Science.gov

Sample records for martensitic phase transformations

  1. Coupled dislocation and martensitic phase transformation dynamics

    NASA Astrophysics Data System (ADS)

    Barros, Kipton; Acharya, Amit; Lookman, Turab

    2013-03-01

    We present a field theoretic model that couples dislocation dynamics and plasticity with martensitic phase transformation. Dislocations produce long-range stress via incompatibility of the elastic-distortion field. Phase transformations are modeled with a non-convex elastic potential that contains the crystal symmetries of austenite and martensite phases. We discuss the effects of dislocation dynamics on material microstructure produced under extreme conditions.

  2. Texture evolution during nitinol martensite detwinning and phase transformation

    SciTech Connect

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

    2013-12-09

    Nitinol has been widely used to make medical devices for years due to its unique shape memory and superelastic properties. However, the texture of the nitinol wires has been largely ignored due to inherent complexity. In this study, in situ synchrotron X-ray diffraction has been carried out during uniaxial tensile testing to investigate the texture evolution of the nitinol wires during martensite detwinning, variant reorientation, and phase transformation. It was found that the thermal martensitic nitinol wire comprised primarily an axial (1{sup ¯}20), (120), and (102)-fiber texture. Detwinning initially converted the (120) and (102) fibers to the (1{sup ¯}20) fiber and progressed to a (1{sup ¯}30)-fiber texture by rigid body rotation. At strains above 10%, the (1{sup ¯}30)-fiber was shifted to the (110) fiber by (21{sup ¯}0) deformation twinning. The austenitic wire exhibited an axial (334)-fiber, which transformed to the near-(1{sup ¯}30) martensite texture after the stress-induced phase transformation.

  3. Texture evolution during nitinol martensite detwinning and phase transformation

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    Nitinol has been widely used to make medical devices for years due to its unique shape memory and superelastic properties. However, the texture of the nitinol wires has been largely ignored due to inherent complexity. In this study, in situ synchrotron X-ray diffraction has been carried out during uniaxial tensile testing to investigate the texture evolution of the nitinol wires during martensite detwinning, variant reorientation, and phase transformation. It was found that the thermal martensitic nitinol wire comprised primarily an axial (1¯20), (120), and (102)-fiber texture. Detwinning initially converted the (120) and (102) fibers to the (1¯20) fiber and progressed to a (1¯30)-fiber texture by rigid body rotation. At strains above 10%, the (1¯30)-fiber was shifted to the (110) fiber by (21¯0) deformation twinning. The austenitic wire exhibited an axial (334)-fiber, which transformed to the near-(1¯30) martensite texture after the stress-induced phase transformation.

  4. Transformation temperatures of martensite in beta phase nickel aluminide

    NASA Technical Reports Server (NTRS)

    Smialek, J. L.; Hehemann, R. F.

    1972-01-01

    Resistivity and thermal arrest measurements determined that the compositional dependence of Ms (martensite state) temperatures for NiAl martensite was linear between 60 and 69 atomic percent nickel, with Ms = 124 Ni - 7410 K. Resistivity and surface relief experiments indicated the presence of thermoelastic martensite for selected alloys. Some aspects of the transformation were studied by hot stage microscopy and related to the behavior observed for alloys exhibiting the shape-memory effect.

  5. Transformation temperatures of martensite in beta-phase nickel aluminide.

    NASA Technical Reports Server (NTRS)

    Smialek, J. L.; Hehemann, R. F.

    1973-01-01

    Resistivity and thermal arrest measurements determined that the compositional dependence of M sub s temperatures for NiAl martensite was linear between 60 and 69 at. % Ni, with M sub s = (124 Ni - 7410)K. Resistivity and surface relief experiments for selected alloys indicated the presence of thermoelastic martensite. Some aspects of the transformation were studied by hot-stage microscopy and related to the behavior observed for alloys exhibiting the shape-memory effect.

  6. Phase-filed modelling and synchrotron validation of phase transformations in martensitic dual-phase steel

    SciTech Connect

    Thiessen, R.G.; Sietsma, J.; Palmer, T.A.; Elmer, J.W.; Richardson, I.M.

    2008-11-12

    A thermodynamically based method to describe the phase transformations during heating and cooling of martensitic dual-phase steel has been developed, and in situ synchrotron measurements of phase transformations have been undertaken to support the model experimentally. Nucleation routines are governed by a novel implementation of the classical nucleation theory in a general phase-field code. Physically-based expressions for the temperature-dependent interface mobility and the driving forces for transformation have also been constructed. Modelling of martensite was accomplished by assuming a carbon supersaturation of the body-centred-cubic ferrite lattice. The simulations predict kinetic aspects of the austenite formation during heating and ferrite formation upon cooling. Simulations of partial austenitising thermal cycles predicted peak and retained austenite percentages of 38.2% and 6.7%, respectively, while measurements yielded peak and retained austenite percentages of 31.0% and 7.2% ({+-}1%). Simulations of a complete austenitisation thermal cycle predicted the measured complete austenitisation and, upon cooling, a retained austenite percentage of 10.3% while 9.8% ({+-}1%) retained austenite was measured.

  7. Influence of Dynamic Compression on Phase Transformation of Martensitic NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Qiu, Ying; Young, Marcus L.; Nie, Xu

    2015-10-01

    Shape memory alloys (SMAs) exhibit high damping capacity in both austenitic and martensitic phases, due to either a stress-induced martensite phase transformation or a stress-induced martensite variant reorientation, making them ideal candidates for vibration suppression devices to protect structural components from damage due to external forces. In this study, both quasi-static and dynamic compression was conducted on a martensitic NiTi SMA using a mechanical loading frame and on a Kolsky compression bar, respectively, to examine the relationship between microstructure and phase transformation characteristics of martensitic NiTi SMAs. Both endothermic and exothermic peaks disappear completely after experiencing deformation at a strain rate of 103 s-1 and to a strain of about 10 pct. The phase transformation peaks reappear after the deformed specimens were annealed at 873 K (600 °C) for 30 minutes. As compared to samples from quasi-static loading, where a large amount of twinning is observed with a small amount of grain distortion and fracture, samples from dynamic loading show much less twinning with a larger amount of grain distortion and fracture.

  8. Martensitic transformation in zirconia

    SciTech Connect

    Deville, Sylvain . E-mail: sylvain.deville@insa-lyon.fr; Guenin, Gerard; Chevalier, Jerome

    2004-11-08

    We investigate by atomic force microscopy (AFM) the surface relief resulting from martensitic tetragonal to monoclinic phase transformation induced by low temperature autoclave aging in ceria-stabilized zirconia. AFM appears as a very powerful tool to investigate martensite relief quantitatively and with a great precision. The crystallographic phenomenological theory is used to predict the expected relief induced by the transformation, for the particular case of lattice correspondence ABC1, where tetragonal c axis becomes the monoclinic c axis. A model for variants spatial arrangement for this lattice correspondence is proposed and validated by the experimental observations. An excellent agreement is found between the quantitative calculations outputs and the experimental measurements at nanometer scale yielded by AFM. All the observed features are explained fully quantitatively by the calculations, with discrepancies between calculations and quantitative experimental measurements within the measurements and calculations precision range. In particular, the crystallographic orientation of the transformed grains is determined from the local characteristics of transformation induced relief. It is finally demonstrated that the strain energy is the controlling factor of the surface transformation induced by low temperature autoclave treatments in this material.

  9. On a phase field approach for martensitic transformations in a crystal plastic material at a loaded surface

    NASA Astrophysics Data System (ADS)

    Schmitt, Regina; Kuhn, Charlotte; Müller, Ralf

    2015-06-01

    A continuum phase field model for martensitic transformations is introduced, including crystal plasticity with different slip systems for the different phases. In a 2D setting, the transformation-induced eigenstrain is taken into account for two martensitic orientation variants. With aid of the model, the phase transition and its dependence on the volume change, crystal plastic material behavior, and the inheritance of plastic deformations from austenite to martensite are studied in detail. The numerical setup is motivated by the process of cryogenic turning. The resulting microstructure qualitatively coincides with an experimentally obtained martensite structure. For the numerical calculations, finite elements together with global and local implicit time integration scheme are employed.

  10. Multi-scale modeling of the iron bcc arrow hcp martensitic phase transformation

    NASA Astrophysics Data System (ADS)

    Caspersen, Kyle; Carter, Emily; Lew, Adrian; Ortiz, Michael

    2004-03-01

    Pressures exceeding 10 GPa induce a martensitic phase transformation in iron, where ferro-magnetic bcc transforms into non-magnetic hcp. The transition pressure is not known precisely, but is thought to depend strongly on shear. To investigate the properties of this transformation and the role of shear, we have developed a multi-scale iron model. This model contains a free energy derived from an ab-initio based non-linear elastic expansion, a kinematically compatible spinodal decomposition of phases, ab-initio based interfacial energies, and a dependence on the bcc rightarrow hcp transformation path(s). The model shows spinodal decomposition behavior (with a slight expected deviation) as well as predicting 10 GPa to be the transformation pressure. Additionally, the model predicted that the inclusion of shear facilitates the transformation, causing transformation pressure to decrease.

  11. Statistical physics concepts for the explanation of effects observed in martensitic phase transformations

    NASA Astrophysics Data System (ADS)

    Oberaigner, Eduard Roman; Leindl, Mario

    2012-09-01

    Structural solid-to-solid transformations play a key role for the behaviour of several materials, e.g., shape memory alloys, steels, polymers and ceramics. A novel theoretical approach modelling martensitic phase transformation is demonstrated in the present study. The generally formulated model is based on the block-spin approach and on renormalization in statistical mechanics and is applied to a representative volume element (resp. representative mole element) which is assumed to be in a local thermodynamic equilibrium. The neighbouring representative volume elements are in a generally different thermodynamic equilibrium. This leads to fluxes between those elements. Using fundamental physical properties of a shape memory alloy (SMA) single crystal as input data the model predicts the order parameter ‘total strain’, the martensitic phase fraction and the stress-assisted transformation accompanied by pseudo-elasticity without the requirement of evolution equations for internal variables and assumptions on the mathematical structure of the classical free energy. In order to demonstrate the novel approach the first computations are carried out for a simple one-dimensional case, which can be generalized to the two- and three-dimensional case. Results for total strain and martensitic phase fraction are in good qualitative agreement with well known experimental data according to their macroscopic strain rearrangement when phase transformation occurs. Further a material softening effect during phase transformation in SMAs is predicted by the statistical physics approach. Formulas are presented for the relevant quantities such as volume fraction, total strain, transformation strain, rates of the volume fractions and of the strains.

  12. Stability analysis of the martensitic phase transformation in Co2NiGa Heusler alloy

    NASA Astrophysics Data System (ADS)

    Talapatra, Anjana; Arróyave, Raymundo; Entel, Peter; Valencia-Jaime, I.; Romero, Aldo H.

    2015-08-01

    Phase competition and the subsequent phase selection are important characteristics of alloy systems exhibiting numerous states of distinct symmetry but comparable energy. The stoichiometric Co2NiGa Heusler alloy exhibits a martensitic transformation with concomitant reduction in symmetry from an austenitic L 21 phase (cubic) to a martensitic L 10 phase (tetragonal). A structural search was carried out for this alloy and it showed the existence of a number of structures with monoclinic and orthorhombic symmetry with ground state energies comparable to and even less than that of the L 10 structure, usually reported as the ground state at low temperatures. We describe these structures and focus in particular on the structural transition path from the L 21 to tetragonal and orthorhombic structures for this material. Calculations were carried out to study the Bain (L 21-L 10 ) and Burgers (L 21-hcp ) transformations. The barrierless Burgers path yielded a stable martensitic phase with orthorhombic symmetry (O ) with energy much lower—beyond the expected uncertainty of the calculation methods—than the known tetragonal L 10 martensitic structure. This low-energy structure (O ) has yet to be observed experimentally and it is thus of scientific interest to discern the cause for the apparent discrepancy between experiments and calculations. It is postulated that the Co2NiGa Heusler system exhibits a classic case of the phase selection problem: although the unexpected O phase may be relatively more stable than the L 10 phase, the energy barrier for the (L 21-O ) transformation may be much higher than the barrier to the (L 21-L 10 ) transformation. To validate this hypothesis, the stability of this structure was investigated by considering the contributions of elastic and vibrational effects, configurational disorder, magnetic disorder, and atomic disorder. The calculations simulating the effect of magnetic disorder/high temperature as well as the atomic disorder

  13. Martensitic phase transformation in Nb/sub 3/Sn - X-Ray observations

    SciTech Connect

    Roberge, R.; Foner, S.; Lehuy, H.

    1985-03-01

    A compilation is presented of room temperature lattice spacing, a /SUB o/ , versus martensitic phase transformation temperature, T /SUB m/ , of Nb/sub 3/Sn for over 50 set of data including data of other investigations. The low temperature tetragonal phase transition occurs with c/a < 1 for a /SUB o/ between 5.289 and 5.2933 A, with c/a > 1 for a /SUB o/ between 5.2865 and 5.2883 A. Nb/sub 3/Sn remains in the cubic phase (no transformation) for a /SUB o/ < 5.2865 A and a /SUB o/ > 5.2933 A, and for a very narrow region between 5.2883 A and 5.289 A. The effect of additives and the effect of matrix strain on the width of T /SUB m/ is also discussed. A detailed tabulation is presented for the various Nb/sub 3/Sn materials and their resultant transformation characteristics.

  14. Influence of Temperature on Fatigue-Induced Martensitic Phase Transformation in a Metastable CrMnNi-Steel

    NASA Astrophysics Data System (ADS)

    Biermann, Horst; Glage, Alexander; Droste, Matthias

    2016-01-01

    Metastable austenitic steels can exhibit a fatigue-induced martensitic phase transformation during cyclic loading. It is generally agreed that a certain strain amplitude and a threshold of the cumulated plastic strain must be exceeded to trigger martensitic phase transformation under cyclic loading. With respect to monotonic loading, the martensitic phase transformation takes place up to a critical temperature—the so-called M d temperature. The goal of the present investigation is to determine an M d,c temperature which would be the highest temperature at which a fatigue-induced martensitic phase transformation can take place. For this purpose, fatigue tests controlled by the total strain were performed at different temperatures. The material investigated was a high-alloy metastable austenitic steel X3CrMnNi16.7.7 (16.3Cr-7.2Mn-6.6Ni-0.03C-0.09N-1.0Si) produced using the hot pressing technique. The temperatures were set in the range of 283 K (10 °C) ≤ T ≤ 473 K (200 °C). Depending on the temperature and strain amplitude, the onset of the martensitic phase transformation shifted to different values of the cumulated plastic strain, or was inhibited completely. Moreover, it is known that metastable austenitic CrMnNi steels with higher nickel contents can exhibit the deformation-induced twinning effect. Thus, at higher temperatures and strain amplitudes, a transition from the deformation-induced martensitic transformation to deformation-induced twinning takes place. The fatigue-induced martensitic phase transformation was monitored during cyclic loading using a ferrite sensor. The microstructure after the fatigue tests was examined using the back-scattered electrons, the electron channeling contrast imaging and the electron backscatter diffraction techniques to study the temperature-dependent dislocation structures and phase transformations.

  15. A comparison of dilatometry and in-situ neutron diffraction in tracking bulk phase transformations in a martensitic stainless steel

    SciTech Connect

    Christien, F.; Telling, M.T.F.; Knight, K.S.

    2013-08-15

    Phase transformations in the 17-4PH martensitic stainless steel have been studied using different in-situ techniques, including dilatometry and high resolution neutron diffraction. Neutron diffraction patterns were quantitatively processed using the Rietveld refinement method, allowing the determination of the temperature-dependence of martensite (α′, bcc) and austenite (γ, fcc) phase fractions and lattice parameters on heating to 1000 °C and then cooling to room temperature. It is demonstrated in this work that dilatometry doesn't permit an accurate determination of the end temperature (Ac3) of the α′ → γ transformation which occurs upon heating to high temperature. The analysis of neutron diffraction data has shown that the respective volumes of the two phases become very close to each other at high temperature, thus making the dilatometric technique almost insensitive in that temperature range. However, there is a very good agreement between neutron diffraction and dilatometry at lower temperature. The martensitic transformation occurring upon cooling has been analysed using the Koistinen–Marburger equation. The thermal expansion coefficients of the two phases have been determined in addition. A comparison of the results obtained in this work with data from literature is presented. - Highlights: • Martensite is still present at very high temperature (> 930 °C) upon heating. • The end of austenitisation cannot be accurately monitored by dilatometry. • The martensite and austenite volumes become similar at high temperature (> ∼ 850 °C)

  16. Martensitic phase transformation and ferromagnetic shape memory effect in iron palladium single crystal

    NASA Astrophysics Data System (ADS)

    Cui, Jun

    In this thesis the ferromagnetic shape memory effect in Fe70Pd 30 alloys is studied in three stages. The first stage is to grow a single crystal of Fe70Pd30 using Bridgman method; the second stage focuses on the characterization of material properties. Both x-ray analysis and DSC measurements show that the FCC-FCT transformation is a weak first order thermoelastic transition. The average lattice parameters are a = 3.822 A and c = 3.6298 A for the FCT martensite, and a0 = 3.7557 A for the cubic austenite. The latent heat is 10.79 +/- 11 J/cm3. The Curie temperature is 300°C. The saturation magnetization is ms = 1217 emu/cm3 for the martensite and ms = 1081 emu/cm 3 for the austenite in Fe70Pd30 alloy; the easy axis is in the [100] or [010] direction (the long axis of the FCT lattice). The magnetic anisotropy is -4.8 x 103 erg/cm 3 for the austenite at 60°C, and it is 3.46 x 10 5 erg/cm3 for the martensite at -20°C. In addition, the effect of heat treatment on the materials properties is investigated. The third stage is to characterize the ferromagnetic shape memory effect of this alloy using magnetomechanical tests and the results are compared with micromagnetic theory. The sign of the field-induced strain agrees with the constrained theory. The maximum ferromagnetic strain in this material is about 0.9%, which is 1/4 of the theoretical prediction. The blocking stress is about -4 MPa, and the work output is about 20 x 103 J/m 3 per cycle at -12 MPa and 10°C. Furthermore, stress has large effect on the phase transformation temperature, for the compressive stress, it is 0.7°C/MPa. The phase transformation temperature can also be changed by applying a magnetic field during cooling or heating. The direction and the degree of changes depends on the direction of the field. The most significant change happens at a [001] field less than 1700 G, where [001] refers to the short axis of the FCT lattice.

  17. Computer simulation of martensitic transformations

    SciTech Connect

    Xu, Ping

    1993-11-01

    The characteristics of martensitic transformations in solids are largely determined by the elastic strain that develops as martensite particles grow and interact. To study the development of microstructure, a finite-element computer simulation model was constructed to mimic the transformation process. The transformation is athermal and simulated at each incremental step by transforming the cell which maximizes the decrease in the free energy. To determine the free energy change, the elastic energy developed during martensite growth is calculated from the theory of linear elasticity for elastically homogeneous media, and updated as the transformation proceeds.

