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Sample records for bulk amorphous alloy

  1. Imprinting bulk amorphous alloy at room temperature

    SciTech Connect

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-11-13

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. In conclusion, our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment.

  2. Imprinting bulk amorphous alloy at room temperature

    PubMed Central

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-01-01

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. Our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment. PMID:26563908

  3. Imprinting bulk amorphous alloy at room temperature.

    PubMed

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T; Lograsso, Thomas A; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-01-01

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. Our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment. PMID:26563908

  4. Imprinting bulk amorphous alloy at room temperature

    DOE PAGESBeta

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-11-13

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the abilitymore » of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. In conclusion, our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment.« less

  5. Bulk amorphous steels based on Fe alloys

    DOEpatents

    Lu, ZhaoPing; Liu, Chain T.

    2006-05-30

    A bulk amorphous alloy has the approximate composition: Fe.sub.(100-a-b-c-d-e)Y.sub.aMn.sub.bT.sub.cM.sub.dX.sub.e wherein: T includes at least one of the group consisting of: Ni, Cu, Cr and Co; M includes at least one of the group consisting of W, Mo, Nb, Ta, Al and Ti; X includes at least one of the group consisting of Co, Ni and Cr; a is an atomic percentage, and a<5; b is an atomic percentage, and b.ltoreq.25; c is an atomic percentage, and c.ltoreq.25; d is an atomic percentage, and d.ltoreq.25; and e is an atomic percentage, and 5.ltoreq.e.ltoreq.30.

  6. Bulk amorphous metallic alloys: Synthesis by fluxing techniques and properties

    SciTech Connect

    He, Yi; Shen, Tongde; Schwarz, R.B.

    1997-05-01

    Bulk amorphous alloys having dimensions of at least 1 cm diameter have been prepared in the Pd-Ni-P, Pd-Cu-P, Pd-Cu-Ni-P, and Pd-Ni-Fe-P systems using a fluxing and water quenching technique. The compositions for bulk glass formation have been determined in these systems. For these bulk metallic glasses, the difference between the crystallization temperature T{sub x}, and the glass transition temperature T{sub g}, {Delta}T = T{sub x} - T{sub g}, ranges from 60 to 1 10 K. These large values of {Delta}T open the possibility for the fabrication of amorphous near net-shape components using techniques such as injection molding. The thermal, elastic, and magnetic properties of these alloys have been studied, and we have found that bulk amorphous Pd{sub 40}Ni{sub 22.5}Fe{sub 17.5}P{sub 20} has spin glass behavior for temperatures below 30 K. 65 refs., 14 figs., 3 tabs.

  7. Effect of Viscosity on the Microformability of Bulk Amorphous Alloy in Supercooled Liquid Region

    SciTech Connect

    Cheng Ming; Zhang Shihong; Wang Ruixue

    2010-06-15

    Previously published results have shown that viscosity greatly influences on the deformation behavior of the bulk amorphous alloy in supercooled liquid region during microforming process. And viscosity is proved to be a component of the evaluation index which indicating microformability. Based on the fluid flow theory and assumptions, bulk amorphous alloy can be regarded as the viscous materials with a certain viscosity. It is helpful to understand how the viscosity plays an important role in viscous materials with various viscosities by numerical simulation on the process. Analysis is carried out by linear state equation in FEM with other three materials, water, lubricant oil and polymer melt, whose viscosities are different obviously. The depths of the materials flow into the U-shaped groove during the microimprinting process are compared in this paper. The result shows that the deformation is quite different when surface tension effect is not considered in the case. With the lowest viscosity, water can reach the bottom of micro groove in a very short time. Lubricant oil and polymer melt slower than it. Moreover bulk amorphous alloys in supercooled liquid state just flow into the groove slightly. Among the alloys of different systems including Pd-, Mg- and Zr-based alloy, Pd-based alloy ranks largest in the depth. Mg-based alloy is the second. And Zr-based alloy is the third. Further more the rank order of the viscosities of the alloys is Pd-, Mg- and Zr-based. It agrees well with the results of calculation. Therefore viscosity plays an important role in the microforming of the bulk amorphous alloy in the supercooled liquid state.

  8. Structural Relaxation and Nanocrystallization-Induced Laser Surface Hardening of Fe-Based Bulk Amorphous Alloys

    NASA Astrophysics Data System (ADS)

    Singh, Ashish K.; Alavi, S. Habib; Paital, Sameer R.; Dahotre, Narendra B.; Harimkar, Sandip P.

    2014-06-01

    Amorphous metallic alloys or bulk metallic glasses are emerging as promising materials for a range of structural, microelectromechanical systems, and biomedical applications. With the recent developments in spark plasma sintering and superplastic forming of the amorphous alloys, it is likely that the amorphous alloys will find a place in new applications. In this article, surface hardening of spark plasma sintered Fe48Cr15Mo14Y2C15B6 bulk amorphous alloys using a continuous-wave Nd:YAG laser is reported. Depending on the processing parameters, the laser surface irradiation causes structural relaxation (enhanced medium-range ordering and/or annihilation of excess free volume) and nanocrystallization of hard carbides (M23C6 and M7C3), resulting in surface hardening. Detailed investigations on the thermal effects, microstructural modifications, and hardness improvements due to laser surface irradiation with laser fluence in the range of 1.77-2.36 J/mm2 are presented. An increase in hardness in the range of 1360-1560 HV for laser surface-treated alloys compared to 1200 HV for as-sintered alloys over a hardening depth of about 50-80 µm is observed.

  9. Densification behavior, nanocrystallization, and mechanical properties of spark plasma sintered Fe-based bulk amorphous alloys

    NASA Astrophysics Data System (ADS)

    Singh, Ashish Kumar

    Fe-based amorphous alloys are gaining increasing attention due to their exceptional wear and corrosion resistance for potential structural applications. Two major challenges that are hindering the commercialization of these amorphous alloys are difficulty in processing of bulk shapes (diameter > 10 mm) and lack of ductility. Spark plasma sintering (SPS) is evolving as a promising technique for processing bulk shapes of amorphous and nanocrystalline materials. The objective of this work is to investigate densification behavior, nanocrystallization, and mechanical properties of SPS sintered Fe-based amorphous alloys of composition Fe48Cr15Mo14Y2C15B6. SPS processing was performed in three distinct temperature ranges of amorphous alloys: (a) below glass transition temperature (Tg), (b) between Tg and crystallization temperature (Tx), and (c) above Tx. Punch displacement data obtained during SPS sintering was correlated with the SPS processing parameters such as temperature, pressure, and sintering time. Powder rearrangement, plastic deformation below T g, and viscous flow of the material between Tg and Tx were observed as the main densification stages during SPS sintering. Micro-scale temperature distributions at the point of contact and macro-scale temperature distribution throughout the sample during SPS of amorphous alloys were modeled. The bulk amorphous alloys are expected to undergo structural relaxation and nanocrystallization during SPS sintering. X-ray diffraction (XRD), small angle neutron scattering (SANS), and transmission electron microscopy (TEM) was performed to investigate the evolution of nanocrystallites in SPS sintered Fe-based bulk amorphous alloys. The SANS analysis showed significant scattering for the samples sintered in the supercooled region indicating local structural and compositional changes with the profuse nucleation of nano-clusters (~4 nm). Compression tests and microhardness were performed on the samples sintered at different

  10. Bulk amorphous materials

    SciTech Connect

    Schwarz, R.B.; Archuleta, J.I.; Sickafus, K.E.

    1998-12-01

    This is the final report for a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The objective of this work was to develop the competency for the synthesis of novel bulk amorphous alloys. The authors researched their synthesis methods and alloy properties, including thermal stability, mechanical, and transport properties. The project also addressed the development of vanadium-spinel alloys for structural applications in hostile environments, the measurement of elastic constants and thermal expansion in single-crystal TiAl from 300 to 750 K, the measurement of elastic constants in gallium nitride, and a study of the shock-induced martensitic transformations in NiTi alloys.

  11. Laser Processing of Fe-Based Bulk Amorphous Alloy Coatings on Titanium

    NASA Astrophysics Data System (ADS)

    Sahasrabudhe, Himanshu; Dittrick, Stanley A.; Bandyopadhyay, Amit

    2013-11-01

    Laser Engineered Net Shaping (LENS™), a solid freeform fabrication technique, was employed for the processing of Fe-based bulk amorphous alloy (Fe BAA) powder on titanium. One and two layers of the Fe BAA were deposited with the same processing parameters. SEM and XRD analyses of the Fe BAA coatings revealed the retention of the feedstock powder's amorphous nature. The mixing of the feedstock powder in the titanium substrate was very small. A crystalline-amorphous composite microstructure evolved from the laser processing in all types of coatings. The coatings were further laser remelted. The amorphous character was found to increase and the crystallites were found to grow during remelting. The Fe BAA coatings showed higher hardness and smaller wear volume compared to the Ti substrate. A further increase in these properties was observed after laser remelting treatment. During the wear testing in NaCl solution, Ti substrate showed intergranular corrosion, whereas the Fe BAA coatings showed signs of low and localized fretting corrosion in a saline environment. Our results demonstrate that using LENS™, amorphous coatings can be deposited on metallic substrates.

  12. Structural and thermal properties of Cu-Hf-Ti bulk amorphous alloys

    NASA Astrophysics Data System (ADS)

    Rontó, V.; Nagy, E.; Svéda, M.; Roósz, A.; Tranta, F.

    2009-01-01

    Cu-Hf-Ti amorphous alloys are high strength and wear resistant materials. Master alloys of Cu57.5Hf27.5Ti15 and Cu57.5Hf25Ti17.5 ternary alloys have been prepared by arc melting, and wedge and rod shaped samples have been cast by centrifugal casting. Liquidus and solidus temperatures of the alloys were determined by DTA. The fully amorphous size was determined by X-ray diffraction. Thermodynamic properties of the amorphous alloys were studied by DSC measurements and Kissinger analyses were performed.

  13. Preliminary Study of Fabricating Bulk Fe-Based Amorphous Alloy by Cold Gas Dynamic Spraying

    NASA Astrophysics Data System (ADS)

    Guan, Leding; Yan, Biao; Long, Ling; Yang, Sha

    Cold gas dynamic spraying (CGDS) technique makes use of high-speed gas current to spray diversified metal, alloy and composite materials under room temperature or with a little heated. It is one kind of novel surface engineering technologies, aimed at eliminating such negative influences as oxidation, gasification, melt, crystallization and gas decomposition and so on existing in hot spraying technologies. Due to its peculiar characteristics such as low spraying temperature, non-oxidation, low stress among coating layers, compactification, and high utilization rate of raw materials, as well as effective applications in the domain of fabricating coatings, the CGDS technique has attracted great attention. As it has the advantages aforementioned, especially avoiding the changes of material properties resulted from high spraying temperature, CGDS provides a kind of revolutionary means for fabricating such heat-sensitive materials as amorphous alloys. The paper reviews the current situation and application development of the CGDS technique, and presents our preliminary exploration of fabricating bulk Fe-based amorphous alloy via CGDS together with mechanical milling process.

  14. Method of casting articles of a bulk-solidifying amorphous alloy

    DOEpatents

    Lin, Xianghong; Johnson, William L.; Peker, Atakan

    1998-01-01

    A casting charge of a bulk-solidifying amorphous alloy is cast into a mold from a temperature greater than its crystallized melting temperature, and permitted to solidify to form an article. The oxygen content of the casting charge is limited to an operable level, as excessively high oxygen contents produce premature crystallization during the casting operation. During melting, the casting charge is preferably heated to a temperature above a threshold temperature to eliminate heterogeneous crystallization nucleation sites within the casting charge. The casting charge may be cast from above the threshold temperature, or it may be cooled to the casting temperature of more than the crystallized melting point but not more than the threshold temperature, optionally held at this temperature for a period of time, and thereafter cast.

  15. Method of casting articles of a bulk-solidifying amorphous alloy

    DOEpatents

    Lin, X.; Johnson, W.L.; Peker, A.

    1998-08-25

    A casting charge of a bulk-solidifying amorphous alloy is cast into a mold from a temperature greater than its crystallized melting temperature, and permitted to solidify to form an article. The oxygen content of the casting charge is limited to an operable level, as excessively high oxygen contents produce premature crystallization during the casting operation. During melting, the casting charge is preferably heated to a temperature above a threshold temperature to eliminate heterogeneous crystallization nucleation sites within the casting charge. The casting charge may be cast from above the threshold temperature, or it may be cooled to the casting temperature of more than the crystallized melting point but not more than the threshold temperature, optionally held at this temperature for a period of time, and thereafter cast. 8 figs.

  16. Fe-based bulk amorphous alloys with iron contents as high as 82 at%

    NASA Astrophysics Data System (ADS)

    Li, Jin-Feng; Liu, Xue; Zhao, Shao-Fan; Ding, Hong-Yu; Yao, Ke-Fu

    2015-07-01

    Fe-based bulk amorphous alloys (BAAs) with high Fe contents are advantageous due to their high saturation magnetization and low cost. However, preparing Fe-based BAAs with Fe contents higher than 80 at% is difficult due to their poor glass forming abilities (GFA). In this study, an Fe81P8.5C5.5B2Si3 BAA with a diameter of 1 mm and a saturation magnetization of 1.56 T was successfully prepared using the fluxing and copper mold casting methods. In addition, by introducing a small amount of elemental Mo to the alloy, an Fe82Mo1P6.5C5.5B2Si3 BAA rod with a diameter of 1 mm, a high saturation magnetization of 1.59 T, a high yield stress of 3265 MPa, and a clear plasticity of 1.3% was prepared in the same way. The cost effectiveness and good magnetic properties of these newly-developed Fe-based BAAs with Fe contents as high as 82 at% would be advantageous and promising for industrial applications.

  17. In situ observation of defect annihilation in Kr ion-irradiated bulk Fe/amorphous-Fe 2 Zr nanocomposite alloy

    DOE PAGESBeta

    Yu, K. Y.; Fan, Z.; Chen, Y.; Song, M.; Liu, Y.; Wang, H.; Kirk, M. A.; Li, M.; Zhang, X.

    2014-08-26

    Enhanced irradiation tolerance in crystalline multilayers has received significant attention lately. However, little is known on the irradiation response of crystal/amorphous nanolayers. We report on in situ Kr ion irradiation studies of a bulk Fe96Zr4 nanocomposite alloy. Irradiation resulted in amorphization of Fe2Zr and formed crystal/amorphous nanolayers. α-Fe layers exhibited drastically lower defect density and size than those in large α-Fe grains. In situ video revealed that mobile dislocation loops in α-Fe layers were confined by the crystal/amorphous interfaces and kept migrating to annihilate other defects. This study provides new insights on the design of irradiation-tolerant crystal/amorphous nanocomposites.

  18. Influence of Kinetic and Thermodynamic Factors on the Glass-Forming Ability of Zirconium-Based Bulk Amorphous Alloys

    SciTech Connect

    Mukherjee, S.; Johnson, W.L.; Rhim, W.-K.; Schroers, J.

    2005-06-24

    The time-temperature-transformation curves for three zirconium-based bulk amorphous alloys are measured to identify the primary factors influencing their glass-forming ability. The melt viscosity is found to have the most pronounced influence on the glass-forming ability compared to other thermodynamic factors. Surprisingly, it is found that the better glass former has a lower crystal-melt interfacial tension. This contradictory finding is explained by the icosahedral short-range order of the undercooled liquid, which on one hand reduces the interfacial tension, while on the other hand increases its viscosity.

  19. Nanocrystallization in spark plasma sintered Fe48Cr15Mo14Y2C15B6 bulk amorphous alloy

    NASA Astrophysics Data System (ADS)

    Singh, Ashish; Katakam, Shravana; Ilavsky, Jan; Dahotre, Narendra B.; Harimkar, Sandip P.

    2013-08-01

    Spark plasma sintering (SPS) is evolving as an attractive process for the processing of multi-component Fe-based bulk amorphous alloys and their in-situ nanocomposites with controlled primary nanocrystallization. Extended Q-range small angle neutron scattering (EQ-SANS) analysis, complemented by x-ray diffraction and transmission electron microscopy, was performed to characterize nanocrystallization behavior of SPS sintered Fe-based bulk amorphous alloys. The SANS experiments show significant scattering for the samples sintered in the supercooled region indicating local structural/compositional changes associated with the profuse nucleation of nanoclusters (˜4 nm). For the samples spark plasma sintered near and above crystallization temperature (>653 °C), the SANS data show the formation of interference maximum indicating the formation and growth of (Fe,Cr)23C6 crystallites. The SANS data also indicate the evolution of bimodal crystallite distribution at higher sintering temperatures (above Tx1). The growth of primary nanocrystallites results in impingement of concentration gradient fields (soft impingement effect), leading to non-random nucleation of crystallites near the primary crystallization.

  20. Effect of the Temperature on the Friction and Wear Properties of Bulk Amorphous Alloy

    NASA Astrophysics Data System (ADS)

    Segu, Dawit Zenebe; Hwang, Pyung; Kim, Seock-Sam

    2014-07-01

    The present paper report the results of an experimental investigation of the temperature effect on the sliding friction and wear properties of the bulk metallic glass (BMG). To improve the friction and wear properties of the BMG, the disk specimens were developed in the alloy system of Fe67.6C7.1Si3.3B5.5P8.7Cr2.3Mo2.6Al2Co1.0 using hot metal and industrial ferro-alloys. The friction and wear test was performed using flat-on-flat contact configuration of unidirectional tribometer and Si3N4 ceramic disk used as a counterpart. The worn surfaces of the BMG were observed by using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The results indicated that the friction and wear properties of the BMG depend on the glass transition and the formation of protective oxide film. The friction coefficient decreased with increasing temperature, while it increased slightly when the temperature passed the glass transition temperature (Tg). The worn specimens were exposed to abrasion, adhesion, oxidation and plastic deformation. In addition, obvious surface flow characteristics was accompany during wear test.

  1. Amorphous metal alloy

    DOEpatents

    Wang, R.; Merz, M.D.

    1980-04-09

    Amorphous metal alloys of the iron-chromium and nickel-chromium type have excellent corrosion resistance and high temperature stability and are suitable for use as a protective coating on less corrosion resistant substrates. The alloys are stabilized in the amorphous state by one or more elements of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten. The alloy is preferably prepared by sputter deposition.

  2. In situ observation of defect annihilation in Kr ion-irradiated bulk Fe/amorphous-Fe 2 Zr nanocomposite alloy

    SciTech Connect

    Yu, K. Y.; Fan, Z.; Chen, Y.; Song, M.; Liu, Y.; Wang, H.; Kirk, M. A.; Li, M.; Zhang, X.

    2014-08-26

    Enhanced irradiation tolerance in crystalline multilayers has received significant attention lately. However, little is known on the irradiation response of crystal/amorphous nanolayers. We report on in situ Kr ion irradiation studies of a bulk Fe96Zr4 nanocomposite alloy. Irradiation resulted in amorphization of Fe2Zr and formed crystal/amorphous nanolayers. α-Fe layers exhibited drastically lower defect density and size than those in large α-Fe grains. In situ video revealed that mobile dislocation loops in α-Fe layers were confined by the crystal/amorphous interfaces and kept migrating to annihilate other defects. This study provides new insights on the design of irradiation-tolerant crystal/amorphous nanocomposites.

  3. Nanocrystal dispersed amorphous alloys

    NASA Technical Reports Server (NTRS)

    Perepezko, John H. (Inventor); Allen, Donald R. (Inventor); Foley, James C. (Inventor)

    2001-01-01

    Compositions and methods for obtaining nanocrystal dispersed amorphous alloys are described. A composition includes an amorphous matrix forming element (e.g., Al or Fe); at least one transition metal element; and at least one crystallizing agent that is insoluble in the resulting amorphous matrix. During devitrification, the crystallizing agent causes the formation of a high density nanocrystal dispersion. The compositions and methods provide advantages in that materials with superior properties are provided.

  4. Positron annihilation Doppler broadening measurement for bulk amorphous alloy by using high energy positron generated from LCS gamma-ray at NEW SUBARU

    NASA Astrophysics Data System (ADS)

    Hori, F.; Ueno, Y.; Ishii, K.; Ishiyama, T.; Iwase, A.; Miyamoto, S.; Terasawa, T.

    2016-01-01

    A simple positron annihilation measurement apparatus via pair creation has been developed using high energetic gamma beam generated by laser Compton scattering (LCS) of 1 GeV electrons circulated in a storage ring and laser light with the power more than 1 W at the New SUBARU synchrotron radiation facility, University of Hyogo. This MeV ordered energy changeable positron apparatus is useful to study defects in bulk materials. In this study, the average energy of 8MeV positron was selected by the wavelength of laser light and circulated electron energy in photon factory. As a demonstrate of non-destruction positron measurement by this apparatus, positron annihilation Doppler broadening measurement has performed for bulk size of amorphous and crystal structured Zr based alloys. The larger Doppler broadening S parameter for amorphous alloy than that for crystallized one has been successfully measured.

  5. Correlation between hereditary structures and properties of an Fe50Cr15Mo14C15B6 bulk-amorphous alloy in the solid and liquid states

    NASA Astrophysics Data System (ADS)

    Filippov, K. S.

    2010-05-01

    An attempt is made to find the effect of a hereditary structure on the physicochemical and structural properties of a solid and liquid Fe50Cr15Mo14C15B6 bulk-amorphous alloy in order to evaluate the possibility of using a precursor, i.e., a solid metal that has a genetic relation to the liquid phase, as an the initial metal of a heat involved in the formation of an amorphous structure. The structural state of the melt is estimated from the temperature dependence of the structural parameters, density, and surface tension with allowance for the validation criterion of the approximation of experimental points R 2.

  6. Wetting behavior of molten In-Sn alloy on bulk amorphous and crystalline Cu{sub 40}Zr{sub 44}Al{sub 8}Ag{sub 8}

    SciTech Connect

    Ma, G. F.; Zhang, H. F.; Li, H.; Hu, Z. Q.

    2007-10-29

    Using the sessile-drop method, the wettability of the molten In-Sn alloy on bulk amorphous and crystalline Cu{sub 40}Zr{sub 44}Al{sub 8}Ag{sub 8} alloy was studied at different temperatures. It was found that the equilibrium contact angle of In-Sn alloy melt on bulk amorphous substrate was smaller than that of the crystalline one. An intermetallic compound existed at the interface of In-Sn alloy on amorphous Cu{sub 40}Zr{sub 44}Al{sub 8}Ag{sub 8}, while no intermediate reaction layer was formed at the interface of In-Sn alloy on crystalline Cu{sub 40}Zr{sub 44}Al{sub 8}Ag{sub 8} in the temperature range studied.

  7. Nano-scratch behavior of a bulk Zr-10Al-5Ti-17.9Cu-14.6Ni amorphous alloy

    SciTech Connect

    Wang, J. G.; Choi, B. W.; Nieh, T. G.; Liu, C. T.

    2000-04-01

    The tribological behavior of a Zr-10Al-5Ti-17.9Cu-14.6Ni (at.%) bulk amorphous alloy, in both the as-cast and annealed states, was investigated using nano-scratch tests, including ramping load scratch and multiple sliding wear techniques. The crystallization sequence of the alloy was also characterized. Mechanical properties, such as Young's modulus, hardness, friction coefficient, and tribological wear were measured. These properties were found to vary with microstructure. In general, an increase in annealing temperature results in an increase in hardness, which in turn produces a decrease in friction coefficient but an increase in wear resistance. Samples having a structure consisting of supercooled liquid matrix with dispersed nanocrystalline particles exhibit the best wear performance. (c) 2000 Materials Research Society.

  8. Spectra of optical parameters in bulk and film amorphous alloys of the Se{sub 95}As{sub 5} system containing samarium (Sm) impurities

    SciTech Connect

    Djalilov, N. Z.; Damirov, G. M.

    2011-09-15

    Reflectance spectra of bulk and film amorphous alloys of the Se{sub 95}As{sub 5} system containing samarium (Sm) impurities are studied in the energy range of 1-6 eV. Spectral dependences of optical constants and derivatives of optical dielectric functions are calculated by the Kramers-Kronig method. Changes in spectra of optical parameters depending on the content of impurities introduced into Se{sub 95}As{sub 5} and conditions of their preparation are explained based on the cluster model. According to the latter, changes in the electron density of states depends on changes in atomic configurations in clusters, i.e., short-range order changes.

  9. Amorphous metal alloy and composite

    DOEpatents

    Wang, Rong; Merz, Martin D.

    1985-01-01

    Amorphous metal alloys of the iron-chromium and nickel-chromium type have excellent corrosion resistance and high temperature stability and are suitable for use as a protective coating on less corrosion resistant substrates. The alloys are stabilized in the amorphous state by one or more elements of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten. The alloy is preferably prepared by sputter deposition.

  10. New Amorphous Silicon Alloy Systems

    NASA Astrophysics Data System (ADS)

    Kapur, Mridula N.

    1990-01-01

    The properties of hydrogenated amorphous silicon (a-Si:H) have been modified by alloying with Al, Ga and S respectively. The Al and Ga alloys are in effect quaternary alloys as they were fabricated in a carbon-rich discharge. The alloys were prepared by the plasma assisted chemical vapor deposition (PACVD) method. This method has several advantages, the major one being the relatively low defect densities of the resulting materials. The PACVD system used to grow the alloy films was designed and constructed in the laboratory. It was first tested with known (a-Si:H and a-Si:As:H) materials. Thus, it was established that device quality alloy films could be grown with the home-made PACVD setup. The chemical composition of the alloys was characterized by secondary ion mass spectrometry (SIMS), and electron probe microanalysis (EPMA). The homogeneous nature of hydrogen distribution in the alloys was established by SIMS depth profile analysis. A quantitative analysis of the bulk elemental content was carried out by EPMA. The analysis indicated that the alloying element was incorporated in the films more efficiently at low input gas concentrations than at the higher concentrations. A topological model was proposed to explain the observed behavior. The optical energy gap of the alloys could be varied in the 0.90 to 1.92 eV range. The Al and Ga alloys were low band gap materials, whereas alloying with S had the effect of widening the energy gap. It was observed that although the Si-Al and Si-Ga alloys contained significant amounts of C and H, the magnitude of the energy gap was determined by the metallic component. The various trends in optical properties could be related to the binding characteristics of the respective alloy systems. A quantitative explanation of the results was provided by White's tight binding model. The dark conductivity-temperature dependence of the alloys was examined. A linear dependence was observed for the Al and Ga systems. Electronic conduction in

  11. Bulk CoNiFe-SiB Amorphous and Nanostructured Alloys Produced by Plasma Spray Deposition and Dynamic Compaction: Formation of Soft Magnetic Properties

    NASA Astrophysics Data System (ADS)

    Denisova, Elena; Kuzovnikova, Ludmila; Iskhakov, Rauf; Kuzovnikov, Aleksandr; Lepeshev, Anatoly; Nemtsev, Ivan; Saunin, Viktor; Telegin, Sergey; Bondarenko, Galina; Mal`tsev, Vadim

    The bulk nanostructured Co58Ni10Fe5B16Si11 alloys were prepared by dynamic compaction and plasma spray deposition techniques. The investigation of structure and magnetic properties of bulk samples was carried out by X-ray diffraction, electron microscopy and correlation magnetometry. The bulk samples produced by both methods can be characterized as a heterophase system. The highest value of permeability 20 · 103 for plasma spraying coating is achieved when volume fraction of nanocrystalline phase with Curie temperature Tc ∼ 640 K is increased to 30%. The magnetic characteristics, such as the saturation magnetization, the Bloch constant, the local magnetic anisotropy field, the ferromagnetic resonance linewidth, and the coercivity remain unchanged after both compaction techniques. It was shown that the plasma spraying method allows to obtain bulk magnetically soft materials with magnetic parameters that are not inferior to the characteristics of a thermally treated rapidly quenched ribbon with the same composition.

  12. Crystallization Kinetics of Fe76.5- x C6.0Si3.3B5.5P8.7Cu x ( x = 0, 0.5, and 1 at. pct) Bulk Amorphous Alloy

    NASA Astrophysics Data System (ADS)

    Jung, Hyo Yun; Stoica, Mihai; Yi, Seonghoon; Kim, Do Hyang; Eckert, Jürgen

    2015-06-01

    The influence of Cu on crystallization kinetics of Fe76.5- x C6.0Si3.3B5.5P8.7Cu x ( x = 0, 0.5, and 1 at. pct) bulk amorphous alloys was investigated by isothermal and isochronal differential scanning calorimetry combined with X-ray diffraction. The thermal analysis revealed that the crystallization of the amorphous matrix proceeds through at least two exothermic events. The Cu-free glassy alloy forms by primary crystallization the metastable Fe23C6 phase, while upon 0.5 at. pct Cu addition the primary crystallized phase is α-Fe. The activation energy for crystallization, calculated using both Kissinger and Ozawa methods, decreases from about 500 kJ/mol to about 330 kJ/mol. Further increase of Cu addition to 1 at. pct promotes the concomitant crystallization of several phases, as α-Fe, FeB, Fe3C, and Fe2P. In order to understand the crystallization behavior of the alloys as a function of Cu content, the Avrami exponent n, evaluated from the Johnson-Mehl-Avrami equation, was in details analyzed. The current study reveals that the minor Cu addition plays a crucial role at the initial stage of the crystallization. Among the studied alloys, the glassy samples with 0.5 at. pct Cu addition have the optimum compositional condition for the single α-Fe formation with a high nucleation rate.

  13. Amorphous phase formation in mechanically alloyed iron-based systems

    NASA Astrophysics Data System (ADS)

    Sharma, Satyajeet

    Bulk metallic glasses have interesting combination of physical, chemical, mechanical, and magnetic properties which make them attractive for a variety of applications. Consequently there has been a lot of interest in understanding the structure and properties of these materials. More varied applications can be sought if one understands the reasons for glass formation and the methods to control them. The glass-forming ability (GFA) of alloys can be substantially increased by a proper selection of alloying elements and the chemical composition of the alloy. High GFA will enable in obtaining large section thickness of amorphous alloys. Ability to produce glassy alloys in larger section thicknesses enables exploitation of these advanced materials for a variety of different applications. The technique of mechanical alloying (MA) is a powerful non-equilibrium processing technique and is known to produce glassy (or amorphous) alloys in several alloy systems. Metallic amorphous alloys have been produced by MA starting from either blended elemental metal powders or pre-alloyed powders. Subsequently, these amorphous alloy powders could be consolidated to full density in the temperature range between the glass transition and crystallization temperatures, where the amorphous phase has a very low viscosity. This Dissertation focuses on identifying the various Fe-based multicomponent alloy systems that can be amorphized using the MA technique, studying the GFA of alloys with emphasis on improving it, and also on analyzing the effect of extended milling time on the constitution of the amorphous alloy powder produced at earlier times. The Dissertation contains seven chapters, where the lead chapter deals with the background, history and introduction to bulk metallic glasses. The following four chapters are the published/to be published work, where the criterion for predicting glass formation, effect of Niobium addition on glass-forming ability (GFA), lattice contraction on

  14. Nanocrystallization in spark plasma sintered Fe{sub 48}Cr{sub 15}Mo{sub 14}Y{sub 2}C{sub 15}B{sub 6} bulk amorphous alloy

    SciTech Connect

    Singh, Ashish; Harimkar, Sandip P.; Katakam, Shravana; Dahotre, Narendra B.; Ilavsky, Jan

    2013-08-07

    Spark plasma sintering (SPS) is evolving as an attractive process for the processing of multi-component Fe-based bulk amorphous alloys and their in-situ nanocomposites with controlled primary nanocrystallization. Extended Q-range small angle neutron scattering (EQ-SANS) analysis, complemented by x-ray diffraction and transmission electron microscopy, was performed to characterize nanocrystallization behavior of SPS sintered Fe-based bulk amorphous alloys. The SANS experiments show significant scattering for the samples sintered in the supercooled region indicating local structural/compositional changes associated with the profuse nucleation of nanoclusters (∼4 nm). For the samples spark plasma sintered near and above crystallization temperature (>653 °C), the SANS data show the formation of interference maximum indicating the formation and growth of (Fe,Cr){sub 23}C{sub 6} crystallites. The SANS data also indicate the evolution of bimodal crystallite distribution at higher sintering temperatures (above T{sub x1}). The growth of primary nanocrystallites results in impingement of concentration gradient fields (soft impingement effect), leading to non-random nucleation of crystallites near the primary crystallization.

  15. Iron-based amorphous alloys and methods of synthesizing iron-based amorphous alloys

    DOEpatents

    Saw, Cheng Kiong; Bauer, William A.; Choi, Jor-Shan; Day, Dan; Farmer, Joseph C.

    2016-05-03

    A method according to one embodiment includes combining an amorphous iron-based alloy and at least one metal selected from a group consisting of molybdenum, chromium, tungsten, boron, gadolinium, nickel phosphorous, yttrium, and alloys thereof to form a mixture, wherein the at least one metal is present in the mixture from about 5 atomic percent (at %) to about 55 at %; and ball milling the mixture at least until an amorphous alloy of the iron-based alloy and the at least one metal is formed. Several amorphous iron-based metal alloys are also presented, including corrosion-resistant amorphous iron-based metal alloys and radiation-shielding amorphous iron-based metal alloys.

  16. Amorphous silicon-tellurium alloys

    NASA Astrophysics Data System (ADS)

    Shufflebotham, P. K.; Card, H. C.; Kao, K. C.; Thanailakis, A.

    1986-09-01

    Amorphous silicon-tellurium alloy thin films were fabricated by coevaporation over the composition range of 0-82 at. % Te. The electronic and optical properties of these films were systematically investigated over this same range of composition. The optical gap of these films was found to decrease monotonically with increasing Te content. Conduction near room temperature was due to extended state conduction, while variable range hopping dominated below 250 K. The incorporation of Te in concentrations of less than 1 at. % was found to produce an increase in the density of localized states at the Fermi level and a decrease in the activation energy. This was attributed to the Te being incorporated as a substitutional, fourfold coordinated, double donor in a-Si. At approximately 60 at. % Te, a decrease in the density of localized states at the Fermi level, and an increase in the activation energy and photoresponse was indicated. This was attributed to the possible formation of a less defective a-Si:Te compound.

  17. Amorphous alloys resistant to corrosion in artificial saliva solution.

    PubMed

    Kwokal, A; Metikos-Huković, M; Radić, N; Poljak-Guberina, R; Catović, A

    2003-07-01

    The tailoring of new corrosion-resistant alloys with specific properties has recently been performed mostly by the sputter deposition technique. The aim of this work was to investigate corrosion resistance of aluminum-tungsten (Al-W) amorphous alloys in artificial saliva solution, pH=5.5, based on the electrochemical methods of cyclic voltammetry and linear polarization. Thin alloy films were prepared on a sapphire substrate by magnetron codeposition. Completely amorphous films were obtained in the Al(80)W(20)-Al(67)W(33) composition range. Amorphous Al-W alloys exhibit very high corrosion resistance due to their homogeneous single-phase nature. The passive films spontaneously formed at their surface are uniform with characteristics of an insulator film and prevent corrosion progression in the bulk in a very demanding oral environment. The mechanism of increasing resistivity of Al-W alloys to pitting corrosion and generalized corrosion has been discussed in the view of increasing tungsten content in the alloy. Considering these exceptional corrosion properties and microhardness which falls in the range 7.5+/-1.6 Pa, Al-W alloys represent promising materials for dental applications. PMID:15348422

  18. Plasma deposition of amorphous metal alloys

    DOEpatents

    Hays, A.K.

    1979-07-18

    Amorphous metal alloy coatings are plasma-deposited by dissociation of vapors of organometallic compounds and metalloid hydrides in the presence of a reducing gas, using a glow discharge. Tetracarbonylnickel, phosphine, and hydrogen constitute a typical reaction mixture of the invention, yielding a NiPC alloy.

  19. Plasma deposition of amorphous metal alloys

    DOEpatents

    Hays, Auda K.

    1986-01-01

    Amorphous metal alloy coatings are plasma-deposited by dissociation of vapors of organometallic compounds and metalloid hydrides in the presence of a reducing gas, using a glow discharge. Tetracarbonylnickel, phosphine, and hydrogen constitute a typical reaction mixture of the invention, yielding a NiPC alloy.

  20. Annealing behavior of high permeability amorphous alloys

    SciTech Connect

    Rabenberg, L.

    1980-06-01

    Effects of low temperature annealing on the magnetic properties of the amorphous alloy Co/sub 71/ /sub 4/Fe/sub 4/ /sub 6/Si/sub 9/ /sub 6/B/sub 14/ /sub 4/ were investigated. Annealing this alloy below 400/sup 0/C results in magnetic hardening; annealing above 400/sup 0/C but below the crystallization temperature results in magnetic softening. Above the crystallization temperature the alloy hardens drastically and irreversibly. Conventional and high resolution transmission electron microscopy were used to show that the magnetic property changes at low temperatures occur while the alloy is truly amorphous. By imaging the magnetic microstructures, Lorentz electron microscopy has been able to detect the presence of microscopic inhomogeneities in this alloy. The low temperature annealing behavior of this alloy has been explained in terms of atomic pair ordering in the presence of the internal molecular field. Lorentz electron microscopy has been used to confirm this explanation.

  1. Crystallization of amorphous Zr-Be alloys

    NASA Astrophysics Data System (ADS)

    Golovkova, E. A.; Surkov, A. V.; Syrykh, G. F.

    2015-02-01

    The thermal stability and structure of binary amorphous Zr100 - x Be x alloys have been studied using differential scanning calorimetry and neutron diffraction over a wide concentration range (30 ≤ x ≤ 65). The amorphous alloys have been prepared by rapid quenching from melt. The studied amorphous system involves the composition range around the eutectic composition with boundary phases α-Zr and ZrBe2. It has been found that the crystallization of alloys with low beryllium contents ("hypoeutectic" alloys with x ≤ 40) proceeds in two stages. Neutron diffraction has demonstrated that, at the first stage, α-Zr crystallizes and the remaining amorphous phase is enriched to the eutectic composition; at the second stage, the alloy crystallizes in the α-Zr and ZrBe2 phases. At higher beryllium contents ("hypereutectic" alloys), one phase transition of the amorphous phase to a mixture of the α-Zr and ZrBe2 phases has been observed. The concentration dependences of the crystallization temperature and activation energy have been revealed.

  2. Production feature of soft magnetic amorphous alloys

    NASA Astrophysics Data System (ADS)

    Tyagunov, A. G.; Baryshev, E. E.; Shmakova, K. Yu

    2016-06-01

    Methods for making nanocrystalline alloys have been discussed. Temperature dependences of the surface tension (σ), electric resistivity (ρ), magnetic susceptibility (χ) and kinematic viscosity (ν) have been obtained. Comparison of the properties of amorphous ribbons obtained by the pilot and serial technologies has been conducted. Science-based technology of multi-component alloy smelting makes it possible to prepare equilibrium smelt, the structure of which has a significant effect on the properties of the amorphous ribbon before spinning and kinetics of its crystallization has been offered.

  3. Cold Spraying of Amorphous Cu50Zr50 Alloys

    NASA Astrophysics Data System (ADS)

    List, A.; Gärtner, F.; Mori, T.; Schulze, M.; Assadi, H.; Kuroda, S.; Klassen, T.

    2015-01-01

    A new range of applications in cold spraying is expected for bulk metallic glass (BMG) coatings. For retaining amorphous structures in cast multi-component BMG parts, typically high purity raw material must be used. The present investigation explores an alternative approach, where cold spraying is used to deposit a technical-grade binary amorphous alloy. This approach is shown to be potentially cost-effective and suitable for rapid manufacturing. For this purpose, amorphous Cu50Zr50 was chosen as a model alloy system, and cold spraying was performed using nitrogen as process gas. By a systematic variation of the spray parameter sets, the critical velocities for coating formation were determined experimentally. Based on the current models of bonding of amorphous Cu50Zr50 powder in cold spraying, a new, more comprehensive concept of bonding and rebound is presented, which also considers the presence of liquefied interfaces and quenching rates for resolidification. Results concerning impact morphologies and coating formation demonstrate that under suitable choice of spray conditions, well-adhering coatings with amorphous structure of the Cu50Zr50 powders can be obtained by cold spraying.

  4. Magnetic properties of the suction-cast bulk amorphous alloy: (Fe0.61Co0.10Zr0.025Hf0.025Ti0.02W0.02B0.20)96Y4

    NASA Astrophysics Data System (ADS)

    Błoch, K.

    2015-09-01

    This paper presents the results of studies into the structural and magnetic properties of the bulk amorphous alloy: (Fe0.61Co0.10Zr0.025Hf0.025Ti0.02W0.02B0.20)96Y4, fabricated in the form of rods of length: 20 mm, and diameters: 1 mm and 2 mm. The samples were produced using the suction-casting method. The amorphicity of the investigated alloy, in the as-quenched state, was verified using X-ray diffractometry and Mössbauer spectroscopy. Studies of the magnetic susceptibility disaccommodation and the approach to magnetic saturation facilitated the conclusion that the investigated alloy, obtained in the form of rods of 2 mm diameter, can be characterized by a higher packing density of atoms; this was further confirmed by the results of Mössbauer spectroscopy.

  5. Microstructure and surface chemistry of amorphous alloys important to their friction and wear behavior

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1983-01-01

    An investigation was conducted to examine the microstructure and surface chemistry of amorphous alloys, and their effects on tribological behavior. The results indicate that the surface oxide layers present on amorphous alloys are effective in providing low friction and a protective film against wear in air. Clustering and crystallization in amorphous alloys can be enhanced as a result of plastic flow during the sliding process at a low sliding velocity, at room temperature. Clusters or crystallines with sizes to 150 nm and a diffused honeycomb-shaped structure are produced on the wear surface. Temperature effects lead to drastic changes in surface chemistry and friction behavior of the alloys at temperatures to 750 C. Contaminants can come from the bulk of the alloys to the surface upon heating and impart to the surface oxides at 350 C and boron nitride above 500 C. The oxides increase friction while the boron nitride reduces friction drastically in vacuum.

  6. Multiple cell photoresponsive amorphous alloys and devices

    SciTech Connect

    Ovshinsky, S.R.; Adler, D.

    1990-01-02

    This patent describes an improved photoresponsive tandem multiple solar cell device. The device comprising: at least a first and second superimposed cell of various materials. The first cell being formed of a silicon alloy material. The second cell including an amorphous silicon alloy semiconductor cell body having an active photoresponsive region in which radiation can impinge to produce charge carriers, the amorphous cell body including at least one density of states reducing element. The element being fluorine. The amorphous cell body further including a band gap adjusting element therein at least in the photoresponsive region to enhance the radiation absorption thereof, the adjusting element being germanium: the second cell being a multi-layer body having deposited semiconductor layers of opposite (p and n) conductivity type; and the first cell being formed with the second cell in substantially direct Junction contact therebetween. The first and second cells designed to generate substantially matched currents from each cell from a light source directed through the first cell and into the second cell.

  7. Amorphous Alloy Surpasses Steel and Titanium

    NASA Technical Reports Server (NTRS)

    2004-01-01

    In the same way that the inventions of steel in the 1800s and plastic in the 1900s sparked revolutions for industry, a new class of amorphous alloys is poised to redefine materials science as we know it in the 21st century. Welcome to the 3rd Revolution, otherwise known as the era of Liquidmetal(R) alloys, where metals behave similar to plastics but possess more than twice the strength of high performance titanium. Liquidmetal alloys were conceived in 1992, as a result of a project funded by the California Institute of Technology (CalTech), NASA, and the U.S. Department of Energy, to study the fundamentals of metallic alloys in an undercooled liquid state, for the development of new aerospace materials. Furthermore, NASA's Marshall Space Flight Center contributed to the development of the alloys by subjecting the materials to testing in its Electrostatic Levitator, a special instrument that is capable of suspending an object in midair so that researchers can heat and cool it in a containerless environment free from contaminants that could otherwise spoil the experiment.

  8. Hydrogenated amorphous silicon-germanium alloys

    SciTech Connect

    Luft, W.

    1988-02-01

    This report describes the effects of the germanium fraction in hydrogenated amorphous silicon-germanium alloys on various parameters, especially those that are indicators of film quality, and the impact of deposition methods, feedgas mixtures, and other deposition parameters on a SiGe:H and a-SiGe:H:F film characteristics and quality. Literature data show the relationship between germanium content, hydrogen content, deposition method (various glow discharges and CVD), feedgas lmixture, and other parameters and properties, such as optical band gap, dark and photoconductivities, photosensitivity, activation energy, Urbach parameter, and spin density. Some of these are convenient quality indicators; another is the absence of microstructure. Examining RF glow discharge with both a diode and triode geometry, DC proximity glow discharge, microwave glow discharge, and photo-CVD, using gas mixtures such as hydrogen-diluted and undiluted mixtures of silane/germane, disilane/germane, silane/germaniumtetrafluoride, and others, it was observed that hydrogen dilution (or inert gas dilution) is essential in achieving high photosensitivity in silicon-germanium alloys (in contradistinction to amorphous hydrogenated silicon). Hydrogen dilution results in a higher photosensitivity than do undiluted gas mixtures. 81 refs., 42 figs., 7 tabs.

  9. Parametrized dielectric functions of amorphous GeSn alloys

    NASA Astrophysics Data System (ADS)

    D'Costa, Vijay Richard; Wang, Wei; Schmidt, Daniel; Yeo, Yee-Chia

    2015-09-01

    We obtained the complex dielectric function of amorphous Ge1-xSnx (0 ≤ x ≤ 0.07) alloys using spectroscopic ellipsometry from 0.4 to 4.5 eV. Amorphous GeSn films were formed by room-temperature implantation of phosphorus into crystalline GeSn alloys grown by molecular beam epitaxy. The optical response of amorphous GeSn alloys is similar to amorphous Ge and can be parametrized using a Kramers-Kronig consistent Cody-Lorentz dispersion model. The parametric model was extended to account for the dielectric functions of amorphous Ge0.75Sn0.25 and Ge0.50Sn0.50 alloys from literature. The compositional dependence of band gap energy Eg and parameters associated with the Lorentzian oscillator have been determined. The behavior of these parameters with varying x can be understood in terms of the alloying effect of Sn on Ge.

  10. Salt Fog Testing Iron-Based Amorphous Alloys

    SciTech Connect

    Rebak, Raul B.; Aprigliano, Louis F.; Day, S. Daniel; Farmer, Joseph C.

    2007-07-01

    Iron-based amorphous alloys are hard and highly corrosion resistant, which make them desirable for salt water and other applications. These alloys can be produced as powder and can be deposited as coatings on any surface that needs to be protected from the environment. It was of interest to examine the behavior of these amorphous alloys in the standard salt-fog testing ASTM B 117. Three different amorphous coating compositions were deposited on 316L SS coupons and exposed for many cycles of the salt fog test. Other common engineering alloys such as 1018 carbon steel, 316L SS and Hastelloy C-22 were also tested together with the amorphous coatings. Results show that amorphous coatings are resistant to rusting in salt fog. Partial devitrification may be responsible for isolated rust spots in one of the coatings. (authors)

  11. Phonon Dispersion in Amorphous Ni-Alloys

    NASA Astrophysics Data System (ADS)

    Vora, A. M.

    2007-06-01

    The well-known model potential is used to investigate the longitudinal and transverse phonon dispersion curves for six Ni-based binary amorphous alloys, viz. Ni31Dy69, Ni33Y67, Ni36Zr64, Ni50Zr50, Ni60 Nb40, and Ni81B19. The thermodynamic and elastic properties are also computed from the elastic limits of the phonon dispersion curves. The theoretical approach given by Hubbard-Beeby is used in the present study to compute the phonon dispersion curves. Five local field correction functions proposed by Hartree, Taylor, Ichimaru-Utsumi, Farid et al. and Sarkar et al. are employed to see the effect of exchange and correlation in the aforesaid properties.

  12. Amorphous powders of Al-Hf prepared by mechanical alloying

    SciTech Connect

    Schwarz, R.B.; Hannigan, J.W.; Sheinberg, H.; Tiainen, T.

    1988-01-01

    We synthesized amorphous Al/sub 50/Hf/sub 50/ alloy powder by mechanically alloying an equimolar mixture of crystalline powders of Al and Hf using hexane as a dispersant. We characterized the powder as a function of mechanical-alloying time by scanning electron microscopy, x-ray diffraction, and differential scanning calorimetry. Amorphous Al/sub 50/Hf/sub 50/ powder heated at 10 K s/sup /minus/1/ crystallizes polymorphously at 1003 K into orthorhombic AlHf (CrB-type structure). During mechanical alloying, some hexane decomposes and hydrogen and carbon are incorporated into the amorphous alloy powder. The hydrogen can be removed by annealing the powder by hot pressing at a temperature approximately 30 K below the crystallization temperature. The amorphous compacts have a diamond pyramidal hardness of 1025 DPH. 24 refs., 7 figs., 1 tab.

  13. Nucleation of shear bands in amorphous alloys

    PubMed Central

    Perepezko, John H.; Imhoff, Seth D.; Chen, Ming-Wei; Wang, Jun-Qiang; Gonzalez, Sergio

    2014-01-01

    The initiation and propagation of shear bands is an important mode of localized inhomogeneous deformation that occurs in a wide range of materials. In metallic glasses, shear band development is considered to center on a structural heterogeneity, a shear transformation zone that evolves into a rapidly propagating shear band under a shear stress above a threshold. Deformation by shear bands is a nucleation-controlled process, but the initiation process is unclear. Here we use nanoindentation to probe shear band nucleation during loading by measuring the first pop-in event in the load–depth curve which is demonstrated to be associated with shear band formation. We analyze a large number of independent measurements on four different bulk metallic glasses (BMGs) alloys and reveal the operation of a bimodal distribution of the first pop-in loads that are associated with different shear band nucleation sites that operate at different stress levels below the glass transition temperature, Tg. The nucleation kinetics, the nucleation barriers, and the density for each site type have been determined. The discovery of multiple shear band nucleation sites challenges the current view of nucleation at a single type of site and offers opportunities for controlling the ductility of BMG alloys. PMID:24594599

  14. Amorphization of C-implanted Fe(Cr) alloys

    SciTech Connect

    Knapp, J.A.; Follstaedt, D.M.; Sorensen, N.R.; Pope, L.E.

    1990-01-01

    The amorphous phase formed by implanting C into Fe alloyed with Cr, which is prototype for the amorphous phase formed by implanting C into stainless steels, is compared to that formed by implanting C plus Ti into Fe and steels. The composition range of the phase has been examined; higher Cr and C concentrations are required than needed with Ti and C. The friction and wear benefits obtained by implanting stainless steels with C alone do not persist for the long durations and high wear loads found with Ti and C. However, the amorphous Fe-Cr-C alloys exhibits good aqueous corrosion resistance. 9 refs., 3 figs., 1 tabs.

  15. Ti Multicomponent Alloy Bulks by Powder Metallurgy

    NASA Astrophysics Data System (ADS)

    Zhang, Kuibao; Wen, Guanjun; Dai, Hongchuan; Teng, Yuancheng; Li, Yuxiang

    2014-10-01

    In this study, CrCuFeMnMo0.5Ti multicomponent alloy bulks were prepared by powder metallurgy of mechanical alloying and sintering. A simple body-centered cubic (bcc) solid solution was prepared after 40 h ball milling of the raw CrCuFeMnMo0.5Ti metallic powder. Particles of the alloyed powder are in microsized structures, which are actually a soft agglomeration of lamellar grains with thicknesses less than 1 μm. Meanwhile, the lamellar granules are consisted of nanosized grains under rigid cold welding. The 80-h ball-milled powder was consolidated by cold pressing and subsequent sintering at 800°C. The observed main phase in the consolidated sample after milling for 80 h is still a bcc solid solution. The solidified sample of 80-h ball-milled powder exhibits a Vickers hardness of 468 HV, which is much higher than 171 HV of the counterpart prepared from the raw metallic powder.

  16. Enhanced Corrosion Resistance of Iron-Based Amorphous Alloys

    SciTech Connect

    Rebak, R B; Day, S D; Lian, T; Aprigliano, L F; Hailey, P D; Farmer, J C

    2007-02-18

    Iron-based amorphous alloys possess enhanced hardness and are highly resistant to corrosion, which make them desirable for wear applications in corrosive environments. It was of interest to examine the behavior of amorphous alloys during anodic polarization in concentrated salt solutions and in the salt-fog testing. Results from the testing of one amorphous material (SAM2X5) both in ribbon form and as an applied coating are reported here. Cyclic polarization tests were performed on SAM2X5 ribbon as well as on other nuclear engineering materials. SAM2X5 showed the highest resistance to localized corrosion in 5 M CaCl{sub 2} solution at 105 C. Salt fog tests of 316L SS and Alloy 22 coupons coated with amorphous SAM2X5 powder showed resistance to rusting. Partial devitrification may be responsible for isolated pinpoint rust spots in some coatings.

  17. Investigation of new type Cu-Hf-Al bulk glassy alloys

    NASA Astrophysics Data System (ADS)

    Nagy, E.; Rontó, V.; Sólyom, J.; Roósz, A.

    2009-01-01

    In the last years new type Cu-Hf-Al ternary alloys were developed with high glass forming ability and ductility. The addition of Al to Cu-Hf alloys results in improvements in glass formation, thermal stability and mechanical properties of these alloys. We have investigated new Cu-based bulk amorphous alloys in Cu-Hf-Al ternary system. The alloys with Cu49Hf42Al9, Cu46Hf45Al9, Cu50Hf42.5Al7.5 and Cu50Hf45Al5 compositions were prepared by arc melting. The samples were made by centrifugal casting and were investigated by X-ray diffraction method. Thermodynamic properties were examined by differential scanning calorimetry and the structure of the crystallising phases by scanning electron microscopy. The determination of liquidus temperatures of alloys were measured by differential thermal analysis.

  18. Synthesis and Performance of Fe-based Amorphous Alloys for Nuclear Waste Applications

    SciTech Connect

    Kaufman, L; Perepezko, J; Hildal, K

    2007-02-06

    Recent developments in multi-component Fe-based amorphous alloys have shown that these novel materials exhibit outstanding corrosion resistance compared to typical crystalline alloys such as high-performance stainless steels and Ni-based C-22 alloy. During the past decade, amorphous alloy synthesis has advanced to allow for the casting of bulk metallic glasses. In several Fe-based alloy systems it is possible to produce glasses with cooling rates as low as 100 K/s. At such low cooling rates, there is an opportunity to produce amorphous solids through industrial processes such as thermal spray-formed coatings. Moreover, since cooling rates in typical thermal spray processing exceed 1000 K/s, novel alloy compositions can be synthesized to maximize corrosion resistance (i.e. adding Cr and Mo) and to improve radiation compatibility (adding B) and still maintain glass forming ability. The applicability of Fe-based amorphous coatings in typical environments where corrosion resistance and thermal stability are critical issues has been examined in terms of amorphous phase stability and glass-forming ability through a coordinated computational analysis and experimental validation. For example, a wedge casting technique has been applied to examine bulk glass forming alloys by combining multiple thermal probes with a measurement based kinetics analysis and a computational thermodynamics evaluation to elucidate the phase selection competition and critical cooling rate conditions. Based upon direct measurements and kinetics modeling it is evident that a critical cooling rate range should be considered to account for nucleation behavior and that the relative heat flow characteristics as well as nucleation kinetics are important in judging ease of glass formation. Similarly, a novel computational thermodynamics approach has been developed to explore the compositional sensitivity of glass-forming ability and thermal stability. Also, the synthesis and characterization of alloys

  19. Parametrized dielectric functions of amorphous GeSn alloys

    SciTech Connect

    D'Costa, Vijay Richard Wang, Wei; Yeo, Yee-Chia; Schmidt, Daniel

    2015-09-28

    We obtained the complex dielectric function of amorphous Ge{sub 1−x}Sn{sub x} (0 ≤ x ≤ 0.07) alloys using spectroscopic ellipsometry from 0.4 to 4.5 eV. Amorphous GeSn films were formed by room-temperature implantation of phosphorus into crystalline GeSn alloys grown by molecular beam epitaxy. The optical response of amorphous GeSn alloys is similar to amorphous Ge and can be parametrized using a Kramers-Kronig consistent Cody-Lorentz dispersion model. The parametric model was extended to account for the dielectric functions of amorphous Ge{sub 0.75}Sn{sub 0.25} and Ge{sub 0.50}Sn{sub 0.50} alloys from literature. The compositional dependence of band gap energy E{sub g} and parameters associated with the Lorentzian oscillator have been determined. The behavior of these parameters with varying x can be understood in terms of the alloying effect of Sn on Ge.

  20. Amorphous Alloy Membranes for High Temperature Hydrogen Separation

    SciTech Connect

    Coulter, K

    2013-09-30

    At the beginning of this project, thin film amorphous alloy membranes were considered a nascent but promising new technology for industrial-scale hydrogen gas separations from coal- derived syngas. This project used a combination of theoretical modeling, advanced physical vapor deposition fabricating, and laboratory and gasifier testing to develop amorphous alloy membranes that had the potential to meet Department of Energy (DOE) targets in the testing strategies outlined in the NETL Membrane Test Protocol. The project is complete with Southwest Research Institute® (SwRI®), Georgia Institute of Technology (GT), and Western Research Institute (WRI) having all operated independently and concurrently. GT studied the hydrogen transport properties of several amorphous alloys and found that ZrCu and ZrCuTi were the most promising candidates. GT also evaluated the hydrogen transport properties of V, Nb and Ta membranes coated with different transition-metal carbides (TMCs) (TM = Ti, Hf, Zr) catalytic layers by employing first-principles calculations together with statistical mechanics methods and determined that TiC was the most promising material to provide catalytic hydrogen dissociation. SwRI developed magnetron coating techniques to deposit a range of amorphous alloys onto both porous discs and tubular substrates. Unfortunately none of the amorphous alloys could be deposited without pinhole defects that undermined the selectivity of the membranes. WRI tested the thermal properties of the ZrCu and ZrNi alloys and found that under reducing environments the upper temperature limit of operation without recrystallization is ~250 °C. There were four publications generated from this project with two additional manuscripts in progress and six presentations were made at national and international technical conferences. The combination of the pinhole defects and the lack of high temperature stability make the theoretically identified most promising candidate amorphous alloys

  1. Bulk Formation of Metallic Glasses and Amorphous Silicon from the Melt

    NASA Technical Reports Server (NTRS)

    Spaepen, F.

    1985-01-01

    By using metallic glass compositions with a high relative glass transition temperature, such as Pd40Ni40P20, homogeneous nucleation also becomes negligible. Large (5g) masses of this alloys were obtained using a molten B2O3 flux. Presently, bulk glass formation in iron based glasses is being investigated. It is expected that if an undercooling of about 250K can be achieved in a Ge or Si melt, formation of the amorphous semiconductor phase (rather than the crystal) may be kinetically favored. The volumetric behavior of undercooled liquid Ga droplet dispersion is investigated by dilatometry. A theoretical model (both analytical and numerical) was developed for transient nucleation in glass forming melts. The model, originally designed for isothermal conditions, was extended to continuous quenching. It is being applied to glass formation in various metallic and oxide systems. A further refinement will be the inclusion of diffusion controlled interfacial rearrangements governing the growth of the crystal embryos.

  2. Catalytic applications of amorphous alloys: Expectations, achievements, and disappointments

    NASA Astrophysics Data System (ADS)

    Molnár, Árpád

    2011-07-01

    This review intends to summarize the major achievements in the application of amorphous alloys as precursors of catalyst materials. This non-traditional catalyst preparation method may provide supported catalysts with novel chemical and structural properties. Selected examples for both glassy alloy precursors and those fabricated by mechanochemistry include CO oxidation over binary and ternary alloys, dehydrogenation over Cu-M (M = Ti, Zr or Hf), one-step synthesis of methyl isobutyl ketone, and selective hydrogenation of unsaturated carbonyl compounds. Ni alloys for methanation developed for the project to solve global warming by recycling carbon dioxide are also discussed.

  3. Magnetostriction behavior of Co-Fe-Si-B amorphous alloys

    SciTech Connect

    Gomez-Polo, C.; Pulido, E. ); Rivero, G.; Hernando, A. )

    1990-05-01

    It is well known that the saturation magnetostriction constant of nearly-zero-magnetostriction amorphous alloys exhibits a dependence on both magnetic field and applied stress. Therefore the anisotropy field induced by the applied stress does not depend linearly on the stress strength. Experiments carried out on Co-rich amorphous alloys show a stress dependence of the anisotropy field as that expected by assuming long-range fluctuations of the magnetoelastic anisotropy. In this report the existence of local fluctuations of saturation magnetostriction is shown to be a reasonable cause of the stress dependence of magnetostriction.

  4. Hydrogen storage characteristics of mechanically alloyed amorphous metals

    SciTech Connect

    Harris, J.H.; Curtin, W.A.; Schultz, L.

    1988-09-01

    The hydrogen storage properties of a series of mechanically alloyed (MA) amorphous Ni/sub 1//sub --//sub x/Zr/sub x/ alloys are studied, using both gas phase and electrochemical techniques, and are compared to H storage of rapidly quenched (RQ) amorphous Ni/sub 1-//sub x/Zr/sub x/. In the MA alloys, hydrogen resides in the Ni/sub 4-//sub n/Zr/sub n/ (n = 4,3,2) tetrahedral interstitial sites, with a maximum hydrogen-to-metal ratio of 1.9(/sup 4//sub n/)x/sup n/(1-x)/sup 4-//sup n/. These features are identical to those of the RQ alloys and indicate that the topological and chemical order of the MA and RQ materials are essentially the same. However, the typical binding energy of hydrogen in a Ni/sub 4-//sub n/Zr/sub n/ site, E/sub n/, is shifted in the MA alloys relative to the RQ alloys and the distribution of binding energies centered on E/sub n/ is significantly broader in the MA samples. Thus, the MA and RQ alloys are not identical and sample annealing does not alter this subtle distinction. The sensitivity of H storage to the presence of chemical order in binary alloys are analyzed theoretically and the data is found to be most consistent with little or no chemical order (random alloys).

  5. On the origin of bulk glass forming ability in Cu-Hf, Zr alloys

    NASA Astrophysics Data System (ADS)

    Ristić, Ramir; Zadro, Krešo; Pajić, Damir; Figueroa, Ignacio A.; Babić, Emil

    2016-04-01

    Understanding the formation of bulk metallic glasses (BMG) in metallic systems and finding a reliable criterion for selection of BMG compositions are among the most important issues in condensed-matter physics and material science. Using the results of magnetic susceptibility measurements performed on both amorphous and crystallized Cu-Hf alloys (30–70 at% Cu) we find a correlation between the difference in magnetic susceptibilities of corresponding glassy and crystalline alloys and the variation in the glass forming ability (GFA) in these alloys. Since the same correlation can be inferred from data for the properties associated with the electronic structure of Cu-Zr alloys, it seems quite general and may apply to other glassy alloys based on early and late transition metals. This correlation is plausible from the free-energy considerations and provides a simple way to select the compositions with high GFA.

  6. Neutron-absorbing amorphous alloys for cladding coatings

    NASA Astrophysics Data System (ADS)

    Sevryukov, O. N.; Fedotov, V. T.; Polyansky, A. A.

    2016-04-01

    This paper shows developed compositions of neutron-absorbing cladding alloys based on nickel and containing such elements as B, Gd, Hf, and Mn. The techniques for application of coatings from these alloys on the surface of structural steels have been improved. It has been shown that the amorphous neutron-absorbing coating is more uniform than the crystalline one. The experimental data on the adhesion of cladding coatings with a steel substrate and their neutron-absorbing capacity have been obtained.

  7. Examination of Galvanic Action between Fe-Based Bulk Metallic Glass and Crystalline Alloys

    NASA Astrophysics Data System (ADS)

    Ha, Hung M.; Payer, Joe H.

    2009-06-01

    Fe-based bulk metallic glasses (amorphous metals) have been developed, and several compositions are shown to have excellent corrosion resistance in chloride solutions. Further, thermal-spray amorphous metals are being developed for use as a barrier coating layer, to protect substrate materials from corrosion. Galvanic action between dissimilar metals and the coating/substrate for the amorphous-alloy coatings is of practical interest for a number of applications. The mixed-potential theory provides a useful approach for examining the corrosion behavior of the component materials in the galvanic couple and is applied in this study. Galvanic action was studied for an Fe-based structurally amorphous metal (SAM) 1651 and several crystalline alloys that included 1018 C-steel, stainless steel (SS) 316L, and alloy 22. Anodic and cathodic polarization curves of each of the metals were measured by potentiodynamic polarization. Based on the mixed-potential theory, the behavior of the component materials in a galvanic cell was predicted. The predictions are compared to the measured behavior of galvanic couples with the crystalline alloys.

  8. Bulk metallic glass formation in the Pd-Ni-P and Pd-Cu-P alloy systems

    SciTech Connect

    Schwarz, R.B.; He, Y.

    1996-12-11

    Bulk metallic glasses were prepared in the Pd-Ni-P and Pd-Cu-P systems using a fluxing technique. The formation of bulk amorphous Pd-Cu-P alloys was reported here for the first time. For both alloy systems, bulk glass formation requires maintaining the phosphorus content near 20 at.%. In the Pd-Ni-P system, 10-mm diameter amorphous Pd{sub x}Ni{sub 80{minus}x}P{sub 20} rods can be formed for 25 {le} x {le} 60. In the Pd-Cu-P system, 7-mm diameter amorphous Pd{sub x}Cu{sub 80{minus}x}P{sub 20} rods can be produced for 40 {le} x {le} 60. From all the ternary alloys studied, Pd{sub 40}Ni{sub 40}P{sub 20} has the highest glass formability, and 25-mm diameter amorphous cylinders, 50 mm in length, can be easily fabricated. The glass stability of the Pd-Ni-P system is wider than that of the Pd-Cu-P system. For most bulk Pd-Ni-P glasses, {Delta}T > 90 K. The {Delta}T values of bulk amorphous Pd-Cu-P alloys are considerably smaller, ranging from 27 to 73 K. The elastic constants of bulk amorphous Pd-Ni-P and Pd-Cu-P alloys were determined using a resonant ultrasound spectroscopy technique. The Pd-Ni-P glasses are slightly stiffer than the Pd-Cu-P glasses. Within each alloy system, the Young`s modulus and the bulk modulus show little change with alloy composition. Of all the bulk glass forming systems so far investigated, the ternary Pd-Ni-P system has the best glass formability. This alloy was one of the first bulk glasses discovered, yet it still remains the best in terms of glass formability. Upon replacing part of Ni by Cu, the critical cooling rates are expected to be further reduced.

  9. Application of Laser Design of Amorphous Feco-Based Alloys for the Formation of Amorphous-Crystalline Composites

    NASA Astrophysics Data System (ADS)

    Permyakova, I. E.; Glezer, A. M.; Ivanov, A. A.; Shelyakov, A. V.

    2016-01-01

    Morphological and fractographic features of change of FeCo-based amorphous alloy surfaces after laser treatment are studied in detail. Regimes of laser treatment that allow various degrees of crystallization of the examined alloys to be obtained, including thin (<1 •m) crystal layers on amorphous alloy surfaces, amorphous-crystalline composites, and completely crystalline alloys are adjusted. The Vickers hardness is estimated in zones of selective laser irradiation. The structure of the examined alloys attendant to the change of their mechanical properties is analyzed.

  10. Integral bypass diodes in an amorphous silicon alloy photovoltaic module

    NASA Technical Reports Server (NTRS)

    Hanak, J. J.; Flaisher, H.

    1991-01-01

    Thin-film, tandem-junction, amorphous silicon (a-Si) photovoltaic modules were constructed in which a part of the a-Si alloy cell material is used to form bypass protection diodes. This integral design circumvents the need for incorporating external, conventional diodes, thus simplifying the manufacturing process and reducing module weight.

  11. Pressure-induced transformations in amorphous Si-Ge alloy

    SciTech Connect

    Coppari, F.; Polian, A.; Menguy, N.; Trapananti, A.; Congeduti, A.; Newville, M.; Prakapenka, V.B.; Choi, Y.; Principi, E.; Di Cicco, A.

    2012-03-14

    The pressure behavior of an amorphous Si-rich SiGe alloy ({alpha}-Si{sub x}Ge{sub 1-x}, x = 0.75) has been investigated up to about 30 GPa, by a combination of Raman spectroscopy, x-ray absorption spectroscopy, and x-ray diffraction measurements. The trends of microscopic structural properties and of the Raman-active phonon modes are presented in the whole pressure range. Nucleation of nanocrystalline alloy particles and metallization have been observed above 12 GPa, with a range of about 2 GPa of coexistence of amorphous and crystalline phases. Transformations from the amorphous tetrahedral, to the crystalline tetragonal ({beta}-Sn) and to the simple hexagonal structures have been observed around 13.8 and 21.8 GPa. The recovered sample upon depressurization, below about 4 GPa, shows a local structure similar to the as-deposited one. Inhomogeneities of the amorphous texture at the nanometric scale, probed by high-resolution transmission electron microscopy, indicate that the recovered amorphous sample has a different ordering at this scale, and therefore the transformations can not be considered fully reversible. The role of disordered grain boundaries at high pressure and the possible presence of a high-density amorphous phase are discussed.

  12. Behaviour of mirrors fabricated from amorphous alloys under impact of deuterium plasma ions

    NASA Astrophysics Data System (ADS)

    Bardamid, A. F.; Belyaeva, A. I.; Bondarenko, V. N.; Galuza, A. A.; Kolesnyk, O. G.; Konovalov, V. G.; Naidenkova, D. I.; Ryzhkov, I. V.; Shapoval, A. N.; Skinner, C. H.; Shtan, A. F.; Solodovchenko, S. I.; Voitsenya, V. S.; Yakimov, K. I.

    2006-04-01

    In-vessel mirrors are necessary for optical and laser diagnostics of plasmas in next-step fusion devices; however obtaining mirror materials that will maintain their performance in the harsh fusion environment remains problematic. At present, mirrors are fabricated from polycrystals or monocrystals, and metal films on metallic substrate mirrors are also being studied. In this paper, we report on a new family of bulk amorphous alloys that are being investigated in the search for new materials for the fusion environment. Their properties are very different from properties of well-known materials and are insufficiently investigated for scientific and technological applications. We present the results of investigation of modification of the surface and optical properties of amorphous mirror fabricated from Zr(41.2%)Ti(13.8%)Cu(12.5%)Ni(10%)Be(22.5%) alloy after bombardment by ions of deuterium plasma with different fluence and energy.

  13. Electrochemical studies of hydrogen storage in amorphous Ni[sub 64]Zr[sub 36] alloy

    SciTech Connect

    Ciureanu, M.; Ryan, D.H.; Stroem-Olsen, J.O. ); Trudeau, M.L. )

    1993-03-01

    The capacity of amorphous Ni-Zr alloys to absorb large amounts of hydrogen has been investigated recently in connection with their possible use for hydrogen storage. This property also makes them possible candidates as anodes in metal hydride-nickel hydroxide rechargeable batteries. The characteristic features of the electrochemical behavior of the amorphous Ni[sub 64]Zr[sub 36] alloy in alkaline media have been investigated. Changes occurring in both the physical state and the composition of the surface layer during chemical etching and electrochemical activation were studied by scanning electron microscopy, Auger electron spectroscopy, x-ray diffraction, and cyclic voltammetry. The kinetics of the hydrogen evolution reaction (HER) on the alloy under investigation was studied in terms of the cathodic polarization curves. The Tafel plots contain two different ranges: (i) a low-overpotential range, in which the slope of the linear [eta] versus log i is characteristic for charge transfer controlled processes; (ii) a high-overvoltage range, in which a combined mechanism, charge transfer and hydrogen diffusion into the bulk, is operative. To get information about the parameters influencing the hydrogen charging and discharging processes, chronopotentiometric experiments were performed. The changes of anodic overvoltage with time during constant current discharge were used to determine the electrochemical parameters i[sub 0] and [beta], as well as the diffusion coefficients (D) of the H atoms in the bulk of the alloy.

