Chenyang; Jin, Ke; Béland, Laurent K; Zhang, Feifei; Yang, Taini; Qiao, Liang; Zhang, Yanwen; Bei, Hongbin; Christen, Hans M; Stoller, Roger E; Wang, Lumin

2016-02-01

Energetic ions have been widely used to evaluate the irradiation tolerance of structural materials for nuclear power applications and to modify material properties. It is important to understand the defect production, annihilation and migration mechanisms during and after collision cascades. In this study, single crystalline pure nickel metal and single-phase concentrated solid solution alloys of 50%Ni50%Co (NiCo) and 50%Ni50%Fe (NiFe) without apparent preexisting defect sinks were employed to study defect dynamics under ion irradiation. Both cross-sectional transmission electron microscopy characterization (TEM) and Rutherford backscattering spectrometry channeling (RBS-C) spectra show that the range of radiation-induced defect clusters far exceed the theoretically predicted depth in all materials after high-dose irradiation. Defects in nickel migrate faster than in NiCo and NiFe. Both vacancy-type stacking fault tetrahedra (SFT) and interstitial loops coexist in the same region, which is consistent with molecular dynamics simulations. Kinetic activation relaxation technique (k-ART) simulations for nickel showed that small vacancy clusters, such as di-vacancies and tri-vacancies, created by collision cascades are highly mobile, even at room temperature. The slower migration of defects in the alloy along with more localized energy dissipation of the displacement cascade may lead to enhanced radiation tolerance.

Direct Observation of Defect Range and Evolution in Ion-Irradiated Single Crystalline Ni and Ni Binary Alloys

PubMed Central

Lu, Chenyang; Jin, Ke; Béland, Laurent K.; Zhang, Feifei; Yang, Taini; Qiao, Liang; Zhang, Yanwen; Bei, Hongbin; Christen, Hans M.; Stoller, Roger E.; Wang, Lumin

2016-01-01

Energetic ions have been widely used to evaluate the irradiation tolerance of structural materials for nuclear power applications and to modify material properties. It is important to understand the defect production, annihilation and migration mechanisms during and after collision cascades. In this study, single crystalline pure nickel metal and single-phase concentrated solid solution alloys of 50%Ni50%Co (NiCo) and 50%Ni50%Fe (NiFe) without apparent preexisting defect sinks were employed to study defect dynamics under ion irradiation. Both cross-sectional transmission electron microscopy characterization (TEM) and Rutherford backscattering spectrometry channeling (RBS-C) spectra show that the range of radiation-induced defect clusters far exceed the theoretically predicted depth in all materials after high-dose irradiation. Defects in nickel migrate faster than in NiCo and NiFe. Both vacancy-type stacking fault tetrahedra (SFT) and interstitial loops coexist in the same region, which is consistent with molecular dynamics simulations. Kinetic activation relaxation technique (k-ART) simulations for nickel showed that small vacancy clusters, such as di-vacancies and tri-vacancies, created by collision cascades are highly mobile, even at room temperature. The slower migration of defects in the alloy along with more localized energy dissipation of the displacement cascade may lead to enhanced radiation tolerance. PMID:26829570

A high-resolution analytical scanning transmission electron microscopy study of the early stages of spinodal decomposition in binary Fe–Cr

DOE Office of Scientific and Technical Information (OSTI.GOV)

Westraadt, J.E., E-mail: johan.westraadt@nmmu.ac.za; Olivier, E.J.; Neethling, J.H.

2015-11-15

Spinodal decomposition (SD) is an important phenomenon in materials science and engineering. For example, it is considered to be responsible for the 475 °C embrittlement of stainless steels comprising the bcc (ferrite) or bct (martensite) phases. Structural characterization of the evolving minute nano-scale concentration fluctuations during SD in the Fe–Cr system is, however, a notable challenge, and has mainly been considered accessible via atom probe tomography (APT) and small-angle neutron scattering. The standard tool for nanostructure characterization, viz. transmission electron microscopy (TEM), has only been successfully applied to late stages of SD when embrittlement is already severe. However, we heremore » demonstrate that the structural evolution in the early stages of SD in binary Fe–Cr, and alloys based on the binary, are accessible via analytical scanning TEM. An Fe–36 wt% Cr alloy aged at 500 °C for 1, 10 and 100 h is investigated using an aberration-corrected microscope and it is found that highly coherent and interconnected Cr-rich regions develop. The wavelength of decomposition is rather insensitive to the sample thickness and it is quantified to 2, 3 and 6 nm after ageing for 1, 10 and 100 h, which is in reasonable agreement with prior APT analysis. The concentration amplitude is more sensitive to the sample thickness and acquisition parameters but the TEM analysis is in good agreement with APT analysis for the longest ageing time. These findings open up for combinatorial TEM studies where both local crystallography and chemistry is required. - Highlights: • STEM-EELS analysis was successfully applied to resolve early stage SD in Fe–Cr. • Compositional wavelength measured with STEM-EELS compares well to previous ATP studies. • Compositional amplitude measured with STEM-EELS is a function of experimental parameters. • STEM-EELS allows for combinatorial studies of SD using complementary techniques.« less

Structural phase transition, electronic structure and optical properties of half Heusler alloys LiBeZ (Z = As, Sb)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amudhavalli, A.; Rajeswarapalanichamy, R., E-mail: rajeswarapalanichamy@gmail.com

2016-05-23

Ab initio calculations are performed to investigate the structural stability, electronic structure, mechanical properties and optical properties of half Heusler alloys (LiBeAs and LiBeSb) for three different phases of zinc blende crystal structure. Among the considered phases, α- phase is found to be the most stable phase for these alloys at normal pressure. A pressure induced structural phase transition from α-phase to β- phase is observed for LiBeAs. The electronic structure reveals that these alloys are semiconductors. The optical properties confirm that these alloys are semiconductor in nature.

Macrosegregation in aluminum alloy ingot cast by the semicontinuous direct chill method

NASA Technical Reports Server (NTRS)

Yu, H.; Granger, D. A.

1984-01-01

A theoretical model of the semicontinuous DC casting method is developed to predict the positive segregation observed at the subsurface and the negative segregation commonly found at the center of large commercial-size aluminum alloy ingot. Qualitative analysis of commercial-size aluminum alloy semicontinuous cast direct chill (DC) ingot is carried out. In the analysis, both positive segregation in the ingot subsurface and negative segregation at the center of the ingot are examined. Ingot subsurface macrosegregation is investigated by considering steady state casting of a circular cross-section binary alloy ingot. Nonequilibrium solidification is assumed with no solid diffusion, constant equilibrium partition ratio, and constant solid density.