  18. Dynamic Thermo-Mechanical Phase-Field Models for Martensitic Transformations in Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Dhote, Rakesh

    Shape memory alloys (SMAs) exhibit complex microstructures and non-linear hysteretic behaviors that arise from a strong interaction between mechanical and thermal phenomena. It is imperative to couple the thermal physics and the mechanical dynamics to study the influence of such coupling on the mechanical properties of SMA systems, including nanostructures. However, the majority of phase-field models in the literature related to SMAs account for structural physics only. With the aim to incorporate thermal physics, in this thesis, first the 2D and 3D dynamic fully coupled thermo-mechanical phase-field models are developed based on the strain-based order parameters. The developed models are highly nonlinear, strongly hysteretic with fourth-order spatial differential terms, which impose several computational challenges. Secondly, to overcome these computational challenges, a numerical formulation based on the isogeometric analysis is developed for a straightforward solution to the fourth-order differential equations using continuously differentiable non-uniform rational B-splines (NURBS). Several numerical examples of microstructure evolution in SMA systems, in particular nanostructures of different geometries, under temperature and stress induced loadings illustrated the flexibility, accuracy and robustness of the developed numerical formulation. The numerical simulations revealed a significant impact of the temperature dynamics on mechanical properties of SMAs. The developed models successfully captured experimentally observed mechanical and thermal hysteresis phenomena, local non-uniform phase transformations and corresponding non-uniform temperature and deformations distributions. The predicted microstructure evolution is in qualitative agreement with the results reported in the literature. The material properties of austenite and martensite phases are different, as observed experimentally during phase transformations. However, the majority of macroscale non

  19. Direct observation of phase transformations in the simulated heat-affected zone of a 9Cr martensitic steel

    SciTech Connect

    Mayr, Peter; Palmer, T. A.; Elmer, J. W.; Specht, Eliot D

    2008-01-01

    An experimental test melt of a boron alloyed 9Cr-3W-3Co-V,Nb steel for high temperature applications in the thermal power generation industry was produced by vacuum induction melting. This grade of steel typically displays a homogeneous tempered martensitic microstructure in the as-received condition. However, after welding, this microstructure is significantly altered, resulting in a loss of its desired properties. The phase transformations during simulated thermal cycles typical of those experienced in the weld heat-affected zone (HAZ) were directly observed by in situ X-ray diffraction experiments using synchrotron radiation. Heating rates of 10 C s-1 and 100 C s-1 up to a peak temperature of 1300 C are investigated here. The final microstructures observed after both simulated weld thermal cycles are primarily composed of martensite with approximately 4% retained delta ferrite and 4% retained austenite, by volume. With the temporal resolution of the in situ X-ray diffraction technique, phase transformations from tempered martensite to austenite to delta ferrite during heating and to martensite during cooling were monitored. With this technique, the evolution of the final microstructure through both heating and cooling is monitored, providing additional context to the microstructural observations.

  20. Features of structure-phase transformations and segregation processes under irradiation of austenitic and ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Neklyudov, I. M.; Voyevodin, V. N.

    1994-09-01

    The difference between crystal lattices of austenitic and ferritic steels leads to distinctive features in mechanisms of physical-mechanical change. This paper presents the results of investigations of dislocation structure and phase evolution, and segregation phenomena in austenitic and ferritic-martensitic steels and alloys during irradiation with heavy ions in the ESUVI and UTI accelerators and by neutrons in fast reactors BOR-60 and BN-600. The influence of different factors (including different alloying elements) on processes of structure-phase transformation was studied.

  1. Effect of aluminum alloying on the structure, the phase composition, and the thermoelastic martensitic transformations in ternary Ni-Mn-Al alloys

    NASA Astrophysics Data System (ADS)

    Belosludtseva, E. S.; Kuranova, N. N.; Kourov, N. I.; Pushin, V. G.; Stukalov, V. Yu.; Uksusnikov, A. N.

    2015-07-01

    The properties, the martensitic transformation, and the structure of Ni50Mn50 - x Al x ( x = 5, 10, 18, 20, 22, 24, 25) alloys are studied by electrical resistivity measurements, transmission electron microscopy, scanning electron microscopy, and X-ray diffraction over wide temperature and composition ranges. It is found that, as the aluminum content increases, the martensite transformation temperature decreases significantly and the structure of martensite changes. Complex multilayer (10 M, 14 M) martensite phases are detected in the ternary alloys. Martensite is shown to have a predominant morphology in the form of hierarchic packets of thin coherent plates of nanoand submicrocrystalline crystallites, which have plane habit boundaries close to {110} B2 and are pairwise twinned along one of the 24 equivalent systems of twinning shear.

  2. Defect-induced incompatability of elastic strains: dislocations within the Landau theory of martensitic phase transformations

    SciTech Connect

    Groger, Roman1; Lockman, Turab; Saxena, Avadh

    2008-01-01

    In dislocation-free martensites the components of the elastic strain tensor are constrained by the Saint-Venant compatibility condition which guarantees continuity of the body during external loading. However, in dislocated materials the plastic part of the distortion tensor introduces a displacement mismatch that is removed by elastic relaxation. The elastic strains are then no longer compatible in the sense of the Saint-Venant law and the ensuing incompatibility tensor is shown to be proportional to the gradients of the Nye dislocation density tensor. We demonstrate that the presence of this incompatibility gives rise to an additional long-range contribution in the inhomogeneous part of the Landau energy functional and to the corresponding stress fields. Competition among the local and long-range interactions results in frustration in the evolving order parameter (elastic) texture. We show how the Peach-Koehler forces and stress fields for any distribution of dislocations in arbitrarily anisotropic media can be calculated and employed in a Fokker-Planck dynamics for the dislocation density. This approach represents a self-consistent scheme that yields the evolutions of both the order parameter field and the continuous dislocation density. We illustrate our method by studying the effects of dislocations on microstructure, particularly twinned domain walls, in an Fe-Pd alloy undergoing a martensitic transformation.

  3. Effect of gallium alloying on the structure, the phase composition, and the thermoelastic martensitic transformations in ternary Ni-Mn-Ga alloys

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    The effect of gallium alloying on the structure, the phase composition, and the properties of quasibinary Ni50Mn50- z Ga z (0 ⩽ z ⩽ 25 at %) alloys is studied over a wide temperature range. The influence of the alloy composition on the type of crystal structure in high-temperature austenite and martensite and the critical martensitic transformation temperatures is analyzed. A general phase diagram of the magnetic and structural transformations in the alloys is plotted. The temperature-concentration boundaries of the B2 and L21 superstructures in the austenite field, the tetragonal L10 (2 M) martensite, and the 10 M and 14 M martensite phases with complex multilayer crystal lattices are found. The predominant morphology of martensite is shown to be determined by the hierarchy of the packets of thin coherent lamellae of nano- and submicrocrystalline crystals with planar habit plane boundaries close to {011} B2. Martensite crystals are twinned along one of the 24 24{ {011} }{< {01bar 1} rangle _{B2}} "soft" twinning shear systems, which provides coherent accommodation of the martensitic transformation-induced elastic stresses.

  4. Effect of thermal cycling on the R-phase and martensitic transformations in a Ti-rich NiTi alloy

    SciTech Connect

    Pelosin, V.; Riviere, A.

    1998-04-01

    The effect of thermal cycling on transformation temperature was studied on a Ti-rich NiTi alloy. The study was carried out by determining the electrical resistance, the internal friction, and the elastic modulus vs temperature. This study shows that the martensite microstructure is modified by the successive cycling transformation. In addition, the authors established that both the martensite internal friction and the transition peak are sensitive to the transient effect (the vibration frequency lies around 300 Hz). But the major results concern the behavior associated with the R phase occurrence and its evolution. They have stated that the premartensitic phase becomes stable following the diminishment of the beginning of the martensite formation (M{sub s}). Interrupted cooling has also shown that, contrary to the martensite, the R phase exhibits no hysteretic behavior.

  5. The effect of tempering temperature on the features of phase transformations in the ferritic-martensitic steel EK-181

    NASA Astrophysics Data System (ADS)

    Polekhina, N. A.; Litovchenko, I. Yu.; Tyumentsev, A. N.; Astafurova, Е. G.; Chernov, V. M.; Leontyeva-Smirnova, M. V.

    2014-12-01

    Using the methods of dilatometry and differential scanning calorimetry, critical points of phase transformations in the low-activation ferritic-martensitic steel EK-181 (RUSFER-EK-181) are identified. The characteristic temperature intervals of precipitation of carbide phases are revealed. It is shown that particles of the metastable carbide M3C are formed within the temperature range (500-600) °C. Formation of the stable phases М23С6 and V(CN) begins at the temperatures higher than Т = 650 °С. An important feature of microstructure after tempering at Т = 720 °С is high density of nanoparticles (⩽10 nm) of vanadium carbonitride V(CN).

  6. Martensitic transformations in shape-memory Cu-Zn-AI alloys with the α-phase particles and the bainite crystals

    NASA Astrophysics Data System (ADS)

    Khomskaya, I.; Zel'Dovich, V.; Frolova, N.

    2003-10-01

    The martensitic transformations in Cu-Zn-A1 alloys undergoing the decomposition of β solid solution with the formation of rod-like α-phase or of plate-type bainite crystals have been studied by optical microscopy, electron microscopy and electron-probe microanalysis. The fine structure of the phases formed upon the partial decomposition of β-phase and upon the subsequent martensitic transformation was studied. The α {to} β transformation was shown to occur in a crystallographically ordered manner and to obey the Kurdyumov-Sachs orientation relationships. The α {to} β transformation includes features of both diffusional and martensitic transformations. The α-phase formation inclues a crystals lattice reconstruction and the nucleation dislocations in periodically arranged slip planes. At the same time, the shape of the α-phase crystals and their coalescence and changes in chemical composition are typical of diffusional transformation. The interactions of martensite crystals with particles of the α phase and bainite crystals were studied.

  7. Langevin Simulation of Microstructure in Martensitic Transformations

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Lookman, T.; Shenoy, S. R.; Saxena, A.; Bishop, A. R.

    1996-03-01

    We present a dynamical model to simulate microstructure in martensitic transformations within the context of shape memory alloys. The Hamiltonian of the system includes a triple-well potential (φ^6 model) in local shear strain, (2) strain gradient terms up to second order in strain and fourth order in gradient, and (3) all symmetry allowed compositional fluctuation induced strain gradient terms. We show the formation of twinned martensite below the transformation temperature and tweed precursors above the transformation temperature, as well as indications of hierarchical structures near the habit plane. These phases result from a competition between short range attraction and long range elastic repulsive forces. The long range interaction is incorporated via Fourier spectral methods as discussed by C. Roland and R.C.Desai [Phys. Rev. B 42, 6658 (1990)].

  8. Phase transformation and impact properties in the experimentally simulated weld heat-affected zone of a reduced activation ferritic/martensitic steel

    NASA Astrophysics Data System (ADS)

    Moon, Joonoh; Lee, Chang-Hoon; Lee, Tae-Ho; Jang, Min-Ho; Park, Min-Gu; Han, Heung Nam

    2014-12-01

    In this work, the phase transformation and impact properties in the weld heat-affected zone (HAZ) of a reduced activation ferritic/martensitic (RAFM) steel are investigated. The HAZs were experimentally simulated using a Gleeble simulator. The base steel consisted of tempered martensite through normalizing at 1000 °C and tempering at 750 °C, while the HAZs consisted of martensite, δ-ferrite and a small volume of autotempered martensite. The impact properties using a Charpy V-notch impact test revealed that the HAZs showed poor impact properties due to the formation of martensite and δ-ferrite as compared with the base steel. In addition, the impact properties of the HAZs further deteriorated with an increase in the δ-ferrite fraction caused by increasing the peak temperature. The impact properties of the HAZs could be improved through the formation of tempered martensite after post weld heat treatment (PWHT), but they remained lower than that of the base steel because the δ-ferrite remained in the tempered HAZs.

  9. A phase field approach with a reaction pathways-based potential to model reconstructive martensitic transformations with a large number of variants

    NASA Astrophysics Data System (ADS)

    Denoual, C.; Vattré, A.

    2016-05-01

    A pathway tree is constructed by recursively duplicating a single reconstructive martensitic transformation path with respect to lattice symmetries and point-group rotations. An energy potential built on this pathway is implemented in a phase-field technique in large strain framework, with the transformational strain as the order parameter. A specific splitting between non-dissipative elastic behavior and the dissipative evolution of the order parameter allows for the modeling of acoustic waves during rapid transformations. A simple toy-model transition from hexa- to square-lattice successfully demonstrates the possibility to model reconstructive martensitic transformations for a large number of variants (more than one hundred). Pure traction applied to our toy-model shows that variants can nucleate into previously created variants, with a hierarchical nucleation of variants spanning over five levels of transformation.

  10. Small-angle neutron scattering study of magnetic ordering and inhomogeneity across the martensitic phase transformation in Ni50–xCoxMn₄₀Sn₁₀ alloys

    DOE PAGESBeta

    Bhatti, Kanwal Preet; El-Khatib, S.; Srivastava, Vijay; James, R. D.; Leighton, C.

    2012-04-27

    The Heusler-derived multiferroic alloy Ni50–xCoxMn₄₀Sn₁₀ has recently been shown to exhibit, at just above room temperature, a highly reversible martensitic phase transformation with an unusually large magnetization change. In this work the nature of the magnetic ordering above and below this transformation has been studied in detail in the critical composition range x = 6–8 via temperature-dependent (5–600 K) magnetometry and small-angle neutron scattering (SANS). We observe fairly typical paramagnetic to long-range-ordered ferromagnetic phase transitions on cooling to 420–430 K, with the expected critical spin fluctuations, followed by first-order martensitic phase transformations to a nonferromagnetic state below 360–390 K. Themore » static magnetization reveals complex magnetism in this low-temperature nonferromagnetic phase, including a Langevin-like field dependence, distinct spin freezing near 60 K, and significant exchange bias effects, consistent with superparamagnetic blocking of ferromagnetic clusters of nanoscopic dimensions. We demonstrate that these spin clusters, whose existence has been hypothesized in a variety of martensitic alloys exhibiting competition between ferromagnetic and antiferromagnetic exchange interactions, can be directly observed by SANS. The scattering data are consistent with a liquidlike spatial distribution of interacting magnetic clusters with a mean center-to-center spacing of 12 nm. Considering the behavior of the superparmagnetism, cooling-field and temperature-dependent exchange bias, and magnetic SANS, we discuss in detail the physical form and origin of these spin clusters, their intercluster interactions, the nature of the ground-state magnetic ordering in the martensitic phase, and the implications for our understanding of such alloy systems.« less

  11. Martensite transformation of epitaxial Ni-Ti films

    SciTech Connect

    Buschbeck, J.; Kozhanov, A.; Kawasaki, J. K.; James, R. D.; Palmstroem, C. J.

    2011-05-09

    The structure and phase transformations of thin Ni-Ti shape memory alloy films grown by molecular beam epitaxy are investigated for compositions from 43 to 56 at. % Ti. Despite the substrate constraint, temperature dependent x-ray diffraction and resistivity measurements reveal reversible, martensitic phase transformations. The results suggest that these occur by an in-plane shear which does not disturb the lattice coherence at interfaces.

  12. The effect of shear deformations on the transition onset pressure of the bcc to hcp pressure induced martensitic phase transformation in iron.

    NASA Astrophysics Data System (ADS)

    Caspersen, K.; Lew, A.; Ortiz, M.; Carter, E.

    2003-12-01

    At a pressure of approximately 13 GPa iron undergoes a martensitic phase transition from ground state ferro-magnetic bcc to a non-magnetic hcp structure. The exact transformation varies between experiments and is postulated to have a strong dependence on shear stresses during the loading process. To study this shear dependence we have developed a multi-scale model of iron, in which we employ a quantum mechanics based free energy, a kinematically compatible spinodal decomposition of phases, and a dependence on the bcc{<->}hcp transition path(s). Using this model we see that that the predicted transformation pressure for pure hydrostatic compression is much higher than expected, however with the inclusion of small initial shear deformations we see the predicted transformation pressure drop considerably and into the experimentally determined pressure range.

  13. Effect of titanium alloying on the structure, the phase composition, and the thermoelastic martensitic transformations in ternary Ni—Mn—Ti alloys

    NASA Astrophysics Data System (ADS)

    Belosludtseva, E. S.; Kuranova, N. N.; Kourov, N. I.; Pushin, V. G.; Uksusnikov, A. N.

    2015-09-01

    The behavior and the properties of Ni50Mn50- y Ti y ( y = 5, 10, 15, 25, 30) alloys are studied by electrical resistivity measurements, transmission electron microscopy, scanning electron microscopy, and X-ray diffraction over a wide temperature range. It is found that the martensite transformation temperature of the complex alloys can be significantly lower than the transformation temperature range of binary Ni50Mn50 and Ni49Mn51 alloys. Apart from tetragonal L10 martensite, a complex multilayer (10 M) crystal lattice is revealed in the alloys. Martensite is shown to have a predominant morphology in the form of hierarchic packets of thin coherent plates of nanoand submicrocrystalline crystallites, which have plane habit boundaries. In the case of tetragonal L10 and 10 M martensite, these boundaries are close to {011} B2 and are pairwise twinned along one of the 24 equivalent twinning shear systems.

  14. Influence of Nb on the β→α″ martensitic phase transformation and properties of the newly designed Ti-Fe-Nb alloys.

    PubMed

    Ehtemam-Haghighi, Shima; Liu, Yujing; Cao, Guanghui; Zhang, Lai-Chang

    2016-03-01

    A series of Ti-7Fe-xNb (x=0, 1, 4, 6, 9, 11 wt.%) alloys was designed and cast to investigate the β→α″ martensitic phase transformation, β phase stability, the resulting microstructure and mechanical properties. Phase analysis revealed that only Ti-7Fe-11Nb alloy shows a single body-centred cubic β phase microstructure while the others are comprised of β and orthorhombic α″ phases. Moreover, Nb addition up to 11 wt.% enhances the stability and volume fraction of β phase in the microstructure, hence reducing the propensity of the alloy system to form α″ phase during quenching. Compressive yield strength and hardness of the alloys are (985-1847) MPa and (325-520) Hv respectively. Additionally, Ti-7Fe-11Nb possesses the lowest Young's modulus (84 GPa) and the highest deformability (42% strain) among the designed alloys due to the single β phase microstructure. This high deformability is also corroborated by the large plastic deformation zone underneath the Vickers indenter. In contrast, the fractured surfaces of Ti-7Fe and Ti-7Fe-1Nb alloys after compressive tests mostly contain shallow dimples, verifying their low ductility. The good combination of mechanical properties obtained for Ti-7Fe-11Nb renders it more desirable than commonly used CP-Ti and Ti-6Al-4V materials and makes it a promising candidate for biomedical application. PMID:26706557

  15. Investigation of Strain-Induced Martensitic Transformation in Metastable Austenite using Nanoindentation

    SciTech Connect

    Ahn, T.-H.; Oh, C.-S.; Kim, D. H.; Oh, K. H.; Bei, Hongbin; George, Easo P; Han, H. N.

    2010-01-01

    Strain-induced martensitic transformation of metastable austenite was investigated by nanoindentation of individual austenite grains in multi-phase steel. A cross-section prepared through one of these indented regions using focused ion beam milling was examined by transmission electron microscopy. The presence of martensite underneath the indent indicates that the pop-ins observed on the load-displacement curve during nanoindentation correspond to the onset of strain-induced martensitic transformation. The pop-ins can be understood as resulting from the selection of a favorable martensite variant during nanoindentation.

  16. Thermoelastic martensitic transformations in ternary Ni50Mn50- z Ga z alloys

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  17. A comparative study of the theory of the O-lattice and the phenomenological theory of martensite crystallography to phase transformations

    SciTech Connect

    Zhang, W.Z.; Weatherly, G.C.

    1998-03-23

    The approaches of the phenomenological theory of martensite crystallography (PTMC) and the theory of the O-lattice (TOL) to describe the elements of a phase transformation are compared for an O-line transformation strain. A number of simple relationships between the O-lattice treatment and the PTMC have been established. The displacement associated with the long range strain component is shown to be identical in both treatments when the planes defined by the path of the O-lines are correlated to the slip plane of the dislocations. A characteristic feature of the TOL approach is that this displacement is allowed to vary for a fixed habit plane. When the displacement is associated with an interfacial step, it is equivalent to a transformation dislocation, whose Burgers vector is explicitly expressed in terms of a D-lattice vector in the TOL formula. This method is extended to consider the tilt or tent-shaped surface relief effects observed at precipitates in a Ti-Cr alloy. Good agreement is found between the predictions of this approach and the measurements reported in the literature.