  14. Developments in the Ni-Nb-Zr amorphous alloy membranes

    NASA Astrophysics Data System (ADS)

    Sarker, S.; Chandra, D.; Hirscher, M.; Dolan, M.; Isheim, D.; Wermer, J.; Viano, D.; Baricco, M.; Udovic, T. J.; Grant, D.; Palumbo, O.; Paolone, A.; Cantelli, R.

    2016-03-01

    Most of the global H2 production is derived from hydrocarbon-based fuels, and efficient H2/CO2 separation is necessary to deliver a high-purity H2 product. Hydrogen-selective alloy membranes are emerging as a viable alternative to traditional pressure swing adsorption processes as a means for H2/CO2 separation. These membranes can be formed from a wide range of alloys, and those based on Pd are the closest to commercial deployment. The high cost of Pd (USD ~31,000 kg-1) is driving the development of less-expensive alternatives, including inexpensive amorphous (Ni60Nb40)100- x Zr x alloys. Amorphous alloy membranes can be fabricated directly from the molten state into continuous ribbons via melt spinning and depending on the composition can exhibit relatively high hydrogen permeability between 473 and 673 K. Here we review recent developments in these low-cost membrane materials, especially with respect to permeation behavior, electrical transport properties, and understanding of local atomic order. To further understand the nature of these solids, atom probe tomography has been performed, revealing amorphous Nb-rich and Zr-rich clusters embedded in majority Ni matrix whose compositions deviated from the nominal overall composition of the membrane.

  15. Amorphous silicon alloy-based roof integrated photovoltaic systems

    SciTech Connect

    Nath, P.; Vogeli, C.; Singh, A.; Call, J.

    1994-12-31

    A roll-to-roll process is used to deposit tandem amorphous silicon alloy solar cell onto thin (0.005 inch) stainless steel substrate. Using this solar cell material, the authors have designed and fabricated a photovoltaic (PV) module which can be integrated into building roofs. The module is fabricated by laminating the large area amorphous silicon on stainless steel solar cell material onto a 0.03 inch thick coated galvanized steel support plate. The module is then formed in such a way to allow installation as a batten and seam roofing system. This paper describes the fabrication and installation details of such PV systems.

  16. 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.

  17. Tungsten solution kinetics and amorphization of nickel in mechanically alloyed Ni-W alloys

    NASA Technical Reports Server (NTRS)

    Aning, A. O.; Wang, Z.; Courtney, T. H.

    1993-01-01

    The kinetics of solution of W, and the subsequent amorphization of Ni, in mechanically alloyed Ni-W alloys has been investigated. As W is a highly abrasive material in the energy intensive devices used for mechanical alloying, we studied the above reactions in different mills. One used hardened steel balls as the grinding media, and the other Al2O3. Abrasion is common to both mills, but Fe wear debris from the hardened steel enters into solution in the Ni rich phases whereas Al2O3 debris is present as small dispersoids. The kinetics of W solution and those of subsequent amorphization do not appear strongly affected by the Fe in solution or the Al2O3 dispersoid. Tungsten dissolves in crystalline Ni in amounts in excess of the equilibrium solubility during alloying. Amorphization of the Ni phase occurs if the W content in this phase exceeds ca. 28 at. pct.

  18. Correlation of atomic packing with the boson peak in amorphous alloys

    SciTech Connect

    Yang, W. M.; Liu, H. S. E-mail: blshen@seu.edu.cn E-mail: jiangjz@zju.edu.cn; Zhao, Y. C.; Liu, X. J.; Chen, G. X.; Man, Q. K.; Chang, C. T.; Li, R. W. E-mail: blshen@seu.edu.cn E-mail: jiangjz@zju.edu.cn; Dun, C. C.; Shen, B. L. E-mail: blshen@seu.edu.cn E-mail: jiangjz@zju.edu.cn; Inoue, A.; and others

    2014-09-28

    Boson peaks (BP) have been observed from phonon specific heats in 10 studied amorphous alloys. Two Einstein-type vibration modes were proposed in this work and all data can be fitted well. By measuring and analyzing local atomic structures of studied amorphous alloys and 56 reported amorphous alloys, it is found that (a) the BP originates from local harmonic vibration modes associated with the lengths of short-range order (SRO) and medium-range order (MRO) in amorphous alloys, and (b) the atomic packing in amorphous alloys follows a universal scaling law, i.e., the ratios of SRO and MRO lengths to solvent atomic diameter are 3 and 7, respectively, which exact match with length ratios of BP vibration frequencies to Debye frequency for the studied amorphous alloys. This finding provides a new perspective for atomic packing in amorphous materials, and has significant implications for quantitative description of the local atomic orders and understanding the structure-property relationship.

  19. Bulk nanostructured alloys prepared by flux melting and melt solidification

    SciTech Connect

    Shen, T.D.; Schwarz, R.B.; Zhang, X.

    2005-10-03

    We have prepared bulk nanostructured Ag{sub 60}Cu{sub 40} alloys by a flux-melting and melt-solidification technique. The flux purifies the melts, leading to a large undercooling and nanometer-sized microstructure. The as-prepared alloys are composed of nanolayered Ag and Cu within micrometer-sized grains. The bulk nanostructured alloys have an ultimate tensile strength of approximately 560 MPa, similar yield strength in tension and compression, elongation of 7% in tension, strain hardening exponent of 0.1, and relatively high mechanical and thermal stability up to 400 deg. C.

  20. Ultralight amorphous silicon alloy photovoltaic modules for space applications

    NASA Technical Reports Server (NTRS)

    Hanak, J. J.; Chen, Englade; Fulton, C.; Myatt, A.; Woodyard, J. R.

    1987-01-01

    Ultralight and ultrathin, flexible, rollup monolithic PV modules have been developed consisting of multijunction, amorphous silicon alloys for either terrestrial or aerospace applications. The rate of progress in increasing conversion efficiency of stable multijunction and multigap PV cells indicates that arrays of these modules can be available for NASA's high power systems in the 1990's. Because of the extremely light module weight and the highly automated process of manufacture, the monolithic a-Si alloy arrays are expected to be strongly competitive with other systems for use in NASA's space station or in other large aerospace applications.

  1. Properties of amorphous FeCoB alloy particles (abstract)

    NASA Astrophysics Data System (ADS)

    Charles, S. W.; Wells, S.; Meagher, A.; Mørup, S.; van Wonterghem, J.

    1988-11-01

    Amorphous and crystalline alloy particles (0.05-0.5 nm) of FexCoyBz in which the ratio x:y ranges from 0 to 1 have been prepared by the borohydride reduction of iron and cobalt salts in aqueous solution. The structure of the particles has been studied using Mössbauer spectroscopy and x-ray diffraction. Magnetic measurements of the saturation magnetization, coercivity, and remanence of the particles have been measured. The transition from the amorphous-to-crystalline state has been studied using differential scanning calorimetry (DSC) and thermomagnetometry up to a temperature of 450 °C (see Fig. 1). It has been shown that the fraction of boron in the alloys (10-35 at. %) is dependent upon the rate of addition of salts to borohydride and the concentration of cobalt present; this in turn influences the crystallinity and magnetic properties .

  2. Sonochemical preparation of nanosized amorphous Fe-Ni alloys

    NASA Astrophysics Data System (ADS)

    Shafi, K. V. P. M.; Gedanken, A.; Goldfarb, R. B.; Felner, I.

    1997-05-01

    Nanosized amorphous alloy powders of Fe20Ni80, Fe40Ni60, and Fe60Ni40 were prepared by sonochemical decomposition of solutions of volatile organic precursors, Fe(CO)5 and Ni(CO)4 in decalin, under an argon pressure of 100 to 150 kPa at 273 K. Magnetic susceptibility of Fe40Ni60 and Fe60Ni40 indicates blocking temperatures of 35 K and a magnetic particle size of about 6 nm. Thermogravimetric measurements of Fe20Ni80 give Curie temperatures of 322 °C for amorphous and 550 °C for crystallized forms. Differential scanning calorimetry exhibits an endothermic transition at 335 °C from a combination of the magnetic phase transition and alloy crystallization. The Mössbauer spectrum of crystallized Fe20Ni80 shows a sextet pattern with a hyperfine field of 25.04 T.

  3. Study of local structure in hyper-eutectic Zr-Cu-Al bulk glassy alloys by positron annihilation techniques

    NASA Astrophysics Data System (ADS)

    Ishiyama, T.; Ishii, K.; Yokoyama, Y.; Konno, T. J.; Iwase, A.; Hori, F.

    2016-01-01

    The Zr-Cu-Al bulk glassy (BG) alloy, which has amorphous structure, possesses various properties such as high strength and toughness with compositional dependence. In the present study, density, positron annihilation lifetime and coincidence Doppler Broadening measurement have been performed for various compositional hyper-eutectic Zr-Cu-Al BG alloys. The density of hyper-eutectic Zr-Cu-Al BG alloys increases with decreasing of Zr fraction. In contrast, positron lifetime for all compositional alloys is almost constant about 165 psec. In addition, the CDB ratio profile is almost the same for hyper-eutectic alloys. This unchanging trend of CDB ratio profile is quite different from that of hypo-eutectic BG alloys. These results reveal that different internal structure exists in hyper and hypo-eutectic BG alloys.

  4. Electrodeposition of amorphous ternary nickel-chromium-phosphorus alloy

    DOEpatents

    Guilinger, Terry R.

    1990-01-01

    Amorphous ternary nickel-chromium-phosphorus alloys are electrodeposited from a bath comprising a nickel salt, a chromium salt, a phosphorus source such as sodium hypophosphite, a complexing agent for the nickel ions, supporting salts to increase conductivity, and a buffering agent. The process is carried out at about room temperature and requires a current density between about 20 to 40 A/dm.sup.2.

  5. Formation of amorphous metal alloys by chemical vapor deposition

    DOEpatents

    Mullendore, A.W.

    1988-03-18

    Amorphous alloys are deposited by a process of thermal dissociation of mixtures of organometallic compounds and metalloid hydrides,e.g., transition metal carbonyl, such as nickel carbonyl and diborane. Various sizes and shapes of deposits can be achieved, including near-net-shape free standing articles, multilayer deposits, and the like. Manipulation or absence of a magnetic field affects the nature and the structure of the deposit. 1 fig.

  6. Formation of amorphous metal alloys by chemical vapor deposition

    DOEpatents

    Mullendore, Arthur W.

    1990-01-01

    Amorphous alloys are deposited by a process of thermal dissociation of mixtures or organometallic compounds and metalloid hydrides, e.g., transition metal carbonyl such as nickel carbonyl, and diborane. Various sizes and shapes of deposits can be achieved, including near-net-shape free standing articles, multilayer deposits, and the like. Manipulation or absence of a magnetic field affects the nature and the structure of the deposit.

  7. Advances in amorphous silicon alloy multijunction cells and modules

    SciTech Connect

    Guha, S.; Yang, J.; Banerjee, A.; Glatfelter, T.; Hoffman, K.; Xu, X.

    1996-01-01

    We discuss the research directions taken to improve the stable efficiency of amorphous silicon alloy multijunction modules. Use of hydrogen dilution during deposition has resulted in improvement of initial efficiency and stability of the component cells in the triple-junction structure. An innovative laser-interconnected module design has resulted in the reduction of optical and electrical losses in the module down to 1{percent}. {copyright} {ital 1996 American Institute of Physics.}

  8. Molecular dynamics simulations of nanometric cutting mechanisms of amorphous alloy

    NASA Astrophysics Data System (ADS)

    Zhu, Peng-Zhe; Qiu, Chen; Fang, Feng-Zhou; Yuan, Dan-Dan; Shen, Xue-Cen

    2014-10-01

    Molecular dynamics simulations are employed to study the nanometric cutting process of Cu50Zr50 amorphous alloy. The effects of cutting depth, cutting speed and tool edge radius on the cutting force, workpiece pile-up and temperature of the cutting region are studied to investigate the mechanisms of the material removal and surface formation in the nanometric cutting process. It is found that the material removal of amorphous alloy workpiece is mainly based on extrusion at the nanoscale instead of shearing at the macroscale. The plastic deformation of amorphous alloy is mainly due to the formation of shear transformation zones during the nanometric cutting process. The results also suggest that bigger cutting depth and cutting speed will lead to larger tangential force and normal force. However, the tool edge radius has a negligible effect on the tangential force although the normal force increases with the increase of tool edge radius. The workpiece pile-up increases with an increase of the cutting depth, but decreases with an increase of the edge radius of the tool. The workpiece pile-up is not significantly affected by the cutting speed. It is also found that larger cutting depth and cutting speed will result in higher temperature in the cutting region of workpiece and the average Newtonian layer temperature of the tool. Tool edge radius has no significant effect on the temperature distribution of the workpiece and the average Newtonian layer temperature of the tool.

  9. Characterization of amorphous Co-P alloy coatings electrodeposited with pulse current using gluconate bath

    NASA Astrophysics Data System (ADS)

    Bera, Parthasarathi; Seenivasan, H.; Rajam, K. S.; William Grips, V. K.

    2012-10-01

    Co-P alloy coatings were electrodeposited with pulse current using gluconate bath and characterized by XRD, FESEM, AFM, DSC and XPS. Co-P alloy coatings are amorphous in nature as demonstrated by XRD. FESEM exhibits the “cauliflower type” morphology that is distinctive of nanocrystalline metals and alloys. Co-P alloys are found to follow instantaneous growth mechanism as revealed by AFM studies. Two exothermic peaks at 320 and 340 °C in DSC profiles of Co-P deposit correspond to the crystallization of the deposit. Detailed XPS studies of these alloy coatings have shown that as-deposited coatings consist of Co metal as well as oxidized Co species. P has mostly been present as bulk alloy on the surface as Pδ- form. Increase in the amounts of Co metal and Pδ- are observed upon intermittent sputtering. No appreciable increase in microhardness is observed with increase in the phosphorous content, but it increases with heat treatment significantly.

  10. Spectral analysis of creep recovery process in finemet type amorphous alloy

    NASA Astrophysics Data System (ADS)

    Juríková, A.; Csach, K.; Ocelík, V.; Miškuf, J.; Bengus, V. Z.

    2002-01-01

    The creep recovery process in Finemet type amorphous alloy has been analyzed using the method for calculating the relaxation time spectra. The influence of structural relaxation and temperature on the spectra shape has been studied. The creep recovery spectrum of the anelastic deformation of the multicomponent Fe-Nb-Cu-Si-B amorphous alloy seems to be more complex in comparison with standard amorphous alloys.

  11. The structure of amorphous bulk and silica-supported copper(II) hydroxides

    SciTech Connect

    Kriventsov, V.V.; Kochubey, D.I.; Elizarova, G.L.; Matvienko, L.G.; Parmon, V.N.

    1999-07-01

    Determination of the structure of surface hydroxocompounds is one of the most delicate areas of environmental chemistry, geochemistry, and catalysis. In nature, these compounds are formed everywhere, mostly by absorption of multicharged metal cations on different soil constitutents from water solutions. The data obtained show that at pH 7 copper(II) ions are adsorbed on a SiO{sub 2} surface as polymeric species of hydroxide nature. The structure of these species is similar to that of the bulk amorphous copper hydroxide. The amorphous state of supported Cu(OH){sub 2} is caused by a small (ca. 11 {angstrom}) size of the surface particles. In contrast, the overstoichiometric water molecules seem to act as ``amorphizers`` of the bulk copper hydroxide. The structures of the bulk and dispersed amorphous copper(II) hydroxide were determined. The amorphous Cu(OH){sub 2} has a layered structure close to the structure of the crystalline hydroxide, but the layers in the amorphous hydroxide are shifted toward one another approximately for {1/4} of the c period of the lattice.

  12. Observation of unique blister-like surface features on amorphous metallic alloys following bombardment with deuterium ions

    NASA Astrophysics Data System (ADS)

    Bardamid, A. F.; Voitsenya, V. S.; Lytvyn, O. S.; Lytvyn, P. M.; Konovalov, V. G.; Shapoval, A. N.; Solodovchenko, S. I.; Yakimov, K. I.

    2008-05-01

    When investigating the impact of deuterium plasma ions (with energy 300 eV) on mirror specimen fabricated of bulk amorphous alloy Zr(41.2)Ti(13.8)Cu(12.5)Ni(10)Be(22.5) some unusual surface features were observed. Their shape differs from blisters observed on the surface of amorphous foils bombarded with high energy helium and hydrogen ions (Refs. [9-11]). In this Letter a short description of characteristics of these 'blister-like' features are presented.

  13. Amorphous silicon-carbon alloys and amorphous carbon from direct methane and ethylene activation by ECR

    SciTech Connect

    Conde, J.P.; Chu, V.; Giorgis, F.; Pirri, C.F.; Arekat, S.

    1997-07-01

    Hydrogenated amorphous silicon-carbon alloys are prepared using electron-cyclotron resonance (ECR) plasma-enhanced chemical vapor deposition. Hydrogen is introduced into the source resonance cavity as an excitation gas. Silane is introduced in the main chamber in the vicinity of the plasma stream, whereas the carbon source gases, methane or ethylene, are introduced either with the silane or with the hydrogen as excitation gases. The effect of the type of carbon-source gas, excitation gas mixture and silane-to-carbon source gas flow ratio on the deposition rate, bandgap, subgap density of states, spin density and hydrogen evolution are studied.

  14. Bulk formation of metallic glasses and amorphous silicon from the melt

    NASA Technical Reports Server (NTRS)

    Spaepen, F.

    1984-01-01

    Procedures and compositions for producing metallic glasses in bulk at slow cooling rates were investigated. An attempt was made to form the amorphous phase of the tetrahedrally coordinated elements (Si or Ge) by undercooling the melt. The crystal nucleation behavior of pure liquids and glass formers were examined.

  15. Comparison of Crevice Corrosion of Fe-Based Amorphous Metal and Crystalline Ni-Cr-Mo Alloy

    SciTech Connect

    Shan, X; Ha, H; Payer, J H

    2008-07-24

    The crevice corrosion behaviors of an Fe-based bulk metallic glass alloy (SAM1651) and a Ni-Cr-Mo crystalline alloy (C-22) were studied in 4M NaCl at 100 C with cyclic potentiodynamic polarization and constant potential tests. The corrosion damage morphologies, corrosion products and the compositions of corroded surfaces of these two alloys were studied with optical 3D reconstruction, Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Auger Electron Spectroscopy (AES). It was found that the Fe-based bulk metallic glass (amorphous alloy) SAM1651 had a more positive breakdown potential and repassivation potential than crystalline alloy C-22 in cyclic potentiodynamic polarization tests and required a more positive oxidizing potential to initiate crevice corrosion in constant potential test. Once crevice corrosion initiated, the corrosion propagation of C-22 was more localized near the crevice border compared to SAM1651, and SAM1651 repassivated more readily than C-22. The EDS results indicated that the corrosion products of both alloys contained high amount of O and were enriched in Mo and Cr. The AES results indicated that a Cr-rich oxide passive film was formed on the surfaces of both alloys, and both alloys were corroded congruently.

  16. Superior Tensile Ductility in Bulk Metallic Glass with Gradient Amorphous Structure

    PubMed Central

    Wang, Q.; Yang, Y.; Jiang, H.; Liu, C. T.; Ruan, H. H.; Lu, J.

    2014-01-01

    Over centuries, structural glasses have been deemed as a strong yet inherently ‘brittle’ material due to their lack of tensile ductility. However, here we report bulk metallic glasses exhibiting both a high strength of ~2 GPa and an unprecedented tensile elongation of 2–4% at room temperature. Our experiments have demonstrated that intense structural evolution can be triggered in theses glasses by the carefully controlled surface mechanical attrition treatment, leading to the formation of gradient amorphous microstructures across the sample thickness. As a result, the engineered amorphous microstructures effectively promote multiple shear banding while delay cavitation in the bulk metallic glass, thus resulting in superior tensile ductility. The outcome of our research uncovers an unusual work-hardening mechanism in monolithic bulk metallic glasses and demonstrates a promising yet low-cost strategy suitable for producing large-sized, ultra-strong and stretchable structural glasses. PMID:24755683

  17. Fabrication of Nb3Al superconducting bulks by mechanical alloying method

    NASA Astrophysics Data System (ADS)

    Qi, Ming; Pan, Xi Feng; Zhang, Ping Xiang; Cui, Li Jun; Li, Cheng Shan; Yan, Guo; Chen, Yong Liang; Zhao, Yong

    2014-06-01

    Since it can directly prepare the Nb-Al supersaturated solid solution, mechanical alloying is thought as a promising method to make high-performance Nb3Al superconductors at a low temperature annealing condition, without the complicated rapid heating, quenching and transformation (RHQT) process. In this paper, we investigate the effects of milling time, the content of Al and annealing temperature on phase formation and superconducting properties of mechanical alloying Nb3Al bulks in detail. The study results show that Nb-Al supersaturated solid solution could be obtained by high energy ball milling, as long as the Nb-Al blended powder is ball milled for 1 h, even the amorphous phase appears with the ball milling time prolonging to 10 h, the Nb-Al intermetalics do not come out either. Amorphous phase is hardly beneficial to synthesizing the Nb3Al phase, instead, it will make the products impurity. By optimizing the milling time, elements composition and annealing temperature , pure Nb3Al phase is obtained and the highest onset superconducting transition temperature (Tc-onset) reaches 15.8 K and the critical current density (Jc) 106 A/cm2 at 8 K without outer field. This paper also discusses the main reasons that affect the superconducting properties of mechanical alloying Nb3Al superconductor.

  18. Comparative Study on the Corrosion Resistance of Fe-Based Amorphous Metal, Borated Stainless Steel and Ni-Cr-Mo-Gd Alloy

    SciTech Connect

    Lian, Tiangan; Day, Daniel; Hailey, Phillip; Choi, Jor-Shan; Farmer, Joseph

    2007-07-01

    Iron-based amorphous alloy Fe{sub 49.7}Cr{sub 17.7}Mn{sub 1.9}Mo{sub 7.4}W{sub 1.6}B{sub 15.2}C{sub 3.8}Si{sub 2.4} was compared to borated stainless steel and Ni-Cr-Mo-Gd alloy on their corrosion resistance in various high-concentration chloride solutions. The melt-spun ribbon of this iron-based amorphous alloy have demonstrated a better corrosion resistance than the bulk borated stainless steel and the bulk Ni-Cr-Mo-Gd alloy, in high-concentration chloride brines at temperatures 90 deg. C or higher. (authors)

  19. Fabrication of Bulk Glassy Alloy Foams by High Pressure Hydrogen

    NASA Astrophysics Data System (ADS)

    Wada, Takeshi; Inoue, Akihisa

    Porous Pd42.5Cu30Ni7.5P20 bulk glassy alloy rods with porosities of up to 70% were successfully prepared by high pressure hydrogen of 15 MPa. The melt of Pd42.5Cu30Ni7.5P20 alloy kept under high pressure hydrogen absorbs hydrogen and subsequent water quenching of the melt causes the homogeneous dispersion of hydrogen bubbles, which was resulted from the decrease of hydrogen solubility with decrease of pressure. Annealing the hydrogen bubble containing sample at a supercooled liquid state under vacuum, the bubbles are allowed to expand due to the decrease of viscosity of metallic glass matrix. Pores expansion continues until glassy matrix crystallizes or the equilibration among pressure of the pores, pressure of the atmosphere and surface tension is achieved. By utilizing these phenomena, pores up to 80 m in diameters are homogeneously distributed over the whole cross-sectional area of a fully glassy matrix. Under compressive deformation, the porous alloys with porosities exceeding 40% did not show macroscopic fracture in a wide compressive strain range up to 0.6 whereas the non-porous alloy fractures instantly after elastic limit of about 0.02. Porous bulk glassy alloys exhibit higher plateau stress, lower Young‧s modulus and higher energy absorption capacity compared with the conventional crystalline metal foams.

  20. Corrosion behavior of amorphous fe-cr-al-p-c ribbon alloys

    NASA Astrophysics Data System (ADS)

    Cho, Kangjo; Hwang, Choll-Hong; Ryeom, Yeong-Jo; Pak, Chang-Su

    1982-05-01

    Corrosion resistance of amorphous Fe72Cr8-xAlxP13C7 ribbons produced by a rapid quenching method has been investigated in several solutions. The corrosion test for amorphous ribbons was carried out, and anodic polarization curves have been measured in the solutions. Resultantly, even in the amorphous Fe72Cr8-xAlxP13C7 ribbons containing a low Cr content, this composition of amorphous alloys showed the high corrosion resistance.

  1. Bulk undercooling, nucleation, and macrosegregation of Pb-Sn alloys

    NASA Technical Reports Server (NTRS)

    Degroh, H. C., III; Laxmanan, V.

    1988-01-01

    Preliminary ground-based studies on the undercooling behavior of large samples (23 g) of lead-tin alloys are presented. Evidence of gravity-related segregation effects is found, and a possible area for future microgravity experimentation is thus identified. Detailed descriptions of the experimental procedure used to achieve bulk undercoolings of between 0.5 and 34 K, depending on composition, are given. The bulk undercoolings obtained in this study are comparable with those found in small droplets. The large size of the present samples enabled the observation of sedimentation and other macrosegregation processes.

  2. Sample-Size Effects on the Compression Behavior of a Ni-BASED Amorphous Alloy

    NASA Astrophysics Data System (ADS)

    Liang, Weizhong; Zhao, Guogang; Wu, Linzhi; Yu, Hongjun; Li, Ming; Zhang, Lin

    Ni42Cu5Ti20Zr21.5Al8Si3.5 bulk metallic glasses rods with diameters of 1 mm and 3 mm, were prepared by arc melting of composing elements in a Ti-gettered argon atmosphere. The compressive deformation and fracture behavior of the amorphous alloy samples with different size were investigated by testing machine and scanning electron microscope. The compressive stress-strain curves of 1 mm and 3 mm samples exhibited 4.5% and 0% plastic strain, while the compressive fracture strength for 1 mm and 3 mm rod is 4691 MPa and 2631 MPa, respectively. The compressive fracture surface of different size sample consisted of shear zone and non-shear one. Typical vein patterns with some melting drops can be seen on the shear region of 1 mm rod, while fish-bone shape patterns can be observed on 3 mm specimen surface. Some interesting different spacing periodic ripples existed on the non-shear zone of 1 and 3 mm rods. On the side surface of 1 mm sample, high density of shear bands was observed. The skip of shear bands can be seen on 1 mm sample surface. The mechanisms of the effect of sample size on fracture strength and plasticity of the Ni-based amorphous alloy are discussed.

  3. Unexpected magnetic behavior in amorphous Co{sub 90}Sc{sub 10} alloy

    SciTech Connect

    Ghafari, M. E-mail: skamali@utsi.edu; Gleiter, H.; Sakurai, Y.; Itou, M.; Peng, G.; Fang, Y. N.; Feng, T.; Hahn, H.; Kamali, S. E-mail: skamali@utsi.edu

    2015-09-28

    An amorphous alloy Co{sub 90}Sc{sub 10} has been prepared by rapid quenching from the melt. The results of magnetization measurements show that this alloy has the highest Curie temperature reported for any amorphous transition metal based alloys. Furthermore, for a Co based amorphous alloy, the magnetic moment is remarkably high. Moreover, the alloy exhibits soft magnetic properties. Based on the findings, amorphous Co{sub 90}Sc{sub 10} appears to be an attractive candidate for applications as a soft magnetic material. The temperature dependence of the reduced magnetization can be described by the Bloch power law. The results show that the B coefficient of the amorphous Co{sub 90}Sc{sub 10} alloy, which is a measure of the rigidity of spin waves, exhibits the lowest value observed until now for any amorphous alloy and is comparable to crystalline alloys. It is found that the Sc atoms in the Co{sub 90}Sc{sub 10} alloy lead to an increase of the itinerant spin moment of Co atoms, and, in contrast to this behaviour, to a decrease of the local 3d-electrons of Co.

  4. Calculating formation range of binary amorphous alloys fabricated by electroless plating

    NASA Astrophysics Data System (ADS)

    Zhang, Bangwei; Liao, Shuzhi; Shu, Xiaolin; Xie, Haowen

    2016-06-01

    A lot of amorphous alloy deposits in the binary (Ni, Co, Cu)-(P, B) alloy systems fabricated by electroless plating (EP) have been reported up to date. But no one reported their theoretical modeling of the amorphous formation and calculated their concentration range of amorphous formation (RAF). Using Miedema model and subregular model scheme, the RAFs for the six EP (Ni, Co, Cu)-(P, B) alloys and three Ni-Cu, Ni-Co and Co-Cu alloys have been calculated systematically for the first time. The calculated results are in agreement with experimental observations. Experiments and calculations for the RAFs in the latter three alloy systems reveal that not any RAF formed except crystalline states. The huge difference between the six metal-metalloid alloys and three metal-metal alloys in RAF has been discussed in detail in the paper.

  5. Radiation Resistance Studies of Amorphous Silicon Alloy Photovoltaic Materials

    NASA Technical Reports Server (NTRS)

    Woodyard, James R.

    1994-01-01

    The radiation resistance of commercial solar cells fabricated from hydrogenated amorphous silicon alloys was investigated. A number of different device structures were irradiated with 1.0 MeV protons. The cells were insensitive to proton fluences below 1E12 sq cm. The parameters of the irradiated cells were restored with annealing at 200 C. The annealing time was dependent on proton fluence. Annealing devices for one hour restores cell parameters for fluences below lE14 sq cm require longer annealing times. A parametric fitting model was used to characterize current mechanisms observed in dark I-V measurements. The current mechanisms were explored with irradiation fluence, and voltage and light soaking times. The thermal generation current density and quality factor increased with proton fluence. Device simulation shows the degradation in cell characteristics may be explained by the reduction of the electric field in the intrinsic layer.

  6. 'Age-hardened alloy' based on bulk polycrystalline oxide ceramic

    NASA Astrophysics Data System (ADS)

    Gurnani, Luv; Singh, Mahesh Kumar; Bhargava, Parag; Mukhopadhyay, Amartya

    2015-05-01

    We report here for the first time the development of 'age-hardened/toughened' ceramic alloy based on MgO in the bulk polycrystalline form. This route allows for the facile development of a 'near-ideal' microstructure characterized by the presence of nanosized and uniformly dispersed second-phase particles (MgFe2O4) within the matrix grains, as well as along the matrix grain boundaries, in a controlled manner. Furthermore, the intragranular second-phase particles are rendered coherent with the matrix (MgO). Development of such microstructural features for two-phase bulk polycrystalline ceramics is extremely challenging following the powder metallurgical route usually adopted for the development of bulk ceramic nanocomposites. Furthermore, unlike for the case of ceramic nanocomposites, the route adopted here does not necessitate the usage of nano-powder, pressure/electric field-assisted sintering techniques and inert/reducing atmosphere. The as-developed bulk polycrystalline MgO-MgFe2O4 alloys possess considerably improved hardness (by ~52%) and indentation toughness (by ~35%), as compared to phase pure MgO.

  7. Formation of Fe-Nb-X (X=Zr, Ti) amorphous alloys from pure metal elements by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Xiao, Zhiyu; Tang, Cuiyong; Leo Ngai, Tungwai; Yang, Chao; Li, Yuanyuan

    2012-01-01

    Fe-based amorphous powders of Fe 56Nb 6Zr 38 and Fe 60Nb 6Ti 34 based on binary eutectic were prepared by mechanical alloying starting from mixtures of pure metal powders. The amorphization behavior and thermal stability were examined by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and differential scanning calorimetry. Results show that Fe 56Nb 6Zr 38 alloy has a better glass forming ability and a relatively lower thermal stability comparing with Fe 60Nb 6Ti 34 alloy. The prepared amorphous powders have homogeneous element distribution and no obvious contaminants coming from mechanical alloying. The synthesized amorphous powders offer the potential for consolidation to full density with desirable mechanical properties through the powder metallurgy methods.

  8. Hydrogenation under high pressure enhancing catalytic activity of Cu-Zr amorphous alloys

    NASA Astrophysics Data System (ADS)

    Szummer, A.; Janik-Czachor, M.; Molnár, Á.; Marchuk, I.; Varga, M.; Filipek, S. M.

    2002-11-01

    High pressures of hydrogen up to 3.0 GPa and temperatures up to 373 K were used as a pretreatment to introduce structural changes in the bulk and on the surface of Cu-Zr amorphous alloys which then were examined by means of x-ray diffraction and microscopy. The hydrogenative pretreatment of high hydrogen fugacity followed by annealing at 623 K, aimed at causing desorption of hydrogen, and an eventual exposure of the samples to air at room temperature to oxidize Zr, resulted in a distinct increase of catalytic activity in the dehydrogenation of 2-propanol. A tentative mechanism to account for the enhancement of the catalytic activity induced by the above combined pretreatment is discussed.

  9. Measurement of Crystallization Temperature Using Thermography for Thin Film Amorphous Alloy Samples

    NASA Astrophysics Data System (ADS)

    Hata, Seiichi; Aono, Yuko; Sakurai, Junpei; Shimokohbe, Akira

    2009-03-01

    This report describes a new non-contact measurement method for the crystallization temperature (Tx) of a thin film amorphous alloy. The thermal emissivity of the amorphous alloy sample is predicted to be modified when it crystallizes. It was attempted to relate this modification to changes in the apparent temperature by thermography. Thin film amorphous alloys of Pt67Si33 and Pt73Si27 were sputtered onto an Al2O3 substrate and then heated at 20 K/min in vacuum, and the film temperature was monitored by thermography. The Tx indicated by the proposed method coincided with the temperature measured by conventional differential scanning calorimeter within 8 K.

  10. Fabrication of nanoporous silver by de-alloying Cu-Zr-Ag amorphous alloys

    NASA Astrophysics Data System (ADS)

    Wang, Hui; Xiao, Shang-gang; Zhang, Tao

    2016-07-01

    Nanoporous silver (NPS) with a ligament size ranging from 15 to 40 nm was fabricated by de-alloying (Cu50Zr50)100- x Ag x ( x = 10at%, 20at%, 30at%, and 40at%) amorphous ribbons in a mixed aqueous solution of hydrofluoric (HF) acid and nitric acid under free corrosion conditions. Nanoporous silver ligaments and pore sizes were able to be fine-tuned through tailoring the chemical composition, corrosion conditions, and de-alloying time. The ligament size increases with an increase in Ag content and de-alloying time, but decreases with an increase in HF concentration. This phenomenon may be attributed to the dissolution of Zr/Cu and the diffusion, aggregation, nucleation, and recrystallization of Ag, leading to an oriented attachment of adjacent nanocrystals as revealed by TEM analysis.

  11. Crystallization kinetics and magnetic properties of FeSiCr amorphous alloy powder cores

    NASA Astrophysics Data System (ADS)

    Xu, Hu-ping; Wang, Ru-wu; Wei, Ding; Zeng, Chun

    2015-07-01

    The crystallization kinetics of FeSiCr amorphous alloy, characterized by the crystallization activation energy, Avrami exponent and frequency factor, was studied by non-isothermal differential scanning calorimetric (DSC) measurements. The crystallization activation energy and frequency factor of amorphous alloy calculated from Augis-Bennett model were 476 kJ/mol and 5.5×1018 s-1, respectively. The Avrami exponent n was calculated to be 2.2 from the Johnson-Mehl-Avrami (JMA) equation. Toroid-shaped Fe-base amorphous powder cores were prepared from the commercial FeSiCr amorphous alloy powder and subsequent cold pressing using binder and insulation. The characteristics of FeSiCr amorphous alloy powder and the effects of compaction pressure and insulation content on the magnetic properties, i.e., effective permeability μe, quality factor Q and DC-bias properties of FeSiCr amorphous alloy powder cores, were investigated. The FeSiCr amorphous alloy powder cores exhibit a high value of quality factor and a stable permeability in the frequency range up to 1 MHz, showing superior DC-bias properties with a "percent permeability" of more than 82% at H=100 Oe.

  12. The use of amorphous boron powder enhances mechanical alloying in soft magnetic FeNbB alloy: A magnetic study

    NASA Astrophysics Data System (ADS)

    Ipus, J. J.; Blázquez, J. S.; Franco, V.; Conde, A.

    2013-05-01

    Saturation magnetization and magnetic anisotropy have been studied during mechanical alloying of Fe75Nb10B15 alloys prepared using crystalline and commercial amorphous boron. The evolution of saturation magnetization indicates a more efficient dissolution of boron into the matrix using amorphous boron, particularly for short milling times. The magnetization of the crystalline phase increases as boron is incorporated into this phase. Two milling time regimes can be used to describe the evolution of magnetic anisotropy: a first regime governed by microstrains and a second one mainly governed by crystal size and amorphous fraction.

  13. The use of amorphous boron powder enhances mechanical alloying in soft magnetic FeNbB alloy: A magnetic study

    SciTech Connect

    Ipus, J. J.; Blazquez, J. S.; Franco, V.; Conde, A.

    2013-05-07

    Saturation magnetization and magnetic anisotropy have been studied during mechanical alloying of Fe{sub 75}Nb{sub 10}B{sub 15} alloys prepared using crystalline and commercial amorphous boron. The evolution of saturation magnetization indicates a more efficient dissolution of boron into the matrix using amorphous boron, particularly for short milling times. The magnetization of the crystalline phase increases as boron is incorporated into this phase. Two milling time regimes can be used to describe the evolution of magnetic anisotropy: a first regime governed by microstrains and a second one mainly governed by crystal size and amorphous fraction.

  14. Effect of High Temperature Aging on the Corrosion Resistance of Iron Based Amorphous Alloys

    SciTech Connect

    Day, S D; Haslam, J J; Farmer, J C; Rebak, R B

    2007-08-10

    Iron-based amorphous alloys can be more resistant to corrosion than polycrystalline materials of similar compositions. However, when the amorphous alloys are exposed to high temperatures they may recrystallize (or devitrify) thus losing their resistance to corrosion. Four different types of amorphous alloys melt spun ribbon specimens were exposed to several temperatures for short periods of time. The resulting corrosion resistance was evaluated in seawater at 90 C and compared with the as-prepared ribbons. Results show that the amorphous alloys can be exposed to 600 C for 1-hr. without losing the corrosion resistance; however, when the ribbons were exposed at 800 C for 1-hr. their localized corrosion resistance decreased significantly.

  15. Enhanced plasticity in a bulk amorphous matrix composite: macroscopic and microscopic viewpoint studies

    SciTech Connect

    Lee, Jae-Chul . E-mail: jclee001@korea.ac.kr; Kim, Yu-Chan; Ahn, Jae-Pyoung; Kim, Hyoung Seop

    2005-01-03

    We developed the (Cu{sub 60}Zr{sub 30}Ti{sub 10}){sub 0.95}Ta{sub 5} amorphous matrix composite, which is a Cu-based bulk amorphous composite reinforced with a micron-sized Ta-rich crystalline phase. The composite demonstrated an ultimate strength of 2332 MPa with a dramatically enhanced fracture strain of 15.3%. Macroscopic observation of the fractured (Cu{sub 60}Zr{sub 30}Ti{sub 10}){sub 0.95}Ta{sub 5} amorphous composite using scanning electron microscopy showed the presence of multiple shear bands along with numerous secondary shear bands, which spread from the primary shear bands. On the other hand, microscopic observation of the fractured composite using transmission electron microscopy showed that the cracks propagate through the amorphous matrix in a jagged manner. The observed macroscopic and microscopic behaviors, involving shear band formation and crack propagation, are believed to be responsible for the enhanced plasticity. Finite element calculations using the Mohr-Coulomb model of hydrostatic pressure dependent materials were conducted, in order to gain a better understanding of various aspects of the macroscopic deformation behavior, such as the interaction of the shear bands with the crystalline particles, the initiation site of the shear bands, and the formation of multiple shear bands, while the microscopic deformation behavior was explained based on the formation of nanocrystallites that had precipitated under quasistatic compression.

  16. Microstructure Evaluation of Fe-BASED Amorphous Alloys Investigated by Doppler Broadening Positron Annihilation Technique

    NASA Astrophysics Data System (ADS)

    Lu, Wei; Huang, Ping; Wang, Yuxin; Yan, Biao

    2013-07-01

    Microstructure of Fe-based amorphous and nanocrystalline soft magnetic alloy has been investigated by X-ray diffraction (XRD), transmission electronic microscopy (TEM) and Doppler broadening positron annihilation technique (PAT). Doppler broadening measurement reveals that amorphous alloys (Finemet, Type I) which can form a nanocrystalline phase have more defects (free volume) than alloys (Metglas, Type II) which cannot form this microstructure. XRD and TEM characterization indicates that the nanocrystallization of amorphous Finemet alloy occurs at 460°C, where nanocrystallites of α-Fe with an average grain size of a few nanometers are formed in an amorphous matrix. With increasing annealing temperature up to 500°C, the average grain size increases up to around 12 nm. During the annealing of Finemet alloy, it has been demonstrated that positron annihilates in quenched-in defect, crystalline nanophase and amorphous-nanocrystalline interfaces. The change of line shape parameter S with annealing temperature in Finemet alloy is mainly due to the structural relaxation, the pre-nucleation of Cu nucleus and the nanocrystallization of α-Fe(Si) phase during annealing. This study throws new insights into positron behavior in the nanocrystallization of metallic glasses, especially in the presence of single or multiple nanophases embedded in the amorphous matrix.

  17. Enhancement of the Thermal Stability and Mechanical Hardness of Zr-Al-Co Amorphous Alloys by Ag Addition

    NASA Astrophysics Data System (ADS)

    Wang, Yongyong; Dong, Xiao; Song, Xiaohui; Wang, Jinfeng; Li, Gong; Liu, Riping

    2016-05-01

    The thermal and mechanical properties of Zr57Al15Co28- X Ag X ( X = 0 and 8) amorphous alloys were investigated using differential scanning calorimetry, in situ high-pressure angle dispersive X-ray diffraction measurements with synchrotron radiation, and nanoindentation. Results show that Ag doping improves effective activation energy, nanohardness, elastic modulus, and bulk modulus. Ag addition enhances topological and chemical short-range orderings, which can improve local packing efficiency and restrain long-range atom diffusion. This approach has implications for the design of the microstructure- and property-controllable functional materials for various applications.

  18. Deployable aerospace PV array based on amorphous silicon alloys

    NASA Technical Reports Server (NTRS)

    Hanak, Joseph J.; Walter, Lee; Dobias, David; Flaisher, Harvey

    1989-01-01

    The development of the first commercial, ultralight, flexible, deployable, PV array for aerospace applications is discussed. It is based on thin-film, amorphous silicon alloy, multijunction, solar cells deposited on a thin metal or polymer by a proprietary, roll-to-roll process. The array generates over 200 W at AM0 and is made of 20 giant cells, each 54 cm x 29 cm (1566 sq cm in area). Each cell is protected with bypass diodes. Fully encapsulated array blanket and the deployment mechanism weigh about 800 and 500 g, respectively. These data yield power per area ratio of over 60 W/sq m specific power of over 250 W/kg (4 kg/kW) for the blanket and 154 W/kg (6.5 kg/kW) for the power system. When stowed, the array is rolled up to a diameter of 7 cm and a length of 1.11 m. It is deployed quickly to its full area of 2.92 m x 1.11 m, for instant power. Potential applications include power for lightweight space vehicles, high altitude balloons, remotely piloted and tethered vehicles. These developments signal the dawning of a new age of lightweight, deployable, low-cost space arrays in the range from tens to tens of thousands of watts for near-term applications and the feasibility of multi-100 kW to MW arrays for future needs.

  19. Anisotropic phase separation in amorphous Fe--Ge alloys

    SciTech Connect

    Regan, M.J.; Bienenstock, A.

    1993-04-01

    Magnetron sputtered amorphous Fe{sub x}Ge{sub 100-x} films have been examined with anomalous small-angle x-ray scattering (ASAXS) in an attempt to characterize composition fluctuations which have been previously reported in this system. Films grown under various deposition conditions have been studied, with the scattering vector both in and oblique to the plane of the films, to search for anisotropy. By manipulating the deposited power flux and rates of growth, films which have the same composition can be grown to different states of phase separation. The total correlation functions have been calculated from the oblique scattering experiments. The anisotropy can be successfully modeled as a close-packing of oriented prolate ellipsoidal particles, with the elongated axis along the direction of film growth. A method for using these measurements to determine the compositions of the phase-separating species has been developed and utilized. The results indicate phase separation into a-Ge and a-FeGe{sub 2} for the a-Fe{sub x}Ge{sub 100-x} (x<33) alloy.

  20. Anisotropic phase separation in amorphous Fe--Ge alloys

    SciTech Connect

    Regan, M.J.; Bienenstock, A.

    1993-04-01

    Magnetron sputtered amorphous Fe[sub x]Ge[sub 100-x] films have been examined with anomalous small-angle x-ray scattering (ASAXS) in an attempt to characterize composition fluctuations which have been previously reported in this system. Films grown under various deposition conditions have been studied, with the scattering vector both in and oblique to the plane of the films, to search for anisotropy. By manipulating the deposited power flux and rates of growth, films which have the same composition can be grown to different states of phase separation. The total correlation functions have been calculated from the oblique scattering experiments. The anisotropy can be successfully modeled as a close-packing of oriented prolate ellipsoidal particles, with the elongated axis along the direction of film growth. A method for using these measurements to determine the compositions of the phase-separating species has been developed and utilized. The results indicate phase separation into a-Ge and a-FeGe[sub 2] for the a-Fe[sub x]Ge[sub 100-x] (x<33) alloy.

  1. Corrosion-resistant amorphous metallic films of Mo49Cr33B18 alloy

    NASA Technical Reports Server (NTRS)

    Ramesham, R.; Distefano, S.; Fitzgerald, D.; Thakoor, A. P.; Khanna, S. K.

    1987-01-01

    Corrosion-resistant amorphous metallic alloy films of Mo49Cr33B18 with a crystallization temperature of 590 C were deposited onto glass and quartz substrates by magnetron sputter-quench technique. The amorphous nature of the films was confirmed by their diffuse X-ray diffraction patterns. The deposited films are densely packed (zone T) and exhibit low stress and good adhesion to the substrate. Corrosion current of as-deposited coating of MoCrB amorphous metallic alloy is approximately three orders of magnitude less than the corrosion current of 304 stainless steel in 1N H2SO4 solution.

  2. Corrosion behaviors of amorphous and nanocrystalline Fe-based alloys in NaCl solution.

    PubMed

    Li, Xiang; Wang, Yuxin; Du, Chunfeng; Yan, Biao

    2010-11-01

    Amorphous Fe(73.5)Si(13.5)B9Nb3Cu1 alloy was prepared by the chill block melt-spinning process and nanocrystalline Fe(73.5)Si(13.5)B9Nb3Cu1 alloy was obtained by annealing. The crystallization behaviors were analysed by DSC, XRD and TEM. The electrochemical corrosion behaviors in different annealed states were performed by linear polarization method and electrochemical impedance spectroscopy in 3.5% NaCl solution. The results show that the crystallization of amorphous alloy occurs in the two steps. Some nanometer crystals appear when annealing in 550 degrees C and 600 degrees C, respectively with grain size 13 nm and 15 nm. The nanocrystalline alloy has a tendency to passivation and lower anodic current density than amorphous alloy. It indicates that nanocrystalline alloy has a higher corrosion resistance. Amorphous Fe(73.5)Si(13.5)B9Nb3Cu1 alloy consisted of only single semi-circle. When the alloy was annealed in 600 degrees C, its EIS consisted of two time constants, i.e., high frequency and low frequency capacitive loops. The charge transfer reaction resistances increases as annealing temperature rises. PMID:21137903

  3. Special features of structural changes of amorphizing nickel alloys in liquid and heterogeneous state

    NASA Astrophysics Data System (ADS)

    Tyagunov, G. B.; Baryshev, E. E.; Shmakova, K. Yu

    2016-06-01

    Polytherms of kinematic viscosity of nickel-based alloys with Cr, Si, Fe and B additives have been studied. It was found out that the first liquid phase volumes appear when temperatures are well below the tabular values of the solidus temperature ts. The critical temperature of the alloy was defined. The ways of obtaining materials of higher amorphization ability were suggested.

  4. Novel Amorphous Fe-Zr-Si(Cu) Boron-free Alloys

    SciTech Connect

    Kopcewicz, M.; Grabias, A.; Latuch, J.; Kowalczyk, M.

    2010-07-13

    Novel amorphous Fe{sub 80}(Zr{sub x}Si{sub 20-x-y})Cu{sub y} boron-free alloys, in which boron was completely replaced by silicon as a glass forming element, have been prepared in the form of ribbons by a melt quenching technique. The X-ray diffraction and Moessbauer spectroscopy measurements revealed that the as-quenched ribbons with the composition of x = 6-10 at. % and y = 0, 1 at. % are predominantly amorphous. DSC measurements allowed the estimation of the crystallization temperatures of the amorphous alloys. The soft magnetic properties have been studied by the specialized rf-Moessbauer technique in which the spectra were recorded during an exposure of the samples to the rf field of 0 to 20 Oe at 61.8 MHz. Since the rf-collapse effect observed is very sensitive to the local anisotropy fields it was possible to evaluate the soft magnetic properties of amorphous alloys studied. The rf-Moessbauer studies were accompanied by the conventional measurements of the quasi-static hysteresis loops from which the magnetization and coercive fields were estimated. It was found that amorphous Fe-Zr-Si(Cu) alloys are magnetically very soft, comparable with those of the conventional amorphous B-containing Fe-based alloys.

  5. CuZrAl amorphous alloys prepared by casting and milling

    NASA Astrophysics Data System (ADS)

    Tomolya, K.; Janovszky, D.; Sveda, M.; Hegman, N.; Solyom, J.; Roosz, A.

    2009-01-01

    Several preparation methods are available for the production of amorphous alloys. During the experiment described in this paper (Cu58Zr42)100-xAlx (x = 0-14,8; in at%) amorphous alloys were prepared by casting and ball-milling. The ingots were produced by arc melting. Wedge-shaped samples were prepared from the ingots by centrifugal casting into copper mould. The microstructures of these samples were defined by SEM. The amorphous samples were analysed by DSC and the activation energy of the crystallization processes was calculated from the measured temperatures. The master alloys of identical composition were milled by ball-mill for different periods of time. The powders were analysed by XRD in order to define the amorphous fractions.

  6. Semiquantitative study of amorphous structures in laser cladding of ZL111 aluminum alloy

    NASA Astrophysics Data System (ADS)

    Li, Xianqin; Cheng, Zhaogu; Liang, Gongying; Xia, Jin'an; Xu, Guoliang

    2000-02-01

    This paper deals with amorphous structures in the laser cladding. A kind of Ni-Cr-Al alloy was sprayed on the substrate, which was ZL111 alloy, to be the coating material. The coating was clad by 5 kW transverse flow CO2 laser. The observation of SEM and TEM revealed that in the laser cladding there were amorphous structures which appeared two different morphologies: one was space curved flake-like, which existed in the white web-like structures; the other was fir leaf-like, which existed in the grain-like structures. Differential thermal analysis (DTA) was used to semi- quantitatively determine the content of the amorphous structures. A curve relation was obtained between the content of amorphous structures and the dimensionless laser cladding parameter C. The changes of the amorphous structures after annealing were also shown.

  7. Synthesis of bulk nanostructured aluminum containing in situ crystallized amorphous particles

    NASA Astrophysics Data System (ADS)

    Zhang, Zhihui

    5083 Al containing in situ crystallized Al85Ni10La 5 amorphous particles (10% and 20% in volume fraction) was synthesized through a powder metallurgy route consisting of cold isostatic pressing, degassing and hot extrusion. The nanostructured 5083 Al powders (grain size ˜28 nm) were produced through mechanical milling in liquid nitrogen. The Al 85Ni10La5 powders were produced via gas atomization using helium gas and the fraction in the size range of <500 mesh (<25 mum), which appeared to be fully amorphous on the basis of X-ray diffraction studies, was isolated for further investigation. The amorphous Al85Ni10La5 alloy exhibited a glass transition at ˜259°C (at a heating rate of 40°C/min) and nanoscale crystallites (< 100 nm) with an equiaxed morphology formed during the subsequent crystallization reactions. At temperatures higher than 283°C, only the equilibrium phases Al, Al3Ni and Al11La 3 were formed. An unusually high nucleation density (1021-22 /m3) was recorded in the crystallization process. The copious nucleation sites were rationalized from the presence of quenched-in Al nuclei, which were evidenced by isothermal calorimetric tracing (235°C) and a direct HRTEM observation of the amorphous Al85Ni10La 5 powders. The feasibility of preparation of nanocrystalline/amorphous particles via melt spinning followed by ball milling was also studied. In the as-extruded composites, the amorphous Al85Ni10 La5 particles underwent complete crystallization resulting in a grain size of 100 ˜ 200 nm; the 5083 Al matrix had a grain size around 200 nm in the fine-grained region interspersed by coarse-grained region with a grain size of 600 ˜ 1500 nm. A metallurgical bond formed between the 5083 Al matrix and Al85Ni10La5 particles showing a grain-boundary-like interface. The compressive fracture strength of the as-extruded 10% and 20% Al85Ni10La5 composites were determined to be 1025 MPa and 837 MPa, respectively. The influence of secondary processing, i.e., swaging

  8. Achieving tailorable magneto-caloric effect in the Gd-Co binary amorphous alloys

    NASA Astrophysics Data System (ADS)

    Wu, C.; Ding, D.; Xia, L.; Chan, K. C.

    2016-03-01

    Tailorable magnetic properties and magneto-caloric effect were achieved in the Gd-Co binary amorphous alloys. It was found that the Curie temperature (Tc) of the GdxCo100-x (x=50, 53, 56, 58, 60) metallic glasses can be tuned by changing the concentration of Gd as Tc =708.8-8.83x, and the mechanism involved was investigated. On the other hand, a linear correlation between the peak value of magnetic entropy change (-Δ Smpeak) and Tc-2/3 is found in the amorphous alloys with a linear correlation coefficients of above 0.992. Therefore, the -ΔSmpeak of the Gd-Co binary amorphous alloys under different magnetic fields can be easily tailored by adjusting the composition of the alloy.

  9. Calorimetry study of the synthesis of amorphous Ni-Ti alloys by mechanical alloying. [Ni33 Ti67

    SciTech Connect

    Schwarz, R.B.; Petrich, R.R.

    1988-01-01

    We synthesized amorphous Ni/sub 33/Ti/sub 67/ alloy powder by ball milling (a) a mixture of elemental nickel and titanium powders and (b) powders of the crystalline intermetallic NiTi/sub 2/. We characterized the reaction products as a function of ball-milling time by differential scanning calorimetry and x-ray diffraction. The measurements suggest that in process (a) the amorphous alloy forms by a solid-state interdiffusion reaction at the clean Ni/Ti interfaces generated by the mechanical attrition. In process (b), the crystalline alloy powder stores energy in the form of chemical disorder and lattice and point defects. The crystal-to-amorphous transformation occurs when the stored energy reaches a critical value. The achievement of the critical stored energy competes with the dynamic recovery of the lattice. 23 refs., 7 figs.

  10. Synthesis of Amorphous Alloy Nanoparticles by Thermal Plasma Jet in a Quenching Tube

    NASA Astrophysics Data System (ADS)

    Choi, Sooseok; Park, Dong-Wha

    2015-09-01

    Recently, amorphous alloy nanoparticles have received a great attention in various applications such as catalysts, compact and highly efficient transformers, electrode material for Li-ion batteries, etc. Several methods such as microwave heating, laser ablation, and sonification have been studied to synthesize amorphous metal nanoparticles. In the present work, a high velocity thermal plasma jet generated by an arc plasma torch was used to produce iron alloy nanoparticles from an amorphous raw material which was a spherical shaped powder with the mean size of 25 μm. In order to synthesize amorphous alloy nanoparticles, a quenching tube where cooling gas was injected in different axial positions. Alloy nanoparticles were produced in a relatively high input power of higher than 10 kW in a fixed powder feeding at 300 mg/min. The crystallinity of synthesized nanoparticles was decreased with increasing the quenching gas flow rate. The amorphous alloy nanoparticles were found when the quenching gas injection position was 200 mm away from the exit of the plasma torch with the highest quenching gas flow rate of 20 L/min. In the numerical analysis, the highest quenching rate was also expected at the same condition.

  11. Orbital-free density functional theory study of amorphous Li-Si alloys and introduction of a simple density decomposition formalism

    NASA Astrophysics Data System (ADS)

    Xia, Junchao; Carter, Emily A.

    2016-03-01

    We propose a simple density decomposition formalism within orbital-free (OF) density functional theory (DFT) based on the Wang-Govind-Carter-decomposition (WGCD) kinetic energy density functional (KEDF). The resulting simple-WGCD (sWGCD) KEDF provides efficient density optimization, full cell relaxation, reasonable bulk properties for various materials compared to both the original OFDFT-WGCD and the Kohn-Sham (KS) DFT values, and has various numerical benefits including more stable convergence and lower computational cost (twice as fast as the WGCD KEDF). We also study amorphous (a-) Li-Si alloys with KSDFT and OFDFT using the Huang-Carter (HC), WGCD, and sWGCD KEDFs. The a-Li-Si alloy samples are prepared with the anneal-and-quench method using NVT molecular dynamics simulations. We report structural properties, equilibrium volumes, bulk moduli, and alloy formation energies for each a-alloy. The HC, WGCD, and sWGCD KEDFs within OFDFT all predict accurate equilibrium volumes compared against KSDFT benchmarks. The HC KEDF bulk moduli agree with KSDFT benchmarks whereas the WGCD/sWGCD KEDFs generally overestimate the bulk moduli, especially for alloys with low Li concentrations. All three KEDFs show limited ability to predict alloy formation energies, which indicates the lack of transferability of these KEDFs among such systems and motivates future developments in OFDFT and KEDF formalisms.

  12. Mechanical behavior of a bulk nanostructured iron alloy

    NASA Astrophysics Data System (ADS)

    Carsley, J. E.; Fisher, A.; Milligan, W. W.; Aifantis, E. C.

    1998-09-01

    Bulk, fully dense materials were prepared from Fe-10Cu with grain diameters between 45 nm and 1.7 µm. The materials were prepared by ball milling of powders in a glove box, followed by hot isostatic pressing (hipping) or powder forging. Larger grain sizes were obtained by thermal treatment of the consolidated powders. The bulk materials were relatively clean, with oxygen levels below 1500 wpm and other contaminants less than 0.1 at. pct. The mechanical behavior of these materials was unique. At temperatures from 77 to 470 K, the first and only mechanism of plastic deformation was intense shear banding, which was accompanied by a perfectly plastic stress-strain response (absence of strain hardening). There was a large tension-compression asymmetry in the strength, and the shear bands did not occur on the plane of maximum shear stress or the plane of zero extension. This behavior, while unusual for metals, has been observed in amorphous polymers and metallic glasses. On the other hand, the fine-grained Fe-10Cu materials behaved like coarse-grained iron in some respects, particularly by obeying the Hall-Petch equation with constants reasonably close to those of pure iron and by exhibiting low-temperature mechanical behavior which was very similar to that of steels. Transmission electron microscopy (TEM) studies found highly elongated grains within shear bands, indicating that shear banding occurred by a dislocation-based mechanism, at least at grain sizes above 100 nm. Similarities and differences between the fine-grained Fe-10Cu and metals, polymers, metallic glasses, radiation-damaged metals, and quench-damaged metals are discussed.

  13. Surface and bulk crystallization of amorphous solid water films: Confirmation of “top-down” crystallization

    DOE PAGESBeta

    Yuan, Chunqing; Smith, R. Scott; Kay, Bruce D.

    2016-01-11

    Here, the crystallization kinetics of nanoscale amorphous solid water (ASW) films are investigated using temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). TPD measurements are used to probe surface crystallization and RAIRS measurements are used to probe bulk crystallization. Isothermal TPD results show that surface crystallization is independent of the film thickness (from 100 to 1000 ML). Conversely, the RAIRS measurements show that the bulk crystallization time increases linearly with increasing film thickness. These results suggest that nucleation and crystallization begin at the ASW/vacuum interface and then the crystallization growth front propagates linearly into the bulk. This mechanism wasmore » confirmed by selective placement of an isotopic layer (5% D2O in H2O) at various positions in an ASW (H2O) film. In this case, the closer the isotopic layer was to the vacuum interface, the earlier the isotopic layer crystallized. These experiments provide direct evidence to confirm that ASW crystallization in vacuum proceeds by a “top-down” crystallization mechanism.« less

  14. Relaxation process of Fe(CuNb)SiB amorphous alloys investigated by dynamical calorimetry

    SciTech Connect

    Zhu, J.; Clavaguera-Mora, M.T.; Clavaguera, N.

    1997-03-01

    Differential scanning calorimetry and dynamic differential scanning calorimetry were used to analyze the relaxation process of Fe(CuNb)SiB amorphous alloys. The Curie temperature (T{sub C}) evolution of the amorphous phase during relaxation as a function of heating rate, time and pre-annealing temperature were measured. Two distinct relaxation processes are observed, consequent with topological and chemical short range order changes. {copyright} {ital 1997 American Institute of Physics.}

  15. Directional growth by low electric-field-controlled crystallization of bulk amorphous lithium tetraborate

    NASA Astrophysics Data System (ADS)

    Kim, S. J.; Kim, J. E.; Yang, Y. S.

    2004-12-01

    Highly oriented rod-shaped crystals were grown during crystallization of bulk amorphous Li2B4O7 under a low ac electric field of ˜5V/mm. The crystal c axis that is the long direction of rods and perpendicular to the flat surface of the sample is parallel to the applied electric-field direction. The oriented crystals, with an alignment within a declined angle of ˜15°, are so long along the c direction compared with those of other directions that the geometrical structure of each rod is quasi-one-dimensional. The measured electromechanical coupling coefficient of kt=0.47 is comparable to that of single-crystal Li2B4O7.

  16. THE IMPACT OF PARTIAL CRYSTALLIZATION ON THE PERMEATION PROPERTIES BULK AMORPHOUS GLASS HYDROGEN SEPARATION MEMBRANES

    SciTech Connect

    Brinkman, K; Paul Korinko, P; Thad Adams, T; Elise Fox, E; Arthur Jurgensen, A

    2008-11-25

    It is recognized that hydrogen separation membranes are a key component of the emerging hydrogen economy. A potentially exciting material for membrane separations are bulk metallic glass materials due to their low cost, high elastic toughness and resistance to hydrogen 'embrittlement' as compared to crystalline Pd-based membrane systems. However, at elevated temperatures and extended operation times structural changes including partial crystallinity may appear in these amorphous metallic systems. A systematic evaluation of the impact of partial crystallinity/devitrification on the diffusion and solubility behavior in multi-component Metallic Glass materials would provide great insight into the potential of these materials for hydrogen applications. This study will report on the development of time and temperature crystallization mapping and their use for interpretation of 'in-situ' hydrogen permeation at elevated temperatures.

  17. Barkhausen noise in FeCoB amorphous alloys (abstract)

    NASA Astrophysics Data System (ADS)

    Durin, G.; Bertotti, G.

    1996-04-01

    In recent years, the Barkhausen effect has been indicated as a promising tool to investigate and verify the ideas about the self-organization of physical complex systems displaying power law distributions and 1/f noise. When measured at low magnetization rates, the Barkhausen signal displays 1/fα-type spectra (with α=1.5÷2) and power law distributions of duration and size of the Barkhausen jumps. These experimental data are quite well described by the model of Alessandro et al. which is based on a stochastic description of the domain wall dynamics over a pinning field with brownian properties. Yet, this model always predicts a 1/f 2 spectrum, and, at the moment, it is not clear if it can take into account possible effects of self-organization of the magnetization process. In order to improve the power of the model and clarify this problem, we have performed a thorough investigation of the noise spectra and the amplitude distributions of a wide set of FeCoB amorphous alloys. The stationary amplitude distribution of the signal is very well fitted by the gamma distribution P(ν)=νc-1 exp(-ν)/Γ(c), where ν is proportional to the domain wall velocity, and c is a dimensionless parameter. As predicted in Ref. , this parameter is found to have a parabolic dependence on the magnetization rate. In particular, the linear coefficient is related to the amplitude of the fluctuations of the pinning field, a parameter which can be measured directly from the power spectra. In all measured cases, the power spectra show α exponents less than 2, and thus poorly fitted by the model. Actually, the absolute value of the high frequency spectral density is not consistent with the c parameter determined from the amplitude distribution data. This discrepancy requires to introduce effects not taken into account in the model, as the propagation of the jumps along the domain wall. This highly enhances the fit of the data and indicates effects of propagation on the scale of a few

  18. Magnetic, magnetocaloric properties and phenomenological model in amorphous Fe60Ru20B20 alloy

    NASA Astrophysics Data System (ADS)

    Boutahar, A.; Lassri, H.; Hlil, E. K.

    2015-11-01

    Magnetic, magnetocaloric properties and phenomenological model of amorphous Fe60Ru20B20 alloy are investigated in detail. The amorphous alloy has been synthesized using melt spinning method. The magnetic transition nature undergoes a second-order magnetic phase transition from ferromagnetic to paramagnetic states with a Curie temperature of 254 K. Basis on the thermodynamic Maxwell's relation, magnetic entropy change (-ΔSM) is calculated. Further, we also report a theoretical investigation of the magnetocaloric effect using a phenomenological model. The best model parameters and their variation with temperature and the magnetic field were determined. The theoretical predictions are found to agree closely with experimental measurements.

  19. Synthesis and Thermal Stability of Amorphous Be-B-X Alloy Coatings

    SciTech Connect

    Jankowski, A F; Wall, M A; Nieh, T G

    2004-10-14

    Amorphous Be-B-X alloys are vapor deposited as coatings. The microstructure and hardness of the Be-B-X coatings are examined using transmission electron microscopy and nanoindentation, respectively. Whereas a Be-B-2.5 at.% Cu amorphous coating is found to crystallize to a cubic Be-33 at.% B phase at 673 K, a coating of Be-B-1.8 at.% Fe-0.4 at.% Cr-0.3 at.% Co does not crystallize until at a higher temperature of 748 K. The hardness of the amorphous Be-B-X coating increases with B content but is less than its crystalline counterparts.

  20. Corrosion resistance and cytocompatibility of biodegradable surgical magnesium alloy coated with hydrogenated amorphous silicon.

    PubMed

    Xin, Yunchang; Jiang, Jiang; Huo, Kaifu; Tang, Guoyi; Tian, Xiubo; Chu, Paul K

    2009-06-01

    The fast degradation rates in the physiological environment constitute the main limitation for the applications of surgical magnesium alloys as biodegradable hard-tissue implants. In this work, a stable and dense hydrogenated amorphous silicon coating (a-Si:H) with desirable bioactivity is deposited on AZ91 magnesium alloy using magnetron sputtering deposition. Raman spectroscopy and Fourier transform infrared spectroscopy reveal that the coating is mainly composed of hydrogenated amorphous silicon. The hardness of the coated alloy is enhanced significantly and the coating is quite hydrophilic as well. Potentiodynamic polarization results show that the corrosion resistance of the coated alloy is enhanced dramatically. In addition, the deterioration process of the coating in simulated body fluids is systematically investigated by open circuit potential evolution and electrochemical impedance spectroscopy. The cytocompatibility of the coated Mg is evaluated for the first time using hFOB1.19 cells and favorable biocompatibility is observed. PMID:18449935

  1. Crystal nucleation in amorphous (Au/100-y/Cu/y/)77Si9Ge14 alloys

    NASA Technical Reports Server (NTRS)

    Thompson, C. V.; Greer, A. L.; Spaepen, F.

    1983-01-01

    Because, unlike most metallic glasses, melt-spun alloys of the series (Au/100-y/Cu/y/)77Si9Ge14 exhibit well separated glass transition and kinetic crystallization temperatures, crystallization can be studied in the fully relaxed amorphous phase. An isothermal calorimetric analysis of the devitrification kinetics of the amorphous alloy indicates sporadic nucleation and a constant growth rate. It is found for the cases of alloys with y values lower than 25 that the classical theory of homogeneous nucleation is consistent with observations, including transient effects. An analysis of the crystallization kinetics shows that slow crystal growth rates play an important role in glass formation in these alloys. Although the reduced glass transition temperature increases with Cu content, glass formation is more difficult at high Cu contents, perhaps because of a difference in nucleus composition.

  2. adwTools Developed: New Bulk Alloy and Surface Analysis Software for the Alloy Design Workbench

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Morse, Jeffrey A.; Noebe, Ronald D.; Abel, Phillip B.

    2004-01-01

    A suite of atomistic modeling software, called the Alloy Design Workbench, has been developed by the Computational Materials Group at the NASA Glenn Research Center and the Ohio Aerospace Institute (OAI). The main goal of this software is to guide and augment experimental materials research and development efforts by creating powerful, yet intuitive, software that combines a graphical user interface with an operating code suitable for real-time atomistic simulations of multicomponent alloy systems. Targeted for experimentalists, the interface is straightforward and requires minimum knowledge of the underlying theory, allowing researchers to focus on the scientific aspects of the work. The centerpiece of the Alloy Design Workbench suite is the adwTools module, which concentrates on the atomistic analysis of surfaces and bulk alloys containing an arbitrary number of elements. An additional module, adwParams, handles ab initio input for the parameterization used in adwTools. Future modules planned for the suite include adwSeg, which will provide numerical predictions for segregation profiles to alloy surfaces and interfaces, and adwReport, which will serve as a window into the database, providing public access to the parameterization data and a repository where users can submit their own findings from the rest of the suite. The entire suite is designed to run on desktop-scale computers. The adwTools module incorporates a custom OAI/Glenn-developed Fortran code based on the BFS (Bozzolo- Ferrante-Smith) method for alloys, ref. 1). The heart of the suite, this code is used to calculate the energetics of different compositions and configurations of atoms.

  3. Kinetic of crystallization and electrical conductance of Ge 5As 38Te 57 amorphous chalcogenide alloy

    NASA Astrophysics Data System (ADS)

    Elshafie, A.; Abdel-All, A.

    1999-07-01

    DTA measurements were made on Ge 5As 38Te 57 amorphous chalcogenide alloy. The glass transition temperature ( Tg), the first exothermic peak ( Tc1) and the second exothermic peak ( Tc2) were found to increase as the heating rate increases. The kinetic parameters were evaluated from the DTA curves and related to the crystallization mechanism where both the bulk and surface cyrstallization were considered. The crystal nucleation and growth of Ge 5As 38Te 57 glass were studied by three simple methods, and the average activation energy of nucleation was found to be 31.74 kcal/mol. The apparent activation energies for crystallization were estimated to be 59.7 and 42.6 kcal/mol for the 1st and 2nd peak, respectively. X-ray analysis for samples, isothermally annealed at temperatures higher than the glass transition and crystallization temperatures indicates that phases of Te and As 2Te 3 were nucleated and grown. The activation energy of conduction as well as the disordered enegy were also calculated.