Subsonic leaky Rayleigh waves at liquid-solid interfaces.

PubMed

Mozhaev, V G; Weihnacht, M

2002-05-01

The paper is devoted to the study of leaky Rayleigh waves at liquid-solid interfaces close to the border of the existence domain of these modes. The real and complex roots of the secular equation are computed for interface waves at the boundary between water and a binary isotropic alloy of gold and silver with continuously variable composition. The change of composition of the alloy allows one to cross a critical velocity for the existence of leaky waves. It is shown that, contrary to popular opinion, the critical velocity does not coincide with the phase velocity of bulk waves in liquid. The true threshold velocity is found to be smaller, the correction being of about 1.45%. Attention is also drawn to the fact that using the real part of the complex phase velocity as a velocity of leaky waves gives only approximate value. The most interesting feature of the waves under consideration is the presence of energy leakage in the subsonic range of the phase velocities where, at first glance, any radiation by harmonic waves is not permitted. A simple physical explanation of this radiation with due regard for inhomogeneity of radiated and radiating waves is given. The controversial question of the existence of leaky Rayleigh waves at a water/ice interface is reexamined. It is shown that the solution considered previously as a leaky wave is in fact the solution of the bulk-wave-reflection problem for inhomogeneous waves.

Ultrasmall PdmMn1-mOx binary alloyed nanoparticles on graphene catalysts for ethanol oxidation in alkaline media

NASA Astrophysics Data System (ADS)

Ahmed, Mohammad Shamsuddin; Park, Dongchul; Jeon, Seungwon

2016-03-01

A rare combination of graphene (G)-supported palladium and manganese in mixed-oxides binary alloyed catalysts (BACs) have been synthesized with the addition of Pd and Mn metals in various ratios (G/PdmMn1-mOx) through a facile wet-chemical method and employed as an efficient anode catalyst for ethanol oxidation reaction (EOR) in alkaline fuel cells. The as prepared G/PdmMn1-mOx BACs have been characterized by several instrumental techniques; the transmission electron microscopy images show that the ultrafine alloyed nanoparticles (NPs) are excellently monodispersed onto the G. The Pd and Mn in G/PdmMn1-mOx BACs have been alloyed homogeneously, and Mn presents in mixed-oxidized form that resulted by X-ray diffraction. The electrochemical performances, kinetics and stability of these catalysts toward EOR have been evaluated using cyclic voltammetry in 1 M KOH electrolyte. Among all G/PdmMn1-mOx BACs, the G/Pd0.5Mn0.5Ox catalyst has shown much superior mass activity and incredible stability than that of pure Pd catalysts (G/Pd1Mn0Ox, Pd/C and Pt/C). The well dispersion, ultrafine size of NPs and higher degree of alloying are the key factor for enhanced and stable EOR electrocatalysis on G/Pd0.5Mn0.5Ox.

Effect of Iron Impurity on the Phase Composition, Structure and Properties of Magnesium Alloys Containing Manganese and Aluminum

NASA Astrophysics Data System (ADS)

Volkova, E. F.

2017-07-01

Results of a study of the interaction between iron impurity and manganese and aluminum alloying elements during formation of phase composition in alloys of the Mg - Mn, Mg - Al, Mg - Al - Mn, and Mg - Al - Zn - Mn systems are presented. It is proved that this interaction results in introduction of Fe into the intermetallic phase. The phase compositions of model magnesium alloys and commercial alloys MA2-1 and MA5 are studied. It is shown that both manganese and aluminum may bind the iron impurity into phases. Composite Fe-containing intermetallic phases of different compositions influence differently the corrosion resistance of magnesium alloys.

In-Vitro Corrosion Studies of Bioabsorbable Alloys

NASA Astrophysics Data System (ADS)

Gill, P.; Munroe, N.

Magnesium alloys have inspired a significant amount of attention from researchers all over the world for cardiovascular and orthopedic applications due to their light weight, mechanical integrity and degradation behavior. In this investigation, cast manufactured binary, ternary and quaternary magnesium alloys were studied for their degradation behavior by potentiodynamic polarization tests in phosphate buffer saline solution (PBS) and PBS containing amino acids (cysteine, C and tryptophan, W) at 37 °C. Electrochemical impedance spectroscopy (EIS) tests were performed to determine the charge transfer resistance and immersion tests were performed to assess corrosion rate and hydrogen evolution from the alloys. Furthermore, the surface morphology and surface chemistry of the alloys were observed by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Alloy Design Data Generated for B2-Ordered Compounds

NASA Technical Reports Server (NTRS)

Noebe, Ronald D.; Bozzolo, Guillermo; Abel, Phillip B.

2003-01-01

Developing alloys based on ordered compounds is significantly more complicated than developing designs based on disordered materials. In ordered compounds, the major constituent elements reside on particular sublattices. Therefore, the addition of a ternary element to a binary-ordered compound is complicated by the manner in which the ternary addition is made (at the expense of which binary component). When ternary additions are substituted for the wrong constituent, the physical and mechanical properties usually degrade. In some cases the resulting degradation in properties can be quite severe. For example, adding alloying additions to NiAl in the wrong combination (i.e., alloying additions that prefer the Al sublattice but are added at the expense of Ni) will severely embrittle the alloy to the point that it can literally fall apart during processing on cooling from the molten state. Consequently, alloying additions that strongly prefer one sublattice over another should always be added at the expense of that component during alloy development. Elements that have a very weak preference for a sublattice can usually be safely added at the expense of either element and will accommodate any deviation from stoichiometry by filling in for the deficient component. Unfortunately, this type of information is not known beforehand for most ordered systems. Therefore, a computational survey study, using a recently developed quantum approximate method, was undertaken at the NASA Glenn Research Center to determine the preferred site occupancy of ternary alloying additions to 12 different B2-ordered compounds including NiAl, FeAl, CoAl, CoFe, CoHf, CoTi, FeTi, RuAl, RuSi, RuHf, RuTi, and RuZr. Some of these compounds are potential high temperature structural alloys; others are used in thin-film magnetic and other electronic applications. The results are summarized. The italicized elements represent the previous sum total alloying information known and verify the computational method used to establish the table. Details of the computational procedures used to determine the preferred site occupancy can be found in reference 2. As further substantiation of the validity of the technique, and its extension to even more complicated systems, it was applied to two simultaneous alloying additions in an ordered alloy.

Stable biomimetic super-hydrophobic engineering materials.