  18. Impurities block the alpha to omega martensitic transformation in titanium.

    PubMed

    Hennig, Richard G; Trinkle, Dallas R; Bouchet, Johann; Srinivasan, Srivilliputhur G; Albers, Robert C; Wilkins, John W

    2005-02-01

    Impurities control phase stability and phase transformations in natural and man-made materials, from shape-memory alloys to steel to planetary cores. Experiments and empirical databases are still central to tuning the impurity effects. What is missing is a broad theoretical underpinning. Consider, for example, the titanium martensitic transformations: diffusionless structural transformations proceeding near the speed of sound. Pure titanium transforms from ductile alpha to brittle omega at 9 GPa, creating serious technological problems for beta-stabilized titanium alloys. Impurities in the titanium alloys A-70 and Ti-6Al-4V (wt%) suppress the transformation up to at least 35 GPa, increasing their technological utility as lightweight materials in aerospace applications. These and other empirical discoveries in technological materials call for broad theoretical understanding. Impurities pose two theoretical challenges: the effect on the relative phase stability, and the energy barrier of the transformation. Ab initio methods calculate both changes due to impurities. We show that interstitial oxygen, nitrogen and carbon retard the transformation whereas substitutional aluminium and vanadium influence the transformation by changing the d-electron concentration. The resulting microscopic picture explains the suppression of the transformation in commercial A-70 and Ti-6Al-4V alloys. In general, the effect of impurities on relative energies and energy barriers is central to understanding structural phase transformations. PMID:15665839

  19. Twinning and martensitic transformations in nickel-enriched 304 austenitic steel during tensile and indentation deformations

    SciTech Connect

    Gussev, Maxim N; Busby, Jeremy T; Byun, Thak Sang; Parish, Chad M

    2013-01-01

    Twinning and martensitic transformation have been investigated in nickel-enriched AISI 304 stainless steel subjected to tensile and indentation deformation. Using electron backscatter diffraction (EBSD), the morphology of alpha- and epsilon-martensite and the effect of grain orientation to load axis on phase and structure transformations were analyzed in detail. It was found that the twinning occurred less frequently under indentation than under tension; also, twinning was not observed in [001] and [101] grains. In tensile tests, the martensite particles preferably formed at the deformation twins, intersections between twins, or at twin-grain boundary intersections. Conversely, martensite formation in the indentation tests was not closely associated with twinning; instead, the majority of martensite was concentrated in the dense colonies near grain boundaries. Martensitic transformation seemed to be obstructed in the [001] grains in both tensile and indentation test cases. Under a tensile stress of 800 MPa, both alpha- and epsilon-martensite were found in the microstructure, but at 1100 MPa only -martensite presented in the specimen. Under indentation, alpha- and epsilon-martensite were observed in the material regardless of stress level.

  20. Hydrogen-assisted damage in austenite/martensite dual-phase steel

    NASA Astrophysics Data System (ADS)

    Koyama, Motomichi; Cem Tasan, Cemal; Nagashima, Tatsuya; Akiyama, Eiji; Raabe, Dierk; Tsuzaki, Kaneaki

    2016-01-01

    For understanding the underlying hydrogen embrittlement mechanism in transformation-induced plasticity steels, the process of damage evolution in a model austenite/martensite dual-phase microstructure following hydrogenation was investigated through multi-scale electron channelling contrast imaging and in situ optical microscopy. Localized diffusible hydrogen in martensite causes cracking through two mechanisms: (1) interaction between {1 1 0}M localized slip and {1 1 2}M twin and (2) cracking of martensite-martensite grain interfaces. The former resulted in nanovoids along the {1 1 2}M twin. The coalescence of the nanovoids generated plate-like microvoids. The latter caused shear localization on the specific plane where the crack along the martensite/martensite boundary exists, which led to additional martensite/martensite boundary cracking.

  1. Possible martensitic transformation and ferrimagnetic properties in Heusler alloy Mn2NiSn

    NASA Astrophysics Data System (ADS)

    Duan, Ying-Ni; Fan, Xiao-Xi; Kutluk, Abdugheni; Du, Xiu-Juan; Zhang, Zheng-Wei; Song, Yu-Ling

    2015-07-01

    The electronic structure and magnetic properties of Hg2CuTi-type Mn2NiSn have been studied by performing the first-principle calculations. It is found that the phase transformation from the cubic to the tetragonal structure reduces the total energy, indicating that the martensitic phase is more stable and the phase transition from austenite to martensite may happen at low temperature for Hg2CuTi-type Mn2NiSn. Concerning the magnetism of Hg2CuTi-type Mn2NiSn, both austenitic and martensitic phases are suggested to be ferrimagnets. Furthermore, martensitic transformation decreases the magnetic moment per formula unit compared with austenitic phase. The results are helpful to accelerate the use of Mn2NiSn alloys in the series for magnetic shape memory applications.

  2. Martensitic transformation and phase stability of In-doped Ni-Mn-Sn shape memory alloys from first-principles calculations

    SciTech Connect

    Xiao, H. B.; Yang, C. P. Wang, R. L.; Luo, X.; Marchenkov, V. V.

    2014-05-28

    The effect of the alloying element Indium (In) on the martensitic transition, magnetic properties, and phase stabilities of Ni{sub 8}Mn{sub 6}Sn{sub 2−x}In{sub x} shape memory alloys has been investigated using the first-principles pseudopotential plane-wave method based on density functional theory. The energy difference between the austenitic and martensitic phases was found to increase with increasing In content, which implies an enhancement of the martensitic phase transition temperature (T{sub M}). Moreover, the formation energy results indicate that In-doping increases the relative stability of Ni{sub 8}Mn{sub 6}Sn{sub 2−x}In{sub x} both in austenite and martensite. This results from a reduction in density of states near the Fermi level regions caused by Ni-3d–In-5p hybridization when Sn is replaced by In. The equilibrium equation of state results show that the alloys Ni{sub 8}Mn{sub 6}Sn{sub 2−x}In{sub x} exhibit an energetically degenerated effect for an In content of x = ∼1.5. This implies the coexistence of antiparallel and parallel configurations in the austenite.

  3. High Temperature Measurements Of Martensitic transformations Using Digital Holography

    SciTech Connect

    Thiesing, Benjamin; Mann, Christopher J; Dryepondt, Sebastien N

    2013-01-01

    During thermal cycling of nickel-aluminum-platinum (NiAlPt) and single crystal Fe-15Cr-15Ni alloys, the structural changes associated with the martensite to austenite phase transformation were measured using dual-wavelength digital holography. Real-time in-situ measurements reveal the formation of striations within the NiPtAl alloy at 70 C and the FeCrNi alloy at 520 C. The results demonstrate that digital holography is an effective technique for acquiring non-contact, high precision information of the surface evolution of alloys at high temperatures.

  4. High temperature measurements of martensitic transformations using digital holography.

    PubMed

    Thiesing, Benjamin P; Mann, Christopher J; Dryepondt, Sebastien

    2013-07-01

    During thermal cycling of nickel-aluminum-platinum (NiAlPt) and single crystal iron-chromium-nickel (FeCrNi) alloys, the structural changes associated with the martensite to austenite phase transformation were measured using dual-wavelength digital holography. Real-time in situ measurements reveal the formation of striations within the NiAlPt alloy at 70°C and the FeCrNi alloy at 520°C. The results demonstrate that digital holography is an effective technique for acquiring noncontact, high precision information of the surface evolution of alloys at high temperatures. PMID:23842235

  5. Martensite Transformation and Magnetic Properties of Ni-Fe-Ga Heusler Alloys

    NASA Astrophysics Data System (ADS)

    Nath, Hrusikesh; Phanikumar, Gandham

    2015-11-01

    Compositional instability and phase formation in Ni-Fe-Ga Heusler alloys are investigated. The alloys are synthesized into two-phase microstructure. Their structures are identified as fcc and L 21, respectively. The γ-phase formation could be suppressed with higher Ga-content in the alloy as Ga stabilizes austenite phase, but Ga lowers the martensite transformation temperature. The increase of Fe content improves the magnetization value and the increase of Ni from 52 to 55 at. pct raises the martensite transformation temperature from 216 K to 357 K (-57 °C to 84 °C). Magnetic properties and martensitic transformation behavior in Ni-Fe-Ga Heusler alloys follow opposite trends, while Ni replaces either Fe or Ga, whereas they follow similar trends, while Fe replaces Ga. Modulated martensite structure has low twinning stress and high magneto crystalline anisotropic properties. Thus, the observation of 10- and 14 M-modulated martensite structures in the studied Ni-Fe-Ga Heusler alloys is beneficial for shape memory applications. The interdependency of alloy composition, phase formation, magnetic properties, and martensite transformation are discussed.

  6. Small-angle neutron scattering study of magnetic ordering and inhomogeneity across the martensitic phase transformation in Ni50–xCoxMn₄₀Sn₁₀ alloys

    SciTech Connect

    Bhatti, Kanwal Preet; El-Khatib, S.; Srivastava, Vijay; James, R. D.; Leighton, C.

    2012-04-27

    The Heusler-derived multiferroic alloy Ni50–xCoxMn₄₀Sn₁₀ has recently been shown to exhibit, at just above room temperature, a highly reversible martensitic phase transformation with an unusually large magnetization change. In this work the nature of the magnetic ordering above and below this transformation has been studied in detail in the critical composition range x = 6–8 via temperature-dependent (5–600 K) magnetometry and small-angle neutron scattering (SANS). We observe fairly typical paramagnetic to long-range-ordered ferromagnetic phase transitions on cooling to 420–430 K, with the expected critical spin fluctuations, followed by first-order martensitic phase transformations to a nonferromagnetic state below 360–390 K. The static magnetization reveals complex magnetism in this low-temperature nonferromagnetic phase, including a Langevin-like field dependence, distinct spin freezing near 60 K, and significant exchange bias effects, consistent with superparamagnetic blocking of ferromagnetic clusters of nanoscopic dimensions. We demonstrate that these spin clusters, whose existence has been hypothesized in a variety of martensitic alloys exhibiting competition between ferromagnetic and antiferromagnetic exchange interactions, can be directly observed by SANS. The scattering data are consistent with a liquidlike spatial distribution of interacting magnetic clusters with a mean center-to-center spacing of 12 nm. Considering the behavior of the superparmagnetism, cooling-field and temperature-dependent exchange bias, and magnetic SANS, we discuss in detail the physical form and origin of these spin clusters, their intercluster interactions, the nature of the ground-state magnetic ordering in the martensitic phase, and the implications for our understanding of such alloy systems.

  7. Dislocation structure of martensitic transformation in carbon steel

    NASA Astrophysics Data System (ADS)

    Satdarova, F. F.

    2016-04-01

    The developed method of diffraction analysis has shown that the martensitic transformation in iron crystals with the interstitial carbon atoms produces the highest natural density of dislocations in metals. The transformation occurs via microscopic shears, which collectively rearrange the lattice. This process becomes more evident due to the high concentration of fine dislocation loops, which has initially been identified in cubic and then in tetragonal martensite crystals.

  8. Nanoscale Twinning and Martensitic Transformation in Shock-Deformed BCC Metals

    SciTech Connect

    Hsiung, L L

    2005-03-22

    Shock-induced twinning and martensitic transformation in BCC-based polycrystalline metals (Ta and U-6wt%Nb) have been observed and studied using transmission electron microscopy (TEM). The length-scale of domain thickness for both twin lamella and martensite phase is found to be smaller than 100 nm. While deformation twinning of {l_brace}112{r_brace}<111>-type is found in Ta when shock-deformed at 15 GPa, both twinning and martensitic transformation are found in Ta when shock-deformed at 45 GPa. Similar phenomena of nanoscale twinning and martensitic transformation are also found in U6Nb shock-deformed at 30 GPa. Since both deformation twinning and martensitic transformation occurred along the {l_brace}211{r_brace}{sub b} planes associated with high resolved shear stresses, it is suggested that both can be regarded as alternative paths for shear transformations to occur in shock-deformed BCC metals. Heterogeneous nucleation mechanisms for shock-induced twinning and martensitic transformation are proposed and discussed.

  9. Microstructure and martensitic transformation in the Fe-Mn-Al-Ni shape memory alloy with B2-type coherent fine particles

    NASA Astrophysics Data System (ADS)

    Omori, T.; Nagasako, M.; Okano, M.; Endo, K.; Kainuma, R.

    2012-12-01

    Microstructure and martensitic transformation yielding a magnetic change were investigated for Fe43.5Mn34Al15Ni7.5 alloy with B2-type fine precipitates. Thermoelastic martensitic transformation from the ferromagnetic parent phase to the weak magnetic martensite with a nano-twinned fcc structure was confirmed. High-angle annular dark-field scanning transmission electron microscopic observation revealed that a β particle of about 10 nm maintains coherency with the matrix martensite phase, even though distorted due to the martensitic transformation. The martensitic transformation temperatures decreased about 75 K by application of a magnetic field of 70 kOe and magnetic field-induced reverse martensitic transformation was confirmed.

  10. Martensitic nature of {delta} {yields} {gamma} allotropic transformation in plutonium

    SciTech Connect

    Lopez, P.C.; Cost, J.R.; Axler, K.M.

    1996-09-01

    Isothermal and isoplethal studies using differential scanning calorimetry have been conducted to characterize the allotropic transformations of plutonium. The {delta}-{gamma} transformation (upon cooling) was observed to have a classic martensitic nature. The work described herein is the first quantitative study of this phenomena in plutonium.

  11. Martensitic transformation, shape memory effects, and other curious mechanical effects

    SciTech Connect

    Vandermeer, R.A.

    1982-01-08

    The objective of this paper is to review tutorially the subject of martensitic transformations in uranium alloys emphasizing their role in the shape memory effect (SME). We examine first what a martensitic transformation is, illustrating some of its characteristics with specific examples. As well as being athermal in nature, as expected, data are presented indicating that martensitic transformations in some uranium alloys also have a strong isothermal component. In addition, a few alloys are known to exhibit thermoelastic martensitic reactions. The SME, which is associated with these, is defined and demonstrated graphically with data from a uranium-6 wt % niobium alloy. Some of the important variables influencing SME behavior are described. Specifically, these are reheat temperature, amount of deformation, crystal structure, and composition. A mechanism for SME is postulated and the association with martensitic transformation is detailed. A self-induced shape instability in the uranium-7.5 wt % niobium-2.5 wt % zirconium alloy with a rationalization of the behavior in terms of texture and lattice parameter change during aging is reviewed and discussed. 24 figures.

  12. A new type of Cu-Al-Ta shape memory alloy with high martensitic transformation temperature

    NASA Astrophysics Data System (ADS)

    Wang, C. P.; Su, Y.; Y Yang, S.; Shi, Z.; Liu, X. J.

    2014-02-01

    In this study, a new type of Cu-Al-Ta (Cu86Al12Ta2 wt%) shape memory alloy with high martensitic transformation temperature is explored. The microstructure, reversible martensitic transformation and shape memory properties are investigated by means of optical microscopy, back-scattered electron, electron probe microanalysis, x-ray diffraction, differential scanning calorimetry and tensile tests. It is proposed that Cu86Al12Ta2 alloy consists of a mixture of primarily {\\beta }_{1}^{\\prime} martensite and a little {\\gamma }_{1}^{\\prime} martensite and some different precipitates. The tiny thin-striped Ta2(Al,Cu)3 precipitate is predominant in the as-quenched condition, whereas the particle-shaped Cu(Al, Ta) precipitate is dominant after hot-rolling. Additionally, the dendritic-shaped γ1(Cu9Al4) phase begins to appear after hot-rolling, but it disappears when the sample is re-quenched. All studied samples have reversible martensitic transformation temperatures higher than 450 ° C. The results show that two-step martensitic transformation behavior is observed for Cu86Al12Ta2 alloy in all three different conditions due to the transformations between ({\\beta }_{1}^{\\prime}+{\\gamma }_{1}^{\\prime}) martensites and the austenite parent phase. The results further show that the recovery ratios are almost 100% when the pre-strains are ≤2.5%, then they gradually decrease with further increase of the pre-strains. The shape memory effects clearly increase as a result of increase of the pre-strains, up to a maximum value of 3.2%.

  13. Modeling of martensitic transformation in adaptive composites

    NASA Astrophysics Data System (ADS)

    Slutsker, J.; Artemev, A.; Roitburd, A. L.

    2003-10-01

    The formation of elastic domains in transforming constrained films is a mechanism of relaxation of internal stresses caused by the misfit between a film and a substrate. The formation and evolution of polydomain microstructure as a result of the cubic-tetragonal transformation in a constrained layer are investigated by phasefield simulation. It has been shown that the three-domain hierarchical structure can be formed in the epitaxial films. With changing a fraction of out-of-plane domain there are two types of morphological transitions: from the three-domain structure to the two-domain one and from the hierarchical three-domain structure to the cellular three-domain structure. The results of the phase-field simulation are compared with available experimental data.

  14. Martensitic transformations in high-strength steels at aging

    NASA Astrophysics Data System (ADS)

    Berezovskaya, V. V.; Bannykh, O. A.

    2011-04-01

    The effect of heat treatment and elastic stresses on the texture of maraging NiTi-steels is studied. The interruption of the decomposition of martensite at the early stages is shown to be accompanied by the γ → α transformation, which proceeds upon cooling from the aging temperature and under elastic (σ < σ0.2) tensile stresses. The martensite has a crystallographic texture, which is caused by the evolution of hot-deformation texture as a result of quenching and decomposition of a supersaturated α solid solution.

  15. Effect of Annealing in Magnetic Field on Ferromagnetic Nanoparticle Formation in Cu-Al-Mn Alloy with Induced Martensite Transformation

    NASA Astrophysics Data System (ADS)

    Titenko, Anatoliy; Demchenko, Lesya

    2016-05-01

    The paper considers the influence of aging of high-temperature phase on subsequent martensitic transformation in Cu-Al-Mn alloy. The morphology of behavior of martensitic transformation as a result of alloy aging under annealing in a constant magnetic field with different sample orientation relatively to the field direction and without field was studied for direct control of the processes of martensite induction at cooling. Temperature dependences of electrical resistance, magnetic susceptibility, and magnetization, as well as field dependences of magnetization, and phase composition were found. The tendency to the oriented growth of precipitated ferromagnetic phase nanoparticles in a direction of applied field and to an increase of their volume fraction under thermal magnetic treatment of material that favors a reversibility of induced martensitic transformation is observed.

  16. Effect of Annealing in Magnetic Field on Ferromagnetic Nanoparticle Formation in Cu-Al-Mn Alloy with Induced Martensite Transformation.

    PubMed

    Titenko, Anatoliy; Demchenko, Lesya

    2016-12-01

    The paper considers the influence of aging of high-temperature phase on subsequent martensitic transformation in Cu-Al-Mn alloy. The morphology of behavior of martensitic transformation as a result of alloy aging under annealing in a constant magnetic field with different sample orientation relatively to the field direction and without field was studied for direct control of the processes of martensite induction at cooling. Temperature dependences of electrical resistance, magnetic susceptibility, and magnetization, as well as field dependences of magnetization, and phase composition were found. The tendency to the oriented growth of precipitated ferromagnetic phase nanoparticles in a direction of applied field and to an increase of their volume fraction under thermal magnetic treatment of material that favors a reversibility of induced martensitic transformation is observed. PMID:27142875

  17. Ferromagnetic interactions and martensitic transformation in Fe doped Ni-Mn-In shape memory alloys

    SciTech Connect

    Lobo, D. N.; Priolkar, K. R.; Emura, S.; Nigam, A. K.

    2014-11-14

    The structure, magnetic, and martensitic properties of Fe doped Ni-Mn-In magnetic shape memory alloys have been studied by differential scanning calorimetry, magnetization, resistivity, X-ray diffraction (XRD), and EXAFS. While Ni{sub 2}MnIn{sub 1−x}Fe{sub x} (0 ≤ x ≤ 0.6) alloys are ferromagnetic and non martensitic, the martensitic transformation temperature in Ni{sub 2}Mn{sub 1.5}In{sub 1−y}Fe{sub y} and Ni{sub 2}Mn{sub 1.6}In{sub 1−y}Fe{sub y} increases for lower Fe concentrations (y ≤ 0.05) before decreasing sharply for higher Fe concentrations. XRD analysis reveals presence of cubic and tetragonal structural phases in Ni{sub 2}MnIn{sub 1−x}Fe{sub x} at room temperature with tetragonal phase content increasing with Fe doping. Even though the local structure around Mn and Ni in these Fe doped alloys is similar to martensitic Mn rich Ni-Mn-In alloys, presence of ferromagnetic interactions and structural disorder induced by Fe affect Mn-Ni-Mn antiferromagnetic interactions resulting in suppression of martensitic transformation in these Fe doped alloys.