  4. Bulk Hydrides and Delayed Hydride Cracking in Zirconium Alloys

    NASA Astrophysics Data System (ADS)

    Tulk, Eric F.

    Zirconium alloys are susceptible to engineering problems associated with the uptake of hydrogen throughout their design lifetime in nuclear reactors. Understanding of hydrogen embrittlement associated with the precipitation of brittle hydride phases and a sub-critical crack growth mechanism known as Delayed Hydride Cracking (DHC) is required to provide the engineering justifications for safe reactor operation. The nature of bulk zirconium hydrides at low concentrations (< 100 wt. ppm) is subject to several contradictory descriptions in the literature associated with the stability and metastability of gamma-phase zirconium hydride. Due to the differing volume expansions (12-17%) and crystallography between gamma and delta hydride phases, it is suggested that the matrix yield strength may have an effect on the phase stability. The present work indicated that although yield strength can shift the phase stability, other factors such as microstructure and phase distribution can be as or more important. This suggests that small material differences are the reason for the literature discrepancies. DHC is characterised by the repeated precipitation, growth, fracture of brittle hydride phases and subsequent crack arrest in the ductile metal. DHC growth is associated primarily the ability of hydrogen to diffuse under a stress induced chemical potential towards a stress raiser. Knowledge of the factors controlling DHC are paramount in being able to appropriately describe DHC for engineering purposes. Most studies characterise DHC upon cooling to the test temperature. DHC upon heating has not been extensively studied and the mechanism by which it occurs is somewhat controversial in the literature. This work shows that previous thermo-mechanical processing of hydrided zirconium can have a significant effect on the dissolution behaviour of the bulk hydride upon heating. DHC tests with gamma-quenched, furnace cooled-delta and reoriented bulk hydrides upon heating and DHC upon

  5. Phase transformation during mechano-synthesis of nanocrystalline/amorphous Fe–32Mn–6Si alloys

    SciTech Connect

    Amini, Rasool; Shamsipoor, Ali; Ghaffari, Mohammad; Alizadeh, Morteza; Okyay, Ali Kemal

    2013-10-15

    Mechano-synthesis of Fe–32Mn–6Si alloy by mechanical alloying of the elemental powder mixtures was evaluated by running the ball milling process under an inert argon gas atmosphere. In order to characterize the as-milled powders, powder sampling was performed at predetermined intervals from 0.5 to 192 h. X-ray florescence analyzer, X-ray diffraction, scanning electron microscope, and high resolution transmission electron microscope were utilized to investigate the chemical composition, structural evolution, morphological changes, and microstructure of the as-milled powders, respectively. According to the results, the nanocrystalline Fe–Mn–Si alloys were completely synthesized after 48 h of milling. Moreover, the formation of a considerable amount of amorphous phase during the milling process was indicated by quantitative X-ray diffraction analysis as well as high resolution transmission electron microscopy image and its selected area diffraction pattern. It was found that the α-to-γ and subsequently the amorphous-to-crystalline (especially martensite) phase transformation occurred by milling development. - Graphical abstract: Mechano-synthesis of nanocrystalline/amorphous Fe–32Mn–6Si shape memory alloys in the powder form: amorphous phase formation, α-to-γ phase transformation, mechano-crystallization of the amorphous, and martensite phase formation during the process. Highlights: • During MA, the α-to-γ phase transformation and amorphization occurred. • Mechano-crystallization of the amorphous phase occurred at sufficient milling time. • The formation of high amount of ε-martensite was evidenced at high milling times. • The platelet, spherical, and then irregular particle shapes was extended by MA. • By MA, the particles size was increased, then reduced, and afterward re-increased.

  6. Magnetocaloric response of amorphous and nanocrystalline Cr-containing Vitroperm-type alloys

    NASA Astrophysics Data System (ADS)

    Moreno-Ramírez, L. M.; Blázquez, J. S.; Franco, V.; Conde, A.; Marsilius, M.; Budinsky, V.; Herzer, G.

    2016-07-01

    The broad compositional range in which transition metal (TM) based amorphous alloys can be obtained, yields an easily tunable magnetocaloric effect (MCE) in a wide temperature range. In some TM-based alloys, anomalous behaviors are reported, as a non-monotonous trend with magnetic moment (e.g. FeZrB alloys). Moreover, in certain Cr-containing Vitroperm alloys anomalously high values of the magnetic entropy change were published. In this work, a systematic study on MCE response of Cr-containing amorphous alloys of composition Fe74-xCrxCu1Nb3Si15.5B6.5 (with x=2, 8, 10, 12, 13, 14 and 20) has been performed in a broad Curie temperature range from 100 K to 550 K. Curie temperature and magnetic entropy change peak of the amorphous alloys decrease with the increase of Cr content at rates of -25.6 K/at% Cr and -54 mJ kg-1 K-1/at% Cr, respectively, following a linear trend with the magnetic moment in both cases. The presence of nanocrystalline phases has been considered as a possible cause in order to explain the anomalies. The samples were nanocrystallized in different stages, however, the magnetocaloric response decreases as crystallization progresses due to the large separation of the Curie temperatures of the two phases.

  7. Ballistic Impact Properties of Zr-Based Amorphous Alloy Composites Reinforced with Woven Continuous Fibers

    NASA Astrophysics Data System (ADS)

    Kim, Gyeong Su; Son, Chang-Young; Lee, Sang-Bok; Lee, Sang-Kwan; Song, Young Buem; Lee, Sunghak

    2012-03-01

    This study aims at investigating ballistic impact properties of Zr-based amorphous alloy (LM1 alloy) matrix composites reinforced with woven stainless steel or glass continuous fibers. The fiber-reinforced composites with excellent fiber/matrix interfaces were fabricated without pores and misinfiltration by liquid pressing process, and contained 35 to 41 vol pct of woven continuous fibers homogeneously distributed in the amorphous matrix. The woven-STS-continuous-fiber-reinforced composite consisted of the LM1 alloy layer of 1.0 mm in thickness in the upper region and the fiber-reinforced composite layer in the lower region. The hard LM1 alloy layer absorbed the ballistic impact energy by forming many cracks, and the fiber-reinforced composite layer interrupted the crack propagation and blocked the impact and traveling of the projectile, thereby resulting in the improvement of ballistic performance by about 20 pct over the LM1 alloy. According to the ballistic impact test data of the woven-glass-continuous-fiber-reinforced composite, glass fibers were preferentially fragmented to form a number of cracks, and the amorphous matrix accelerated the fragmentation of glass fibers and the initiation of cracks. Because of the absorption process of ballistic impact energy by forming very large amounts of cracks, fragments, and debris, the glass-fiber-reinforced composite showed better ballistic performance than the LM1 alloy.

  8. SYNTHESIS AND PERFORMANCE OF FE-BASED AMORPHOUS ALLOYS FOR NUCLEAR WASTE REPOSITORY APPLICATIONS

    SciTech Connect

    Kaufman, L; Perepezko, J; Hildal, K

    2007-02-08

    In several Fe-based alloy systems it is possible to produce glasses with cooling rates as low as 100 K/s that exhibit outstanding corrosion resistance compared to typical crystalline alloys such as high-performance stainless steels and Ni-based C-22 alloy. Moreover, novel alloy compositions can be synthesized to maximize corrosion resistance (i.e. adding Cr and Mo) and to improve radiation compatibility (adding B) and still maintain glass forming ability. The applicability of Fe-based amorphous coatings in typical environments where corrosion resistance and thermal stability are critical issues has been examined in terms of amorphous phase stability and glass-forming ability through a coordinated computational analysis and experimental validation. Similarly, a novel computational thermodynamics approach has been developed to explore the compositional sensitivity of glass-forming ability and thermal stability. Also, the synthesis and characterization of alloys with increased cross-section for thermal neutron capture will be outlined to demonstrate that through careful design of alloy composition it is possible to tailor the material properties of the thermally spray-formed amorphous coating to accommodate the challenges anticipated in typical nuclear waste storage applications over tens of thousands of years in a variety of corrosive environments.

  9. Structural transformations in amorphous ↔ crystalline phase change of Ga-Sb alloys

    SciTech Connect

    Edwards, T. G.; Sen, S.; Hung, I.; Gan, Z.; Kalkan, B.; Raoux, S.

    2013-12-21

    Ga-Sb alloys with compositions ranging between ∼12 and 50 at. % Ga are promising materials for phase change random access memory applications. The short-range structures of two such alloys with compositions Ga{sub 14}Sb{sub 86} and Ga{sub 46}Sb{sub 54} are investigated, in their amorphous and crystalline states, using {sup 71}Ga and {sup 121}Sb nuclear magnetic resonance spectroscopy and synchrotron x-ray diffraction. The Ga and Sb atoms are fourfold coordinated in the as-deposited amorphous Ga{sub 46}Sb{sub 54} with nearly 40% of the constituent atoms being involved in Ga-Ga and Sb-Sb homopolar bonding. This necessitates extensive bond switching and elimination of homopolar bonds during crystallization. On the other hand, Ga and Sb atoms are all threefold coordinated in the as-deposited amorphous Ga{sub 14}Sb{sub 86}. Crystallization of this material involves phase separation of GaSb domains in Sb matrix and a concomitant increase in the Ga coordination number from 3 to 4. Results from crystallization kinetics experiments suggest that the melt-quenching results in the elimination of structural “defects” such as the homopolar bonds and threefold coordinated Ga atoms in the amorphous phases of these alloys, thereby rendering them structurally more similar to the corresponding crystalline states compared to the as-deposited amorphous phases.

  10. Tribological properties of amorphous alloys and the role of surfaces in abrasive wear of materials

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1982-01-01

    The research approach undertaken by the authors relative to the subject, and examples of results from the authors are reviewed. The studies include programs in adhesion, friction, and various wear mechanisms (adhesive and abrasive wear). The materials which have been studied include such ceramic and metallic materials as silicon carbide, ferrites, diamond, and amorphous alloys.

  11. Electronic structure of Fe-based amorphous alloys studied using electron-energy-loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, H. J.; Gu, X. J.; Poon, S. J.; Shiflet, G. J.

    2008-01-01

    The local atomic electronic structures of Fe-Mo-C-B metallic glasses are investigated using electron energy-loss spectroscopy (EELS). The fracture behavior of this Fe-based amorphous alloy system undergoes the transition from being ductile to exhibiting brittleness when alloyed with Cr or Er atoms. In addition, the glass-forming ability is also enhanced. This plastic-to-brittle transition is suggested to correlate with the change of local atomic short-range order or bonding configurations. Therefore, the bonding configuration of Fe-Mo-C-B-Er(Cr) amorphous alloys is investigated by studying the electronic structure of Fe and C atoms using electron energy-loss spectroscopy. It is shown that the normalized EELS white line intensities of Fe-L2,3 edges decrease slightly with an increasing amount of Er additions, while no noticeable difference is obtained with Cr additions. As for the C K edge, a prominent change of edge shape is observed for both alloy systems, where the first peak corresponding to a 1s→1π* transition increases with increasing Er and Cr additions. Accordingly, it is concluded that changes in the local atomic and electronic structure occur around Fe and C atoms when Er and Cr are introduced into the alloys. Furthermore, it is pointed out that the formation of Er-C and Cr-C carbide like local order inferred from the observed C K edge spectra can provide a plausible explanation for the plastic-to-brittle transition observed in these Fe-based amorphous alloys. In spite of the complexity of electronic and atomic structure in this multicomponent Fe-based metallic glass system, this study could serve as a starting point for providing a qualitative interpretation between electronic structure and plasticity in the Fe-Mo-C-B amorphous alloy system. Complimentary techniques, such as x-ray diffraction and high-resolution transmission electron microscope are also employed, providing a more complete structural characterization.

  12. Surface morphology study of Zr-based amorphous alloys after immersion in boiling nitric acid medium

    NASA Astrophysics Data System (ADS)

    Sharma, Poonam; Dhawan, Anil; Sharma, S. K.

    2016-05-01

    Weight loss studies have been performed to determine the corrosion resistance of amorphous Zr60Nb2Al10Ni8Cu20 and Zr59Nb3Al10Ni8Cu20 alloys in aqueous HNO3 media at boiling temperature. The FESEM micrographs has been obtained to know the surface morphology of specimens after immersion in 11.5M boiling aqueous HNO3 media. Zr59Nb3Al10Ni8Cu20 alloy shows better corrosion resistance in nitric acid media than Zr60Nb2Al10Ni8Cu20 alloy.

  13. New bulk glassy alloys in Cu-Zr-Ag ternary system prepared by casting and milling

    NASA Astrophysics Data System (ADS)

    Janovszky, D.; Tomolya, K.; Sveda, M.; Solyom, J.; Roosz, A.

    2009-01-01

    The thermal stability, crystallization behaviour and glass forming ability of Cu-Zr-Ag system have been investigated on the basis of a ternary phase diagram. We altered the concentration of the alloys from the Cu58Zr42 to the concentration of the deep eutectic point of the Cu-Zr-Ag ternary system and we calculated the glass forming ability parameters. This paper summerises the results of the procedure during which Cu-Zr-Ag amorphous alloys with different Ag content (0-25%) were prepared by casting and ball-milling. Wedge-shaped samples were prepared from the ingots by centrifugal casting into copper mold. The supercooled liquid region (ΔTx) exceeded 75K. Following the characterization of the cast alloys, master alloys of identical composition were milled in a Fritsch Pulverisette 2 ball-mill. The powders, milled for various periods of time were analysed by XRD in order to define the amorphous fraction.

  14. Structural analysis of quaternary Se85-xSb10In5Agx bulk glassy alloys

    NASA Astrophysics Data System (ADS)

    Sharma, Rita; Sharma, Shaveta; Kumar, Praveen; Chander, Ravi; Thangaraj, R.; Mian, M.

    2015-08-01

    The physical properties of chalcogenide semiconductor have attracted much attention recently due to their applications in optical recording media and inorganic resist due to photo induced structural transformations observed in these materials. The bulk samples of Se85-xSb10In5Agx system are prepared by melt-quenching technique. X-ray diffraction technique and RAMAN spectroscopy have been used to study the role of Ag additive on the amorphous/crystalline nature and molecular structure of Se85Sb10In5 glassy alloys. The phases Sb2Se3, In-Sb and In2Se3 has been observed by X-ray diffraction. The formation of AgInSe2 phase along with the enhancement in intensity has been observed with the Ag addition.Three bands observed by raman spectroscopy for Se85Sb10In5 are at 70 cm-1, 212cm-1 and 252cm-1. The formation of small bands up to wavenumber 188cm-1 and shifting in second band along with the increase in intensity up to sample x=5 has been observed with the Ag addition. The enhancement in intensity in third band with Ag content has been observed.

  15. An amorphous alloy stress sensor for wireless battery-free applications

    NASA Astrophysics Data System (ADS)

    Bowles, Adrian; Gore, Jon; Tomka, George

    2005-05-01

    Battery-free sensor systems would benefit from the availability of a stress or strain sensor that exhibits a large enough property change to allow simplification and power reductions in sensor interface and data transmission circuitry. A new sensor has been developed specifically for this purpose, which uses the large stress induced impedance changes exhibited by ribbons of amorphous magnetic alloy. In comparison to semiconductor strain gauges, which show a change in resistance of 15% when strained to their maximum recommended stress level, the amorphous alloy sensor demonstrates a change in inductance of 315%, when strained to its maximum working level. Although, amorphous magnetic alloys are inherently sensitive to external magnetic fields, a simple, biasing technique renders the stress-sensing device insensitive to modest field strengths. The amorphous magnetic alloys are produced in large volumes and realize an extremely low cost sensor. A low cost and low power analogue electrical circuit has been designed that, in combination with the amorphous alloy sensor, functions as a battery-free sensor 'tag'. The sensor tag can transmit stress data to a transceiver system via an inductive link, negating the need for battery power or a hardwire connection. The system"s range is directly related to the transceiver and tag antenna dimensions; however a system with 20cm diameter antennas has been demonstrated operating over a range of up to 60cm. This range is achieved through the extremely low power demands of the sensor tag (<1mW). A demonstration unit has been developed for vehicle tyre pressure monitoring applications.

  16. Magneto-caloric effect of a Gd50Co50 amorphous alloy near the freezing point of water

    NASA Astrophysics Data System (ADS)

    Xia, L.; Wu, C.; Chen, S. H.; Chan, K. C.

    2015-09-01

    In the present work, we report the magneto-caloric effect (MCE) of a binary Gd50Co50 amorphous alloy near the freezing temperature of water. The Curie temperature of Gd50Co50 amorphous ribbons is about 267.5 K, which is very close to room temperature. The peak value of the magnetic entropy change (-ΔSmpeak) and the resulting adiabatic temperature rise (ΔTad.) of the Gd50Co50 amorphous ribbons is much higher than that of any other amorphous alloys previously reported with a Tc near room temperature. On the other hand, although the -ΔSmpeak of Gd50Co50 amorphous ribbons is not as high as those of crystalline alloys near room temperature, its refrigeration capacity (RC) is still much larger than the RC values of these crystalline alloys. The binary Gd50Co50 amorphous alloy provides a basic alloy for developing high performance multi-component amorphous alloys near room temperature.

  17. In Situ Nanocrystallization-Induced Hardening of Amorphous Alloy Matrix Composites Consolidated by Spark Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Singh, Ashish; Paul, Tanaji; Katakam, Shravana; Dahotre, Narendra B.; Harimkar, Sandip P.

    2016-04-01

    In situ nanocrystallization of amorphous alloys has recently emerged as a suitable technique for forming nanocomposites with improved mechanical properties. In this paper, we report on the spark plasma sintering (SPS) of Fe-based amorphous alloys with in situ-formed nanocrystals of (Fe,Cr)23(C,B)6. The SPS was performed with a range of sintering temperatures (570-800°C) in and above the supercooled liquid region of the alloy. Significant enhancement in relative density was observed with increasing sintering temperature due to particle deformation and improved interparticle contacts. The formation of nanocrystalline particles and enhanced densification resulted in an increase in the hardness of the nanocomposites from about 1150-1375 VHN.

  18. Structural Changes of Amorphous Ge1-xSnx Alloy Films by Annealing

    NASA Astrophysics Data System (ADS)

    Fukumoto, Hirofumi; Myoren, Hiroaki; Nakashita, Toshio; Imura, Takeshi; Osaka, Yukio

    1986-09-01

    Microcrystalline (μc-) grains of Ge1-ySny (0.1≲ y≲ 0.4) were precipitated by thermal treatments of amorphous films of a Ge1-xSnx(x≲ 0.4) alloy deposited by co-sputtering. At higher temperatures grains of β-Sn came out, co-existing with those of μc-Ge1-ySny. Mössbauer spectroscopy was used to characterize states of Sn in a Ge-Sn alloy film. Optical properties, such as the real part \\varepsilon1 of the complex dielectric constant for Ge0.65Sn0.35, also changed as the structure change, especially at a photon energy of 1.6˜ 1.8 eV, where \\varepsilon1 took a maximum. It was suggested that an amorphous Ge-Sn alloy might be a good material for archival-type optical storage.

  19. In Situ Nanocrystallization-Induced Hardening of Amorphous Alloy Matrix Composites Consolidated by Spark Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Singh, Ashish; Paul, Tanaji; Katakam, Shravana; Dahotre, Narendra B.; Harimkar, Sandip P.

    2016-07-01

    In situ nanocrystallization of amorphous alloys has recently emerged as a suitable technique for forming nanocomposites with improved mechanical properties. In this paper, we report on the spark plasma sintering (SPS) of Fe-based amorphous alloys with in situ-formed nanocrystals of (Fe,Cr)23(C,B)6. The SPS was performed with a range of sintering temperatures (570-800°C) in and above the supercooled liquid region of the alloy. Significant enhancement in relative density was observed with increasing sintering temperature due to particle deformation and improved interparticle contacts. The formation of nanocrystalline particles and enhanced densification resulted in an increase in the hardness of the nanocomposites from about 1150-1375 VHN.

  20. Formation and analysis of amorphous and nanocrystalline phases in Al-Cu-Mg alloy under friction stir processing

    NASA Astrophysics Data System (ADS)

    Liu, Peng; Shi, Qing-yu

    2015-06-01

    Homogeneous amorphous and nanocrystalline phases formed in the nugget zone of a friction stir-processed Al-Cu-Mg alloy have been studied. X-ray diffraction analysis indicated a diffuse scattering peak with characteristics of an amorphous phase existed in the range 15°-29°. Further, TEM analysis proved the existence of an amorphous structure. Friction stir processing provides special physical conditions, such as high temperature, high hydrostatic pressure and large shear stress, which could induce the amorphization of the alloy.

  1. Bulk mixed ion electron conduction in amorphous gallium oxide causes memristive behaviour.

    PubMed

    Aoki, Yoshitaka; Wiemann, Carsten; Feyer, Vitaliy; Kim, Hong-Seok; Schneider, Claus Michael; Ill-Yoo, Han; Martin, Manfred

    2014-01-01

    In thin films of mixed ionic electronic conductors sandwiched by two ion-blocking electrodes, the homogeneous migration of ions and their polarization will modify the electronic carrier distribution across the conductor, thereby enabling homogeneous resistive switching. Here we report non-filamentary memristive switching based on the bulk oxide ion conductivity of amorphous GaOx (x~1.1) thin films. We directly observe reversible enrichment and depletion of oxygen ions at the blocking electrodes responding to the bias polarity by using photoemission and transmission electron microscopies, thus proving that oxygen ion mobility at room temperature causes memristive behaviour. The shape of the hysteresis I-V curves is tunable by the bias history, ranging from narrow counter figure-eight loops to wide hysteresis, triangle loops as found in the mathematically derived memristor model. This dynamical behaviour can be attributed to the coupled ion drift and diffusion motion and the oxygen concentration profile acting as a state function of the memristor. PMID:24632885

  2. Bulk mixed ion electron conduction in amorphous gallium oxide causes memristive behaviour

    NASA Astrophysics Data System (ADS)

    Aoki, Yoshitaka; Wiemann, Carsten; Feyer, Vitaliy; Kim, Hong-Seok; Schneider, Claus Michael; Ill-Yoo, Han; Martin, Manfred

    2014-03-01

    In thin films of mixed ionic electronic conductors sandwiched by two ion-blocking electrodes, the homogeneous migration of ions and their polarization will modify the electronic carrier distribution across the conductor, thereby enabling homogeneous resistive switching. Here we report non-filamentary memristive switching based on the bulk oxide ion conductivity of amorphous GaOx (x~1.1) thin films. We directly observe reversible enrichment and depletion of oxygen ions at the blocking electrodes responding to the bias polarity by using photoemission and transmission electron microscopies, thus proving that oxygen ion mobility at room temperature causes memristive behaviour. The shape of the hysteresis I-V curves is tunable by the bias history, ranging from narrow counter figure-eight loops to wide hysteresis, triangle loops as found in the mathematically derived memristor model. This dynamical behaviour can be attributed to the coupled ion drift and diffusion motion and the oxygen concentration profile acting as a state function of the memristor.

  3. Tensile stress distribution sensors based on amorphous alloys

    NASA Astrophysics Data System (ADS)

    Hristoforou, E.; Reilly, R. E.

    1993-02-01

    In this paper, we report experimental results on the response of tensile stress sensors based on the magnetostrictive delay line technique, operating under pulsed field excitation. Their operation is based on the change of the magnetic circuit due to the change of the relative permeability of an amorphous ribbon when tensile stress is applied on it. They are low compliance sensors and can be used in cases where large displacement of the active core is not desirable.

  4. Influence of Weak External Magnetic Field on Amorphous and Nanocrystalline Fe-based Alloys

    SciTech Connect

    Degmova, J.; Sitek, J.

    2010-07-13

    Nanoperm, Hitperm and Finamet amorphous and nanocrystalline alloys were measured by Moessbauer spectrometry in a weak external magnetic field of 0.5 T. It was shown that the most sensitive parameters of Moessbauer spectra are the intensities of the 2nd and the 5th lines. Rather small changes were observed also in the case of internal magnetic field values. The spectrum of nanocrystalline Nanoperm showed the increase in A{sub 23} parameter (ratio of line intensities) from 2.4 to 3.7 and decrease of internal magnetic field from 20 to 19 T for amorphous subspectrum under the influence of magnetic field. Spectrum of nanocrystalline Finemet shown decrease in A{sub 23} parameter from 3.5 to 2.6 almost without a change in the internal magnetic field value. In the case of amorphous Nanoperm and Finemet samples, the changes are almost negligible. Hitperm alloy showed the highest sensitivity to the weak magnetic field, when the A{sub 23} parameter increased from 0.4 to 2.5 in the external magnetic fields. The A{sub 23} parameter of crystalline subspectrum increased from 2.7 to 3.8 and the value of internal magnetic field corresponding to amorphous subspectrum increased from 22 to 24 T. The behavior of nanocrystalline alloys under weak external magnetic field was analyzed within the three-level relaxation model of magnetic dynamics in an assembly of single-domain particles.

  5. Understanding the magnetic anisotropy in Fe-Si amorphous alloys

    SciTech Connect

    Diaz, J.; Hamdan, N.M.; Jalil, P.; Hussain, Z.; Valvidares, S.M.; Alameda, J.M.

    2002-08-01

    The origin of the magnetic anisotropy in a very disordered Fe-Si alloy has been investigated. The alloy containing 40 percent at. Si was prepared in the form of a thin film in a DC magnetron sputtering chamber. Structural disorder was obtained from Extended X-ray Absorption Fine Structure spectroscopy. The uniformity and lack of inhomogeneities at a microscopic level was checked by measuring their transverse magnetic susceptibility and hysteresis loops. The orbital component of the magnetic moment was measured by X-ray Magnetic Circular Dichroism spectroscopy. The orbital moment was extraordinary high, 0.4mB. Such a high value contrasted with the relatively small uniaxial anisotropy energy of the thin film (2kJ/m3). This suggests that the cause of the magnetic anisotropy in this alloy was a small degree of correlation in the orientation of the local orbital moments along a preferential direction.

  6. Industrial Environmental Testing of Coupons and Prototype Cylinders Coated With Iron-Based Amorphous Alloys

    SciTech Connect

    Rebak, R B; Aprigliano, L F; Day, S D; Lian, T; Farmer, J C

    2007-03-06

    Iron-based amorphous alloys are desirable for many industrial applications due to their dual capacity to resist corrosion and wear. These alloys may also contain a significant amount of boron which makes them candidates for criticality control, for example, in high-level nuclear waste disposition applications. The Fe-based amorphous alloys can be produced in powder form and then deposited using a HVOF thermal spray process on any surface that needs to be protected. For the current testing coupons of 316L stainless steels were coated with the amorphous alloy SAM2X5 and then tested for corrosion resistance in the salt-fog chamber and in other industrial environments. Prototype cylinders were also prepared and environmentally tested. One cylinder was 30-inch diameter, 88-inch long, and 3/8-inch thick. The coating thickness was 0.015 to 0.019-inch thick. The cylinder was in good condition after the test. Along the body of the cylinder only two pinpoint spot sized signs of rust were seen. Test results will be compared with the behavior of witness materials under the same tested conditions.

  7. Chemical, electronic, and magnetic structure of LaFeCoSi alloy: Surface and bulk properties

    SciTech Connect

    Lollobrigida, V.; Basso, V.; Kuepferling, M.; Coïsson, M.; Olivetti, E. S.; Celegato, F.; Borgatti, F.; Torelli, P.; Panaccione, G.; Tortora, L.; Stefani, G.; Offi, F.

    2014-05-28

    We investigate the chemical, electronic, and magnetic structure of the magnetocaloric LaFeCoSi compound with bulk and surface sensitive techniques. We put in evidence that the surface retains a soft ferromagnetic behavior at temperatures higher than the Curie temperature of the bulk due to the presence of Fe clusters at the surface only. This peculiar magnetic surface effect is attributed to the exchange interaction between the ferromagnetic Fe clusters located at the surface and the bulk magnetocaloric alloy, and it is used here to monitor the magnetic properties of the alloy itself.

  8. High-temperature oxidation of a rapidly solidified amorphous Ta-Ir alloy

    NASA Technical Reports Server (NTRS)

    Cotell, Catherine M.; Yurek, Gregory J.

    1986-01-01

    The oxidation products formed at 500 and 700 C on an amorphous Ta-44.5 at. pct Ir alloy in an Ar-0.1 percent O2 gas mixture were characterized using SEM, XRD, EPMA, TEM, STEM, AES, and XPS. Initially, a thin (3-4 nm) layer of Ta2O5 formed at the surface of the alloy. Continued growth of the Ta2O5, which occurred very rapidly, involved diffusion of oxygen anions from the Ta2O5/gas interface to the alloy/Ta2O5 interface, where tantalum was selectively oxidized. Because the oxide grew more quickly than iridium could diffuse back into the alloy, the iridium coalesced into platelets of crystalline iridium-rich alloy that were oriented approximately parallel to the oxide/alloy interface, and which became embedded in a matrix of Ta2O5. The unoxidized core remained in the glassy state. The oxidation process and/or the dissolution of oxygen into the unoxidized alloy caused the alloy to become embrittled.

  9. Dissolution of amorphous Ti-Zr-Si alloy during anodic oxidation with formation of barrier films

    SciTech Connect

    Isaev, N.I.; Yakovlev, V.B.; Iovdal'skii, A.A.; Gorshkov, T.P.

    1988-07-01

    Radiometric analysis of a solution has been used to study kinetic mechanisms for dissolution of amorphous alloy components in acid aqueous solutions with anodic oxidation in different regimes. In a galvanostatic regime for alloy and crystalline Ti, Zr, and Ta two sections are detected: an initial section of accelerated dissolution and a steady section. An increase in dissolution of zirconium from the alloy has been revealed compared with pure crystalline zirconium. Potentiostatic oxidation is accompanied by a slowdown in dissolution similar to a change in current. Current yield has been analyzed for dissolution of the main elements and nonrectifying impurities of the alloy (for example copper). Gamma spectroscopy using the gamma radiation from neutron-activated isotopes of the components and impurities was performed.

  10. Effect of residual strain in Fe-based amorphous alloys on field induced magnetic anisotropy and domain structure

    NASA Astrophysics Data System (ADS)

    Azuma, Daichi; Hasegawa, Ryusuke; Saito, Shin; Takahashi, Migaku

    2013-05-01

    Field induced magnetic anisotropy in two Fe-based amorphous alloys with different saturation induction levels (1.56 T and 1.64 T) was investigated by varying magnetic field strength and annealing temperature and domain images were taken on these samples. Residual strain was evaluated by measuring coercivities of the materials after stress-relief annealing. These results are discussed, clarifying the difference between the two Fe-based amorphous alloys.

  11. Mössbauer study on surface crystallization behavior of amorphous Fe90Zr10 alloy ribbon

    NASA Astrophysics Data System (ADS)

    Fujinami, Masanori; Ujihira, Yusuke

    1986-03-01

    The precipitous drop of crystallization temperature at the surface of amorphous Fe90Zr10 ribbon is confirmed by TMS and CEMS. The deficiency in Zr at the surface amorphous phase, caused by the absorption and the diffusion of oxygen, is found to be responsible for it. The final crystalline products are assigned to α-Fe, Fe3Zr and Fe2Zr, whereas only α-Fe precipitates at the surfaces. Moreover, it is indicated that the crystallization behavior of the bulk is influenced by the ambient gases during annealing and quite different between in vacuum and in air.

  12. Structure of amorphous Ag/Ge/S alloys: experimentally constrained density functional study.

    PubMed

    Akola, J; Beuneu, B; Jones, R O; Jóvári, P; Kaban, I; Kolář, J; Voleská, I; Wágner, T

    2015-12-01

    Density functional/molecular dynamics simulations have been performed to determine structural and other properties of amorphous Ag/Ge/S and Ge/S alloys. In the former, the calculations have been combined with experimental data (x-ray and neutron diffraction, extended x-ray absorption fine structure). Ag/Ge/As alloys have high ionic conductivity and are among the most promising candidates for future memristor technology. We find excellent agreement between the experimental results and large-scale (500 atoms) simulations in Ag/Ge/S, and we compare and contrast the structures of Ge/S and Ag/Ge/S. The calculated electronic structures, vibrational densities of states, ionic mobilities, and cavity distributions of the amorphous materials are discussed and compared with data on crystalline phases where available. The high mobility of Ag in solid state electrolyte applications is related to the presence of cavities and can occur via jumps to a neighbouring vacant site. PMID:26569035

  13. Structure of amorphous Ag/Ge/S alloys: experimentally constrained density functional study

    NASA Astrophysics Data System (ADS)

    Akola, J.; Beuneu, B.; Jones, R. O.; Jóvári, P.; Kaban, I.; Kolář, J.; Voleská, I.; Wágner, T.

    2015-12-01

    Density functional/molecular dynamics simulations have been performed to determine structural and other properties of amorphous Ag/Ge/S and Ge/S alloys. In the former, the calculations have been combined with experimental data (x-ray and neutron diffraction, extended x-ray absorption fine structure). Ag/Ge/As alloys have high ionic conductivity and are among the most promising candidates for future memristor technology. We find excellent agreement between the experimental results and large-scale (500 atoms) simulations in Ag/Ge/S, and we compare and contrast the structures of Ge/S and Ag/Ge/S. The calculated electronic structures, vibrational densities of states, ionic mobilities, and cavity distributions of the amorphous materials are discussed and compared with data on crystalline phases where available. The high mobility of Ag in solid state electrolyte applications is related to the presence of cavities and can occur via jumps to a neighbouring vacant site.

  14. Ion beam mixing in binary amorphous metallic alloys. [Cu-Er; Ni-Ti

    SciTech Connect

    Hahn, H.; Averback, R.S.; Diaz de la Rubia, T.; Okamoto, P.R.

    1985-12-01

    Ion beam mixing (IM) was measured in homogeneous amorphous metallic alloys of Cu-Er and Ni-Ti as a function of temperature using tracer impurities, i.e., the so-called ''marker geometry''. In Cu-Er, a strong temperature dependence in IM was observed between 80 and 373K, indicating that radiation-enhanced diffusion mechanisms are operative in this metallic glass. Phase separation of the Cu-Er alloy was also observed under irradiation as Er segregated to the vacuum and SiO2 interfaces of the specimen. At low-temperatures, the amount of mixing in amorphous Ni-Ti is similar to that in pure Ni or Ti, but it is much greater in Cu-Er than in either Cu or Er.

  15. Surface mico-structures on amorphous alloys induced by vortex femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Ran, Ling-Ling; Qu, Shi-Liang; Guo, Zhong-Yi

    2010-03-01

    This paper investigates the generation of self-organized surface structures on amorphous alloys by vortex femtosecond laser pulses. The scanning electron microscope characterizations show that the as-formed structures are periodic ripples, aperiodic ripples, and 'coral-like' structures. Optimal conditions for forming these surface structures are determined in terms of pulses number at a given pulse energy. The applicable mechanism is suggested to interpret the formation and evolution of the 'coral-like' structures.

  16. Amorphous Alloy Membranes Prepared by Melt-Spin methods for Long-Term use in Hydrogen Separation Applications

    SciTech Connect

    Chandra, Dhanesh; Kim, Sang-Mun; Adibhatla, Anasuya; Dolan, Michael; Paglieri, Steve; Flanagan, Ted; Chien, Wen-Ming; Talekar, Anjali; Wermer, Joseph

    2013-02-28

    Amorphous Ni-based alloy membranes show great promise as inexpensive, hydrogenselective membrane materials. In this study, we developed membranes based on nonprecious Ni-Nb-Zr alloys by adjusting the alloying content and using additives. Several studies on crystallization of the amorphous ribbons, in-situ x-ray diffraction, SEM and TEM, hydrogen permeation, hydrogen solubility, hydrogen deuterium exchange, and electrochemical studies were conducted. An important part of the study was to completely eliminate Palladium coatings of the NiNbZr alloys by hydrogen heattreatment. The amorphous alloy (Ni0.6Nb0.4)80Zr20 membrane appears to be the best with high hydrogen permeability and good thermal stability.

  17. Annealing temperature effect on microstructure, magnetic and microwave properties of Fe-based amorphous alloy powders

    NASA Astrophysics Data System (ADS)

    He, Jinghua; Wang, Wei; Wang, Aimin; Guan, Jianguo

    2012-09-01

    Fe74Ni3Si13Cr6W4 amorphous alloy powders were annealed at different temperature (T) for 1.5 h to fabricate the corresponding amorphous and nanocrystalline powders. The influences of T on the crystalline structure, morphology, magnetic and microwave electromagnetic properties of the resultant samples were investigated via X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer and vector network analyzer. The results show that the powder samples obtained at T of 650 °C or more are composed of lots of ultra-fine α-Fe(Si) grains embedded in an amorphous matrix. When T increases from 350 to 750 °C, the saturated magnetization and coercivity of the as-annealed powder samples both increase monotonously whereas the relative real permittivity shows a minimal value and the relative real permeability shows a maximal value at T of 650 °C. Thus the powder samples annealed at 650 °C show optimal reflection loss under -10 dB in the whole C-band. These results here suggest that the annealing heat treatment of Fe-based amorphous alloy is an effective approach to fabricate high performance microwave absorber with reasonable permittivity and large permeability simultaneously via adjusting T.

  18. Some industrial applications of amorphous and nanocrystalline alloys

    NASA Astrophysics Data System (ADS)

    Nosenko, V. K.; Maslov, V. V.; Kirilchuk, V. V.; Kochkubey, A. P.

    2008-02-01

    The example of successful realization of developments of Institute for Metal Physics of National Academy of Sciences of Ukraine in the field of nanotechnology is organization and successful, during 14 years, functioning of production of modern precision amorphous and nanocrystalline magnetic cores in the frames of the small research-and-production enterprise MELTA Ltd. The most important, from the practical standpoint, high heat-time stability of initial magnetic permeability of cores is provided by using new methods of final treatment of cores, minimization of their package influence on characteristics of the process using liquid impregnation heat-resistant materials and new polymeric coatings. The most effective fields of industrial use of MELTA® magnetic cores are ground leakage current sensors, current measuring transformers (converters), power medium frequency, broadband and pulse small-size transformers, filter chokes, reactors, storage transformers and ferroprobes.

  19. Corrosion Properties of Ultrasonic Electrodeposited Nanocrystalline and Amorphous Patterned Ni-W Alloy Coatings

    NASA Astrophysics Data System (ADS)

    Yang, Ying; Zhang, Yu; Zhang, Yuhong; Yan, Biao; Mo, Fan

    2013-07-01

    Ni-W alloy coating is a kind of promising environmental friendly alloy to substitute for hard chrome plating, for its excellent functional properties. Their properties depend mainly on the structure and defect, such as cracks. The crack is catastrophe to both physical and chemical properties and crystalline state also affect their properties and application. In this work, nanocrystalline nickel tungsten alloy (nc Ni-W) coating, amorphous nickel tungsten alloy (a Ni-W) coating and crystalline nickel tungsten alloy (c Ni-W) coating were prepared under ultrasonic direct current (UDC) electroplating. The aim of the present study is to achieve structure control and high surface quality of Ni-W alloy coatings, and investigate corrosion properties of these coatings to explain the contradiction of better corrosion resistance of nc Ni-W coating than a Ni-W coating in experiment and theory. Thus X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) were used to examine the composition, crystalline state, microstructures and defects of the samples. Moreover, potentiodynamic polarization test was used to study the corrosion behavior of electroplated nickel-tungsten alloys.

  20. Compositional ordering and stability in nanostructured, bulk thermoelectric alloys.

    SciTech Connect

    Hekmaty, Michelle A.; Faleev, S.; Medlin, Douglas L.; Leonard, F.; Lensch-Falk, J.; Sharma, Peter Anand; Sugar, J. D.

    2009-09-01

    Thermoelectric materials have many applications in the conversion of thermal energy to electrical power and in solid-state cooling. One route to improving thermoelectric energy conversion efficiency in bulk material is to embed nanoscale inclusions. This report summarize key results from a recently completed LDRD project exploring the science underpinning the formation and stability of nanostructures in bulk thermoelectric and the quantitative relationships between such structures and thermoelectric properties.

  1. Effects of Phosphorus and Carbon Contents on Amorphous Forming Ability in Fe-based Amorphous Alloys Used for Thermal Spray Coatings

    NASA Astrophysics Data System (ADS)

    Do, Jeonghyeon; Jung, Seungmun; Lee, Hyuk-Joong; Lee, Byeong-Joo; Cha, Gil-up; Jo, Chang Yong; Lee, Sunghak

    2013-06-01

    Cost-effective Fe-based amorphous alloys used for thermal spray coatings were developed by varying contents of P and C, and their microstructure, hardness, and corrosion resistance were analyzed. In order to achieve chemical compositions having high amorphous forming ability, thermodynamically calculated phase diagrams of Fe-Al-P-C-B five-component system were used, from which compositions of super-cooled liquid having the lowest driving force of formation of crystalline phases were obtained. The thermodynamic calculation results showed that only phases of Fe3P and Fe3C were formed in the Fe78Al2P(18.3- x)C x B1.7 alloy system. Considering driving force curves of Fe3P and Fe3C, the carbon contents were selected to be 6.90 and 7.47 at. pct, when the thermodynamic calculation temperatures were 697 K (414 °C) and 715 K (442 °C), respectively. According to the microstructural analysis of suction-cast alloys, the Fe78Al2P10.83C7.47B1.7 alloy showed a fully amorphous microstructure, whereas the Fe78Al2P11.40C6.9B1.7 and Fe78Al2P10.3C8.0B1.7 alloys contained Fe3P and Fe3C phases. This Fe78Al2P10.83C7.47B1.7 alloy showed the better hardness and corrosion resistance than those of conventional thermal spray coating alloys, and its production cost could be lowered using cheaper alloying elements, thereby leading to the practical application to amorphous thermal spray coatings.

  2. Partial amorphization of a Cu-Zr-Ti alloy by high pressure torsion

    SciTech Connect

    Revesz, Adam; Hobor, Sandor; Labar, Janos L.; Zhilyaev, Alex P.; Kovacs, Zsolt

    2006-11-15

    High pressure torsion was applied to produce disk-shape specimen of Cu{sub 60}Zr{sub 20}Ti{sub 20} composition. Radial dependence of the microstructure was monitored by x-ray diffraction, scanning, and transmission electron microscopies. The disk consists of a top surface layer, homogeneous on a micrometer scale with an average thickness of 10-20 {mu}m, and an inhomogeneous bulk region of 200 {mu}m thickness. Calorimetric studies revealed that the disk contains detectable amount of amorphous phase. Characteristics of this amorphous content were compared to a fully amorphous melt-quenched Cu{sub 60}Zr{sub 20}Ti{sub 20} ribbon.

  3. Microstructure and magnetic properties of soft magnetic powder cores of amorphous and nanocrystalline alloys

    NASA Astrophysics Data System (ADS)

    Liu, Yapi; Yi, Yide; Shao, Wei; Shao, Yanfang

    2013-03-01

    With the development of modern ferromagnetic technology, soft magnetic powder cores (MPCs) of amorphous and nanocrystalline alloys have been intensively studied for their excellent soft magnetic properties such as high flux density, low coercivity and reduced core loss due to amorphous state and nanocrystalline grains of 10-20 nm dispersed in a residual amorphous matrix. In this paper, the microstructures and soft magnetic properties, i.e., maximum magnetic induction Bm, effective permeability μe, DC-bias properties and volume power losses PCV of MPCs made from amorphous powder of gas atomization and nanocrystalline powder of pulverized melt-spun ribbon were investigated and also compared on the basis of the same level of μe. It is found that μe of both kinds of MPC keeps unchanged up to 1 MHz. The amorphous MPC has lower PCV at lower frequency range, while the nanocrystalline MPC has lower PCV at high frequency range instead. Also, the nanocrystalline MPC has better DC-bias property. Moreover, the DC magnetic properties and the changes of PCV of both MPCs with frequency and flux density are also studied. Furthermore, the electromagnetic characteristics, the microstructures and the mechanisms accounting for these phenomena of both MPCs are also discussed.

  4. Photoassisted amorphization of the phase-change memory alloy Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Fons, P.; Osawa, H.; Kolobov, A. V.; Fukaya, T.; Suzuki, M.; Uruga, T.; Kawamura, N.; Tanida, H.; Tominaga, J.

    2010-07-01

    Subnanosecond time-resolved x-ray absorption measurements have been used to probe dynamical changes in the local structure about Ge atoms in the phase-change alloy Ge2Sb2Te5 during the optical recording (amorphization) process using an optical pump and x-ray probe technique to examine the reversible phase transition from the metastable crystalline phase to the amorphous phase. We provide unambiguous evidence that the amorphization process does not proceed via the molten state but is a photoassisted process. We argue that the transition to the amorphous phase is a consequence of photoassisted destabilization of the resonant bonding present in the crystalline phase. This observation challenges the currently existing paradigm of the phase-change process which implicitly assumes the existence of the molten phase as a prerequisite for the creation of the amorphous phase. Implications from this finding are discussed, including the possibility to use the polarization of light as an extra coordinate for data recording.

  5. CORROSION OF AMORPHOUS AND NANOCRYSTALLINE Fe-BASED ALLOYS IN NaCl AND H2SO4 SOLUTIONS

    NASA Astrophysics Data System (ADS)

    Li, Xiang; Lu, Wei; Wang, Yuxin; Yan, Biao; Pan, Deng

    2013-07-01

    Corrosion resistance of nanocrystalline Fe73.5Si13.5B9Nb3Cu1 alloy was investigated and compared to its amorphous counterpart. Low-temperature crystallization occurred during the annealing of amorphous tapes was used to obtain a nanocrystalline structure. The influence of annealing condition on the structure and corrosion resistance of the alloy in NaCl and H2SO4 solutions was investigated. Based on the testing results, it was found that nanocrystalline tapes have higher corrosion resistance than amorphous counterpart and H2SO4 can promote the occurrence of corrosion compared with NaCl.

  6. The bulk and interfacial electronic and chemical structure of amorphous hydrogenated boron carbide

    NASA Astrophysics Data System (ADS)

    Driver, Marcus Sky

    The chemical and electronic structure, as related to the surface, interface and bulk of amorphous hydrogenated boron carbide (a-BxC:H y), is of interest in neutron detection and microelectronics. This dissertation investigates the chemical and electronic structure of semiconducting thin-film a-BxC:Hy grown by plasma enhanced chemical vapor deposition (PECVD) of ortho-carborane (1,2-C2B10H12). Experimental methods used include: x-ray and ultraviolet photoelectron spectroscopies (XPS/UPS) and x-ray absorption/emission spectroscopies (XAS/XES). These methods were used to investigate the chemical species, bonding and hybridizations, and band gaps of a-BxC:Hy prepared or treated under varying conditions. Additionally, a detailed examination of the formation of Schottky barriers was implemented. Throughout this dissertation the chemical structure was studied. One study was to understand various growth conditions. The effects of the PECVD growth parameters were evaluated by comparing changes in atomic percentages (at.%'s) between thin-films from various substrate temperatures. Additionally, detailed studies of the photoelectron core level under two different growth conditions were undertaken to evaluate the effects of pre-/post- argon ion etching (Ar+) for the following: the chemical structural change for both an as grown (AG) and in-situ thermal treatment (500°C), and post Ar+ etch of samples thermally treated ranging from as grown to 850°C. The as grown and in-situ treated samples were used in conjunction to determine the formation of the Schottky barrier. The electronic structure was determined by the changes within the valence band of the thermally treated samples and formation of Schottky barrier. Thermally treated samples (as grown to 850°C) were further evaluated with respect to their occupied and unoccupied electronic states. The atomic percentage gave a stoichiometry range for a-B xC:Hy (given as x=1.5 to 3.0 with y= decreases with thermal treatment and Oz: z

  7. Influence of the chemical composition of Al-based amorphous alloys on thermally induced embrittlement

    NASA Astrophysics Data System (ADS)

    Sviridova, E. A.; Maksimov, V. V.; Rassolov, S. G.; Nosenko, V. K.; Tkach, V. I.

    2014-07-01

    Structural changes of rapidly cooled ribbons of the amorphous alloys Al88-86(Ni,Co,Fe)6-8(Y,Gd,Nd,La)5-6, which occur during heating at a rate of 10 K/min and lead to a loss of ductility, have been investigated experimentally. It has been shown that samples of the studied alloys are divided into two groups, in the first of which the loss of ductility is due to the formation of a nanocomposite structure, whereas the embrittlement of samples in the second group is caused by processes of structural relaxation in the amorphous phase (decrease in the concentration of a free volume). It has been established for the first time that there is an empirical correlation between the dynamic temperature, after heating to which the alloys lose their ductility at room temperature, and the ratio of the shear modulus to the elastic modulus of the alloys, which is calculated from the nominal chemical composition.

  8. Effect of chromium and phosphorus on the physical properties of iron and titanium-based amorphous metallic alloy films

    NASA Technical Reports Server (NTRS)

    Distefano, S.; Rameshan, R.; Fitzgerald, D. J.

    1991-01-01

    Amorphous iron and titanium-based alloys containing various amounts of chromium, phosphorus, and boron exhibit high corrosion resistance. Some physical properties of Fe and Ti-based metallic alloy films deposited on a glass substrate by a dc-magnetron sputtering technique are reported. The films were characterized using differential scanning calorimetry, stress analysis, SEM, XRD, SIMS, electron microprobe, and potentiodynamic polarization techniques.

  9. Analysis of Surface and Bulk Behavior in Ni-Pd Alloys

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Noebe, Rondald D.

    2003-01-01

    The most salient features of the surface structure and bulk behavior of Ni-Pd alloys have been studied using the BFS method for alloys. Large-scale atomistic simulations were performed to investigate surface segregation profiles as a function of temperature, crystal face, and composition. Pd enrichment of the first layer was observed in (111) and (100) surfaces, and enrichment of the top two layers occurred for (110) surfaces. In all cases, the segregation profile shows alternate planes enriched and depleted in Pd. In addition, the phase structure of bulk Ni-Pd alloys as a function of temperature and composition was studied. A weak ordering tendency was observed at low temperatures, which helps explain the compositional oscillations in the segregation profiles. Finally, based on atom-by-atom static energy calculations, a comprehensive explanation for the observed surface and bulk features will be presented in terms of competing chemical and strain energy effects.

  10. Characterization of mechanical nanocrystallization process of amorphous Fe{endash}Mo{endash}Si{endash}B alloy by transmission Moessbauer spectroscopy

    SciTech Connect

    Liu, X.D.; Lu, K.; Umemoto, M.

    1997-03-01

    The nanocrystallization process of the amorphous Fe{endash}Mo{endash}Si{endash}B alloy under ball milling is characterization by means of transmission M{umlt o}ssbauer spectroscopy in the present paper. It was found that a single {alpha}-Fe phase with the bcc structure is formed under ball-milling the amorphous Fe{endash}Mo{endash}Si{endash}B alloy. A significant increase in the relative area of the subspectra of 8 Fenn and 7 Fenn and a remarkable decrease in isomer shift and half linewidth of the subspectra of various Fe configurations, especially in the case of 6 Fenn, were observed during the ball milling process. The diffusion of metalloid atoms from the bcc {alpha}-Fe phase to the remaining amorphous phase and {alpha}-Fe/{alpha}-Fe grain boundaries is suggested to occur during the mechanical crystallization of the current amorphous alloy based on the above TMES investigations. {copyright} {ital 1997 Materials Research Society.}

  11. Development of amorphous Fe-B based alloys for choke and inductor applications

    SciTech Connect

    Major, R.V.; Cruickshank, K.J.; Jasko, T.M.

    1984-09-01

    This paper describes a method of obtaining linear permeability characteristics from Fe-B based amorphous alloys, suitable for choke and inductor applications. The properties are developed by heat treatment at temperatures above those conventionally used to develop the optimum low or high frequency magnetic properties in these alloys. Within a narrow heat treatment temperature range it is possible to develop permeabilities of between 200 and 700, linear up to high flux density levels. D.C. Energy Storage Curves are presented for Fe /sub 77.5/ B/sub 13/ Si /sub 9.5/ alloy, toroidal tape wound cores, heat treated in this manner. These curves indicate the potential advantages of these cores over powder cores and gapped ferrites in D.C. choke applications.

  12. The corrosion resistance and neutron-absorbing properties of coatings based on amorphous alloys

    NASA Astrophysics Data System (ADS)

    Sevryukov, O. N.; Polyansky, A. A.

    2016-04-01

    The object of the present study was the corrosion-resistant amorphizing alloys with an increased content of boron for cladding the surface of metals, rapidly quenched alloys without boron for protective coatings on a high-boron cladding layer, as well as steel samples with a protective coating with a high content of boron and without boron. The aim of the work is to investigate the corrosion resistance of a coating in water at the temperature of 40 °C in conditions of an open access of oxygen for 1000 h, as well as the features of the microstructure of clad samples before and after the corrosion tests. New data on the corrosion resistance of Cr18Ni10Ti steel samples with a protective layer from a rapidly quenched alloy Ni-19Cr-10Si (in wt.%) on a high-boron coating have been obtained.

  13. Electrical transport properties of amorphous Ni32Pd53P15 alloy

    NASA Astrophysics Data System (ADS)

    Prakruti, Chaudhari; Joshi, R. H.; Bhatt, N. K.; Thakore, B. Y.

    2015-08-01

    A ternary alloy containing nickel, palladium and phosphorous in amorphous form has been studied. The electrical transport properties viz. electrical resistivity, thermoelectrical power (TEP), thermal conductivity are computed using our recently proposed potential. In the present work, five screening functions have been employed to incorporate the exchange and correlation effects. The theoretical structure factors due to hard core fluid theory have been used in the calculations. The liquid alloy is studied as a function of its composition at temperature 294 K. The partial structure factors of the compound-forming Ni32Pd53P15 ternary alloy has been calculated by considering Hoshino's m-component hard-sphere mixture, which is based on Percus-Yevic equation of Hiroike.

  14. Thermal stability of amorphous GaN{sub 1-x}As{sub x} alloys

    SciTech Connect

    Levander, A. X.; Broesler, R.; Dubon, O. D.; Wu, J.; Liliental-Weber, Z.; Hawkridge, M. E.; Walukiewicz, W.; Yu, K. M.; Novikov, S. V.; Foxon, C. T.

    2011-04-18

    GaN{sub 1-x}As{sub x} alloys grown across the composition range by low temperature molecular beam epitaxy have great technological potential for photovoltaic applications owing to their strong absorption coefficient and wide tunability of band gap and band edges. We found that amorphous GaN{sub 1-x}As{sub x} alloys that are formed for the compositions x, in the range of x{approx}0.3-0.7 are stable up to 700 deg. C. This is surprising since growth of GaN{sub 1-x}As{sub x} above 400 deg. C results in phase segregation. At annealing temperatures higher than 700 deg. C the alloy phase segregates into GaAs:N and GaN:As. The relative size of the nanocrystals depends on the initial film composition and annealing conditions.

  15. Magnetic properties of Nd-Fe-Co(Cu)-Al-B amorphous alloys prepared by nonequilibrium techniques

    NASA Astrophysics Data System (ADS)

    Kumar, G.; Eckert, J.; Roth, S.; Löser, W.; Ram, S.; Schultz, L.

    2002-03-01

    The amorphous alloys Nd40Fe40Co5Al8B7, Nd57Fe20Co5Al10B8, and Nd57Fe20Cu5Al10B8 were prepared by copper mold casting, melt spinning, and mechanical alloying. Despite their similar x-ray diffraction patterns, samples display different magnetic and thermal behavior correlated with the method of preparation. The fully amorphous melt-spun ribbons exhibit relatively soft magnetic properties with coercivities ≈40 kA/m at room temperature and a Curie temperature (TC)≈474 K. Apparently only the mold-cast cylinders of 3 mm diameter show hard magnetic behavior with a coercivity in the range of 258-270 kA/m (depending on composition) and have approximately the same TC as that of the melt-spun ribbons. An additional magnetic transition at 585 K due to the presence of Nd2Fe14B phase in the case of Nd40Fe40Co5Al8B7 cast rod has been observed. Heat treatment above crystallization temperature in as-cast Nd57Fe20Co5Al10B8 and Nd57Fe20Cu5Al10B8 samples destroys the hard magnetic properties. In contrast, mechanically alloyed amorphous samples are soft magnetic with maximum coercivity up to 11 kA/m but show an entirely different TC≈680-740 K, which is rather characteristic of an Fe solid solution. The magnetic properties are discussed in terms of different local atomic environment and cluster sizes in amorphous samples prepared by different methods.

  16. Characterization of amorphous selenium alloy detectors for x-rays and high energy nuclear radiation detection

    NASA Astrophysics Data System (ADS)

    Mandal, Krishna C.; Mehta, Abhinav; Chaudhuri, Sandeep K.; Cui, Yunlong; Groza, Michael; Burger, Arnold

    2013-09-01

    Synthesized amorphous selenium (a-Se) alloy materials have been characterized for room temperature high-energy nuclear radiation detector and x-ray detection applications. The alloy composition has been optimized to ensure good charge transport properties and detector performance. The synthesis of a-Se (As, Cl) alloys has been carried out by thoroughly mixing zone-refined (ZR) Se (~7N) with previously synthesized a-Se(As) and a-Se(Cl) master alloys (MS). The synthesized alloys have been characterized by x-ray diffraction (XRD), glow discharge mass spectroscopy (GDMS), differential scanning calorimetry (DSC), x-ray photoelectron spectroscopy (XPS), and current-voltage (I-V) characteristics measurements. Raman spectroscopy demonstrated that the a-Se(As) master alloy samples were in metastable monoclinic Se8 states, in which seven vibrational modes are located at 40(41), 59(60), 77, 110, 133, 227(228) and 251(252) cm-1. However, a-Se(Cl) master alloy samples are in stable form of trigonal structure of Se8 ring, in which two modes at 142 and 234 cm-1 were found. Both Raman and energy dispersive spectroscopy (EDS) exhibited that a small amount of tellurium (Te) existed in a-Se (As, Cl) master alloy samples. DSC measurements showed that a-Se (Cl) MS and a-Se (As) MS samples have one melting point, located at ~219.6°C, whereas a-Se-As (0.52%)-Cl and Se- As(10.2%)-Cl(60 ppm) both possess two melting points, located at 221 and 220.3°C respectively. The a-Se alloy plate detectors have been fabricated and tested and the results showed high dark resistivity (1012 - 1013 Ω-cm) with good charge transport properties and cost-effective large-area scalability.

  17. Boundary Engineering for the Thermoelectric Performance of Bulk Alloys Based on Bismuth Telluride.

    PubMed

    Mun, Hyeona; Choi, Soon-Mok; Lee, Kyu Hyoung; Kim, Sung Wng

    2015-07-20

    Thermoelectrics, which transports heat for refrigeration or converts heat into electricity directly, is a key technology for renewable energy harvesting and solid-state refrigeration. Despite its importance, the widespread use of thermoelectric devices is constrained because of the low efficiency of thermoelectric bulk alloys. However, boundary engineering has been demonstrated as one of the most effective ways to enhance the thermoelectric performance of conventional thermoelectric materials such as Bi2 Te3 , PbTe, and SiGe alloys because their thermal and electronic transport properties can be manipulated separately by this approach. We review our recent progress on the enhancement of the thermoelectric figure of merit through boundary engineering together with the processing technologies for boundary engineering developed most recently using Bi2 Te3 -based bulk alloys. A brief discussion of the principles and current status of boundary-engineered bulk alloys for the enhancement of the thermoelectric figure of merit is presented. We focus mainly on (1) the reduction of the thermal conductivity by grain boundary engineering and (2) the reduction of thermal conductivity without deterioration of the electrical conductivity by phase boundary engineering. We also discuss the next potential approach using two boundary engineering strategies for a breakthrough in the area of bulk thermoelectric alloys. PMID:25782971

  18. A Combinatorial Approach to the Investigation of Metal Systems that Form Both Bulk Metallic Glasses and High Entropy Alloys

    NASA Astrophysics Data System (ADS)

    Welk, Brian A.; Gibson, Mark A.; Fraser, Hamish L.

    2016-03-01

    In this work, compositionally graded specimens were deposited using the laser engineered net-shaping (LENS™) additive manufacturing technique to study the glass-forming ability of two bulk metallic glass (BMG) and high entropy alloy (HEA) composite systems. The first graded specimen varied from Zr57Ti5Al10Cu20Ni8 (BMG) to CoCrFeNiCu0.5 (HEA) and the second graded specimen varied from TiZrCuNb (BMG) to (TiZrCuNb)65Ni35 (HEA). After deposition, laser surface melting experiments were performed parallel to the gradient to remelt and rapidly solidify the specimen. Scanning electron microscopy and energy dispersive x-ray spectroscopy were used to determine the morphology and composition variations in the as-deposited and laser surface melted phases. Selected area diffraction of the melt pool regions confirmed an almost fully amorphous region in the first gradient and an amorphous matrix/crystalline dendrite composite structure in the second gradient.

  19. Ion-implantation-induced amorphization of InxGa1-xP alloys as functions of stoichiometry and temperature

    NASA Astrophysics Data System (ADS)

    Hussain, Z. S.; Wendler, E.; Wesch, W.; Schnohr, C. S.; Ridgway, M. C.

    2016-05-01

    Rutherford Backscattering Spectrometry/Channeling and Extended X-ray Absorption Fine Structure measurements have been combined to investigate the amorphization of InxGa1-xP alloys at 15 and 300 K for selected stoichiometries representative of the entire stoichiometric range. The amorphization kinetics differs considerably for the two temperatures: at 15 K, the amorphization kinetics of InxGa1-xP is intermediate between the two binary extremes while at 300 K, InxGa1-xP is more easily amorphized than both InP and GaP. Direct impact and stimulated amorphization both contribute to the amorphization process at 15 K. Dynamic annealing via thermally induced Frenkel pair recombination reduces the influence of direct impact amorphization at 300 K such that the stimulated amorphization is dominant. At this temperature, stimulated amorphization in ternary InxGa1-xP alloys is supported by the structural disorder inherent from the bimodal bond length distribution.

  20. Amorphous nickel boride membrane on a platinum–nickel alloy surface for enhanced oxygen reduction reaction

    PubMed Central

    He, Daping; Zhang, Libo; He, Dongsheng; Zhou, Gang; Lin, Yue; Deng, Zhaoxiang; Hong, Xun; Wu, Yuen; Chen, Chen; Li, Yadong

    2016-01-01

    The low activity of the oxygen reduction reaction in polymer electrolyte membrane fuel cells is a major barrier for electrocatalysis, and hence needs to be optimized. Tuning the surface electronic structure of platinum-based bimetallic alloys, a promising oxygen reduction reaction catalyst, plays a key role in controlling its interaction with reactants, and thus affects the efficiency. Here we report that a dealloying process can be utilized to experimentally fabricate the interface between dealloyed platinum–nickel alloy and amorphous nickel boride membrane. The coating membrane works as an electron acceptor to tune the surface electronic structure of the platinum–nickel catalyst, and this composite catalyst composed of crystalline platinum–nickel covered by amorphous nickel boride achieves a 27-times enhancement in mass activity relative to commercial platinum/carbon at 0.9 V for the oxygen reduction reaction performance. Moreover, this interactional effect between a crystalline surface and amorphous membrane can be readily generalized to facilitate the 3-times higher catalytic activity of commercial platinum/carbon. PMID:27503412

  1. Amorphous nickel boride membrane on a platinum-nickel alloy surface for enhanced oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    He, Daping; Zhang, Libo; He, Dongsheng; Zhou, Gang; Lin, Yue; Deng, Zhaoxiang; Hong, Xun; Wu, Yuen; Chen, Chen; Li, Yadong

    2016-08-01

    The low activity of the oxygen reduction reaction in polymer electrolyte membrane fuel cells is a major barrier for electrocatalysis, and hence needs to be optimized. Tuning the surface electronic structure of platinum-based bimetallic alloys, a promising oxygen reduction reaction catalyst, plays a key role in controlling its interaction with reactants, and thus affects the efficiency. Here we report that a dealloying process can be utilized to experimentally fabricate the interface between dealloyed platinum-nickel alloy and amorphous nickel boride membrane. The coating membrane works as an electron acceptor to tune the surface electronic structure of the platinum-nickel catalyst, and this composite catalyst composed of crystalline platinum-nickel covered by amorphous nickel boride achieves a 27-times enhancement in mass activity relative to commercial platinum/carbon at 0.9 V for the oxygen reduction reaction performance. Moreover, this interactional effect between a crystalline surface and amorphous membrane can be readily generalized to facilitate the 3-times higher catalytic activity of commercial platinum/carbon.

  2. Electron-Rich Driven Electrochemical Solid-State Amorphization in Li-Si Alloys

    SciTech Connect

    Wang, Zhiguo; Gu, Meng; Zhou, Yungang; Zu, Xiaotao; Connell, Justin G.; Xiao, Jie; Perea, Daniel E.; Lauhon, Lincoln J.; Bang, Junhyeok; Zhang, Shengbai; Wang, Chong M.; Gao, Fei

    2013-08-14

    The physical and chemical behaviors of materials used in energy storage devices, such as lithium-ion batteries (LIBs), are mainly controlled by an electrochemical process, which normally involves insertion/extraction of ions into/from a host lattice with a concurrent flow of electrons to compensate charge balance. The fundamental physics and chemistry governing the behavior of materials in response to the ions insertion/extraction is not known. Herein, a combination of in situ lithiation experiments and large-scale ab initio molecular dynamics simulations are performed to explore the mechanisms of the electrochemically driven solid-state amorphization in Li-Si systems. We find that local electron-rich condition governs the electrochemically driven solid-state amorphization of Li-Si alloys. This discovery provides the fundamental explanation of why lithium insertion in semiconductor and insulators leads to amorphization, whereas in metals, it leads to a crystalline alloy. The present work correlates electrochemically driven reactions with ion insertion, electron transfer, lattice stability and phase equilibrium.

  3. Determination of the location of hydrogen in the CuTi amorphous alloys by neutron diffraction

    NASA Astrophysics Data System (ADS)

    Rodmacq, B.; Billard, L.; Chamberod, A.; Mangin, Ph.

    1986-02-01

    Neutron diffraction experiments have been performed on hydrogenated and deuterated Cu xTi 1- x amorphous alloys ( x = 0.67, 0.50, 0.35). The evolution of the interference functions as a function of hydrogen and deuterium concentration has shown that the hydrogen atoms have no copper atoms as first neighbours but are surrounded only by titanium atoms. The metal-hydrogen first distances compare well to those found in the corresponding crystalline hydrides. A model for the Cu 50Ti 50 amorphous alloy has been built up. The introduction of hydrogen or deuterium atoms in Ti 4 tetrahedra leads to calculated pair correlation functions very close to the experimental ones. Finally, the thermal evolution of CuTiH and CuTiD samples as been studied. Increasing the temperature leads to the precipitation of TiH 2 particles in the amorphous matrix. This is followed by the crystallization of the matrix and by the desorption of hydrogen at still higher temperature.

  4. Amorphous nickel boride membrane on a platinum-nickel alloy surface for enhanced oxygen reduction reaction.

    PubMed

    He, Daping; Zhang, Libo; He, Dongsheng; Zhou, Gang; Lin, Yue; Deng, Zhaoxiang; Hong, Xun; Wu, Yuen; Chen, Chen; Li, Yadong

    2016-01-01

    The low activity of the oxygen reduction reaction in polymer electrolyte membrane fuel cells is a major barrier for electrocatalysis, and hence needs to be optimized. Tuning the surface electronic structure of platinum-based bimetallic alloys, a promising oxygen reduction reaction catalyst, plays a key role in controlling its interaction with reactants, and thus affects the efficiency. Here we report that a dealloying process can be utilized to experimentally fabricate the interface between dealloyed platinum-nickel alloy and amorphous nickel boride membrane. The coating membrane works as an electron acceptor to tune the surface electronic structure of the platinum-nickel catalyst, and this composite catalyst composed of crystalline platinum-nickel covered by amorphous nickel boride achieves a 27-times enhancement in mass activity relative to commercial platinum/carbon at 0.9 V for the oxygen reduction reaction performance. Moreover, this interactional effect between a crystalline surface and amorphous membrane can be readily generalized to facilitate the 3-times higher catalytic activity of commercial platinum/carbon. PMID:27503412

  5. Relaxation of bending stresses and the reversibility of residual stresses in amorphous soft magnetic alloys

    SciTech Connect

    Kekalo, I. B.; Mogil’nikov, P. S.

    2015-06-15

    The reversibility of residual bending stresses is revealed in ribbon samples of cobalt- and iron-based amorphous alloys Co{sub 69}Fe{sub 3.7}Cr{sub 3.8}Si{sub 12.5}B{sub 11} and Fe{sub 57}Co{sub 31}Si{sub 2.9}B{sub 9.1}: the ribbons that are free of applied stresses and bent under the action of residual stresses become completely or incompletely straight upon annealing at the initial temperatures. The influence of annealing on the relaxation of bending stresses is studied. Preliminary annealing is found to sharply decrease the relaxation rate of bending stresses, and the initial stage of fast relaxation of these stresses is absent. Complete straightening of preliminarily annealed ribbons is shown to occur at significantly higher temperatures than that of the initial ribbons. Incomplete straightening of the ribbons is explained by the fact that bending stresses relaxation at high annealing temperatures proceeds due to both reversible anelastic deformation and viscous flow, which is a fully irreversible process. Incomplete reversibility is also caused by irreversible processes, such as the release of excess free volume and clustering (detected by small-angle X-ray scattering). The revealed differences in the relaxation processes that occur in the cobalt- and iron-based amorphous alloys are discussed in terms of different atomic diffusion mobilities in these alloys.

  6. Invar and Elinvar type amorphous Fe-Cr-B alloys with high corrosion resistance

    NASA Technical Reports Server (NTRS)

    Kikuci, M.; Fukamichi, K.; Masumoto, T.

    1987-01-01

    Amorphous (Fe(1-x)Cr(x))85B15 alloys (x = 0 to 0.15) were prepared from the melts by rapid quenching using a single roller techinque, and their Invar and Elinvar characteristics and corrosion resistance were investigated. With an increase in chromium content the Curie temperature and the saturation magnetic moment per iron atom decreased monotonically, while the crystallization temperature incresed gradually. The thermal expansion coefficient alpha around room temperature became slightly larger with increasing chromium content. Nevertheless, these amorphous alloys exhibited excellent Invar characteristics below the Curie temperature. The value of Young's modulus increased remarkably in a relatively low magnetic field and then saturated at a field of about 80 kA/m, showing a large delta E effect. Its value as well as a longitudinal linear magnetostriction became smaller with an increase in chromium content. The temperature coefficient of Young's modulus changed from postive to negative, and the temperature range showing the Elinvar characteristics became narrower with chromium content. The temperature coefficient of delay time determined from the values of alpha and e was very small. The corrosion resistance of these alloys was extremely improved by chromium addition.

  7. Band gap structure modification of amorphous anodic Al oxide film by Ti-alloying

    SciTech Connect

    Canulescu, S. Schou, J.; Rechendorff, K.; Pleth Nielsen, L.; Borca, C. N.; Jones, N. C.; Hoffmann, S. V.; Bordo, K.; Ambat, R.