PubMed

Guo, Zhiguang; Zhou, Feng; Hao, Jingcheng; Liu, Weimin

2005-11-16

We describe a simple and inexpensive method to produce super-hydrophobic surfaces on aluminum and its alloy by oxidation and chemical modification. Water or aqueous solutions (pH = 1-14) have contact angles of 168 +/- 2 and 161 +/- 2 degrees on the treated surfaces of Al and Al alloy, respectively. The super-hydrophobic surfaces are produced by the cooperation of binary structures at micro- and nanometer scales, thus reducing the energies of the surfaces. Such super-hydrophobic properties will greatly extend the applications of aluminum and its alloy as lubricating materials.

PROCESS OF DISSOLVING ZIRCONIUM ALLOYS

DOEpatents

Shor, R.S.; Vogler, S.

1958-01-21

A process is described for dissolving binary zirconium-uranium alloys where the uranium content is about 2%. In prior dissolution procedures for these alloys, an oxidizing agent was added to prevent the precipitation of uranium tetrafluoride. In the present method complete dissolution is accomplished without the use of the oxidizing agent by using only the stoichiometric amount or slight excess of HF required by the zirconium. The concentration of the acid may range from 2M to 10M and the dissolution is advatageously carried out at a temperature of 80 deg C.

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys

PubMed Central

Holder, Aaron M.; Siol, Sebastian; Ndione, Paul F.; Peng, Haowei; Deml, Ann M.; Matthews, Bethany E.; Schelhas, Laura T.; Toney, Michael F.; Gordon, Roy G.; Tumas, William; Perkins, John D.; Ginley, David S.; Gorman, Brian P.; Tate, Janet; Zakutayev, Andriy; Lany, Stephan

2017-01-01

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region. PMID:28630928

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys.

PubMed

Holder, Aaron M; Siol, Sebastian; Ndione, Paul F; Peng, Haowei; Deml, Ann M; Matthews, Bethany E; Schelhas, Laura T; Toney, Michael F; Gordon, Roy G; Tumas, William; Perkins, John D; Ginley, David S; Gorman, Brian P; Tate, Janet; Zakutayev, Andriy; Lany, Stephan

2017-06-01

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys

DOE PAGES

Holder, Aaron M.; Siol, Sebastian; Ndione, Paul F.; ...

2017-06-07

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the criticalmore » composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Furthermore, thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.« less

Role of valence electrons in phase transformation kinetics of thallium and its dilute alloys

NASA Technical Reports Server (NTRS)

Ahmed, R.; Ahmed, S.

1991-01-01

The kinetics of the phase transformation of thallium and its dilute alloys were investigated using XRD and calorimetry. Pure thallium exhibits a beta(bcc) to alpha(hcp) phase transformation on cooling at 508 K. With alloying additions, the crystal structure for each phase does not change, although the size of the unit cell increases. The enthalpy and the temperature of phase transformation of each alloy have been determined. The chemical free energy change associated with the phase transformation of each alloy was calculated. The valence electrons make an outstanding contribution to the chemical free energy change required for the phase change.

Half-metallic Co-based quaternary Heusler alloys for spintronics: Defect- and pressure-induced transitions and properties

DOE PAGES

Enamullah, .; Johnson, D. D.; Suresh, K. G.; ...

2016-11-07

Heusler compounds offer potential as spintronic devices due to their spin polarization and half-metallicity properties, where electron spin-majority (minority) manifold exhibits states (band gap) at the electronic chemical potential, yielding full spin polarization in a single manifold. Yet, Heuslers often exhibit intrinsic disorder that degrades its half-metallicity and spin polarization. Using density-functional theory, we analyze the electronic and magnetic properties of equiatomic Heusler (L2 1) CoMnCrAl and CoFeCrGe alloys for effects of hydrostatic pressure and intrinsic disorder (thermal antisites, binary swaps, and vacancies). Under pressure, CoMnCrAl undergoes a metallic transition, while half-metallicity in CoFeCrGe is retained for a limited range.more » Antisite disorder between Cr-Al pair in CoMnCrAl alloy is energetically the most favorable, and retains half-metallic character in Cr-excess regime. However, Co-deficient samples in both alloys undergo a transition from half-metallic to metallic, with a discontinuity in the saturation magnetization. For binary swaps, configurations that compete with the ground state are identified and show no loss of half-metallicity; however, the minority-spin band gap and magnetic moments vary depending on the atoms swapped. For single binary swaps, there is a significant energy cost in CoMnCrAl but with no loss of half-metallicity. Although a few configurations in CoFeCrGe energetically compete with the ground state, the minority-spin band gap and magnetic moments vary depending on the atoms swapped. Furthermore, this information should help in controlling these potential spintronic materials.« less

Half-metallic Co-based quaternary Heusler alloys for spintronics: Defect- and pressure-induced transitions and properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Enamullah, .; Johnson, D. D.; Suresh, K. G.

Heusler compounds offer potential as spintronic devices due to their spin polarization and half-metallicity properties, where electron spin-majority (minority) manifold exhibits states (band gap) at the electronic chemical potential, yielding full spin polarization in a single manifold. Yet, Heuslers often exhibit intrinsic disorder that degrades its half-metallicity and spin polarization. Using density-functional theory, we analyze the electronic and magnetic properties of equiatomic Heusler (L2 1) CoMnCrAl and CoFeCrGe alloys for effects of hydrostatic pressure and intrinsic disorder (thermal antisites, binary swaps, and vacancies). Under pressure, CoMnCrAl undergoes a metallic transition, while half-metallicity in CoFeCrGe is retained for a limited range.more » Antisite disorder between Cr-Al pair in CoMnCrAl alloy is energetically the most favorable, and retains half-metallic character in Cr-excess regime. However, Co-deficient samples in both alloys undergo a transition from half-metallic to metallic, with a discontinuity in the saturation magnetization. For binary swaps, configurations that compete with the ground state are identified and show no loss of half-metallicity; however, the minority-spin band gap and magnetic moments vary depending on the atoms swapped. For single binary swaps, there is a significant energy cost in CoMnCrAl but with no loss of half-metallicity. Although a few configurations in CoFeCrGe energetically compete with the ground state, the minority-spin band gap and magnetic moments vary depending on the atoms swapped. Furthermore, this information should help in controlling these potential spintronic materials.« less

An experimental study of energy dependence of saturation thickness of multiply scattered gamma rays in binary alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Gurvinderjit; Singh, Bhajan, E-mail: bhajan2k1@yahoo.co.in; Sandhu, B. S.