  18. Chirality Switching by Martensitic Transformation in Protein Cylindrical Crystals: Application to Bacterial Flagella

    NASA Astrophysics Data System (ADS)

    Komai, Ricardo Kiyohiro

    Martensitic transformations provide unique engineering properties that, when designed properly, become important parts of new technology. Martensitic transformations have been studied for many years in traditional alloys (iron, steel, titanium, etc.), however there is still much to be learned in regards to these transformations in biological materials. Olson and Hartman showed in 1982 that these transformations are also observed in bacterial flagella and T4 bacteriophage viral sheaths, allowing for propulsion of bacteria in a fluid environment and, for the virus, is responsible for the infection mechanism. This work demonstrates, using the bacterial flagella as an example, that these transformations can be modelled using thermodynamic methods that are also used to model the transformations in alloys. This thesis work attempts to explain the transformations that occur in bacterial flagella, which are capable of small strain, highly reversible martensitic transformations. The first stress/temperature phase diagrams of these flagella were created by adding the mechanical energy of the transformation of the flagella to limited chemical thermodynamics information of the transformation. Mechanical energy is critical to the transformation process because the bacterial body applies a torque to the radius of the flagella. Finally, work has begun and will be completed in regards to understanding the kinetics of the transformation of the flagella. The motion of the transformation interface can be predicted by using a Landau-Ginzburg model. The crystallography of the transformation in bacterial flagella is also being computed to determine the invariant lines of transformation that occur within this cylindrical crystal. This work has shown that it is possible to treat proteins in a similar manner that alloys are treated when using thermodynamic modelling. Much can be learned from translating what is known regarding phase transformations in hard material systems to soft, organic

  19. Study of the martensitic transformation in the Co-9 at % Al alloy

    NASA Astrophysics Data System (ADS)

    Kazantseva, N. V.; Stepanova, N. N.; Vinogradova, N. I.; Demakov, S. L.; Yurovskikh, A. S.; Davydov, D. I.; Shishkin, D. A.; Rigmant, M. B.; Romanov, E. P.

    2016-01-01

    Phase transformations in the Co-9 at % Al have been investigated after slow furnace cooling. It has been shown that the structure and phase composition of the alloy after slow cooling do not correspond to the equilibrium phase diagram of the alloy of this chemical composition. It has been established that the α → ɛ martensitic transformation does not require overcooling and occurs even during a slow cooling of the alloy. It has been found that the formation of 4 H modulated martensite is a specific feature of the binary alloys of cobalt and is not connected with the rate of their cooling. The Curie temperatures for the B2, α, and ɛ phases have been determined.

  20. First-principles investigation of possible martensitic transformation and magnetic properties of Heusler-type Pt2-xMn1+xIn alloys

    NASA Astrophysics Data System (ADS)

    Feng, Lin; Zhang, Wenxing; Liu, Enke; Wang, Wenhong; Wu, Guangheng

    2015-06-01

    The phase stability, electronic structure and magnetism of Pt2-xMn1+xIn (x = 0, 0.25, 0.5, 0.75, 1) alloys are studied by first-principles calculations. The possible magnetic martensitic transformation in this series has been investigated. For all the five compounds, the energy minimums occur around c/a = 1.30, and the energy differences between the austenitic and martensitic phases are large enough to overcome the resistance of phase transformation. By comparing the electronic structures of austenitic and martensitic phases, we can find that the phase stability is enhanced by the martensitic transformation. The magnetic structures of the austenitic and martensitic phases are also discussed.

  1. First principles calculations for analysis martensitic transformations

    SciTech Connect

    Harmon, B.N.; Zhao, G.L.; Ho, K.M.; Chan, C.T.; Ye, Y.Y.; Ding, Y.; Zhang, B.L.

    1993-10-01

    The change in crystal energy is calculated for atomic displacements corresponding to phonons, elastic shears, and lattice transformations. Anomalies in the phonon dispersion curves of NiAl and NiTi are analyzed and recent calculations for TiPd alloys are presented.

  2. Stress-induced martensitic transformation in metastable austenitic stainless steels: Effect on fatigue crack growth rate

    NASA Astrophysics Data System (ADS)

    Khan, Z.; Ahmed, M.

    1996-04-01

    This paper addresses the influence of cyclic stress-induced martensitic transformation on fatigue crack growth rates in metastable austenitic stainless steels. At low applied stress and mean stress values in AISI type 301 stainless steel, fatigue crack growth rate is substantially retarded due to a cyclic stress-induced γ-α' and γ-ɛ martensitic transformation occurring at the crack-tip plastic zone. It is suggested that the transformation products produce a compressive residual stress at the tip of the fatigue crack, which essentially lowers the effective stress intensity and hence retards the fatigue crack growth rate. At high applied stress or mean stress values, fatigue crack growth rates in AISI type 301 steels become almost equal to those of stable AISI type 302 alloy. As the amount of transformed products increases (with an increase in applied or mean stress), the strain-hardening effect brought about by the transformed martensite phase appears to accelerate fatigue crack growth, offsetting the contribution from the compressive residual stress produced by the positive volume change of γ → α' or ɛ transformation.

  3. Non-instantaneous growth characteristics of martensitic transformation in high Cr ferritic creep-resistant steel

    NASA Astrophysics Data System (ADS)

    Liu, Chenxi; Shao, Yi; Chen, Jianguo; Liu, Yongchang

    2016-08-01

    Microstructural observation and high-resolution dilatometry were employed to investigate kinetics of martensitic transformation in high Cr ferritic creep-resistant steel upon different quenching/cooling rates. By incorporating the classical athermal nucleation and impingement correction, a non-instantaneous growth model for martensitic transformation has been developed. The developed model describes austenite/martensite interface mobility during martensite growth. The growth rate of martensite is found to be varied from 1 × 10-6 to 3 × 10-6 m/s. The low interface mobility suggests that it is not appropriate to presume the instantaneous growth behavior of martensite. Moreover, based on the proposed model, nucleation rate of martensite under different cooling rates is found to be nearly the same, while the growth rate of martensite is promoted by increasing the cooling rate.

  4. Structure and thermoelastic martensitic transformations in ternary Ni-Ti-Hf alloys with a high-temperature shape memory effect

    NASA Astrophysics Data System (ADS)

    Pushin, V. G.; Kuranova, N. N.; Pushin, A. V.; Uksusnikov, A. N.; Kourov, N. I.

    2016-07-01

    The effect of alloying by 12-20 at % Hf on the structure, the phase composition, and the thermoelastic martensitic transformations in ternary alloys of the quasi-binary NiTi-NiHf section is studied by transmission electron microscopy, scanning electron microscopy, electron diffraction, and X-ray diffraction. The electrical resistivity is measured at various temperatures to determine the critical transformation temperatures. The data on phase composition are used to plot a full diagram for the high-temperature thermoelastic B2 ↔ B19' martensitic transformations, which occur in the temperature range 320-600 K when the hafnium content increases from 12 to 20 at %. The lattice parameters of the B2 and B19' phases are measured, and the microstructure of the B19' martensite is analyzed.

  5. Fatigue Hardening Behavior of 1.5 GPa Grade Transformation-Induced Plasticity-Aided Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Sugimoto, Koh-Ichi; Hojo, Tomohiko

    2016-04-01

    Low cycle fatigue hardening/softening behavior of a 0.2 pct C-1.5 pct Si-1.5 pct Mn-1.0 pct Cr-0.2 pct Mo-0.05 pct Nb transformation-induced plasticity (TRIP)-aided steel consisting of a wide lath martensite structure matrix and a narrow lath martensite-metastable retained austenite mixture was investigated. The steel exhibited notable fatigue hardening in the same way as TRIP-aided bainitic ferrite steel, although conventional martensitic steel such as SCM420 steel with the same tensile strength exhibited fatigue softening. The considerable fatigue hardening of this steel is believed to be associated mainly with the compressive internal stress that results from a difference in flow stress between the matrix and the martensite-austenite-like phase, with a small contribution from the strain-induced transformation and dislocation hardenings.

  6. On the interpretation of differential scanning calorimetry results for thermoelastic martensitic transformations: Athermal versus thermally activated kinetics

    SciTech Connect

    Van Humbeeck, J.; Planes, A.

    1996-05-01

    Experimentally, two distinct classes of martensitic transformations are considered: athermal and isothermal. In the former class, on cooling, at some well-defined start temperature (M{sub s}), isolated small regions of the martensitic product begin to appear in the parent phase. The transformation at any temperature appears to be instantaneous in practical time scales, and the amount of transformed material (x) does not depend on time, i.e., it increases at each step of lowering temperature. The transition is not completed until the temperature is lowered below M{sub f} (martensite finish temperature). The transformation temperatures are only determined by chemical (composition and degree of order) and microstructural factors. The external controlling parameter (T or applied stress) determines the free energy difference between the high and the low temperature phases, which provides the driving force for the transition. In the development of athermal martensite activation kinetics is secondary. Athermal martensite, as observed in the well known shape memory alloys Cu-Zn-Al, Cu-Al-Ni and Ni-Ti, cannot be attributed to a thermally activated mechanism for which kinetics are generally described by the Arrhenius rate equation. However, the latter has been applied by Lipe and Morris to results for the Martensitic Transformation of Cu-Al-Ni-B-Mn obtained by conventional Differential Scanning Calorimetry (DSC). It is the concern of the authors of this letter to point out the incongruences arising from the analysis of calorimetric results, corresponding to forward and reverse thermoelastic martensitic transformations, in terms of standard kinetic analysis based on the Arrhenius rate equation.

  7. Optical and magneto-optical studies of martensitic transformation in Ni-Mn-Ga magnetic shape memory alloys

    SciTech Connect

    Beran, L.; Cejpek, P.; Kulda, M.; Antos, R.; Holy, V.; Veis, M.; Straka, L.; Heczko, O.

    2015-05-07

    Optical and magneto-optical properties of single crystal of Ni{sub 50.1}Mn{sub 28.4}Ga{sub 21.5} magnetic shape memory alloy during its transformation from martensite to austenite phase were systematically studied. Crystal orientation was approximately along (100) planes of parent cubic austenite. X-ray reciprocal mapping confirmed modulated 10 M martensite phase. Temperature depended measurements of saturation magnetization revealed the martensitic transformation at 335 K during heating. Magneto-optical spectroscopy and spectroscopic ellipsometry were measured in the sample temperature range from 297 to 373 K and photon energy range from 1.2 to 6.5 eV. Magneto-optical spectra of polar Kerr rotation as well as the spectra of ellipsometric parameter Ψ exhibited significant changes when crossing the transformation temperature. These changes were assigned to different optical properties of Ni-Mn-Ga in martensite and austenite phases due to modification of electronic structure near the Fermi energy during martensitic transformation.

  8. Optical and magneto-optical studies of martensitic transformation in Ni-Mn-Ga magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Beran, L.; Cejpek, P.; Kulda, M.; Antos, R.; Holy, V.; Veis, M.; Straka, L.; Heczko, O.

    2015-05-01

    Optical and magneto-optical properties of single crystal of Ni50.1Mn28.4Ga21.5 magnetic shape memory alloy during its transformation from martensite to austenite phase were systematically studied. Crystal orientation was approximately along {100} planes of parent cubic austenite. X-ray reciprocal mapping confirmed modulated 10 M martensite phase. Temperature depended measurements of saturation magnetization revealed the martensitic transformation at 335 K during heating. Magneto-optical spectroscopy and spectroscopic ellipsometry were measured in the sample temperature range from 297 to 373 K and photon energy range from 1.2 to 6.5 eV. Magneto-optical spectra of polar Kerr rotation as well as the spectra of ellipsometric parameter Ψ exhibited significant changes when crossing the transformation temperature. These changes were assigned to different optical properties of Ni-Mn-Ga in martensite and austenite phases due to modification of electronic structure near the Fermi energy during martensitic transformation.

  9. Anomalous physical properties of Heusler-type Co2Cr (Ga,Si) alloys and thermodynamic study on reentrant martensitic transformation

    NASA Astrophysics Data System (ADS)

    Xu, Xiao; Nagasako, Makoto; Kataoka, Mitsuo; Umetsu, Rie Y.; Omori, Toshihiro; Kanomata, Takeshi; Kainuma, Ryosuke

    2015-03-01

    Electronic, magnetic, and thermodynamic properties of Co2Cr(Ga,Si) -based shape-memory alloys, which exhibit reentrant martensitic transformation (RMT) behavior, were studied experimentally. For electric resistivity (ER), an inverse (semiconductor-like) temperature dependence in the parent phase was found, along with anomalous behavior below its Curie temperature. A pseudobinary phase diagram was determined, which gives a "martensite loop" clearly showing the reentrant behavior. Differential scanning calorimetry and specific-heat measurements were used to derive the entropy change Δ S between martensite and parent phases. The temperature dependence of the derived Δ S was analyzed thermodynamically to confirm the appearances of both the RMT and normal martensitic transformation. Detailed studies on the specific heat in martensite and parent phases at low temperatures were also conducted.

  10. Role of Chemical Driving Force in Martensitic Transformations of High-Purity Fe-Cr-Ni Alloys

    NASA Astrophysics Data System (ADS)

    Behjati, P.; Najafizadeh, A.

    2011-12-01

    The main objective of the present work is to point out the respective roles of chemical driving force and stacking fault energy (SFE) in the occurrence of martensitic transformations in high-purity Fe-Cr-Ni alloys. For this purpose, the transmission electron microscope (TEM), X-ray diffractometer, thermal differential microanalyzer (TDA), and tension test were employed to report M s temperatures, austenite stacking fault energies, and driving forces for the concerned alloys. It was observed that the martensitic transformations in the studied alloys occur through the γ → ɛ → α' steps. As a remarkable result, it was shown that a low SFE, if necessary to ɛ-phase nucleation, is not a sufficient condition for nucleation of α' phase. In fact, the formation of stable α' nuclei from α' embryos occur if the required chemical driving force is provided. Also, an equation was proposed for the kinetics of spontaneous martensitic transformation as a function of driving force.

  11. A structured continuum modelling framework for martensitic transformation and reorientation in shape memory materials.

    PubMed

    Bernardini, Davide; Pence, Thomas J

    2016-04-28

    Models for shape memory material behaviour can be posed in the framework of a structured continuum theory. We study such a framework in which a scalar phase fraction field and a tensor field of martensite reorientation describe the material microstructure, in the context of finite strains. Gradients of the microstructural descriptors naturally enter the formulation and offer the possibility to describe and resolve phase transformation localizations. The constitutive theory is thoroughly described by a single free energy function in conjunction with a path-dependent dissipation function. Balance laws in the form of differential equations are obtained and contain both bulk and surface terms, the latter in terms of microstreses. A natural constraint on the tensor field for martensite reorientation gives rise to reactive fields in these balance laws. Conditions ensuring objectivity as well as the relation of this framework to that provided by currently used models for shape memory alloy behaviour are discussed. PMID:27002064

  12. Narrowing of hysteresis of cubic-tetragonal martensitic transformation by weak axial stressing of ferromagnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Kosogor, Anna

    2016-06-01

    An influence of axial mechanical stress on the hysteresis of martensitic transformation and ordinary magnetostriction of ferromagnetic shape memory alloy has been described in the framework of a Landau-type theory of phase transitions. It has been shown that weak stress can noticeably reduce the hysteresis of martensitic transformation. Moreover, the anhysteretic deformation can be observed when the applied mechanical stress exceeds a critical stress value. The main theoretical results were compared with recent experimental data. It is argued that shape memory alloys with extremely low values of shear elastic modulus are the candidates for the experimental observation of large anhysteretic deformations.

  13. Thermoelastic Martensitic Transformations in Single Crystals of FeNiCoAlX(B) Alloys

    NASA Astrophysics Data System (ADS)

    Chumlyakov, Yu. I.; Kireeva, I. V.; Kuts, O. A.; Platonova, Yu. N.; Poklonov, V. V.; Kukshauzen, I. V.; Kukshauzen, D. A.; Panchenko, M. Yu.; Reunova, K. A.

    2016-03-01

    Using single crystals of Fe-based disordered alloys (Fe - 28% Ni - 17% Co - 11.5% Al - 2.5% X (0.05% B) (at.%) (X = Ti, Nb(B), (Ti + Nb)B), undergoing thermoelastic γ-α '-martensitic transformations (MTs), it is shown that precipitation of particles of the ordered γ'-phase in the course of aging at T = 973 K for 5 h results in the development of shape memory (SME) and superelasticity (SE) effects. It is experimentally found that variation in chemical composition and size of disperse particles of the γ'-phase allows controlling both mechanical and functional properties - SME and SE.

  14. Energetic shape recovery associated with martensitic transformation in shape-memory alloys

    SciTech Connect

    Golestaneh, A.A.

    1980-01-01

    The present paper contains an investigation of the mechanical energy associated with the transformation of the stress-induced martensite, ..beta..', to the parent phase, ..beta.., during the shape recovery (SR) of a deformed shape-memory (SM) material. We describe a heat-mechanical energy converter, or solid-state engine, which operates by this SR phenomenon. The energy output of such an engine is expressed in terms of a fraction ..cap alpha.. of the latent heat ..delta..H of the martensitic reaction. This ..cap alpha.. is found to depend on two parameters. One is the difference between the ..delta..H of the ..beta..' ..-->.. ..beta.. reaction and the ..delta..H of the transformation of the quench-induced martensite, ..gamma..', to ..beta.., the other is the fraction of ..gamma..' which can be transformed via the channel ..gamma..' ..-->.. ..beta..' ..-->.. ..beta.. instead of the direct channel ..gamma..' ..-->.. ..beta... Moreover, it is shown that within certain ranges of temperature T and applied strain epsilon, the heat-mechanical energy balance equation leads to an expression identical in form to the Clapeyron-Clausius equation, which is usually valid for a first-order transition. Within these epsilon and T ranges the coefficient ..cap alpha.. is also found to be equal to log (T/sub csigma//T/sub c/) where T/sub csigma/ and T/sub c/ are the SR critical temperatures with and without the presence of an applied stress sigma, respectively. We discuss the role of the ..gamma..' martensite in this process and explain the so-called two-way SR phenomenon. In addition, the parameters that limit the output of the SR energy are evaluated. This output depends sensitively on both ..cap alpha.. and the material characteristic temperature h = C/sup -1/..delta..H, where C is the specific heat. For a solid-state engine made with the Ni-Ti SM alloy, the efficiency is found to be limited to about 5%.

  15. Martensitic Transformation During Compressive Deformation of a Non-conventional Stainless Steel and Its Quantitative Assessment

    NASA Astrophysics Data System (ADS)

    Kreethi, R.; Sampark, P.; Majhi, Goutam Kumar; Dutta, Krishna

    2015-11-01

    This report aims to examine the extent of deformation-induced phase transformation in a non-conventional austenitic stainless steel known as ISO/TR 15510 X12CrMnNiN17-7-5, upon compressive loading at room temperature. Experiments were carried out under varying length to diameter ratios (0.8, 1.0, 1.2, 1.4, and 1.6). TFE (Tetrafluoroethylene)-fluorocarbon tapes were used at specimen-platen interfaces to reduce the effect of friction. The results indicate that the lubrication was effective up to 15% of strain. Optical microscopy and x-ray diffraction (XRD) studies indicated martensitic phase transformation in the deformed specimens. The extent of phase transformation was determined by analyzing the XRD peaks using integrated intensity of the corresponding phases. The results are correlated with the extent of deformation in the respective samples. The presence of γ and α'-martensite on the deformed samples has been substantiated by some limited experiments using transmission electron microscopy.

  16. Irreversibility of the martensitic transformation in Ni-Mn-In single crystal studied by resistivity under pressure and in situ optical observations

    NASA Astrophysics Data System (ADS)

    Porcar, L.; Courtois, P.; Crouigneau, G.; Debray, J.; Bourgault, D.

    2014-10-01

    Optical observations under uniaxial pressure and in-situ resistivity measurements were undertaken in Ni-Mn-In single crystals as a function of temperature to study the thermal hysteresis of the martensitic transformation. The irreversibility of the isothermal transformation under pressure was clearly observed, and it was possible to stabilize the martensitic phase with large and coarsen variants by applying a pressure at a stable temperature Ms reached during cooling down (cooling branch of the hysteresis). When the uniaxial pressure is applied in the heating branch of the hysteresis, the martensitic transformation occurs in a complete reversible way as the hysteresis delimitates the metastability of the martensitic/austenitic phases and the energy barrier to overcome for the transformation. This procedure leads to a piezoresistance as large as 200%.