    2014-03-24

    The band structure of pure and Ti-alloyed anodic aluminum oxide has been examined as a function of Ti concentration varying from 2 to 20 at. %. The band gap energy of Ti-alloyed anodic Al oxide decreases with increasing Ti concentration. X-ray absorption spectroscopy reveals that Ti atoms are not located in a TiO{sub 2} unit in the oxide layer, but rather in a mixed Ti-Al oxide layer. The optical band gap energy of the anodic oxide layers was determined by vacuum ultraviolet spectroscopy in the energy range from 4.1 to 9.2 eV (300–135 nm). The results indicate that amorphous anodic Al{sub 2}O{sub 3} has a direct band gap of 7.3 eV, which is about ∼1.4 eV lower than its crystalline counterpart (single-crystal Al{sub 2}O{sub 3}). Upon Ti-alloying, extra bands appear within the band gap of amorphous Al{sub 2}O{sub 3}, mainly caused by Ti 3d orbitals localized at the Ti site.

  8. On the amorphization behavior and hydrogenation performance of high-energy ball-milled Mg{sub 2}Ni alloys

    SciTech Connect

    Kou, Hongchao; Hou, Xiaojiang; Zhang, Tiebang Hu, Rui; Li, Jinshan; Xue, Xiangyi

    2013-06-15

    Amorphous Mg{sub 2}Ni alloy was prepared by high energy ball-milling starting with polycrystalline Mg{sub 2}Ni which was prepared with the help of a metallurgy method by using a SPEX 8000D mill. The microstructural and phase structure characterization of the prepared materials was performed via scanning electron microscopy, transition electron microscope and X-ray diffraction. The thermal stabilities were investigated by differential scanning calorimetry. The apparent activation energies were determined by means of the Kissinger method. The first and second crystallization reactions take place at ∼ 255 °C and ∼ 410 °C, and the corresponding activation energy of crystallization is E{sub a1} = 276.9 and E{sub a2} = 382.4 kJ/mol, respectively. At 3 MPa hydrogen pressure and 250 °C, the hydrogen absorption capacities of crystalline, partially and fully amorphous Mg{sub 2}Ni alloy are 2.0 wt.%, 3.2 wt.% and 3.5 wt.% within 30 min, respectively. - Graphical Abstract: We mainly focus on the amorphization behavior of crystalline Mg{sub 2}Ni alloy in the high energy ball-milling process and the crystallization behavior of the amorphous Mg{sub 2}Ni alloy in a follow-up heating process. The relationship of milling, microstructure and hydrogenation properties is established and explained by models. - Highlights: • Amorphous Mg{sub 2}Ni has been obtained by high energy ball milling the as-cast alloy. • The amorphization behavior of polycrystalline Mg{sub 2}Ni is presented. • The crystallization behavior of the amorphous Mg{sub 2}Ni alloy is illustrated. • Establish the relationship of milling, microstructure and hydrogenation properties.

  9. Reactive wetting of amorphous silica by molten Al-Mg alloys and their interfacial structures

    NASA Astrophysics Data System (ADS)

    Shi, Laixin; Shen, Ping; Zhang, Dan; Jiang, Qichuan

    2016-07-01

    The reactive wetting of amorphous silica substrates by molten Al-Mg alloys over a wide composition range was studied using a dispensed sessile drop method in a flowing Ar atmosphere. The effects of the nominal Mg concentration and temperature on the wetting and interfacial microstructures were discussed. The initial contact angle for pure Al on the SiO2 surface was 115° while that for pure Mg was 35° at 1073 K. For the Al-Mg alloy drop, it decreased with increasing nominal Mg concentration. The reaction zone was characterized by layered structures, whose formation was primarily controlled by the variation in the alloy concentration due to the evaporation of Mg and the interfacial reaction from the viewpoint of thermodynamics as well as by the penetration or diffusion of Mg, Al and Si from the viewpoint of kinetics. In addition, the effects of the reaction and the evaporation of Mg on the movement of the triple line were examined. The spreading of the Al-Mg alloy on the SiO2 surface was mainly attributed to the formation of Mg2Si at the interface and the recession of the triple line to the diminishing Mg concentration in the alloy.

  10. First-principle simulation on the crystallization tendency and enhanced magnetization of Fe76B19P5 amorphous alloy

    NASA Astrophysics Data System (ADS)

    Wang, Yaocen; Zhang, Yan; Takeuchi, Akira; Makino, Akihiro; Liang, Yunye; Kawazoe, Yoshiyuki

    2015-01-01

    Iron-based amorphous alloys have attracted a growing interest due to their potential in the application of magnetic coil production. However, the magnetization of this kind of material is usually low due to the lack of long range ordering and high alloying element content. In this paper, an Fe76B19P5 amorphous alloy was simulated with ab initio molecular dynamics based on a previous simulation work on an Fe76Si9B10P5 amorphous alloy exhibiting that electron absorbers such as B and P can help enhance the magnetization of nearby Fe atoms. The present simulation results show that replacing Si with B can destabilize the amorphous structure, making it easier to crystallize, but no separate α-Fe participation can be observed in experiments during annealing due to its high B/P content. The results also show an increase in saturation magnetization by 8% can be expected due to the intensified electron transfer from Fe to B/P, and the glass forming ability decreases correspondingly. The idea of enhancing electron transfer can be applied to the development of other Fe-based amorphous alloys for the purpose of larger saturation magnetization.

  11. Computational study of structural change through the glass transition in an amorphous and liquid Zr-Ni alloy

    SciTech Connect

    Aihara, Tomoyasu Jr.; Aoki, Kiyoshi; Masumoto, Tsuyoshi )

    1993-04-15

    Amorphous alloys are experimentally or industrially produced by rapid quenching (RQ) from the melt. If a liquid alloy is rapidly cooled at a rate on the order of 10[sup 6]Ks[sup [minus]1], it enters the supercooled liquid regime and its viscosity increases. Finally, the system reaches a state of frozen random structure, which is called the amorphous state. In the attempt to control the properties of amorphous alloys, it is important to understand their structural changes through the glass transition. By a laboratory experiment, however, it is usually difficult to obtain information about the glass transition and supercooled state of an amorphous alloy because of competitive crystallization. Molecular dynamics (MD) simulation, a numerical experiment to solve the N-body problem of Newtonian mechanics, has been performed to investigate the structure of solid and liquid. As the MD simulation can be carried out on the order of picoseconds, one can detect the glass transition without crystallization during RQ. Thus, the authors performed the MD simulation for the production of an amorphous Zr-Ni alloy by RQ and detected static structure and thermodynamic changes through the glass transition. Both properties are related with interatomic potentials.

  12. Superconductivity of amorphous Mg 0.70Zn 0.30-xGa x alloys

    NASA Astrophysics Data System (ADS)

    Vora, Aditya M.

    2008-06-01

    The screening dependence theoretical investigations of the superconducting state parameters (SSP) viz. electron-phonon coupling strength λ, Coulomb pseudopotential μ∗, transition temperature TC , isotope effect exponent α and effective interaction strength NOV of five Mg 0.70Zn 0.30-xGa x ( x = 0.0, 0.06, 0.10, 0.15 and 0.20) ternary amorphous alloys viz. Mg 0.70Zn 0.30Ga 0.00, Mg 0.70Zn 0.24Ga 0.06, Mg 0.70Zn 0.20Ga 0.10, Mg 0.70Zn 0.15Ga 0.15 and Mg 0.70Zn 0.10Ga 0.20 have been reported for the first time using Ashcroft’s empty core (EMC) model potential. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used in the present investigation to study the screening influence on the aforesaid properties. It is observed that the electron-phonon coupling strength λ and the transition temperature TC are quite sensitive to the selection of the local field correction functions, whereas the Coulomb pseudopotential μ∗, isotope effect exponent α and effective interaction strength NOV show weak dependences on the local field correction functions. The transition temperature TC obtained from H-local field correction function is found in an excellent agreement with available experimental data. Quadratic TC equation has been proposed, which provide successfully the TC values of ternary amorphous alloys under consideration. Also, the present results are found in qualitative agreement with other such earlier reported data, which confirms the superconducting phase in the ternary amorphous alloys.

  13. Fim study on the relaxation and crystallization processes of a Cu-Zr amorphous alloy

    NASA Astrophysics Data System (ADS)

    H, Lu; Lu, Hua; D, S. Tang; Tang, Disheng; Y, Y. Xiong; Xiong, Yanyun

    1987-09-01

    The relaxation of the Cu-50at.%Zr amorphous alloy was revealed by FIM as a process of formation of clusters consisting of 2, 3, or 4 atoms, which afterwards migrate towards some definite centers, predominantly the quenched-in "embryos", to construct ordered structure. This dynamic picture, so far as we know, is observed for the first time. Crystallized regions were determined by atom-probe analysis as Cu10Zr7 phase, and the coexisting phase CuZr2 was not revealed simultaneously.

  14. Nanoscale order and crystallization in nitrogen-alloyed amorphous GeTe

    SciTech Connect

    Darmawikarta, Kristof; Abelson, John R.; Raoux, Simone; Bishop, Stephen G.

    2014-11-10

    The nanoscale order in amorphous GeTe thin films is measured using fluctuation transmission electron microscopy (FTEM). The order increases upon annealing at 145 °C, which indicates a coarsening of subcritical nuclei. This correlates with a reduction in the nucleation delay time in laser crystallization. A shift in the FTEM peak positions may indicate a transformation in local bonding. In samples alloyed with 12 at. % nitrogen, the order does not change upon annealing, the peak does not shift, and the nucleation time is longer. The FTEM data indicate that nitrogen suppresses the structural evolution necessary for the nucleation process and increases the thermal stability of the material.

  15. Measurements of the Barkhausen effect in FeCoB amorphous alloys

    NASA Astrophysics Data System (ADS)

    Durin, G.; Magni, A.; Bertotti, G.

    1996-07-01

    The Barkhausen noise of a wide series of amorphous Fe 85- xCo xB 15 alloys is studied. In spite of the great variability of their magnetic properties, the signal amplitude always follows the same type of distribution, while the power spectra show a 1/ω β behavior at high frequencies (with β = 1.5-2), with a transition to a 1/ω behavior at lower frequencies. This transition frequency is found to be strictly related to the parameter describing the amplitude distribution.

  16. High efficiency multijunction amorphous silicon alloy-based solar cells and modules

    SciTech Connect

    Guha, S.; Yang, J.; Banerjeee, A.; Glatfelter, T.; Hoffman, K.; Xu, X. )

    1994-06-30

    We have achieved initial efficiency of 11.4% as confirmed by National Renewable Energy Laboratory (NREL) on a multijunction amorphous silicon alloy photovoltaic module of one-square-foot-area. [bold This] [bold is] [bold the] [bold highest] [bold initial] [bold efficiency] [bold confirmed] [bold by] [bold NREL] [bold for] [bold any] [bold thin] [bold film] [bold photovoltaic] [bold module]. After light soaking for 1000 hours at 50 [degree]C under one-sun illumination, a module with initial efficiency of 11.1% shows a stabilized efficiency of 9.5%. Key factors that led to this high performance are discussed.

  17. Fe 65B 22Nd 9Mo 4 bulk nanocomposite permanent magnets produced by crystallizing amorphous precursors

    NASA Astrophysics Data System (ADS)

    Tao, Shan; Ahmad, Zubair; Ma, Tianyu; Jian, Hong; Jiang, Yinzhu; Yan, Mi

    2012-04-01

    The Fe65B22Nd9Mo4 nanocomposite permanent magnets in the form of a rectangular cross sectioned rod have been prepared by annealing the amorphous precursors. The thermal behavior, structure and magnetic properties of the magnets have been investigated by differential scanning calorimetry, X-ray diffractometry, electron microscopy and magnetometry techniques. The as-cast Fe65B22Nd9Mo4 alloy showed soft magnetic properties, which changed into magnetically hard after annealing. Results provoke that the magnetic properties of the alloy are sensitive to thermal processing conditions. The optimum hard magnetic properties with a remanence (Br) of 0.56 T, coercivity (iHc) of 920.7 kA/m and maximum energy product (BH)max of 50.15 kJ/m3 were achieved after annealing the alloy at 983 K for 10 min. The good magnetic properties of Fe65B22Nd9Mo4 magnets are ascribed to the exchange coupling between the nano-scaled soft α-Fe, Fe3B and hard Nd2Fe14B magnetic grains.

  18. Effect of the nanocrystallization of amorphous soft magnetic Fe-P-Nb alloys on corrosion resistance in a damp SO2-polluted atmosphere

    NASA Astrophysics Data System (ADS)

    Vavilova, V. V.; Zabolotnyi, V. T.; Korneev, V. P.; Anosova, M. O.; Baldokhin, Yu. V.

    2014-09-01

    The effect of the nanocrystallization of amorphous soft magnetic Fe-P-Nb alloys on their electrochemical behavior in a damp SO2-polluted industrial atmosphere is studied. It is shown that their electro-chemical characteristics shit toward positive values when the phosphorus content in the Fe-P-Nb alloys increases and when they undergo nanocrystallization from an amorphous state.

  19. Room-temperature amorphous alloy field-effect transistor exhibiting particle and wave electronic transport

    SciTech Connect

    Fukuhara, M.; Kawarada, H.

    2015-02-28

    The realization of room-temperature macroscopic field effect transistors (FETs) will lead to new epoch-making possibilities for electronic applications. The I{sub d}-V{sub g} characteristics of the millimeter-sized aluminum-oxide amorphous alloy (Ni{sub 0.36}Nb{sub 0.24}Zr{sub 0.40}){sub 90}H{sub 10} FETs were measured at a gate-drain bias voltage of 0–60 μV in nonmagnetic conditions and under a magnetic fields at room temperature. Application of dc voltages to the gate electrode resulted in the transistor exhibiting one-electron Coulomb oscillation with a period of 0.28 mV, Fabry-Perot interference with a period of 2.35 μV under nonmagnetic conditions, and a Fano effect with a period of 0.26 mV for Vg and 0.2 T under a magnetic field. The realization of a low-energy controllable device made from millimeter-sized Ni-Nb-Zr-H amorphous alloy throws new light on cluster electronics.

  20. Dynamic magnetic characteristics of Fe78Si13B9 amorphous alloy subjected to operating temperature

    NASA Astrophysics Data System (ADS)

    He, Aina; Wang, Anding; Yue, Shiqiang; Zhao, Chengliang; Chang, Chuntao; Men, He; Wang, Xinmin; Li, Run-Wei

    2016-06-01

    The operating temperature dependence of dynamic magnetic characteristics of the annealed Fe78Si13B9 amorphous alloy core was systematically investigated. The core loss, magnetic induction intensity and complex permeability of the amorphous core were analyzed by means of AC B-H loop tracer and impedance analyzer. It is found that the operating temperature below 403 K has little impact on core loss when the induction (B) is less than 1.25 T. As B becomes higher, core loss measured at high temperature becomes higher. For the cores measured at power frequency, the B at 80 A/m and the coercivity (Hc) at 1 T decline slightly as the temperature goes up. Furthermore, the real part of permeability (μ‧) increases with the rise of temperature. The imaginary part of permeability (μ″) maxima shifts to lower frequency side with increasing temperature, indicating the magnetic relaxation behavior in the sample. In addition, with the rise in the operating temperature of the annealed amorphous core, the relaxation time tends to increase.

  1. Amorphous structure and properties in laser-clad Ni-Cr-Al coating on Al-Si alloy

    NASA Astrophysics Data System (ADS)

    Liang, Gongying; Wong, T. T.; Su, J. Y.; Woo, C. H.

    1999-09-01

    A Ni-Cr-Al coating was clad by a 5 kW CO2 laser with different laser power on Al-Si alloy. Using transmission electron microscopy, a mixing microstructure containing Ni- based amorphous structures was observed in the laser clad zones. As the uniformity of chemical composition and temperature is poor in the laser cladding, the amorphous structure with some Ni3Al crystals coexisted in the cladding. According to the morphologies of Ni-based amorphous structures, the amorphous structure existed not only in the net-like boundaries surrounding the granular structure but also in the granular structure. The microhardness of the mixture amorphous structure is between HV 600 - 800, which is lower than that of crystal phases in the coating. A differential thermal analysis showed that Ni- based amorphous structure exhibits a higher initial crystallizing temperature (about 588 degree(s)C), which is slightly higher than that of the eutectic temperature of Al- Si alloy. The wear experimental results showed that some amorphous structure exist in the laser cladding can reduce the peeling of the granular phases from matrix, and improve the its wear resistance.

  2. Core level shifts in Cu-Pd alloys as a function of bulk composition and structure

    NASA Astrophysics Data System (ADS)

    Boes, Jacob R.; Kondratyuk, Peter; Yin, Chunrong; Miller, James B.; Gellman, Andrew J.; Kitchin, John R.

    2015-10-01

    CuPd alloys are important materials in hydrogen purification, where they are used as dense Pd-based separation membranes. Cu is added to impart sulfur tolerance and improved mechanical properties. At intermediate compositions and T < 873 K, a BCC alloy (B2) phase occurs, which has superior separation characteristics to those of the FCC phases that form at high Cu and high Pd compositions. Identifying the composition and temperature window where the B2 phase forms is a critical need to enable the design of improved alloys. A composition spread alloy film of Cu and Pd was synthesized. The film was characterized by electron back scatter diffraction and X-ray photoelectron spectroscopy, providing the core level shifts as a function of bulk composition and bulk structure. An anomalous deviation in the Cu core level shift was observed in the composition range 0.33 < xPd < 0.55 over which the B2 phase occurs. Density functional theory calculations were used to simulate core level shifts in the FCC and B2 alloy structures. They suggest that the anomalous deviation in core level shift is due to formation of the ordered B2 phase in this composition range.

  3. Unified picture of spin-dependent transport in GMR multilayered structures and bulk ferromagnetic alloys

    NASA Astrophysics Data System (ADS)

    Schroeder, P. A.; Holody, P.; Loloee, R.; Vouille, C.; Barthelemy, A.; Fert, A.; Hsu, S. Y.

    1998-01-01

    We have observed a positive (inverse) CPP-MR in magnetic multilayers of the forms: (a) ( XY/Cu/Co/Cu) n with XY being the alloys FeCr, FeV, NiCr, CoCr, and (b) (Z/Cr/NiFe/Cr) n with Z = Fe and Co. For (a) the inverted results arise primarily from spin-dependent scattering in the bulk of the alloy, and are linked consistently to: (1) their magnetization; (2) band-structure calculations and (3) resistivity of bulk alloys. For (b) samples, the inverse MRs arise primarily from the scattering at the Fe/Cr and Co/Cr interfaces. Inverse MR for X/Y interfaces and XY alloys (eg. Fe/Cr and FeCr) arises from the similarity of the matching problem of X and Y d levels at interfaces and in alloys. For all XY the CIP-MR was negative, confirming that CIP-MR is strongly influenced by channeling effect and current inhomogenieties.

  4. Nano-crystallization and magnetic mechanisms of Fe85Si2B8P4Cu1 amorphous alloy by ab initio molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Wang, Yaocen; Takeuchi, Akira; Makino, Akihiro; Liang, Yunye; Kawazoe, Yoshiyuki

    2014-05-01

    Iron-based amorphous and nano-crystalline alloys have attracted a growing interest due to their potential in the application of magnetic coil production. However, fundamental understanding of the nano-crystallization mechanisms and magnetic features in the amorphous structure are still lack of knowledge. In the present work, we performed ab initio molecular dynamics simulation to clarify the ionic and electronic structure in atomic scale, and to derive the origin of the good magnetic property of Fe85Si2B8P4Cu1 amorphous alloy. The simulation gave a direct evidence of the Cu-P bonding preference in the amorphous alloy, which may promote nucleation in nano-crystallization process. On the other hand, the electron transfer and the band/orbital features in the amorphous alloy suggests that alloying elements with large electronegativity and the potential to expand Fe disordered matrix are preferred for enhancing the magnetization.

  5. Small Angle Neutron Scattering with Hydrogenated Amorphous Cu50 Ti50 and Ni-Ti-Si Alloys

    NASA Astrophysics Data System (ADS)

    Lamparter, P.; Boucher, B.

    1993-11-01

    The metallic glasses Cu50Ti50, Ni30Ti60Si10, Ni32Ti52Si16 , Ni16Ti68Si16 and Ti84Si16 were produced by melt spinning. The alloys in the blank state as well as after loading with hydrogen or deuterium were investigated by small angle neutron (SANS) and X-ray (SAXS) scattering. The scattering of the different amorphous alloys exhibited common features. SANS follows a power-law with exponent of the scattering vector between -3 and -4. The melt-spun glasses contain extended structural inhomogeneities which are associated rather with the local composition than with the local density. SAXS measurements did not show effects above the background level. Loading the alloys with hydrogen or deuterium causes strong effects in the SANS behaviour. From the results it is concluded that the amorphous alloys contain inner surfaces where the hydrogen atoms segregate.

  6. Anomalous small angle x-ray scattering studies of amorphous metal-germanium alloys

    SciTech Connect

    Rice, M.

    1993-12-01

    This dissertation addresses the issue of composition modulation in sputtered amorphous metal-germanium thin films with the aim of understanding the intermediate range structure of these films as a function of composition. The investigative tool used in this work is anomalous small-angle X-ray scattering (ASAXS). The primary focus of this investigation is the amorphous iron-germanium (a-Fe{sub x}Ge{sub 100-x}) system with particular emphasis on the semiconductor-rich regime. Brief excursions are made into the amorphous tungsten-germanium (a-W{sub x}Ge{sub 100-x}) and the amorphous molybdenum-germanium (a-Mo{sub x}Ge{sub 100-x}) systems. All three systems exhibit an amorphous structure over a broad composition range extending from pure amorphous germanium to approximately 70 atomic percent metal when prepared as sputtered films. Across this composition range the structures change from the open, covalently bonded, tetrahedral network of pure a-Ge to densely packed metals. The structural changes are accompanied by a semiconductor-metal transition in all three systems as well as a ferromagnetic transition in the a-Fe{sub x}Ge{sub 100-x} system and a superconducting transition in the a-Mo{sub x}Ge{sub 100-x} system. A long standing question, particularly in the a-Fe{sub x}Ge{sub 100-x} and the a-Mo{sub x}Ge{sub 100-x} systems, has been whether the structural changes (and therefore the accompanying electrical and magnetic transitions) are accomplished by homogeneous alloy formation or phase separation. The application of ASAXS to this problem proves unambiguously that fine scale composition modulations, as distinct from the simple density fluctuations that arise from cracks and voids, are present in the a-Fe{sub x}Ge{sub 100-x}, a-W{sub x}Ge{sub 100-x}, and a-Mo{sub x}Ge{sub 100-x} systems in the semiconductor-metal transition region. Furthermore, ASAXS shows that germanium is distributed uniformly throughout each sample in the x<25 regime of all three systems.

  7. Prediction of Failure Due to Thermal Aging, Corrosion and Environmental Fracture in Amorphous and Titanium Alloys

    SciTech Connect

    Farmer, J C

    2003-04-15

    DARPA is exploring a number of advanced materials for military applications, including amorphous metals and titanium-based alloys. Equipment made from these materials can undergo degradation due to thermal aging, uniform corrosion, pitting, crevice corrosion, denting, stress corrosion cracking, corrosion fatigue, hydrogen induced cracking and microbial influenced corrosion. Amorphous alloys have exceptional resistance to corrosion, due in part to the absence of grain boundaries, but can undergo crystallization and other phase instabilities during heating and welding. Titanium alloys are extremely corrosion resistant due to the formation of a tenacious passive film of titanium oxide, but is prone to hydrogen absorption in crevices, and hydrogen induced cracking after hydrogen absorption. Accurate predictions of equipment reliability, necessary for strategic planning, requires integrated models that account for all relevant modes of attack, and that can make probabilistic predictions. Once developed, model parameters must be determined experimentally, and the validity of models must be established through careful laboratory and field tests. Such validation testing requires state-of-the-art surface analytical techniques, as well as electrochemical and fracture mechanics tests. The interaction between those processes that perturb the local environment on a surface and those that alter metallurgical condition must be integrated in predictive models. The material and environment come together to drive various modes of corrosive attack (Figure 1). Models must be supported through comprehensive materials testing capabilities. Such capabilities are available at LLNL and include: the Long Term Corrosion Test Facility (LTCTF) where large numbers of standard samples can be exposed to realistic test media at several temperature levels; a reverse DC machine that can be used to monitor the propagation of stress corrosion cracking (SCC) in situ; and banks of potentiostats with

  8. Formation of Pu amorphous alloys or metastable structures in Pu-Fe, Pu-Ta, and Pu-Si alloys

    SciTech Connect

    Rizzo, H.F.; Echeverria, A.W.

    1985-08-20

    Sputter deposition technique was used to study the possible formation of amorphous structures in Pu-Fe, Pu-Ta, and Pu-Si systems. A triode sputtering system was used to prepare sputtered coatings: 13 to 59 at. % (a/o) Fe, 10 to 50 a/o Si, and 15 to 65 a/o Ta. Structure of the coatings was determined by x-ray diffraction techniques. The temperature stability of the obtained structures was determined by Differential Scanning Calorimetry (DSC) measurements. The Pu-Fe and Pu-Si binary systems showed strong evidence for the formation of amorphous phases in the sputtered coatings. X-ray analyses indicated the presence of Pu6Fe in the 13 to 20 a/o Fe range of Pu-Fe alloys and no apparent crystalline phases over the entire 10 to 50 a/o Si range of Pu-Si alloys. In the Pu-Ta system, the DSC data obtained for compositions below 50 a/o Ta did not show typical crystallization exotherms. At compositions above 50 a/o Ta, a metastable bcc alpha Ta structure was observed with an expanded lattice parameter. The calculated volume expansion (2.9%) corresponds to 29 a/o of Pu in solid solution if the lattice parameter is assumed to follow Vegards Law. After storage in a nitrogen glovebox atmosphere for over two years, the Pu-Si and Pu-Ta coatings have maintained a metallic luster and have shown no visible evidence of surface oxidation.

  9. Bulk metallic glass formation in Zr-Cu-Fe-Al alloys

    SciTech Connect

    Jin Kaifeng; Loeffler, Joerg F.

    2005-06-13

    We have discovered a series of bulk metallic glass-forming alloys of composition (Zr{sub x}Cu{sub 100-x}){sub 80}(Fe{sub 40}Al{sub 60}){sub 20} with x=68-77 and have investigated them by x-ray diffraction, small-angle neutron scattering, and differential scanning calorimetry. All of these alloys exhibit a calorimetric glass transition temperature of 670 Kalloy Zr{sub 58}Cu{sub 22}Fe{sub 8}Al{sub 12}. In rod shape this alloy has a critical casting thickness of 13 mm, as verified by detailed casting experiments, while alloys with x=68 and 77 can still be cast to a thickness of 5 mm. Furthermore, the region where glassy samples with a thickness of 0.5 mm can be prepared extends from x=62-81. The best glass-former, Zr{sub 58}Cu{sub 22}Fe{sub 8}Al{sub 12}, has a tensile yield strength of 1.71 GPa and shows an elastic limit of 2.25%. This new class of Ni-free Zr-based alloys is potentially very interesting for biomedical applications.

  10. Nickel Alloy Primary Water Bulk Surface and SCC Corrosion Film Analytical Characterization and SCC Mechanistic Implications

    SciTech Connect

    Morton, D.; Lewis, N.; Hanson, M.; Rice, S.; Sanders, P.

    2007-04-18

    Alloy 600 corrosion coupon tests were performed: (1) to quantify the temperature dependency of general corrosion and (2) to characterize the composition and structure of bulk surface corrosion films for comparison with ongoing primary water SCC (PWSCC) crack tip corrosion film analyses. Results suggest that the thermal activation energy of Alloy 600 corrosion is consistent with the thermal activation energy of nickel alloy PWSCC. Analytical investigations of the structure and composition of Alloy 600 bulk surface corrosion oxides revealed a duplex (inner and outer) oxide layer structure. The outer layer is discontinuous and comprised of relatively large (1 to 3 {micro}m) nickel ferrite crystals and smaller ({approx}0.1 {micro}m) chromium containing nickel ferrite crystals. The inner layer consists of a relatively continuous chromite spinel (major phase) and chromia (Cr{sub 2}O{sub 3} minor phase) which formed through non-selective oxidation. Chromia and dealloyed Alloy 600 (highly Ni enriched metal) were only observed at 337 C (640 F) and only along the boundaries of deformation induced fine grains and subcells. Specimens having deformation free surfaces exhibited continuous uniform inner chromite spinel oxide layers. Specimens with machining induced surface deformation produced non-uniform inner layer oxides (chromite spinel, Cr{sub 2}O{sub 3} and unoxidized material). PWSCC crack tip oxides, in contrast, were fine grain (no duplex structure) and consisted of both chromium rich spinels and ''NiO'' structure oxides. Generally, nickel rich oxides were more abundant under more oxidized conditions (reduced coolant hydrogen) and spinel rich crack tip oxides were favored under more reducing conditions (increased coolant hydrogen). Bulk surface corrosion film thickness did not correlate with observed SCC growth rates. These results suggest that corrosion is not the rate controlling step of PWSCC but rather that PWSCC and corrosion have a common rate controlling sub

  11. Bulk glassy Cu-based alloys with a large supercooled liquid region of 110 K

    NASA Astrophysics Data System (ADS)

    Inoue, Akihisa; Zhang, Wei

    2003-09-01

    The replacement of Cu by 5%Ag for Cu50Hf45Al5 glassy alloy was found to increase significantly the stability of supercooled liquid against crystallization. The supercooled liquid region reached as large as 110 K for Cu45Hf45Al5Ag5. The extension of the supercooled liquid region is due to an increase in the crystallization temperature, accompanying the change in the primary crystalline phases. The effectiveness of Ag addition was interpreted to result from the retardation of long-range atomic rearrangements for the progress of crystallization reaction. The selection of the quaternary composition enabled us to form bulk glassy alloys with diameters up to 3 mm. The Young's modulus and compressive fracture strength of the 5%Ag-containing alloy are 119 GPa and 2220 MPa, respectively.

  12. Local structure of amorphous GaN{sub 1-x}As{sub x} semiconductor alloys across the composition range

    SciTech Connect

    Levander, A. X.; Dubon, O. D.; Wu, J.; Yu, K. M.; Liliental-Weber, Z.; Walukiewicz, W.; Novikov, S. V.; Foxon, C. T.

    2013-06-28

    Typically only dilute (up to {approx}10%) highly mismatched alloys can be grown due to the large differences in atomic size and electronegativity of the host and the alloying elements. We have overcome the miscibility gap of the GaN{sub 1-x}As{sub x} system using low temperature molecular beam epitaxy. In the intermediate composition range (0.10 < x < 0.75), the resulting alloys are amorphous. To gain a better understanding of the amorphous structure, the local environment of the As and Ga atoms was investigated using extended x-ray absorption fine structure (EXAFS). The EXAFS analysis shows a high concentration of dangling bonds compared to the crystalline binary endpoint compounds of the alloy system. The disorder parameter was larger for amorphous films compared to crystalline references, but comparable with other amorphous semiconductors. By examining the Ga local environment, the dangling bond density and disorder associated with As-related and N-related bonds could be decoupled. The N-related bonds had a lower dangling bond density and lower disorder.

  13. Synthesis and characterization of Mg-based amorphous alloys and their use for decolorization of Azo dyes

    NASA Astrophysics Data System (ADS)

    Iqbal, M.; Wang, W. H.

    2014-06-01

    Mg-based alloys are light weight and have wide range of applications in the automotive industry. These alloys are widely used because of their very attractive physical and mechanical properties and corrosion resistance. The properties and applications can be further improved by changing the nature of materials from crystalline to amorphous. In this study, melt spun ribbons (MSRs) of Mg70Zn25Ca5 Mg68Zn27Ca5 alloys were prepared by melt spinning technique by using 3-4N pure metals. Characterization of the samples was done by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and energy dispersive x-ray analyzer (EDAX). Microstructural investigations were conducted by using scanning electron microscopy (SEM), atomic force microscopy (AFM) as well as optical and stereo scan microscopy techniques. DSC results showed multistage crystallization. Activation energy was found to be 225 kJ/mol by Kissinger method indicating good thermal stability against crystallization. XRD, DSC, SEM and EDS (energy dispersive spectroscopy) results are agreed very well. In order to study decolorization, the MSRs of Mg70Zn25Ca5 Mg68Zn27Ca5 alloys were treated repeatedly with various azo dyes at room temperature. In order to compare the results, MSRs of amorphous Zr- and Ni-based metallic glasses were also treated. Reaction of MSRs with azo dyes results in their decolorization in a few hours. Decolorization of azo dyes takes place by introducing amorphous MSRs which results in breaking the -N=N- bonds that exist in dye contents. It is concluded that Mg-based alloys are useful for paint and dye industries and will be beneficial to control water pollution. Comparison of results showed that Mg-based alloys are more efficient than Zr- and Ni-based amorphous alloys for decolorization of azo dyes.

  14. Ab Initio Modeling of Bulk and Intragranular Diffusion in Ni Alloys

    SciTech Connect

    Alexandrov, Vitali Y.; Sushko, Maria L.; Schreiber, Daniel K.; Bruemmer, Stephen M.; Rosso, Kevin M.

    2015-05-07

    importance for understanding mechanisms of grain boundary (GB) oxidation causing environmental degradation and cracking of Ni-base structural alloys. In this study, first-principles calculations of vacancy-mediated diffusion are performed across a wide series of alloying elements commonly used in Ni-based superalloys, as well as interstitial diffusion of atomic oxygen and sulfur in the bulk, at the (111) surface, <110> symmetric tilt GBs of Ni corresponding to model low- (Σ=3/(111)) and high-energy (Σ=9/(221)) GBs. A substantial enhancement of diffusion is found for all species at the high-energy GB as compared to the bulk and the low-energy GB, with Cr, Mn and Ti exhibiting remarkably small activation barriers (<0.1 eV; ~10 times lower than in the bulk). Calculations also show that the bulk diffusion mechanism and kinetics differ for oxygen and sulfur, with oxygen having a faster mobility and preferentially diffusing through the tetrahedral interstitial sites in Ni matrix where it can be trapped in a local minimum.

  15. Ab Initio Modeling of Bulk and Intragranular Diffusion in Ni Alloys.

    PubMed

    Alexandrov, Vitaly; Sushko, Maria L; Schreiber, Daniel K; Bruemmer, Stephen M; Rosso, Kevin M

    2015-05-01

    Knowledge of solid-state and interfacial species diffusion kinetics is of paramount importance for understanding mechanisms of grain boundary (GB) oxidation causing environmental degradation and cracking of Ni-base structural alloys. In this study, first-principles calculations of vacancy-mediated diffusion are performed across a wide series of alloying elements commonly used in Ni-based superalloys, as well as interstitial diffusion of atomic oxygen and sulfur in the bulk, at the (111) surface, ⟨110⟩ symmetric tilt GBs of Ni corresponding to model low- (Σ = 3/(111)) and high-energy (Σ = 9/(221)) GBs. A substantial enhancement of diffusion is found for all species at the high-energy GB as compared with the bulk and the low-energy GB, with Cr, Mn, and Ti exhibiting remarkably small activation barriers (<0.1 eV; ~10 times lower than in the bulk). Calculations also show that the bulk diffusion mechanism and kinetics differ for oxygen and sulfur, with oxygen having a faster mobility and preferentially diffusing through the tetrahedral interstitial sites in Ni matrix, where it can be trapped in a local minimum. PMID:26263324

  16. Electronegativity calculation of bulk modulus and band gap of ternary ZnO-based alloys

    SciTech Connect

    Li, Keyan; Kang, Congying; Xue, Dongfeng; State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022

    2012-10-15

    In this work, the bulk moduli and band gaps of M{sub x}Zn{sub 1−x}O (M = Be, Mg, Ca, Cd) alloys in the whole composition range were quantitatively calculated by using the electronegativity-related models for bulk modulus and band gap, respectively. We found that the change trends of bulk modulus and band gap with an increase of M concentration x are same for Be{sub x}Zn{sub 1−x}O and Cd{sub x}Zn{sub 1−x}O, while the change trends are reverse for Mg{sub x}Zn{sub 1−x}O and Ca{sub x}Zn{sub 1−x}O. It was revealed that the bulk modulus is related to the valence electron density of atoms whereas the band gap is strongly influenced by the detailed chemical bonding behaviors of constituent atoms. The current work provides us a useful guide to compositionally design advanced alloy materials with both good mechanical and optoelectronic properties.

  17. Effect of chemically active medium on frequency dependence of magnetic losses in soft magnetic Fe-based amorphous alloys

    NASA Astrophysics Data System (ADS)

    Skulkina, N. A.; Ivanov, O. A.; Stepanova, E. A.; Pavlova, I. O.

    2013-03-01

    The effects of the electrolytic hydrogenation and oxidation and of the interaction of the surface ribbon with water and vapor on the frequency dependence of magnetic losses per magnetization-reversal cycle are studied based on the example of soft magnetic Fe81B13Si4C2 amorphous alloy, which exhibits a positive saturation magnetostriction. It was shown that, after the hydrogenation and oxidation of soft magnetic amorphous alloys, their frequency dependences of magnetic losses per magnetization-reversal cycle, which are reduced to unit induction, exhibit groups of hydrogen- and oxygen-related peaks in the frequency ranges of 35-55 and 55-80 Hz, which can be explained by the formation of O- A and H- A atomic pairs (where A are atoms of alloy components) and their reorientation in a magnetic field in the course of magnetization reversal at certain frequencies. The formation of analogous groups of peaks for samples of soft magnetic Fe-based amorphous alloys was observed after the interaction of the ribbon surface with water and vapor and after heat treatment in air. This fact confirms the possibility of the hydrogenation and oxidation of the alloys during the aforementioned processes.

  18. General laws of the effect of hydrogen on the crystallization of amorphous alloys based on the quasi-binary TiNi-TiCu system

    NASA Astrophysics Data System (ADS)

    Spivak, L. V.; Shelyakov, A. V.; Shchepina, N. E.

    2014-02-01

    The crystallization processes that occur during heating of hydrogen-containing melt-quenched alloys based on the quasi-binary TiNi-TiCu system alloyed with aluminum, iron, hafnium, and zirconium are studied by high-resolution differential scanning calorimetry. The general laws of the transition of the hydrogen-containing alloys from an amorphous into a crystalline state are determined.

  19. Amorphous and nanocrystalline phase formation in highly-driven Al-based binary alloys

    SciTech Connect

    Kalay, Yunus Eren

    2009-01-01

    Remarkable advances have been made since rapid solidification was first introduced to the field of materials science and technology. New types of materials such as amorphous alloys and nanostructure materials have been developed as a result of rapid solidification techniques. While these advances are, in many respects, ground breaking, much remains to be discerned concerning the fundamental relationships that exist between a liquid and a rapidly solidified solid. The scope of the current dissertation involves an extensive set of experimental, analytical, and computational studies designed to increase the overall understanding of morphological selection, phase competition, and structural hierarchy that occurs under far-from equilibrium conditions. High pressure gas atomization and Cu-block melt-spinning are the two different rapid solidification techniques applied in this study. The research is mainly focused on Al-Si and Al-Sm alloy systems. Silicon and samarium produce different, yet favorable, systems for exploration when alloyed with aluminum under far-from equilibrium conditions. One of the main differences comes from the positions of their respective T0 curves, which makes Al-Si a good candidate for solubility extension while the plunging T0 line in Al-Sm promotes glass formation. The rapidly solidified gas-atomized Al-Si powders within a composition range of 15 to 50 wt% Si are examined using scanning and transmission electron microscopy. The non-equilibrium partitioning and morphological selection observed by examining powders at different size classes are described via a microstructure map. The interface velocities and the amount of undercooling present in the powders are estimated from measured eutectic spacings based on Jackson-Hunt (JH) and Trivedi-Magnin-Kurz (TMK) models, which permit a direct comparison of theoretical predictions. For an average particle size of 10 {micro}m with a Peclet number of ~0.2, JH and TMK deviate from

  20. Coercivity of domain wall motion in thin films of amorphous rare earth-transition metal alloys

    NASA Technical Reports Server (NTRS)

    Mansuripur, M.; Giles, R. C.; Patterson, G.

    1991-01-01

    Computer simulations of a two dimensional lattice of magnetic dipoles are performed on the Connection Machine. The lattice is a discrete model for thin films of amorphous rare-earth transition metal alloys, which have application as the storage media in erasable optical data storage systems. In these simulations, the dipoles follow the dynamic Landau-Lifshitz-Gilbert equation under the influence of an effective field arising from local anisotropy, near-neighbor exchange, classical dipole-dipole interactions, and an externally applied field. Various sources of coercivity, such as defects and/or inhomogeneities in the lattice, are introduced and the subsequent motion of domain walls in response to external fields is investigated.

  1. Tracer diffusion of /sup 60/Co and /sup 63/Ni in amorphous NiZr alloy

    SciTech Connect

    Hoshino, K.; Averback, R.S.; Hahn, H.; Rothman, S.J.

    1987-01-01

    Tracer diffusion of /sup 60/Co and /sup 63/Ni in equiatomic amorphous NiZr alloy in the temperature range between 486 and 641/sup 0/K can be described by: D/sub Co/sup */ = 3.7 x 10/sup -7/ exp(-(135 +- 14) kJ mole/sup -1//RT) m/sup 2//sec and D/sub Ni//sup */ = 1.7 x 10/sup -7/ exp(-(140 +- 9) kJ mole/sup -1//RT) m/sup 2//sec. The values of D/sub Ni//sup */ are in reasonable agreement with those measured by the Rutherford backscattering technique. The measured diffusivities were independent of time, indicating that no relaxation took place during diffusion. 27 refs., 2 tabs.

  2. High-field magnetization measurements on a ferromagnetic amorphous alloy from 295 to 5K

    SciTech Connect

    Szymczak, P. ); Graham, C.D. Jr. ); Gibbs, M.R.J. )

    1994-11-01

    Magnetization measurements on an amorphous ferromagnetic alloy Fe[sub 78](SiB)[sub 22] have been made over the temperature range from 5 to 295K and in fields to 5T, using a SQUID magnetometer and a superconducting magnet. As-received and field-annealed samples were measured. Having data over a range of temperatures allows the spin-wave contribution to the magnetization to be determined, and then subtracted. When the spin-wave contribution is removed, a substantial high-field susceptibility remains, which is independent of temperature. Attempts to fit the corrected curves to one of two theoretical equations were not conclusive, but the best fit seems to be to M = M[sub 0] + aH[sup [minus]0.5] + bH. The annealing treatment has no significant effect on the high-field magnetization.

  3. Amorphous and nanocrystalline phase formation in highly-driven aluminum-based binary alloys

    NASA Astrophysics Data System (ADS)

    Kalay, Yunus Eren

    Remarkable advances have been made since rapid solidification was first introduced to the field of materials science and technology. New types of materials such as amorphous alloys and nanostructure materials have been developed as a result of rapid solidification techniques. While these advances are, in many respects, ground breaking, much remains to be discerned concerning the fundamental relationships that exist between a liquid and a rapidly solidified solid. The scope of the current dissertation involves an extensive set of experimental, analytical, and computational studies designed to increase the overall understanding of morphological selection, phase competition, and structural hierarchy that occurs under far-from equilibrium conditions. High pressure gas atomization and Cu-block melt-spinning are the two different rapid solidification techniques applied in this study. The research is mainly focused on Al-Si and Al-Sm alloy systems. Silicon and samarium produce different, yet favorable, systems for exploration when alloyed with aluminum under far-from equilibrium conditions. One of the main differences comes from the positions of their respective T0 curves, which makes Al-Si a good candidate for solubility extension while the plunging T0 line in Al-Sm promotes glass formation. The rapidly solidified gas-atomized Al-Si powders within a composition range of 15 to 50 wt% Si are examined using scanning and transmission electron microscopy. The non-equilibrium partitioning and morphological selection observed by examining powders at different size classes are described via a microstructure map. The interface velocities and the amount of undercooling present in the powders are estimated from measured eutectic spacings based on Jackson-Hunt (JH) and Trivedi-Magnin-Kurz (TMK) models, which permit a direct comparison of theoretical predictions. For an average particle size of 10 microm with a Peclet number of ~0.2, JH and TMK deviate from each other. This deviation

  4. Advances in amorphous silicon alloy-based multijunction cells and modules

    SciTech Connect

    Guha, S.; Yang, J.; Banerjee, A.; Glatfelter, T.; Xu, X. )

    1992-12-01

    Multijunction amorphous silicon alloy-based solar cells and modules offer the potential of obtaining high efficiency with long-term stability against light-induced degradation. We have studied the stability of the component cells of the multijunction devices prepared under different deposition conditions. We observe a definite correlation between the microstructure of the intrinsic material and initial and light-degraded performance of the cells. Using suitable deposition conditions and optimum matching of the component cells, we have fabricated double-junction dual-bandgap cells which show stabilized active-area efficiency of 11% after 600 hours of one-sun illumination at 50 [degree]C. Double-junction and triple-junction modules of 900 cm[sup 2] area have been fabricated, and the performance of these panels will be discussed.

  5. Intensity dependence of the minority-carrier difusion length in amorphous silicon based alloys

    NASA Astrophysics Data System (ADS)

    Hack, M.; Shur, M.

    1984-04-01

    Many of the recent measurements of the minority-carrier diffusion length (Lp) in amorphous silicon based alloys have been based on a utilization of the surface photovoltage (SPV). In this case an equation relating photon flux and Lp under ideal conditions has to be modified because of the back diffusion of carriers and the effects of high field regions. To account for the high field region, the 'aparent' diffusion length has been determined for varying intensities of bias light. In the present investigation, a theoretical analysis shows that the zero field diffusion length is indeed intensity dependent and that this dependence can be directly related to the slope of the density of states near the valence band edge. The intensity dependence of the minority carrier diffusion length and the energy slope of the density of states near the valence band edge are obtained on the basis of experimental results.

  6. First-principles study of the structural and dynamic properties of the liquid and amorphous Li-Si alloys

    NASA Astrophysics Data System (ADS)

    Chiang, Han-Hsin; Lu, Jian-Ming; Kuo, Chin-Lung

    2016-01-01

    We have performed density functional theory calculations and ab initio molecular dynamics to investigate the structures and dynamic properties of the liquid and amorphous LixSi alloys over a range of composition from x = 1.0 - 4.8. Our results show that Si atoms can form a variety of covalently bonded polyanions with diverse local bonding structures in the liquid alloys. Like in c-LiSi, Si atoms can form a continuous bond network in liquid Li1.0Si at 1050 K, while it gradually disintegrates into many smaller Si polyanions as the Li content increases in the alloys. The average sizes of Si polyanions in these liquid alloys were found to be relatively larger than those in their crystalline counterparts, which can even persist in the highly lithiated Li4.81Si alloy at 1500 K. Our results also show that amorphous LixSi alloys have similar local bonding structures but a largely increased short-range order as compared to their liquid counterparts. The differences between the average coordination number of each atomic pair in amorphous solids and that in the liquids are less than 1.1. Furthermore, our calculations reveal that Li and Si atoms can exhibit very distinct dynamic behaviors in the liquids and their diffusivities appear to be largely dependent on the chemical composition of the alloys. The diffusivity of Li was found to increase with the Li content in the alloys primarily because of the reduced interactions between Li and Si atoms, while the Si diffusivity also increases due to the gradual disintegration of the strongly interconnected Si bond network. The diffusivity of Li in amorphous LixSi was predicted to lie in the range between 10-7 and 10-9 cm2/s at 300 K, which is more than 20-fold larger than that of Si over the composition range considered. Our calculations further show that the diffusivities of both Li and Si can increase by two orders of magnitude as x increases from 1.0 to 3.57 in amorphous LixSi, indicating a more profound dependence on the alloy

  7. First-principles study of the structural and dynamic properties of the liquid and amorphous Li-Si alloys.

    PubMed

    Chiang, Han-Hsin; Lu, Jian-Ming; Kuo, Chin-Lung

    2016-01-21

    We have performed density functional theory calculations and ab initio molecular dynamics to investigate the structures and dynamic properties of the liquid and amorphous LixSi alloys over a range of composition from x = 1.0 - 4.8. Our results show that Si atoms can form a variety of covalently bonded polyanions with diverse local bonding structures in the liquid alloys. Like in c-LiSi, Si atoms can form a continuous bond network in liquid Li1.0Si at 1050 K, while it gradually disintegrates into many smaller Si polyanions as the Li content increases in the alloys. The average sizes of Si polyanions in these liquid alloys were found to be relatively larger than those in their crystalline counterparts, which can even persist in the highly lithiated Li4.81Si alloy at 1500 K. Our results also show that amorphous LixSi alloys have similar local bonding structures but a largely increased short-range order as compared to their liquid counterparts. The differences between the average coordination number of each atomic pair in amorphous solids and that in the liquids are less than 1.1. Furthermore, our calculations reveal that Li and Si atoms can exhibit very distinct dynamic behaviors in the liquids and their diffusivities appear to be largely dependent on the chemical composition of the alloys. The diffusivity of Li was found to increase with the Li content in the alloys primarily because of the reduced interactions between Li and Si atoms, while the Si diffusivity also increases due to the gradual disintegration of the strongly interconnected Si bond network. The diffusivity of Li in amorphous LixSi was predicted to lie in the range between 10(-7) and 10(-9) cm(2)/s at 300 K, which is more than 20-fold larger than that of Si over the composition range considered. Our calculations further show that the diffusivities of both Li and Si can increase by two orders of magnitude as x increases from 1.0 to 3.57 in amorphous LixSi, indicating a more profound dependence on the

  8. Determination of local atomic arrangements in a bulk-immiscible surface alloy

    NASA Astrophysics Data System (ADS)

    Witkowski, Kristine Rose

    Surface alloys are two-dimensional phases confined to near-surface regions, and are known to form from atomic species that are immiscible in the bulk. In order to achieve a better understanding of this phenomenon, it is necessary to be able to accurately determine the bond lengths present within the surface alloy. The present work focuses on surface alloying in the bulk-immiscible Au-Ni system, which forms surface alloy phases that are amongst the most studied to date. First principles electronic density functional theory calculations were conducted for both "monomer" (single Au atom), and "dimer" (pair of Au atoms) surface alloying models for the Au-Ni(110) surface. Both of the models exhibited surface interlayer contractions and expansions similar to those reported for a Ni(110) surface. The resulting atomic positions corresponded to Au-Ni bond lengths of 2.61-2.80 A in the monomer model and 2.54-2.84 A in the dimer model. Surface extended x-ray absorption fine structure (SEXAFS) measurements were taken from Au-Co11Ni89(110) surface alloys. The software program FEFF8 was used in combination with the first principles calculated atomic positions for the surface alloy models to simulate the SEXAFS from each of the surface alloy models. Fits were conducted from these models resulting in the determination of Au-Ni bond lengths of 2.55-2.74 A with the monomer model, and 2.46-2.76 A with the dimer model. The present work features the first theoretical first principles study of all of the sub-monolayer structures of the Au-Ni(110) system. This work was also the first to employ DFT calculated atomic positions as initial models for simulating theoretical SEXAFS spectra to assist in the fitting of experimental measurements. In doing this, the theoretical calculations allowed for a much better starting point in the fits, while the results from the fits gave an indication to the strengths and weaknesses of the surface calculations, since they highlighted an apparent slight

  9. Highly mismatched crystalline and amorphous GaN(1-x)As(x) alloys in the whole composition range

    SciTech Connect

    Yu, K. M.; Novikov, S. V.; Broesler, R.; Demchenko, I. N.; Denlinger, J. D.; Liliental-Weber, Z.; Luckert, F.; Martin, R. W.; Walukiewicz, W.; Foxon, C. T.

    2009-08-29

    Alloying is a commonly accepted method to tailor properties of semiconductor materials for specific applications. Only a limited number of semiconductor alloys can be easily synthesized in the full composition range. Such alloys are, in general, formed of component elements that are well matched in terms of ionicity, atom size, and electronegativity. In contrast there is a broad class of potential semiconductor alloys formed of component materials with distinctly different properties. In most instances these mismatched alloys are immiscible under standard growth conditions. Here we report on the properties of GaN1-xAsx, a highly mismatched, immiscible alloy system that was successfully synthesized in the whole composition range using a nonequilibrium low temperature molecular beam epitaxy technique. The alloys are amorphous in the composition range of 0.17amorphous films have smooth morphology, homogeneous composition, and sharp, well defined optical absorption edges. The band gap energy varies in a broad energy range from ~;;3.4 eV in GaN to ~;;0.8 eV at x~;;0.85. The reduction in the band gap can be attributed primarily to the downward movement of the conduction band for alloys with x>0.2, and to the upward movement of the valence band for alloys with x<0.2. The unique features of the band structure offer an opportunity of using GaN1-xAsx alloys for various types of solar power conversion devices.

  10. EXAFS Measurements and Reverse Monte Carlo Modeling of Atomic Structure in Amorphous Ni80P20 Alloys

    SciTech Connect

    Luo,W.; Ma, E.

    2008-01-01

    This paper presents a full account of the EXAFS measurements and reverse Monte Carlo (RMC) modeling of the atomic arrangements and short-to-medium range structure in an amorphous Ni-P alloy, expanding on the description included in our recent publication. The atomic packing is analyzed from the standpoint of solute atoms. The short-to-medium range structure is discussed based on single-solute-centered quasi-equivalent clusters that form due to strong chemical short-range ordering, and the topological order is described in terms of both intra-cluster and inter-cluster dense packing for efficient filling of space. This analysis is also conducted for amorphous Ni80P20 prepared via different processing routes, to observe if the polyamorphism suggested in literature for amorphous Ni-P can be confirmed from the local structure perspective. The structural differences between the proposed polymorphs are apparently subtle and a full resolution of this issue is found to be beyond the capabilities of our EXAFS/RMC modeling approach. The amorphous structural features uncovered are also compared briefly with those observed before in amorphous alloy systems with positive heat of mixing.

  11. In vivo evaluation of Zr-based bulk metallic glass alloy intramedullary nails in rat femora.

    PubMed

    Imai, Kazuhiro; Hiromoto, Sachiko

    2014-03-01

    Zr-based bulk metallic glasses (BMG) show high corrosion resistance in vitro and higher strength and lower Young's modulus than crystalline alloys with the similar composition. This study aimed to perform an in vivo evaluation of Zr65Al7.5Ni10Cu17.5 BMG. Osteotomy of the femur was done in rats and stabilized with intramedullary nails made of Zr65Al7.5Ni10Cu17.5 BMG, Ti-6Al-4V alloy, or 316L stainless steel. Systemic and local effects of each type of nail were evaluated by measuring the levels of Cu and Ni in the blood and the surrounding soft tissue. Changes of the surface of each nail were examined by scanning electron microscopy (SEM). Healing of the osteotomy was evaluated by peripheral quantitative computed tomography and mechanical testing. No increase of Cu and Ni levels was recognized. Surface of the BMG showed no noticeable change, while Ti-6Al-4V alloy showed Ca and P deposition and 316L stainless steel showed surface irregularities and pitting by SEM observation. The stress strain index, maximum torque, torsional stiffness, and energy absorption values were larger for the BMG than those for Ti-6Al-4V alloy, although there was no significant difference. The Zr-based BMG can promote osteotomy healing as fast as Ti-6Al-4V alloy, with the possible advantage of the Zr-based BMG that bone bonding is less likely, allowing easier nail removal compared with Ti-6Al-4V alloy. The Zr-based BMG is promising for the use in osteosynthetic devices that are eventually removed. PMID:24281655

  12. Study of the effects of metalloid elements (P, C, B) on Fe-based amorphous alloys by ab initio molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Zhang, Wenbiao; Li, Qiang; Duan, Haiming

    2015-03-01

    In order to understand the effects of the metalloid elements M (M: P, C, B) on the atomic structure, glass formation ability (GFA) and magnetic properties of Fe-based amorphous alloys, Fe80P13C7, Fe80P14B6 and Fe80B14C6 amorphous alloys are chosen to study through first-principle simulations in the present work. The atomic structure characteristic of the three amorphous alloys is investigated through the pair distribution functions (PDFs) and Voronoi Polyhedra (VPs) analyses. The PDFs and VPs analyses suggest that the GFA of the three alloys dropped in the order of Fe80P13C7, Fe80P14B6, and Fe80B14C6, which is well consistent with the experimental results. The density of state (DOS) of the three amorphous alloys is calculated to investigate their magnetic properties. Based on the DOS analysis, the average magnetic moment of Fe atom in Fe80P13C7 and Fe80P14B6 amorphous alloys can be estimated to be 1.71 μB and 1.70 μB, respectively, which are in acceptable agreement with the experimental results. However, the calculated average magnetic moment of Fe atom in Fe80B14C6 amorphous alloy is about 1.62 μB, which is far less than the experimental result.

  13. In vivo evaluation of a Ti-based bulk metallic glass alloy bar.

    PubMed

    Kokubun, Ryo; Wang, Wei; Zhu, Shengli; Xie, Guoqiang; Ichinose, Shizuko; Itoh, Soichiro; Takakuda, Kazuo

    2015-01-01

    Ti-based bulk metallic glasses are reported with high strength, low Young modulus and high corrosion resistance, suggesting their potentials in biomedical applications. However a thorough in vivo evaluation of its biocompatibilities has not been conducted yet. In this study, we implanted bars of Ti-based bulk metallic glass in the femoral bone of rats, followed up local tissue reaction as well as its component ions' diffusion in local area and whole body. The Ti-based BMG (Ti40Zr10Cu34Pd14Sn2) alloy exhibited favorable features of both high strength and high elasticity. In vivo implant evaluation showed that it has a good tissue compatibility, equivalent bone integration and bonding ability with Ti sample. No component ion diffusion was detected up to 3 months post implantation. The possibility and efficacy of its use for bone implant is confirmed. Thus further long term implant study is recommended. PMID:26484551

  14. Microstructure development and hydrogen gas interaction of oxidized Zr65Pd35 and Zr60Pd35Ce5 amorphous alloys

    NASA Astrophysics Data System (ADS)

    Ozawa, Masakuni; Kato, Shiro; Kobayashi, Katsutoshi; Yogo, Toshinobu; Yamamura, Shin-ichi

    2016-01-01

    The microstructure of composites derived from amorphous Zr65Pd35 and Zr65Pd35Ce5 alloys was studied. X-ray diffractograms, Raman spectroscopy profiles and scanning electron micrographs indicated that the mixtures containing ZrO2, metallic Pd, and PdO were formed for both amorphous alloys after heat treatment in air. The amorphous Zr60Pd35Ce5 alloy at temperatures of 280-400 °C changed to the composites in which very small Pd precipitates with a diameter less than 100 nm were embedded in a ZrO2 matrix. The hydrogen-temperature-programmed reduction was applied to study the reactivity of hydrogen gas with the oxidized Zr60Pd35Ce5 material. A rapid hydrogen absorption and release behavior was observed on the composite derived from the amorphous alloy.

  15. The formation of hysteretic magnetic properties in amorphous alloys of various classes upon thermomagmetic treatment in a transverse magnetic field

    NASA Astrophysics Data System (ADS)

    Kekalo, I. B.; Mogil'nikov, P. S.

    2016-06-01

    In this paper, we have studied the effects of the thermomagnetic treatment in a transverse magnetic field (TMaT⊥) on the permeability of the amorphous alloy Co69Fe3.7Cr3.8Si12.5B11 with such a low saturation magnetostriction ( λ s 10-7) that, in the ribbons of this alloy rolled into a toroid, a sharp longitudinal magnetic texture is observed ( K sq > 0.90). It has been revealed that the permeability μ4 ( H = 4 mOe, f = 1 kHz) as a function of the annealing temperature or time of holding at a temperature is described by a curve with a maximum. This maximum is observed at a coefficient of the squareness of the hysteresis loop K sq,m in the range of 0.2 ≤ K sq,m ≤ 0.4. The regimes of the TMaT have been determined that provide optimum values of the permeability μ4 (15000) without a loss of the ductile state of the ribbons of this alloy. Based on the example of an iron-based alloy of composition Fe57Co31Si2.9B9.1 with λs = 35 × 10-6, it has been shown that the formation of the hysteretic magnetic properties upon the TMaT⊥ depends substantially on the magnitude of the magnetostriction and the Curie temperature of the amorphous alloys.

  16. Dependence of the mechanical characteristics of fast-quenched amorphous Zr-Cu-Al alloys on their composition

    NASA Astrophysics Data System (ADS)

    Arutyunyan, N. A.; Zaitsev, A. I.; Dunaev, S. F.; Kalmykov, K. B.; Plokhikh, A. I.; Fedotova, N. L.

    2016-06-01

    The thermal and mechanical characteristics of fast-quenched amorphous Zr-Cu-Al alloys with various concentrations of copper and aluminum are studied. It is shown that the crystallization temperature of glass-like compositions increases when copper is replaced with aluminum in concentrations of up to 10 at %, and that the hardness, Young's modulus, and fracture stress increase only at low concentrations of aluminum (no more than 6 at %). Upon a further increase in the concentration of the alloying element, fracture stress σf decreases because σf the change in the fracture mechanism, despite high hardness and Young's modulus.

  17. Domain structure and magnetization loss in a toroidal core based on an Fe-based amorphous alloy

    NASA Astrophysics Data System (ADS)

    Azuma, Daichi; Hasegawa, Ryusuke; Saito, Shin; Takahashi, Migaku

    2012-04-01

    By utilizing a wide-view Kerr-effect magnetic domain observation system designed for domain observation on curved surfaces, domain images were taken on the surface of a toroidal core based on an Fe-based amorphous alloy. The results of the observation are discussed in terms of Bertotti's eddy-current loss model, helping to clarify the concept of magnetic objects proposed by the model.

  18. Structural and magnetic peculiarities of Al86Ni8Sm6 alloy in amorphous, crystalline, and liquid states

    NASA Astrophysics Data System (ADS)

    Uporov, S. A.; Ryl'tsev, R. E.; Uporova, N. S.; Bykov, V. A.; Murzakaev, A. M.; Pryanichnikov, S. V.

    2015-02-01

    Magnetic, structural, and thermal characteristics of the Al86Ni8Sm6 alloy in amorphous, crystalline, and liquid states have been studied over a wide temperature range of 4-1900 K. It has been found that the amorphous alloy has a pronounced cluster structure with an average cluster size of 2-3 nm. The crystallization process occurs in four stages and no apparent thermal effect at the glass-transition temperature is observed. The amorphous ribbon has no magnetic order up to 4 K but demonstrates superparamagneic behavior. An analysis of isothermal magnetization curves indicates a possible correlation between structural and magnetically ordered clusters. Anomalous changes in the magnetic susceptibility in the liquid state have been found at temperatures substantially higher than the liquidus temperature; the anomalies indicate structural changes in the melt. The magnetic susceptibility in the amorphous, crystalline, and liquid states was found to be characterized by a high Van Vleck paramagnetic contribution and can be described adequately in terms of the classic Van Vleck theory with allowance for mixed valence effects. The obtained results are interpreted using a concept on the existence of a specific covalent-metallic interaction between aluminum and rare-earth metal atoms.

  19. Large Magnetocaloric Effect Around Room Temperature in Amorphous Fe-Gd-Zr Alloy Ribbon with Short-Range Interactions

    NASA Astrophysics Data System (ADS)

    Thanh, Tran Dang; Yen, Nguyen Hai; Duc, Nguyen Huu; Phan, The-Long; Dan, Nguyen Huy; Yu, Seong-Cho

    2016-05-01

    In this work, we present a detailed study on the magnetocaloric effect and the critical behaviors of an amorphous Fe88Gd2Zr10 alloy ribbon prepared by using a rapid quenching method. We point out that the value of maximum magnetic entropy change (|∆ S max|) of amorphous Fe88Gd2Zr10 alloy ribbon appeared at near room temperature and versus Δ H obeys a power law, |∆ S max| = a·Δ H n. In addition, all Δ S m( T, Δ H) data measured at different Δ H values are collapsed onto a universal master curve. Interestingly, M 2 versus H/ M curves prove amorphous Fe88Gd2Zr10 ribbon exhibitied a second-order magnetic phase transition. The critical exponents ( β, γ, and δ) obtained from the modified Arrott plots and the Kouvel-Fisher methods, and critical isotherm analysis are very close to those expected for the 3D-Heisenberg model, proving ferromagnetic short-range interactions exist in amorphous Fe88Gd2Zr10 ribbon.

  20. All-thermal switching of amorphous Gd-Fe alloys: Analysis of structural properties and magnetization dynamics

    NASA Astrophysics Data System (ADS)

    Chimata, Raghuveer; Isaeva, Leyla; Kádas, Krisztina; Bergman, Anders; Sanyal, Biplab; Mentink, Johan H.; Katsnelson, Mikhail I.; Rasing, Theo; Kirilyuk, Andrei; Kimel, Alexey; Eriksson, Olle; Pereiro, Manuel

    2015-09-01

    In recent years there has been an intense interest in understanding the microscopic mechanism of thermally induced magnetization switching driven by a femtosecond laser pulse. Most of the effort has been dedicated to periodic crystalline structures while the amorphous counterparts have been less studied. By using a multiscale approach, i.e., first-principles density functional theory combined with atomistic spin dynamics, we report here on the very intricate structural and magnetic nature of amorphous Gd-Fe alloys for a wide range of Gd and Fe atomic concentrations at the nanoscale level. Both structural and dynamical properties of Gd-Fe alloys reported in this work are in good agreement with previous experiments. We calculated the dynamic behavior of homogeneous and inhomogeneous amorphous Gd-Fe alloys and their response under the influence of a femtosecond laser pulse. In the homogeneous sample, the Fe sublattice switches its magnetization before the Gd one. However, the temporal sequence of the switching of the two sublattices is reversed in the inhomogeneous sample. We propose a possible explanation based on a mechanism driven by a combination of the Dzyaloshinskii-Moriya interaction and exchange frustration, modeled by an antiferromagnetic second-neighbor exchange interaction between Gd atoms in the Gd-rich region. We also report on the influence of laser fluence and damping effects in the all-thermal switching.

  1. Microstructures of the silicon carbide nanowires obtained by annealing the mechanically-alloyed amorphous powders

    SciTech Connect

    Zhang, Pengfei Li, Xinli

    2015-07-15

    Silicon, graphite and boron nitride powders were mechanically alloyed for 40 h in argon. The as-milled powders were annealed at 1700 °C in nitrogen for 30 min. The annealed powders are covered by a thick layer of gray–green SiC nanowires, which are 300 nm to 1000 nm in diameter and several hundred microns in length. Trace iron in the raw powders acts as a catalyst, promoting the V–L–S process. It follows that the actual substances contributing to the growth of the SiC nanowires may be silicon, graphite and the metal impurities in the raw powders. The results from HRTEM and XRD reveal that the products contain both straight α/β-SiC nanowires and nodular α/β-SiC nanochains. It is interestingly found that 6H–SiC coexists with 3C–SiC in one nodular nanowire. This novel structure may introduce periodic potential field along the longitudinal direction of the nanowires, and may find applications in the highly integrated optoelectronic devices. - Graphical abstract: Display Omitted - Highlights: • SiC nanowires were prepared by annealing the mechanically alloyed amorphous powders. • SiC nanowires are 300 nm to 1000 nm in diameter and several hundred microns in length. • The products contain both straight α/β-SiC nanowires and nodular α/β-SiC nanochains. • Trace Fe in the raw powders acts as a catalyst, promoting the V–L–S process. • 6H–SiC coexists with 3C–SiC in one nodular SiC nanowire.

  2. Investigation of thermally evaporated high resistive B-doped amorphous selenium alloy films and metal contact studies

    NASA Astrophysics Data System (ADS)

    Oner, Cihan; Nguyen, Khai V.; Pak, Rahmi O.; Mannan, Mohammad A.; Mandal, Krishna C.

    2015-08-01

    Amorphous selenium (a-Se) alloy materials with arsenic, chlorine, boron, and lithium doping were synthesized for room temperature nuclear radiation detector applications using an optimized alloy composition for enhanced charge transport properties. A multi-step synthetic process has been implemented to first synthesize Se-As and Se-Cl master alloys from zone-refined Se (~ 7N), and then synthesized the final alloys for thermally evaporated large-area thin-film deposition on oxidized aluminum (Al/Al2O3) and indium tin oxide (ITO) coated glass substrates. Material purity, morphology, and compositional characteristics of the alloy materials and films were examined using glow discharge mass spectroscopy (GDMS), inductively coupled plasma mass spectroscopy (ICP-MS), differential scanning calorimetry (DSC), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive analysis by x-rays (EDAX). Current-Voltage (I-V) measurements were carried out to confirm very high resistivity of the alloy thin-films. We have further investigated the junction properties of the alloy films with a wide variety of metals with different work functions (Au, Ni, W, Pd, Cu, Mo, In, and Sn). The aim was to investigate whether the choice of metal can improve the performance of fabricated detectors by minimizing the dark leakage current. For various metal contacts, we have found significant dependencies of metal work functions on current transients by applying voltages from -800 V to +1000 V.

  3. Amorphous oxide alloys as interfacial layers with broadly tunable electronic structures for organic photovoltaic cells.

    PubMed

    Zhou, Nanjia; Kim, Myung-Gil; Loser, Stephen; Smith, Jeremy; Yoshida, Hiroyuki; Guo, Xugang; Song, Charles; Jin, Hosub; Chen, Zhihua; Yoon, Seok Min; Freeman, Arthur J; Chang, Robert P H; Facchetti, Antonio; Marks, Tobin J

    2015-06-30

    In diverse classes of organic optoelectronic devices, controlling charge injection, extraction, and blocking across organic semiconductor-inorganic electrode interfaces is crucial for enhancing quantum efficiency and output voltage. To this end, the strategy of inserting engineered interfacial layers (IFLs) between electrical contacts and organic semiconductors has significantly advanced organic light-emitting diode and organic thin film transistor performance. For organic photovoltaic (OPV) devices, an electronically flexible IFL design strategy to incrementally tune energy level matching between the inorganic electrode system and the organic photoactive components without varying the surface chemistry would permit OPV cells to adapt to ever-changing generations of photoactive materials. Here we report the implementation of chemically/environmentally robust, low-temperature solution-processed amorphous transparent semiconducting oxide alloys, In-Ga-O and Ga-Zn-Sn-O, as IFLs for inverted OPVs. Continuous variation of the IFL compositions tunes the conduction band minima over a broad range, affording optimized OPV power conversion efficiencies for multiple classes of organic active layer materials and establishing clear correlations between IFL/photoactive layer energetics and device performance. PMID:26080437

  4. Temperature dependence of Raman scattering in amorphous films of In 1- xSe x alloys

    NASA Astrophysics Data System (ADS)

    Weszka, J.; Daniel, Ph.; Burian, A. M.; Burian, A.; Żelechower, M.