2015-08-28

The present measurements are carried out to investigate the multiple scattering of 662 keV gamma photons emerging from targets of binary alloys (brass and soldering material). The scattered photons are detected by 51 mm × 51 mm NaI(Tl) scintillation detector whose response unscrambling converting the observed pulse–height distribution to a true photon energy spectrum, is obtained with the help of 10 × 10 inverse response matrix. The numbers of multiply scattered events, having same energy as in the singly scattered distribution, first increases with target thickness and then saturate. The application of response function of scintillation detector does not result in anymore » change of measured saturation thickness. Monte Carlo calculation supports the present experimental results.« less

Influence of convection on microstructure

NASA Technical Reports Server (NTRS)

Wilcox, William R.; Caram, Rubens; Mohanty, A. P.; Seth, Jayshree

1990-01-01

In eutectic growth, as the solid phases grow they reject atoms to the liquid. This results in a variation of melt composition along the solid/liquid interface. In the past, mass transfer in eutectic solidification, in the absence of convection, was considered to be governed only by the diffusion induced by compositional gradients. However, mass transfer can also be generated by a temperature gradient. This is called thermotransport, thermomigration, thermal diffusion or the Soret effect. A theoretical model of the influence of the Soret effect on the growth of eutectic alloys is presented. A differential equation describing the compositional field near the interface during unidirectional solidification of a binary eutectic alloy was formulated by including the contributions of both compositional and thermal gradients in the liquid. A steady-state solution of the differential equation was obtained by applying appropriate boundary conditions and accounting for heat flow in the melt. Following that, the average interfacial composition was converted to a variation of undercooling at the interface, and consequently to microstructural parameters. The results obtained show that thermotransport can, under certain circumstances, be a parameter of paramount importance.

Effect of Phase Contiguity and Morphology on the Evolution of Deformation Texture in Two-Phase Alloys

NASA Astrophysics Data System (ADS)

Gurao, N. P.; Suwas, Satyam

2017-02-01

Deformation texture evolution in two-phase xFe- yNi-(100- x- y)Cr model alloys and Ti-13Nb-13Zr alloy was studied during rolling to develop an understanding of micro-mechanisms of deformation in industrially relevant two-phase FCC-BCC steels and HCP-BCC titanium alloys, respectively. It was found that volume fraction and contiguity of phases lead to systematic changes in texture, while morphology affects the strength of texture. There was a characteristic change in texture from typical Brass-type to a weaker Copper-type texture in the austenite phase accompanied with a change from alpha fiber to gamma fiber in ferrite phase for Fe-Ni-Cr alloys with increase in fraction of harder ferrite phase. However, similar characteristic texture evolution was noted in both α and β phase irrespective of the different initial morphologies in Ti-13Nb-13Zr alloy. Viscoplastic self-consistent simulations with two-phase scheme were able to qualitatively predict texture evolution in individual phases. It is proposed that the transition from iso-strain-type behavior for equiaxed microstructure at low strain to iso-stress-type behavior at higher strain is aided by the presence of higher volume fraction of the second phase and increasing aspect ratio of individual phases in two-phase alloys.

Method for preparing homogeneous single crystal ternary III-V alloys

DOEpatents

Ciszek, Theodore F.

1991-01-01

A method for producing homogeneous, single-crystal III-V ternary alloys of high crystal perfection using a floating crucible system in which the outer crucible holds a ternary alloy of the composition desired to be produced in the crystal and an inner floating crucible having a narrow, melt-passing channel in its bottom wall holds a small quantity of melt of a pseudo-binary liquidus composition that would freeze into the desired crystal composition. The alloy of the floating crucilbe is maintained at a predetermined lower temperature than the alloy of the outer crucible, and a single crystal of the desired homogeneous alloy is pulled out of the floating crucible melt, as melt from the outer crucible flows into a bottom channel of the floating crucible at a rate that corresponds to the rate of growth of the crystal.

Thermal conductivity of disordered two-dimensional binary alloys.

PubMed

Zhou, Yang; Guo, Zhi-Xin; Cao, Hai-Yuan; Chen, Shi-You; Xiang, Hong-Jun; Gong, Xin-Gao

2016-10-20

Using non-equilibrium molecular dynamics simulations, we have studied the effect of disorder on the thermal conductivity of two-dimensional (2D) C 1-x N x alloys. We find that the thermal conductivity not only depends on the substitution concentration of nitrogen, but also strongly depends on the disorder distribution. A general linear relationship is revealed between the thermal conductivity and the participation ratio of phonons in 2D alloys. Localization mode analysis further indicates that the thermal conductivity variation in the ordered alloys can be attributed to the number of inequivalent atoms. As for the disordered alloys, we find that the thermal conductivity variation can be described by a simple linear formula with the disorder degree and the substitution concentration. The present study suggests some general guidance for phonon manipulation and thermal engineering in low dimensional alloys.

Effect of Nb on magnetic and mechanical properties of TbDyFe alloys

NASA Astrophysics Data System (ADS)

Wang, Naijuan; Liu, Yuan; Zhang, Huawei; Chen, Xiang; Li, Yanxiang

2018-03-01

The intrinsic brittleness in giant magnetostrictive material TbDyFe alloy has devastating influence on the machinability and properties of the alloy, thus affecting its applications. The purpose of this paper is to study the mechanical properties of the TbDyFe alloy by alloying with Nb element. The samples (Tb0.3Dy0.7)xFe2xNby (y = 0, 0.01, 0.04, 0.07, 0.1; 3x + y = 1) were melted in an arc melting furnace under high purity argon atmosphere. The microstructure, magnetostrictive properties and mechanical performance of the alloys were studied systematically. The results showed that NbFe2 phases were observed in the alloys with the addition of Nb. Moreover, both the NbFe2 phases and rare earth (RE)-rich phases were increased with the increasing of Nb element. The mechanical properties results revealed that the fracture toughness of the alloy with the addition of Nb enhanced 1.5-5 times of the Nb-free alloy. Both the NbFe2 phase and the RE-rich phase had the ability to prevent crack propagation, so that they can strengthen the REFe2 body. However, NbFe2 phase is a paramagnetic phase, which can reduce the magnetostrictive properties of the alloy by excessive precipitation.