  17. Phase transformations in engineering materials

    SciTech Connect

    Bourke, M.A.M.; Lawson, A.C.; Dunand, D.C.; Priesmeyer, H.G.

    1996-06-01

    Phase transformations in engineering materials are inevitably related to mechanical behavior and are often precursors to residual stress and distortion. Neutron scattering in general is a valuable tool for studying their effects, and pulsed neutrons are of special value, because of the inherently comprehensive crystallographic coverage they provide in each measurement. At the Manuel Lujan neutron scattering center several different research programs have addressed the relationships between phase transformation/mechanical behavior and residual strains. Three disparate examples are presented; (1) stress induced transformation in a NiTi shape memory alloy, (2) cryogenically induced transformation in a quenched 5180 steel, and (3) time resolved evolution of strain induced martensite in 304 stainless steel. In each case a brief description of the principle result will be discussed in the context of using neutrons for the measurement.

  18. Gradient Distribution of Martensite Phase in Melt-Spun Ribbons of a Fe-Ni-Ti-Al Alloy

    NASA Astrophysics Data System (ADS)

    Bondar, Volodymyr; Danilchenko, Vitalij; Dzevin, Ievgenij

    2016-02-01

    Metallographic, X-ray diffraction and magnetometric analysis were used to study the regularities of martensitic transformation in melt-spun ribbons of a Fe - 28 wt. % Ni - 2.1 wt. % Ti - 2 wt. % Al - 0.05 wt. % C alloy. The substantial differences in volume fractions of the martensite phase in local regions of thin melt-spun ribbons of the alloy are related to the size effect of the transformation and structural inhomogeneity of the ribbons. The distribution of austenitic grain size in different local areas of melt-spun ribbons is significantly different. The principal factor for changing the completeness of the martensitic transformation is the size effect of transformation. Difference in the martensite volume fraction in local regions of a ribbon is mainly determined by the different volume fractions of ultrafine-grained (500-1000 nm) and nanosized (80-100 nm and less) initial austenite grains, in which the transformation was slowed down or completely suppressed. Other factors almost do not affect the completeness of the martensitic transformation. The strong stabilizing effect of the reverse α-γ transformation with respect to the subsequent direct γ-α transformation in the melt-spun ribbons is also related to the grain size effect.

  19. Gradient Distribution of Martensite Phase in Melt-Spun Ribbons of a Fe-Ni-Ti-Al Alloy.

    PubMed

    Bondar, Volodymyr; Danilchenko, Vitalij; Dzevin, Ievgenij

    2016-12-01

    Metallographic, X-ray diffraction and magnetometric analysis were used to study the regularities of martensitic transformation in melt-spun ribbons of a Fe - 28 wt. % Ni - 2.1 wt. % Ti - 2 wt. % Al - 0.05 wt. % C alloy. The substantial differences in volume fractions of the martensite phase in local regions of thin melt-spun ribbons of the alloy are related to the size effect of the transformation and structural inhomogeneity of the ribbons. The distribution of austenitic grain size in different local areas of melt-spun ribbons is significantly different. The principal factor for changing the completeness of the martensitic transformation is the size effect of transformation. Difference in the martensite volume fraction in local regions of a ribbon is mainly determined by the different volume fractions of ultrafine-grained (500-1000 nm) and nanosized (80-100 nm and less) initial austenite grains, in which the transformation was slowed down or completely suppressed. Other factors almost do not affect the completeness of the martensitic transformation. The strong stabilizing effect of the reverse α-γ transformation with respect to the subsequent direct γ-α transformation in the melt-spun ribbons is also related to the grain size effect. PMID:26897002

  20. The Formation of Crystal Defects in a Fe-Mn-Si Alloy Under Cyclic Martensitic Transformations.

    PubMed

    Bondar, Vladimir I; Danilchenko, Vitaliy E; Iakovlev, Viktor E

    2016-12-01

    Formation of crystalline defects due to cyclic martensitic transformations (CMT) in the iron-manganese Fe-18 wt.% Mn-2 wt.% Si alloy was investigated using X-ray diffractometry. Conditions for accumulation of fragment sub-boundaries with low-angle misorientations and chaotic stacking faults in crystal lattice of austenite and ε-martensite were analyzed. PMID:26960743

  1. Stress-induced martensitic transformations in NiTi and NiTi-TiC composites investigated by neutron diffraction

    SciTech Connect

    Vaidyanathan, R.; Bourke, M.A.M.; Dunand, D.C.

    1998-12-31

    Superelastic NiTi (51.0 at% Ni) with 0, 10 and 20 vol% TiC particles were deformed under uniaxial compression as neutron diffraction spectra were simultaneously obtained. The experiments yielded in-situ measurements of the thermoelastic stress-induced transformation. A detailed Rietveld determination is made of the phase fractions and the evolving strains in the reinforcing TiC particles and the austenite as it transforms to martensite on loading (and its subsequent back transformation on unloading). These strains are used to shed light on the phenomenon of load transfer in composites where the matrix undergoes a stress-induced phase transformation.

  2. In situ SEM studies of the transformation sequence of multistage martensitic transformations in aged Ti-50.8 at.% Ni alloys

    NASA Astrophysics Data System (ADS)

    Karbakhsh Ravari, B.; Nishida, M.

    2013-06-01

    The transformation behaviour of the multistage martensitic transformation in aged Ti-50.8 at.% Ni alloys was investigated by differential scanning calorimetry (DSC) and in situ scanning electron microscopy (SEM). The specimens aged from 673 to 748 K for 3.6 ks under an unregulated heat treatment atmosphere exhibited the double-stage transformation during cooling. The quadruple-stage transformation was observed in the specimens aged at 773 and 798 K, and the triple-stage transformation appeared in the specimen aged at 823 K under an unregulated heat treatment atmosphere. The distribution and size of Ti3Ni4 precipitates were heterogeneous in these specimens. The single-stage transformation in the specimen aged at 848 K was similar to that of the solution-treated specimen. In the forward quadruple-stage transformation, the R-phase transformation occurred in the intermediate region and around the grain boundary. The first martensitic transformation, which corresponded to the M1 peak in the DSC cooling curve, took place in the intermediate region of grains via the R phase. The second transformation, which corresponded to the M2 peak, occurred around the grain boundary via the R phase. The final transformation, which corresponded to the M3 peak, arose directly from the B2 parent phase at the grain centre. The transformation sequence and areas described above were quantitatively verified by comparing the SEM observations with the DSC measurements. The transformation sequence of the triple-stage transformation was also discussed.

  3. Micromechanics of stress-induced martensitic transformation in mono- and polycrystalline shape memory alloys: Ni-Ti

    SciTech Connect

    Liang, Y.; Taya, M.; Mori, T.

    1999-07-01

    Stress-induced martensitic transformation in single crystals and polycrystals are examined on the basis of micromechanics. A simple method to find a stress- and elastic energy-free martensite plate (combined variant), which consists of two variants, is presented. External and internal stresses preferentially produce a combined variant, to which the stresses supply the largest work upon its formation. Using the chemical energy change with temperature, the phase boundary between the parent and martensitic phases is determined in stress-temperature diagrams. The method is extended to a polycrystal, modeled as an aggregate of spherical grains. The grains constitute axisymmetric multiple fiber textures and a uniaxial load is applied to the fiber axis. The occurrence and progress of transformation are followed by examining a stress state in the grains. The stress is the sum of the external stress and internal stress. The difference in the fraction of transformation and, thus, in transformation strains between the grains causes the internal stress, which is calculated with the average field method. After a short transition stage, all the grains start to transform, and the external uniaxial stress to continue the transformation increases linearly thereafter. The external stress at the end of the transition is defined as the macroscopic yield stress due to the transformation in polycrystals. The yield stress tends to saturate, as the number of the textures increases.

  4. Nucleation and growth of the Alpha-Prime Phase martensitic phase in Pu-Ga Alloys

    SciTech Connect

    Blobaum, K M; Krenn, C R; Wall, M A; Massalski, T B; Schwartz, A J

    2005-02-09

    In a Pu-2.0 at% Ga alloy, it is observed experimentally that the amount of the martensitic alpha-prime product formed upon cooling the metastable delta phase below the martensite burst temperature (M{sub b}) is a function of the holding temperature and holding time of a prior conditioning (''annealing'') treatment. Before subjecting a sample to a cooling and heating cycle to form and revert the alpha-prime phase, it was first homogenized for 8 hours at 375 C to remove any microstructural memory of prior transformations. Subsequently, conditioning was carried out in a differential scanning calorimeter apparatus at temperatures in the range between -50 C and 370 C for periods of up to 70 hours to determine the holding time and temperature that produced the largest volume fraction of alpha-prime upon subsequent cooling. Using transformation peak areas (i.e., the heats of transformation) as a measure of the amount of alpha-prime formed, the largest amount of alpha-prime was obtained following holding at 25 C for at prime least 6 hours. Additional time at 25 C, up to 70 hours, did not increase the amount of subsequent alpha-prime formation. At 25 C, the Pu-2.0 at% Ga alloy is below the eutectoid transformation temperature in the phase diagram and the expected equilibrium phases are {alpha} and Pu{sub 3}Ga, although a complete eutectoid decomposition of delta to these phases is expected to be extremely slow. It is proposed here that the influence of the conditioning treatment can be attributed to the activation of alpha-phase embryos in the matrix as a beginning step toward the eutectoid decomposition, and we discuss the effects of spontaneous self-irradiation accompanying the Pu radioactive decay on the activation process. Subsequently, upon cooling, certain embryos appear to be active as sites for the burst growth of martensitic alpha-prime particles, and their amount, distribution, and potency appear to contribute to the total amount of martensitic product formed. A

  5. Transformation-rate maxima during lath martensite formation: plastic vs. elastic shape strain accommodation

    NASA Astrophysics Data System (ADS)

    Loewy, Sarah; Rheingans, Bastian; Mittemeijer, Eric J.

    2016-05-01

    Recently, a modulated formation behaviour of lath martensite in Fe-Ni(-based) alloys was observed, exhibiting a series of transformation-rate maxima. This peculiar transformation behaviour was explained on the basis of the hierarchical microstructure of lath martensite, minimising the net shape strain associated with martensite formation, by a block-by-block formation of martensite packages occurring simultaneously in all packages. In the present work, the martensitic transformation upon slow cooling of two Fe-Ni alloys, containing 22 and 25 at.% of Ni, respectively, was investigated by high-resolution dilatometry with the aim of identifying the influence of alloy composition on the modulated transformation behaviour. The differences observed for the two alloys, a more rapid sequence of the transformation-rate maxima and a narrower temperature range in case of Fe-25 at.% Ni, can be explained consistently as a consequence of the lower transformation temperatures in Fe-25 at.% Ni, highlighting the role of temporary accommodation of the shape strain during formation of the lath martensite microstructure: the depression of the transformation toward lower temperatures leads to a higher strength of the austenite, hence resulting in a more elastic (less plastic) temporary accommodation of the shape strain upon block formation and thereby in a more effective mutual compensation of the shape strain by neighbouring blocks. A kinetic model on the basis of energy-change considerations is presented which is able to describe the observed modulated transformation behaviour.

  6. Dynamic theory of morphological characteristics of crystals of ɛ and γ phases, including Headley-Brooks orientation relationships upon the α-ɛ and α-ɛ-γ martensitic transformations

    NASA Astrophysics Data System (ADS)

    Kashchenko, M. P.; Chashchina, V. G.

    2015-10-01

    Different variants of the formation of martensite crystals upon the α-γ transformation caused by the tension-compression deformation of {110}α planes have been considered according to the dynamic theory of martensitic transformations. In contrast to previous works, here we take into account the deviation (angle θ) of the principal directions of deformation from the symmetry axes < {1bar 10} rangle _α and <001>α. It has been shown that the requirement of the symmetry of the arrangement of atoms in the basal plane {0001}ɛ is satisfied in the range of angular deviations-arctan √ {2/3} ≤slant θ ≤slant arctan √ {2/3}. The algorithm for calculating the morphological characteristics is illustrated based on the example of an elastically isotropic medium, which does not require assigning concrete values of elastic moduli. The estimations performed make it possible, in particular, to explain the physical nature of the Headley-Brooks orientation relationships as a result of the inheritance of one of the variants of permissible material orientation relationships for the α-ɛ transformation in the course of the ɛ-γ transformation at θ 35°. The changes in the other morphological signs are also discussed.

  7. Effect of strain on the martensitic phase transition in superconducting Nb/sub 3/Sn

    SciTech Connect

    Hoard, R.W.; Scanlan, R.M.; Smith, G.S.; Farrell, C.L.

    1980-09-22

    The connection between the cubic-to-tetragonal martensitic phase transformation and the phenomenon of superconductivity in A15 compounds is being investigated. The degradation of the critical parameters, such as T/sub c/, H/sub c2/, and J/sub c/, with mechanical straining is of particular interest. Low-temperature x-ray diffraction experiments are performed on Nb/sub 3/Sn ribbons (with the bronze layers etched off) mounted on copper and indium sample stages. The cryostat used is unique in that it has a vacuum mechanical insert which allows the superconductor to be placed under both compressive and tensile strains while at low temperatures. Preliminary results indicate that the martensitic phase transition temperature, T/sub m/, increases with compressive strains. Other effects of strain on tetragonal phase production are also discussed.

  8. The effect of substrate constraint on the martensitic transformation of Ni-Ti thin films

    SciTech Connect

    Mathews, S.A.; Wuttig, M.; Su, Q.

    1996-09-01

    Previous work on an equiatomic alloy of nickel and titanium (nitinol) indicates that the martensitic transformation in thin films may be suppressed by interfacial constraint imposed by the substrate. Ni{sub 50}Ti{sub 50} films were deposited at room temperature on oxidized (100) Si substrates and tested to determine when the martensitic transformation occurred for both attached and free-standing conditions.

  9. High-energy X-ray diffuse scattering studies on deformation-induced spatially confined martensitic transformations in multifunctional Ti-24Nb-4Zr-8Sn alloy

    SciTech Connect

    Liu, J. P.; Wang, Y. D.; Hao, Y. L.; Wang, H. L.; Wang, Y.; Nie, Z. H.; Su, R.; Wang, D.; Ren, Y.; Lu, Z. P.; Wang, J. G.; Hui, X. D.; Yang, R.

    2014-12-01

    Two main explanations exist for the deformation mechanisms in Ti-Nb-based gum metals, i.e. the formation of reversible nanodisturbance and reversible stress-induced martensitic transformation. In this work, we used the in situ synchrotron-based high-energy X-ray diffuse-scattering technique to reveal the existence of a specific deformation mechanism, i.e. deformation-induced spatially confined martensitic transformations, in Ti-24Nb-4Zr-8Sn-0.10O single crystals with cubic 13 parent phase, which explains well some anomalous mechanical properties of the alloy such as low elastic modulus and nonlinear superelasticity. Two kinds of nanosized martensites with different crystal structures were found during uniaxial tensile loading along the [11 0](beta) axis at room temperature and 190 K, respectively. The detailed changes in the martensitic phase transformation characteristics and the transformation kinetics were experimentally observed at different temperatures. The domain switch from non-modulated martensite to a modulated one occurred at 190 K, with its physical origin attributed to the heterogeneity of local phonon softening depending on temperature and inhomogeneous composition in the parent phase. An in-depth understanding of the formation of stress-induced spatially confined nanosized martensites with a large gradient in chemical composition may benefit designs of high-strength and high-ductility alloys. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  10. Mesoscale kinetics produces martensitic microstructure

    NASA Astrophysics Data System (ADS)

    Kastner, Oliver; Ackland, Graeme J.

    2009-01-01

    We present molecular dynamics (MD) simulations of a martensitic phase transformation studying post-transformation microstructure and moving austenite-martensite interfaces. Unlike in energy-minimisation theories, the transformation dynamics dominate the martensite morphology. We use a binary Lennard-Jones potential to describe a square-to-hexagonal transformation by shear-and-shuffle. The high-T stable square lattice and low-T hexagonal lattice represent austenite and martensite, giving four martensitic variants. Compatible twin variants have no lattice misfit and zero interfacial energies which makes our model directly comparable with the crystallographic theory of martensite. Although our dynamical interpretation is different to previous work, our MD simulations exhibit very similar martensitic morphologies to real materials. We observe the nucleation of wedge-shaped, twinned martensite plates, plate growth at narrow, travelling transformation zones, subsonic transformation waves, elastic precursors inducing secondary nucleations and the formation of martensitic domains. Martensite is produced within narrow transformation zones where atoms change their lattice sites in a co-operative manner so as to form crystallographic layers. These motions produce inertia forces on the mesoscopic length-scale which induce the formation of twin variants in the subsequent layers to transform.

  11. Energetic shape recovery associated with martensitic transformation in shape-memory alloys

    SciTech Connect

    Golestaneh, A.A.

    1980-10-01

    The present paper contains an investigation of the mechanical energy associated with the transformation of the stress-induced martensite, ..beta..', to the parent phase, ..beta.., during the shape recovery (SR) of a deformed shape-memory (SM) material. We describe a heat-mechanical energy converter, or solid-state engine, which operates by this SR phenomenon. The energy output of such an engine is expressed in terms of a fraction ..cap alpha.. of the latent heat ..delta..H of the martensitic reaction. This ..cap alpha.. is found to depend on two parameters. One is the difference between the ..delta..H of the ..beta..' ..-->.. ..beta.. reaction and the ..delta..H of the transformation of the quench-induced martensite, ..gamma..', to ..beta.., the other is the fraction of ..gamma..' which can be transformed via the channel ..gamma..' ..-->.. ..beta..' ..-->.. ..beta.. instead of the direct channel ..gamma..' ..-->.. ..beta... Moreover, it is shown that within certain ranges of temperature T and applied strain epsilon, the heat-mechanical energy balance equation leads to an expression identical in form to the Clapeyron-Clausius equation, which is usually valid for a first-order transition. Within these epsilon and T ranges the coefficient ..cap alpha.. is also found to be equal to log(T/sub c sigma//T/sub c/) where T/sub c sigma/ and T/sub c/ are the SR critical temperatures with and without the presence of an applied stress sigma, respectively. We discuss the role of the ..gamma..' martensite in this process and explain the so-called two-way SR phenomenon. In addition, the parameters that limit the output of the SR energy are evaluated. This output depends sensitively on both ..cap alpha.. and the material characteristic temperature h = C/sup -1/..delta..H, where C is the specific heat. For a solid-state engine made with the Ni-Ti SM alloy, the efficiency is found to be limited to about 5%.

  12. Direct evidence for stress-induced transformation between coexisting multiple martensites in a Ni-Mn-Ga multifunctional alloy

    SciTech Connect

    Huang, L.; Cong, D. Y.; Wang, Z. L.; Nie, Z. H.; Dong, Y. H.; Zhang, Y.; Ren, Yang; Wang, Y. D.

    2015-07-08

    The structural response of coexisting multiple martensites to stress field in a Ni-Mn-Ga multifunctional alloy was investigated by the in situ high-energy x-ray diffraction technique. Stress-induced transformation between coexisting multiple martensites was observed at 110 K, at which five-layered modulated (5M), seven-layered modulated (7M) and non-modulated (NM) martensites coexist. We found that a tiny stress of as low as 0.5 MPa could trigger the transformation from 5M and 7M martensites to NM martensite and this transformation is partly reversible. Besides the transformation between coexisting multiple martensites, rearrangement of martensite variants also occurs during loading, at least at high stress levels. The present study is instructive for designing advanced multifunctional alloys with easy actuation.

  13. Direct evidence for stress-induced transformation between coexisting multiple martensites in a Ni-Mn-Ga multifunctional alloy

    SciTech Connect

    Huang, L.; Cong, D. Y.; Wang, Z. L.; Nie, Z. H.; Dong, Y. H.; Zhang, Y.; Ren, Yang; Wang, Y. D.

    2015-06-03

    The structural response of coexisting multiple martensites to stress field in a Ni-Mn-Ga multifunctional alloy was investigated by the in situ high-energy x-ray diffraction technique. Stress-induced transformation between coexisting multiple martensites was observed at 110 K, at which five-layered modulated (5M), seven-layered modulated (7M) and non-modulated (NM) martensites coexist. We found that a tiny stress of as low as 0.5 MPa could trigger the transformation from 5M and 7M martensites to NM martensite and this transformation is partly reversible. Besides the transformation between coexisting multiple martensites, rearrangement of martensite variants also occurs during loading, at least at high stress levels. The present study is instructive for designing advanced multifunctional alloys with easy actuation.