    2001-08-01

    Raman scattering (RS) in amorphous films of In 1- xSe x with 0.70≥ x≥0.38 has been studied in backscattering geometry with the use of a single channel Raman spectrometer at room and 10 K temperatures. The recorded RS spectra reveal dominant vibrational density-of-states character. They exhibit a continuum, spanning the Rayleigh line up to a shoulder at about 250 cm -1, that moves towards lower frequencies as x decreases from 0.70 to 0.38. The bands at about 104, 125 and at 143 and 237 cm -1 are attributed to In-In, Se 8 ring molecules and Se-chain oscillations, respectively. The structure of In 1- xSe x alloys is deduced to be a continuous random network based on InSe 4/2 tetrahedral clusters interconnected by Se atoms at the shared corners or local Se-chain fragments or Se 8 rings. With growing In content, some Se atoms in such clusters are replaced by In atoms to an extent dependent on In content. The disappearance of the 143 and 237 cm -1 bands in the low temperature spectra taken on the In 0.30Se 0.70 film is attributed to the contraction of interatomic bonds, making conditions favorable for breaking Se polymer chains and Se 8 ring molecule formation.

  5. Morphology and kinetics of crystallization of amorphous V75Si25 thin-alloy films

    NASA Astrophysics Data System (ADS)

    Nava, F.; Weiss, B. Z.; Tu, K. N.; Smith, D. A.; Psaras, P. A.

    1986-10-01

    Electrical and microstructural changes of coevaporated V75Si25 alloy thin films have been studied as a function of temperature from room temperature to 830 °C. In situ resistivity measurements, hot-stage transmission electron microscopy, Rutherford backscattering spectroscopy and the Seeman-Bohlin glancing angle incidence x-ray diffraction technique were applied. Upon heat treatment at a heating rate of 8 °C/min, a sharp decrease in resistivity occurs at ˜670 °C which results from an amorphous to crystalline phase transformation. The crystallized phase was identified as V3Si. The mechanism of transformation is random nucleation at a rapidly decreasing rate and a fast quasi-isotropic growth. The kinetics of crystallization have been studied by utilizing electrical resistivity measurements during isothermal heat treatment. Six different temperatures between 570 °C and 630 °C were adopted. The apparent activation energy (˜3.6 eV) obtained from isothermal measurements was found to be in agreement with that obtained from nonisothermal treatments at varying rates of heating. The distinct change of the Avrami mode parameter from 4 to 2 at a constant value of t/τ during the process of crystallization is not immediately understood.

  6. Amorphous oxide alloys as interfacial layers with broadly tunable electronic structures for organic photovoltaic cells

    PubMed Central

    Zhou, Nanjia; Kim, Myung-Gil; Loser, Stephen; Smith, Jeremy; Yoshida, Hiroyuki; Guo, Xugang; Song, Charles; Jin, Hosub; Chen, Zhihua; Yoon, Seok Min; Freeman, Arthur J.; Chang, Robert P. H.; Facchetti, Antonio; Marks, Tobin J.

    2015-01-01

    In diverse classes of organic optoelectronic devices, controlling charge injection, extraction, and blocking across organic semiconductor–inorganic electrode interfaces is crucial for enhancing quantum efficiency and output voltage. To this end, the strategy of inserting engineered interfacial layers (IFLs) between electrical contacts and organic semiconductors has significantly advanced organic light-emitting diode and organic thin film transistor performance. For organic photovoltaic (OPV) devices, an electronically flexible IFL design strategy to incrementally tune energy level matching between the inorganic electrode system and the organic photoactive components without varying the surface chemistry would permit OPV cells to adapt to ever-changing generations of photoactive materials. Here we report the implementation of chemically/environmentally robust, low-temperature solution-processed amorphous transparent semiconducting oxide alloys, In-Ga-O and Ga-Zn-Sn-O, as IFLs for inverted OPVs. Continuous variation of the IFL compositions tunes the conduction band minima over a broad range, affording optimized OPV power conversion efficiencies for multiple classes of organic active layer materials and establishing clear correlations between IFL/photoactive layer energetics and device performance. PMID:26080437

  7. On-demand release of corrosion-inhibiting ions from amorphous Al-Co-Ce alloys.

    PubMed

    Jakab, M A; Scully, J R

    2005-09-01

    Controlled release technologies are often used to supply chemicals or drugs at given rates. Release often occurs on contact with solution. However, some applications, such as corrosion protection, require containment of the active species in a reservoir and their slow release when needed. Conductive polymers have been used as reservoirs for corrosion inhibitors whose triggered release occurs by galvanic reduction or ion exchange. This work shows one of the first examples of pH-controlled release of corrosion-inhibiting ions from an amorphous metallic coating where the pH change that triggers release is a consequence of the onset of corrosion. This corrosion-inhibition strategy provides further corrosion protection beyond the traditional roles of barrier and sacrificial cathodic protection using a metal coating. For instance, zinc galvanizing provides sacrificial cathodic protection and acts as a barrier, but does not supply inhibitor ions. In the coating described here, protection of an underlying structural alloy exposed at coating defects is demonstrated by inhibitor ion release in addition to barrier function and sacrificial cathodic protection. PMID:16086020

  8. Tunneling Spectroscopy of Amorphous Magnetic Rare Earth-Si Alloys near the Metal-Insulator Transition

    NASA Astrophysics Data System (ADS)

    Xiong, P.; Zink, B. L.; Tran, M. Q.; Gebala, A. E.; Wilcox, E. M.; Hellman, F.; Dynes, R. C.

    1997-03-01

    Amorphous dilute magnetic semiconductors exhibit striking differences in the electrical and magneto-transport behavior from their crystalline or nonmagnetic analogs.(F. Hellman et al., Phys. Rev. Lett. 77, 4652 (1996).) Magnetic impurities cause a large suppression of conductivity below 50 K in a-Si_xGd_1-x and a-Si_xTb_1-x relative to the nonmagnetic a-Si_xY_1-x (x ~ 0.85-0.9). Application of a magnetic field increases the conductivity by orders of magnitude. We have fabricated good quality tunnel junctions on a-Si:Gd and the nonmagnetic a-Si:Y to probe the electronic density of states in these two systems. We present the results of the tunneling spectroscopy and its magnetic field dependence for a series of the two alloys at different compositions. We will discuss the correlation between the tunneling spectra and the transport properties and its implications on the possible origin of the magnetic field tuned insulator-metal transition in a-Si:Gd. Research Supported by ONR Grant No. N000149151320 and NSF Grant No. DMR-9208599.

  9. Carrier scattering mechanisms in p-type transparent copper-alloyed ZnS: Crystalline vs. amorphous

    NASA Astrophysics Data System (ADS)

    Woods-Robinson, Rachel; Faghaninia, Alireza; Cooper, Jason K.; Pham, Hieu H.; Lo, Cynthia; Wang, Lin-Wang; Ager, Joel W.

    2015-03-01

    Crystalline (wurtzite and sphalerite) and amorphous forms of copper-alloyed ZnS (CuxZn1-xS) are p-type conducting transparent thin film materials with near-record figures of merit for applications in photovoltaics and optoelectronics. Remarkably, the conductivity of amorphous CuxZn1-xS, 42 S/cm at x = 0.30, is nearly as high as crystalline CuxZn1-xS (54 S/cm at x = 0.21). This contrasts with typical observations of poorer carrier transport in amorphous materials. By combining experiment and computation, we investigate the defect physics underlying hole transport in amorphous and crystalline CuxZn1-xS. Structural probes (EXAFS, TEM and wide-angle XRD) are used to determine bonding characteristics and lattice order, and serve as inputs to ab initio hybrid functional HSE calculations of the electronic band structure. Hall effect, temperature dependent conductivity (15K to 500K), and XPS valence band measurements and ab initio calculations show that hole conduction occurs in a hybridized S-3p and Cu-3d valence band for amorphous and crystalline films. The hole scattering mechanisms which limit the conductivity will be discussed in the context of theoretical carrier transport model based on Boltzmann transport equation, ab initio calculated band structure, and phonon dispersion.

  10. Interpretation of Fracture Toughness and R-Curve Behavior by Direct Observation of Microfracture Process in Ti-Based Dendrite-Containing Amorphous Alloys

    NASA Astrophysics Data System (ADS)

    Jeon, Changwoo; Kim, Choongnyun Paul; Kim, Hyoung Seop; Lee, Sunghak

    2015-04-01

    Fracture properties of Ti-based amorphous alloys containing ductile β dendrites were explained by directly observing microfracture processes. Three Ti-based amorphous alloys were fabricated by adding Ti, Zr, V, Ni, Al, and Be into a Ti-6Al-4V alloy by a vacuum arc melting method. The effective sizes of dendrites varied from 63 to 104 μm, while their volume fractions were almost constant within the range from 74 to 76 pct. The observation of the microfracture of the alloy containing coarse dendrites revealed that a microcrack initiated at the amorphous matrix of the notch tip and propagated along the amorphous matrix. In the alloy containing fine dendrites, the crack propagation was frequently blocked by dendrites, and many deformation bands were formed near or in front of the propagating crack, thereby resulting in a zig-zag fracture path. Crack initiation toughness was almost the same at 35 to 36 MPa√m within error ranges in the three alloys because it was heavily affected by the stress applied to the specimen at the time of crack initiation at the crack tip as well as strength levels of the alloys. According to the R-curve behavior, however, the best overall fracture properties in the alloy containing fine dendrites were explained by mechanisms of blocking of the crack growth and crack blunting and deformation band formation at dendrites.

  11. The potential of hydrogenated amorphous silicon-chalcogen alloys for photovoltaic applications: The role of persistent photoconductivity

    SciTech Connect

    Wang, S.L.; Viner, J.M.; Taylor, P.C.; Itoh, T.; Nitta, S.

    1997-02-01

    The potential improvement in stability of hydrogenated silicon-sulfur alloys (a-SiS{sub x}:H) with respect to ordinary hydrogenated amorphous silicon (a-Si:H) has been attributed to the introduction of an additional metastability known as persistent photoconductivity (PPC). In order to examine the PPC process in more detail we examine a series of alloys with large sulfur concentrations (x{gt}0.01). Although these alloys are not useful in photovoltaic devices, the high sulfur concentrations accentuate the PPC effect and allow one to study this effect with little competition from the ordinary Staebler-Wronski effect that dominates the metastable processes that occur in a -Si:H. {copyright} {ital 1997 American Institute of Physics.}

  12. Structural evolution and the kinetics of Cu clustering in the amorphous phase of Fe-Cu-Nb-Si-B alloy

    NASA Astrophysics Data System (ADS)

    Gupta, P.; Gupta, A.; Shukla, A.; Ganguli, Tapas; Sinha, A. K.; Principi, G.; Maddalena, A.

    2011-08-01

    An attempt has been made to investigate the evolution of the structure of the amorphous phase of Fe73.9 Cu0.9 Nb3.1 Si13.2 B8.9 (finemet) alloy by a combination of wide-angle x-ray scattering, small angle x-ray scattering (SAXS), Mössbauer spectroscopy and X-ray absorption near edge spectroscopy on the supposition that they would provide complementary information. Before the onset of nanocrystallization, the amorphous phase undergoes a structural relaxation resulting in small increase in the hyperfine field and a decrease in the width of the first diffraction maxima. There is an increase in the topological ordering in the system, though chemical inhomogeneity sets-in due to the clustering of Cu atoms in the pure amorphous state of this alloy. Annealing at 400 °C (well below the crystallization temperature) for different time durations results in occurrence of Cu clusters having fcc structure. Kinetics of Cu clustering is studied using SAXS. The incubation time for the clustering at 400 °C is ˜120 min. With further annealing, the average cluster size gradually increases from the initial value of ˜0.4 nm, reaching a value of ˜0.6 nm after annealing for 720 min. Cluster size exhibits a t1/2 dependence, suggesting a diffusion controlled growth.

  13. Magnetic properties of bulk nanocomposite permanent magnets based on NdDyFeB alloys with additions

    NASA Astrophysics Data System (ADS)

    Marinescu, M.; Chiriac, H.; Grigoras, M.

    2005-04-01

    NdFeB-based bulk nanocomposite permanent magnets with addition of Mo, Ti, Zr, Cu, Nb, V, respectively, Dy substitution for Nd and Co substitution for Fe, in form of rods with diameters ranging from 0.5 to 0.8 mm, have been prepared by devitrification annealing of amorphous and partly-amorphous precursors produced by injection die casting. A fully amorphous structure was obtained for rods with the diameter as large as 0.6 mm. The best-achieved magnetic properties have been obtained for the optimum devitrification annealed Nd 3Dy 1Fe 66Co 10B 20 rods with 0.6 mm diameter and are: iH c=296 kA/m, μ0Mr=0.86 T, Mr/ Mmax=0.65 and ( BH) max=74 kJ/m 3.

  14. Enhancement of the fracture strength and glass-forming ability of CoFeTaB bulk glassy alloy

    NASA Astrophysics Data System (ADS)

    Shen, Baolong; Inoue, Akihisa

    2005-09-01

    Co43Fe20Ta5.5B31.5 bulk glassy alloy has the best glass-forming ability (GFA) among the Co-based glassy alloys, and the highest strength (the compressive true strength σf = 5185 MPa) among all known bulk crystalline and glassy alloys. With the aim of synthesizing new Co-based bulk glassy alloys with much higher strength and much larger GFA, we investigated the effect of Mo and Si additions on the enhancement of σf and GFA in the Co-(Fe, Mo, Ta)-(B, Si) system. The small amount of 2 at.% Mo added to the Co-Fe-Ta-B glassy alloy resulted in obtaining an ultrahigh true fracture strength of 5545 MPa and high Young's modulus (E) of 282 GPa. By further adding 1 and 2 at.% Si, Co-(Fe, Mo, Ta)-(B, Si) bulk glassy alloys were synthesized in the diameter range up to 3 mm, and they exhibited σf of over 4450 MPa and E of over 227 GPa. In addition, the ultrahigh-strength glassy alloys simultaneously exhibited excellent soft magnetic properties, i.e., saturation magnetization of 0.32-0.35 T, low coercive force of 0.7-1.1 A m-1, and high effective permeability of 3.9-4.77 × 104 at 1 kHz. The improvement of GFA and σf is interpreted to result from the enhanced atomic bonding nature by adding Mo and Si.

  15. Development of radiation detectors based on hydrogenated amorphous silicon and its alloys

    SciTech Connect

    Hong, Wan-Shick

    1995-04-01

    Hydrogenated amorphous silicon and related materials have been applied to radiation detectors, utilizing their good radiation resistance and the feasibility of making deposits over a large area at low cost. Effects of deposition parameters on various material properties of a-Si:H have been studied to produce a material satisfying the requirements for specific detection application. Thick(-{approximately}50 {mu}m), device quality a-Si:H p-i-n diodes for direct detection of minimum ionizing particles have been prepared with low internal stress by a combination of low temperature growth, He-dilution of silane, and post annealing. The structure of the new film contained voids and tiny crystalline inclusions and was different from the one observed in conventional a-Si:H. Deposition on patterned substrates was attempted as an alternative to controlling deposition parameters to minimize substrate bending and delamination of thick a-Si:H films. Growth on an inversed-pyramid pattern reduced the substrate bending by a factor of 3{approximately}4 for the same thickness film. Thin (0.1 {approximately} 0.2 {mu}m) films of a-Si:H and a-SiC:H have been applied to microstrip gas chambers to control gain instabilities due to charges on the substrate. Light sensitivity of the a-Si:H sheet resistance was minimized and the surface resistivity was successfully` controlled in the range of 10{sup 12} {approximately} 10{sup 17} {Omega}/{four_gradient} by carbon alloying and boron doping. Performance of the detectors with boron-doped a-Si:C:H layers was comparable to that of electronic-conducting glass. Hydrogen dilution of silane has been explored to improve electrical transport properties of a-Si:H material for high speed photo-detectors and TFT applications.

  16. Formation of amorphous Fe 50Si 50 alloy by diffusion reaction

    NASA Astrophysics Data System (ADS)

    Yan, Zhihua; Wang, Wenkui; Li, Jingfeng; Wang, Yuming

    1989-02-01

    The solid state reaction in the multilayer film with alternative polycrystalline Fe and amorphous Si layers has been studied with X-ray diffraction. Amorphous Fe 50Si 50 phase was formed after annealing isothermally at 300°C, which is explained in view of the consideration that an amorphous phase can be more favorable to form than a supersaturated solution in thermodynamics as well as than an equilibrium compound FeSi in kenetics.

  17. Study of the effects of metalloid elements (P, C, B) on Fe-based amorphous alloys by ab initio molecular dynamics simulations

    SciTech Connect

    Zhang, Wenbiao; Li, Qiang E-mail: dhm@xju.edu.cn; Duan, Haiming E-mail: dhm@xju.edu.cn

    2015-03-14

    In order to understand the effects of the metalloid elements M (M: P, C, B) on the atomic structure, glass formation ability (GFA) and magnetic properties of Fe-based amorphous alloys, Fe{sub 80}P{sub 13}C{sub 7}, Fe{sub 80}P{sub 14}B{sub 6} and Fe{sub 80}B{sub 14}C{sub 6} amorphous alloys are chosen to study through first-principle simulations in the present work. The atomic structure characteristic of the three amorphous alloys is investigated through the pair distribution functions (PDFs) and Voronoi Polyhedra (VPs) analyses. The PDFs and VPs analyses suggest that the GFA of the three alloys dropped in the order of Fe{sub 80}P{sub 13}C{sub 7}, Fe{sub 80}P{sub 14}B{sub 6}, and Fe{sub 80}B{sub 14}C{sub 6}, which is well consistent with the experimental results. The density of state (DOS) of the three amorphous alloys is calculated to investigate their magnetic properties. Based on the DOS analysis, the average magnetic moment of Fe atom in Fe{sub 80}P{sub 13}C{sub 7} and Fe{sub 80}P{sub 14}B{sub 6} amorphous alloys can be estimated to be 1.71 μ{sub B} and 1.70 μ{sub B}, respectively, which are in acceptable agreement with the experimental results. However, the calculated average magnetic moment of Fe atom in Fe{sub 80}B{sub 14}C{sub 6} amorphous alloy is about 1.62 μ{sub B}, which is far less than the experimental result.

  18. The effects of reactive-element, ion-implantation-induced amorphous layers on the oxidation of Co-12Cr and Ni-12Cr alloys

    SciTech Connect

    Hampikian, J.M.

    1998-08-01

    Nickel-chromium (Ni-12Cr, wt.%) and cobalt-chromium (Co-12Cr, wt.%) alloys were ion implanted with 150 keV yttrium to fluences that ranged between 2 {times} 10{sup 16} and 1 {times} 0{sup 17} ions/cm{sup 2}. The influence of the implantation on the microstructure of the alloy was determined. The effect of the highest dose implantation on the alloys` oxidation response at 1,000 C, 48 hr was measured. Both alloys contained an amorphous surface phase as a result of this fluence and one of the effects of oxidation was to recrystallize the amorphized alloy in the first few minutes of oxidation. The lower doses of 2 {times} 10{sup 16} ions/cm{sup 2} were sufficient to cause amorphization of both the Ni-12Cr and the Co-12Cr. The implantation reduced the isothermal mass gain by a factor of 25% for the Ni-12Cr, but had a negligible effect on the Co-12Cr alloy. Short-term oxidation of experiments at 600 C showed via transmission electron microscopy that, in the absence of the yttrium implant, the Ni-12Cr alloy forms NiO in the first minute of oxidation and the Co-12Cr alloy forms CoO and CoCr{sub 2}O{sub 4}. The implanted Ni-12Cr, on the other hand (1 {times} 10{sup 17} Y{sup +}/cm{sup 2}), forms recrystallized Ni-Cr, Y{sub 2}O{sub 3}, and NiO in the near-surface region, while the implanted Co-12Cr alloy forms CoO, CoCr{sub 2}O{sub 4}, and a recrystallized intermetallic alloy from the amorphized region.

  19. Free-electron-like Hall effect and deviations from free-electron behavior in Ca-Al amorphous alloys

    NASA Astrophysics Data System (ADS)

    Mayeya, F. M.; Hickey, B. J.; Howson, M. A.

    1995-06-01

    The Hall coefficients of Ca-Al amorphous alloys have been measured at 4.2 K over a wide range of compositions. It is shown that the magnitude of the Hall coefficients are close to the nearly-free-electron (NFE) prediction for low Ca concentrations but deviate significantly from the NFE values for Ca concentration greater than 45 at. %. The deviations from the free-electron values have previously been attributed to the effects of s-d hybridization, while a reduction in magnitude by Au doping has been argued to result from the side-jump effect.

  20. Spectroscopic ellipsometry study of hydrogenated amorphous silicon carbon alloy films deposited by plasma enhanced chemical vapor deposition

    SciTech Connect

    Basa, D. K.; Abbate, G.; Ambrosone, G.; Marino, A.; Coscia, U.

    2010-01-15

    The optical properties of the hydrogenated amorphous silicon carbon alloy films, prepared by plasma enhanced chemical vapor deposition technique from silane and methane gas mixture diluted in helium, have been investigated using variable angle spectroscopic ellipsometry in the photon energy range from 0.73 to 4.59 eV. Tauc-Lorentz model has been employed for the analysis of the optical spectra and it has been demonstrated that the model parameters are correlated with the carbon content as well as to the structural properties of the studied films.

  1. Liquid phase electroepitaxial bulk growth of binary and ternary alloy semiconductors under external magnetic field

    NASA Astrophysics Data System (ADS)

    Sheibani, Hamdi

    2002-01-01

    Liquid Phase Electroepitaxy (LPEE) and is a relatively new, promising technique for producing high quality, thick compound semiconductors and their alloys. The main objectives are to reduce the adverse effect of natural convection and to determine the optimum growth conditions for reproducible desired crystals for the optoelectronic and electronic device industry. Among the available techniques for suppressing the adverse effect of natural convection, the application of an external magnetic field seems the most feasible one. The research work in this dissertation consists of two parts. The first part is focused on the design and development of a state of the art LPEE facility with a novel crucible design, that can produce bulk crystals of quality higher than those achieved by the existing LPEE system. A growth procedure was developed to take advantage of this novel crucible design. The research of the growth of InGaAs single crystals presented in this thesis will be a basis for the future LPEE growth of other important material and is an ideal vehicle for the development of a ternary crystal growth process. The second part of the research program is the experimental study of the LPEE growth process of high quality bulk single crystals of binary/ternary semiconductors under applied magnetic field. The compositional uniformity of grown crystals was measured by Electron Probe Micro-analysis (EPMA) and X-ray microanalysis. The state-of-the-art LPEE system developed at University of Victoria, because of its novel design features, has achieved a growth rate of about 4.5 mm/day (with the application of an external fixed magnetic field of 4.5 KGauss and 3 A/cm2 electric current density), and a growth rate of about 11 mm/day (with 4.5 KGauss magnetic field and 7 A/cm2 electric current density). This achievement is simply a breakthrough in LPEE, making this growth technique absolutely a bulk growth technique and putting it in competition with other bulk growth techniques

  2. {sup 57}Fe and {sup 119}Sn Moessbauer Effect Study of Fe-Sn-B Amorphous Alloys

    SciTech Connect

    Miglierini, M.; Rusakov, V. S.

    2010-07-13

    Ribbons of Fe{sub 100-x}Sn{sub 5}B{sub x} (x = 15, 17, 20) metallic glass are studied using {sup 57}Fe and {sup 119}Sn Moessbauer spectrometry. The obtained Moessbauer spectra are evaluated by distributions of hyperfine magnetic fields in addition to crystalline components. The as-quenched alloys are XRD amorphous for x =15 and 17 whereas for x =20, traces of quenched-in crystallites are revealed. Progress of crystallization is followed on samples annealed for 30 min at temperatures that cover the first crystallization peak. The evolution of crystalline fraction as well as average values of hyperfine magnetic fields and isomer shifts are discussed as a function of the alloy composition and temperature of annealing.

  3. STRUCTURAL INTERACTIONS OF HYDROGEN WITH BULK AMORPHOUS MICROSTRUCTURES IN METALLIC SYSTEMS UNDERSTANDING THE ROLE OF PARTIAL CRYSTALLINITY ON PERMEATION AND EMBRITTLEMENT

    SciTech Connect

    Brinkman, Kyle; Fox, Elise; Korinko, Paul; Adams, Thad

    2010-05-10

    The development of metallic glasses in bulk form has led to a resurgence of interest into the utilization of these materials for a variety of applications. A potentially exciting application for these bulk metallic glass (BMG) materials is their use as composite membranes to replace high cost Pd/Pd-alloy membranes for enhanced gas separation processes. One of the major drawbacks to the industrial use of Pd/Pd-alloy membranes is that during cycling above and below a critical temperature an irreversible change takes place in the palladium lattice structure which can result in significant damage to the membrane. Furthermore, the cost associated with Pd-based membranes is a potential detractor for their continued use and BMG alloys offer a potentially attractive alternative. Several BMG alloys have been shown to possess high permeation rates, comparable to those measured for pure Pd metal. In addition, high strength and toughness when either in-situ or ex-situ second phase dispersoids are present. Both of these properties, high permeation and high strength/toughness, potentially make these materials attractive for gas separation membranes that could resist hydrogen 'embrittlement'. However, a fundamental understanding of the relationship between partially crystalline 'structure'/devitrification and permeation/embrittlement in these BMG materials is required in order to determine the operating window for separation membranes and provide additional input to the material synthesis community for improved alloy design. This project aims to fill the knowledge gap regarding the impact of crystallization on the permeation properties of metallic glass materials. The objectives of this study are to (i) determine the crystallization behavior in different gas environments of Fe and Zr based commercially available bulk metallic glass and (ii) quantify the effects of partial crystallinity on the hydrogen permeation properties of these metallic glass membranes.

  4. Microstructural and nuclear magnetic resonance studies of solid-state amorphization in Al-Ti-Si composites prepared by mechanical alloying

    SciTech Connect

    Manna, I.; Nandi, P.; Bandyopadhyay, B.; Ghoshray, K.; Ghoshray, A

    2004-08-16

    Three Al{sub 30}Ti{sub 70-x} Si{sub x} (x=10, 20, 30), along with an Al-rich (Al{sub 50}Ti{sub 40}Si{sub 10}) and an Al-lean (Al{sub 10}Ti{sub 60}Si{sub 30}) elemental powder blends were subjected to mechanical alloying by high-energy planetary ball milling to yield a composite microstructure with varying proportions of amorphous and nanocrystalline intermetallic phases. Microstructural characterization at different stages of milling was carried out by X-ray diffraction, high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. Furthermore, {sup 27}Al nuclear magnetic resonance (NMR) studies were undertaken to probe the mechanism of solid-state amorphization. Ball milling leads to alloying, nanocrystallization and partial solid-state amorphization followed/accompanied by strain-induced nucleation of nanocrystalline intermetallic phases from an amorphous solid solution. Both these amorphous and nano-intermetallic phases are associated with characteristic NMR peaks at lower frequencies (than that of pure Al). Thus, mechanical alloying of Al-Ti-Si appears a suitable technique for developing nanocrystalline intermetallic phase/compound dispersed amorphous matrix composites.

  5. HRTEM and TEM studies of amorphous structures in ZrNiTiCu base alloys obtained by rapid solidification or ball milling.

    PubMed

    Dutkiewicz, J; Lityńska, L; Maziarz, W; Kocisko, R; Molnarová, M; Kovácová, A

    2009-01-01

    Amorphous structure of Ti(25)Zr(17)Ni(29)Cu(29) composition was studied. Alloys were prepared either by rapid solidification using melt spinning or by high-energy ball milling. The composition of multi-component eutectic in slowly cooled samples of ZrNiTiCu alloy was determined using EDS measurements in scanning microscope of slowly cooled cast samples. The alloys of eutectic composition were melt-spun or ball-milled. Transmission electron microscopy (TEM) studies of melt-spun ribbons from alloys near eutectic composition did not show presence of nanocrystals within the amorphous structure. TEM studies of ball-milled powders showed presence of nanocrystallites of size 2-5 nm. The electron diffraction pattern showed intense diffused ring due to the presence of the amorphous phase and a weak spot due to crystalline phases which were difficult to identify. The high temperature high-pressure compaction in vacuum of amorphous ball-milled powders resulted in a similar structure like in the powders showing nanocrystals embedded in the amorphous matrix. The crystallites were imaged using HREM. Interplanar distances were measured in pictures obtained by inverse fast Fourier transform (IFFT) of atomic planes to obtain better contrast. Analysis of the IFFT from high-resolution micrographs allowed to identify Cu(10)Zr(7) phase. Point analysis and elemental mapping performed using nondispersive X-ray energy spectroscopy showed uniform elements distribution indicating that chemical segregation to nanocrystals is within measurement error. PMID:18614372

  6. Electrical and Magneto-Resistivity Measurements on Amorphous Copper-Titanium Alloys at Low Temperatures

    NASA Astrophysics Data System (ADS)

    Fan, Renyong

    1992-01-01

    The anomalous transport properties of highly disordered metallic glasses, which require corrections to the classical Boltzmann theory, are due to quantum interference effects of the scattered electron waves. These corrections provide new contributions to the resistivity: "weak localization" and "electron-electron interaction". To study these quantum interference effects, we have made the highest-precision measurements, so far, of the resistances of the amorphous rm Cu_{50}Ti_{50 } and rm Cu_{60}Ti _{40} ribbons at much lower temperatures than before (15mK < T < 6K) and in small magnetic fields (0T < B < 0.2T). To measure the resistance and temperature accurately, we developed a novel method: measuring the resistance perpendicular to the ribbons with potassium as the non-superconducting glue between the CuTi ribbons and two Cu electrodes in order to make excellent electrical and thermal contact. With this method, we were able to measure the resistances with a relative precision of Deltarho/rho = 10^{-7}-10 ^{-8} and temperatures reliably down to 15mK with an error of less than 1mK. The zero field resistances and magnetoresistances were analyzed using weak localization theories that include the Zeeman splitting and electron-electron interaction theories. Possible background contributions from the K layers, the Cu electrodes, and their boundaries are quantified in the analysis. In zero field, these background contributions were negligible for T<3K. At zero magnetic field and T<0.15K, we found that electron -electron interaction dominates the resistance, while weak localization makes a nontrivial contribution to the resistance for T>0.15K. In contrast, at the lowest temperatures, the magnetoresistances were dominated by weak localization with Zeeman splitting and Maki-Thompson superconducting fluctuations. For higher magnetic fields and lowest temperatures (B/T > 1 T/K), we find discrepancies between our data and the theoretical calculations. We found that most of the

  7. Triple-junction amorphous silicon alloy solar cell with 14.6{percent} initial and 13.0{percent} stable conversion efficiencies

    SciTech Connect

    Yang, J.; Banerjee, A.; Guha, S.

    1997-06-01

    We have achieved 14.6{percent} initial and 13.0{percent} stable conversion efficiencies using an amorphous silicon-based alloy in a spectrum-splitting, triple-junction structure. These efficiencies have been confirmed independently by the National Renewable Energy Laboratory. Key factors leading to this major advance include improvements made in the low band-gap amorphous silicon{endash}germanium alloy cell, the pn tunnel junction between the component cells, and the top conducting oxide. {copyright} {ital 1997 American Institute of Physics.}

  8. Formation of amorphous alloys on 4H-SiC with NbNi film using pulsed-laser annealing

    NASA Astrophysics Data System (ADS)

    De Silva, Milantha; Ishikawa, Seiji; Miyazaki, Takamichi; Kikkawa, Takamaro; Kuroki, Shin-Ichiro

    2016-07-01

    Amorphous alloys containing Ni-Si-Nb-C were formed on 4H-SiC creating a low resistance Ohmic contact electrode. In a conventional nickel silicide (NiSi) electrode on SiC, a carbon agglomeration at the silicide/SiC interface occurs, and contact resistance between NiSi and SiC substrate becomes larger. For carbon agglomeration suppression, nanosecond non-equilibrium laser annealing was introduced, and to form metal carbides, carbon-interstitial type metals Nb and Mo were introduced. Ni, Nb, Mo, Nb/Ni, Mo/Ni multilayer contacts, and NbNi mixed contact were formed on the C-face side of n-type 4H-SiC wafers. The electrical contact properties were investigated after a 45 ns pulse laser annealing in N2 ambient. As a result, with NbNi film, an amorphous alloy with Ni-Si-Nb-C was formed, and a low specific contact resistance of 5.3 × 10-4 Ω cm2 was realized.

  9. Top-view approach for in-situ observation of growth morphology in bulk transparent organic alloys

    NASA Astrophysics Data System (ADS)

    Witusiewicz, V. T.; Hecht, U.; Rex, S.

    2012-08-01

    A new experimental method for in-situ observation of microstructure formation in top view during unidirectional solidification of bulk, transparent, organic alloys is presented. This method allows observing growth patterns over an extended interface area with high resolution and minimal optical aberrations. With (D)camphor-neopentylglycol-succinonitrile (DC-NPG-SCN) alloys a series of unidirectional solidification experiments were performed in order to validate the set-up. By means of multi-focus exposition eutectic cells were observed over a depth of several millimeters, followed by 3D reconstruction of their shape. The method also allows capturing the integral interface dynamics and measuring its relative undercooling.

  10. Enhanced magnetocaloric response in Cr /Mo containing Nanoperm-type amorphous alloys

    NASA Astrophysics Data System (ADS)

    Franco, V.; Conde, C. F.; Conde, A.; Kiss, L. F.

    2007-01-01

    The magnetocaloric effect of Fe76Cr8-xMoxCu1B15 (x=0,4) alloys is studied. Although the combined addition of Cr and Mo is more efficient in tuning the Curie temperature of the alloy, the Mo-free alloy presents a higher magnetocaloric response. The refrigerant capacity (RC) for the Mo-containing alloy is comparable to that of Gd5Ge1.9Si2Fe0.1 (for a field of 50kOe, RC =273Jkg-1 for the Mo alloy vs 240Jkg-1 for the Gd-based one), with a larger temperature span of the optimal refrigeration cycle (250K vs 90K, respectively). The restriction of the temperature span to 90K gives RC =187Jkg-1 for the Mo alloy. A master curve behavior for the magnetic entropy change is also evidenced.

  11. Thermal and magnetic properties of melt-spun Co-Fe-B-Si-(Cr/Ta) amorphous alloys

    NASA Astrophysics Data System (ADS)

    Jo, Hye-in; Han, Bokyeong; Yim, Haein Choi; Kwon, Woojun

    2013-02-01

    The ferromagnetic amorphous alloys Co-Fe-B-Si-Cr and Co-Fe-B-Si-Ta were systemically investigated. [(Co1- x Fe x )0.75B0.2Si0.05]96Cr4 ( x = 0, 0.1, 0.4, 0.7, 1.0) and [(Co1- x Fe x )0.75B0.2Si0.05]96Ta4 ( x = 0, 0.1, 0.3, 0.5, 1.0) ribbons were prepared by using the melt-spinning technique. Amorphous structures were confirmed by the presence of a broad and halo peak in X-ray diffraction (XRD). The thermal characteristics, such as the glass transition temperature ( T g ), the crystallization temperature ( T x ) and the supercooled liquid region (Δ T x = T x - T g ), were measured by means of a differential scanning calorimeter (DSC). For the Co-Fe-B-Si-Cr alloys, the values of Δ T x were in the range of 51.6-61.4 K, and for Co-Fe-B-Si-Ta alloys, they were in the range of 39.3-55.5 K. The magnetic properties were examined by means of a vibrating sample magnetometer (VSM) at a maximum field strength of 3000 Oe. These glassy ribbons exhibited soft magnetic properties. The saturation magnetization ( M s ) and the coercive force ( H c ) were in the ranges of 307.85-854.52 emu·cm3 and 0.64-0.89 Oe, respectively.

  12. Highly processable bulk metallic glass-forming alloys in the Pt-Co-Ni-Cu-P system

    NASA Astrophysics Data System (ADS)

    Schroers, Jan; Johnson, William L.

    2004-05-01

    Highly processable bulk metallic glass alloys in the Pt-Co-Ni-Cu-P system were discovered. The alloys show low liquidus temperature below 900 K, excellent processability with low critical cooling rate reflecting in maximum casting thicknesses in quartz tubes of up to 20 mm, and a large supercooled liquid region. The Pt57.5Cu14.7Ni5.3P22.5 composition has a liquidus temperature of 795 K, a glass transition temperature of 508 K with a supercooled liquid region of 98 K. For medical and jewelry applications a Ni-free alloy, Pt60Cu16Co2P22 was discovered with a liquidus temperature of 881 K, a glass transition temperature of 506 K, and a supercooled liquid region of 63 K. Glass formation was observed in a wider composition range. Vickers hardness of these alloys is in the 400 Hv range. The alloys can be processed in the supercooled liquid region in air without any measurable oxidation. In this region, a large processing window is available in which the material does not embrittle. Embrittlement in these alloys is correlated with crystallization. It can be avoided as long as substantial crystallization does not take place during isothermal processing in the supercooled liquid region. Also, liquid processing can be performed in air when flux with B2O3.

  13. Formation ranges of icosahedral, amorphous and crystalline phases in rapidly solidified Ti-Zr-Hf-Ni alloys

    SciTech Connect

    Chen, N. . E-mail: asyzxy@imr.edu; Louzguine, D.V.; Ranganathan, S.; Inoue, A.

    2005-02-01

    From the quaternary Ti-Zr-Hf-Ni phase diagram, the cross-section at 20 at.% Ni was selected for investigation. The icosahedral quasicrystalline, crystalline and amorphous phases were observed to form in nine kinds of rapidly solidified (Ti{sub x}Zr{sub y}Hf{sub z}){sub 80}Ni{sub 20} (x + y + z = 1) alloys at different compositions. The quasilattice constants of 0.519 and 0.531 nm were obtained for the icosahedral phase formed in the melt-spun Ti{sub 40}Zr{sub 20}Hf{sub 20}Ni{sub 20} and Ti{sub 20}Zr{sub 40}Hf{sub 20}Ni{sub 20} alloys, respectively. The icosahedral phase formed in the melt-spun Ti{sub 40}Zr{sub 20}Hf{sub 20}Ni{sub 20} alloy especially is thermodynamically stable. The supercooled liquid region of the Ti{sub 20}Zr{sub 20}Hf{sub 40}Ni{sub 20} glassy alloy reached 64 K. From these results a comparison of quasicrystal-forming and glass-forming abilities was carried out. The quasicrystal-forming ability was reduced and glass-forming ability was improved with an increase in Hf and Zr contents in the (Ti{sub x}Zr{sub y}Hf{sub z}){sub 80}Ni{sub 20} alloys. On the other hand, an increase in Ti content caused an improvement in quasicrystal-forming ability.

  14. The effect of mechanical milling on the soft magnetic properties of amorphous FINEMET alloy

    NASA Astrophysics Data System (ADS)

    Gheiratmand, T.; Hosseini, H. R. Madaah; Davami, P.; Gjoka, M.; Song, M.

    2015-05-01

    The effect of milling time on the magnetic properties of FINEMET amorphous ribbons has been investigated using X-ray diffraction, Mössbauer spectroscopy, thermo-magnetic measurements, transmission electron microscopy and SQUID magnetometery. Ribbons were melt-spun at a wheel speed of 38 ms-1 and then mechanically milled for different periods up to 45 min. The results showed that the partially crystallization of the amorphous powder occurs during milling. TEM observations confirmed the formation of small volume fraction of the crystalline phase with ~9 nm crystallite size in the amorphous matrix for the ribbon milled for 45 min. Thermo-magnetic measurements indicated the enhancement of the Curie temperature of amorphous phase during milling which is due to the annihilation of free volumes and microstructural ordering. The Hopkinson effect led to the monotonic increase of magnetization with respect to the temperature before reaching the Curie temperature of the milled samples. Moreover; the magnetization increased with the formation of the Fe(Si) phase while the coercivity decreased. Mössbauer spectroscopy and thermo-magnetic measurements revealed the existence of 13% Fe in crystalline phase. The composition of crystalline phase was determined as Fe-16.5Si. Hyperfine field values increased with milling time, suggesting the ordering of the structure and enhancement of the number of Fe-Fe atomic pairs in the crystalline phase comparing to the primary amorphous ribbon.

  15. Bulk-alloy microstructural analogues for transient liquid-phase bonds in the NiAl/Cu/Ni system

    SciTech Connect

    Gale, W.F.; Abdo, Z.A.M.

    1999-12-01

    Transient liquid-phase (TLP) bonds between dissimilar materials can have complex microstructures that evolve both during holding at the bonding temperature and on cooling. In this article, an examination is made of the feasibility of producing bulk-alloy microstructural analogues for individual microstructural features of dissimilar material TLP bonds. The ultimate intent of this work is to enable the contribution of individual microstructural features to the overall properties of TLP bonds to be determined. Specifically, the article focuses on the production, characterization, and applications of microstructural analogues for TLP bonds in an NiAl/Cu/Ni model system. The article examines the use of five different cast Ni-Al-Cu alloys, together with heat treatment of selected materials, as bulk analogues for six distinct microstructural regions of the NiAl/Cu/Ni bonds. Each of these analogues is characterized in detail by transmission electron microscopy (TEM) and compared to the relevant target region of the bond. An initial examination is also made of the use of bulk alloys in aiding an understanding of phase transformations and structure-property relationships in these bonds.

  16. Thermal conductivity of bulk and nanowire Mg₂SixSn1–x alloys from first principles

    DOE PAGESBeta

    Li, Wu; Lindsay, L.; Broido, D. A.; Stewart, Derek A.; Mingo, Natalio

    2012-11-29

    The lattice thermal conductivity (κ) of the thermoelectric materials, Mg₂Si, Mg₂Sn, and their alloys, are calculated for bulk and nanowires, without adjustable parameters. We find good agreement with bulk experimental results. For large nanowire diameters, size effects are stronger for the alloy than for the pure compounds. For example, in 200 nm diameter nanowires κ is lower than its bulk value by 30%, 20%, and 20% for Mg₂Si₀.₆Sn₀.₄, Mg₂Si, and Mg₂Sn, respectively. For nanowires less than 20 nm thick, the relative decrease surpasses 50%, and it becomes larger in the pure compounds than in the alloy. At room temperature, κmore » of Mg₂SixSn1–x is less sensitive to nanostructuring size effects than SixGe1–x, but more sensitive than PbTexSe1–x. This suggests that further improvement of Mg₂SixSn1–x as a nontoxic thermoelectric may be possible.« less

  17. Characterization of oxide layers on amorphous Zr-based alloys by Auger electron spectroscopy with sputter depth profiling

    NASA Astrophysics Data System (ADS)

    Baunack, S.; Mudali, U. Kamachi; Gebert, A.

    2005-09-01

    Amorphous Zr-Cu-Ni-Al-[Ti, Nb] ribbons prepared by melt spinning under argon atmosphere were subjected to electrochemical investigations. Passive films developed at potentiostatic anodic polarization in sulphuric acid solution were investigated by Auger electron spectroscopy (AES) and sputter depth profiling. Changes in the shape of the Auger peaks have been analyzed by factor analysis of the spectra obtained during depth profiling. Pronounced changes in shape and position occur for the Zr, Al, and Ti Auger transitions, but not for Cu and Ni. At least three different peak shapes for O(KVV) were found and attributed to different oxygen binding states. The alloy composition has no significant effect on the thickness and composition of the oxide layer. In multi-element alloys preferential sputtering is a common phenomenon. In the steady state of sputtering, a significant depletion in Cu is found. At the oxide/metal interface, a distinct enrichment of copper is found for all alloys and treatments. The degree of this Cu enrichment depends on the pretreatment. It is higher for the electrochemically-passivated samples than for samples with oxide layers grown during melt spinning.

  18. Bulk deformation of Ti-6.8Mo-4.5Fe-1.5Al (timetal LCB) alloy

    NASA Astrophysics Data System (ADS)

    Weiss, I.; Srinivasan, R.; Saqib, M.; Stefansson, N.; Jackson, A. G.; Leclair, S. R.

    1996-06-01

    Recently, a low-cost near-β titanium alloy (Timetal LCB Ti-6.8Mo-4.5Fe-l.5Al wt %) containing iron and molybdenum has been developed. This alloy is cold formable in the β microstructure and can be aged to high strengths by precipitating the a phase. Due to its combination of cold formability and high strength, the alloy is a potential replacement for steel components in the automotive industry. The current study was undertaken to evaluate the cold bulk forming characteristics of Timetal LCB for use in lightweight automotive applications. Room-temperature compression tests conducted over a strain-rate range of 0.01 to 5/s indicate that the bulk cold compression of the alloy is affected by two factors: the microstructure and the length-to-diameter aspect ratio of the specimen. In the aged condition, when the microstructure has a-phase particles distributed along flow lines in the β-phase matrix, the alloy has the propensity for shear failure when deformed in compression in a direction parallel to the flow lines. In the solution-heat-treated condition, the microstructure consists of β grains with athermal ω phase. In this condition, the alloy can be cold compressed to 75 % reduction in height using specimens with aspect ratio of 1.125, but fails by shear for a larger aspect ratio of 1.5. Plastic deformation of the material occurs initially by single slip in most grains, but changes to multiple slip at true plastic strains larger than about 0.15. At a slow strain rate, the deformation is uniform, and the material work hardens continuously. At high strain rates, shear bands develop, and the localized deformation and temperature rise due to deformation heating leads to flow softening during compression. Although there is a considerable rise in temperature (200 to 500 °) during deformation, precipitation of the a phase was not observed.

  19. Enhancing the efficiency of wastewater treatment by addition of Fe-based amorphous alloy powders with H2O2 in ferrofluid

    NASA Astrophysics Data System (ADS)

    Yang, Chun-Cheng; Bian, Xiu-Fang; Yang, Jian-Fei

    2014-03-01

    Using combination of ferrofluid (FF) and Fe-based amorphous alloy in the advanced treatment of high concentration, organic wastewater was investigated. The addition of Fe73.5Nb3Cu1Si13.5B9 amorphous alloy powders into a FF give rise to a dramatic enhancement in decreasing chemical oxygen demand (COD) and decolorization. The removal rate of COD by using FF that combined Fe73.5Nb3Cu1Si13.5B9 metallic glass (MG) particles reached 92% in the presence of H2O2, nearly more than 50% higher than that by using only FF. Furthermore, compared with the FF, the decolorizing effect of the combination was 20% higher. It has been found that MG powders with the amorphous structures have high efficiency of waste water treatment and lead to high catalytic ability.

  20. Structural analysis of quaternary Se{sub 85−x}Sb{sub 10}In{sub 5}Ag{sub x} bulk glassy alloys

    SciTech Connect

    Sharma, Rita Sharma, Shaveta; Kumar, Praveen; Chander, Ravi; Thangaraj, R.; Mian, M.

    2015-08-28

    The physical properties of chalcogenide semiconductor have attracted much attention recently due to their applications in optical recording media and inorganic resist due to photo induced structural transformations observed in these materials. The bulk samples of Se{sub 85-x}Sb{sub 10}In{sub 5}Ag{sub x} system are prepared by melt-quenching technique. X-ray diffraction technique and RAMAN spectroscopy have been used to study the role of Ag additive on the amorphous/crystalline nature and molecular structure of Se{sub 85}Sb{sub 10}In{sub 5} glassy alloys. The phases Sb{sub 2}Se{sub 3}, In-Sb and In{sub 2}Se{sub 3} has been observed by X-ray diffraction. The formation of AgInSe{sub 2} phase along with the enhancement in intensity has been observed with the Ag addition.Three bands observed by raman spectroscopy for Se85Sb10In5 are at 70 cm-1, 212cm-1 and 252cm-1. The formation of small bands up to wavenumber 188cm{sup -1} and shifting in second band along with the increase in intensity up to sample x=5 has been observed with the Ag addition. The enhancement in intensity in third band with Ag content has been observed.

  1. The detrimental effect of flux-induced boron alloying in Pd–Si–Cu bulk metallic glasses

    SciTech Connect

    Granata, D.; Fischer, E.; Wessels, V.; Löffler, J. F.

    2015-01-05

    We report on advanced insights into the fluxing of Pd–Si–Cu bulk metallic glasses. Flux-induced boron alloying and trapping of oxides are found to be associated with the employed boron oxide fluxing agent, and both influence the attainable glass-forming ability (GFA) in opposite ways. Incorporated boron strongly deteriorates the GFA due to a rising liquidus temperature, while the oxygen reduction improves it. Thus, proper fine-tuning of the fluxing time and overheating characteristics leads to an enhancement of GFA. In the current case, the critical diameter of Pd{sub 77.5}Si{sub 16.5}Cu{sub 6} bulk metallic glasses can be increased to 15 mm, as compared to 3 mm in the unfluxed case. Based on these results, we illustrate that the development of further fluxing agents is crucial for enhancement of the key properties of bulk metallic glasses.

  2. Glass formation and magnetic properties in the Co and Fe-based amorphous alloy with small Mo or Nb additions

    NASA Astrophysics Data System (ADS)

    Jo, Hye-In; Choi-Yim, Haein

    2012-02-01

    The ferromagnetic metallic glass alloys in the Co-Fe-B-Si-M (M = Mo or Nb) system were investigated. Ingots of [(Co1- x Fe x )0.75B0.2Si0.05]96Mo4 ( x = 0, 0.2, 0.5, 0.8, 1.0) and [(Co1- x Fe x )0.75 B0.2Si0.05]96Nb4 ( x = 0, 0.2, 0.5, 0.8, 1.0) alloys were cast into about 30 µm-thick ribbons by using a melt spinning method. As-spun ribbons were identified as being fully amorphous by using X-ray diffraction (XRD). The thermal stability parameters, such as the supercooled liquid region (Δ T x = T g - T x ) and the exothermic heat (Δ H Exo ), were measured by using differential scanning calorimetry (DSC). For Co-Fe-B-Si-Mo alloys, Δ T x and Δ H Exo were in the range of 41.4-81.7 K and 23.40-104.21 J/g, and for Co-Fe-B-Si-Nb alloys, Δ T x and Δ H Exo were in the range of 60.4-88.0 K and 18.45-62.05 J/g, respectively. These glassy ribbons also exhibited semi-hard magnetic properties, i.e., a coercive force ( H c ) of 67.26-100.68 Oe and a saturation magnetization ( M s ) of 341.288-746.176 emu·cm3.

  3. Characterization of atomic-level structure in Fe-based amorphous and nanocrystalline alloy by experimental and modeling methods

    SciTech Connect

    Babilas, Rafał

    2015-09-15

    The atomic structure of Fe{sub 70}Nb{sub 10}B{sub 20} alloy in “as-cast” state and after annealing was investigated using high-energy X-ray diffraction (XRD), Mössbauer spectroscopy (MS) and high resolution transmission electron microscopy (HRTEM). The HRTEM observations allowed to indicate some medium-range order (MRO) regions about 2 nm in size and formation of some kinds of short-range order (SRO) structures represented by atomic clusters with diameter ca. 0.5 nm. The Reverse Monte Carlo (RMC) method basing on the results of XRD measurements was used in modeling the atomic structure of Fe-based alloy. The structural model was described by peak values of partial pair correlation functions and coordination numbers determined by Mössbauer spectroscopy investigations. The three-dimensional configuration box of atoms was obtained from the RMC simulation and the representative Fe-centered clusters were taken from the calculated structure. According to the Gonser et al. approach, the measured spectra of alloy studied were decomposed into 5 subspectra representing average Fe–Fe coordination numbers. Basing on the results of disaccommodation of magnetic permeability, which is sensitive to the short order of the random packing of atoms, it was stated that an occurrence of free volume is not detected after nanocrystallization process. - Highlights: • Atomic cluster model of amorphous structure was proposed for studied glassy alloy. • Short range order (ca. 0.5 nm) regions interpreted as clusters were identified by HREM. • Clusters correspond to coordination numbers (N = 4,6,8,9) calculated by using Gonser approach. • Medium-range order (ca. 2 nm) could be referred to few atomic clusters. • SRO regions are able to grow up as nuclei of crystalline bcc Fe and iron borides. • Crystalline particles have spherical morphology with an average diameter of 20 nm.

  4. Comparison of the Crystallization Behavior of Fe-Si-B-Cu and Fe-Si-B-Cu-Nb-Based Amorphous Soft Magnetic Alloys

    NASA Astrophysics Data System (ADS)

    Smith, Casey; Katakam, Shravana; Nag, Soumya; Zhang, Y. R.; Law, J. Y.; Ramanujan, Raju V.; Dahotre, Narendra B.; Banerjee, Rajarshi

    2014-06-01

    The role of the solute elements, copper, and niobium, on the different stages of de-vitrification or crystallization of two amorphous soft magnetic alloys, Fe73.5Si13.5B9Nb3Cu1, also referred to as FINEMET, and a Fe76.5Si13.5B9Cu1 alloy, a model composition without Nb, has been investigated in detail by coupling atom probe tomography and transmission electron microscopy. The effects of copper clustering and niobium pile-up at the propagating interface between the α-Fe3Si nanocrystals and the amorphous matrix, on the nucleation and growth kinetics have been addressed. The results demonstrate that while Cu clustering takes place in both alloys in the early stages, the added presence of Nb in FINEMET severely restricts the diffusivity of solute elements such as Cu, Si, and B. Therefore, the kinetics of solute partitioning and mobility of the nanocrystal/amorphous matrix interface is substantially slower in FINEMET as compared to the Fe76.5Si13.5B9Cu1 alloy. Consequently, the presence of Nb limits the growth rate of the α-Fe3Si nanocrystals in FINEMET and results in the activation of a larger no. of nucleation sites, leading to a substantially more refined microstructure as compared to the Fe76.5Si13.5B9Cu1 alloy.

  5. Magnetization kinetics in tension and field annealed Fe-based amorphous alloys

    NASA Astrophysics Data System (ADS)

    Hasegawa, Ryusuke; Takahashi, Kengo; Francoeur, Bruno; Couture, Pierre

    2013-05-01

    Magnetization kinetics in tension-annealed and field-annealed amorphous magnetic materials indicates that strain and magnetic fields are equally effective in inducing and relaxing local structural and magnetic anisotropy changes. This observation is based on the thermomagnetic aging of the magnetic properties obtained in the materials studied.

  6. Effect of annealing on atomic ordering of amorphous ZrTaTiNbSi alloy

    NASA Astrophysics Data System (ADS)

    Yang, Tsung-Han; Huang, Rong-Tang; Wu, Cheng-An; Chen, Fu-Rong; Gan, Jon-Yiew; Yeh, Jien-Wei; Narayan, Jagdish

    2009-12-01

    In this letter, we have reported on initial stages of atomic ordering in ZrTaTiNbSi amorphous films during annealing. The atomic ordering and structure evolution were studied in Zr17Ta16Ti19Nb22Si26 amorphous films as a function of annealing temperature in the temperature range from 473 to 1173 K. Up to annealing temperature of 1173 K, the films retained amorphous structure, but the degree of disorder is increased with the increase in temperature. The formation of Si-M covalent bonds, which contributed to the local atomic arrangement, occurred in the initial stages of ordering. The bonding reactions between Si and other metal species explain the anomalous structural changes which were observed in x-ray diffraction and transmission electron microscopy. We discuss the stages of phase transformation for amorphous films as a function of annealing temperature. From these results, we propose that annealing leads to formation of random Si-M4 tetrahedron, and two observed rings, a first and second in the electron diffraction patterns compared to M-M and Si-M bond length, respectively.

  7. Deuterium dynamics in the icosahedral and amorphous phases of the Ti40Zr40Ni20 hydrogen-absorbing alloy studied by 2H NMR

    NASA Astrophysics Data System (ADS)

    Gradišek, A.; Kocjan, A.; McGuiness, P. J.; Apih, T.; Kim, Hae Jin; Dolinšek, J.

    2008-11-01

    The Ti40Zr40Ni20 hydrogen-absorbing alloy was prepared in the icosahedral and amorphous phases by controlling the rotation speed of the melt-spinning method of sample preparation, and the deuterium dynamics was investigated by 2H NMR dynamic lineshape and spin-lattice relaxation. The results were analysed by the lineshape and relaxation models that assume deuterium thermally activated hopping within a manifold of different chemical environments. The observed 8% larger activation energy for the deuterium hopping over the interstitial sites and the 10% larger static spectrum width of the amorphous phase, as compared to the icosahedral phase, can be accounted for by the larger deuterium content of the investigated amorphous sample. From the deuterium dynamics point of view, the icosahedral phase is not special with respect to the amorphous modification of the same material.

  8. Fabrication of MEMS-based Micro-fluxgate Sensor with Runway-shaped Co-based Amorphous Alloy Core

    NASA Astrophysics Data System (ADS)

    Wu, Shaobin; Chen, Shi; Ouyang, Jun; Zuo, Chao; Yu, Lei; Yang, Xiaofei

    2011-01-01

    High-precision magnetic micro-sensor is an interdisciplinary subject of magnetic field measurement techniques and micro-electromechanical systems (MEMS) technology. A micro-fluxgate magnetic sensor based MEMS technology was designed and fabricated in this paper. This device is a micro-magnetic sensor with a symmetric construction, closed magnetic circuits and differential form. A 25μm thick Fluxgate core of runway model, made by Co-based amorphous alloy, was etched by laser and pasted on the substrate accurately. Excitation coil and sensing coil of 3D solenoid structure were prepared by RF magnetron sputtering and UV-lithography. The minimum line width of the coil is 50 μm. The experimental result shows that micro-fluxgate devices with the size of 5.7mm×7.1mm×60μm had a stable structure.

  9. A tunable amorphous p-type ternary oxide system: The highly mismatched alloy of copper tin oxide

    SciTech Connect

    Isherwood, Patrick J. M. Walls, John M.; Butler, Keith T.; Walsh, Aron

    2015-09-14

    The approach of combining two mismatched materials to form an amorphous alloy was used to synthesise ternary oxides of CuO and SnO{sub 2}. These materials were analysed across a range of compositions, and the electronic structure was modelled using density functional theory. In contrast to the gradual reduction in optical band gap, the films show a sharp reduction in both transparency and electrical resistivity with copper contents greater than 50%. Simulations indicate that this change is caused by a transition from a dominant Sn 5s to Cu 3d contribution to the upper valence band. A corresponding decrease in energetic disorder results in increased charge percolation pathways: a “compositional mobility edge.” Contributions from Cu(II) sub band-gap states are responsible for the reduction in optical transparency.

  10. Morphology and magnetic behavior of cobalt rich amorphous/nanocrystalline (Co-Ni)70Ti10B20 alloyed powders

    NASA Astrophysics Data System (ADS)

    Raanaei, Hossein; Mohammad-Hosseini, Vahid

    2016-09-01

    The effect of milling time on microstructural and magnetic behavior of mechanically alloyed Co49Ni21Ti10B20 is investigated by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, differential scanning calorimetry and vibrating sample magnetometer. It is shown, with increasing milling time, the crystallite size decreases and finally reaches to a low value after 190 h of milling time. The increase in microstrain is also observed during the milling process. The results indicate the coexistence between amorphous and nanocrystalline phases after 190 h of milling time. Moreover, the lowest magnetic coercivity of about 39 Oe at the final milling stage is observed. The results of annealed sample reveal structural ordering of constituent elements.

  11. Evidence for highly anharmonic low-frequency vibrational modes in bulk amorphous Pd40Cu40P20

    NASA Astrophysics Data System (ADS)

    Safarik, D. J.; Schwarz, R. B.

    2009-09-01

    We have measured the elastic constants of amorphous Pd40Cu40P20 (isotropic, two independent elastic constants), single crystal Pd40Cu40P20 (tetragonal, six elastic constants), and single crystal Pd50Cu50 (fcc, three elastic constants) over the range 3.9amorphous Pd40Cu40P20 includes an additional contribution, ΔCE(T) , which becomes dominant for T<20K : C(T)=C(0)-BT2+ΔCLat(T)+ΔCE(T) . The ΔCE(T) contribution can be explained by the presence of a small number of low-frequency, highly anharmonic vibrational modes, which we characterize as Einstein oscillators with temperature θE≈12K and Grüneisen parameter γEC'≫2 . Theory and computer modeling suggest that these modes involve the collective vibration of stringlike arrays of atoms.

  12. Thermal evolution of short-range order in Cu-Hf-based amorphous alloys

    NASA Astrophysics Data System (ADS)

    Damonte, L. C.; Pasquevich, A. F.; Mendoza-Zélis, L.

    2010-04-01

    A Perturbed Angular Correlation study on melt-spun Cu60Hf20Ti20 and Cu60Hf40 is presented. The influence of Ti addition on thermal stability and crystallization mechanism is followed by differential scanning calorimetry. The evolution of quadrupole parameters with measurement temperature is analyzed in both alloys in order to get insight into the crystallization process. Although an intricate crystallization mechanism is observed for the Ti containing alloy, the final stage is similar, irrespective of minority atom.

  13. Impact of corrosive mediums on mechanical properties of amorphous alloys under influence of impulse current

    NASA Astrophysics Data System (ADS)

    Pluzhnikova, Tatyana; Fedorov, Victor; Sidorov, Sergey; Gubanova, Victoria; Pluzhnikov, Sergey

    2016-01-01

    Impact of corrosion mediums (solutions of NACE and H2SO4, HCl) on σ - ɛ graphs for alloys has been studied at synchronous passage of electrical current impulses accompanying momentary dropping of mechanical stress. Relations between dropping of mechanical stress and density of impulse electrical current have been established in studied materials. Structural and morphological condition of surface has been researched after influence of corrosive mediums with different concentration in studied alloys.

  14. Density and glass forming ability in amorphous atomic alloys: The role of the particle softness.

    PubMed

    Douglass, Ian; Hudson, Toby; Harrowell, Peter

    2016-04-14

    A key property of glass forming alloys, the anomalously small volume difference with respect to the crystal, is shown to arise as a direct consequence of the soft repulsive potentials between metals. This feature of the inter-atomic potential is demonstrated to be responsible for a significant component of the glass forming ability of alloys due to the decrease in the enthalpy of fusion and the associated depression of the freezing point. PMID:27083733

  15. Density and glass forming ability in amorphous atomic alloys: The role of the particle softness

    NASA Astrophysics Data System (ADS)

    Douglass, Ian; Hudson, Toby; Harrowell, Peter

    2016-04-01

    A key property of glass forming alloys, the anomalously small volume difference with respect to the crystal, is shown to arise as a direct consequence of the soft repulsive potentials between metals. This feature of the inter-atomic potential is demonstrated to be responsible for a significant component of the glass forming ability of alloys due to the decrease in the enthalpy of fusion and the associated depression of the freezing point.

  16. Electronic Structure of NiPdP Amorphous Metals

    NASA Astrophysics Data System (ADS)

    Swihart, J. C.; Nicholson, D. M. C.; Shelton, W. A.; Wang, Y.

    1996-03-01

    The understanding of the structure, properties and required cooling rates for bulk amorphous alloys is hindered by the the large number of constituents in the typical alloy. One of the compositionally simplest systems that can be cast into bulk specimens is Ni_0.4Pd_0.4P_0.2. Furthermore, the thoroughly studied structure of amorphous Ni_0.8P_0.2 provides a useful starting point for its investigation. We use the locally selfconsistent multiple scattering (LSMS) method to determine the electronic structure, mass density, and energy as Pd is substituted at random for Ni in the Ni_0.8P_0.2 amorphous structure. Work supported by Laboratory Directors Research Development program at Oak Ridge National Laboratory, Division of Materials Science, and the Mathematical Information and Computational Science Division of the Office of Computational Technology Research, US DOE under subcontract DEAC05-84OR21400 with Lockheed-Martin Energy Systems, Inc.

  17. An environment-dependent interatomic potential for silicon carbide: calculation of bulk properties, high-pressure phases, point and extended defects, and amorphous structures.

    PubMed

    Lucas, G; Bertolus, M; Pizzagalli, L

    2010-01-27

    An interatomic potential has been developed to describe interactions in silicon, carbon and silicon carbide, based on the environment-dependent interatomic potential (EDIP) (Bazant et al 1997 Phys. Rev. B 56 8542). The functional form of the original EDIP has been generalized and two sets of parameters have been proposed. Tests with these two potentials have been performed for many properties of SiC, including bulk properties, high-pressure phases, point and extended defects, and amorphous structures. One parameter set allows us to keep the original EDIP formulation for silicon, and is shown to be well suited for modelling irradiation-induced effects in silicon carbide, with a very good description of point defects and of the disordered phase. The other set, including a new parametrization for silicon, has been shown to be efficient for modelling point and extended defects, as well as high-pressure phases. PMID:21386297

  18. Replication of surface features from a master model to an amorphous metallic article

    DOEpatents

    Johnson, William L.; Bakke, Eric; Peker, Atakan

    1999-01-01

    The surface features of an article are replicated by preparing a master model having a preselected surface feature thereon which is to be replicated, and replicating the preselected surface feature of the master model. The replication is accomplished by providing a piece of a bulk-solidifying amorphous metallic alloy, contacting the piece of the bulk-solidifying amorphous metallic alloy to the surface of the master model at an elevated replication temperature to transfer a negative copy of the preselected surface feature of the master model to the piece, and separating the piece having the negative copy of the preselected surface feature from the master model.

  19. Anomalous small-angle X-ray scattering of nanoporous two-phase atomistic models for amorphous silicon–germanium alloys

    SciTech Connect

    Chehaidar, A.

    2015-09-15

    The present work deals with a detailed analysis of the anomalous small-angle X-ray scattering in amorphous silicon–germanium alloy using the simulation technique. We envisage the nanoporous two-phase alloy model consisting in a mixture of Ge-rich and Ge-poor domains and voids at the nanoscale. By substituting Ge atoms for Si atoms in nanoporous amorphous silicon network, compositionally heterogeneous alloys are generated with various composition-contrasts between the two phases. After relaxing the as-generated structure, we compute its radial distribution function, and then we deduce by the Fourier transform technique its anomalous X-ray scattering pattern. Using a smoothing procedure, the computed X-ray scattering patterns are corrected for the termination errors due to the finite size of the model, allowing so a rigorous quantitative analysis of the anomalous small-angle scattering. Our simulation shows that, as expected, the anomalous small-angle X-ray scattering technique is a tool of choice for characterizing compositional heterogeneities coexisting with structural inhomogeneities in an amorphous alloy. Furthermore, the sizes of the compositional nanoheterogeneities, as measured by anomalous small-angle X-ray scattering technique, are X-ray energy independent. A quantitative analysis of the separated reduced anomalous small-angle X-ray scattering, as defined in this work, provided a good estimate of their size.

  20. Electric and magnetic properties of Al86Ni8R6 (R=Sm, Gd, Ho) alloys in liquid and amorphous states

    NASA Astrophysics Data System (ADS)

    Sidorov, V.; Svec, P.; Svec, P.; Janickovic, D.; Mikhailov, V.; Sidorova, E.; Son, L.

    2016-06-01

    Electrical resistivity and magnetic susceptibility of Al86Ni8Sm6, Al86Ni8Gd6 and Al86Ni8Ho6 alloys are studied in a wide temperature range including amorphous, crystalline and liquid states. The negative value of resistivity temperature coefficient in amorphous ribbons is explained by the structural separation starting much before the beginning of their crystallization. The effective magnetic moments per Gd and Ho atoms are found to be essentially lower than for R3+ ions. The results are discussed in supposition of directed bonds between rare earth and aluminum atoms.

  1. An observation of amorphous-crystalline phase transitions at severe plastic deformation of the Ti{sub 50}Ni{sub 25}Cu{sub 25} alloy

    SciTech Connect

    Nosova, G. I.; Shalimova, A. V.; Sundeev, R. V.; Glezer, A. M. Pankova, M. N.; Shelyakov, A. V.

    2009-11-15

    The features of structural and phase transitions during severe plastic deformation (in Bridgman anvils) of the amorphous Ti{sub 50}Ni{sub 25}Cu{sub 25} alloy have been studied by X-ray diffraction and transmission electron microscopy. Application of successively increasing deformation has revealed three cycles of successive phase transitions from amorphous to crystalline state and vice versa. The results obtained are explained in terms of the superposition of the different channels of elastic energy dissipation, which are activated during severe plastic deformation.

  2. Magnetic anisotropy of Fe1-yXyPt-L10 [X = Cr, Mn, Co, Ni, Cu] bulk alloys

    NASA Astrophysics Data System (ADS)

    Cuadrado, R.; Klemmer, Timothy J.; Chantrell, R. W.

    2014-10-01

    We demonstrate by means of fully relativistic first principles calculations that, by substitution of Fe by Cr, Mn, Co, Ni, or Cu in FePt-L10 bulk alloys, with fixed Pt content, it is possible to tune the magnetocrystalline anisotropy energy by adjusting the content of the non-magnetic species in the material. The changes in the geometry due to the inclusion of each element induces different values of the tetragonality and hence changes in the magnetic anisotropy and in the net magnetic moment. The site resolved magnetic moments of Fe increase with the X content while those of Pt and X are simultaneously reduced. The calculations are in good quantitative agreement with experimental data and demonstrate that models with fixed band structure but varying numbers of electrons per unit cell are insufficient to describe the experimental data for doped FePt-L10 alloys.

  3. First-principles calculations for AlN, GaN, and InN: Bulk and alloy properties

    SciTech Connect

    Wright, A.F.; Nelson, J.S.

    1995-02-01

    First-principles density-functional calculations utilizing ab initio pseudopotentials and plane-wave expansions are used to determine lattice parameters, bulk moduli, and band structures for AlN, GaN and InN. It is found that large numbers of plane waves are necessary to resolve the nitrogen 2p wave functions and that explicit treatment of the gallium 3d and indium 4d electrons is important for an accurate description of GaN and InN. Several properties of ternary zinc-blende alloys are determined including their bond-length and bond-angle relaxation and their energy-gap bowing parameters. The similarity of the calculated zinc-blende and wurtzite direct gaps also allows estimates to be made of the energy gap versus composition for wurtzite alloys.

  4. Characterization of the interface between the bulk glass forming alloy Zr{sub 41}Ti{sub 14}Cu{sub 12}Ni{sub 10}Be{sub 23} with pure metals and ceramics

    SciTech Connect

    Schroers, Jan; Samwer, Konrad; Szuecs, Frigyes; Johnson, William L.

    2000-07-01

    The reaction of the bulk glass forming alloy Zr{sub 41}Ti{sub 14}Cu{sub 12}Ni{sub 10}Be{sub 23} (Vit 1) with W, Ta, Mo, AlN, Al{sub 2}O{sub 3}, Si, graphite, and amorphous carbon was investigated. Vit 1 samples were melted and subsequently solidified after different processing times on discs of the different materials. Sessile drop examinations of the macroscopic wetting of Vit 1 on the discs as a function of temperature were carried out in situ with a digital optical camera. The reactions at the interfaces between the Vit 1 sample and the different disc materials were investigated with an electron microprobe. The structure and thermal stability of the processed Vit 1 samples were examined by x-ray diffraction and differential scanning calorimetry. The results are discussed in terms of possible applications for composite materials. (c) 2000 Materials Research Society.

  5. Semiconductor to metallic transition in bulk accumulated amorphous indium-gallium-zinc-oxide dual gate thin-film transistor

    SciTech Connect

    Chun, Minkyu; Chowdhury, Md Delwar Hossain; Jang, Jin

    2015-05-15

    We investigated the effects of top gate voltage (V{sub TG}) and temperature (in the range of 25 to 70 {sup o}C) on dual-gate (DG) back-channel-etched (BCE) amorphous-indium-gallium-zinc-oxide (a-IGZO) thin film transistors (TFTs) characteristics. The increment of V{sub TG} from -20V to +20V, decreases the threshold voltage (V{sub TH}) from 19.6V to 3.8V and increases the electron density to 8.8 x 10{sup 18}cm{sup −3}. Temperature dependent field-effect mobility in saturation regime, extracted from bottom gate sweep, show a critical dependency on V{sub TG}. At V{sub TG} of 20V, the mobility decreases from 19.1 to 15.4 cm{sup 2}/V ⋅ s with increasing temperature, showing a metallic conduction. On the other hand, at V{sub TG} of - 20V, the mobility increases from 6.4 to 7.5cm{sup 2}/V ⋅ s with increasing temperature. Since the top gate bias controls the position of Fermi level, the temperature dependent mobility shows metallic conduction when the Fermi level is above the conduction band edge, by applying high positive bias to the top gate.