Composite Ni/NiO-Cr2O3 Catalyst for Alkaline Hydrogen Evolution Reaction

PubMed Central

Bates, Michael K.; Jia, Qingying; Ramaswamy, Nagappan; Allen, Robert J.; Mukerjee, Sanjeev

2015-01-01

We report a Ni–Cr/C electrocatalyst with unprecedented mass-activity for the hydrogen evolution reaction (HER) in alkaline electrolyte. The HER kinetics of numerous binary and ternary Ni-alloys and composite Ni/metal-oxide/C samples were evaluated in aqueous 0.1 M KOH electrolyte. The highest HER mass-activity was observed for Ni–Cr materials which exhibit metallic Ni as well as NiOx and Cr2O3 phases as determined by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) analysis. The onset of the HER is significantly improved compared to numerous binary and ternary Ni-alloys, including Ni–Mo materials. It is likely that at adjacent Ni/NiOx sites, the oxide acts as a sink for OHads, while the metallic Ni acts as a sink for the Hads intermediate of the HER, thus minimizing the high activation energy of hydrogen evolution via water reduction. This is confirmed by in situ XAS studies that show that the synergistic HER enhancement is due to NiOx content and that the Cr2O3 appears to stabilize the composite NiOx component under HER conditions (where NiOx would typically be reduced to metallic Ni0). Furthermore, in contrast to Pt, the Ni(Ox)/Cr2O3 catalyst appears resistant to poisoning by the anion exchange ionomer (AEI), a serious consideration when applied to an anionic polymer electrolyte interface. Furthermore, we report a detailed model of the double layer interface which helps explain the observed ensemble effect in the presence of AEI. PMID:26191118

BCAT Setup

NASA Image and Video Library

2011-10-24

ISS029-E-032412 (24 Oct. 2011) --- NASA Mike Fossum, Expedition 29 commander, conducts a session with the Binary Colloidal Alloy Test-6 (BCAT-6) experiment in the Kibo laboratory of the International Space Station.

BCAT Setup

NASA Image and Video Library

2011-10-24

ISS029-E-032414 (24 Oct. 2011) --- NASA Mike Fossum, Expedition 29 commander, conducts a session with the Binary Colloidal Alloy Test-6 (BCAT-6) experiment in the Kibo laboratory of the International Space Station.

BCAT Setup

NASA Image and Video Library

2011-10-24

ISS029-E-032422 (24 Oct. 2011) --- NASA Mike Fossum, Expedition 29 commander, conducts a session with the Binary Colloidal Alloy Test-6 (BCAT-6) experiment in the Kibo laboratory of the International Space Station.

BCAT Setup

NASA Image and Video Library

2011-10-24

ISS029-E-032410 (24 Oct. 2011) --- NASA Mike Fossum, Expedition 29 commander, conducts a session with the Binary Colloidal Alloy Test-6 (BCAT-6) experiment in the Kibo laboratory of the International Space Station.

Mechanical property, biocorrosion and in vitro biocompatibility evaluations of Mg-Li-(Al)-(RE) alloys for future cardiovascular stent application.

PubMed

Zhou, W R; Zheng, Y F; Leeflang, M A; Zhou, J

2013-11-01

Mg-Li-based alloys were investigated for future cardiovascular stent application as they possess excellent ductility. However, Mg-Li binary alloys exhibited reduced mechanical strengths due to the presence of lithium. To improve the mechanical strengths of Mg-Li binary alloys, aluminum and rare earth (RE) elements were added to form Mg-Li-Al ternary and Mg-Li-Al-RE quarternary alloys. In the present study, six Mg-Li-(Al)-(RE) alloys were fabricated. Their microstructures, mechanical properties and biocorrosion behavior were evaluated by using optical microscopy, X-ray diffraction, scanning electronic microscopy, tensile tests, immersion tests and electrochemical measurements. Microstructure characterization indicated that grain sizes were moderately refined by the addition of rare earth elements. Tensile testing showed that enhanced mechanical strengths were obtained, while electrochemical and immersion tests showed reduced corrosion resistance caused by intermetallic compounds distributed throughout the magnesium matrix in the rare-earth-containing Mg-Li alloys. Cytotoxicity assays, hemolysis tests as well as platelet adhesion tests were performed to evaluate in vitro biocompatibilities of the Mg-Li-based alloys. The results of cytotoxicity assays clearly showed that the Mg-3.5Li-2Al-2RE, Mg-3.5Li-4Al-2RE and Mg-8.5Li-2Al-2RE alloys suppressed vascular smooth muscle cell proliferation after 5day incubation, while the Mg-3.5Li, Mg-8.5Li and Mg-8.5Li-1Al alloys were proven to be tolerated. In the case of human umbilical vein endothelial cells, the Mg-Li-based alloys showed no significantly reduced cell viabilities except for the Mg-8.5Li-2Al-2RE alloy, with no obvious differences in cell viability between different culture periods. With the exception of Mg-8.5Li-2Al-2RE, all of the other Mg-Li-(Al)-(RE) alloys exhibited acceptable hemolysis ratios, and no sign of thrombogenicity was found. These in vitro experimental results indicate the potential of Mg-Li-(Al)-(RE) alloys as biomaterials for future cardiovascular stent application and the worthiness of investigating their biodegradation behaviors in vivo. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Biomimetic hydrophobic surface fabricated by chemical etching method from hierarchically structured magnesium alloy substrate

NASA Astrophysics Data System (ADS)

Liu, Yan; Yin, Xiaoming; Zhang, Jijia; Wang, Yaming; Han, Zhiwu; Ren, Luquan

2013-09-01

As one of the lightest metal materials, magnesium alloy plays an important role in industry such as automobile, airplane and electronic product. However, magnesium alloy is hindered due to its high chemical activity and easily corroded. Here, inspired by typical plant surfaces such as lotus leaves and petals of red rose with super-hydrophobic character, the new hydrophobic surface is fabricated on magnesium alloy to improve anti-corrosion by two-step methodology. The procedure is that the samples are processed by laser first and then immersed and etched in the aqueous AgNO3 solution concentrations of 0.1 mol/L, 0.3 mol/L and 0.5 mol/L for different times of 15 s, 40 s and 60 s, respectively, finally modified by DTS (CH3(CH2)11Si(OCH3)3). The microstructure, chemical composition, wettability and anti-corrosion are characterized by means of SEM, XPS, water contact angle measurement and electrochemical method. The hydrophobic surfaces with microscale crater-like and nanoscale flower-like binary structure are obtained. The low-energy material is contained in surface after DTS treatment. The contact angles could reach up to 138.4 ± 2°, which hydrophobic property is both related to the micro-nano binary structure and chemical composition. The results of electrochemical measurements show that anti-corrosion property of magnesium alloy is improved. Furthermore, our research is expected to create some ideas from natural enlightenment to improve anti-corrosion property of magnesium alloy while this method can be easily extended to other metal materials.

Quasicrystal-reinforced Mg alloys.