  14. Structure fragmentation in Fe-based alloys by means of cyclic martensitic transformations of different types

    PubMed Central

    2014-01-01

    The effect of martensite transformations of different types on the misorientation of austenite crystalline lattice, which characterizes the degree of structure fragmentation, was investigated for Fe-Ni and Fe-Mn alloys. As a result of multiple face-centered cubic (f.c.c.)-body-centered cubic (b.c.c.)-f.c.c. transformations, an austenite single-crystalline specimen is transformed in a polycrystalline one due to progressive fragmentation. It was shown that the degree of fragmentation depends on the magnitude of volume change and the density of dislocations generated on martensitic transformations. PMID:24565160

  15. Thermodynamic modeling of martensitic transformations in shape memory alloys

    NASA Astrophysics Data System (ADS)

    Guthikonda, Venkata Suresh Reddy

    The unusual properties of shape memory alloys (SMAs) are due to solid-to-solid martensitic transformations (MTs) which correspond to a lattice level instability of the crystal structure. Currently, there exists a shortage of material models that can capture the details of lattice level MTs occurring in SMAs. In the first part of this work, an effective interaction potential (EIP) model is developed for the SMA AuCd. EIPs are atomic interaction potentials that are explicit functions of temperature. In particular, the Morse pair potential is used and its adjustable coefficients are taken to be temperature dependent. A hysteretic temperature-induced MT between the B2 cubic and B19 orthorhombic crystal structures is predicted. This is the behavior that is observed in the real material. The model predicts, to reasonable accuracy, the transformation strain tensor and captures the latent heat and thermal hysteresis to within an order of magnitude. The second part of this work consists of developing a lattice dynamics model to simulate the MTs. The atomic interactions are modeled using temperature independent Morse pair potentials. The effects of atomic vibrations on the material properties are captured using the first-order self-consistent approach which consists of renormalizing the frequencies of atomic vibration using self-consistent equations. These renormalized frequencies are dependent on both configuration and temperature. The model is applied for the case of a one-dimensional bi-atomic chain. The constant Morse pair potential parameters are chosen to demonstrate the usefulness of the current model. The resulting model is evaluated by generating equilibrium paths with temperature and mechanical load as the loading parameters. In both types of loading, a first-order MT is predicted indicating that the current model is able to capture the first-order MTs that occur in SMAs. This qualitative prediction of a first-order MT indicates the likely-hood that the current

  16. Effect of Intercritical Annealing Temperature on Phase Transformations in Medium Carbon Dual Phase Steels

    NASA Astrophysics Data System (ADS)

    Erişir, Ersoy; Bilir, Oğuz Gürkan

    2014-03-01

    This paper presents a study concerning phase transformations during quenching of a medium carbon dual phase steel using thermodynamic equilibrium calculations and dilatometry. Medium carbon steel was subjected to the intermediate quenching to produce a fine grained ferrite/martensite dual phase steel. 4 samples quenched after intercritical annealing at 725, 730, 740, and 750 °C. Martensite-start and bainite-start temperatures were calculated from dilatometric curves using plastodilotemeter. Experimental findings are supported by calculated phase diagrams and equilibrium phase compositions using ThermoCalc® and calculations from different empirical formulas. It is concluded that martensite-start temperature depend on chemical composition and grain size of austenite.

  17. Effects of high magnetic fields on the martensitic transformation and on the mechanical behavior of cryogenic Fe-9Ni steel

    SciTech Connect

    Fior, G.O.

    1984-11-01

    The advancement of high field superconducting magnet technology requires structural steel that can bear large stresses at cryogenic temperatures in the presence of high magnetic fields. One class of candidate materials is high strength ferritic steels, such as Fe-9Ni steel, which are commonly toughened for cryogenic service by a two-phase tempering treatment that forms small austenite (..gamma..) precipitates. A fine dispersion of sub-micron sized ..gamma.. is retained upon cooling to cryogenic temperatures and its presence is believed to play an important role in the suppression of the ductile-to-brittle transition of this materials. The retained ..gamma.., however, is metastable with respect to the martensitic transformation, and since the magnetic properties of ..gamma.. (paramagnetic) differ from those of the martensite (..cap alpha..') matrix (ferromagnetic), it is argued that a high magnetic field will influence the stability of ..gamma... This investigation was devoted to the study of high magnetic field effects on the martensitic transformation of retained ..gamma.. and the corresponding effects on the mechanical properties of cryogenic Fe-9Ni steel. Thermomagnetic exposure to 16 Tesla pulsed fields and thermo-magneto-mechanical exposure to 18.1 Tesla steady fields confirmed the presence of magnetically induced ..gamma.. ..-->.. ..cap alpha..' transformation in the liquid helium to room temperature range. The amount of transformation exceeded that expected from equilibrium thermodynamics and resulted in a detrimental effect on the mechanical behavior of this material. The detrimental effect of the ..gamma.. ..-->.. ..cap alpha..' transformation on the mechanical properties correlated to an increase in quasi-cleavage fracture surface area. Microstructural characterization of the ..gamma.. ..-->.. ..cap alpha..' transformation identified the crystallographic degradation of the martensitic matrix as the source of inferior mechanical properties.

  18. A Kinetics Model for Martensite Transformation in Plain Carbon and Low-Alloyed Steels

    NASA Astrophysics Data System (ADS)

    Lee, Seok-Jae; van Tyne, Chester J.

    2012-02-01

    An empirical martensite kinetics model is proposed that both captures the sigmodial transformation behavior for alloy steels and remains computationally efficient. The model improves on the Koistinen and Marburger model and the van Bohemen and Sietsma model with a function that better represents the transformation rate, especially during the early stages. When compared with existing models, the proposed model exhibits better predictions of volume fraction of martensite. The proposed model also predicts various other transformation properties accurately, such as M90 temperatures and retained austenite.

  19. Deformation of a Ti-Nb alloy containing α'-martensite and omega phases

    SciTech Connect

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

    2015-03-30

    Microscopic deformation of a Ti-17at. %Nb alloy with high fractions of α″-martensite and ω phases was studied by in-situ synchrotron X-ray diffraction. Textures, phase fractions, individual lattice strains, and peak intensities during deformation were studied. It is found that, to accommodate the external tensile strain, some of the α″ and ω grains were first transformed to the β-phase, which then continuously transformed to the α″-phase with chosen variants that effectively accommodate the deformation strain. A strong (010){sub α″} fiber texture was formed at the expense of the (001){sub α″} and (111){sub α″} fiber textures. Above 400 MPa applied stress, (110){sub α″} deformation twinning was triggered with a simultaneous stress relaxation in the (110){sub α″} family and a slight increase in its texture strength in the loading direction.

  20. Deformation of a Ti-Nb alloy containing a"-martensite and omega phases

    SciTech Connect

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

    2015-03-30

    Microscopic deformation of a Ti-17at. %Nb alloy with high fractions of alpha"-martensite and omega phases was studied by in-situ synchrotron X-ray diffraction. Textures, phase fractions, individual lattice strains, and peak intensities during deformation were studied. It is found that, to accommodate the external tensile strain, some of the alpha" and omega grains were first transformed to the beta-phase, which then continuously transformed to the alpha"-phase with chosen variants that effectively accommodate the deformation strain. A strong (010)(alpha") fiber texture was formed at the expense of the (001)(alpha") and (111)(alpha") fiber textures. Above 400 MPa applied stress, (110)(alpha") deformation twinning was triggered with a simultaneous stress relaxation in the (110)(alpha") family and a slight increase in its texture strength in the loading direction. (C) 2015 AIP Publishing LLC.

  1. Coexistence pressure for a martensitic transformation from theory and experiment: Revisiting the bcc-hcp transition of iron under pressure

    SciTech Connect

    Zarkevich, N. A.; Johnson, D. D.

    2015-05-12

    We revisit results from decades of pressure experiments on the bcc ↔ hcp transformations in iron, which are sensitive to non-hydrostatic conditions and sample size. We emphasize the role of martensitic stress in the observed pressure hysteresis and address the large spread in values for onset pressures of the nucleating phase. From electronic-structure calculations, we find a bcc ↔ hcp equilibrium coexistence pressure of 8.4 GPa. Accounting for non-hydrostatic martensitic stress and a stress-dependent transition barrier, we suggest a pressure inequality for better comparison to experiment and observed hysteresis. We construct the equation of state for bcc and hcp phases under hydrostatic pressure, and compare to experiments and previous calculations.

  2. Recent research on the elastic unstableness of shape memory alloy in martensite transformation by micro-high-speed photography

    NASA Astrophysics Data System (ADS)

    Yang, Jie; Wu, Yuehua; Uyemura, Tsuneyoshi

    1993-01-01

    The paper reports the research results on the phenomenon of elastic unstableness in martensite transformation of Cu-Al-Ni shape memory alloy (SMA). We use the method of micro-high speed photography. The martensite of Cu-Al-Ni SMA presents thermoelastic strain in the heating and cooling process. While the sample is heated to As, the martensite begins to contract and the temperature reaches Af point, the martensite is gradually reducing. It is possible that the martensite suddenly disappears from certain visible size at the instant it is heated to Af temperature.

  3. Prediction of precipitate evolution and martensite transformation in Ti-Ni-Cu shape memory alloys by computational thermodynamics

    NASA Astrophysics Data System (ADS)

    Povoden-Karadeniz, A.; Cirstea, D. C.; Kozeschnik, E.

    2016-04-01

    Ti-50Ni to Ti-55Ni (at.%) can be termed as the pioneer of shape memory alloys (SMA). Intermetallic precipitates play an important role for strengthening. Their influence on the start temperature of the martensitic transformation is a crucial property for the shape memory effect. Efforts for increasing the martensite start temperature include replacement of a part of Ni atoms by Cu. The influence of Cu-addition to Ti-Ni SMA on T0- temperatures and the character of the austenite-martensite transformation is evaluated using a new thermodynamic database for the Ti-Ni-system extended by Cu. Trends of precipitation of intermetallic phases are simulated by combining the assessed thermodynamics of the Ti-Ni-Cu system with assessed diffusion mobility data and kinetic models, as implemented in the solid-state transformation software MatCalc and are presented in the form of time-temperature-precipitation diagrams. Thermodynamic equilibrium considerations, complemented by predictive thermo-kinetic precipitation simulation, facilitates SMA alloy design and definition of optimized aging conditions.

  4. A physically based model for the isothermal martensitic transformation in a maraging steel

    NASA Astrophysics Data System (ADS)

    Kruijver, S. O.; Blaauw, H. S.; Beyer, J.; Post, J.

    2003-10-01

    Isothermal transformation from austenite to martensite in steel products during or after the production process often show residual stresses which can create unacceptable dimensional changes in the final product. Tn order to gain more insight in the effects infiuencing the isothermai transformation, the overall kinetics in a low Carbon-Nickel maraging steel is investigated. The influence of the austenitizing température, time and quenching rate on the transformation is measured magnetically and yields information about the transformation rate and final amount of transformation. A physically based model describing the nucleation and growth of martensite is used to explain the observed effects. The results show a very good fit of the experimental values and the model description of the transformation, within the limitations of the inhomogeneities (carbides and intermetallics, size and distribution in the material and stress state) and experimental conditions.

  5. Influence of nonmartensitic transformation products on mechanical properties of tempered martensite

    NASA Technical Reports Server (NTRS)

    Hodge, J M; Lankford, W T

    1952-01-01

    The influence of nonmartensitic transformations products on the mechanical properties of tempered martensite is presented for samples of a SAE 4340 steel, partially isothermally transformed to specific high-temperature transformation products and quenched and tempered to hardness values of from 25 to 40 Rockwell c. The effects of upper bainite in amounts of 1,5, 10, 20 and 50 percent, of 5 percent ferrite, and of 5 percent pearlite on the tensile, impact, and fatigue properties are evaluated. (author)

  6. Coexistence pressure for a martensitic transformation from theory and experiment: Revisiting the bcc-hcp transition of iron under pressure

    DOE PAGESBeta

    Zarkevich, N. A.; Johnson, D. D.

    2015-05-12

    We revisit results from decades of pressure experiments on the bcc ↔ hcp transformations in iron, which are sensitive to non-hydrostatic conditions and sample size. We emphasize the role of martensitic stress in the observed pressure hysteresis and address the large spread in values for onset pressures of the nucleating phase. From electronic-structure calculations, we find a bcc ↔ hcp equilibrium coexistence pressure of 8.4 GPa. Accounting for non-hydrostatic martensitic stress and a stress-dependent transition barrier, we suggest a pressure inequality for better comparison to experiment and observed hysteresis. We construct the equation of state for bcc and hcp phasesmore » under hydrostatic pressure, and compare to experiments and previous calculations.« less

  7. PHONON PRECURSORS TO THE HIGH TEMPERATURE MARTENSITIC TRANSFORMATION IN TI50PD42CR8.

    SciTech Connect

    SHAPIRO,S.M.; WINN,B.L.; SCHLAGEL,D.L.; LOGRASSO,T.; ERWIN,R.

    2002-06-10

    Inelastic neutron scattering measurements were carried out on the Ti{sub 50}Pd{sub 50-x}Cr{sub x} alloy, which has the potential for being a high temperature shape memory material. For x = 0, the transformation temperature is {approx}800K and for the composition studied (x = 8 at.%) T{sub M} {approx} 400K. The majority of the measurements were performed in the parent, {beta}-phase, up to 873K. Most of the phonons propagating along the three symmetry directions [{zeta}00], [{zeta}{zeta}{zeta}], and [{zeta}{zeta}0] were well defined with the exception of the [{zeta}{zeta}0] transverse acoustic mode with displacements along the [-{zeta}{zeta}0] corresponding to the C{prime} = 1/2(C{sub 11}-C{sub 12}) elastic constant. These phonons are well defined for small {zeta}, but for {zeta} > 0.15 they are strongly overdamped near the transition temperature, but become better defined at higher temperatures. An elastic peak develop in the cubic phase at {zeta} = 0.22 and increases in intensity as T{sub M} is approached. However, this dispersion curves show no anomaly at this particular wavevector, in marked contrast to the lattice dynamic studies of other systems exhibiting Martensitic transformations.

  8. Measurement of transformation temperatures and specific heat capacity of tungsten added reduced activation ferritic-martensitic steel

    NASA Astrophysics Data System (ADS)

    Raju, S.; Jeya Ganesh, B.; Rai, Arun Kumar; Mythili, R.; Saroja, S.; Mohandas, E.; Vijayalakshmi, M.; Rao, K. B. S.; Raj, Baldev

    2009-06-01

    The on-heating phase transformation temperatures up to the melting regime and the specific heat capacity of a reduced activation ferritic-martensitic steel (RAFM) with a nominal composition (wt%): 9Cr-0.09C-0.56Mn-0.23V-1W-0.063Ta-0.02N, have been measured using high temperature differential scanning calorimetry. The α -ferrite + carbides → γ-austenite transformation start and finish temperatures, namely A c1, and A c3, are found to be 1104 and 1144 K, respectively for a typical normalized and tempered microstructure. It is also observed that the martensite start ( MS) and finish ( Mf) temperatures are sensitive to the austenitising conditions. Typical MS and Mf values for the 1273 K normalized and 1033 K tempered samples are of the order 714 and 614 K, respectively. The heat capacity CP of the RAFM steel has been measured in the temperature range 473-1273 K, for different normalized and tempered samples. In essence, it is found that the CP of the fully martensitic microstructure is found to be lower than that of its tempered counterpart, and this difference begins to increase in an appreciable manner from about 800 K. The heat capacity of the normalized microstructure is found to vary from 480 to 500 J kg -1 K -1 at 500 K, where as that of the tempered steel is found to be higher by about, 150 J kg -1 K -1.

  9. Dissecting the Mechanism of Martensitic Transformation via Atomic-Scale Observations

    NASA Astrophysics Data System (ADS)

    Yang, Xu-Sheng; Sun, Sheng; Wu, Xiao-Lei; Ma, Evan; Zhang, Tong-Yi

    2014-08-01

    Martensitic transformation plays a pivotal role in the microstructural evolution and plasticity of many engineering materials. However, so far the underlying atomic processes that accomplish the displacive transformation have been obscured by the difficulty in directly observing key microstructural signatures on atomic scale. To resolve this long-standing problem, here we examine an AISI 304 austenitic stainless steel that has a strain/microstructure-gradient induced by surface mechanical attrition, which allowed us to capture in one sample all the key interphase regions generated during the γ(fcc) --> ɛ(hcp) --> α'(bcc) transition, a prototypical case of deformation induced martensitic transformation (DIMT). High-resolution transmission electron microscopy (HRTEM) observations confirm the crucial role of partial dislocations, and reveal tell-tale features including the lattice rotation of the α' martensite inclusion, the transition lattices at the ɛ/α' interfaces that cater the shears, and the excess reverse shear-shuffling induced γ necks in the ɛ martensite plates. These direct observations verify for the first time the 50-year-old Bogers-Burgers-Olson-Cohen (BBOC) model, and enrich our understanding of DIMT mechanisms. Our findings have implications for improved microstructural control in metals and alloys.

  10. Dissecting the mechanism of martensitic transformation via atomic-scale observations.

    PubMed

    Yang, Xu-Sheng; Sun, Sheng; Wu, Xiao-Lei; Ma, Evan; Zhang, Tong-Yi

    2014-01-01

    Martensitic transformation plays a pivotal role in the microstructural evolution and plasticity of many engineering materials. However, so far the underlying atomic processes that accomplish the displacive transformation have been obscured by the difficulty in directly observing key microstructural signatures on atomic scale. To resolve this long-standing problem, here we examine an AISI 304 austenitic stainless steel that has a strain/microstructure-gradient induced by surface mechanical attrition, which allowed us to capture in one sample all the key interphase regions generated during the γ(fcc) → ε(hcp) → α'(bcc) transition, a prototypical case of deformation induced martensitic transformation (DIMT). High-resolution transmission electron microscopy (HRTEM) observations confirm the crucial role of partial dislocations, and reveal tell-tale features including the lattice rotation of the α' martensite inclusion, the transition lattices at the ε/α' interfaces that cater the shears, and the excess reverse shear-shuffling induced γ necks in the ε martensite plates. These direct observations verify for the first time the 50-year-old Bogers-Burgers-Olson-Cohen (BBOC) model, and enrich our understanding of DIMT mechanisms. Our findings have implications for improved microstructural control in metals and alloys. PMID:25142283

  11. Dissecting the Mechanism of Martensitic Transformation via Atomic-Scale Observations

    PubMed Central

    Yang, Xu-Sheng; Sun, Sheng; Wu, Xiao-Lei; Ma, Evan; Zhang, Tong-Yi

    2014-01-01

    Martensitic transformation plays a pivotal role in the microstructural evolution and plasticity of many engineering materials. However, so far the underlying atomic processes that accomplish the displacive transformation have been obscured by the difficulty in directly observing key microstructural signatures on atomic scale. To resolve this long-standing problem, here we examine an AISI 304 austenitic stainless steel that has a strain/microstructure-gradient induced by surface mechanical attrition, which allowed us to capture in one sample all the key interphase regions generated during the γ(fcc) → ε(hcp) → α′(bcc) transition, a prototypical case of deformation induced martensitic transformation (DIMT). High-resolution transmission electron microscopy (HRTEM) observations confirm the crucial role of partial dislocations, and reveal tell-tale features including the lattice rotation of the α′ martensite inclusion, the transition lattices at the ε/α′ interfaces that cater the shears, and the excess reverse shear-shuffling induced γ necks in the ε martensite plates. These direct observations verify for the first time the 50-year-old Bogers-Burgers-Olson-Cohen (BBOC) model, and enrich our understanding of DIMT mechanisms. Our findings have implications for improved microstructural control in metals and alloys. PMID:25142283

  12. In-situ Studies of the Martensitic Transformation in Ti Thin Films using the Dynamic Transmission Microscope (DTEM)

    SciTech Connect

    LaGrange, T B; Campbell, G H; Colvin, J D; King, W E; Browning, N D; Armstrong, M R; Reed, B W; Kim, J S; Stuart, B C

    2005-11-21

    The {alpha} to {beta} transition in pure Ti occurs mainly by a 'martensitic type' phase transformation. In such transformations, growth rates and interface velocities tend to be very large, on the order of 10{sup 3} m/s, making it difficult to observe the transformation experimentally. With thin films, it becomes even more difficult to observe, since the large surface augments the nucleation and transformation rates to levels that require nanosecond temporal resolution for experimental observations. The elucidation of the transformational mechanisms in these materials yearns for an apparatus that has both high spatial and temporal resolution. We have constructed such an instrument at LLNL (the dynamical transmission electron microscope or DTEM) that combines pulsed lasers systems and optical pump-probe techniques with a conventional TEM. We have used the DTEM to observe the transient events of the {alpha}-{beta} transformation in nanocrystalline Ti films via single shot diffraction patterns with 1.5 ns resolution. With pulsed, nanosecond laser irradiation (pump laser), the films were heated at an extreme rate of 10{sup 10} K/s. was observed At 500 ns after the initial pump laser hit, the HCP, alpha phase was almost completely transformed to the BCC, beta phase. Post-mortem investigations of the laser treated films revealed that substantial grain growth occurred and lath microstructure, containing no apparent dislocations. The lack of dislocations may indicate that the {alpha} to {beta} transformation may also proceed by a 'massive' type mechanism (short range diffusion).