  6. Magnetocaloric effect and refrigeration cooling power in amorphous Gd7Ru3 alloys

    NASA Astrophysics Data System (ADS)

    Kumar, Pramod; Kumar, Rachana

    2015-07-01

    In this paper, we report the magnetic, heat capacity and magneto-caloric effect (MCE) of amorphous Gd7Ru3 compound. Both, temperature dependent magnetization and heat capacity data reveals that two transitions at 58 K and 34 K. MCE has been calculated in terms of isothermal entropy change (ΔSM) and adiabatic temperature change (ΔTad) using the heat capacity data in different fields. The maximum values of ΔSM and ΔTad are 21 Jmol-1K-1 and 5 K respectively, for field change of 50 kOe whereas relative cooling power (RCP) is ˜735 J/kg for the same field change.

  7. Growth mechanisms and characterization of hydrogenated amorphous- silicon-alloy films

    SciTech Connect

    Gallagher, A.; Ostrom, R.: Stutzin, G.; Tanenbaum, D. )

    1993-02-01

    This report describes an apparatus, constructed and tested, that allows measurement of the surface morphology of as-grown hydrogenated amorphous silicon films with atomic resolution using a scanning tunneling microscope. Surface topologies of 100-[degree][Lambda]-thick intrinsic films, deposited on atomically flat, crystalline Si and GaAs, are reported. These films surfaces are relatively flat on the atomic scale, indicating fairly homogeneous, compact initial film growth. The effect of probe-tip size on the observed topology and the development of atomically sharp probes is discussed. 17 refs, 9 figs.

  8. A Comparison of the Corrosion Resistance of Iron-Based Amorphous Metals and Austenitic Alloys in Synthetic Brines at Elevated Temperature

    SciTech Connect

    Farmer, J C

    2008-11-25

    Several hard, corrosion-resistant and neutron-absorbing iron-based amorphous alloys have now been developed that can be applied as thermal spray coatings. These new alloys include relatively high concentrations of Cr, Mo, and W for enhanced corrosion resistance, and substantial B to enable both glass formation and neutron absorption. The corrosion resistances of these novel alloys have been compared to that of several austenitic alloys in a broad range of synthetic brines, with and without nitrate inhibitor, at elevated temperature. Linear polarization and electrochemical impedance spectroscopy have been used for in situ measurement of corrosion rates for prolonged periods of time, while scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDAX) have been used for ex situ characterization of samples at the end of tests. The application of these new coatings for the protection of spent nuclear fuel storage systems, equipment in nuclear service, steel-reinforced concrete will be discussed.

  9. Triple-junction amorphous silicon alloy PV manufacturing plant of 5 MW annual capacity

    SciTech Connect

    Guha, S.; Yang, J.; Banerjee, A.

    1997-12-31

    A spectral-splitting, triple-junction a-Si alloy solar cell processor has been designed, built and optimized. A roll-to-roll process has been used to deposit two layers of back reflector, a triple-cell structure with nine layers of a-Si and a-SiGe alloys and a single layer of antireflection coating consecutively on a half-a-mile roll of stainless steel. The coated web is next slabbed and processed to make a variety of products. The design of the machine and processes used incorporate several key features developed for improving cell efficiency. In order to reduce manufacturing cost, higher deposition rates and thinner cells than are used in R and D have been used. The back reflector also consists of Al/ZnO rather than Ag/ZnO. Large-scale production has begun, and products are being shipped for a wide range of applications.

  10. Critical behavior and its correlation with magnetocaloric effect in amorphous Fe80-xVxB12Si8 (x=8, 10 and 13.7) alloys

    NASA Astrophysics Data System (ADS)

    Boutahar, A.; Lassri, H.; Hlil, E. K.; Fruchart, D.

    2016-01-01

    The critical exponents in Fe80-xVxB12Si8 (x=8, 10 and 13.7) amorphous alloys were investigated near ferromagnetic to paramagnetic phase transition temperature. All amorphous alloys exhibit a second order ferromagnetic to paramagnetic phase transition (SOMT). The critical exponents (β, γ and δ) were estimated using the modified Arrott plot technique (MAP), the Widom scaling relation (WSR), and the critical isotherm analysis (CIA). In addition, an independent analysis of the critical behavior is presented in terms of the magnetocaloric effect (MCE). It shows in accordance with conclusion from magnetization data analysis. The estimated critical exponent values are found to be consistent and comparable to those predicted by the mean field model. This result points out to the ferromagnetic exchange interaction of long-range type.

  11. New class of Si-based superlattices - Alternating layers of crystalline Si and porous amorphous Si(1-x)Ge(x) alloys

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; George, T.; Jones, E. W.; Pike, W. T.; Ksendzov, A.; Vasquez, R. P.

    1992-01-01

    Superlattices consisting of alternating layers of crystalline Si and porous amorphous Si(1-x)Ge(x) have been fabricated. This is accomplished by first growing a Si/Si(0.7)Ge(0.3) superlattice by molecular beam epitaxy, followed by Ar-ion milling to form mesa structures, and finally by immersion in HF:HNO3:H2O. This solution creates a porous structure similar to that created by anodic etching, and a high selectivity is observed for the conversion of the alloy layers relative to the Si layers. The degree of selectivity is found to depend on alloy-layer thickness and strain. Superlattices have been fabricated from 1-micron wide mesas with Si(0.7)Ge(0.3) layers fully converted to 5-nm thick porous amorphous material.

  12. High thermal shock resistance of the hot rolled and swaged bulk W-ZrC alloys

    NASA Astrophysics Data System (ADS)

    Xie, Z. M.; Liu, R.; Miao, S.; Yang, X. D.; Zhang, T.; Fang, Q. F.; Wang, X. P.; Liu, C. S.; Lian, Y. Y.; Liu, X.; Luo, G. N.

    2016-02-01

    The thermal shock (single shot) resistance and mechanical properties of the W-0.5wt% ZrC (WZC) alloys manufactured by ordinary sintering followed by swaging or rolling process were investigated. No cracks or surface melting were detected on the surface of the rolled WZC alloy plates after thermal shock at a power density of 0.66 GW/m2 for 5 ms, while primary intergranular cracks appear on the surface of the swaged WZC samples after thermal shock at a power density of 0.44 GW/m2 for 5 ms. Three point bending tests indicate that the rolled WZC alloy has a flexural strength of ˜2.4 GPa and a total strain of 1.8% at room temperature, which are 100% and 260% higher than those of the swaged WZC, respectively. The fracture energy density of the rolled WZC alloy is 3.23 × 107 J/m3, about 10 times higher than that of the swaged WZC (2.9 × 106 J/m3). The high thermal shock resistance of the rolled WZC alloys can be ascribed to their extraordinary ductility and plasticity.

  13. Influence of the microstructure on the corrosion behavior of magnetron sputter-quenched amorphous metallic alloys

    NASA Technical Reports Server (NTRS)

    Thakoor, A. P.; Khanna, S. K.; Williams, R. M.; Landel, R. F.

    1983-01-01

    The microstructure and corrosion behavior of magnetron sputter deposited amorphous metallic films of (Mo6ORu40)82B18 under varying sputtering atmospheres have been investigated. The microstructural details and topology of the films have been studied by scanning electron microscopy and correlated with the deposition conditions. By reducing the pressure of pure argon gas, the characteristic features of rough surface and columnar growth full of vertical voids can be converted into a mirror-smooth finish with very dense deposits. Films deposited in the presence of O2 or N2 exhibit columnar structure with vertical voids. Film deposited in pure argon at low pressure show remarkably high corrosion resistance due to the formation of a uniform passive surface layer. The influence of the microstructure and surface texture on the corrosion behavior is discussed.

  14. Combined measurements of modulus and length and their correlation for different amorphous alloys

    SciTech Connect

    Porscha, B.; Neuhaeuser, H.

    1995-03-15

    Combined measurements of length and modulus change on the same specimen of Ni{sub 78}Si{sub 8}B{sub 14}, Cu{sub 64}Ti{sub 36} and Co{sub 66}Fe{sub 4}(MoSiB){sub 30} are presented. These properties are sensitive to different aspects of structural changes during relaxation in the amorphous state. The change of length is mainly sensitive to the topological long range relaxation. The change of the eigenfrequency is mainly sensitive to atomic rearrangements changing the chemical short range order. The results of the correlation between the effect of relaxation of frequency versus that of length can be described as follows: the observed structural relaxation in the amorphous states of each material can be divided up into two regimes. The first regime (I) with a prevailing change of eigenfrequency is attributed to short range rearrangements of the chemically different atomic species in the material; the second regime (II) with a larger amount of length change is interpreted as a long range topological relaxation with enhanced loss of free volume. This interpretation is supported by a comparison of the diffusion coefficients at the characteristic transition temperature {Tc} between the regimes I and II. It shows that the average diffusion path lengths of the possible diffusors below the characteristic temperature are in the order of 2 to 5 next neighbor distances, i.e., diffusion is only possible in a short range changing the species of neighboring atoms. Above {Tc}, the average diffusion path lengths are in the order of 5 to 50 next neighbor distances suggesting long range relaxation rearrangements by a diffusion process preferentially connected with the annihilation of free volume.

  15. Corrosion of boiler tube alloys in refuse firing: Shredded vs bulk refuse

    SciTech Connect

    Krause, H.H. ); Daniel, P.L.; Blue, J.D. )

    1994-08-01

    Results of corrosion probe exposures at two mass burning incinerators were compared with those conducted in a unit burning refuse-derived fuel. Tests were conducted with carbon steel, low-alloy steels, stainless steels, and high nickel-chromium alloys. Corrosion rates at similar metal and gas temperatures were essentially the same for both types of fuel. Boiler tube performance in the waterwalls of other incinerators confirmed these results. Boiler design and operating conditions appear to be more important factors in tube wastage than the extent of refuse processing.

  16. Molecular Packing and Electronic Processes in Amorphous-like Polymer Bulk Heterojunction Solar Cells with Fullerene Intercalation

    NASA Astrophysics Data System (ADS)

    Xiao, Ting; Xu, Haihua; Grancini, Giulia; Mai, Jiangquan; Petrozza, Annamaria; Jeng, U.-Ser; Wang, Yan; Xin, Xin; Lu, Yong; Choon, Ng Siu; Xiao, Hu; Ong, Beng S.; Lu, Xinhui; Zhao, Ni

    2014-06-01

    The interpenetrating morphology formed by the electron donor and acceptor materials is critical for the performance of polymer:fullerene bulk heterojunction (BHJ) photovoltaic (PV) cells. In this work we carried out a systematic investigation on a high PV efficiency (>6%) BHJ system consisting of a newly developed 5,6-difluorobenzo[c] thiadiazole-based copolymer, PFBT-T20TT, and a fullerene derivative. Grazing incidence X-ray scattering measurements reveal the lower-ordered nature of the BHJ system as well as an intermixing morphology with intercalation of fullerene molecules between the PFBT-T20TT lamella. Steady-state and transient photo-induced absorption spectroscopy reveal ultrafast charge transfer (CT) at the PFBT-T20TT/fullerene interface, indicating that the CT process is no longer limited by exciton diffusion. Furthermore, we extracted the hole mobility based on the space limited current (SCLC) model and found that more efficient hole transport is achieved in the PFBT-T20TT:fullerene BHJ as compared to pure PFBT-T20TT, showing a different trend as compared to the previously reported highly crystalline polymer:fullerene blend with a similar intercalation manner. Our study correlates the fullerene intercalated polymer lamella morphology with device performance and provides a coherent model to interpret the high photovoltaic performance of some of the recently developed weakly-ordered BHJ systems based on conjugated polymers with branched side-chain.

  17. Molecular packing and electronic processes in amorphous-like polymer bulk heterojunction solar cells with fullerene intercalation.

    PubMed

    Xiao, Ting; Xu, Haihua; Grancini, Giulia; Mai, Jiangquan; Petrozza, Annamaria; Jeng, U-Ser; Wang, Yan; Xin, Xin; Lu, Yong; Choon, Ng Siu; Xiao, Hu; Ong, Beng S; Lu, Xinhui; Zhao, Ni

    2014-01-01

    The interpenetrating morphology formed by the electron donor and acceptor materials is critical for the performance of polymer:fullerene bulk heterojunction (BHJ) photovoltaic (PV) cells. In this work we carried out a systematic investigation on a high PV efficiency (>6%) BHJ system consisting of a newly developed 5,6-difluorobenzo[c] thiadiazole-based copolymer, PFBT-T20TT, and a fullerene derivative. Grazing incidence X-ray scattering measurements reveal the lower-ordered nature of the BHJ system as well as an intermixing morphology with intercalation of fullerene molecules between the PFBT-T20TT lamella. Steady-state and transient photo-induced absorption spectroscopy reveal ultrafast charge transfer (CT) at the PFBT-T20TT/fullerene interface, indicating that the CT process is no longer limited by exciton diffusion. Furthermore, we extracted the hole mobility based on the space limited current (SCLC) model and found that more efficient hole transport is achieved in the PFBT-T20TT:fullerene BHJ as compared to pure PFBT-T20TT, showing a different trend as compared to the previously reported highly crystalline polymer:fullerene blend with a similar intercalation manner. Our study correlates the fullerene intercalated polymer lamella morphology with device performance and provides a coherent model to interpret the high photovoltaic performance of some of the recently developed weakly-ordered BHJ systems based on conjugated polymers with branched side-chain. PMID:24909640

  18. Phase separation and crystallization process of amorphous Fe{sub 78}B{sub 12}Si{sub 9}Ni{sub 1} alloy

    SciTech Connect

    Mukhgalin, V. V.; Lad’yanov, V. I.

    2015-08-17

    The influence of the melt heat treatment on the structure and crystallization process of the rapidly quenched amorphous Fe{sub 78}B{sub 12}Si{sub 9}Ni{sub 1} alloys have been investigated by means of x-ray diffraction, DSC and TEM. Amorphous phase separation has been observed in the alloys quenched after the preliminary high temperature heat treatment of the liquid alloy (heating above 1400°C). Comparative analysis of the pair distribution functions demonstrates that this phase separation accompanied by a changes in the local atomic arrangement. It has been found that crystallization process at heating is strongly dependent on the initial amorphous phase structure - homogeneous or phase separated. In the last case crystallization goes through the formation of a new metastable hexagonal phase [a=12.2849(9) Ǻ, c=7.6657(8) Ǻ]. At the same time the activation energy for crystallization (Ea) reduces from 555 to 475 kJ mole{sup −1}.

  19. Synthesis and photocatlytic performance of nano-sized TiO{sub 2} materials prepared by dealloying Ti–Cu–Pd amorphous alloys

    SciTech Connect

    Jiang, Jing; Zhu, Shengli; Xu, Wence; Cui, Zhenduo; Yang, Xianjin

    2015-05-15

    Highlights: • TiO{sub 2} nanospindles were synthesized by dealloying Ti–Cu–Pd amorphous alloy. • Pd significantly enhanced the exposure of high-energy (0 0 1) facet of TiO{sub 2}. • TiO{sub 2} with high-energy (0 0 1) facet showed good photocatalytic activity. - Abstract: TiO{sub 2} nanospindles with exposed (0 0 1) facet were synthesized through a simple dealloying reaction. The rutile photocatalysts were characterized by X-ray diffraction, scanning electron microscope and transmission electron microscope, inductively coupled plasma optical emission spectrometry and ultraviolet–visible spectrophotometer. A Rhodamine B dye (RhB) was used to detect the photocatalytic activity of TiO{sub 2} under full light irradiation. The presence of Pd in the original amorphous alloy reduced the surface free energy of TiO{sub 2}, stabilized the (0 0 1) facet. The Pd8-TiO{sub 2} sample exhibited the largest crystal size along the direction which is perpendicular to the (0 0 1) facet. The photocatalytic degradation rate of RhB was improved due to the Pd addition in the original amorphous alloy. This indicated that the exposure of (0 0 1) facets could enhance the activity of TiO{sub 2} photocatalyst. In addition, the presence of isolated Pd atoms on the surface of TiO{sub 2} would be another probable reason for the improvement of photocatalytic activity.

  20. Local deformation and bulk properties in gamma-TiAl based alloys

    NASA Astrophysics Data System (ADS)

    Biery, Nicholas Eben

    Gamma-TiAl alloys are potential replacements for conventional titanium and nickel-based alloys due to their high specific stiffness and good oxidation resistance at intermediate temperatures. One obstacle to implementation of these alloys is their relatively low ductility and the variation in that property. This work is an attempt to quantify ductility variability and understand the microstructural variables that affect it. It was found that a three-parameter Weibull analysis of tensile data using yield strength as the minimum failure strength isolates the variation in ductility from that in yield strength, and provides a useful way to quantify this variability. The properties of cast gamma-TiAl alloys are consistent with a volume-distributed flaw population, including exhibiting the expected reduction in strength with increased sample volume. Although other factors affect both strength and average ductility, the variability appears to be controlled by grain size alone; alloys with different microstructures but similar grain sizes had similar Weibull moduli. Fracture surface examinations indicated that the 'flaws' are intrinsic in nature; the fracture origins were generally not associated with pores, inclusions, or second phase particles. Instead, the typical origin was located in a small region that had undergone extensive plastic deformation. A technique, called AMaSD, was developed to accurately measure small-scale surface strains and identify the microstructural features associated with these areas of local high strain. These studies found that several factors affect the development of strain localization, including relative grain orientation, segregation, and phase distribution, but the relative importance of these factors are difficult to quantify. Finally, the cast structures of these materials were examined using texture measurements and statistical segregation studies, since texture and segregation had been identified as factors that could affect the

  1. Superconducting and Mechanical Properties of Bi-2223/Metal Alloy Wires Composite Bulk

    NASA Astrophysics Data System (ADS)

    Yoshizawa, S.; Hirano, S.; Oya-Seimiya, Y.; Hishinuma, Y.; Nishimura, A.

    2006-03-01

    Bi-2223 sintered bulk samples with addition of AgMg wires or Ag-plated Ni wires have been prepared to improve both the superconducting and the mechanical properties, simultaneously. When 24 AgMg wires of 0.4 mm in diameter were added into Bi-2223 bulk composite sample, the critical current density (Jc) at 77 K increased from 2 A/mm2 to 7 A/mm2. The mechanical properties have been estimated by a three-point bending test. The maximum bending stress of 70 - 90 MPa at the rupture was obtained for Bi-2223/metal wires composite bulk, regardless of the number of the wires. After the maximum bending stress, Bi-2223 bulk without metal wires fractured separately, while the composite did not fracture but fine cracks were induced only. The Jc values of the composites just after the fracture were about half of the Jc value in the composites without bending. It has been observed that the superconducting current flows even after cracking, in Bi-2223 bulk with metal wires. This is due to the fact that metal wires suppress progress of fine cracks just after the fracture, while the superconducting current flows in the uncracked region. This current still remaining after the fracture is a very important feature for the applications.

  2. Structure of amorphous Ge8Sb2Te11 : GeTe-Sb2Te3 alloys and optical storage

    NASA Astrophysics Data System (ADS)

    Akola, J.; Jones, R. O.

    2009-04-01

    The amorphous structure of Ge8Sb2Te11 , an alloy used in the Blu-ray Disc, the de facto successor to digital versatile disk (DVD) optical storage, has been characterized by large-scale (630 atoms, 0.4 ns) density-functional/molecular-dynamics simulations using the new PBEsol approximation for the exchange-correlation energy functional. The geometry and electronic structure agree well with available x-ray diffraction data and photoelectron measurements. The total coordination numbers are Ge: 4.0, Sb: 3.7, and Te: 2.9, and the Ge-Ge partial coordination number is 0.7. Most atoms (particularly Sb) prefer octahedral coordination but 42% of Ge atoms are “tetrahedral.” Structural details, including ring statistics, local coordination, and cavities (12% of total volume), are strikingly similar to those of Ge2Sb2Te5 , which is used in DVD-random access memory. The presence of less than 10% Sb atoms leads to significant changes from GeTe.

  3. Atomic simulation of mechanical behavior of Mg in a super-lattice of nanocrystalline Mg and amorphous Mg-Al alloy

    SciTech Connect

    Song, H. Y.; An, M. R.; Li, Y. L. Deng, Q.

    2014-12-07

    The mechanical properties of a super-lattice architecture composed of nanocrystalline Mg and Mg-Al amorphous alloy are investigated using molecular dynamics simulation. The results indicate that deformation mechanism of nanocrystalline Mg is obviously affected by the amorphous boundary spacing and temperature. The strength of the material increases with the decrease of amorphous boundary spacing, presenting a Hall-Petch effect at both 10 K and 300 K. A stress platform and following stiffness softening, as well as a linear strengthening in the plastic stage, are observed when the amorphous boundary spacing below 8.792 nm at 10 K. The implying reason may be that the amorphous boundary acts as the dislocations emission and absorption source. However, the second stress peak is not observed for the models at 300 K. Instead, the flow stress in plastic stage is a nearly constant value. The simulation demonstrates the emergence of the new grain, accompanied by the deformation twins and stacking faults associated with the plastic behaviors at 300 K. The general conclusions derived from this work may provide a guideline for the design of high-performance hexagonal close-packed metals.

  4. Structural and thermal investigations of an amorphous GaSe9 alloy using EXAFS, cumulant expansion, and reverse Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Siqueira, M. C.; Maia, R. N. A.; Araujo, R. M. T.; Machado, K. D.; Stolf, S. F.

    2015-02-01

    In this article, we investigated structural and thermal properties of an amorphous alloy of the Ga-Se system. The amorphous GaSe9 alloy was produced by mechanical alloying and it was studied using EXAFS spectroscopy and cumulant expansion method. We also made reverse Monte Carlo simulations using the total structure factor S(K) obtained from x-ray diffraction and the EXAFS χ(k) oscillations on Se and Ga K edges as input data. Several parameters, such as average coordination numbers and interatomic distances, structural and thermal disorders, asymmetry of the partial distribution functions gij(r), and Einstein and Debye temperatures, were determined. The gi j E ( r ) functions were reconstructed from the cumulants C1, C2, and C3 obtained from the Einstein model, and they were compared to the gi j RMC ( r ) functions obtained from the simulations. The simulations also furnished the partial bond angle distribution functions Θijℓ(cosθ), which describe the angular distribution of bonds between first neighbors, and give information about the kind of structural units present in the alloy.

  5. Structural and thermal investigations of an amorphous GaSe{sub 9} alloy using EXAFS, cumulant expansion, and reverse Monte Carlo simulations

    SciTech Connect

    Siqueira, M. C.; Maia, R. N. A.; Araujo, R. M. T.; Machado, K. D.; Stolf, S. F.

    2015-02-07

    In this article, we investigated structural and thermal properties of an amorphous alloy of the Ga–Se system. The amorphous GaSe{sub 9} alloy was produced by mechanical alloying and it was studied using EXAFS spectroscopy and cumulant expansion method. We also made reverse Monte Carlo simulations using the total structure factor S(K) obtained from x-ray diffraction and the EXAFS χ(k) oscillations on Se and Ga K edges as input data. Several parameters, such as average coordination numbers and interatomic distances, structural and thermal disorders, asymmetry of the partial distribution functions g{sub ij}(r), and Einstein and Debye temperatures, were determined. The g{sub ij}{sup E}(r) functions were reconstructed from the cumulants C{sub 1}, C{sub 2}, and C{sub 3} obtained from the Einstein model, and they were compared to the g{sub ij}{sup RMC}(r) functions obtained from the simulations. The simulations also furnished the partial bond angle distribution functions Θ{sub ijℓ}(cosθ), which describe the angular distribution of bonds between first neighbors, and give information about the kind of structural units present in the alloy.

  6. Experimental and Theoretical Studies on Oxidation of Cu-Au Alloy Surfaces: Effect of Bulk Au Concentration

    PubMed Central

    Okada, Michio; Tsuda, Yasutaka; Oka, Kohei; Kojima, Kazuki; Diño, Wilson Agerico; Yoshigoe, Akitaka; Kasai, Hideaki

    2016-01-01

    We report results of our experimental and theoretical studies on the oxidation of Cu-Au alloy surfaces, viz., Cu3Au(111), CuAu(111), and Au3Cu(111), using hyperthermal O2 molecular beam (HOMB). We observed strong Au segregation to the top layer of the corresponding clean (111) surfaces. This forms a protective layer that hinders further oxidation into the bulk. The higher the concentration of Au in the protective layer formed, the higher the protective efficacy. As a result, of the three Cu-Au surfaces studied, Au3Cu(111) is the most stable against dissociative adsorption of O2, even with HOMB. We also found that this protective property breaks down for oxidations occurring at temperatures above 300 K. PMID:27516137

  7. Experimental and Theoretical Studies on Oxidation of Cu-Au Alloy Surfaces: Effect of Bulk Au Concentration.

    PubMed

    Okada, Michio; Tsuda, Yasutaka; Oka, Kohei; Kojima, Kazuki; Diño, Wilson Agerico; Yoshigoe, Akitaka; Kasai, Hideaki

    2016-01-01

    We report results of our experimental and theoretical studies on the oxidation of Cu-Au alloy surfaces, viz., Cu3Au(111), CuAu(111), and Au3Cu(111), using hyperthermal O2 molecular beam (HOMB). We observed strong Au segregation to the top layer of the corresponding clean (111) surfaces. This forms a protective layer that hinders further oxidation into the bulk. The higher the concentration of Au in the protective layer formed, the higher the protective efficacy. As a result, of the three Cu-Au surfaces studied, Au3Cu(111) is the most stable against dissociative adsorption of O2, even with HOMB. We also found that this protective property breaks down for oxidations occurring at temperatures above 300 K. PMID:27516137

  8. Deformation-induced localized solid-state amorphization in nanocrystalline nickel

    PubMed Central

    Han, Shuang; Zhao, Lei; Jiang, Qing; Lian, Jianshe

    2012-01-01

    Although amorphous structures have been widely obtained in various multi-component metallic alloys, amorphization in pure metals has seldom been observed and remains a long-standing scientific curiosity and technological interest. Here we present experimental evidence of localized solid-state amorphization in bulk nanocrystalline nickel introduced by quasi-static compression at room temperature. High-resolution electron microscope observations illustrate that nano-scale amorphous structures present at the regions where severe deformation occurred, e.g. along crack paths or surrounding nano-voids. These findings have indicated that nanocrystalline structures are highly desirable for promoting solid-state amorphization, which may provide new insights for understanding the nature of the crystalline-to-amorphous transformation and suggested a potential method to produce elemental metallic glasses that have hardly been available hitherto through rapid solidification. PMID:22768383

  9. Impact of the hydrogen content on the photoluminescence efficiency of amorphous silicon alloys

    SciTech Connect

    Kistner, J.; Schubert, M. B.

    2013-12-07

    This paper analyzes the impact of hydrogen on the photoluminescence (PL) efficiency of the three wide gap silicon alloys: silicon carbide (a-SiC{sub x}), silicon nitride (a-SiN{sub x}): silicon oxide (a-SiO{sub x}). All three materials behave similarly. The progression of the PL efficiency over the Si content splits into two regions. With decreasing Si content, the PL efficiency increases until a maximum is reached. With a further decrease of the Si content, the PL efficiency declines again. A comprehensive analysis of the sample structure reveals that the PL efficiency depends on the degree of passivation of Si and Y atoms (Y = C, N, O) with hydrogen. For samples with a high Si content, an effective passivation of incorporated Y atoms gives rise to an increasing PL efficiency. The PL efficiency of samples with a low Si content is limited due to a rising amount of unpassivated Si defect states. We find that a minimum amount of 0.2 H atoms per Si atom is required to maintain effective luminescence.

  10. In-situ observation of dynamic recrystallization in the bulk of zirconium alloy.

    SciTech Connect

    Liss, K.-D.; Garbe, U.; Li, H. J.; Schambron, T.; Almer, J. D.; Yan, K.; Australian Nuclear Science and Tech. Organisation; Univ. of Wollongong

    2009-08-01

    Dynamic recrystallization and related effects have been followed in situ and in real time while a metal undergoes rapid thermo-mechanical processing. Statistics and orientation correlations of embedded/bulk material grains were deduced from two-dimensional X-ray diffraction patterns and give deep insight into the formation of the microstructure. Applications are relevant in materials design, simulation, and in geological systems.

  11. Bulk and surface properties of demixing liquid Al-Sn and Sn-Tl alloys

    NASA Astrophysics Data System (ADS)

    Odusote, Y. A.; Popoola, A. I.; Oluyamo, S. S.

    2016-02-01

    The energetics of mixing in Al-Sn and Sn-Tl-segregating binary alloys has been explained through the study of surface properties (surface concentrations and surface tension) and various concentration-dependent thermodynamic (free energy of mixing, entropy of mixing and enthalpy of mixing) and transport (chemical diffusion) properties as well as the microscopic functions (concentration fluctuations in the long-wavelength limits and chemical short-range order parameter) using a statistical mechanical theory in conjunction with the self-association model (SAM). The theoretical property values obtained by the SAM were compared to the corresponding experimental values available in literature.

  12. Formation of amorphous alloys by ion beam mixing and its multiscale theoretical modeling in the equilibrium immiscible Sc-W system.

    PubMed

    Zhang, R F; Shen, Y X; Yan, H F; Liu, B X

    2005-03-17

    Unique amorphous alloys are synthesized at the compositions of 25 and 40 atom % of W by ion beam mixing in the equilibrium immiscible Sc-W system characterized by a positive heat of formation of +14 kJ/mol. In thermodynamic modeling, a Gibbs free energy diagram is constructed based on Miedema's theory, and the diagram predicts a glass-forming range of the Sc-W system to be within 12-58 atom % of W. To develop an atomistic model, ab initio calculations are first conducted to assist the construction of an n-body Sc-W potential under the embedded atom method. The proven realistic potential is applied in molecular dynamic simulations to study the crystal-to-amorphous transition in the Sc-W solid solutions, thus determining the glass-forming ability of the system to be within 15-50 atom % of W. Apparently, both theoretical predicted glass-forming ranges cover the experimentally measured one, showing an excellent agreement. We report, in this paper, the experimental results from ion beam mixing and the multiscale theoretical modeling concerning the amorphous alloy formation in the Sc-W system together with a brief discussion of the structural transition mechanism. PMID:16851507

  13. Effect of nano-crystallization of high velocity oxy-fuel-sprayed amorphous NiCrBSi alloy on properties of the coatings

    NASA Astrophysics Data System (ADS)

    Li, Chang-Jiu; Wang, Yu-Yue; Li, Hua

    2004-09-01

    NiCrBSi self-fluxing alloy coatings were deposited by high velocity oxy-fuel (HVOF) spraying. Annealing treatment was applied to the as-sprayed coatings to develop the microstructure of the Ni-based coating. The microstructure of the coating was characterized using optical microscopy, x-ray diffraction and transmission electron microscopy. The crystallization behavior of the amorphous coating was also characterized by differential scanning calorimetry. The properties of the coating were characterized by microhardness and abrasive wear tests. The results showed that the as-sprayed HVOF coating deposited by well melted spray particles exhibited a dense microstructure of amorphous phase. It was revealed that the crystallization of the amorphous phase in HVOF NiCrBSi coating occurs at a temperature of about 502°C. Annealing at temperature a little higher than recrystallization temperature leads to the formation of the nano-crystalline microstructure. The subsequent nanostructured Ni-based coating presents higher microhardness and excellent wear performance. With the further increase in annealing temperature, the growth of the nano-crystalline grains occurs and, accordingly, the microhardness of the coating and the wear performance decrease. Thereafter, the microstructure and properties of the Ni-based self-fluxing alloy coating can be controlled through postannealing treatment.

  14. High-field magneto-thermo-mechanical testing system for characterizing multiferroic bulk alloys.

    PubMed

    Bruno, Nickolaus M; Karaman, Ibrahim; Ross, Joseph H; Chumlyakov, Yuriy I

    2015-11-01

    Multiferroic meta-magnetic shape memory alloys are well known for exhibiting large magnetic field induced actuation strains, giant magnetocaloric effects, magneto-resistance, and structural and magnetic glassy behaviors. Thus, they are candidates for improving modern day sensing, actuation, magneto-resistance, and solid-state refrigeration processes. Until now, however, experimental apparatuses have typically been able to probe a limited ferroic parameter space in these materials, i.e., only concurrent thermal and mechanical responses, or magnetic and thermal responses. To overcome this barrier and better understand the coupling of multiple fields on materials behavior, a magneto-thermo-mechanical characterization device has been designed and implemented. This device is capable of compressing a specimen at load levels up to 5300 N collinearly with applied fields up to 9 T between temperatures of -100 °C and 120 °C. Uniaxial stress, strain, temperature, magnetic field, and the volumetric average magnetization have been simultaneously measured under mixed loading conditions on a NiCoMnIn meta-magnetic shape memory alloy and a few selected results are presented here. PMID:26628146

  15. High-field magneto-thermo-mechanical testing system for characterizing multiferroic bulk alloys

    NASA Astrophysics Data System (ADS)

    Bruno, Nickolaus M.; Karaman, Ibrahim; Ross, Joseph H.; Chumlyakov, Yuriy I.

    2015-11-01

    Multiferroic meta-magnetic shape memory alloys are well known for exhibiting large magnetic field induced actuation strains, giant magnetocaloric effects, magneto-resistance, and structural and magnetic glassy behaviors. Thus, they are candidates for improving modern day sensing, actuation, magneto-resistance, and solid-state refrigeration processes. Until now, however, experimental apparatuses have typically been able to probe a limited ferroic parameter space in these materials, i.e., only concurrent thermal and mechanical responses, or magnetic and thermal responses. To overcome this barrier and better understand the coupling of multiple fields on materials behavior, a magneto-thermo-mechanical characterization device has been designed and implemented. This device is capable of compressing a specimen at load levels up to 5300 N collinearly with applied fields up to 9 T between temperatures of -100 °C and 120 °C. Uniaxial stress, strain, temperature, magnetic field, and the volumetric average magnetization have been simultaneously measured under mixed loading conditions on a NiCoMnIn meta-magnetic shape memory alloy and a few selected results are presented here.

  16. Ultrafast crystalline-to-amorphous phase transition in Ge{sub 2}Sb{sub 2}Te{sub 5} chalcogenide alloy thin film using single-shot imaging spectroscopy

    SciTech Connect

    Takeda, Jun Oba, Wataru; Minami, Yasuo; Katayama, Ikufumi; Saiki, Toshiharu

    2014-06-30

    We have observed an irreversible ultrafast crystalline-to-amorphous phase transition in Ge{sub 2}Sb{sub 2}Te{sub 5} chalcogenide alloy thin film using broadband single-shot imaging spectroscopy. The absorbance change that accompanied the ultrafast amorphization was measured via single-shot detection even for laser fluences above the critical value, where a permanent amorphized mark was formed. The observed rise time to reach the amorphization was found to be ∼130–200 fs, which was in good agreement with the half period of the A{sub 1} phonon frequency in the octahedral GeTe{sub 6} structure. This result strongly suggests that the ultrafast amorphization can be attributed to the rearrangement of Ge atoms from an octahedral structure to a tetrahedral structure. Finally, based on the dependence of the absorbance change on the laser fluence, the stability of the photoinduced amorphous phase is discussed.

  17. Changes in cluster magnetism and suppression of local superconductivity in amorphous FeCrB alloy irradiated by Ar+ ions

    NASA Astrophysics Data System (ADS)

    Okunev, V. D.; Samoilenko, Z. A.; Szymczak, H.; Szewczyk, A.; Szymczak, R.; Lewandowski, S. J.; Aleshkevych, P.; Malinowski, A.; Gierłowski, P.; Więckowski, J.; Wolny-Marszałek, M.; Jeżabek, M.; Varyukhin, V. N.; Antoshina, I. A.

    2016-02-01

    We show that cluster magnetism in ferromagnetic amorphous Fe67Cr18B15 alloy is related to the presence of large, D=150-250 Å, α-(Fe Cr) clusters responsible for basic changes in cluster magnetism, small, D=30-100 Å, α-(Fe, Cr) and Fe3B clusters and subcluster atomic α-(Fe, Cr, B) groupings, D=10-20 Å, in disordered intercluster medium. For initial sample and irradiated one (Φ=1.5×1018 ions/cm2) superconductivity exists in the cluster shells of metallic α-(Fe, Cr) phase where ferromagnetism of iron is counterbalanced by antiferromagnetism of chromium. At Φ=3×1018 ions/cm2, the internal stresses intensify and the process of iron and chromium phase separation, favorable for mesoscopic superconductivity, changes for inverse one promoting more homogeneous distribution of iron and chromium in the clusters as well as gigantic (twice as much) increase in density of the samples. As a result, in the cluster shells ferromagnetism is restored leading to the increase in magnetization of the sample and suppression of local superconductivity. For initial samples, the temperature dependence of resistivity ρ(T)~T2 is determined by the electron scattering on quantum defects. In strongly inhomogeneous samples, after irradiation by fluence Φ=1.5×1018 ions/cm2, the transition to a dependence ρ(T)~T1/2 is caused by the effects of weak localization. In more homogeneous samples, at Φ=3×1018 ions/cm2, a return to the dependence ρ(T)~T2 is observed.

  18. Effect of amorphous Mg{sub 50}Ni{sub 50} on hydriding and dehydriding behavior of Mg{sub 2}Ni alloy

    SciTech Connect

    Guzman, D.; Ordonez, S.; Fernandez, J.F.; Sanchez, C.; Serafini, D.; Rojas, P.A.; Aguilar, C.; Tapia, P.

    2011-04-15

    Composite Mg{sub 2}Ni (25 wt.%) amorphous Mg{sub 50}Ni{sub 50} was prepared by mechanical milling starting with nanocrystalline Mg{sub 2}Ni and amorphous Mg{sub 50}Ni{sub 50} powders, by using a SPEX 8000 D mill. The morphological and microstructural characterization of the powders was performed via scanning electron microscopy and X-ray diffraction. The hydriding characterization of the composite was performed via a solid gas reaction method in a Sievert's-type apparatus at 363 K under an initial hydrogen pressure of 2 MPa. The dehydriding behavior was studied by differential thermogravimetry. On the basis of the results, it is possible to conclude that amorphous Mg{sub 50}Ni{sub 50} improved the hydriding and dehydriding kinetics of Mg{sub 2}Ni alloy upon cycling. A tentative rationalization of experimental observations is proposed. - Research Highlights: {yields} First study of the hydriding behavior of composite Mg{sub 2}Ni (25 wt.%) amorphous Mg{sub 50}Ni{sub 50}. {yields} Microstructural characterization of composite material using XRD and SEM was obtained. {yields} An improved effect of Mg{sub 50}Ni{sub 50} on the Mg{sub 2}Ni hydriding behavior was verified. {yields} The apparent activation energy for the hydrogen desorption of composite was obtained.

  19. Effects of interface and bulk properties of gate-dielectric on the performance and stability of hydrogenated amorphous silicon thin-film transistors

    NASA Astrophysics Data System (ADS)

    Ando, M.; Wakagi, M.; Onisawa, K.

    2015-12-01

    In order to investigate the effects of interface and bulk properties of gate insulator on the threshold voltage (Vth) and the gate-bias induced instability of hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs), four kinds of TFT structures were fabricated with SiNx and SiOx insulators stacked to make different combinations of the bulk and interface in the gate-dielectric layers. It was found that the Vth and the stability are independently controlled by tuning stoichiometry and thickness of the SiOx insertion layer between a-Si:H and SiNx. In TFTs with SiOx insertion layer of 50 nm thickness, on increasing oxygen/silicon (O/Si = x) ratio from 1.7 to 1.9, Vth increased from 0 V to 9 V. In these TFTs with a relatively thick SiOx insertion layer, positive Vth shift with negative bias stress was observed, confirmed to be due to defect creation in a-Si:H with the thermalization barrier energy of 0.83 eV. On reducing the thickness of the SiOx insertion layer down to approximately 1 nm, thin enough for hole injection through SiOx by tunneling effect, stable operation was obtained while keeping the high Vth value under negative stress bias. These results are consistently explained as follows: (1) the high value for Vth is caused by the dipole generated at the interface between a-Si:H and SiOx; and (2) two causes for Vth shift, charge injection to the gate insulator and defect creation in a-Si:H, are mutually related to each other through the "effective bias stress," Vbseff = Vbs - ΔVfb (Vbs: applied bias stress and ΔVfb: flat band voltage shift due to the charge injection). It was experimentally confirmed that there should be an optimum thickness of SiOx insertion layer of approximately 1 nm with stable high Vth, where enhanced injection increases ΔVfb, reduces Vbseff to reduce defect creation, and totally minimizes Vth shift.

  20. Low-temperature magnetization of amorphous and nanocrystalline Fe 76.5- xU xCu 1Si 13.5B 9 alloys

    NASA Astrophysics Data System (ADS)

    Duša, O.; Kováč, J.; Konč, M.; Švec, T.; Kavečanský, V.

    1996-03-01

    The low-temperature magnetization of amorphous and nanocrystalline Fe 76.5- xU xCu 1Si 13.5B 9 alloys ( x = 0-11) has been studied in the 4.2-300 K range. All examined magnetic parameters (exchange integral J, range of exchange interactions < r2>, magnetic moment per Fe atom, μFe, spin wave stiffness constant D) are markedly influenced by the uranium substitution for iron. Both the μFe and D are found to increase with decreasing Fe content in amorphous alloys for x = 0 up to about 4. The noncollinear spin structures as a result of competing interactions are supposed to explain this behaviour. Some samples (with U contents of 2-6 at%) annealed for 1 h at 813 K appear to be nanocrystalline. Uranium seems to inhibit grain growth in the investigated FeUCuSiB system, just as Nb does in FeNbCuSiB nanocrystalline alloys.

  1. Magnetic anisotropy of C and N doped bulk FeCo alloy: A first principles study

    NASA Astrophysics Data System (ADS)

    Khan, Imran; Hong, Jisang

    2015-08-01

    Using the full potential linearized augmented plane wave (FLAPW) method, we investigated the magnetocrystalline anisotropy of carbon and nitrogen doped FeCo in the interstitial site. Here, we have considered 3.125% impurity doping concentration. The impurity doping induces a tetragonal distortion in the FeCo lattice, and both carbon and nitrogen impurities play a similar role for lattice distortion. The local magnetic moment of Fe atom around the impurity site was greatly reduced, whereas the Co had rather robust magnetic moment. We found a uniaxial magnetocrystalline anisotropy constant of 0.65 and 0.58 MJ/m3 for C and N doped bulk FeCo, and this was mainly due to the tetragonal distortion induced by C and N impurity, not from the hybridization effect with Fe or Co. Additionally, the estimated maximum energy product and coercive field were 81.4, 72.5 MGOe and 600, 530 kA m-1 for C and N doped bulk FeCo, respectively. These results may imply that the interstitial C or N doped FeCo can be used for potential rare earth free permanent magnet although those values are likely to be suppressed in real samples due to micromagnetic factors such as structural defects, geometrical effect, or grain boundary effect.

  2. Enthalpy Effect of Adding Cobalt to Liquid Sn-3.8Ag-0.7Cu Lead-Free Solder Alloy: Difference between Bulk and Nanosized Cobalt

    PubMed Central

    2016-01-01

    Heat effects for the addition of Co in bulk and nanosized forms into the liquid Sn-3.8Ag-0.7Cu alloy were studied using drop calorimetry at four temperatures between 673 and 1173 K. Significant differences in the heat effects between nano and bulk Co additions were observed. The considerably more exothermic values of the measured enthalpy for nano Co additions are connected with the loss of the surface enthalpy of the nanoparticles due to the elimination of the surface of the nanoparticles upon their dissolution in the liquid alloy. This effect is shown to be independent of the calorimeter temperature (it depends only on the dropping temperature through the temperature dependence of the surface energy of the nanoparticles). Integral and partial enthalpies of mixing for Co in the liquid SAC-alloy were evaluated from the experimental data. PMID:26877829

  3. Time of isothermal holding in the course of in-air heat treatment of soft magnetic Fe-based amorphous alloys and their magnetic properties

    NASA Astrophysics Data System (ADS)

    Skulkina, N. A.; Ivanov, O. A.; Pavlova, I. O.; Minina, O. A.

    2011-12-01

    On the example of soft magnetic Fe81B13Si4C2 and Fe77Ni1Si9B13 amorphous alloys, the relation between the level of magnetic properties and duration of isothermal holding in the course of heat treatment in air has been studied. The optimum temperature-dependent time τ of isothermal holding has been shown to be related to the volume fraction of domains ( V orth) with orthogonal magnetization in the initial (quenched) ribbon by equation V orth = ττ1/3. A temperature dependence of the proportionality coefficient α, which determines the degree of diffusion-process activity, has been determined. The results obtained allow us to substantially simplify the choice of optimum conditions of atmospheric heat treatment of soft magnetic Fe-based amorphous ribbons.

  4. Nano-crystallization and magnetic mechanisms of Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1} amorphous alloy by ab initio molecular dynamics simulation

    SciTech Connect

    Wang, Yaocen; Takeuchi, Akira; Makino, Akihiro; Liang, Yunye; Kawazoe, Yoshiyuki

    2014-05-07

    Iron-based amorphous and nano-crystalline alloys have attracted a growing interest due to their potential in the application of magnetic coil production. However, fundamental understanding of the nano-crystallization mechanisms and magnetic features in the amorphous structure are still lack of knowledge. In the present work, we performed ab initio molecular dynamics simulation to clarify the ionic and electronic structure in atomic scale, and to derive the origin of the good magnetic property of Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1} amorphous alloy. The simulation gave a direct evidence of the Cu-P bonding preference in the amorphous alloy, which may promote nucleation in nano-crystallization process. On the other hand, the electron transfer and the band/orbital features in the amorphous alloy suggests that alloying elements with large electronegativity and the potential to expand Fe disordered matrix are preferred for enhancing the magnetization.

  5. Comparison of high temperature, high frequency core loss and dynamic B-H loops of two 50 Ni-Fe crystalline alloys and an iron-based amorphous alloy

    SciTech Connect

    Wieserman, W.R.; Schwarze, G.E.; Niedra, J.M.

    1994-09-01

    The availability of experimental data that characterizes the performance of soft magnetic materials for the combined conditions of high temperature and high frequency is almost non-existent. An experimental investigation was conducted over the temperature range of 23 to 300 C and frequency range of 1 to 50 kHz to determine the effects of temperature and frequency on the core loss and dynamic B-H loops of three different soft magnetic materials; an oriented-grain 50Ni-50Fe alloy, a nonoriented-grain 50Ni-50Fe alloy, and an iron-based amorphous material (Metglas 2605SC). A comparison of these materials show that the nonoriented-grain 50Ni-50Fe alloy tends to have either the lowest or next lowest core loss for all temperatures and frequencies investigated.

  6. Comparison of high temperature, high frequency core loss and dynamic B-H loops of two 50 Ni-Fe crystalline alloys and an iron-based amorphous alloy

    NASA Technical Reports Server (NTRS)

    Wieserman, W. R.; Schwarze, G. E.; Niedra, J. M.

    1991-01-01

    The availability of experimental data that characterizes the performance of soft magnetic materials for the combined conditions of high temperature and high frequency is almost nonexistent. An experimental investigation was conducted over the temperature range of 23 to 300 C and frequency range of 1 to 50 kHz to determine the effects of temperature and frequency on the core loss and dynamic B-H loops of three different soft magnetic materials; and oriented grain 50Ni-50Fe alloy, a nonoriented grain 50Ni-Fe alloy, and an iron based amorphous material (Metglas 2605SC). A comparison of these materials shows that the nonoriented grain 50Ni-50Fe alloy tends to have either the lowest or next lowest core loss for all temperatures and frequencies investigated.

  7. Comparison of high temperature, high frequency core loss and dynamic B-H loops of two 50 Ni-Fe crystalline alloys and an iron-based amorphous alloy

    NASA Technical Reports Server (NTRS)

    Wieserman, W. R.; Schwarze, G. E.; Niedra, J. M.

    1991-01-01

    The availability of experimental data that characterize the performance of soft magnetic materials for the combined conditions of high temperature and high frequency is almost nonexistent. An experimental investigation was conducted over the temperature range of 23 to 300 C and frequency range of 1 to 50 kHz to determine the effects of temperature and frequency on the core loss and dynamic B-H loops of three different soft magnetic materials: an oriented-grain 50Ni-50Fe alloy, a nonoriented-grain 50Ni-50Fe alloy, and an iron-based amorphous material (Metglas 2605SC). A comparison of these materials shows that the nonoriented-grain 50Ni-50Fe alloy tends to have either the lowest or the next lowest core loss for all temperatures and frequencies investigated.

  8. XPS Study of Thermally Evaporated Ge-Sb-Te Amorphous Thin Films

    SciTech Connect

    Kumar, Sandeep; Singh, Digvijay; Thangaraj, R.

    2011-12-12

    Amorphous thin films were prepared from the bulk composition of Ge{sub 22}Sb{sub 22}Te{sub 56}(GST) alloy by thermal evaporation in good vacuum condition. The amorphous nature of as-deposited films was checked with x-ray diffraction (XRD) studies. X-ray photoelectron spectroscopy (XPS) has been used to determine the binding energies of the core electrons in amorphous thin GST films. In XPS, we performed the survey scan from the binding energy (BE) range from 0-1100 eV and core level spectra of Ge 3d, Sb 3d and Te 3d.

  9. Iron-based amorphous and nanocrystalline nanocomposite soft ferromagnetic materials

    NASA Astrophysics Data System (ADS)

    Um, Changyong

    Synthesis → structure → properties relationships have been studied and compared for new multicomponent amorphous alloy systems and amorphous precursors to state of the art magnetic nanocomposite alloys. The research was aimed at comparing and contrasting the crystallization mechanisms (in both bulk and thin film form) in these systems as well as the technical magnetic and mechanical properties deriving from the as-cast and crystallized microstructures. The ultimate goal was to synthesize new alloys with properties which exceeded those of state of the art materials at higher operational frequencies and temperatures of operation. Fe-based multicomponent amorphous alloys with nominal compositions of Fe82-xCoxNb3Ta1Mo1B 13 (x = 0, 6, 12, 18, 20.5, 24, 30, 36, and 41) have been evaluated for soft magnetic applications. Preferential Co partitioning into the amorphous matrix during primary crystallization is inferred from thermomagnetic measurements. The alloy with x = 20.5 composition is shown to be the best candidate for soft magnetic applications. In this alloy system, precipitation of nonmagnetic (FeCo)23B6 phase is found to be responsible for an abrupt decrease in magnetization at secondary crystallization temperature. However, a different mechanism of secondary crystallization is demonstrated for the alloy with x = 20.5 composition. The core loss of the alloy with x = 20.5 is found to exceed the commercial Fe-based amorphous magnetic cores in high frequency (higher than 300 kHz) condition and predicted to be comparable with FINEMET nanocomposite cores in high magnetic induction condition (larger than 12 kG). Nanocrystallization kinetics of NANONPERM thin films with various thicknesses have been investigated. Thickness-dependent crystallization kinetics were observed from thermomagnetic and time-dependent magnetization measurements. Formation of crystallization layer at the interface between Si substrate and NANOPERM layer affects the crystallization during a

  10. Influence of germanium nano-inclusions on the thermoelectric power factor of bulk bismuth telluride alloy

    SciTech Connect

    Satyala, Nikhil; Zamanipour, Zahra; Norouzzadeh, Payam; Krasinski, Jerzy S.; Vashaee, Daryoosh; Tahmasbi Rad, Armin; Tayebi, Lobat

    2014-05-28

    Nanocomposite thermoelectric compound of bismuth telluride (Bi{sub 2}Te{sub 3}) with 5 at. % germanium nano-inclusions was prepared via mechanically alloying and sintering techniques. The influence of Ge nano-inclusions and long duration annealing on the thermoelectric properties of nanostructured Bi{sub 2}Te{sub 3} were investigated. It was found that annealing has significant effect on the carrier concentration, Seebeck coefficient, and the power factor of the thermoelectric compound. The systematic heat treatment also reduced the density of donor type defects thereby decreasing the electron concentration. While the as-pressed nanocomposite materials showed n-type properties, it was observed that with the increase of annealing time, the nanocomposite gradually transformed to an abundantly hole-dominated (p-type) sample. The long duration annealing (∼500 h) resulted in a significantly enhanced electrical conductivity pertaining to the augmentation in the density and the structural properties of the sample. Therefore, a simultaneous enhancement in both electrical and Seebeck coefficient characteristics resulted in a remarkable increase in the thermoelectric power factor.

  11. In situ detection method for obtaining permeability of Fe-based amorphous alloys: ac resistance measurement for Fe{sub 84}Nb{sub 7}B{sub 9}

    SciTech Connect

    Ichitsubo, Tetsu; Matsubara, Eiichiro; Tanaka, Satoshi; Nishiyama, Nobuyuki; Amiya, Kenji

    2005-01-17

    In this letter, we propose an in situ detection method for obtaining permeability of soft magnetic Fe-based amorphous alloys. The temperature dependence of ac resistance was measured at different frequencies during heat treatment of Fe{sub 84}Nb{sub 7}B{sub 9} amorphous alloys. A significant increase in the ac ({approx}1000 kHz) resistance appears at around 920 K during the heating process, which arises from the skin effect caused by a marked increase in sample permeability. This skin effect diminishes when the sample is heated to approximately 1100 K, which corresponds to the decrease in its permeability. Consequently, we note that the ac resistance measurement is useful for quick in situ assessment to achieve the soft magnetic property of an Fe-based amorphous alloy.

  12. Corrosion behavior of bulk metallic glasses in different aqueous solutions

    NASA Astrophysics Data System (ADS)

    Li, Gong; Huang, Lei; Dong, Yanguo; He, Guowei; Qi, Li; Jing, Qin; Ma, Mingzhen; Liu, Riping

    2010-03-01

    The corrosion behavior of as-cast fully amorphous, structural relaxed amorphous and crystallized Fe65.5Cr4Mo4Ga4P12C5B5.5 bulk metallic glasses (BMGs) in NaCl, HCl and NaOH solutions was investigated by electrochemical polarization and immersion methods. X-ray photoelectron spectroscopy measurements was used to analyze the changes of the elements on the alloy surface before and after immersion in various solutions. The corrosion resistance of the Fe65.5Cr4Mo4Ga4P12C5B5.5 BMG was better than its structural relaxation/crystallization counterparts and common alloys (such as stainless steel, carbonized steel, and steel) in the selected aqueous solutions. The high corrosion resistance of this alloy in corrosive solutions leads to the formation of Fe-, Cr- and Mo-enriched protective thin surface films.

  13. Comparison of boron precipitation in p-type bulk nanostructured and polycrystalline silicon germanium alloy

    NASA Astrophysics Data System (ADS)

    Zamanipour, Zahra; Krasinski, Jerzy S.; Vashaee, Daryoosh

    2013-04-01

    Boron precipitation process and its effect on electronic properties of p-type bulk nanostructured silicon germanium (Si0.8Ge0.2) compared with large grain polycrystalline Si0.8Ge0.2 have been studied. The structures were synthesized and their thermoelectric properties were measured versus temperature during heating and cooling cycles. The experimental data showed stronger temperature variation of Seebeck coefficient, carrier concentration, and conductivity in the nanostructured Si0.8Ge0.2 compared with the polycrystalline form indicating stronger boron precipitation in this structure. The electrical properties of both samples were calculated using a multi-band semi-classical model. The theoretical calculations confirm that the increase of boron precipitation in the nanostructured Si0.8Ge0.2 is responsible for its higher thermal instability. Since the thermoelectric properties of the nanostructured sample degrade as a result of thermal cycling, the material is appropriate only for continuous operation at high temperature without cooling.

  14. Development and structural characterization of exchange-spring-like nanomagnets in (Fe,Co)-Pt bulk nanocrystalline alloys

    NASA Astrophysics Data System (ADS)

    Crisan, O.; Crisan, A. D.; Mercioniu, I.; Nicula, R.; Vasiliu, F.

    2016-03-01

    FePt-based alloys are currently under scrutiny for their possible use as materials for perpendicular magnetic recording. Another possible application is in the field of permanent magnets without rare-earths, magnets that may operate at higher temperatures than the classic Nd-Fe-B magnets. Within this study, FeCoPt alloys prepared by rapid solidification from the melt are structurally and magnetically characterized. In the as-cast FeCoPt ribbons, a three-phase structure comprising well-ordered CoFePt and CoPt L10 phases embedded in a disordered fcc FePt matrix was evidenced by XRD, HREM and SAED. Extended transmission electron microscopy analysis demonstrates the incipient formation of ordered L10 phases. X-ray diffraction was used to characterize the phase structure and to obtain the structural parameters of interest for L10 ordering. In the as-cast state, the co-existence of hard magnetic CoFePt and CoPt L10 tetragonal phases with the soft fcc FePt phase is obtained within a refined microstructure made of alternatively disposed grains (grain sizes from 1 to 7 nm). Following a thermal treatment of 1 h at 670 °C, the soft magnetic fcc matrix phase transforms to tetragonal L10 phases (disorder-order transition). The resulting CoPt and CoFePt L10 phases have grains of around 5-20 nm in size. In the as-cast state, magnetic measurements show a quite large remanence (0.75 T), close to the value of the parent L10 FePt phase. Coercive fields of about 200 kA/m at 5 K were obtained, comparable with those reported for some FePt-based bulk alloys. Upon annealing both remanence and coercivity are increased and values of up to 254 kA/m at 300 K are obtained. The polycrystalline structure of the annealed FeCoPt samples, as well as the formation of multiple c-axis domains in different CoPt and CoFePt regions (which leads to a reduction of the magneto-crystalline anisotropy) may account for the observed coercive fields that are lower than in the case of very thin FeCoPt films. A

  15. High-Efficiency Amorphous Silicon Alloy Based Solar Cells and Modules; Final Technical Progress Report, 30 May 2002--31 May 2005

    SciTech Connect

    Guha, S.; Yang, J.

    2005-10-01

    The principal objective of this R&D program is to expand, enhance, and accelerate knowledge and capabilities for development of high-efficiency hydrogenated amorphous silicon (a-Si:H) and amorphous silicon-germanium alloy (a-SiGe:H) related thin-film multijunction solar cells and modules with low manufacturing cost and high reliability. Our strategy has been to use the spectrum-splitting triple-junction structure, a-Si:H/a-SiGe:H/a-SiGe:H, to improve solar cell and module efficiency, stability, and throughput of production. The methodology used to achieve the objectives included: (1) explore the highest stable efficiency using the triple-junction structure deposited using RF glow discharge at a low rate, (2) fabricate the devices at a high deposition rate for high throughput and low cost, and (3) develop an optimized recipe using the R&D batch large-area reactor to help the design and optimization of the roll-to-roll production machines. For short-term goals, we have worked on the improvement of a-Si:H and a-SiGe:H alloy solar cells. a-Si:H and a-SiGe:H are the foundation of current a-Si:H based thin-film photovoltaic technology. Any improvement in cell efficiency, throughput, and cost reduction will immediately improve operation efficiency of our manufacturing plant, allowing us to further expand our production capacity.

  16. Molecular level assessment of thermal transport and thermoelectricity in materials: From bulk alloys to nanostructures

    NASA Astrophysics Data System (ADS)

    Kinaci, Alper

    The ability to manipulate material response to dynamical processes depends on the extent of understanding of transport properties and their variation with chemical and structural features in materials. In this perspective, current work focuses on the thermal and electronic transport behavior of technologically important bulk and nanomaterials. Strontium titanate is a potential thermoelectric material due to its large Seebeck coefficient. Here, first principles electronic band structure and Boltzmann transport calculations are employed in studying the thermoelectric properties of this material in doped and deformed states. The calculations verified that excessive carrier concentrations are needed for this material to be used in thermoelectric applications. Carbon- and boron nitride-based nanomaterials also offer new opportunities in many applications from thermoelectrics to fast heat removers. For these materials, molecular dynamics calculations are used to evaluate lattice thermal transport. To do this, first, an energy moment term is reformulated for periodic boundary conditions and tested to calculate thermal conductivity from Einstein relation in various systems. The influences of the structural details (size, dimensionality) and defects (vacancies, Stone-Wales defects, edge roughness, isotopic disorder) on the thermal conductivity of C and BN nanostructures are explored. It is observed that single vacancies scatter phonons stronger than other type of defects due to unsatisfied bonds in their structure. In pristine states, BN nanostructures have 4-6 times lower thermal conductivity compared to C counterparts. The reason of this observation is investigated on the basis of phonon group velocities, life times and heat capacities. The calculations show that both phonon group velocities and life times are smaller in BN systems. Quantum corrections are also discussed for these classical simulations. The chemical and structural diversity that could be attained by

  17. Low temperature diffusion process using rare earth-Cu eutectic alloys for hot-deformed Nd-Fe-B bulk magnets

    SciTech Connect

    Akiya, T. Sepehri-Amin, H.; Ohkubo, T.; Liu, J.; Hono, K.; Hioki, K.; Hattori, A.

    2014-05-07

    The low temperature grain boundary diffusion process using RE{sub 70}Cu{sub 30} (RE = Pr, Nd) eutectic alloy powders was applied to sintered and hot-deformed Nd-Fe-B bulk magnets. Although only marginal coercivity increase was observed in sintered magnets, a substantial enhancement in coercivity was observed when the process was applied to hot-deformed anisotropic bulk magnets. Using Pr{sub 70}Cu{sub 30} eutectic alloy as a diffusion source, the coercivity was enhanced from 1.65 T to 2.56 T. The hot-deformed sample expanded along c-axis direction only after the diffusion process as RE rich intergranular layers parallel to the broad surface of the Nd{sub 2}Fe{sub 14}B are thickened in the c-axis direction.

  18. Stability of metastable phase and soft magnetic properties of bulk Fe-B nano-eutectic alloy prepared by undercooling solidification combined with CU-mold chilling

    NASA Astrophysics Data System (ADS)

    Yang, Changlin; Zhang, Jun; Huang, Huili; Song, Qijiao; Liu, Feng

    2015-11-01

    Bulk Fe83B17 nano-eutectic alloys were prepared by undercooling solidification combined with Cu-mold chilling method. Stable phase Fe2B and metastable phase Fe3B were found to coexist in the as-solidified microstructure. The soft magnetic properties were improved significantly by the nano-lamellar eutectic and the metastable phase and, were increased further by annealing at 1173 K for 1.5 h after which the metastable phase was decomposed completely.

  19. Development of High Quality 1.36 eV Amorphous SiGe:H Alloy by RF Glow Discharge under Helium Dilution

    NASA Astrophysics Data System (ADS)

    Hazra, Sukti; Middya, Abdul; Rath, Jatindra; Basak, Subhashis; Ray, Swati

    1995-11-01

    The use of 1.35 eV amorphous silicon-germanium (a-SiGe:H) alloy as the second/third intrinsic layer along with 1.85 eV front layer in double/triple tandem solar cells is believed to be the best combination for the maximum power output for multijunction cells. In this study high quality low-band-gap (1.36 eV) a-SiGe:H alloy has been developed by RF glow discharge optimizing the deposition parameters and helium dilution of source gases. It has been observed that the structural, electronic properties and defect densities of alloy films developed under the deposition condition which is the transition from low-discharge-power to high-discharge-power regime, become optimum. In the present case this deposition condition is a combination of chamber pressure 0.8 Torr and RF power 60 mW/cm2. The properties of the alloy films developed under helium dilution improve and defect density decreases with the increase of deposition rate up to 120 Å/min. The 1.36 eV alloy film prepared under this condition has very low defect density ( 3.2×1016 cm-3 eV-1). The analysis of spectral response of Pd/a-SiGe:H Schottky barrier solar cells reveals that the hole transport properties improve due to increase of RF power from 15 to 60 mW/cm2 and also due to increase of growth rate from 51 to 120 Å/min.

  20. Bismuth-induced effects on optical, lattice vibrational, and structural properties of bulk GaAsBi alloys

    PubMed Central

    2014-01-01

    Bulk GaAs1 - xBix/GaAs alloys with various bismuth compositions are studied using power- and temperature-dependent photoluminescence (PL), Raman scattering, and atomic force microscopy (AFM). PL measurements exhibit that the bandgap of the alloy decreases with increasing bismuth composition. Moreover, PL peak energy and PL characteristic are found to be excitation intensity dependent. The PL signal is detectable below 150 K at low excitation intensities, but quenches at higher temperatures. As excitation intensity is increased, PL can be observable at room temperature and PL peak energy blueshifts. The quenching temperature of the PL signal tends to shift to higher temperatures with increasing bismuth composition, giving rise to an increase in Bi-related localization energy of disorders. The composition dependence of the PL is also found to be power dependent, changing from about 63 to 87 meV/Bi% as excitation intensity is increased. In addition, S-shaped temperature dependence at low excitation intensities is observed, a well-known signature of localized levels above valence band. Applying Varshni’s law to the temperature dependence of the PL peak energy, the concentration dependence of Debye temperature (β) and thermal expansion coefficient (α) are determined. AFM observations show that bismuth islands are randomly distributed on the surface and the diameter of the islands tends to increase with increasing bismuth composition. Raman scattering spectra show that incorporation of Bi into GaAs causes a new feature at around 185 cm-1 with slightly increasing Raman intensity as the Bi concentration increases. A broad feature located between 210 and 250 cm-1 is also observed and its intensity increases with increasing Bi content. Furthermore, the forbidden transverse optical (TO) mode becomes more pronounced for the samples with higher bismuth composition, which can be attributed to the effect of Bi-induced disorders on crystal symmetry. PACS 78.55Cr 78.55-m 78

  1. Predeformation and Subsequent Annealing—A Way for Controlling Morphology of Carbides in Large Dimensional Bulk Nanocrystalline Fe-Al-Cr Alloy

    NASA Astrophysics Data System (ADS)

    Wang, Hongding; La, Peiqing; Shi, Ting; Wei, Yupeng; Jiao, Huisheng

    2014-01-01

    In this study, a processing route is introduced to control the morphology of carbide and the grain size of nanocrystalline matrix of Fe-Al-Cr alloy. After predeformation followed by annealing treatment, the grain size of nanocrystalline matrix decreased slightly and the Cr7C3 phases transformed from a fiber shape to the globular shape. The yield strength and the flow stress of the alloy increased from 1048 to 1338 MPa and 1150 to 1550 MPa, respectively, while the ductility of the alloy also became better. This proposed method may open a way for controlling the morphology of carbide and the grain size of matrix in bulk nanocrystalline materials to receive higher strength and better plasticity.

  2. Thermal conductivity of bulk and nanowire Mg₂SixSn1–x alloys from first principles

    SciTech Connect

    Li, Wu; Lindsay, L.; Broido, D. A.; Stewart, Derek A.; Mingo, Natalio

    2012-11-29

    The lattice thermal conductivity (κ) of the thermoelectric materials, Mg₂Si, Mg₂Sn, and their alloys, are calculated for bulk and nanowires, without adjustable parameters. We find good agreement with bulk experimental results. For large nanowire diameters, size effects are stronger for the alloy than for the pure compounds. For example, in 200 nm diameter nanowires κ is lower than its bulk value by 30%, 20%, and 20% for Mg₂Si₀.₆Sn₀.₄, Mg₂Si, and Mg₂Sn, respectively. For nanowires less than 20 nm thick, the relative decrease surpasses 50%, and it becomes larger in the pure compounds than in the alloy. At room temperature, κ of Mg₂SixSn1–x is less sensitive to nanostructuring size effects than SixGe1–x, but more sensitive than PbTexSe1–x. This suggests that further improvement of Mg₂SixSn1–x as a nontoxic thermoelectric may be possible.

  3. Radiation-induced crystalline-to-amorphous transition in intermetallic compounds of the Cu-Ti alloy system

    SciTech Connect

    Lam, N.Q.; Okamoto, P.R.; Devanathan, R. ); Sabochick, M.J. . Computer Applications Div.)

    1992-02-01

    Recent progress in molecular-dynamics studies of radiation-induced crystalline-to-amorphous transition in the ordered intermetallic compounds of the Cu-Ti system is discussed. The effect of irradiation was simulated by the generation of Frenkel pairs,which resulted in both the formation of stable point defects and chemical disorder upon defect recombination. The thermodynamic, structural and mechanical responses of the compounds during irradiation were determined by monitoring changes in the system potential energy, volume expansion, pair correlation function, diffraction patterns, and elastic constants. It was found that the intermetallics Cu{sub 4}Ti{sub 3}, CuTi, and CuTi{sub 2} could be rendered amorphous by the creation of Frenkel pairs, but Cu{sub 4}Ti could not, consistent with experimental observations during electron irradiation. However, the simulations showed that Cu{sub 4}Ti did become amorphous when clusters of Frenkel pairs were introduced, indicating that this compound may be susceptible to amorphization by heavy-ion bombardment. A generalization of the Lindemann criterion was used to develop a thermodynamic description of solid-state amorphization as a disorder- induced melting process.

  4. Low-band-gap, amorphous-silicon-based alloys by photochemical vapor deposition: Final report, 1 October 1985--30 November 1986

    SciTech Connect

    Baron, B.N.; Hegedus, S.S.; Jackson, S.C.

    1988-02-01

    Thin films of hydrogenated amorphous silicon-germanium alloys were deposited by mercury-sensitized photochemical vapor deposition using a novel photo-CVD reactor. Thin films of a-Si/sub 1-x/Ge/sub x/:H with 0 less than or equal to x less than or equal to 1 and 1.0 less than E/sub g/ less than 1.8 eV were deposited from mixtures of silane and disilane with germane and inert gas diluents at substrate temperatures from 160/degree/ to 200/degree/C. Alloy films were characterized by measurements of photo- and dark conductivity, electron mobility-lifetime product, sub-band-gap absorption, and density of states. Dilution with hydrogen increased the photoconductivity to 10/sup /minus/5/ Scm and mobility-lifetime product to 6 /times/ 10/sup /minus/8/ cm/sup 2/V for alloys having a band gap of 1.4 eV.

  5. Variation of the electronic densities of states as a function of impurity concentration in amorphous bismuth alloys

    NASA Astrophysics Data System (ADS)

    Mata-Pinzon, Zaahel; Valladares, Ariel Alberto; Valladares, Alexander; Valladares, Renela Maria

    2014-03-01

    The properties of materials are strongly related to their atomic topology, especially when we compare properties related to the ordered and disordered phases. Using Density Functional Theory methods on 64-atom supercells we obtain the structure and calculate the electronic density of states (eDOS) as a function of the concentration of lead, thallium or antimony in an amorphous bismuth supercell. This is done to investigate how the eDOS affects the superconducting transition temperature (Tc), taking into account the measurements made by Shier and Ginsberg[2] on contaminated amorphous bismuth thin films. Supported by CONACYT and DGAPA (UNAM).

  6. Castable Amorphous Metal Mirrors and Mirror Assemblies

    NASA Technical Reports Server (NTRS)

    Hofmann, Douglas C.; Davis, Gregory L.; Agnes, Gregory S.; Shapiro, Andrew A.