PubMed

Kyun Kim, Young; Tae Kim, Won; Hyang Kim, Do

2014-04-01

The formation of the icosahedral phase (I-phase) as a secondary solidification phase in Mg-Zn-Y and Mg-Zn-Al base systems provides useful advantages in designing high performance wrought magnesium alloys. The strengthening in two-phase composites (I-phase + α -Mg) can be explained by dispersion hardening due to the presence of I-phase particles and by the strong bonding property at the I-phase/matrix interface. The presence of an additional secondary solidification phase can further enhance formability and mechanical properties. In Mg-Zn-Y alloys, the co-presence of I and Ca 2 Mg 6 Zn 3 phases by addition of Ca can significantly enhance formability, while in Mg-Zn-Al alloys, the co-presence of the I-phase and Mg 2 Sn phase leads to the enhancement of mechanical properties. Dynamic and static recrystallization are significantly accelerated by addition of Ca in Mg-Zn-Y alloy, resulting in much smaller grain size and more random texture. The high strength of Mg-Zn-Al-Sn alloys is attributed to the presence of finely distributed Mg 2 Sn and I-phase particles embedded in the α -Mg matrix.

Quasicrystal-reinforced Mg alloys

PubMed Central

Kyun Kim, Young; Tae Kim, Won; Hyang Kim, Do

2014-01-01

The formation of the icosahedral phase (I-phase) as a secondary solidification phase in Mg–Zn–Y and Mg–Zn–Al base systems provides useful advantages in designing high performance wrought magnesium alloys. The strengthening in two-phase composites (I-phase + α-Mg) can be explained by dispersion hardening due to the presence of I-phase particles and by the strong bonding property at the I-phase/matrix interface. The presence of an additional secondary solidification phase can further enhance formability and mechanical properties. In Mg–Zn–Y alloys, the co-presence of I and Ca2Mg6Zn3 phases by addition of Ca can significantly enhance formability, while in Mg–Zn–Al alloys, the co-presence of the I-phase and Mg2Sn phase leads to the enhancement of mechanical properties. Dynamic and static recrystallization are significantly accelerated by addition of Ca in Mg–Zn–Y alloy, resulting in much smaller grain size and more random texture. The high strength of Mg–Zn–Al–Sn alloys is attributed to the presence of finely distributed Mg2Sn and I-phase particles embedded in the α-Mg matrix. PMID:27877660

Liquidus Projections of Bi-Se-Ga and Bi-Se-Te Ternary Systems

NASA Astrophysics Data System (ADS)

Lin, Po-han; Chen, Sinn-wen; Hwang, Jenn-dong; Chu, Hsu-shen

2016-12-01

This study determines the liquidus projections of both Bi-Se-Ga and Bi-Se-Te ternary systems which are constituent ternary systems of promising Bi-Se-Te-Ga thermoelectric materials. Ternary Bi-Se-Ga and Bi-Se-Te alloys are prepared. Their primary solidification phases are experimentally determined, and thermal analysis experiments are carried out. The liquidus projections are determined based on the ternary experimental results and phase diagrams of constituent binary systems. The Bi-Se-Ga system includes seven primary solidification phases, Bi, Ga, GaSe, Ga2Se3, Se, Bi2Se3, and (Bi2)n(Bi2Se3)m. In the Bi-Se-Te system, there are five primary solidification phases, Bi, (Bi2)n(Bi2Te3)m, Bi2(Se,Te)3, (Se,Te), and (Bi2)n(Bi2Se3)m. Both the (Bi2)n(Bi2Te3)m and (Bi2)n(Bi2Se3)m phases are not a single phase, but a collection of series undetermined phases. Large miscibility gaps are observed in the Bi-Se-Ga system. The temperatures of the invariant reactions, Liquid + Bi + GaSe = Ga and Liquid + Ga2Se3 = Bi + GaSe, are at 495 K (222 °C) and 533 K (260 °C), respectively.

Re-evaluation of the impact of ternary additions of Ni and Cu on the A1 to L1{sub 0} transformation in FePt films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, B.; Barmak, K.

2011-06-15

The impact of ternary additions of Ni (1.6-21.5 at. %) and Cu (1.3-17.3 at. %) on the A1 (face centered cubic, fcc) to L1{sub 0} phase transformation in FePt films has been re-evaluated based on compositions obtained using energy dispersive x-ray spectrometry (EDS). The data presented here serve as corrections to results reported in six previous studies [D. C. Berry and K. Barmak, J. Appl. Phys. 102, 024912 (2007); 101, 014905 (2007); 99, 08G901 (2006); D. C. Berry, J. Kim, K. Barmak, K. Wierman, E. B. Svedberg, and J. K. Howard, Scr. Mater. 53, 423 (2005); K. Barmak, J. Kim,more » D. C. Berry, W. N. Hanani, K. Wierman, E. B. Svedberg, and J. K. Howard, J. Appl. Phys. 97, 024902 (2005); K. Barmak, J. Kim, D. C. Berry, K. W. Wierman, E. B. Svedberg, and J. K. Howard, ibid. 95, 7486 (2004)]. The new EDS compositions do not change the following conclusions of these previous studies: (i) when ternary FeNiPt and FeCuPt alloys are compared with binary FePt alloys with the same Pt content, it is seen that additions of Ni slow the transformation kinetics, whereas additions of Cu have no measurable impact on the kinetics, (ii) the Curie temperature of the L1{sub 0} phase is lowered by additions of Ni or Cu, (iii) the Curie temperature of the A1 phase is increased by additions of Ni, but lowered by additions of Cu, and (iv) the transformation enthalpy is lowered by large additions of Ni, but is unaffected by additions of Cu. The ordering behavior of FeCuPt alloys as evidenced by the kinetic ordering temperature is compared with other reports in the literature based on magnetic measurements.« less

Modeling creep deformation of a two-phase TiAI/Ti3Al alloy with a lamellar microstructure

NASA Astrophysics Data System (ADS)

Bartholomeusz, Michael F.; Wert, John A.

1994-10-01

A two-phase TiAl/Ti3Al alloy with a lamellar microstructure has been previously shown to exhibit a lower minimum creep rate than the minimum creep rates of the constituent TiAl and Ti3Al single-phase alloys. Fiducial-line experiments described in the present article demonstrate that the creep rates of the constituent phases within the two-phase TiAl/Ti3Al lamellar alloy tested in compression are more than an order of magnitude lower than the creep rates of single-phase TiAl and Ti3Al alloys tested in compression at the same stress and temperature. Additionally, the fiducial-line experiments show that no interfacial sliding of the phases in the TiAl/Ti3Al lamellar alloy occurs during creep. The lower creep rate of the lamellar alloy is attributed to enhanced hardening of the constituent phases within the lamellar microstructure. A composite-strength model has been formulated to predict the creep rate of the lamellar alloy, taking into account the lower creep rates of the constituent phases within the lamellar micro-structure. Application of the model yields a very good correlation between predicted and experimentally observed minimum creep rates over moderate stress and temperature ranges.