  13. Microstructure and martensitic transformation in Si-coated TiNi powders prepared by ball milling

    SciTech Connect

    Kim, Jae-hyun; Cho, Gyu-bong; Im, Yeon-min; Chun, Byong-sun; Kim, Yeon-wook; Nam, Tae-hyun

    2013-12-15

    Graphical abstract: - Highlights: • Amorphous Si-coated TiNi powders were prepared successfully by ball milling. • Ti{sub 4}Ni{sub 4}Si{sub 7} was formed at the interface between Si and TiNi after annealing. • Si-coated Ti–Ni powders displayed the R phase after annealing. - Abstract: Si was coated on the surface of Ti–49Ni (at%) alloy powders by ball milling in order to improve the electrochemical properties of the Si electrodes of secondary Li ion batteries and then the microstructure and martensitic transformation behavior were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Ti–Ni powders coated with Si were fabricated successfully by ball milling. As-milled powders consisted of highly deformed Ti–Ni powders with the B2 phase and amorphous Si layers. The thickness of the Si layer coated on the surface of the Ti–Ni powders increased from 3–5 μm to 10–15 μm by extending the milling time from 3 h to 48 h. However, severe contamination from the grinding media, ZrO{sub 2} occurred when the ball milling time was as long as 48 h. By heating as-milled powders to various temperatures in the range of 673–873 K, the highly deformed Ti–Ni powders were recovered and Ti{sub 4}Ni{sub 4}Si{sub 7} was formed. Two-stage B2–R–B19′ transformation occurred when as-milled Si-coated Ti–49Ni alloy powders were heated to temperatures below 873 K, above this temperature one-stage B2–B19′ transformation occurred.

  14. Influence of Martensite Volume Fraction on Impact Properties of Triple Phase (TP) Steels

    NASA Astrophysics Data System (ADS)

    Zare, Ahmad; Ekrami, A.

    2013-03-01

    Ferrite-bainite-martensite triple phase (TP) microstructures with different volume fractions of martensite were obtained by changing heat treatment time during austempering at 300 °C. Room temperature impact properties of TP steels with different martensite volume fractions ( V M) were determined by means of Charpy impact testing. The effects of test temperature on impact properties were also investigated for two selected microstructures containing 0 (the DP steel) and 8.5 vol.% martensite. Test results showed reduction in toughness with increasing V M in TP steels. Fracture toughness values for the DP and TP steels with 8.5 vol.% martensite were obtained from correlation between fracture toughness and the Charpy impact energy. Fractography of Charpy specimens confirmed decrease in TP steels' toughness with increasing V M by considering and comparing radial marks and crack initiation regions at the fracture surfaces of the studied steels.

  15. Stabilization of Fe-C Martensitic Phase by Low-Temperature Ageing

    SciTech Connect

    Dabrowski, L.; Winek, T.; Neov, S.

    2007-04-23

    Martensite containing 0.87 wt.% carbon was aged at liquid nitrogen temperature during 30 days. X-ray diffraction measurements showed that ageing does not lead to the phase transition {alpha} {yields} {kappa} up to 800 K.

  16. Stabilization of Fe-C Martensitic Phase by Low-Temperature Ageing

    NASA Astrophysics Data System (ADS)

    Dabrowski, L.; Neov, S.; Winek, T.

    2007-04-01

    Martensite containing 0.87 wt.% carbon was aged at liquid nitrogen temperature during 30 days. X-ray diffraction measurements showed that ageing does not lead to the phase transition α ==> κ up to 800 K.

  17. Iron alloys with new functional properties obtained during reverse martensitic transformation

    NASA Astrophysics Data System (ADS)

    Sagaradze, V. V.; Danilchenko, V. E.; L'Heritier, P.; Sagaradze, I. V.

    2003-10-01

    It was shown that different types of the austenite (homogeneous and inhomogeneous polyhedral, or submicrocrystalline and nanocrystalline plate austenite) can be formed, providing new functional properties of various steels and alloys. The austenite formed during a partial αtoγ transformation increases considerably the strength of the martensite, enhances the coercive force and improves the square shape of the hysteresis loop of maraging steels. The thermal expansion coefficient of the austenitic alloy type 32Ni can be adjusted over broad limits thanks to different αtoγ transformation conditions. A stainless steel with a structure of alternating laths of the martensite and the austenite has a high resistance to radiation void formation.

  18. Neutron diffraction study of the martensitic transformation and chemical order in Heusler alloy Ni1.91Mn1.29Ga0.8

    DOE PAGESBeta

    Ari-Gur, Pnina; Garlea, Vasile O.; Cao, Huibo; Ge, Y.; Aaltio, I.; Hannula, S. P.; Koledov, V.

    2015-11-05

    In this study, Heusler alloys of Ni-Mn-Ga compositions demonstrate ferromagnetic shape memory effect in the martensitic state. The transformation temperature and the chemical order depend strongly on the composition. In the current work, the structure and chemical order of the martensitic phase of Ni1.91Mn1.29Ga0.8 were studied using neutron diffraction; the diffraction pattern was refined using the FullProf software. It was determined that the structural transition occurs around 330 K. At room temperature, 300 K, which is below the martensite transformation temperature, all the Bragg reflections can be described by a monoclinic lattice with a symmetry of space group P 1more » 2/m 1 and lattice constants of a = 4.23047(7) [Å], b = 5.58333(6) [Å], c = 21.0179(2) [Å], beta = 90.328(1). The chemical order is of critical importance in these alloys, and it was previously studied at 363 K. Analysis of the neutron diffraction in the monoclinic phase shows that the chemical order is maintained during the martensitic transformation.« less

  19. Investigations on Ni-Co-Mn-Sn thin films: Effect of substrate temperature and Ar gas pressure on the martensitic transformations and exchange bias properties

    SciTech Connect

    Machavarapu, Ramudu Jakob, Gerhard

    2015-03-15

    We report the effect of substrate temperature (T{sub S}) and Ar gas pressure (P{sub D}) on the martensitic transformations, magnetic and exchange bias (EB) properties in Heusler type Ni-Co-Mn-Sn epitaxial thin films. Martensitic transformation temperatures and EB fields at 5 K were found to increase with increasing T{sub S}. The observed maximum EB value of 320 Oe after field cooling in the film deposited at 650 {sup ∘}C is high among the values reported for Ni-Mn-Sn thin films which is attributed to the coexistence of ferromagnetic (FM) and antiferromagnetic (AF) phases in the martensitic state. In the case of P{sub D} variation, with increase in P{sub D}, martensitic transformation temperatures were increased and a sharp transformation was observed in the film deposited at 0.06 mbar. Magnetization values at 5 K were higher for increasing P{sub D}. These observations are attributed to the compositional shift. EB effect is also present in these films. Microstructural features observed using atomic force microscopy (AFM) shows a fine twinning and reduced precipitation with increase in P{sub D}, which is also confirmed from the scanning electron microscopy (SEM) images. EB effects in both series were confirmed from the training effect. Target ageing effect has been observed in the films deposited before and after ninety days of time interval. This has been confirmed both on substrate temperature and Ar gas pressure variations.

  20. Investigations on Ni-Co-Mn-Sn thin films: Effect of substrate temperature and Ar gas pressure on the martensitic transformations and exchange bias properties

    NASA Astrophysics Data System (ADS)

    Machavarapu, Ramudu; Jakob, Gerhard

    2015-03-01

    We report the effect of substrate temperature (TS) and Ar gas pressure (PD) on the martensitic transformations, magnetic and exchange bias (EB) properties in Heusler type Ni-Co-Mn-Sn epitaxial thin films. Martensitic transformation temperatures and EB fields at 5 K were found to increase with increasing TS. The observed maximum EB value of 320 Oe after field cooling in the film deposited at 650 ∘C is high among the values reported for Ni-Mn-Sn thin films which is attributed to the coexistence of ferromagnetic (FM) and antiferromagnetic (AF) phases in the martensitic state. In the case of PD variation, with increase in PD, martensitic transformation temperatures were increased and a sharp transformation was observed in the film deposited at 0.06 mbar. Magnetization values at 5 K were higher for increasing PD. These observations are attributed to the compositional shift. EB effect is also present in these films. Microstructural features observed using atomic force microscopy (AFM) shows a fine twinning and reduced precipitation with increase in PD, which is also confirmed from the scanning electron microscopy (SEM) images. EB effects in both series were confirmed from the training effect. Target ageing effect has been observed in the films deposited before and after ninety days of time interval. This has been confirmed both on substrate temperature and Ar gas pressure variations.

  1. Latent heat contribution to the direct magnetocaloric effect in Ni–Mn–Ga shape memory alloys with coupled martensitic and magnetic transformations

    NASA Astrophysics Data System (ADS)

    Caballero-Flores, R.; Sánchez-Alarcos, V.; Recarte, V.; Pérez-Landazábal, J. I.; Gómez-Polo, C.

    2016-05-01

    We report the direct magnetocaloric response of materials that present a second-order phase transition in the temperature range where a first-order structural transition also occurs. In particular, the influence of the latent heat on the field-induced adiabatic temperature change has been analyzed in a Ni–Mn–Ga alloy with coupled martensitic and magnetic transformations. It is found that discrepancies around 20% arise depending on whether the latent heat is taken into account or not. From the observed results, a general expression for the indirect determination of the adiabatic temperature change, that takes into account the contributions of both the martensitic and magnetic transformations, is proposed and experimentally confirmed. The observed key role of the latent heat allows us to understand why materials with first-order transformations do not present adiabatic temperature changes as higher as those which would correspond to materials undergoing second-order transformations with similar isothermal entropy change.

  2. Molecular dynamics simulation of a glissile dislocation interface propagating a martensitic transformation.

    PubMed

    Lill, J V; Broughton, J Q

    2000-06-19

    The method of Parrinello and Rahman is generalized to include slip in addition to deformation of the simulation cell. Equations of motion are derived, and a microscopic expression for traction is introduced. Lagrangian constraints are imposed so that the combination of deformation and slip conform to the invariant plane shear characteristic of martensites. Simulation of a model transformation demonstrates the nucleation and propagation of a glissile dislocation interface. PMID:10991054

  3. Analysis of the strain induced martensitic transformation in austenitic steel subjected to dynamic perforation

    NASA Astrophysics Data System (ADS)

    Rodríguez-Martínez, J. A.; Rusinek, A.; Pesci, R.; Zaera, R.

    2012-08-01

    An experimental and numerical analysis on the martensitic transformation in AISI 304 steel sheets subjected to perforation by conical and hemispherical projectiles is reported. Two target thicknesses are considered, 0.5 and 1.0 mm, and impact velocities range from 35 to 200 m/s. The perforation mechanisms are identified and the effect of the projectile nose-shape on the ability of the target for energy absorption is evaluated. Martensite has been detected in all the impacted samples and the role played by the projectile nose-shape on the transformation is highlighted. A 3D model implemented in ABAQUS/Explicit allowed to simulate the perforation tests. The material is defined through a constitutive description developed by the authors to describe the strain induced martensitic transformation taking place in metastable austenitic steels at high strain rates. The numerical results are compared with the experimental evidence and satisfactory matching is obtained. The numerical model succeeds in describing the perforation mechanisms associated to each projectile-target configuration analysed.

  4. Development and application of a Ni-Ti interatomic potential with high predictive accuracy of the martensitic phase transition

    NASA Astrophysics Data System (ADS)

    Ko, Won-Seok; Grabowski, Blazej; Neugebauer, Jörg

    2015-10-01

    Phase transitions in nickel-titanium shape-memory alloys are investigated by means of atomistic simulations. A second nearest-neighbor modified embedded-atom method interatomic potential for the binary nickel-titanium system is determined by improving the unary descriptions of pure nickel and pure titanium, especially regarding the physical properties at finite temperatures. The resulting potential reproduces accurately the hexagonal-close-packed to body-centered-cubic phase transition in Ti and the martensitic B 2 -B 19' transformation in equiatomic NiTi. Subsequent large-scale molecular-dynamics simulations validate that the developed potential can be successfully applied for studies on temperature- and stress-induced martensitic phase transitions related to core applications of shape-memory alloys. A simulation of the temperature-induced phase transition provides insights into the effect of sizes and constraints on the formation of nanotwinned martensite structures with multiple domains. A simulation of the stress-induced phase transition of a nanosized pillar indicates a full recovery of the initial structure after the loading and unloading processes, illustrating a superelastic behavior of the target system.

  5. Distribution of plates' sizes tell the thermal history in a simulated martensitic-like phase transition

    NASA Astrophysics Data System (ADS)

    Ţolea, F.; Ţolea, M.; Sofronie, M.; Văleanu, M.

    2015-07-01

    A phenomenological 2D model, simulating the martensitic transformation, is built upon existing experimental observations that the size of the formed plates - in direct transformation - decreases as the temperature is lowered; then they transform back in reversed order. As such, if a reverse transformation is incomplete (arrested), the subsequent direct one will show anomalously a large number of big size plates - old plus newly formed - but consequentially a depletion of intermediate sizes, due to geometrical constraints, phenomenon that generates thermal memory.

  6. Influence of Martensite Mechanical Properties on Failure Mode and Ductility of Dual Phase Steels

    SciTech Connect

    Choi, Kyoo Sil; Liu, Wenning N.; Sun, Xin; Khaleel, Mohammad A.

    2009-04-01

    In this paper, the effects of the mechanical properties of the martensite phase on the failure mode and ductility of dual phase (DP) steels are investigated using a micromechanics-based finite element method. Actual microstructures of DP sheet steels obtained from scanning electron microscopy are used as representative volume element (RVE) in two-dimensional plane-stress finite element calculations. Failure is predicted as plastic strain localization in the RVE during deformation. The mechanical properties of the ferrite and martensite phases in a commercial DP 980 steel are obtained based on the in-situ X-ray diffraction measurements of a uniaxial tensile test. Computations are then conducted on the RVE in order to investigate the influence of the martensite mechanical properties and volume fraction on the macroscopic behavior and failure mode of DP steels. The computations show that, as the strength and volume fraction of the martensite phase increase, the ultimate tensile strength (UTS) of DP steels increases but the UTS strain and failure strain decrease. These results agree well with the general experimental observations on DP steels. Additionally, shear dominant failure modes usually develop for DP steels with lower martensite strengths, whereas split failure modes typically develop for DP steels with higher martensite strengths.

  7. Shape-memory transformations of NiTi: Minimum-energy pathways between austenite, martensites, and kinetically limited intermediate states

    DOE PAGESBeta

    Zarkevich, N. A.; Johnson, D. D.

    2014-12-24

    NiTi is the most used shape-memory alloy, nonetheless, a lack of understanding remains regarding the associated structures and transitions, including their barriers. Using a generalized solid-state nudge elastic band (GSSNEB) method implemented via density-functional theory, we detail the structural transformations in NiTi relevant to shape memory: those between body-centered orthorhombic (BCO) groundstate and a newly identified stable austenite (“glassy” B2-like) structure, including energy barriers (hysteresis) and intermediate structures (observed as a kinetically limited R-phase), and between martensite variants (BCO orientations). All results are in good agreement with available experiment. We contrast the austenite results to those from the often-assumed, butmore » unstable B2. Furthermore, these high- and low-temperature structures and structural transformations provide much needed atomic-scale detail for transitions responsible for NiTi shape-memory effects.« less

  8. Shape-memory transformations of NiTi: Minimum-energy pathways between austenite, martensites, and kinetically limited intermediate states

    SciTech Connect

    Zarkevich, N. A.; Johnson, D. D.

    2014-12-24

    NiTi is the most used shape-memory alloy, nonetheless, a lack of understanding remains regarding the associated structures and transitions, including their barriers. Using a generalized solid-state nudge elastic band (GSSNEB) method implemented via density-functional theory, we detail the structural transformations in NiTi relevant to shape memory: those between body-centered orthorhombic (BCO) groundstate and a newly identified stable austenite (“glassy” B2-like) structure, including energy barriers (hysteresis) and intermediate structures (observed as a kinetically limited R-phase), and between martensite variants (BCO orientations). All results are in good agreement with available experiment. We contrast the austenite results to those from the often-assumed, but unstable B2. Furthermore, these high- and low-temperature structures and structural transformations provide much needed atomic-scale detail for transitions responsible for NiTi shape-memory effects.

  9. Precipitation Effects on the Martensitic Transformation in a Cu-Al-Ni Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Suru, Marius-Gabriel; Lohan, Nicoleta-Monica; Pricop, Bogdan; Mihalache, Elena; Mocanu, Mihai; Bujoreanu, Leandru-Gheorghe

    2016-04-01

    This paper describes the effects of precipitation of α-phase on a Cu-Al-Ni shape memory alloy (SMA) with chemical composition bordering on β region. By differential scanning calorimetry, a series of reproducible heat flow fluctuations was determined on heating a hot-rolled martensitic Cu-Al-Ni SMA, which was associated with the precipitation of α-phase. Two heat treatments were given to the SMA so as to "freeze" its states before and after the thermal range for precipitation, respectively. The corresponding microstructures of the two heat-treated states were observed by optical and scanning electron microscopy and were compared with the initial martensitic state. Energy dispersive spectroscopy experiments were carried out to determine the chemical compositions of the different phases formed in heat-treated specimens. The initial as well as the heat-treated specimens with a lamellar shape were further comparatively investigated by dynamic mechanical analysis and two-way shape memory effect (TWSME) tests comprising heating-cooling cycles under a bending load. Temperature scans were applied to the three types of specimens (initial and heat-treated states), so as to bring out the effects of heat treatment. The storage modulus increased, corresponding to the reversion of thermoelastic martensite and disappeared with the formation of precipitates. These features are finally discussed in association with TWSME under bending.

  10. Crystal grain growth during room temperature high pressure Martensitic alpha to omega transformation in zirconium

    SciTech Connect

    Velisavljevic, Nenad; Chesnut, Gary N; Stevens, Lewis L; Dattelbaum, Dana M

    2008-01-01

    Systematic increase in transition pressure with increase in interstitial impurities is observed for the martensitic {alpha} {yields} {omega} structural phase transition in Zr. Significant room temperature crystal grain growth is also observed for the two highest purity samples at this transition, while in the case of the lowest purity sample interstitial impurities obstruct grain growth even as the sample is heated to 1279 K. Our results show the importance of impurities in controlling structural phase stability and other mechanical properties associated with the {alpha} {yields} {omega} structural phase transition.

  11. Internal friction due to domain-wall motion in martensitically transformed A15 compounds

    SciTech Connect

    Snead, C.L. Jr.; Welch, D.O.