    2013-01-01

    A revolutionary way to produce a mirror and mirror assembly is to cast the entire part at once from a metal alloy that combines all of the desired features into the final part: optical smoothness, curvature, flexures, tabs, isogrids, low CTE, and toughness. In this work, it has been demonstrated that castable mirrors are possible using bulk metallic glasses (BMGs, also called amorphous metals) and BMG matrix composites (BMGMCs). These novel alloys have all of the desired mechanical and thermal properties to fabricate an entire mirror assembly without machining, bonding, brazing, welding, or epoxy. BMGs are multi-component metal alloys that have been cooled in such a manner as to avoid crystallization leading to an amorphous (non-crystalline) microstructure. This lack of crystal structure and the fact that these alloys are glasses, leads to a wide assortment of mechanical and thermal properties that are unlike those observed in crystalline metals. Among these are high yield strength, carbide-like hardness, low melting temperatures (making them castable like aluminum), a thermoplastic processing region (for improving smoothness), low stiffness, high strength-to-weight ratios, relatively low CTE, density similar to titanium alloys, high elasticity and ultra-smooth cast parts (as low as 0.2-nm surface roughness has been demonstrated in cast BMGs). BMGMCs are composite alloys that consist of a BMG matrix with crystalline dendrites embedded throughout. BMGMCs are used to overcome the typically brittle failure observed in monolithic BMGs by adding a soft phase that arrests the formation of cracks in the BMG matrix. In some cases, BMGMCs offer superior castability, toughness, and fatigue resistance, if not as good a surface finish as BMGs. This work has demonstrated that BMGs and BMGMCs can be cast into prototype mirrors and mirror assemblies without difficulty.

  7. Properties and durability of the passive films on a nickel-chromium-molybdenum alloy and an iron-based bulk metallic glass

    NASA Astrophysics Data System (ADS)

    Pharkya, Pallavi

    Alloy 22, a Ni-Cr-Mo-W alloy, and SAM1651, an Fe-Cr-Mo-B-Y-C bulk metallic glass are highly corrosion-resistant alloys. The high corrosion resistance of these alloys is due to the formation of tenacious oxide films on their surfaces. This study examines the reformation behavior of the passive films as a function of the corrosion resistance of the alloys and the corrosivity of the environment. The main tasks of this study were (i) to determine the chemical durability of passive films on these highly corrosion-resistant alloys in aggressive environments, (ii) to investigate the durability after mechanically damaging the passive films either locally or over the entire surface area and to study the reformation kinetics, (iii) to compare the durability of the passive films of the aforementioned highly corrosion resistant alloys with an alloy of intermediate corrosion resistance, AL6XN, and an alloy of less corrosion resistance, 316L SS, (iv) to examine the evolution of the electronic properties of the passive films on alloy 22 and SAM1651 under different environmental conditions such as concentrated chloride solution, acidic solution, temperature, potential and oxyanions, and (v) to develop an understanding of the relationship between the passive films' composition, electronic and electrochemical properties and the performance. A combination of techniques was utilized to meet the above mentioned objectives. Cyclic potentiodynamic polarization (CPP) was used to determine the electrochemical parameters such as freely corroding, breakdown and repassivation potentials. Electrochemical impedance spectroscopy (EIS) was used to determine the electronic properties such as impedance, thickness and capacitance of the passive films. Mott-Schottky (M-S) analysis was used to determine the type and the density of the defects in the passive films. The mechanical durability and reformation kinetics of the passive films was investigated using a scratch-repassivation method. The quality

  8. Effect of Cr addition on the glass-forming ability, magnetic properties, and corrosion resistance in FeMoGaPCBSi bulk glassy alloys

    NASA Astrophysics Data System (ADS)

    Shen, Baolong; Akiba, Masahiro; Inoue, Akihisa

    2006-08-01

    The effect of Cr addition on the glass-forming ability (GFA), the magnetic properties, and corrosion resistance in Fe-Mo-Ga-P-C-B-Si glassy alloys was investigated. In addition to a slight increase of supercooled liquid region from 50to55K, the substitution of a small amount of Fe with Cr was found to be effective for approaching alloy to a eutectic point, resulting in an increase in GFA. By copper mold casting, bulk glassy alloy rods with diameters up to 3mm were produced. These glassy alloys exhibit a rather high saturation magnetization of 0.84-1.11T with good soft-magnetic properties, i.e., low coercive force of 2.3-2.9A/m, and high effective permeability of 13 360-15 960 at 1kHz under a field of 1A/m. The passive current density of the glassy alloy rod in 3mass% NaCl solution decreased significantly from 1×102to3×10-1A/m2 with an increase in Cr content, indicating that the addition of Cr is effective in enhancing the corrosion resistance.

  9. Investigation of the stability and 1.0 MeV proton radiation resistance of commercially produced hydrogenated amorphous silicon alloy solar cells

    NASA Technical Reports Server (NTRS)

    Lord, Kenneth R., II; Walters, Michael R.; Woodyard, James R.

    1994-01-01

    The radiation resistance of commercial solar cells fabricated from hydrogenated amorphous silicon alloys is reported. A number of different device structures were irradiated with 1.0 MeV protons. The cells were annealing at 200 C. The annealing time was dependent on proton fluence. Annealing devices for one hour restores cell parameters or fluences below 1(exp 14) cm(exp -2); fluences above 1(exp 14) cm(exp -2) require longer annealing times. A parametric fitting model was used to characterize current mechanisms observed in dark I-V measurements. The current mechanisms were explored with irradiation fluence, and voltage and light soaking times. The thermal generation current density and quality factor increased with proton fluence. Device simulation shows the degradation in cell characteristics may be explained by the reduction of the electric field in the intrinsic layer.

  10. Investigation of the Stability and 1.0 MeV Proton Radiation Resistance of Commercially Produced Hydrogenated Amorphous Silicon Alloy Solar Cells

    NASA Technical Reports Server (NTRS)

    Lord, Kenneth R., II; Walters, Michael R.; Woodyard, James R.

    1994-01-01

    The radiation resistance of commercial solar cells fabricated from hydrogenated amorphous silicon alloys is reported. A number of different device structures were irradiated with 1.0 MeV protons. The cells were insensitive to proton fluences below 1E12 sq cm. The parameters of the irradiated cells were restored with annealing at 200 C. The annealing time was dependent on proton fluence. Annealing devices for one hour restores cell parameters for fluences below 1E14 sq cm fluences above 1E14 sq cm require longer annealing times. A parametric fitting model was used to characterize current mechanisms observed In dark I-V measurements. The current mechanism were explored with irradiation fluence, and voltage and light soaking times. The thermal generation current density and quality factor increased with proton fluence. Device simulation shows the degradation in cell characteristics may be explained by the reduction of the electric field in the intrinsic layer.

  11. High-rate ( similar to 50-A/s) deposition of ZnO films for amorphous silicon alloy solar-cell back-reflector application

    SciTech Connect

    Banerjee, A.; Wolf, D.; Yang, J.; Guha, S. )

    1991-08-01

    Back reflectors have been fabricated by the deposition of ZnO films on textured Ag films. High deposition rates of {similar to}50 A/s have been achieved by the dc magnetron sputtering technique. The ZnO target used has been prepared in our laboratory. Amorphous silicon alloy solar cells have been deposited on the ZnO/textured Ag back reflector. Control samples have been prepared by the deposition of identical cells on the same back reflector, but in which the ZnO films have been prepared by a low-rate {similar to}5-A/s rf sputtering process. The short-circuit current density, which has been used as the primary test parameter for evaluating the back reflectors, is slightly superior in the case of the high-rate ZnO back reflector. The high-rate deposition process is, therefore, attractive for large-volume production application.

  12. Temperature and field-induced magnetization flips in amorphous Er{endash}Fe alloys evidenced by x-ray magnetic circular dichroism

    SciTech Connect

    Garcia, L.M.; Pizzini, S.; Rueff, J.P.; Vogel, J.; Galera, R.M.; Fontaine, A.; Kappler, J.P.; Krill, G.; Goedkoop, J.

    1996-04-01

    Magnetic properties of amorphous Er{sub 1{minus}{ital x}}Fe{sub {ital x}} alloys with {ital x}{approx_equal}0.7 have been studied. Macroscopic characterization has been performed by measuring temperature- and field-dependent magnetization. Applying a magnetic field the compensation temperature first decreases, but increases again at larger fields. This {open_quote}{open_quote}exotic{close_quote}{close_quote} behavior has been interpreted in terms of the sperimagnetic character of both subnetworks. The suggested scheme has been checked by measuring x-ray circular magnetic dichroism at the Er {ital M}{sub 5}-edge. Using this atom-sensitive technique we have been able to detect temperature-induced as well as field-induced flips of the Er-subnetwork with respect to the direction of the applied field. {copyright} {ital 1996 American Institute of Physics.}

  13. Hydrogen-induced phase separation in amorphous Cu0.5Ti0.5 alloys. I. Room-temperature experiments

    NASA Astrophysics Data System (ADS)

    Rodmacq, B.; Maret, M.; Laugier, J.; Billard, L.; Chamberod, A.

    1988-07-01

    The influence of hydrogen on the structure of an amorphous Cu0.5Ti0.5 alloy has been studied by means of x-ray and neutron scattering. These experiments include large-angle x-ray and neutron scattering and small-angle neutron scattering with hydrogen-deuterium substitution. The results indicate that large hydrogen contents (hydrogen-to-metal ratio of 0.84) induce a phase separation into Cu and TiHx regions on a scale of about 10-15 Å. Experiments on samples loaded with hydrogen by electrolysis or from the gas phase show that such a phase separation does not depend on the method of hydrogen loading. The results of a computer simulation with nearest-neighbor Cu-Ti permutations reproduce the main features of the diffraction data and confirm the large change of chemical ordering between Cu and Ti atoms upon hydrogen absorption.

  14. Evolution of thermoelectric performance for (Bi,Sb)2Te3 alloys from cutting waste powders to bulks with high figure of merit

    NASA Astrophysics Data System (ADS)

    Fan, Xi‧an; Cai, Xin zhi; Han, Xue wu; Zhang, Cheng cheng; Rong, Zhen zhou; Yang, Fan; Li, Guang qiang

    2016-01-01

    Bi2Te3 based cutting waste powders from cutting wafers were firstly selected as raw materials to prepare p-type Bi2Te3 based thermoelectric (TE) materials. Through washing, reducing, composition correction, smelting and resistance pressing sintering (RPS) process, p-type (Bi,Sb)2Te3 alloy bulks with different nominal stoichiometries were successfully obtained. The evolution of microstructure and TE performance for (Bi,Sb)2Te3 alloys were investigated in detail. All evidences confirmed that most of contaminants from line cutting process such as cutting fluid and oxides of Bi, Sb or Te could be removed by washing, reducing and smelting process used in this work. The carrier content and corresponding TE properties could be adjusted effectively by appropriate composition correction treatment. At lastly, a bulk with a nominal stoichiometry of Bi0.44Sb1.56Te3 was obtained and its' dimensionless figure of merit (ZT) was about 1.16 at 90 °C. The ZT values of Bi0.36Sb1.64Te3 and Bi0.4Sb1.6Te3 alloy bulks could also reach 0.98 and 1.08, respectively. Different from the conventional recycling technology such as hydrometallurgy extraction methods, the separation and extraction of beneficial elements such as Bi, Sb and Te did not need to be performed and the Bi2Te3 based bulks with high TE properties could be directly obtained from the cutting waste powders. In addition, the recycling technology introduced here was green and more suitable for practical industrial application. It can improve material utilization and lower raw material costs of manufacturers.

  15. Plasticity in the Supercooled Liquid Region of Bulk Metallic Glasses

    SciTech Connect

    Nieh, T G; Wadsworth, J; Liu, C T; Ice, G E

    2000-10-30

    Intensive efforts have been carried out over the past decade to develop means to slow down the phase transformation kinetics during the forming of metallic glasses. As a result of these efforts, some metallic glasses can now be fabricated in bulk forms (BMG) from the liquid state at cooling rates on the order of 1-10 K/s, which is close to that of conventional casting. This enables the production of bulk amorphous alloys with a thickness of {approx}10 mm. While advances in amorphous metallic alloy development have been impressive, they have been made largely through experience [1]. Three main conclusions drawn from this study are: (1) Bulk metallic glasses generally have excellent mechanical formability in the supercooled liquid region. (2) Bulk metallic glasses may not be necessarily behave like a Newtonian fluid (i.e. m=1). The non-Newtonian behavior is associated with glass instability during deformation. (3) Multi-component Bulk metallic glasses can be used as the precursor of a nanocrystalline solid. However, the nanocrystalline solid is not necessarily superplastic. The non-superplastic behavior is caused by the difficult strain accommodation at grain triple junctions.

  16. Pressure tunes electrical resistivity by four orders of magnitude in amorphous Ge2Sb2Te5 phase-change memory alloy.

    PubMed

    Xu, M; Cheng, Y Q; Wang, L; Sheng, H W; Meng, Y; Yang, W G; Han, X D; Ma, E

    2012-05-01

    Ge-Sb-Te-based phase-change memory is one of the most promising candidates to succeed the current flash memories. The application of phase-change materials for data storage and memory devices takes advantage of the fast phase transition (on the order of nanoseconds) and the large property contrasts (e.g., several orders of magnitude difference in electrical resistivity) between the amorphous and the crystalline states. Despite the importance of Ge-Sb-Te alloys and the intense research they have received, the possible phases in the temperature-pressure diagram, as well as the corresponding structure-property correlations, remain to be systematically explored. In this study, by subjecting the amorphous Ge(2)Sb(2)Te(5) (a-GST) to hydrostatic-like pressure (P), the thermodynamic variable alternative to temperature, we are able to tune its electrical resistivity by several orders of magnitude, similar to the resistivity contrast corresponding to the usually investigated amorphous-to-crystalline (a-GST to rock-salt GST) transition used in current phase-change memories. In particular, the electrical resistivity drops precipitously in the P = 0 to 8 GPa regime. A prominent structural signature representing the underlying evolution in atomic arrangements and bonding in this pressure regime, as revealed by the ab initio molecular dynamics simulations, is the reduction of low-electron-density regions, which contributes to the narrowing of band gap and delocalization of trapped electrons. At P > 8 GPa, we have observed major changes of the average local structures (bond angle and coordination numbers), gradually transforming the a-GST into a high-density, metallic-like state. This high-pressure glass is characterized by local motifs that bear similarities to the body-centered-cubic GST (bcc-GST) it eventually crystallizes into at 28 GPa, and hence represents a bcc-type polyamorph of a-GST. PMID:22509004

  17. Pressure tunes electrical resistivity by four orders of magnitude in amorphous Ge[subscript 2]Sb[subscript 2]Te[subscript 5] phase-change memory alloy

    SciTech Connect

    Xu, M.; Cheng, Y.Q.; Wang, L.; Sheng, H.W.; Meng, Y.; Yang, W.G.; Hang, X.D.; Ma, E.

    2012-05-22

    Ge-Sb-Te-based phase-change memory is one of the most promising candidates to succeed the current flash memories. The application of phase-change materials for data storage and memory devices takes advantage of the fast phase transition (on the order of nanoseconds) and the large property contrasts (e.g., several orders of magnitude difference in electrical resistivity) between the amorphous and the crystalline states. Despite the importance of Ge-Sb-Te alloys and the intense research they have received, the possible phases in the temperature-pressure diagram, as well as the corresponding structure-property correlations, remain to be systematically explored. In this study, by subjecting the amorphous Ge{sub 2}Sb{sub 2}Te{sub 5} (a-GST) to hydrostatic-like pressure (P), the thermodynamic variable alternative to temperature, we are able to tune its electrical resistivity by several orders of magnitude, similar to the resistivity contrast corresponding to the usually investigated amorphous-to-crystalline (a-GST to rock-salt GST) transition used in current phase-change memories. In particular, the electrical resistivity drops precipitously in the P = 0 to 8 GPa regime. A prominent structural signature representing the underlying evolution in atomic arrangements and bonding in this pressure regime, as revealed by the ab initio molecular dynamics simulations, is the reduction of low-electron-density regions, which contributes to the narrowing of band gap and delocalization of trapped electrons. At P > 8 GPa, we have observed major changes of the average local structures (bond angle and coordination numbers), gradually transforming the a-GST into a high-density, metallic-like state. This high-pressure glass is characterized by local motifs that bear similarities to the body-centered-cubic GST (bcc-GST) it eventually crystallizes into at 28 GPa, and hence represents a bcc-type polyamorph of a-GST.

  18. Reversible amorphous-crystalline phase changes in a wide range of Se(1-x)Te(x) alloys studied using ultrafast differential scanning calorimetry.

    PubMed

    Vermeulen, Paul A; Momand, Jamo; Kooi, Bart J

    2014-07-14

    The reversible amorphous-crystalline phase change in a chalcogenide material, specifically the Se1-xTex alloy, has been investigated for the first time using ultrafast differential scanning calorimetry. Heating rates and cooling rates up to 5000 K/s were used. Repeated reversible amorphous-crystalline phase switching was achieved by consecutively melting, melt-quenching, and recrystallizing upon heating. Using a well-conditioned method, the composition of a single sample was allowed to shift slowly from 15 at. %Te to 60 at. %Te, eliminating sample-to-sample variability from the measurements. Using Energy Dispersive X-ray Spectroscopy composition analysis, the onset of melting for different Te-concentrations was confirmed to coincide with the literature solidus line, validating the use of the onset of melting Tm as a composition indicator. The glass transition Tg and crystallization temperature Tc could be determined accurately, allowing the construction of extended phase diagrams. It was found that Tm and Tg increase (but Tg/Tm decrease slightly) with increasing Te-concentration. Contrarily, the Tc decreases substantially, indicating that the amorphous phase becomes progressively unfavorable. This coincides well with the observation that the critical quench rate to prevent crystallization increases about three orders of magnitude with increasing Te concentration. Due to the employment of a large range of heating rates, non-Arrhenius behavior was detected, indicating that the undercooled liquid SeTe is a fragile liquid. The activation energy of crystallization was found to increase 0.5-0.6 eV when the Te concentration increases from 15 to 30 at. % Te, but it ceases to increase when approaching 50 at. % Te. PMID:25028022

  19. A record setting amorphous silicon alloy triple-junction solar cell with 14.6{percent} initial and 12.8{percent} stable efficiencies

    SciTech Connect

    Yang, J.; Banerjee, A.; Guha, S.

    1997-02-01

    World record 14.6{percent} initial and 12.8{percent} stable conversion efficiencies have been achieved using amorphous silicon based alloy in a spectrum-splitting, triple-junction structure. This performance exceeds our previous record of 13.2{percent} initial and 11.8{percent} stable efficiencies and establishes a new milestone toward reaching the 15{percent} stable module goal. Key factors leading to this major advance include: (a) Improvement in the low bandgap amorphous silicon-germanium component cell that resulted in enhanced red response and provided desired current mismatching, (b) improvement in the pn tunnel junction between component cells by incorporating microcrystalline p and n layers in a multilayered structure that resulted in reduced optical and electrical losses, and (c) improvement in the top conducting oxide that resulted in reduced absorption and enhanced blue response without increasing the top cell thickness. Details of these advances along with light-soaking data for high efficiency cells will be discussed. {copyright} {ital 1997 American Institute of Physics.}

  20. Increasing Ti-6Al-4V brazed joint strength equal to the base metal by Ti and Zr amorphous filler alloys

    SciTech Connect

    Ganjeh, E.; Sarkhosh, H.; Bajgholi, M.E.; Khorsand, H.; Ghaffari, M.

    2012-09-15

    Microstructural features developed along with mechanical properties in furnace brazing of Ti-6Al-4V alloy using STEMET 1228 (Ti-26.8Zr-13Ni-13.9Cu, wt.%) and STEMET 1406 (Zr-9.7Ti-12.4Ni-11.2Cu, wt.%) amorphous filler alloys. Brazing temperatures employed were 900-950 Degree-Sign C for the titanium-based filler and 900-990 Degree-Sign C for the zirconium-based filler alloys, respectively. The brazing time durations were 600, 1200 and 1800 s. The brazed joints were evaluated by ultrasonic test, and their microstructures and phase constitutions analyzed by metallography, scanning electron microscopy and X-ray diffraction analysis. Since microstructural evolution across the furnace brazed joints primarily depends on their alloying elements such as Cu, Ni and Zr along the joint. Accordingly, existence of Zr{sub 2}Cu, Ti{sub 2}Cu and (Ti,Zr){sub 2}Ni intermetallic compounds was identified in the brazed joints. The chemical composition of segregation region in the center of brazed joints was identical to virgin filler alloy content which greatly deteriorated the shear strength of the joints. Adequate brazing time (1800 s) and/or temperature (950 Degree-Sign C for Ti-based and 990 Degree-Sign C for Zr-based) resulted in an acicular Widmanstaetten microstructure throughout the entire joint section due to eutectoid reaction. This microstructure increased the shear strength of the brazed joints up to the Ti-6Al-4V tensile strength level. Consequently, Ti-6Al-4V can be furnace brazed by Ti and Zr base foils produced excellent joint strengths. - Highlights: Black-Right-Pointing-Pointer Temperature or time was the main factors of controlling braze joint strength. Black-Right-Pointing-Pointer Developing a Widmanstaetten microstructure generates equal strength to base metal. Black-Right-Pointing-Pointer Brittle intermetallic compounds like (Ti,Zr){sub 2}Ni/Cu deteriorate shear strength. Black-Right-Pointing-Pointer Ti and Zr base filler alloys were the best choice for brazing Ti

  1. Surface and bulk infrared modes of crystalline and amorphous silica particles: a study of the relation of surface structure to cytotoxicity of respirable silica.

    PubMed Central

    Pandurangi, R S; Seehra, M S; Razzaboni, B L; Bolsaitis, P

    1990-01-01

    Surface IR (infrared) modes of crystalline and fumed (amorphous) silica particles, calcined at temperatures up to 1095 degrees C, have been studied by Fourier transform infrared spectroscopy. The ability of these same particles to lyse cells has been measured by a hemolysis protocol. The untreated crystalline and amorphous materials differ by a factor of 40 in specific surface area, and the intensity per unit mass of the sharp surface silanol band near 3745 cm-1 in the amorphous material is an order of magnitude larger than in the crystalline material. A similar difference is observed in the lysing potential of the two materials. The intensity of the silanol band increases after calcination for both materials, reaching peak values near 500 degrees C, followed by a dramatic drop at higher calcination temperatures, and reaching negligible values for materials calcined near 1100 degrees C. The lysing potential data follow essentially the same pattern for both crystalline and fumed silica. These results are consistent with the hypothesis that the surface silanol groups are involved in cell lysis. Further experiments are suggested to evaluate the relationship between the surface structure of silica particles and their potential cytotoxicity. Images FIGURE 2. A FIGURE 2. B FIGURE 2. C FIGURE 2. D PMID:2169410

  2. Mechanical Property and Corrosion Resistance Evaluations of Ti-6Al-7Nb Alloy Brazed with Bulk Metallic Glasses

    SciTech Connect

    Miura, E.; Kato, H.; Ogata, Toshiaki; Nishiyama, Nobuyuki; Specht, Eliot D; Shiraishi, Takanobu; Inoue, A.; Hisatsune, K.

    2007-01-01

    Exploitation of metallic glass as new brazing filler for Ti-based biomedical alloy was attempted. Ti-6Al-7Nb was used as a brazed material, and candidates of bulk metallic glass brazing filler were Cu60Hf25Ti15, Mg65Cu25Gd10, Zr55Cu30Al10Ni5 and Pd40Cu30P20Ni10. Convergence infrared-ray brazing was conducted for brazing Ti-6Al-7Nb/metallic glass in Ar atmosphere. After brazing, hardness measurement, X-ray tomography, cross-sectional observation, artificial saliva immersion test and tensile test were performed to evaluate brazability, mechanical property and corrosion resistance of the obtained brazing joints. The results of brazing using these metallic glass fillers show that all the metallic glasses were brazable to Ti-6Al-7Nb except for Mg65Cu25Gd10. Mg65Cu25Gd10, Cu60Hf25Ti15 and their joints collapsed rapidly during immersion test. Zr55Cu30Al10Ni5 joint was the best in terms of degradation resistance; however, tensile strength was inferior to the conventional one. Pd40Cu30Ni10P20 filler and Zr55Cu30Al10Ni5 filler and their joints did not show any collapse or tarnish during the immersion test. Pd40Cu30Ni10P20 joint showed the excellent properties in terms of both corrosion resistance and tensile strength, which were superior to a joint brazed using Ti-15Cu-25Ni conventional filler. X-ray tomograph indicates that fracture tends to occur in the vicinity of the brazing interface after tensile test. The brazed metallic glass fillers were fully crystallized, excluding Pd40Cu30Ni10P20 filler. Pd40Cu30Ni10P20 brazed filler contained mapleleaf like primary dendrite, peritectoid and a few microns interfacial reaction layer in glassy matrix. The results indicated that Pd40Cu30Ni10P20 is promising brazing filler for dental or biomaterial devices.

  3. In-plane/out-of-plane disorder influence on the magnetic anisotropy of Fe1-yMnyPt-L10 bulk alloy

    NASA Astrophysics Data System (ADS)

    Cuadrado, R.; Liu, Kai; Klemmer, Timothy J.; Chantrell, R. W.

    2016-03-01

    The random substitution of a non-magnetic species instead of Fe atoms in FePt-L10 bulk alloy will permit to tune the magnetic anisotropy energy of this material. We have performed by means of first principles calculations a study of Fe1-yMnyPt-L10 (y = 0.0, 0.08, 0.12, 0.17, 0.22, and 0.25) bulk alloy for a fixed Pt concentration when the Mn species have ferro-/antiferromagnetic (FM,AFM) alignment at the same(different) atomic plane(s). This substitution will promote several in-plane lattice values for a fixed amount of Mn. Charge hybridization will change compared to the FePt-L10 bulk due to this lattice variation leading to a site resolved magnetic moment modification. We demonstrate that this translates into a total magnetic anisotropy reduction for the AFM phase and an enhancement for the FM alignment. Several geometric configurations were taken into account for a fixed Mn concentration because of different possible Mn positions in the simulation cell.

  4. Surface characterization and catalytic CO + H 2 reaction on Fe 82.2B 17.8 amorphous alloy

    NASA Astrophysics Data System (ADS)

    Kisfaludi, G.; Lázár, K.; Schay, Z.; Guczi, L.; Fetzer, Cs.; Konczos, G.; Lovas, A.

    1985-09-01

    Fe 82.2B 17.8 amorphous ribbon has been used as a catalyst for the Fischer-Tropsch-type reaction of CO+H 2. Specific activity has been found to be at least an order of magnitude higher than that of either the crystallized ribbon of identical composition or the supported iron catalyst. Before and after the catalytic tests the ribbons were characterized by XRD, XPS, UPS and Mössbauer spectroscopy in transmission and in conversion electron modes. Conversion electron Mössbauer spectroscopy and UPS proved that the surface of the amorphous ribbons is being partially crystallized during 8000 min reaction time at a maximum reaction temperature of 560 K. The superior catalytic activity has been explained by stabilization of the small iron particles and Fe 2O 3 by boron atoms at the surface and by suppressed carbide formation.

  5. Thermal and structural stability of cosputtered amorphous Ta(x)Cu(1-x) alloy thin films on GaAs

    NASA Technical Reports Server (NTRS)

    Oh, J. E.; Woolam, J. A.; Aylesworth, K. D.; Sellmyer, D. J.; Pouch, J. J.

    1986-01-01

    The characteristics of thin films of Ta-Cu, prepared over a wide range of compositions by cosputter deposition onto GaAs and fused quartz substrates, are studied by X-ray diffraction and van der Pauw resistivity measurement. Results show films to be amorphous over the range of 55-95 at. pct, and show Ta(93)Cu(7) barriers to be effective in preventing Au in-diffusion, with a 3000-A layer remaining unpenetrated after an annealing at 700 C for 20 min. Diffusion of Ga and/or As into amorphous 93 at. pct Ta is found to be more rapid than that of Au, and interfacial reactions were shown to form compounds including Ta3Au, CuAu, TaAs2, and Ga3Cu7 above 700 C.

  6. Combined effects of magnetic interaction and domain wall pinning on the coercivity in a bulk Nd60Fe30Al10 ferromagnet

    PubMed Central

    Tan, X. H.; Chan, S. F.; Han, K.; Xu, H.

    2014-01-01

    Understanding the coercivity mechanism has a substantial impact on developing novel permanent materials. However, the current coercivity mechanisms used widely in permanent alloys cannot explain well the amorphous phase produced hard magnetic behavior of Nd-based bulk amorphous alloys (BAAs). Here, we propose that the coercivity in as-cast Nd60Fe30Al10 alloy is from the combination of magnetic interaction and strong pinning of domain walls. Moreover, the role of domain wall pinning is less affected after crystallization, while the magnetic interaction is dependent on the annealing temperature. Our findings give further insight into the coercivity mechanism of Nd-based bulk ferromagnets and provide a new idea to design prospective permanent alloys with coercivity from the combination of magnetic interaction and pinning of domain walls. PMID:25348232

  7. Combined effects of magnetic interaction and domain wall pinning on the coercivity in a bulk Nd₆₀Fe₃₀Al₁₀ ferromagnet.

    PubMed

    Tan, X H; Chan, S F; Han, K; Xu, H

    2014-01-01

    Understanding the coercivity mechanism has a substantial impact on developing novel permanent materials. However, the current coercivity mechanisms used widely in permanent alloys cannot explain well the amorphous phase produced hard magnetic behavior of Nd-based bulk amorphous alloys (BAAs). Here, we propose that the coercivity in as-cast Nd60Fe30Al10 alloy is from the combination of magnetic interaction and strong pinning of domain walls. Moreover, the role of domain wall pinning is less affected after crystallization, while the magnetic interaction is dependent on the annealing temperature. Our findings give further insight into the coercivity mechanism of Nd-based bulk ferromagnets and provide a new idea to design prospective permanent alloys with coercivity from the combination of magnetic interaction and pinning of domain walls. PMID:25348232

  8. High-Velocity Oxygen Fuel Thermal Spray of Fe-Based Amorphous Alloy: a Numerical and Experimental Study

    NASA Astrophysics Data System (ADS)

    Ajdelsztajn, L.; Dannenberg, J.; Lopez, J.; Yang, N.; Farmer, J.; Lavernia, E. J.

    2009-09-01

    The fabrication of dense coatings with appropriate properties using a high velocity oxygen fuel (HVOF) spray process requires an in-depth understanding of the complete gas flow field and particle behavior during the process. A computational fluid dynamics (CFD) model is implemented to investigate the gas flow behavior that occurs during the HVOF process and a simplified one-dimensional decoupled model of the in-flight thermal behavior of the amorphous Fe-based powder particles was developed and applied for three different spray conditions. The numerical results were used to rationalize the different coating microstructures described in the experimental results. Low porosity and amorphous coatings were produced using two different particle size distributions (16 to 25 μm and 25 to 53 μm). The amorphous characteristics of the powder were retained in the coating due to melting and rapid solidification in the case of very fine powder or ligaments (<16 μm) and to the fact that the crystallization temperature was not reached in the case of the large particles (16 to 53 μm).

  9. Low-band-gap, amorphous-silicon-based alloys by chemical vapor deposition: Annual subcontract report, 1 October 1985-31 January 1986

    SciTech Connect

    Baron, B.N.; Jackson, S.C.

    1986-12-01

    This research was conducted to determine the potential of photochemical vapor deposition (photo-CVD) for producing high-quality, low-band-gap amorphous silicon germanium alloys for use in high-efficiency, multijunction, thin-film photovoltaic solar cells. A photo-CVD reactor for mercury-sensitized photolysis of silane-germane and disilane-germane mixtures was developed. Alloy thin films of undoped a-Si/sub 1-x/Ge/sub x/:H were deposited using mercury vapor mixed with SiH/sub 4/ or Si/sub 2/H/sub 6/, GeH/sub 4/, and diluent gas of Ar, He, or H/sub 2/. Materials properties were characterized by measurements of Ge content, optical transmission and reflection, and dark and photo-conductivity. Opto-electronic properties of photo-CVD a-Si/sub 1-x/Ge/sub x/:H were found to be comparable to glow discharge and sputtered materials. Moreover, p-i-n solar cells with low-band-gap i-layers were able to be fabricated by photo-CVD.

  10. Effect of bending stresses on the high-frequency magnetic properties and their time stability in a cobalt-based amorphous alloy with an extremely low magnetostriction

    NASA Astrophysics Data System (ADS)

    Kekalo, I. B.; Mogil'nikov, P. S.

    2015-12-01

    An unusual effect of the stresses of bending (toroidal sample diameter D) on the hysteretic magnetic properties ( H c , μ5) of an amorphous Co69Fe3.7Cr3.8Si12B11 alloy with an extremely low magnetostriction (|λ s | ≤ 10-7) is revealed. These properties are measured in a dynamic regime at a magnetic-field frequency f = 0.1-20 kHz. The coercive force of the alloy H c weakly depends on D at low frequencies ( f < 1 kHz), and permeability μ5 ( H = 5 mOe), in contrast, is independent of D at high frequencies and is dependent on D at low frequencies. The samples subjected to high-temperature (390°C) annealing followed by water quenching exhibit "anomalous" dependences: permeability μ5 increases with decreasing toroidal sample radius, i.e., with increasing bending stresses. The detected dependences are related to the fact that magnetization reversal via the displacement of rigid domain walls is predominant at low frequencies and during static measurements and magnetization reversal via the displacement of flexible domain walls is predominant at high frequencies.

  11. Electrolytic Deposition and Diffusion of Lithium onto Magnesium-9 Wt Pct Yttrium Bulk Alloy in Low-Temperature Molten Salt of Lithium Chloride and Potassium Chloride

    NASA Astrophysics Data System (ADS)

    Dong, Hanwu; Wu, Yaoming; Wang, Lidong; Wang, Limin

    2009-10-01

    The electrolytic deposition and diffusion of lithium onto bulk magnesium-9 wt pct yttrium alloy cathode in molten salt of 47 wt pct lithium chloride and 53 wt pct potassium chloride at 693 K were investigated. Results show that magnesium-yttrium-lithium ternary alloys are formed on the surface of the cathodes, and a penetration depth of 642 μm is acquired after 2 hours of electrolysis at the cathodic current density of 0.06 A·cm-2. The diffusion of lithium results in a great amount of precipitates in the lithium containing layer. These precipitates are the compound of Mg41Y5, which arrange along the grain boundaries and hinder the diffusion of lithium, and solid solution of yttrium in magnesium. The grain boundaries and the twins of the magnesium-9 wt pct yttrium substrate also have negative effects on the diffusion of lithium.

  12. Brazing ZrO{sub 2} ceramic to Ti–6Al–4V alloy using NiCrSiB amorphous filler foil: Interfacial microstructure and joint properties

    SciTech Connect

    Cao, J.; Song, X.G.; Li, C.; Zhao, L.Y.; Feng, J.C.

    2013-07-15

    Reliable brazing of ZrO{sub 2} ceramic and Ti–6Al–4V alloy was achieved using NiCrSiB amorphous filler foil. The interfacial microstructure of ZrO{sub 2}/Ti–6Al–4V joints was characterized by scanning electron microscope, energy dispersive spectrometer and micro-focused X-ray diffractometer. The effects of brazing temperature on the interfacial microstructure and joining properties of brazed joints were investigated in detail. Active Ti of Ti–6Al–4V alloy dissolved into molten filler metal and reacted with ZrO{sub 2} ceramic to form a continuous TiO reaction layer, which played an important role in brazing. Various reaction phases including Ti{sub 2}Ni, Ti{sub 5}Si{sub 3} and β-Ti were formed in brazed joints. With an increasing of brazing temperature, the TiO layer thickened gradually while the Ti{sub 2}Ni amount reduced. Shear test indicated that brazed joints tend to fracture at the interface between ZrO{sub 2} ceramic and brazing seam or Ti{sub 2}Ni intermetallic layer. The maximum average shear strength reached 284.6 MPa when brazed at 1025 °C for 10 min. - Graphical Abstract: Interfacial microstructure of ZrO{sub 2}/TC4 joint brazed using NiCrSiB amorphous filler foil was: ZrO{sub 2}/TiO/Ti{sub 2}Ni + β-Ti + Ti{sub 5}Si{sub 3}/β-Ti/Widmanstätten structure/TC4. - Highlights: • Brazing of ZrO{sub 2} ceramic and Ti-6Al-4V alloy was achieved. • Interfacial microstructure was TiO/Ti{sub 2}Ni + β + Ti{sub 5}Si{sub 3}/β/Widmanstätten structure. • The formation of TiO produced the darkening effect of ZrO{sub 2} ceramic. • The highest joining strength of 284.6MPa was obtained.

  13. Studies of hydrogenated amorphous silicon

    SciTech Connect

    Bishop, S G; Carlos, W E

    1984-07-01

    This report discusses the results of probing the defect structure and bonding of hydrogenated amorphous silicon films using both nuclear magnetic resonance (NMR) and electron spin resonance (ESR). The doping efficiency of boron in a-Si:H was found to be less than 1%, with 90% of the boron in a threefold coordinated state. On the other hand, phosphorus NMR chemical shift measurements yielded a ration of threefold to fourfold P sites of roughly 4 to 1. Various resonance lines were observed in heavily boron- and phosphorus-doped films and a-SiC:H alloys. These lines were attributed to band tail states on twofold coordinated silicon. In a-SiC:H films, a strong resonance was attributed to dangling bonds on carbon atoms. ESR measurements on low-pressure chemical-vapor-deposited (LPCVD) a-Si:H were performed on samples. The defect density in the bulk of the films was 10/sup 17//cc with a factor of 3 increase at the surface of the sample. The ESR spectrum of LPCVD-prepared films was not affected by prolonged exposure to strong light. Microcrystalline silicon samples were also examined. The phosphorus-doped films showed a strong signal from the crystalline material and no resonance from the amorphous matrix. This shows that phosphorus is incorporated in the crystals and is active as a dopant. No signal was recorded from the boron-doped films.

  14. Glass Formation Ability and Kinetics of the Gd55Al20Ni25 Bulk Metallic Glass

    NASA Astrophysics Data System (ADS)

    Jo, Chol-Lyong; Xia, Lei; Ding, Ding; Dong, Yuan-Da

    2006-03-01

    We report a new bulk glass-forming alloy Gd55Al20Ni25. The bulk sample of the alloy is prepared in the shape of rods in diameter 2 mm by suction casting. The rod exhibits typical amorphous characteristics in the x-ray diffraction pattern, paramagnetic property at 300 K, distinct glass transition and multi-step crystallization behaviour in differential scanning calorimetry traces. The glass formation ability of the alloy is investigated by using the reduced glass transition temperature Trg and the parameter γ. Kinetics of glass transition and primary crystallization is also studied. The fragility parameter m obtained from the Vogel-Fulcher-Tammann dependence of glass transition temperature Tg on ln phi (phi is the heating rate) classifies the bulk metallic glasses into the intermediate category according to Angell's classification.

  15. Understanding of martensitic (TiCu)-based bulk metallic glasses through deformation behavior of a binary Ti{sub 50}Cu{sub 50} martensitic alloy

    SciTech Connect

    Kim, K. B.; Song, K. A.; Zhang, X. F.; Yi, S.

    2008-06-16

    A binary Ti{sub 50}Cu{sub 50} martensitic alloy having similar atomic clusters to (TiCu)-based martensitic bulk metallic glasses presents a large plastic strain of 18.04% with high fracture strength of 1705 MPa. Detailed microstructural investigations point out that martensite embedded in {gamma}-TiCu matrix is effective to dissipate localization of the shear stress thus leading to rotational propagation, interaction, and multiplication of the shear bands. Furthermore, the propagation of microcracks formed by local stress transition during deformation is hindered by the martensite.

  16. Narrow band gap amorphous silicon semiconductors

    DOEpatents

    Madan, A.; Mahan, A.H.

    1985-01-10

    Disclosed is a narrow band gap amorphous silicon semiconductor comprising an alloy of amorphous silicon and a band gap narrowing element selected from the group consisting of Sn, Ge, and Pb, with an electron donor dopant selected from the group consisting of P, As, Sb, Bi and N. The process for producing the narrow band gap amorphous silicon semiconductor comprises the steps of forming an alloy comprising amorphous silicon and at least one of the aforesaid band gap narrowing elements in amount sufficient to narrow the band gap of the silicon semiconductor alloy below that of amorphous silicon, and also utilizing sufficient amounts of the aforesaid electron donor dopant to maintain the amorphous silicon alloy as an n-type semiconductor.

  17. Comparison of high frequency, high temperature core loss and B-H loop characteristics of an 80 Ni-Fe crystalline alloy and two iron-based amorphous alloys. [Ni; Fe

    SciTech Connect

    Wieserman, W.R. ); Schwarze, G.E. ); Niedra, J.M. )

    1991-01-10

    Limited experimental data exists for the specific core loss and dynamic B-H loops for soft magnetic materials for the combined conditions of high frequency and high temperature. This experimental study investigates the specific core loss and dynamic B-H characteristics of a nickel-iron crystalline magnetic alloy (Supermalloy) and two-iron-based amorphous magnetic materials (Metglas 2605S-3A and Metglas 2605SC) over the frequency range of 1--50 kHz and temperature range of 23--300 C under sinusoidal voltage excitation. The effects of maximum magnetic flux density, frequency, and temperature on the specific core loss and on the size and shape of the B-H loops are examined. The Supermalloy and Metglas 2605S-3A and 2605SC data are used to compare the core loss of transformers with identical kVA and voltage ratings.

  18. Comparison of high frequency, high temperature core loss and B-H loop characteristics of an 80 Ni-Fe crystalline alloy and two iron-based amorphous alloys

    NASA Technical Reports Server (NTRS)

    Wieserman, William R.; Schwarze, Gene E.; Niedra, Janis M.

    1991-01-01

    Limited experimental data exists for the specific core loss and dynamic B-H loops for soft magnetic materials for the combined conditions of high frequency and high temperature. This experimental study investigates the specific core loss and dynamic B-H characteristics of a nickel-iron crystalline magnetic alloy (Supermalloy) and two iron-based amorphous magnetic materials (Metglas 2605S-3A and Metglas 2605SC) over the frequency range of 1-50 kHz and temperature range of 23-300 C under sinusoidal voltage excitation. The effects of maximum magnetic flux density, frequency, and temperature on the specific core loss and on the size and shape of the B-H loops are examined. The Supermalloy and Metglass 2605S-3A and 2605SC data are used to compare the core loss of transformers with identical kVA and voltage ratings.

  19. Amorphous alloy catalysis: VII. Activation and surface characterization of an amorphous Cu-Ti alloy catalyst precursor in the dehydrogenation of 2-propanol and comparison with Cu-Zr

    SciTech Connect

    Katona, T.; Molnar, A.

    1995-05-01

    The activation and catalytic properties of Cu-Ti and Cu-Zr metallic glass precursors in the dehydrogenation of 2-propanol differ substantially. In contrast with Cu-Zr, Cu-Ti can only be activated with HF solution. The pretreatment of Cu-Ti results in catalysts with BET and copper surface areas one order of magnitude smaller than those of Cu-Zr under the same conditions. Cu-Ti exhibits decreasing catalytic activity, while Cu-Zr displays stable activity in the course of the reaction. Crystallization of the metallic glasses prior to HF treatment results in a weaker reactivity toward hydrogen fluoride for both alloys. Scanning electron micrographs of the alloys reveal that HF etching results in surfaces with deep grooves, and copper-rich flakes, a Raney-Cu-like catalyst. Auger electron spectroscopic studies show copper enrichment in the surface region on both alloys after HF treatment. On the surface of Cu-Ti, mostly Cu(II) is detected, whereas Cu(O) and Cu(II) coexist on Cu-Zr. 54 refs., 11 figs., 2 tabs.

  20. Formation of large voids in the amorphous phase-change memory Ge2Sb2Te5 alloy.

    PubMed

    Sun, Zhimei; Zhou, Jian; Blomqvist, Andreas; Johansson, Börje; Ahuja, Rajeev

    2009-02-20

    On the basis of ab initio molecular dynamics simulations, large voids mainly surrounded by Te atoms are observed in molten and amorphous Ge2Sb2Te5, which is due to the clustering of two- and threefold coordinated Te atoms. Furthermore, pressure shows a significant effect on the clustering of the under coordinated Te atoms and hence the formation of large voids. The present results demonstrate that both vacancies and Te play an important role in the fast reversible phase transition process. PMID:19257687

  1. Microstructural characterization of Mg-based bulk metallic glass and nanocomposite

    SciTech Connect

    Babilas, Rafał; Nowosielski, Ryszard; Pawlyta, Mirosława; Fitch, Andy; Burian, Andrzej

    2015-04-15

    New magnesium-based bulk metallic glasses Mg{sub 60}Cu{sub 30}Y{sub 10} have been prepared by pressure casting. Glassy alloys were successfully annealed to become nanocomposite containing 200 nm crystallites in an amorphous matrix. The microstructure of bulk glassy alloy and nanocomposite obtained during heat treatment was examined by X-ray diffraction and scanning and high-resolution electron microscopy. Metallic glass has been also studied to explain the structural characteristics by the reverse Monte Carlo (RMC) modeling based on the diffraction data. The HRTEM images allow to indicate some medium-range order (MRO) regions about 2–3 nm in size and formation of local atomic clusters. The RMC modeling results confirmed some kinds of short range order (SRO) structures. It was found that the structure of bulk metallic glass formed by the pressure casting is homogeneous. The composite material contained very small particles in the amorphous matrix. Homogeneous glassy alloy had better corrosion resistance than a composite containing nanocrystalline particles in a glassy matrix. - Highlights: • RMC modeling demonstrates some kinds of SRO structures in Mg-based BMGs. • HRTEM indicated MRO regions about 2–3 nm and SRO regions about 0.5 nm in size. • Mg-based glassy alloys were successfully annealed to become nanocomposite material. • Crystalline particles have spherical morphology with an average diameter of 200 nm. • Glassy alloy had higher corrosion resistance than a nanocomposite sample.

  2. Annealing characteristics of amorphous silicon alloy solar cells irradiated with 1.00 MeV protons

    NASA Technical Reports Server (NTRS)

    Abdulaziz, Salman S.; Woodyard, James R.

    1991-01-01

    Amorphous Si:H and amorphous Si sub x, Ge sub (1-x):H solar cells were irradiated with 1.00 MeV proton fluences in the range of 1.00E14 to 1.25E15 cm (exp -2). Annealing of the short circuit current density was studied at 0, 22, 50, 100, and 150 C. Annealing times ranged from an hour to several days. The measurements confirmed that annealing occurs at 0 C and the initial characteristics of the cells are restored by annealing at 200 C. The rate of annealing does not appear to follow a simple nth order reaction rate model. Calculations of the short-circuit current density using quantum efficiency measurements and the standard AM1.5 global spectrum compare favorably with measured values. It is proposed that the degradation in J sub sc with irradiation is due to carrier recombination through the fraction of D (o) states bounded by the quasi-Fermi energies. The time dependence of the rate of annealing of J sub sc does appear to be consistent with the interpretation that there is a thermally activated dispersive transport mechanism which leads to the passivation of the irradiation induced defects.

  3. Study on Corrosion Resistance of Fe-based Amorphous Coating by Laser Cladding in Hydrochloric Acid

    NASA Astrophysics Data System (ADS)

    Chen, Q. J.; Guo, S. B.; Yang, X. J.; Zhou, X. L.; Hua, X. Z.; Zhu, X. H.; Duan, Z.

    In this study, the Fe41Co7Cr15Mo14C15B6Y2 bulk amorphous alloy with high glass-forming ability was prepared using the arc- melting copper mold casting technique, and corresponding amorphous coating was obtained using the laser melt amorphous powders on the surface of carbon steel. The corrosion resistance performance of the laser cladding coating in hydrochloric acid was analyzed and tested in experiments under the conditions of different laser cladding speeds. The amorphous alloy coating with different fabrication parameters have the difference internal structure, which lead to the difference corrosion resistance in the same environment to some extent. The nature of amorphous alloy and the corrosion morphology were investigated using XRD and SEM method, respectively. The corrosion experiments showed that: when the laser power was 3300W, the corrosion resistance of four kinds of samples in hydrochloric acid from strong to weak as follows: as-cast sample > the coating with laser cladding speed 110 mm/min > the coating with laser cladding speed 120 mm/min > the coating with laser cladding speed 130 mm/min. The free corrosion current density of casting sample, sample 1, sample 2 and sample 3 is 3.304 × 10-6 A/cm2, 2.600×10-3 A/cm2, 2.030×10-3 A/cm2 and 3.396×10-4 A/cm2, respectively.

  4. Tunable magnetism and half-metallicity in bulk and (1 0 0) surface of quaternary Co2MnGe1-xGax Heusler alloy

    NASA Astrophysics Data System (ADS)

    Wu, Bo; Yuan, Hongkuan; Kuang, Anlong; Feng, Yu; Chen, Hong

    2011-10-01

    The structural, magnetic and half-metallic properties of the bulk and (1 0 0) surface of quaternary Heusler alloy Co2MnGe1-xGax are investigated from the first-principles calculations. For the bulk, the lattice constant and total magnetic moment follow the Vegard law and Slater-Pauling rule well, respectively. Except for Co2MnGa, the Co2MnGe1-xGax series are half-metallic. Because the Fermi level of Co2MnGe0.5Ga0.5 is just located at the middle of the minority-spin gap, we predict that it bears the most robust half-metallicity as against remnant doped alloys. As for the Co2MnGe1-xGax(1 0 0) surface, the analyses on relaxed atomic positions and surface energies reveal that Co-Ge and Co-Ga bonding are more favourable than Co-Mn bonding and the terminations involving surface Mn atoms are more stable than CoCo terminations. By comparing with the bulk values, the surface Co and Mn magnetic moments are enhanced obviously. The calculated PDOS of all accessible 'ideal' surfaces show that the half-metallicity observed in bulk has been destroyed by the surface states, which is a possible reason why the tunnel magnetoresistence steeply drops as temperature increases. However, in the pure atomic terminations the surface properties can be slightly adjusted by the Ga-doped concentrations in bulk through the dipolar interaction. As a result, in the MnMn termination of Co2MnGe0.5Ga0.5(1 0 0) the spin polarization of 1 0 0% is detected, indicating that in the pure Mn atomic termination the half-metallicity of the (1 0 0) surface can remain if the corresponding bulk presents excellent half-metallic stability. Thus we predict that this thin film will present a higher potential for applications in ferromagnetic electrodes.

  5. Extraordinary high ductility/strength of the interface designed bulk W-ZrC alloy plate at relatively low temperature

    PubMed Central

    Xie, Z. M.; Liu, R.; Miao, S.; Yang, X. D.; Zhang, T.; Wang, X. P.; Fang, Q. F.; Liu, C. S.; Luo, G. N.; Lian, Y. Y.; Liu, X.

    2015-01-01

    The refractory tungsten alloys with high ductility/strength/plasticity are highly desirable for a wide range of critical applications. Here we report an interface design strategy that achieves 8.5 mm thick W-0.5 wt. %ZrC alloy plates with a flexural strength of 2.5 GPa and a strain of 3% at room temperature (RT) and ductile-to-brittle transition temperature of about 100 °C. The tensile strength is about 991 MPa at RT and 582 MPa at 500 °C, as well as total elongation is about 1.1% at RT and as large as 41% at 500 °C, respectively. In addition, the W-ZrC alloy plate can sustain 3.3 MJ/m2 thermal load without any cracks. This processing route offers the special coherent interfaces of grain/phase boundaries (GB/PBs) and the diminishing O impurity at GBs, which significantly strengthens GB/PBs and thereby enhances the ductility/strength/plasticity of W alloy. The design thought can be used in the future to prepare new alloys with higher ductility/strength. PMID:26531172

  6. Extraordinary high ductility/strength of the interface designed bulk W-ZrC alloy plate at relatively low temperature

    NASA Astrophysics Data System (ADS)

    Xie, Z. M.; Liu, R.; Miao, S.; Yang, X. D.; Zhang, T.; Wang, X. P.; Fang, Q. F.; Liu, C. S.; Luo, G. N.; Lian, Y. Y.; Liu, X.

    2015-11-01

    The refractory tungsten alloys with high ductility/strength/plasticity are highly desirable for a wide range of critical applications. Here we report an interface design strategy that achieves 8.5 mm thick W-0.5 wt. %ZrC alloy plates with a flexural strength of 2.5 GPa and a strain of 3% at room temperature (RT) and ductile-to-brittle transition temperature of about 100 °C. The tensile strength is about 991 MPa at RT and 582 MPa at 500 °C, as well as total elongation is about 1.1% at RT and as large as 41% at 500 °C, respectively. In addition, the W-ZrC alloy plate can sustain 3.3 MJ/m2 thermal load without any cracks. This processing route offers the special coherent interfaces of grain/phase boundaries (GB/PBs) and the diminishing O impurity at GBs, which significantly strengthens GB/PBs and thereby enhances the ductility/strength/plasticity of W alloy. The design thought can be used in the future to prepare new alloys with higher ductility/strength.

  7. Influence of the chemical composition of rapidly quenched amorphous alloys (Ni, Fe, Cr)-B-Si on its crystallization process

    NASA Astrophysics Data System (ADS)

    Elmanov, G.; Dzhumaev, P.; Ivanitskaya, E.; Skrytnyi, V.; Ruslanov, A.

    2016-04-01

    This paper presents results of research of the structure and phase transformations during the multistage crystallization of the metallic glasses with the compositions Ni71,5Cr6,8Fe2,7B11,9Si7,1 and Ni63,4Cr7,4Fe4,3Mn0,8B15,6Si8,5 labeled as AWS BNi-2 according to American Welding Society. Differential scanning calorimetry (DSC), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDX) were used as experimental research methods. The influence of the alloys chemical composition (boron, manganese and iron) on the temperatures and the exothermic heat effects of phase transformations, as well as on the phase composition of alloys at three stages of crystallization was analyzed. We present a thermodynamic explanation of the observed heat effects. It has been shown that manganese has the main influence on the phase transformations temperatures and heat effects in these two alloys. It is also assumed that at the final crystallization stage simultaneously with the formation of phases Ni3B and β1-Ni3Si should occur the nucleation of borides of CrB type with high Cr and low Si content.

  8. Two-current model of the composition dependence of resistivity in amorphous (Fe100-xCox)(89-y)Zr7B4Cuy alloys using a rigid-band assumption

    SciTech Connect

    Shen, S; Ohodnicki, PR; Kernion, SJ; McHenry, ME

    2012-11-15

    Composition dependence of resistivity is studied in amorphous (Fe100-xCox)(89-y)Zr7B4Cuy (0 <= x <= 50, y = 0, 1) alloys. The two-current model proposed by Mott for crystalline materials is extended to a disordered amorphous system where s-d scattering is dominant in electron conduction. A rigid-band assumption is made due to the small atomic number difference between Fe and Co. Band structures with a constant density of states (DOS), parabolic distributed DOS, and Gaussian distributed DOS were investigated to fit experimental data. The Gaussian distributed DOS was found to simulate the resistivity maximum and magnetic moment maximum in the Fe-rich region. The basic concepts presented here can potentially provide insight into the optimization of FeCo-based HITPERM alloys for applications at increased frequencies. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765673

  9. Atomic packing and diffusion in Fe{sub 85}Si{sub 2}B{sub 9}P{sub 4} amorphous alloy analyzed by ab initio molecular dynamics simulation

    SciTech Connect

    Wang, Yaocen; Takeuchi, Akira; Makino, Akihiro; Liang, Yunye; Kawazoe, Yoshiyuki

    2015-05-07

    In the work reported in this paper, ab initio molecular dynamics simulation was performed on Fe{sub 85}Si{sub 2}B{sub 9}P{sub 4} amorphous alloy. Preferred atomic environment of the elements was analyzed with Voronoi polyhedrons. It showed that B and P atoms prefer less neighbors compared with Fe and Si, making them structurally incompatible with Fe rich structure and repulsive to the formation of α-Fe. However, due to the low bonding energy of B and P caused by low coordination number, the diffusion rates of them were considerably large, resulting in the requirement of fast annealing for achieving optimum nano-crystallization for its soft magnetic property. The simulation work also indicates that diffusion rate in amorphous alloy is largely determined by bonding energy rather than atomic size.

  10. In situ X-ray diffraction study of structural evaluation in Fe73Cu1.5Nd3Si13.5B9 amorphous alloy at high temperature

    NASA Astrophysics Data System (ADS)

    Li, Gong; Xu, Tao; Gao, Yunpeng; Liu, Riping

    2008-04-01

    The thermodynamics structural relaxation of Fe73Cu1.5Nd3Si13.5B9 amorphous alloy from room temperature to 400°C has been investigated by measuring the structure factor with in situ X-ray diffraction. The structural information of the atomic configuration such as radial distribution function (RDF) and neighbor atomic distance was gained by Fourier transformation. The research result shows that the amorphous structure remains stable in the temperature range of 30 to 400°C but exhibits distinct changes in local atomic configuration with the increase of temperature. The quantitative determination of the neighbor atomic distance suggests that the degree of short-range order changes by the temperature altering the second nearest neighbor local atomic configuration of the amorphous when structural relaxation occurs.

  11. SANS of bulk metallic ZrTiCuNiBe glasses

    SciTech Connect

    Schneider, S.; Geyer, U.; Thiyagarajan, P.; Johnson, W.L.

    1997-07-21

    The evolution of decomposition and succeeding primary crystallization in the bulk amorphous Zr{sub 41.2}Ti{sub 13.8}Cu{sub 12.5}Ni{sub 10}Be{sub 22.5} alloy have been studied by small angle neutron scattering. Samples annealed isothermally in the supercooled liquid and in the solid state exhibit correlation peaks indicating quasiperiodic inhomogeneities in the scattering length density. The peak positions vary as a function of temperature as predicted by the linear Cahn-Hilliard theory of spinodal decomposition. Variations of the Be-Ti composition ratio of the alloy leads to significant changes in scattering signals. The initially homogeneous alloy separates into two amorphous phases. In the decomposed regions, crystallization probability increases leading to polymorphic crystallization.

  12. Sn and Nb modified ultrafine Ti-based bulk alloys with high-strength and enhanced ductility

    SciTech Connect

    Cao, G. H.; Schneider, R.; Gerthsen, D.; Chulist, R.; Schaarschuch, R.; Oertel, C.-G.; Skrotzki, W.

    2013-02-11

    Sn and Nb modified ultrafine eutectic Ti-Fe alloys with high strength and plasticity prepared by cold crucible levitation melting were tested in compression at room temperature. (Ti{sub 70.5}Fe{sub 29.5}){sub 93.15}Sn{sub 3.85}Nb{sub 3} alloy exhibited an ultimate compressive strength of 2.36 GPa at 15% plastic strain. Electron microscopy revealed that lamellar structures in Ti{sub 70.5}Fe{sub 29.5} alloy could be tailored by the addition of Sn and Nb to obtain a globular structure. The microstructural refinement, morphology of phase constituents, and their relationships to the mechanical properties are discussed.

  13. Bulk undercooling

    NASA Technical Reports Server (NTRS)

    Kattamis, T. Z.

    1984-01-01

    Bulk undercooling methods and procedures will first be reviewed. Measurement of various parameters which are necessary to understand the solidification mechanism during and after recalescence will be discussed. During recalescence of levitated, glass-encased large droplets (5 to 8 mm diam) high speed temperature sensing devices coupled with a rapid response oscilloscope are now being used at MIT to measure local thermal behavior in hypoeutectic and eutectic binary Ni-Sn alloys. Dendrite tip velocities were measured by various investigators using thermal sensors or high speed cinematography. The confirmation of the validity of solidification models of bulk-undercooled melts is made difficult by the fineness of the final microstructure, the ultra-rapid evolution of the solidifying system which makes measurements very awkward, and the continuous modification of the microstructure which formed during recalescence because of precipitation, remelting and rapid coarsening.

  14. Characterisation of radiation damage in W and W-based alloys from 2MeV self-ion near-bulk implantations

    DOE PAGESBeta

    Yi, Xiaoou; Culham Science Centre, Abingdon; Jenkins, Michael L.; Hattar, Khalid; Edmondson, Philip D.; Roberts, Steve G.; Culham Science Centre, Abingdon

    2015-04-21

    The displacement damage induced in bulk W and W-5 wt.% Re and W-5 wt.% Ta alloys by 2 MeV W+ irradiation to doses 3.3×1017 - 2.5×1019 W+/m2 at temperatures ranging from 300 to750°C has been characterized by transmission electron microscopy. An automated sizing and counting approach based on Image J has been proposed and performed for all irradiation data. In all cases the damage comprised dislocation loops, mostly of interstitial type, with Burgers vectors b = ½<111> (> 60%) and b = <100>. The diameters of loops did not exceed 20 nm, with the majority being ≤ 6 nm. Themore » loop number density varied between 1022 and 1023 loops/m3 . With increasing irradiation temperature, the loop size distributions shifted towards larger sizes, and there was a substantial decrease in loop number densities. The damage microstructure was less sensitive to dose than to temperature. Under the same irradiation conditions, loop number densities in the alloys were higher than in pure W but loops were smaller. In grains with normals close to z = <001>, loop strings developed in W at temperatures ≥ 500°C and doses ≥ 1.2 dpa, but such strings were not observed in the W-Re or W-Ta alloys. However, in other grain orientations complex structures appeared in all materials and dense dislocation networks formed at higher doses.« less

  15. Surface passivation and interface properties of bulk GaAs and epitaxial-GaAs/Ge using atomic layer deposited TiAlO alloy dielectric.

    PubMed

    Dalapati, G K; Chia, C K; Tan, C C; Tan, H R; Chiam, S Y; Dong, J R; Das, A; Chattopadhyay, S; Mahata, C; Maiti, C K; Chi, D Z

    2013-02-01

    High quality surface passivation on bulk-GaAs substrates and epitaxial-GaAs/Ge (epi-GaAs) layers were achieved by using atomic layer deposited (ALD) titanium aluminum oxide (TiAlO) alloy dielectric. The TiAlO alloy dielectric suppresses the formation of defective native oxide on GaAs layers. X-ray photoelectron spectroscopy (XPS) analysis shows interfacial arsenic oxide (As(x)O(y)) and elemental arsenic (As) were completely removed from the GaAs surface. Energy dispersive X-ray diffraction (EDX) analysis and secondary ion mass spectroscopy (SIMS) analysis showed that TiAlO dielectric is an effective barrier layer for reducing the out-diffusion of elemental atoms, enhancing the electrical properties of bulk-GaAs based metal-oxide-semiconductor (MOS) devices. Moreover, ALD TiAlO alloy dielectric on epi-GaAs with AlGaAs buffer layer realized smooth interface between epi-GaAs layers and TiAlO dielectric, yielding a high quality surface passivation on epi-GaAs layers, much sought-after for high-speed transistor applications on a silicon platform. Presence of a thin AlGaAs buffer layer between epi-GaAs and Ge substrates improved interface quality and gate dielectric quality through the reduction of interfacial layer formation (Ga(x)O(y)) and suppression of elemental out-diffusion (Ga and As). The AlGaAs buffer layer and TiAlO dielectric play a key role to suppress the roughening, interfacial layer formation, and impurity diffusion into the dielectric, which in turn largely enhances the electrical property of the epi-GaAs MOS devices. PMID:23331503

  16. Structural Amorphous Steels

    NASA Astrophysics Data System (ADS)

    Lu, Z. P.; Liu, C. T.; Thompson, J. R.; Porter, W. D.

    2004-06-01

    Recent advancement in bulk metallic glasses, whose properties are usually superior to their crystalline counterparts, has stimulated great interest in fabricating bulk amorphous steels. While a great deal of effort has been devoted to this field, the fabrication of structural amorphous steels with large cross sections has remained an alchemist’s dream because of the limited glass-forming ability (GFA) of these materials. Here we report the discovery of structural amorphous steels that can be cast into glasses with large cross-section sizes using conventional drop-casting methods. These new steels showed interesting physical, magnetic, and mechanical properties, along with high thermal stability. The underlying mechanisms for the superior GFA of these materials are discussed.

  17. 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.

  18. Enhancement of glass-forming ability of FeCoNiBSiNb bulk glassy alloys with superhigh strength and good soft-magnetic properties

    NASA Astrophysics Data System (ADS)

    Shen, Baolong; Chang, Chuntao; Zhang, Zhefeng; Inoue, Akihisa

    2007-07-01

    The effect of Zr addition on the glass-forming ability (GFA) of FeCoNiBSiNb glassy alloys in [(Fe0.6Co0.3Ni0.1)0.75B0.2Si0.05]96-xNb4Zrx system was investigated. In addition to slight increases of glass transition temperature from 818to822K and supercooled liquid region from 60to65K, the 1at.% Zr addition was found to be effective in approaching alloy to a eutectic point as well as decreasing liquidus temperature from 1427to1400K, resulting in an increase in GFA. By copper mold casting, [(Fe0.6Co0.3Ni0.1)0.75B0.2Si0.05]95Nb4Zr1 bulk glassy alloys (BGAs) with diameters in the range up to 6mm were produced. The BGA exhibits a superhigh fracture strength of 4180MPa, and Young's modulus of 200GPa, combined with an elastic strain of 0.02. The glassy alloy exhibits good soft-magnetic properties as well, i.e., rather high saturation magnetization of 1.1T, low coercive force of 2A/m, and high permeability of 16 700 at 1kHz under a field of 1A/m. The reason why only 1at.% Zr is effective in improving GFA and the fracture mechanisms during compression of this Fe-based BGA were discussed.

  19. Microstructure and mechanical properties of a large-dimensional bulk nanocrystalline-based Fe-Al-Cr alloy prepared by an aluminothermic reaction casting and followed annealing at 1000 °C

    NASA Astrophysics Data System (ADS)

    La, Peiqing; Wang, Hongding; Liu, Xuemei; Wei, Yupeng; Jiao, Huisheng

    2013-06-01

    A large-dimensional bulk nanocrystalline phase-based Fe-Al-Cr alloy with 10 wt.% Cr, which was about 200 mm in diameter and 10 mm in thickness, was prepared by an aluminothermic reaction casting and followed annealing at 1000 °C. Microstructures of the alloy were investigated by optical microscope, electron probe microscope, scanning electron microscope attached with electron backscattered diffraction, X-ray diffraction and transmission electron microscope. The magnetization curves of the alloy were tested by Lake Shore 7410 vibrating sample magnetometer. Compressive properties of the alloy were tested. The results show the alloy was consisted of a Fe-Al-Cr nanocrystalline matrix, Cr7C3 phase and contaminants in micrometre. Average grain size of the nanocrystalline matrix was 19 nm. Volume fraction of the Cr7C3 phase in the alloy was about 4.5%. After annealing, the saturated intensity of magnetization and the specific magnetic susceptibility of the alloy increased slightly from 99 emu/g and 0.083 emu/g Oe to 104 emu/g and 0.113 emu/g Oe, respectively. Compressive strength of the alloy was 1200 MPa and much higher than that of the small-scale nanocrystalline alloy and alloy with grains in micrometre.

  20. Far-Infrared and Raman Spectroscopy Investigation of Phonon Modes in Amorphous and Crystalline Epitaxial GeTe-Sb2Te3 Alloys

    PubMed Central

    Bragaglia, V.; Holldack, K.; Boschker, J. E.; Arciprete, F.; Zallo, E.; Flissikowski, T.; Calarco, R.

    2016-01-01

    A combination of far-infrared and Raman spectroscopy is employed to investigate vibrational modes and the carrier behavior in amorphous and crystalline ordered GeTe-Sb2Te3 alloys (GST) epitaxially grown on Si(111). The infrared active GST mode is not observed in the Raman spectra and vice versa, indication of the fact that inversion symmetry is preserved in the metastable cubic phase in accordance with the Fm3 space group. For the trigonal phase, instead, a partial symmetry break due to Ge/Sb mixed anion layers is observed. By studying the crystallization process upon annealing with both the techniques, we identify temperature regions corresponding to the occurrence of different phases as well as the transition from one phase to the next. Activation energies of 0.43 eV and 0.08 eV for the electron conduction are obtained for both cubic and trigonal phases, respectively. In addition a metal-insulator transition is clearly identified to occur at the onset of the transition between the disordered and the ordered cubic phase. PMID:27340085

  1. Investigation of amorphous RuMoC alloy films as a seedless diffusion barrier for Cu/ p-SiOC:H ultralow- k dielectric integration

    NASA Astrophysics Data System (ADS)

    Jiao, Guohua; Liu, Bo; Li, Qiran

    2015-08-01

    Ultrathin RuMoC amorphous films prepared by magnetron co-sputtering with Ru and MoC targets in a sandwiched scheme Si/ p-SiOC:H/RuMoC/Cu were investigated as barrier in copper metallization. The evolution of final microstructure of RuMoC alloy films show sensitive correlation with the content of doped Mo and C elements and can be easily controlled by adjusting the sputtering power of the MoC target. There was no signal of interdiffusion between the Cu and SiOC:H layer in the sample of Cu/RuMoC/ p-SiOC:H/Si, even annealing up to 500 °C. Very weak signal of oxygen have been confirmed in the RuMoC barrier layer both as-deposited and after being annealed, and a good performance on preventing oxygen diffusion has been proved. Leakage current and resistivity evaluations also reveal the excellent thermal reliability of this Si/ p-SiOC:H/RuMoC/Cu film stack at the temperatures up to 500 °C, indicating its potential application in the advanced barrierless Cu metallization.

  2. Low-Energy Amorphization of Ti1Sb2Te5 Phase Change Alloy Induced by TiTe2 Nano-Lamellae.

    PubMed

    Ding, Keyuan; Rao, Feng; Lv, Shilong; Cheng, Yan; Wu, Liangcai; Song, Zhitang

    2016-01-01

    Increasing SET operation speed and reducing RESET operation energy have always been the innovation direction of phase change memory (PCM) technology. Here, we demonstrate that ∼87% and ∼42% reductions of RESET operation energy can be achieved on PCM cell based on stoichiometric Ti1Sb2Te5 alloy, compared with Ge2Sb2Te5 and non-stoichiometric Ti0.4Sb2Te3 based PCM cells at the same size, respectively. The Ti1Sb2Te5 based PCM cell also shows one order of magnitude faster SET operation speed compared to that of the Ge2Sb2Te5 based one. The enhancements may be caused by substantially increased concentration of TiTe2 nano-lamellae in crystalline Ti1Sb2Te5 phase. The highly electrical conduction and lowly thermal dissipation of the TiTe2 nano-lamellae play a major role in enhancing the thermal efficiency of the amorphization, prompting the low-energy RESET operation. Our work may inspire the interests to more thorough understanding and tailoring of the nature of the (TiTe2)n(Sb2Te3)m pseudobinary system which will be advantageous to realize high-speed and low-energy PCM applications. PMID:27469931

  3. Far-Infrared and Raman Spectroscopy Investigation of Phonon Modes in Amorphous and Crystalline Epitaxial GeTe-Sb2Te3 Alloys

    NASA Astrophysics Data System (ADS)

    Bragaglia, V.; Holldack, K.; Boschker, J. E.; Arciprete, F.; Zallo, E.; Flissikowski, T.; Calarco, R.