HEAT TREATED U-Nb ALLOYS

DOEpatents

McGeary, R.K.; Justusson, W.M.

1959-11-24

A fuel element for a nuclear reactor is described comprising an alloy containing uranium and from 7 to 20 wt.% niobium, the alloy being substantially in the gamma phase and having been produced by working an ingot of the alloy into the desired shape, homogenizing it by annealing it at a temperature in the gamma phase field, and quenching it to retain the gamma phase structure of the alloy.

Deposition behavior of mixed binary metallic powders in cold spraying process

NASA Astrophysics Data System (ADS)

Zhou, X. L.; Mou, S. J.; Wu, X. K.; Zhang, J. S.

2011-10-01

In the present study, Zn/Al composite coating was selected for the typical case to study the deposition behavior and the deformation of binary mixing particles in cold spraying process by means of an experiment and numerical simulation. The experimental results demonstrated that the coating had a dense microstructure, and that Zn and Al were uniformly distributed in the coating. Al particles deformed more severely than Zn particles, and extensively deformed Al particles had a local jet-metallic mixing area. The steel substrate underwent a small amount of deformation when impacted by Zn particles, whereas the substrate did not deform when impacted by Al particles. XRD results show that the Zn/Al composite coating did not form a new phase, and only resulted in the mechanical mixing of Zn and Al, producing a pseudo-alloy coating. In addition, a binary Zn/Al multiparticle impact was first simulated using the finite element analysis software ANSYS/LS-DYNA. The effective plastic strain contour, which enabled the description of the particle deposit procedure, was demonstrated. The plastic deformation evolution of Zn and Al particles in the composite coating was analyzed individually, and the curves of effective plastic strain versus time of typical monitored elements at the edge of the Zn and Al particles were plotted. The simulations showed good concordance with the experimental results.

Natural ageing responses of duplex structured Mg-Li based alloys

PubMed Central

Li, C. Q.; Xu, D. K.; Wang, B. J.; Sheng, L. Y.; Qiao, Y. X.; Han, E. H.

2017-01-01

Natural ageing responses of duplex structured Mg-6%Li and Mg-6%Li-6%Zn-1.2%Y alloys have been investigated. Microstructural analyses revealed that the precipitation and coarsening process of α-Mg particles could occur in β-Li phases of both two alloys during ageing process. Since a certain amount of Mg atoms in β-Li phases were consumed for the precipitation of abundant tiny MgLiZn particles, the size of α-Mg precipitates in Mg-6%Li-6%Zn-1.2%Y alloy was relatively smaller than that in Mg-6%Li alloy. Micro hardness measurements demonstrated that with the ageing time increasing, the α-Mg phases in Mg-6%Li alloy could have a constant hardness value of 41 HV, but the contained β-Li phases exhibited a slight age-softening response. Compared with the Mg-6%Li alloy, the age-softening response of β-Li phases in Mg-6%Li-6%Zn-1.2%Y alloy was much more profound. Meanwhile, a normal age-hardening response of α-Mg phases was maintained. Tensile results indicated that obvious ageing-softening phenomenon in terms of macro tensile strength occurred in both two alloys. Failure analysis demonstrated that for the Mg-6%Li alloy, cracks were preferentially initiated at α-Mg/β-Li interfaces. For the Mg-6%Li-6%Zn-1.2%Y alloy, cracks occurred at both α-Mg/β-Li interfaces and slip bands in α-Mg and β-Li phases. PMID:28053318

Dual-phase Cr-Ta alloys for structural applications

DOEpatents

Liu, Chain T.; Brady, Michael P.; Zhu, Jiahong; Tortorelli, Peter F.

2001-01-01

Dual phase alloys of chromium containing 2 to 11 atomic percent tantalum with minor amounts of Mo, Cr, Ti, Y, La, Cr, Si and Ge are disclosed. These alloys contain two phases including Laves phase and Cr-rich solid solution in either eutectic structures or dispersed Laves phase particles in the Cr-rich solid solution matrix. The alloys have superior mechanical properties at high temperature and good oxidation resistance when heated to above 1000.degree. C. in air.

BCAT setup in Kibo

NASA Image and Video Library

2014-06-03

ISS040-E-006891 (3 June 2014) --- NASA astronaut Reid Wiseman, Expedition 40 flight engineer, conducts a session with the Binary Colloidal Alloy Test (BCAT) experiment in the Kibo laboratory of the International Space Station.

Microstructural analyses of two high noble gold-platinum alloys before and after conditioning in a cell culture medium

NASA Astrophysics Data System (ADS)

Rudolf, R.; Anzel, I.; Gusel, L.; Stamenkovi, D.; Todorovi, A.; Colic, M.

2010-12-01

Microstructures of two high noble experimental Au-Pt alloys were compared before and after conditioning for biocompatibility, in order to identify phases and microelements responsible for the alloys' corrosive behaviour. Microstructural characterization was carried-out by optical and scanning electron microscopy, in addition to energy dispersive X-ray analysis. X-ray diffraction was applied to determine the phases' composition and their contribution in the alloys. Additionally, simultaneous thermal analysis was used to identify the temperatures of phase transformations. An overall assessment before conditioning showed that Au-Pt I is a two-phase alloy containing a dominant Au-rich α1 phase and a minor Pt-rich α2 phase, while the Au-Pt II alloy contains in addition three minor phases: AuZn3, Pt3Zn and Au1.4Zn0.52. The highest content of Zn (up to 6.76 wt.%) was detected in the Pt3Zn phase. After RPMI cell culture medium conditioning, the Pt3Zn and AuZn3 phases disappeared, suggesting that they are predominantly responsible for Zn loss and the lower corrosive stability of the Au-Pt II alloy.

Effect of heat treatment on the corrosion resistance of modified aluminum-magnesium alloys in seawater

NASA Astrophysics Data System (ADS)

Ahmad, Z.; Aleem, A.

1993-10-01

Study of modified Al-2.5Mg alloys containing chromium, silica, iron, and manganese in various tempers (O, H-18, T-4, T-6, T-18, and H-34) has shown that their corrosion resistance is significantly altered by thermomechanical treatment and the beneficial effect of chromium on microstructural changes. Modified binary Al-2.5Mg alloys in the T-6 and T-4 tempers exhibit a higher resistance to corrosion in Arabian Gulf water than H-34 tempers due to the beneficial effect of chromium on microstructural changes.

Analysis and Thermodynamic Prediction of Hydrogen Solution in Solid and Liquid Multicomponent Aluminum Alloys

NASA Astrophysics Data System (ADS)

Anyalebechi, P. N.

Reported experimentally determined values of hydrogen solubility in liquid and solid Al-H and Al-H-X (where X = Cu, Si, Zn, Mg, Li, Fe or Ti) systems have been critically reviewed and analyzed in terms of Wagner's interaction parameter. An attempt has been made to use Wagner's interaction parameter and statistic linear regression models derived from reported hydrogen solubility limits for binary aluminum alloys to predict the hydrogen solubility limits in liquid and solid (commercial) multicomponent aluminum alloys. Reasons for the observed poor agreement between the predicted and experimentally determined hydrogen solubility limits are discussed.

Behavior of sheets from Ti-alloys by rolling and heat treatment

NASA Astrophysics Data System (ADS)

Isaenkova, M.; Perlovich, Yu.; Fesenko, V.; Gritskevich, M.; Stolbov, S.; Zaripova, M.

2017-10-01

Sheets from single- and two-phase Ti-alloys (VT1-0, Ti-22Nb-9%Zr and VT-16) were rolled at the room temperature up to various deformation degrees and annealed at temperatures 500-900 °C. The regularities of texture formation in both phases were established. In the technically pure Ti (VT1-0) with the single α-Ti phase the final stable texture component is (0001)±30-40°ND-TD<101 ¯0>. In the two-phase alloy the reorientation of basal axes of α-Ti occurs by the same trajectories as in the single phase alloy. However, in the case of two-phase alloy texture development in α-Ti stops at the intermediate stage, when this texture consists of components with rolling planes (0001)±15-20°ND-RD and (0001)±30-40°ND-TD. The stability of the first components can be provided both by the mutually balanced operation of pyramidal and basal slip systems, activity of which remains at the high deformation degree of two-phase alloy, and by the dynamic α↔β phase transformations, taking place in the distorted structures of α- and β-phases in the course of its cold rolling. At recrystallization of technically pure Ti the basal component disappears in its texture. At the same time, prismatic axes turn by angles 20÷30° depending on the heating rate of the rolled sheet and annealing temperature. At recrystallization of the two-phase Ti-alloy prismatic axes of its α-grains doesn't turn relative to their positions in the rolling texture, as it occurs in the single-phase alloy. This fact indicates to some alternative mode of arising new recrystallized grains in two-phase alloys.

Binary Solid-Liquid Phase Diagram of Phenol and t-Butanol: An Undergraduate Physical Chemistry Experiment

ERIC Educational Resources Information Center

Xu, Xinhua; Wang, Xiaogang; Wu, Meifen

2014-01-01

The determination of the solid-liquid phase diagram of a binary system is always used as an experiment in the undergraduate physical chemistry laboratory courses. However, most phase diagrams investigated in the lab are simple eutectic ones, despite the fact that complex binary solid-liquid phase diagrams are more common. In this article, the…

Al-Cu-Li and Al-Mg-Li alloys: Phase composition, texture, and anisotropy of mechanical properties (Review)

NASA Astrophysics Data System (ADS)

Betsofen, S. Ya.; Antipov, V. V.; Knyazev, M. I.

2016-04-01

The results of studying the phase transformations, the texture formation, and the anisotropy of the mechanical properties in Al-Cu-Li and Al-Mg-Li alloys are generalized. A technique and equations are developed to calculate the amounts of the S1 (Al2MgLi), T1 (Al2CuLi), and δ' (Al3Li) phases. The fraction of the δ' phase in Al-Cu-Li alloys is shown to be significantly higher than in Al-Mg-Li alloys. Therefore, the role of the T1 phase in the hardening of Al-Cu-Li alloys is thought to be overestimated, especially in alloys with more than 1.5% Li. A new model is proposed to describe the hardening of Al-Cu-Li alloys upon aging, and the results obtained with this model agree well with the experimental data. A texture, which is analogous to that in aluminum alloys, is shown to form in sheets semiproducts made of Al-Cu-Li and Al-Mg-Li alloys. The more pronounced anisotropy of the properties of lithium-containing aluminum alloys is caused by a significant fraction of the ordered coherent δ' phase, the deformation mechanism in which differs radically from that in the solid solution.

Effect of solution treatment on the microstructure, tensile properties, and corrosion behavior of the Mg-5Sn-2Zn-0.1Mn alloy

NASA Astrophysics Data System (ADS)

El Mahallawy, N.; Hammouda, R.; Shoeib, M.; Diaa, Alia A.

2018-01-01

Working on magnesium alloys containing relatively inexpensive alloying elements such as tin, zinc, and manganese have been a target for many studies. The binary Mg-Sn and Mg-Zn systems have a wide range of solid solubility which make them heat-treatable alloys. In the present study, the microstructure, tensile properties, and corrosion behavior of the Mg-5Sn-2Zn-0.1Mn alloy was studied in the as cast state and after heat treatment at a temperature reaching 450 °C for about 24 h. It was found that a noticeable enhancement in strength and corrosion resistance was achieved through heat treatment. The strength of the as cast alloy increased from 76.24 ± 6.21 MPa to 187.33 ± 10.3 MPa, while the corrosion rate decreased from 1.129 to 0.399 mm y-1.

Performance of ethanol electro-oxidation on Ni-Cu alloy nanowires through composition modulation.

PubMed

Tian, Xi-Ke; Zhao, Xiao-Yu; Zhang, Li-de; Yang, Chao; Pi, Zhen-Bang; Zhang, Su-Xin

2008-05-28

To reduce the cost of the catalyst for direct ethanol fuel cells and improve its catalytic activity, highly ordered Ni-Cu alloy nanowire arrays have been fabricated successfully by differential pulse current electro-deposition into the pores of a porous anodic alumina membrane (AAMs). The energy dispersion spectrum, scanning and transmission electron microscopy were utilized to characterize the composition and morphology of the Ni-Cu alloy nanowire arrays. The results reveal that the nanowires in the array are uniform, well isolated and parallel to each other. The catalytic activity of the nanowire electrode arrays for ethanol oxidation was tested and the binary alloy nanowire array possesses good catalytic activity for the electro-oxidation of ethanol. The performance of ethanol electro-oxidation was controlled by varying the Cu content in the Ni-Cu alloy and the Ni-Cu alloy nanowire electrode shows much better stability than the pure Ni one.