    2016-06-01

    A combination of far-infrared and Raman spectroscopy is employed to investigate vibrational modes and the carrier behavior in amorphous and crystalline ordered GeTe-Sb2Te3 alloys (GST) epitaxially grown on Si(111). The infrared active GST mode is not observed in the Raman spectra and vice versa, indication of the fact that inversion symmetry is preserved in the metastable cubic phase in accordance with the Fm3 space group. For the trigonal phase, instead, a partial symmetry break due to Ge/Sb mixed anion layers is observed. By studying the crystallization process upon annealing with both the techniques, we identify temperature regions corresponding to the occurrence of different phases as well as the transition from one phase to the next. Activation energies of 0.43 eV and 0.08 eV for the electron conduction are obtained for both cubic and trigonal phases, respectively. In addition a metal-insulator transition is clearly identified to occur at the onset of the transition between the disordered and the ordered cubic phase.

  4. Thin-film amorphous silicon alloy research partnership. Phase 2, Annual technical progress report, 2 February 1996--1 February 1997

    SciTech Connect

    Guha, S

    1997-06-01

    This is Phase II of a 3-phase, 3-year program. It is intended to expand, enhance, and accelerate knowledge and capabilities for developing high-performance, two-terminal multijunction amorphous Si alloy modules. We discuss investigations on back reflectors to improve cell performance and investigate uniformity in performance over a 1-sq.-ft. area. We present results on component cell performance, both in the initial and in the light-degraded states, deposited over a 1-sq.-ft. area. The uniformity in deposited is investigated by studying the performance of subcells deposited over the entire area. We also present results on the performance of triple- junction cells and modules. The modules use grid-lines and encapsulants compatible with our production technology. We discuss the novel laser-processing technique that has bee developed at United Solar to improve energy-conversion efficiency and reduce manufacturing costs. We discuss in detail the optimization of the processing steps, and the performance of a laser-processed, triple- junction device of 12.6 cm{sup 2} area is presented. We also present experimental results on investigations of module reliability.

  5. Low-Energy Amorphization of Ti1Sb2Te5 Phase Change Alloy Induced by TiTe2 Nano-Lamellae

    PubMed Central

    Ding, Keyuan; Rao, Feng; Lv, Shilong; Cheng, Yan; Wu, Liangcai; Song, Zhitang

    2016-01-01

    Increasing SET operation speed and reducing RESET operation energy have always been the innovation direction of phase change memory (PCM) technology. Here, we demonstrate that ∼87% and ∼42% reductions of RESET operation energy can be achieved on PCM cell based on stoichiometric Ti1Sb2Te5 alloy, compared with Ge2Sb2Te5 and non-stoichiometric Ti0.4Sb2Te3 based PCM cells at the same size, respectively. The Ti1Sb2Te5 based PCM cell also shows one order of magnitude faster SET operation speed compared to that of the Ge2Sb2Te5 based one. The enhancements may be caused by substantially increased concentration of TiTe2 nano-lamellae in crystalline Ti1Sb2Te5 phase. The highly electrical conduction and lowly thermal dissipation of the TiTe2 nano-lamellae play a major role in enhancing the thermal efficiency of the amorphization, prompting the low-energy RESET operation. Our work may inspire the interests to more thorough understanding and tailoring of the nature of the (TiTe2)n(Sb2Te3)m pseudobinary system which will be advantageous to realize high-speed and low-energy PCM applications. PMID:27469931

  6. Urchin-Like Amorphous Ni2B Alloys: Efficient Antibacterial Materials and Catalysts for Hydrous Hydrazine Decomposition to Produce H2.

    PubMed

    Deng, Miao; Fu, Shi Yan; Yang, Fan; Wu, Ping; Tong, Dong Ge

    2016-03-01

    Urchin-like amorphous Ni2B alloys were successfully prepared for the first time from a mixture of Ni(NH3)6(2+) and polyvinyl alcohol (PVA) via a solution plasma process (SPP). The as-synthesized samples were characterized by X-ray powder diffraction (XRD), inductively coupled plasma atomic emission spectrometry (ICP-AES) X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), selected-area electron diffraction patterns (SAED) and nitrogen adsorption-desorption isotherms. In the performance test, the obtained Ni-B urchins showed great antibacterial activities, comparable with those of amikacin and kanamycin, especially towards Pseudomonas aeruginosa (P. aeruginosa). Meanwhile, the magnetic properties of Ni-B urchins are enhanced in comparison with those of conventional Ni-B. During hydrous hydrazine (N2H4) decomposition, the dehydrogenation performance of Ni-B urchins is superior to those of Raney Ni and conventional Ni-B. The enhanced catalytic performance of Ni-B urchins is attributed to their high surface area of active species nickel and the enhanced intrinsic activity resulting from their unique structure. PMID:27455647

  7. Far-Infrared and Raman Spectroscopy Investigation of Phonon Modes in Amorphous and Crystalline Epitaxial GeTe-Sb2Te3 Alloys.

    PubMed

    Bragaglia, V; Holldack, K; Boschker, J E; Arciprete, F; Zallo, E; Flissikowski, T; Calarco, R

    2016-01-01

    A combination of far-infrared and Raman spectroscopy is employed to investigate vibrational modes and the carrier behavior in amorphous and crystalline ordered GeTe-Sb2Te3 alloys (GST) epitaxially grown on Si(111). The infrared active GST mode is not observed in the Raman spectra and vice versa, indication of the fact that inversion symmetry is preserved in the metastable cubic phase in accordance with the Fm3 space group. For the trigonal phase, instead, a partial symmetry break due to Ge/Sb mixed anion layers is observed. By studying the crystallization process upon annealing with both the techniques, we identify temperature regions corresponding to the occurrence of different phases as well as the transition from one phase to the next. Activation energies of 0.43 eV and 0.08 eV for the electron conduction are obtained for both cubic and trigonal phases, respectively. In addition a metal-insulator transition is clearly identified to occur at the onset of the transition between the disordered and the ordered cubic phase. PMID:27340085

  8. Low-Energy Amorphization of Ti1Sb2Te5 Phase Change Alloy Induced by TiTe2 Nano-Lamellae

    NASA Astrophysics Data System (ADS)

    Ding, Keyuan; Rao, Feng; Lv, Shilong; Cheng, Yan; Wu, Liangcai; Song, Zhitang

    2016-07-01

    Increasing SET operation speed and reducing RESET operation energy have always been the innovation direction of phase change memory (PCM) technology. Here, we demonstrate that ∼87% and ∼42% reductions of RESET operation energy can be achieved on PCM cell based on stoichiometric Ti1Sb2Te5 alloy, compared with Ge2Sb2Te5 and non-stoichiometric Ti0.4Sb2Te3 based PCM cells at the same size, respectively. The Ti1Sb2Te5 based PCM cell also shows one order of magnitude faster SET operation speed compared to that of the Ge2Sb2Te5 based one. The enhancements may be caused by substantially increased concentration of TiTe2 nano-lamellae in crystalline Ti1Sb2Te5 phase. The highly electrical conduction and lowly thermal dissipation of the TiTe2 nano-lamellae play a major role in enhancing the thermal efficiency of the amorphization, prompting the low-energy RESET operation. Our work may inspire the interests to more thorough understanding and tailoring of the nature of the (TiTe2)n(Sb2Te3)m pseudobinary system which will be advantageous to realize high-speed and low-energy PCM applications.

  9. Amorphization of Ti1- x Mn x

    NASA Astrophysics Data System (ADS)

    Chu, B.-L.; Chen, C.-C.; Perng, T.-P.

    1992-08-01

    Three amorphous Ti1- x Mn x alloy powders, with x = 0.4, 0.5, and 0.6, were prepared by mechanical alloying (MA) of the elemental powders in a high-energy ball mill. The amorphous powders were characterized by X-ray diffraction (XRD) and high-resolution transmission elec- tron microscopy (HRTEM). The crystallization temperatures for these alloys detected by dif- ferential scanning calorimetry (DSC) varied from 769 to 830 K. The calculated enthalpies of mixing in these amorphous phases are relatively small compared with those for other Ti-base binary alloys. The criteria for solid-state amorphization reaction are examined. It is suggested that the kinetics of nucleation and growth favors the formation of the amorphous phases and the supply of atoms for nucleation and growth is predominantly through the defective regions induced by MA.

  10. The effect of high energy concentration source irradiation on structure and properties of Fe-based bulk metallic glass

    NASA Astrophysics Data System (ADS)

    Pilarczyk, Wirginia

    2016-06-01

    Metallic glasses exhibit metastable structure and maintain this relatively stable amorphous state within certain temperature range. High intensity laser beam was used for the surface irradiation of Fe-Co-B-Si-Nb bulk metallic glasses. The variable parameter was laser beam pulse energy. For the analysis of structure and properties of bulk metallic glasses and their surface after laser remelting the X-ray analysis, microscopic observation and test of mechanical properties were carried out. Examination of the nanostructure of amorphous materials obtained by high pressure copper mold casting method and the irradiated with the use of TITAN 80-300 HRTEM was carried out. Nanohardness and reduced Young's modulus of particular amorphous and amorphous-crystalline material zone of the laser beam were examined with the use of Hysitron TI950 Triboindenter nanoindenter and with the use of Berkovich's indenter. The XRD and microscopic analysis showed that the test material is amorphous in its structure before irradiation. Microstructure observation with electron transmission microscopy gave information about alloy crystallization in the irradiated process. Identification of given crystal phases allows to determine the kind of crystal phases created in the first place and also further changes of phase composition of alloy. The main value of the nanohardness of the surface prepared by laser beam has the order of magnitude similar to bulk metallic glasses formed by casting process irrespective of the laser beam energy used. Research results analysis showed that the area between parent material and fusion zone is characterized by extraordinarily interesting structure which is and will be the subject of further analysis in the scope of bulk metallic glasses amorphous structure and high energy concentration source. The main goal of this work is the results' presentation of structure and chosen properties of the selected bulk metallic glasses after casting process and after irradiation

  11. Amorphous Ni-B alloy nanoparticle film on Ni foam: rapid alternately dipping deposition for efficient overall water splitting

    NASA Astrophysics Data System (ADS)

    Liang, Yanhui; Sun, Xuping; Asiri, Abdullah M.; He, Yuquan

    2016-03-01

    It is highly attractive, but still remains challenging, to develop noble metal-free bifunctional electrocatalysts efficient for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. In this letter, we describe the rapid electroless deposition of amorphous Ni-B nanoparticle film on Ni foam (Ni-B/Ni foam) by alternative dipping of Ni foam into Ni precursor and reducing solutions. This Ni-B/Ni foam acts as an efficient and durable 3D catalytic electrode for water splitting, affording 100 mA cm-2 at 360 mV overpotential for the OER and 20 mA cm-2 at 125 mV overpotential for the HER in 1.0 M KOH, and its two-electrode electrolyzer demands a cell voltage of 1.69 V to afford 15 mA cm-2 water-splitting current. Moreover, the catalyst loading can be easily tuned and this alternately dipping deposition technique works universally for other conductive substrates.

  12. Amorphous Ni-B alloy nanoparticle film on Ni foam: rapid alternately dipping deposition for efficient overall water splitting.

    PubMed

    Liang, Yanhui; Sun, Xuping; Asiri, Abdullah M; He, Yuquan

    2016-03-29

    It is highly attractive, but still remains challenging, to develop noble metal-free bifunctional electrocatalysts efficient for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. In this letter, we describe the rapid electroless deposition of amorphous Ni-B nanoparticle film on Ni foam (Ni-B/Ni foam) by alternative dipping of Ni foam into Ni precursor and reducing solutions. This Ni-B/Ni foam acts as an efficient and durable 3D catalytic electrode for water splitting, affording 100 mA cm(-2) at 360 mV overpotential for the OER and 20 mA cm(-2) at 125 mV overpotential for the HER in 1.0 M KOH, and its two-electrode electrolyzer demands a cell voltage of 1.69 V to afford 15 mA cm(-2) water-splitting current. Moreover, the catalyst loading can be easily tuned and this alternately dipping deposition technique works universally for other conductive substrates. PMID:26891459

  13. Fundamental studies of defect generation in amorphous silicon alloys grown by remote plasma-enhanced chemical-vapor deposition. Final subcontract report, 1 July 1989--31 December 1992

    SciTech Connect

    Lucovsky, G.

    1993-08-01

    This report describes research to reduce the intrinsic bonding defects in amorphous and microcrystalline Si alloys by controlling the bonding chemistry and the microstructure via the deposition process reactions. The specific approach was to use remote plasma-enhanced, chemical-vapor deposition (PECVD) and reactive magnetron sputtering to limit the multiplicity of deposition inaction pathways, and thereby gain increased control over the thin-film chemistry and microstrucre. The research included (1) the deposition of amorphous and microcrystalline Si alloy materials by the PECVD process and by reactive magnetron sputtering, and (2) the evaluation of the material properties of these films for potential applications in PV devices. The focus of the research was on pining a fundamental understanding of the relationships between deposition reaction pathways, the bonding of dopant and alloy atoms, and the electrical provides of importance for PV applications. This involved studying the factors that contribute to defect generation and to defect removal and/or neutralization. In addition to the experimental studies, the research also included theoretical and modeling studies aimed at understanding the relationships between local atomic arrangements of Si and alloy atoms, and the electrical, optical, vibrational, and defect properties.

  14. Phase selection and nanocrystallization in Cu-free soft magnetic FeSiNbB amorphous alloy upon rapid annealing

    NASA Astrophysics Data System (ADS)

    Morsdorf, L.; Pradeep, K. G.; Herzer, G.; Kovács, A.; Dunin-Borkowski, R. E.; Povstugar, I.; Konygin, G.; Choi, P.; Raabe, D.

    2016-03-01

    Nucleation of soft magnetic Fe3Si nanocrystals in Cu-free Fe74.5Si15.5Nb3B7 alloy, upon rapid (10 s) and conventional (30 min) annealing, was investigated using x-ray diffraction, transmission electron microscopy, Mössbauer spectroscopy, and atom probe tomography. By employing rapid annealing, preferential nucleation of Fe3Si nanocrystals was achieved, whereas otherwise there is simultaneous nucleation of both Fe3Si and undesired Fe-B compound phases. Analysis revealed that the enhanced Nb diffusivity, achieved during rapid annealing, facilitates homogeneous nucleation of Fe3Si nanocrystals while shifting the secondary Fe-B crystallization to higher temperatures resulting in pure soft magnetic nanocrystallization with very low coercivities of ˜10 A/m.

  15. Electrum, the Gold-Silver Alloy, from the Bulk Scale to the Nanoscale: Synthesis, Properties, and Segregation Rules.

    PubMed

    Guisbiers, Grégory; Mendoza-Cruz, Rubén; Bazán-Díaz, Lourdes; Velázquez-Salazar, J Jesús; Mendoza-Perez, Rafael; Robledo-Torres, José Antonio; Rodriguez-Lopez, José-Luis; Montejano-Carrizales, Juan Martín; Whetten, Robert L; José-Yacamán, Miguel

    2016-01-26

    The alloy Au-Ag system is an important noble bimetallic phase, both historically (as "Electrum") and now especially in nanotechnology, as it is applied in catalysis and nanomedicine. To comprehend the structural characteristics and the thermodynamic stability of this alloy, a knowledge of its phase diagram is required that considers explicitly its size and shape (morphology) dependence. However, as the experimental determination remains quite challenging at the nanoscale, theoretical guidance can provide significant advantages. Using a regular solution model within a nanothermodynamic approach to evaluate the size effect on all the parameters (melting temperature, melting enthalpy, and interaction parameters in both phases), the nanophase diagram is predicted. Besides an overall shift downward, there is a "tilting" effect on the solidus-liquidus curves for some particular shapes exposing the (100) and (110) facets (cube, rhombic dodecahedron, and cuboctahedron). The segregation calculation reveals the preferential presence of silver at the surface for all the polyhedral shapes considered, in excellent agreement with the latest transmission electron microscopy observations and energy dispersive spectroscopy analysis. By reviewing the nature of the surface segregated element of different bimetallic nanoalloys, two surface segregation rules, based on the melting temperatures and surface energies, are deduced. Finally, the optical properties of Au-Ag nanoparticles, calculated within the discrete dipole approximation, show the control that can be achieved in the tuning of the local surface plasmon resonance, depending of the alloy content, the chemical ordering, the morphology, the size of the nanoparticle, and the nature of the surrounding environment. PMID:26605557

  16. Observation of giant exchange bias in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy

    SciTech Connect

    Sharma, Jyoti; Suresh, K. G.

    2015-02-16

    We report a giant exchange bias (EB) field of 3520 Oe in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy. The low temperature magnetic state of the martensite phase has been studied by DC magnetization and AC susceptibility measurements. Frequency dependence of spin freezing temperature (T{sub f}) on critical slowing down relation and observation of memory effect in zero field cooling mode confirms the super spin glass (SSG) phase at low temperatures. Large EB is attributed to the strong exchange coupling between the SSG clusters formed by small regions of ferromagnetic order embedded in an antiferromagnetic (AFM) matrix. The temperature and cooling field dependence of EB have been studied and related to the change in unidirectional anisotropy at SSG/AFM interface. The training effect also corroborates with the presence of frozen (SSG) moments at the interface and their role in EB.

  17. Electrum, the Gold–Silver Alloy, from the Bulk Scale to the Nanoscale: Synthesis, Properties, and Segregation Rules

    PubMed Central

    2015-01-01

    The alloy Au–Ag system is an important noble bimetallic phase, both historically (as “Electrum”) and now especially in nanotechnology, as it is applied in catalysis and nanomedicine. To comprehend the structural characteristics and the thermodynamic stability of this alloy, a knowledge of its phase diagram is required that considers explicitly its size and shape (morphology) dependence. However, as the experimental determination remains quite challenging at the nanoscale, theoretical guidance can provide significant advantages. Using a regular solution model within a nanothermodynamic approach to evaluate the size effect on all the parameters (melting temperature, melting enthalpy, and interaction parameters in both phases), the nanophase diagram is predicted. Besides an overall shift downward, there is a “tilting” effect on the solidus–liquidus curves for some particular shapes exposing the (100) and (110) facets (cube, rhombic dodecahedron, and cuboctahedron). The segregation calculation reveals the preferential presence of silver at the surface for all the polyhedral shapes considered, in excellent agreement with the latest transmission electron microscopy observations and energy dispersive spectroscopy analysis. By reviewing the nature of the surface segregated element of different bimetallic nanoalloys, two surface segregation rules, based on the melting temperatures and surface energies, are deduced. Finally, the optical properties of Au–Ag nanoparticles, calculated within the discrete dipole approximation, show the control that can be achieved in the tuning of the local surface plasmon resonance, depending of the alloy content, the chemical ordering, the morphology, the size of the nanoparticle, and the nature of the surrounding environment. PMID:26605557

  18. Effect of Oxygen Contamination on the Electronic Properties of Hot-Wire CVD Amorphous Silicon Germanium Alloys

    SciTech Connect

    Datta, S.; Cohen, J. D.; Golledge, S. L.; Xu, Y.; Mahan, A. H.; Doyle, J. R.; Branz, H. M.

    2006-01-01

    A series of four a Si,Ge:H alloy samples with Ge fractions near 30 at.% were deposited by hot-wire CVD (HWCVD) using a Ta filament maintained at 1800 C. During film growth, the level of oxygen contamination was varied from less than 10{sup 19} cm{sup -3} to roughly 5 x 10{sup 20} cm{sup -3} using a controlled air-leak. The electronic properties of these films were then characterized using transient photocapacitance (TPC) and transient photocurrent (TPI) spectroscopy, as well as the drive-level capacitance profiling (DLCP) techniques. We observed an unexpected systematic improvement of the electronic properties of these HWCVD a Si,Ge:H with increasing oxygen impurity level, which was reflected by a decrease in the deduced Urbach energies. Comparing these with films co-deposited on stainless-steel versus p+ c-Si substrates, we found significantly better electronic properties in the latter case. Comparisons of the TPC and TPI spectra indicated a very high level of hole collection, consistent with these narrow bandtail distributions.

  19. Characterisation of radiation damage in W and W-based alloys from 2MeV self-ion near-bulk implantations

    SciTech Connect

    Yi, Xiaoou; Jenkins, Michael L.; Hattar, Khalid; Edmondson, Philip D.; Roberts, Steve G.

    2015-04-21

    The displacement damage induced in bulk W and W-5 wt.% Re and W-5 wt.% Ta alloys by 2 MeV W+ irradiation to doses 3.3×1017 - 2.5×1019 W+/m2 at temperatures ranging from 300 to750°C has been characterized by transmission electron microscopy. An automated sizing and counting approach based on Image J has been proposed and performed for all irradiation data. In all cases the damage comprised dislocation loops, mostly of interstitial type, with Burgers vectors b = ½<111> (> 60%) and b = <100>. The diameters of loops did not exceed 20 nm, with the majority being ≤ 6 nm. The loop number density varied between 1022 and 1023 loops/m3 . With increasing irradiation temperature, the loop size distributions shifted towards larger sizes, and there was a substantial decrease in loop number densities. The damage microstructure was less sensitive to dose than to temperature. Under the same irradiation conditions, loop number densities in the alloys were higher than in pure W but loops were smaller. In grains with normals close to z = <001>, loop strings developed in W at temperatures ≥ 500°C and doses ≥ 1.2 dpa, but such strings were not observed in the W-Re or W-Ta alloys. However, in other grain orientations complex structures appeared in all materials and dense dislocation networks formed at higher doses.

  20. Wetting and reaction characteristics of crystalline and amorphous SiO2 derived rice-husk ash and SiO2/SiC substrates with Al-Si-Mg alloys

    NASA Astrophysics Data System (ADS)

    Bahrami, A.; Pech-Canul, M. I.; Gutiérrez, C. A.; Soltani, N.

    2015-12-01

    A study of the wetting behavior of three substrate types (SiC, SiO2-derived RHA and SiC/SiO2-derived RHA) by two Al-Si-Mg alloys using the sessile drop method has been conducted, using amorphous and crystalline SiO2 in the experiment. Mostly, there is a transition from non-wetting to wetting contact angles, being the lowest θ values achieved with the alloy of high Mg content in contact with amorphous SiO2. The observed wetting behavior is attributed to the deposited Mg on the substrates. A strong diffusion of Si from the SiC/Amorphous RHA substrate into the metal drop explains the free Si segregated at the drop/substrate interface and drop surface. Although incorporation of both SiO2-derived RHA structures into the SiC powder compact substrates increases the contact angles in comparison with the SiC substrate alone, the still observed acute contact angles in RHA/SiC substrates make them promising for fabrication of composites with high volume fraction of reinforcement by the pressureless infiltration technique. The observed wetting characteristics, with decrease in surface tension and contact angles is explained by surface related phenomena. Based on contact angle changes, drop dimensions and surface tension values, as well as on the interfacial elemental mapping, and XRD analysis of substrates, some wetting and reaction pathways are proposed and discussed.

  1. In-situ study of crystallization kinetics in ternary bulk metallic glass alloys with different glass forming abilities

    SciTech Connect

    Lan, Si; Wei, Xiaoya; Wu, Xuelian; Wang, Xun-Li; Zhou, Jie; Lu, Zhaoping; Feygenson, Mikhail; Neuefeind, Jörg

    2014-11-17

    In-situ transmission electron microcopy and time-resolved neutron diffraction were used to study crystallization kinetics of two ternary bulk metallic glasses during isothermal annealing in the supercooled liquid region. It is found that the crystallization of Zr{sub 56}Cu{sub 36}Al{sub 8}, an average glass former, follows continuous nucleation and growth, while that of Zr{sub 46}Cu{sub 46}Al{sub 8}, a better glass former, is characterized by site-saturated nucleation, followed by slow growth. Possible mechanisms for the observed differences and the relationship to the glass forming ability are discussed.

  2. In-situ study of crystallization kinetics in ternary bulk metallic glass alloys with different glass forming abilities

    DOE PAGESBeta

    Lan, Si; Wei, Xiaoya; Zhou, Jie; Lu, Zhaoping; Wu, Xuelian; Feygenson, Mikhail; Neuefeind, Jorg C.; Wang, Xun-Li

    2014-11-18

    In-situ transmission electron microcopy and time-resolved neutron diffraction were used to study crystallization kinetics of two ternary bulk metallic glasses during isothermal annealing in the supercooled liquid region. It is found that the crystallization of Zr56Cu36Al8, an average glass former, follows continuous nucleation and growth, while that of Zr46Cu46Al8, a better glass former, is characterized by site-saturated nucleation, followed by slow growth. Possible mechanisms for the observed differences and the relationship to the glass forming ability are discussed.

  3. Study on glass-forming ability and hydrogen storage properties of amorphous Mg{sub 60}Ni{sub 30}La{sub 10−x}Co{sub x} (x = 0, 4) alloys

    SciTech Connect

    Lv, Peng; Wang, Zhong-min Zhang, Huai-gang; Balogun, Muhammad-Sadeeq; Ji, Zi-jun; Deng, Jian-qiu; Zhou, Huai-ying

    2013-12-15

    Mg{sub 60}Ni{sub 30}La{sub 10−x}Co{sub x} (x = 0, 4) amorphous alloys were prepared by rapid solidification, using a melt-spinning technique. X-ray diffraction and differential scanning calorimetry analysis were employed to measure their microstructure, thermal stability and glass-forming ability, and hydrogen storage properties were studied by means of PCTPro2000. Based on differential scanning calorimetry results, their glass-forming ability and thermal stability were investigated by Kissinger method, Lasocka curves and atomic cluster model, respectively. The results indicate that glass-forming ability, thermal properties and hydrogen storage properties in the Mg-rich corner of Mg–Ni–La–Co system alloys were enhanced by Co substitution for La. It can be found that the smaller activation energy (ΔΕ) and frequency factor (υ{sub 0}), the bigger value of B (glass transition point in Lasocka curves), and higher glass-forming ability of Mg–Ni–La–Co alloys would be followed. In addition, atomic structure parameter (λ), deduced from atomic cluster model is valuable in the design of Mg–Ni–La–Co system alloys with good glass-forming ability. With an increase of Co content from 0 to 4, the hydrogen desorption capacity within 4000 s rises from 2.25 to 2.85 wt.% at 573 K. - Highlights: • Amorphous Mg{sub 60}Ni{sub 30}La{sub 10−x}Co{sub x} (x = 0 and 4) alloys were produced by melt spinning. • The GFA and hydrogen storage properties were enhanced by Co substitution for La. • With an increase of Co content, the hydrogen desorption capacity rises at 573 K.

  4. Enhanced mechanical properties and in vitro corrosion behavior of amorphous and devitrified Ti40Zr10Cu38Pd12 metallic glass.

    PubMed

    Fornell, J; Van Steenberge, N; Varea, A; Rossinyol, E; Pellicer, E; Suriñach, S; Baró, M D; Sort, J

    2011-11-01

    The effects of annealing treatments on the microstructure, elastic/mechanical properties, wear resistance and corrosion behavior of rod-shaped Ti40Zr10Cu38Pd12 bulk glassy alloys, synthesized by copper mold casting, are investigated. Formation of ultrafine crystals embedded in an amorphous matrix is observed for intermediate annealing temperatures, whereas a fully crystalline microstructure develops after heating to sufficiently high temperatures. The glassy alloy exhibits large hardness, relatively low Young's modulus, good wear resistance and excellent corrosion behavior. Nanoindentation measurements reveal that the sample annealed in the supercooled liquid region exhibits a hardness value of 9.4 GPa, which is 20% larger than in the completely amorphous state and much larger than the hardness of commercial Ti-6Al-4V alloy. The Young's modulus of the as-cast alloy (around 100 GPa, as determined from acoustic measurements) increases only slightly during partial devitrification. Finally, the anticorrosion performance of the Ti40Zr10Cu38Pd12 alloy in Hank's solution has been shown to ameliorate as crystallization proceeds and is roughly as good as in the commercial Ti-6Al-4V alloy. The outstanding mechanical and corrosion properties of the Ti40Zr10Cu38Pd12 alloy, both in amorphous and crystalline states, are appealing for its use in biomedical applications. PMID:22098871

  5. Soft magnetic composites manufactured by warm co-extrusion of bulk metallic glass and steel powders

    SciTech Connect

    Johnson, Francis; Raber, Thomas R.; Zabala, Robert J.; Buresh, Steve J.; Tanico, Brian

    2013-05-07

    Soft magnetic composites of Fe-based bulk metallic glass and low-alloy steel have been manufactured by warm co-extrusion of precursor powders at temperatures within the supercooled liquid region of the glass. Composites were manufactured with amorphous volume fractions of 75%, 67%, and 100%. Full consolidation of the constituent powders was observed with the bulk metallic glass remaining substantially amorphous. The composite electrical resistivity was observed to be anisotropic with a resistivity of 79 {mu}{Omega} cm measured transverse to the extrusion axis in a sample with 75% amorphous volume fraction. A 0-3 connectivity pattern with the low-resistivity steel phase embedded in a 3-dimensionally connected high-resistivity bulk metallic glass phase was observed with scanning electron microscopy. This confirms that the flow characteristics of the bulk metallic glass and the steel powders were comparable during extrusion at these temperatures. The saturation magnetization of 1.3 T was consistent with the volume weighted average of the saturation magnetization of the two phases. A relatively high quasistatic coercivity of 8 Oe was measured and is likely due to slight crystallization of the bulk metallic glass as well as domain wall pinning at prior particle boundaries. Careful control of the thermal environment during the extrusion process is required to minimize glass crystallization and achieve the desired balance of magnetic and electrical properties.

  6. Soft magnetic composites manufactured by warm co-extrusion of bulk metallic glass and steel powders

    NASA Astrophysics Data System (ADS)

    Johnson, Francis; Raber, Thomas R.; Zabala, Robert J.; Buresh, Steve J.; Tanico, Brian

    2013-05-01

    Soft magnetic composites of Fe-based bulk metallic glass and low-alloy steel have been manufactured by warm co-extrusion of precursor powders at temperatures within the supercooled liquid region of the glass. Composites were manufactured with amorphous volume fractions of 75%, 67%, and 100%. Full consolidation of the constituent powders was observed with the bulk metallic glass remaining substantially amorphous. The composite electrical resistivity was observed to be anisotropic with a resistivity of 79 μΩ cm measured transverse to the extrusion axis in a sample with 75% amorphous volume fraction. A 0-3 connectivity pattern with the low-resistivity steel phase embedded in a 3-dimensionally connected high-resistivity bulk metallic glass phase was observed with scanning electron microscopy. This confirms that the flow characteristics of the bulk metallic glass and the steel powders were comparable during extrusion at these temperatures. The saturation magnetization of 1.3 T was consistent with the volume weighted average of the saturation magnetization of the two phases. A relatively high quasistatic coercivity of 8 Oe was measured and is likely due to slight crystallization of the bulk metallic glass as well as domain wall pinning at prior particle boundaries. Careful control of the thermal environment during the extrusion process is required to minimize glass crystallization and achieve the desired balance of magnetic and electrical properties.

  7. In-situ ductile metal/bulk metallic glass matrix composites formed by chemical partitioning

    DOEpatents

    Kim, Choong Paul; Hays, Charles C.; Johnson, William L.

    2004-03-23

    A composite metal object comprises ductile crystalline metal particles in an amorphous metal matrix. An alloy is heated above its liquidus temperature. Upon cooling from the high temperature melt, the alloy chemically partitions, forming dendrites in the melt. Upon cooling the remaining liquid below the glass transition temperature it freezes to the amorphous state, producing a two-phase microstructure containing crystalline particles in an amorphous metal matrix. The ductile metal particles have a size in the range of from 0.1 to 15 micrometers and spacing in the range of from 0.1 to 20 micrometers. Preferably, the particle size is in the range of from 0.5 to 8 micrometers and spacing is in the range of from 1 to 10 micrometers. The volume proportion of particles is in the range of from 5 to 50% and preferably 15 to 35%. Differential cooling can produce oriented dendrites of ductile metal phase in an amorphous matrix. Examples are given in the Zr--Ti--Cu--Ni--Be alloy bulk glass forming system with added niobium.

  8. In-situ ductile metal/bulk metallic glass matrix composites formed by chemical partitioning

    DOEpatents

    Kim, Choong Paul; Hays, Charles C.; Johnson, William L.

    2007-07-17

    A composite metal object comprises ductile crystalline metal particles in an amorphous metal matrix. An alloy is heated above its liquidus temperature. Upon cooling from the high temperature melt, the alloy chemically partitions, forming dendrites in the melt. Upon cooling the remaining liquid below the glass transition temperature it freezes to the amorphous state, producing a two-phase microstructure containing crystalline particles in an amorphous metal matrix. The ductile metal particles have a size in the range of from 0.1 to 15 micrometers and spacing in the range of from 0.1 to 20 micrometers. Preferably, the particle size is in the range of from 0.5 to 8 micrometers and spacing is in the range of from 1 to 10 micrometers. The volume proportion of particles is in the range of from 5 to 50% and preferably 15 to 35%. Differential cooling can produce oriented dendrites of ductile metal phase in an amorphous matrix. Examples are given in the Zr--Ti--Cu--Ni--Be alloy bulk glass forming system with added niobium.

  9. In-situ study of crystallization kinetics in ternary bulk metallic glass alloys with different glass forming abilities

    SciTech Connect

    Lan, Si; Wei, Xiaoya; Zhou, Jie; Lu, Zhaoping; Wu, Xuelian; Feygenson, Mikhail; Neuefeind, Jorg C.; Wang, Xun-Li

    2014-11-18

    In-situ transmission electron microcopy and time-resolved neutron diffraction were used to study crystallization kinetics of two ternary bulk metallic glasses during isothermal annealing in the supercooled liquid region. It is found that the crystallization of Zr56Cu36Al8, an average glass former, follows continuous nucleation and growth, while that of Zr46Cu46Al8, a better glass former, is characterized by site-saturated nucleation, followed by slow growth. Possible mechanisms for the observed differences and the relationship to the glass forming ability are discussed.

  10. Preparing Zr65Al7.5Ni10Cu17.5 bulk metallic glasses based on point-line-face-body theory.

    PubMed

    Chang, Zexin; Wang, Wenxian; Ge, Yaqiong

    2016-05-10

    Zr65Al7.5Ni10Cu17.5 bulk metallic glasses (BMGs) were prepared based on point-line-face-body (PLFB) theory with the pre-laid powder method from laser processing. The thickness of the prepared bulk amorphous alloy was about 1.6 mm. The microstructure evolution, phase composition, chemical component distribution, and corrosion behavior of the bulk amorphous alloy were investigated. The results showed that the amorphization ratio increased with the increase of the thickness of Zr65Al7.5Ni10Cu17.5 BMGs; furthermore, the volume fraction of the amorphous phase in the bottom layer (first layer), the middle layer (fourth layer), and the surface layer (seventh layer) was approximately 52%, 66%, and 74%, respectively. Due to different thermal cycles during the PLFB-forming process, the amorphous and crystallization coexisted in the deposited layers. For the corrosion property, the experiments of potentiodynamic polarization plots, Nyquist plots, and the equivalent circuits were performed in 3.5 wt. % sodium chloride solution. The seventh layer exhibits better corrosion-resistance performance than the other layers, which can be attributed to a higher amorphization ratio in the surface layer. PMID:27168294

  11. Effects of configurational changes on electrical resistivity during glass-liquid transition of two bulk metal-alloy glasses.

    PubMed

    Aji, D P B; Johari, G P

    2014-12-14

    Consequences of increase in structural fluctuations on heating Pd40Ni10Cu30P20 and Zr46.75Ti8.25Cu7.5Ni10Be27.5 through their glass to liquid transition range were investigated by measuring the electrical resistivity, ρ, an electron scattering property. The temperature coefficient of resistivity (TCR = (1/ρ) dρ/dT) of the liquid and glassy states is negative. The plots of their ρ against T in the Tg (glass to liquid transition) range show a gradual change in the slope similar to the change observed generally for the plots of the density, elastic modulus, and refractive index. As fluctuations in the melt structure involve fewer configurations on cooling, ρ increases. In the energy landscape description, the melt's structure explores fewer minima with decrease in T, vibrational frequencies increase, and electron scattering and ρ increase. Plots of (-dρ/dT) against T resemble the plot of the specific heat of other glasses and show a sub-Tg feature and a rapid rise at T near Tg. Analysis shows that the magnitude of negative TCR is dominated by change in the phonon characteristics, and configurational fluctuations make it more negative. The TCR of the liquid and glassy states seems qualitatively consistent with the variation in the structure factor in Ziman's model for pure liquid metals as extended by Nagel to metal alloys and used to explain the negative TCR of a two-component metal glass. PMID:25494761

  12. Photoemission study of ternary to penternary Fe-based metallic glasses: Chemical analysis of surface and bulk

    NASA Astrophysics Data System (ADS)

    Büttner, M.; Wang, H.-J.; Dongare, A. M.; Shiflet, G. J.; Reinke, P.; Oelhafen, P.; Mun, B. S.; Gu, X. J.; Poon, S. J.

    2007-08-01

    Bulk metallic glasses consisting of Fe, Mo, Cr, C, B, and Er have been investigated by x-ray photoelectron spectroscopy, aimed to elucidate the local atomic structure of the amorphous phase. In order to examine the electronic properties of this class of material, photon energy dependent measurements in combination with argon-ion irradiation were employed to identify and separate surface and bulk contributions to the spectra. The core levels suggest the presence of a carbon-rich surface layer with oxidized boron and metals, and metal carbides and borides in the bulk. Exposure to molecular oxygen and annealing experiments probe the chemical reactivity of the material. Formation of boron oxides at comparably low temperatures (300°C) might have consequences for the stability of the amorphous phase. We observe variations in binding energy of the Fe 3p core level with respect to the alloy composition, which indicate changes in the chemical state of iron.

  13. Effects of configurational changes on electrical resistivity during glass-liquid transition of two bulk metal-alloy glasses

    SciTech Connect

    Aji, D. P. B.; Johari, G. P.

    2014-12-14

    Consequences of increase in structural fluctuations on heating Pd{sub 40}Ni{sub 10}Cu{sub 30}P{sub 20} and Zr{sub 46.75}Ti{sub 8.25}Cu{sub 7.5}Ni{sub 10}Be{sub 27.5} through their glass to liquid transition range were investigated by measuring the electrical resistivity, ρ, an electron scattering property. The temperature coefficient of resistivity (TCR = (1/ρ) dρ/dT) of the liquid and glassy states is negative. The plots of their ρ against T in the T{sub g} (glass to liquid transition) range show a gradual change in the slope similar to the change observed generally for the plots of the density, elastic modulus, and refractive index. As fluctuations in the melt structure involve fewer configurations on cooling, ρ increases. In the energy landscape description, the melt's structure explores fewer minima with decrease in T, vibrational frequencies increase, and electron scattering and ρ increase. Plots of (−dρ/dT) against T resemble the plot of the specific heat of other glasses and show a sub-T{sub g} feature and a rapid rise at T near T{sub g}. Analysis shows that the magnitude of negative TCR is dominated by change in the phonon characteristics, and configurational fluctuations make it more negative. The TCR of the liquid and glassy states seems qualitatively consistent with the variation in the structure factor in Ziman's model for pure liquid metals as extended by Nagel to metal alloys and used to explain the negative TCR of a two-component metal glass.

  14. Corrosive electrochemical behavior of amorphous and nanocrystalline Fe-P-Si-Mn-V alloys in a moist SO2-contaminated atmosphere

    NASA Astrophysics Data System (ADS)

    Vavilova, V. V.; Korneev, V. P.; Anosova, M. O.

    2016-01-01

    Nanocrystalline soft magnetic Finemet alloys, which are currently used in power electrical engineering and electrical equipment, are alloyed with expensive and scarce metals (Nb, Cu). We searched for low-cost soft magnetic alloys that are comparable with Finemets in the corrosion resistance.

  15. Amorphous metallic foam: Synthesis and mechanical properties

    NASA Astrophysics Data System (ADS)

    Veazey, Chris

    2007-12-01

    Bulk metallic glass alloys were processed into foam by several synthesis routes. These methods utilize the thermodynamic stability and thermoplastic formability of the supercooled liquid state to produce low-density homogeneous foams. The cellular structure is shown to evolve by growth of randomly distributed spherical bubbles towards polyhedral-like cells separated by microscopic intracellular membranes exhibiting random orientations and aspect ratios. The ability of amorphous metals to develop such random cellular morphologies is attributed primarily to the high ductility exhibited by their softened state, which enables large superplastic membrane elongations during foaming. Upon loading, moderate porosity foams are known to deform plastically by recurring non-linear yielding transitions followed by non-catastrophic collapse events. The ability of these foams to yield non-catastrophically is a result of the plastic deformability of amorphous metals in sub-millimeter dimensions. Nonlinear yielding is found to be accommodated by clusters involving 4--6 cells, which yield by intracellular membrane buckling and ultimately collapse plastically to produce a localized plastic collapse band. By comparison, high-porosity foams deform plastically by multiple recurring non-catastrophic collapse events without undergoing macroscopic failure. The numerous minor collapse events are associated with localized ligament collapse, and the few major collapse events are associated with the cooperative collapse of several adjacent ligaments and the formation of a collapse band. On average, the serrated flow responses between major events appear to be self-similar and resemble the recurring nonlinear yielding responses exhibited by moderate porosity foams.

  16. Spectroscopic ellipsometry-based study of optical properties of amorphous and crystalline ZnSnO alloys and Zn2SnO4 thin films grown using sputtering deposition: Dielectric function and subgap states

    NASA Astrophysics Data System (ADS)

    Ko, Kun Hee; So, Hyeon Seob; Jung, Dae Ho; Park, Jun Woo; Lee, Hosun

    2016-04-01

    We investigated the optical properties of amorphous and crystalline zinc tin oxide (ZTO) thin films grown on SiO2/Si substrates with varying compositions via a co-sputtering deposition method at room temperature. The co-sputtering targets consist of SnO2 and ZnO. By varying the relative power ratio of the two targets, we demonstrate the ability to control the Sn and Zn composition of the resulting ZTO thin films. The ratio of [Sn]/([Sn] + [Zn]) atomic compositions was estimated at 11%, 29%, 42%, 54%, and 60%. Using a 600 °C annealing process, the as-grown amorphous ZTO films were transformed into crystalline ZTO films. The dielectric functions were obtained based on the measured ellipsometric angles, ψ and Δ. We determined the dielectric functions, absorption coefficients, and optical gap energies of ZTO thin films with varying compositions. The dielectric functions, absorption coefficients, and optical gap energies of amorphous and crystalline Zn2SnO4 thin films were obtained at 29 at. % of Sn. Subgap states at 1.6 eV (A) and 2.8 eV (B) of ZnSnO alloys and Zn2SnO4 films were found in the imaginary part of the dielectric function spectra. The subgap state intensities were reduced via a nitrogen gas annealing. Possible origins of the observed subgap states will be discussed.

  17. Amorphous Computing

    NASA Astrophysics Data System (ADS)

    Sussman, Gerald

    2002-03-01

    Digital computers have always been constructed to behave as precise arrangements of reliable parts, and our techniques for organizing computations depend upon this precision and reliability. Two emerging technologies, however, are begnning to undercut these assumptions about constructing and programming computers. These technologies -- microfabrication and bioengineering -- will make it possible to assemble systems composed of myriad information- processing units at almost no cost, provided: 1) that not all the units need to work correctly; and 2) that there is no need to manufacture precise geometrical arrangements or interconnection patterns among them. Microelectronic mechanical components are becoming so inexpensive to manufacture that we can anticipate combining logic circuits, microsensors, actuators, and communications devices integrated on the same chip to produce particles that could be mixed with bulk materials, such as paints, gels, and concrete. Imagine coating bridges or buildings with smart paint that can sense and report on traffic and wind loads and monitor structural integrity of the bridge. A smart paint coating on a wall could sense vibrations, monitor the premises for intruders, or cancel noise. Even more striking, there has been such astounding progress in understanding the biochemical mechanisms in individual cells, that it appears we'll be able to harness these mechanisms to construct digital- logic circuits. Imagine a discipline of cellular engineering that could tailor-make biological cells that function as sensors and actuators, as programmable delivery vehicles for pharmaceuticals, as chemical factories for the assembly of nanoscale structures. Fabricating such systems seem to be within our reach, even if it is not yet within our grasp Fabrication, however, is only part of the story. We can envision producing vast quantities of individual computing elements, whether microfabricated particles, engineered cells, or macromolecular computing

  18. First-principles study on magnetism and half-metallicity in bulk and various (001) surfaces of Heusler alloy Zr2VSn with Hg2CuTi-type structure

    NASA Astrophysics Data System (ADS)

    Deng, Zun-Yi; Zhang, Jian-Min

    2016-07-01

    Structural, electronic and magnetic properties in the bulk and five different (001) surfaces (ZrV-, ZrSn-, VV-, ZrZr- and SnSn-terminations) of Zr2 VSn Heusler alloy with Hg2 CuTi -type structure are studied by using first-principles calculations based on density-functional theory. The bulk Zr2 VSn Heusler alloy is ferrimagnetic half-metallicity with equilibrium lattice constant 6.815 Å and total magnetic moment -1.000 μB / f.u . , following the Slater-Pauling rule μt =Zt - 18 . The atoms on different surface layers exhibit different displacements, electronic and magnetic properties. All five (001) surfaces lose the half-metallicity and are not usable in spintronics devices.

  19. Containerless processing of hypermonotectic and glass forming alloys using the Marshall Space Flight Center 100 meter drop tube facility

    NASA Technical Reports Server (NTRS)

    Andrews, J. B.

    1986-01-01

    Two separate projects were carried out to study alloys whose solidification structures can be strongly influenced by the presence of a container during melting and solidifications. One project involved containerless solidification of hypermonotectic Au35Rh65 alloys. This alloy exhibits liquid immiscibility over a temperature range. It has been suggested that containerless melting might be one solution to the problem of sedimentation in the dispersions of immiscible liquid phases. However, surface tension driven flows could also lead to accumulation of the minority liquid phase at the external surface of a containerlessly melted alloy. The research underway is a first step in determining the influence of containerless, microgravity processing on immiscible alloys. Nickel-niobium alloys were studied using the drop tube facility. One alloy in this system, a Ni60Nb40 alloy, is a good candidate for the formation of a bulk metallic glass. Amorphous alloys of this composition were produced using thin film and mechanical alloying techniques. However, theory indicates that if heterogeneous nucleation can be avoided, it should be possible to produce an amorphous structure in this system using a moderate cooling rate from the melt. The containerless melting and solidification capabilities of the drop tube faciltiy provide ideal conditions for a study of this type. To date, several Ni60Nb40 samples have been levitated, melted and cooled during 4.6 seconds of free fall in the 100 meter drop tube. Structures obtained are discussed.

  20. Embrittlement and conditions of the optimization of magnetic properties in the amorphous alloy Co69Fe3.7Cr3.8Si12.5B11 in the absence of a viscous-brittle transition

    NASA Astrophysics Data System (ADS)

    Kekalo, I. B.; Mogil'nikov, P. S.

    2016-07-01

    The influence of the holding time upon annealing on the temperature of the viscous-brittle transition (temperature of embrittlement) T f in a cobalt-based amorphous alloy of the composition Co69Fe3.7Cr3.8Si12.5B11 with a very low saturation magnetostriction λs (<10-7) has been studied. It has been established that the dependence of the embrittlement temperature T f on the of time of holding t a can be described by an Arrhenius equation and that the embrittlement at the annealing temperatures above and below 300°C is described by different kinetic parameters. In the alloy under study, irrespective of the holding time, embrittlement occurs in a very narrow range of annealing temperatures, which does not exceed 5 K. Based on the experimental data on the evolution of the hysteresis magnetic properties upon the isochronous annealings and upon the isothermal holding, the regime of heat treatment that ensures a very high (about 50000) magnitude of the permeability µ5 ( H = 5 mOe, f = 1 kHz) without the transition of the alloy into a brittle state has been determined.

  1. Thermoplastic Micro-Forming of Bulk Metallic Glasses: A Review

    NASA Astrophysics Data System (ADS)

    Li, Ning; Chen, Wen; Liu, Lin

    2016-04-01

    Bulk metallic glasses are a fascinating class of metallic alloys with an isotropic amorphous structure that is rapidly quenched from liquid melts. The absence of a crystalline micro-structure endows them with a portfolio of properties such as high strength, high elasticity, and excellent corrosion resistance. Whereas the limited plasticity and hence poor workability at ambient temperature impede the structural application of bulk metallic glasses, the unique superplasticity within the supercooled liquid region opens an alternative window of so-called thermoplastic forming, which allows precise and versatile net-shaping of complex geometries on length scales ranging from nanometers to centimeters that were previously unachievable with conventional crystalline metal processing. Thermoplastic forming not only breaks through the bottleneck of the manufacture of bulk metallic glasses at ambient temperature but also offers an alluring prospect in micro-engineering applications. This paper comprehensively reviews some pivotal aspects of bulk metallic glasses during thermoplastic micro-forming, including an in-depth understanding of the crystallization kinetics of bulk metallic glasses and the thermoplastic processing time window, the thermoplastic forming map that clarifies the relationship between the flow characteristics and the formability, the interfacial friction in micro-forming and novel forming methods to improve the formability, and the potential applications of the hot-embossed micro-patterns/components.

  2. Structural Properties of Mismatched Alloys

    NASA Astrophysics Data System (ADS)

    Mousseau, Normand

    The problem of understanding the local structure of disordered alloys has been around for a long time. In this thesis, I look more specifically at the effect of size-mismatch disorder in binary alloys under many forms: metallic and semiconductor alloys, bulk and surfaces, two and three dimensional systems. I have studied the limitations of a central-force model (CFM) and an embedded-atom potential (EAM) in describing the local structure of binary metallic alloys composed of Ag, Au, Cu, Ni, Pd, or Pt. Although an analytical model developed using the CFM explains qualitatively well the experimental and numerical results, in many cases, it is important to add electronic density effects through a more sophisticated potential like EAM in order to agree quantitatively with experiment. I have also looked at amorphous and crystalline silicon-germanium alloys. It turns out that the effect of size-mismatch is the same on a crystalline and an amorphous lattice. In the latter case, it can be seen as a perturbation of the much larger disorder due to the amorphisation process. However, the analytical predictions differ, for both the crystalline and amorphous alloys, from the experimental results. If one is to believe the data, there is only one possible explanation for this inconsistency: large amounts of hydrogen are present in the samples used for the measurements. Since the data analysis of EXAFS results is not always straightforward, I have proposed some experiments that could shed light on this problem. One of these experiments would be to look at the (111) surface of a Si-Ge alloy with a scanning tunneling microscope. I also present in this thesis the theoretical predictions for the height distribution at the surface as well as some more general structural information about the relaxation in the network as one goes away from the surface. Finally, I have studied the effect of size -mismatch in a purely two dimensional lattice, looking for mismatch-driven phase transitions

  3. Femtosecond laser-induced phase transformations in amorphous Cu{sub 77}Ni{sub 6}Sn{sub 10}P{sub 7} alloy

    SciTech Connect

    Zhang, Y.; Zou, G.; Wu, A.; Bai, H.; Liu, L.; Chen, N.; Zhou, Y.

    2015-01-14

    In this study, the femtosecond laser-induced crystallization of CuNiSnP amorphous ribbons was investigated by utilizing an amplified Ti:sapphire laser system. X-ray diffraction and scanning electronic microscope were applied to examine the phase and morphology changes of the amorphous ribbons. Micromachining without crystallization, surface patterning, and selective crystallization were successfully achieved by changing laser parameters. Obvious crystallization occurred under the condition that the laser fluence was smaller than the ablation threshold, indicating that the structural evolution of the material depends strongly on the laser parameters. Back cooling method was used to inhibit heat accumulation; a reversible transformation between the disordered amorphous and crystalline phases can be achieved by using this method.

  4. Tellurium n-type doping of highly mismatched amorphous GaN1-xAsx alloys in plasma-assisted molecular beam epitaxy

    DOE PAGESBeta

    Novikov, S. V.; Ting, M.; Yu, K. M.; Sarney, W. L.; Martin, R. W.; Svensson, S. P.; Walukiewicz, W.; Foxon, C. T.

    2014-10-01

    In this paper we report our study on n-type Te doping of amorphous GaN1-xAsx layers grown by plasma-assisted molecular beam epitaxy. We have used a low temperature PbTe source as a source of tellurium. Reproducible and uniform tellurium incorporation in amorphous GaN1-xAsx layers has been successfully achieved with a maximum Te concentration of 9×10²⁰ cm⁻³. Tellurium incorporation resulted in n-doping of GaN1-xAsx layers with Hall carrier concentrations up to 3×10¹⁹ cm⁻³ and mobilities of ~1 cm²/V s. The optimal growth temperature window for efficient Te doping of the amorphous GaN1-xAsx layers has been determined.

  5. Tellurium n-type doping of highly mismatched amorphous GaN1-xAsx alloys in plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.; Ting, M.; Yu, K. M.; Sarney, W. L.; Martin, R. W.; Svensson, S. P.; Walukiewicz, W.; Foxon, C. T.

    2014-10-01

    In this paper we report our study on n-type Te doping of amorphous GaN1-xAsx layers grown by plasma-assisted molecular beam epitaxy. We have used a low temperature PbTe source as a source of tellurium. Reproducible and uniform tellurium incorporation in amorphous GaN1-xAsx layers has been successfully achieved with a maximum Te concentration of 9×1020 cm-3. Tellurium incorporation resulted in n-doping of GaN1-xAsx layers with Hall carrier concentrations up to 3×1019 cm-3 and mobilities of ~1 cm2/V s. The optimal growth temperature window for efficient Te doping of the amorphous GaN1-xAsx layers has been determined.

  6. Nanophase Nickel-Zirconium Alloys for Fuel Cells

    NASA Technical Reports Server (NTRS)

    Narayanan, Sekharipuram; Whitacre, jay; Valdez, Thomas

    2008-01-01

    Nanophase nickel-zirconium alloys have been investigated for use as electrically conductive coatings and catalyst supports in fuel cells. Heretofore, noble metals have been used because they resist corrosion in the harsh, acidic fuel cell interior environments. However, the high cost of noble metals has prompted a search for less-costly substitutes. Nickel-zirconium alloys belong to a class of base metal alloys formed from transition elements of widely different d-electron configurations. These alloys generally exhibit unique physical, chemical, and metallurgical properties that can include corrosion resistance. Inasmuch as corrosion is accelerated by free-energy differences between bulk material and grain boundaries, it was conjectured that amorphous (glassy) and nanophase forms of these alloys could offer the desired corrosion resistance. For experiments to test the conjecture, thin alloy films containing various proportions of nickel and zirconium were deposited by magnetron and radiofrequency co-sputtering of nickel and zirconium. The results of x-ray diffraction studies of the deposited films suggested that the films had a nanophase and nearly amorphous character.

  7. Amorphization of embedded Cu nanocrystals by ion irradiation

    NASA Astrophysics Data System (ADS)

    Johannessen, B.; Kluth, P.; Llewellyn, D. J.; Foran, G. J.; Cookson, D. J.; Ridgway, M. C.

    2007-02-01

    While bulk crystalline elemental metals cannot be amorphized by ion irradiation in the absence of chemical impurities, the authors demonstrate that finite-size effects enable the amorphization of embedded Cu nanocrystals. The authors form and compare the atomic-scale structure of the polycrystalline, nanocrystalline, and amorphous phases, present an explanation for the extreme sensitivity to irradiation exhibited by nanocrystals, and show that low-temperature annealing is sufficient to return amorphized material to the crystalline form.

  8. Microfabrication with femtosecond laser processing : (A) laser ablation of ferrous alloys, (B) direct-write embedded optical waveguides and integrated optics in bulk glasses.

    SciTech Connect

    Guo, Junpeng; McDaniel, Karen Lynn; Palmer, Jeremy Andrew; Yang, Pin; Griffith, Michelle Lynn; Vawter, Gregory Allen; Harris, Marc F.; Tallant, David Robert; Luk, Ting Shan; Burns, George Robert

    2004-11-01

    At Sandia National Laboratories, miniaturization dominates future hardware designs, and technologies that address the manufacture of micro-scale to nano-scale features are in demand. Currently, Sandia is developing technologies such as photolithography/etching (e.g. silicon MEMS), LIGA, micro-electro-discharge machining (micro-EDM), and focused ion beam (FIB) machining to fulfill some of the component design requirements. Some processes are more encompassing than others, but each process has its niche, where all performance characteristics cannot be met by one technology. For example, micro-EDM creates highly accurate micro-scale features but the choice of materials is limited to conductive materials. With silicon-based MEMS technology, highly accurate nano-scale integrated devices are fabricated but the mechanical performance may not meet the requirements. Femtosecond laser processing has the potential to fulfill a broad range of design demands, both in terms of feature resolution and material choices, thereby improving fabrication of micro-components. One of the unique features of femtosecond lasers is the ability to ablate nearly all materials with little heat transfer, and therefore melting or damage, to the surrounding material, resulting in highly accurate micro-scale features. Another unique aspect to femtosecond radiation is the ability to create localized structural changes thought nonlinear absorption processes. By scanning the focal point within transparent material, we can create three-dimensional waveguides for biological sensors and optical components. In this report, we utilized the special characteristics of femtosecond laser processing for microfabrication. Special emphasis was placed on the laser-material interactions to gain a science-based understanding of the process and to determine the process parameter space for laser processing of metals and glasses. Two areas were investigated, including laser ablation of ferrous alloys and direct

  9. Magnetic anisotropy of Fe{sub 1−y}X{sub y}Pt-L1{sub 0} [X = Cr, Mn, Co, Ni, Cu] bulk alloys

    SciTech Connect

    Cuadrado, R.; Chantrell, R. W.; Klemmer, Timothy J.

    2014-10-13

    We demonstrate by means of fully relativistic first principles calculations that, by substitution of Fe by Cr, Mn, Co, Ni, or Cu in FePt-L1{sub 0} bulk alloys, with fixed Pt content, it is possible to tune the magnetocrystalline anisotropy energy by adjusting the content of the non-magnetic species in the material. The changes in the geometry due to the inclusion of each element induces different values of the tetragonality and hence changes in the magnetic anisotropy and in the net magnetic moment. The site resolved magnetic moments of Fe increase with the X content while those of Pt and X are simultaneously reduced. The calculations are in good quantitative agreement with experimental data and demonstrate that models with fixed band structure but varying numbers of electrons per unit cell are insufficient to describe the experimental data for doped FePt-L1{sub 0} alloys.

  10. The role of stoichiometric vacancy periodicity in pressure-induced amorphization of the Ga{sub 2}SeTe{sub 2} semiconductor alloy

    SciTech Connect

    Abdul-Jabbar, N. M.; Kalkan, B.; MacDowell, A. A.; Huang, G.-Y.; Gronsky, R.; Bourret-Courchesne, E. D.; Wirth, B. D.

    2014-08-04

    We observe that pressure-induced amorphization of Ga{sub 2}SeTe{sub 2} (a III-VI semiconductor) is directly influenced by the periodicity of its intrinsic defect structures. Specimens with periodic and semi-periodic two-dimensional vacancy structures become amorphous around 10–11 GPa in contrast to those with aperiodic structures, which amorphize around 7–8 GPa. The result is an instance of altering material phase-change properties via rearrangement of stoichiometric vacancies as opposed to adjusting their concentrations. Based on our experimental findings, we posit that periodic two-dimensional vacancy structures in Ga{sub 2}SeTe{sub 2} provide an energetically preferred crystal lattice that is less prone to collapse under applied pressure. This is corroborated through first-principles electronic structure calculations, which demonstrate that the energy stability of III-VI structures under hydrostatic pressure is highly dependent on the configuration of intrinsic vacancies.

  11. Amorphous rare earth magnet powders

    SciTech Connect

    Sellers, C.H.; Branagan, D.J.; Hyde, T.A.; Lewis, L.H.; Panchanathan, V.

    1996-08-01

    Gas atomization (GA) processing does not generally have a high enough cooling rate to produce the initial amorphous microstructure needed to obtain optimal magnetic properties in RE{sub 2}Fe{sub 14}B alloys. Phase separation and an underquenched microstructure result from detrimental {alpha}-Fe precipitation, and the resulting magnetic domain structure is very coarse. Additionally, there is a dramatic dependence of the magnetic properties on the cooling rate (and therefore the particle size) and the powders can be sensitive to environmental degradation. Alloy compositions designed just for GA (as opposed to melt spinning) are necessary to produce an amorphous structure that can be crystallized to result in a fine structure with magnetic properties which are independent of particle size. The addition of titanium and carbon to the melt has been found to change the solidification process sufficiently to result in an ``overquenched`` state in which most of the powder size fractions have an amorphous component. Crystallization with a brief heat treatment produces a structure which has improved magnetic properties, in part due to the ability to use compositions with higher Fe contents without {alpha}-Fe precipitation. Results from magnetometry, magnetic force microscopy, and x-ray analyses will be used to contrast the microstructure, domain structure, and magnetic properties of this new generation of amorphous powders with their multiphase predecessors.

  12. Amorphic complexity

    NASA Astrophysics Data System (ADS)

    Fuhrmann, G.; Gröger, M.; Jäger, T.

    2016-02-01

    We introduce amorphic complexity as a new topological invariant that measures the complexity of dynamical systems in the regime of zero entropy. Its main purpose is to detect the very onset of disorder in the asymptotic behaviour. For instance, it gives positive value to Denjoy examples on the circle and Sturmian subshifts, while being zero for all isometries and Morse-Smale systems. After discussing basic properties and examples, we show that amorphic complexity and the underlying asymptotic separation numbers can be used to distinguish almost automorphic minimal systems from equicontinuous ones. For symbolic systems, amorphic complexity equals the box dimension of the associated Besicovitch space. In this context, we concentrate on regular Toeplitz flows and give a detailed description of the relation to the scaling behaviour of the densities of the p-skeletons. Finally, we take a look at strange non-chaotic attractors appearing in so-called pinched skew product systems. Continuous-time systems, more general group actions and the application to cut and project quasicrystals will be treated in subsequent work.

  13. The electrochemical evaluation of a Zr-based bulk metallic glass in a phosphate-buffered saline electrolyte.

    PubMed

    Morrison, M L; Buchanan, R A; Leon, R V; Liu, C T; Green, B A; Liaw, P K; Horton, J A

    2005-09-01

    Bulk metallic glasses (BMGs) represent an emerging class of materials with an amorphous structure and a unique combination of properties. The objectives of this investigation were to define the electrochemical behavior of a specific Zr-based BMG alloy in a physiologically relevant environment and to compare these properties to standard, crystalline biomaterials as well as other Zr-based BMG compositions. Cyclic-anodic-polarization studies were conducted with a Zr52.5Cu17.9Ni14.6Al10.0Ti5.0 (at %) BMG in a phosphate-buffered saline electrolyte with a physiologically relevant oxygen content at 37 degrees C. The results were compared to three common, crystalline biomaterials: CoCrMo, 316L stainless steel, and Ti-6Al-4V. The BMG alloy was found to have a lower corrosion penetration rate (CPR), as compared to the 316L stainless steel, and an equivalent CPR, as compared to the CoCrMo and Ti-6Al-4V alloys. Furthermore, the BMG alloy demonstrated better localized corrosion resistance than the 316L stainless steel. However, the localized corrosion resistance of the BMG alloy was not as high as those of the CoCrMo and Ti-6Al-4V alloys in the tested environment. The excellent electrochemical properties demonstrated by the BMG alloy are combined with a low modulus and unparalleled strength. This unique combination of properties dramatically demonstrates the potential for amorphous alloys as a new generation of biomaterials. PMID:16013063

  14. The electrochemical Evaluation of a Zr-Based Bulk Metallic Glass in a Phosphate-Buffered Saline Electrolyte

    SciTech Connect

    Morrison, M. L.; Buchanan, R. A.; Leon, R. V.; Liu, Chain T; Green, B. A.; Liaw, Peter K; Horton Jr, Joe A

    2005-01-01

    Bulk metallic glasses (BMGs) represent an emerging class of materials with an amorphous structure and a unique combination of properties. The objectives of this investigation were to define the electrochemical behavior of a specific Zr-based BMG alloy in a physiologically relevant environment and to compare these properties to standard, crystalline biomaterials as well as other Zr-based BMG compositions. Cyclic-anodic-polarization studies were conducted with a Zr{sub 52.5}Cu{sub 17.9}Ni{sub 14.6}Al{sub 10.0}Ti{sub 5.0} (at %) BMG in a phosphate-buffered saline electrolyte with a physiologically relevant oxygen content at 37 C. The results were compared to three common, crystalline biomaterials: CoCrMo, 316L stainless steel, and Ti-6Al-4V. The BMG alloy was found to have a lower corrosion penetration rate (CPR), as compared to the 316L stainless steel, and an equivalent CPR, as compared to the CoCrMo and Ti-6Al-4V alloys. Furthermore, the BMG alloy demonstrated better localized corrosion resistance than the 316L stainless steel. However, the localized corrosion resistance of the BMG alloy was not as high as those of the CoCrMo and Ti-6Al-4V alloys in the tested environment. The excellent electrochemical properties demonstrated by the BMG alloy are combined with a low modulus and unparalleled strength. This unique combination of properties dramatically demonstrates the potential for amorphous alloys as a new generation of biomaterials.

  15. Preparation of amorphous sulfide sieves

    DOEpatents

    Siadati, Mohammad H.; Alonso, Gabriel; Chianelli, Russell R.

    2006-11-07

    The present invention involves methods and compositions for synthesizing catalysts/porous materials. In some embodiments, the resulting materials are amorphous sulfide sieves that can be mass-produced for a variety of uses. In some embodiments, methods of the invention concern any suitable precursor (such as thiomolybdate salt) that is exposed to a high pressure pre-compaction, if need be. For instance, in some cases the final bulk shape (but highly porous) may be same as the original bulk shape. The compacted/uncompacted precursor is then subjected to an open-flow hot isostatic pressing, which causes the precursor to decompose and convert to a highly porous material/catalyst.

  16. Nanomoulding with amorphous metals.

    PubMed

    Kumar, Golden; Tang, Hong X; Schroers, Jan

    2009-02-12

    Nanoimprinting promises low-cost fabrication of micro- and nano-devices by embossing features from a hard mould onto thermoplastic materials, typically polymers with low glass transition temperature. The success and proliferation of such methods critically rely on the manufacturing of robust and durable master moulds. Silicon-based moulds are brittle and have limited longevity. Metal moulds are stronger than semiconductors, but patterning of metals on the nanometre scale is limited by their finite grain size. Amorphous metals (metallic glasses) exhibit superior mechanical properties and are intrinsically free from grain size limitations. Here we demonstrate direct nanopatterning of metallic glasses by hot embossing, generating feature sizes as small as 13 nm. After subsequently crystallizing the as-formed metallic glass mould, we show that another amorphous sample of the same alloy can be formed on the crystallized mould. In addition, metallic glass replicas can also be used as moulds for polymers or other metallic glasses with lower softening temperatures. Using this 'spawning' process, we can massively replicate patterned surfaces through direct moulding without using conventional lithography. We anticipate that our findings will catalyse the development of micro- and nanoscale metallic glass applications that capitalize on the outstanding mechanical properties, microstructural homogeneity and isotropy, and ease of thermoplastic forming exhibited by these materials. PMID:19212407

  17. Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films

    SciTech Connect

    Hellman, Frances

    1998-10-03

    OAK B204 Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films. The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and hTi-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials.

  18. Two-current model of the composition dependence of resistivity in amorphous (Fe{sub 100-x}Co{sub x}){sub 89-y}Zr{sub 7}B{sub 4}Cu{sub y} alloys using a rigid-band assumption

    SciTech Connect

    Shen, S.; Ohodnicki, P. R.; Kernion, S. J.; McHenry, M. E.

    2012-11-15

    Composition dependence of resistivity is studied in amorphous (Fe{sub 100−x}Co{sub x}){sub 89−y}Zr{sub 7}B{sub 4}Cu{sub y} (0 ≤ x ≤ 50, y = 0, 1) alloys. The two-current model proposed by Mott for crystalline materials is extended to a disordered amorphous system where s-d scattering is dominant in electron conduction. A rigid-band assumption is made due to the small atomic number difference between Fe and Co. Band structures with a constant density of states (DOS), parabolic distributed DOS, and Gaussian distributed DOS were investigated to fit experimental data. The Gaussian distributed DOS was found to simulate the resistivity maximum and magnetic moment maximum in the Fe-rich region. The basic concepts presented here can potentially provide insight into the optimization of FeCo-based HITPERM alloys for applications at increased frequencies.

  19. Effect of Surface Modifications of Ti40Zr10Cu38Pd12 Bulk Metallic Glass and Ti-6Al-4V Alloy on Human Osteoblasts In Vitro Biocompatibility

    PubMed Central

    Blanquer, Andreu; Hynowska, Anna; Nogués, Carme; Ibáñez, Elena; Sort, Jordi; Baró, Maria Dolors; Özkale, Berna; Pané, Salvador; Pellicer, Eva

    2016-01-01

    The use of biocompatible materials, including bulk metallic glasses (BMGs), for tissue regeneration and transplantation is increasing. The good mechanical and corrosion properties of Ti40Zr10Cu38Pd12 BMG and its previously described biocompatibility makes it a potential candidate for medical applications. However, it is known that surface properties like topography might play an important role in regulating cell adhesion, proliferation and differentiation. Thus, in the present study, Ti40Zr10Cu38Pd12 BMG and Ti6-Al-4V alloy were surface-modified electrochemically (nanomesh) or physically (microscratched) to investigate the effect of material topography on human osteoblasts cells (Saos-2) adhesion, proliferation and differentiation. For comparative purposes, the effect of mirror-like polished surfaces was also studied. Electrochemical treatments led to a highly interconnected hierarchical porous structure rich in oxides, which have been described to improve corrosion resistance, whereas microscratched surfaces showed a groove pattern with parallel trenches. Cell viability was higher than 96% for the three topographies tested and for both alloy compositions. In all cases, cells were able to adhere, proliferate and differentiate on the alloys, hence indicating that surface topography plays a minor role on these processes, although a clear cell orientation was observed on microscratched surfaces. Overall, our results provide further evidence that Ti40Zr10Cu38Pd12 BMG is an excellent candidate, in the present two topographies, for bone repair purposes. PMID:27243628

  20. Measuring strain distributions in amorphous materials

    NASA Astrophysics Data System (ADS)

    Poulsen, Henning F.; Wert, John A.; Neuefeind, Jörg; Honkimäki, Veijo; Daymond, Mark

    2005-01-01

    A number of properties of amorphous materials including fatigue, fracture and component performance are governed by the magnitude of strain fields around inhomogeneities such as inclusions, voids and cracks. At present, localized strain information is only available from surface probes such as optical or electron microscopy. This is unfortunate because surface and bulk characteristics in general differ. Hence, to a large extent, the assessment of strain distributions relies on untested models. Here we present a universal diffraction method for characterizing bulk stress and strain fields in amorphous materials and demonstrate its efficacy by work on a material of current interest in materials engineering: a bulk metallic glass. The macroscopic response is shown to be less stiff than the atomic next-neighbour bonds because of structural rearrangements at the scale of 4-10 Å. The method is also applicable to composites comprising an amorphous matrix and crystalline inclusions.