    1985-01-01

    A lattice instability in A15 materials in some cases leads to a cubic-to-tetragonal martensitic transformation at low temperatures. The transformed material orients in lamellae with c axes alternately aligned along the <100> directions producing domain walls between the lamellae. An internal-friction (delta) feature below T/sub m/ is attributed to stress-induced domain-wall motion. The magnitude of the friction increases as temperature is lowered below T/sub m/ as (1-c/a) increases, and behaves as (1-c/a)/sup 2/ from T/sub m/ down to the superconducting critical temperature where the increasing tetragonality is inhibited. The effect of strain in the lattice is to decrease the domain-wall internal friction, but not affect T/sub m/. Neutron-induced disorder and the addition of some third-elements in alloying decrease both delta and T/sub m/, with some elements reducing only the former. Less than 1 at. % H is seen to completely suppress both delta and T/sub m. Martensitically transformed V/sub 2/Zr demonstrates low-temperature internal-friction and modulus behavior consists with easy ..beta../m wall motion relative to the easy m/m motion of the A15's. For the V/sub 2/Zr, a peak in delta is observed, qualitatively in agreement with expected ..beta../m wall motion.

  12. Determination of the crystallographic parameters of cubic-to-tetragonal martensitic transformation using the infinitesimal deformation approach and wechsler, lieberman, and read theory

    NASA Astrophysics Data System (ADS)

    Navruz, N.

    2001-02-01

    The aim of the present study is to discuss the infinitesimal deformation (ID) approach’s application and practical applicability. Therefore, ID theory was reformulated and applied to the face centered cubic (fcc) to body centered tetragonal (bct) martensitic transformation for the case of the (110) [bar 110] slip system as the lattice invariant shear (LIS). The analytical solutions for the habit plane orientation, the magnitude of the lattice invariant shear, the orientation relation between parent and product phases, etc. were derived for fcc to bct martensitic transformation in an Fe-7 pct Al-2 pct C alloy. In order to compare with phenomenological theory’s results, crystallographic parameters were also calculated by using Wechsler, Lieberman, and Read (W-L-R) phenomenological theory. Agreement between the two results obtained from ID approach and W-L-R theory was found to be excellent.

  13. Quantitative microstructural characterisation of Fe-30Ni alloy after martensitic transformations by means of stereological and magnetic methods

    SciTech Connect

    Ciura, Franciszek . E-mail: ciura@uci.agh.edu.pl; Dubiel, Beata; Satora, Kazimierz

    2006-06-15

    In the Fe-30Ni alloy investigated a martensitic transformation can occur both during quenching or plastic deformation. Martensite formed during plastic deformation, depending on the thermo-mechanical treatment applied, exhibits a different morphology from that achieved during quenching and forms the so-called composite-like structure. The morphology and volume fraction of martensite depends both on strain and temperature. In the present studies Fe-30Ni alloy was deformed by monotonic rolling in one path and perpendicular rolling in the temperature range M {sub D}-M {sub S}. The aim of the investigations was a determination of martensite volume fraction depending on the strain and temperature. To examine the influence of strain, the alloy was deformed by rolling in one path or perpendicular rolling at a temperature of - 30 deg. C, in the strain range of 10-30%. The dependence of temperature was investigated by rolling with 30% strain in a temperature range from - 30 deg. C to - 80 deg. C. The variants of thermo-mechanical treatment performed enabled us to achieve different martensite morphologies and volume fractions. Microstructural analysis was performed by means of light microscopy and transmission electron microscopy. The results of quantitative microstructural analysis of martensite and retained austenite volume fractions formed in different thermo-mechanical treatments were compared with those obtained by magnetic measurements. The fraction of deformation-induced martensite determined varied from 2% to 86%. The partial volume fractions V {sub V} {sup MF} of martensite formed in different deformation directions were also determined. It was found that the influence of the temperature on the martensite volume fraction is more pronounced than the influence of strain.

  14. Evidence of martensitic phase transitions in magnetic Ni-Mn-In thin films

    SciTech Connect

    Sokolov, A.; Zhang, Le; Dubenko, I.; Samanta, T.; Ali, N.; Stadler, S.

    2013-02-18

    Ni{sub 50}Mn{sub 35}In{sub 15} Heusler alloy thin films (with thicknesses of about 10 nm) have been grown on single crystal MgO and SrTiO{sub 3} (STO) (100) substrates using a laser-assisted molecular beam epitaxy method. Films of mixed austenitic and martensitic phases and of pure martensitic phase have been detected for those grown on MgO and STO substrates, respectively. Thermomagnetic curves were measured using a SQUID magnetometer and are consistent with those of off-stoichiometric In-based bulk Heusler alloys, including a martensitic transition at T = 315 K for films grown on MgO. The differences in the properties of the films grown on MgO and STO are discussed.

  15. Effect of Cu addition on the martensitic transformation of powder metallurgy processed Ti–Ni alloys

    SciTech Connect

    Kim, Yeon-wook; Choi, Eunsoo

    2014-10-15

    Highlights: • M{sub s} of Ti{sub 50}Ni{sub 50} powders is 22 °C, while M{sub s} of SPS-sintered porous bulk increases up to 50 °C. • M{sub s} of Ti{sub 50}Ni{sub 40}Cu{sub 20} porous bulk is only 2 °C higher than that of the powders. • Recovered stain of porous TiNi and TiNiCu alloy is more than 1.5%. - Abstract: Ti{sub 50}Ni{sub 50} and Ti{sub 50}Ni{sub 30}Cu{sub 20} powders were prepared by gas atomization and their transformation behaviors were examined by means of differential scanning calorimetry and X-ray diffraction. One-step B2–B19’ transformation occurred in Ti{sub 50}Ni{sub 50} powders, while Ti{sub 50}Ni{sub 30}Cu{sub 20} powders showed B2–B19 transformation behavior. Porous bulks with 24% porosity were fabricated by spark plasma sintering. The martensitic transformation start temperature (50 °C) of Ti{sub 50}Ni{sub 50} porous bulk is much higher than that (22 °C) of the as-solidified powders. However, the martensitic transformation start temperature (35 °C) of Ti{sub 50}Ni{sub 30}Cu{sub 20} porous bulk is almost the same as that (33 °C) of the powders. When the specimens were compressed to the strain of 8% and then unloaded, the residual strains of Ti{sub 50}Ni{sub 50} and Ti{sub 50}Ni{sub 30}Cu{sub 20} alloy bulks were 3.95 and 3.7%, respectively. However, these residual strains were recovered up to 1.7% after heating by the shape memory phenomenon.

  16. Determination of the normal and anomalous hall effect coefficients in ferromagnetic Ni{sub 50}Mn{sub 35}In{sub 15-x}Si{sub x} Heusler alloys at the martensitic transformation

    SciTech Connect

    Granovskii, A. B. Prudnikov, V. N.; Kazakov, A. P.; Zhukov, A. P.; Dubenko, I. S.

    2012-11-15

    The magnetization, the electrical resistivity, the magnetoresistance, and the Hall resistivity of Ni{sub 50}Mn{sub 35}In{sub 15-x}Si{sub x} (x = 1.0, 3.0, 4.0) Heusler alloys are studied at T = 80-320 K. The martensitic transformation in these alloys occurs at T = 220-280 K from the high-temperature ferromagnetic austenite phase into the low-temperature martensite phase having a substantially lower magnetization. A method is proposed to determine the normal and anomalous Hall effect coefficients in the presence of magnetoresistance and a possible magnetization dependence of these coefficients. The resistivity of the alloys increases jumpwise during the martensitic transformation, reaches 150-200 {mu}{Omega} cm, and is almost temperature-independent. The normal Hall effect coefficient is negative, is higher than that of nickel by an order of magnitude at T = 80 K, decreases monotonically with increasing temperature, approaches zero in austenite, and does not undergo sharp changes in the vicinity of the martensitic transformation. At x = 3, a normal Hall effect nonlinear in magnetization is detected in the immediate vicinity of the martensitic transformation. The temperature dependences of the anomalous Hall effect coefficient in both martensite and austenite and, especially, in the vicinity of the martensitic transformation cannot be described in terms of the skew scattering, the side jump, and the Karplus-Lutinger mechanisms from the anomalous Hall effect theory. The possible causes of this behavior of the magnetotransport properties in Heusler alloys are discussed.

  17. Micromechanics of plastic deformation and phase transformation in a three-phase TRIP-assisted advanced high strength steel: Experiments and modeling

    NASA Astrophysics Data System (ADS)

    Srivastava, Ankit; Ghassemi-Armaki, Hassan; Sung, Hyokyung; Chen, Peng; Kumar, Sharvan; Bower, Allan F.

    2015-05-01

    The micromechanics of plastic deformation and phase transformation in a three-phase advanced high strength steel are analyzed both experimentally and by microstructure-based simulations. The steel examined is a three-phase (ferrite, martensite and retained austenite) quenched and partitioned sheet steel with a tensile strength of ~980 MPa. The macroscopic flow behavior and the volume fraction of martensite resulting from the austenite-martensite transformation during deformation were measured. In addition, micropillar compression specimens were extracted from the individual ferrite grains and the martensite particles, and using a flat-punch nanoindenter, stress-strain curves were obtained. Finite element simulations idealize the microstructure as a composite that contains ferrite, martensite and retained austenite. All three phases are discretely modeled using appropriate crystal plasticity based constitutive relations. Material parameters for ferrite and martensite are determined by fitting numerical predictions to the micropillar data. The constitutive relation for retained austenite takes into account contributions to the strain rate from the austenite-martensite transformation, as well as slip in both the untransformed austenite and product martensite. Parameters for the retained austenite are then determined by fitting the predicted flow stress and transformed austenite volume fraction in a 3D microstructure to experimental measurements. Simulations are used to probe the role of the retained austenite in controlling the strain hardening behavior as well as internal stress and strain distributions in the microstructure.

  18. A Study of the Properties of a Room Temperature Martensitic Binary Nitinol Alloy Above and Below its Martensite to Austenite Transformation Temperature

    NASA Astrophysics Data System (ADS)

    Norwich, Dennis W.

    2011-07-01

    Room temperature martensitic Nitinol alloys provide a challenge to end users of the material because they are martensitic and soft at room temperature. These are commonly referred to as Shape Memory alloys as they revert to their superelastic (pseudoelastic) form and austenitic structure at a temperature above ambient. For this study, a NiTi wire, Ti-55.3 wt.%Ni in composition (Alloy-B) and heat-treated to an Af ≈ 60 °C was used. Tensile testing was performed to fully characterize the performance of the material at a series of temperatures above and below its transformation temperature. This article will summarize the properties of the material along with the effects of multiple strains on key material performance characteristics.

  19. The impact of substrate stimulated functional interface on magnetic and magneto-transport signature of martensitic transformation in NiMnIn shape memory alloy

    NASA Astrophysics Data System (ADS)

    Sabirianov, R.; Sokolov, A.; Kirianov, E.; Zlenko, A.; Quetz, A.; Aryal, A.; Pandey, S.; Dubenko, I.; Ali, N.; Stadler, S.; Al-Aqtash, N.

    We study the impact of the substrate on the martensite transformation of Ni-Mn-In thin films by Hall resistance measurements and discuss it using density functional theory calculations. Similarly to the bulk systems, thin films grown on MgO exhibit the martensitic transformation accompanied by large magnetoresistance and a sign reversal of the ordinary as well as anomalous Hall coefficient. Martensite transition temperature of films grown on (100) surface of MgO is near 170K, while the films grown on (111) surface of MgO show the change of Hall coefficient at 110K. The calculated total energy difference between FM austenite and FiM martensite states in Ni2Mn1.5In0.5 film on MgO (001) substrate (with Ni/MgO interface) is 0.20eV per NiMnIn f.u, compared to 0.24eV in the bulk at the same equilibrium lattice parameters, i.e. when film is ``unstrained''. When lattice parameters of Ni2Mn1.5In0.5/MgO are of those of MgO substrate, i.e. when the film experiences strong bi-axial tensile strain Δa / a = 2.4%, the energy difference is 0.08eV per NiMnIn f.u. These results clearly indicate strong interplay between lattice strain/stress and the relative stability martensite and austenite phase The work is supported by NSF.

  20. High-resolution transmission electron microscopy investigation of the face-centered cubic/hexagonal close-packed martensite transformation in Co-31.8 wt pct Ni alloy: Part 2. Plate intersections, extended defects, and nucleation mechanisms

    NASA Astrophysics Data System (ADS)

    Bray, D. W.; Howe, J. M.

    1996-11-01

    The face-centered cubic/hexagonal close-packed (fcc/hcp) martensite phase transformation in a Co-31.8 wt pct Ni alloy was studied by high-resolution transmission electron microscopy (HRTEM). The HRTEM was used to study the structure and properties of intersections between martensite plates and other defects observed in the alloy such as stacking fault tetrahedra (SFT) and Z-type defects. The HRTEM was also used to attempt to determine if various proposed mechanisms for the fcc/hcp martensite transformation were operating. There is evidence to suggest that the reflection mechanism proposed by Bollmann and the dipole mechanism proposed by Hirth are active in the fcc/hcp martensitic transformation, although the evidence is not completely certain in either case. Growth of the hcp phase by a four- or six-plane mechanism as proposed by Mahajan et al. is possible in theory but was not observed in this study. Transformation by previously proposed pole mechanisms was also not observed in this study, although evidence for a new type of pole mechanism was found. The formation of SFT along the fcc/hcp martensite interface was observed to occur by the cross-slip of Shockley partial dislocations out of the fcc/hcp interface onto conjugate fcc matrix planes, followed by further cross-slip to form the SFT, as previously observed for grain boundaries in fcc alloys.

  1. Phase transformations in binary colloidal monolayers.

    PubMed

    Yang, Ye; Fu, Lin; Marcoux, Catherine; Socolar, Joshua E S; Charbonneau, Patrick; Yellen, Benjamin B

    2015-03-28

    Phase transformations can be difficult to characterize at the microscopic level due to the inability to directly observe individual atomic motions. Model colloidal systems, by contrast, permit the direct observation of individual particle dynamics and of collective rearrangements, which allows for real-space characterization of phase transitions. Here, we study a quasi-two-dimensional, binary colloidal alloy that exhibits liquid-solid and solid-solid phase transitions, focusing on the kinetics of a diffusionless transformation between two crystal phases. Experiments are conducted on a monolayer of magnetic and nonmagnetic spheres suspended in a thin layer of ferrofluid and exposed to a tunable magnetic field. A theoretical model of hard spheres with point dipoles at their centers is used to guide the choice of experimental parameters and characterize the underlying materials physics. When the applied field is normal to the fluid layer, a checkerboard crystal forms; when the angle between the field and the normal is sufficiently large, a striped crystal assembles. As the field is slowly tilted away from the normal, we find that the transformation pathway between the two phases depends strongly on crystal orientation, field strength, and degree of confinement of the monolayer. In some cases, the pathway occurs by smooth magnetostrictive shear, while in others it involves the sudden formation of martensitic plates. PMID:25677504

  2. The effect of microstructure on stress-induced martensitic transformation under cyclic loading in the SMA Nickel-Titanium

    NASA Astrophysics Data System (ADS)

    Kimiecik, Michael; Jones, J. Wayne; Daly, Samantha

    2016-04-01

    A combined experimental and analytical study to determine the configurations of transforming martensite during ambient temperature cyclic deformation of superelastic Nickel-Titanium has been conducted. Full-field, sub-grain-size microscale strain measurements were made in situ during cycling using distortion-corrected Digital Image Correlation combined with Scanning Electron Microscopy (SEM-DIC). Using grain orientation maps from Electron Backscatter Diffraction analysis, possible configurations of martensite formed during cyclic deformation were identified by matching the calculated and measured strain fields. This analysis showed that the inclusion of Correspondence Variants (CVs) in addition to Habit Plane Variants (HPVs) of transformed martensite was necessary to provide a robust fit between calculated and measured strain fields. The approach also provided evidence that there was a more rapid accumulation of residual strain in CV regions and that a correlation existed between residual strain accumulation and the loss of actively transforming martensite in later cycles. It was also found that regions of CVs could coexist with untransformed austenite and Habit Plane Variants (HPVs) in individual grains throughout the microstructure, and that these regions of CVs formed before the end of the macroscopic stress plateau. The CV structure that forms during the initial superelastic deformation of Nickel-Titanium plays a critical role in shaping and stabilizing subsequent martensite recovery during cyclic loading.

  3. Driving force for {gamma} {yields} {var{underscore}epsilon} martensitic transformation and stacking fault energy of {gamma} in Fe-Mn binary system

    SciTech Connect

    Lee, Y.K.; Choi, C.S.

    2000-02-01

    A regular solution model for the difference of the chemical free energy between {gamma} and {var{underscore}epsilon} phases during {gamma} {yields} {var{underscore}epsilon} martensitic transformation in the Fe-Mn binary system has been reexamined and partly modified based on many articles concerning the M{sub s} and A{sub s} temperatures of Fe-Mn alloys. Using the regular solution model, the measured M{sub s} temperatures, and a thermodynamic model for the stacking fault energy (SFE) of austenite ({gamma}), the driving force for {gamma} {yields} {epsilon} martensitic transformation, and the SFE of {gamma} have been calculated. The driving force for {gamma} {yields} {epsilon} martensitic transformation increases linearly from {minus}68 to {minus}120 J/mole with increasing Mn content from 16 to 24 wt pct. The SFE of {gamma} decreases to approximately 13 at. pct Mn and then increases with increasing Mn content, which is in better agreement with Schumann's result rather than Volosevich et al.'s result.

  4. Thermoelastic behaviour of martensitic alloy in the vicinity of critical point in the stress-temperature phase diagram

    NASA Astrophysics Data System (ADS)

    L'vov, V. A.; Matsishin, N.; Glavatska, N.

    2010-04-01

    The theoretical phase diagram of the shape memory alloy, which exhibits the first-order martensitic phase transition of the cubic-tetragonal type, has been considered. The thermoelastic behaviour of the ultra-soft Ni-Mn-Ga alloy in the vicinity of the endpoint of the phase transitions line has been modelled. To this end, the strain-temperature and stress-strain dependencies have been computed with the account of the temperature dependence of the elastic modulus of the alloy. Two important features of thermoelastic behaviour of the alloy have been disclosed: (1) even in the case of complete stress-induced martensitic transformation (MT), the MT strain determined from the length of the plateaus at the stress-strain curves is smaller than the 'spontaneous' tetragonal distortion of the crystal lattice, which arises on cooling of the alloy and (2) the stress-strain loops may include the plateau-like segment even at temperatures above the critical temperature, which corresponds to the endpoint of the stress-strain phase diagram. These features render the observation of the endpoint of phase transitions line impossible with the help of the stress-strain tests and make preferable the direct structural studies of MTs in the stressed single-crystalline specimens.

  5. Analyses of Transformation Kinetics of Carbide-Free Bainite Above and Below the Athermal Martensite-Start Temperature

    NASA Astrophysics Data System (ADS)

    Yakubtsov, I. A.; Purdy, G. R.

    2012-02-01

    The isothermal transformation kinetics of austenite decomposition in Fe-0.4C-2.78Mn-1.81Si was analyzed by an electrical resistivity technique in the temperature interval 723 K to 418 K (450 °C to 145 °C). The analysis of transformation kinetics of the bainite transformation was performed using the Johnson-Mehl-Avrami-Kolgomorov (JMAK) and Austin-Rickett (AR) approaches. The kinetic parameters, the reaction constant n, rate constant k = k( T), and apparent activation energy Q were evaluated for isothermal transformations below and above the martensite-start temperature M S = 548 K (275 °C), which was determined experimentally. The formation of strain-induced martensite, which starts to accompany the bainite transformation at just above M S , increases the rate of transformation and decreases the apparent activation energy of austenite decomposition.

  6. Elastically driven metamagnetic-like phase transformations of shape memory alloys

    NASA Astrophysics Data System (ADS)

    Danilevich, A. G.; L'vov, V. A.

    2016-03-01

    A theoretical model of metamagnetic-like (ferromagnetic-paramagnetic and ferromagnetic-antiferromagnetic) phase transitions is developed for the interpretation of experimental results obtained recently for the Ni-Mn-Co-X (X  =  In, Sn, Ga) shape memory alloys. The conditions of elastically driven (caused by the martensitic transformation of alloy) metamagnetic-like phase transitions are determined. These conditions are: high magnetic susceptibility of paramagnetic/antiferromagnetic phase; large (but real for some alloys) volume change during the martensitic transformation; and large value of volume magnetostriction caused by the metamagnetic-like phase transition. The magnetoelastic mechanism is proposed for the explanation of magnetic field influence on the martensitic transformation. The elastically driven ferromagnetic-paramagnetic phase transition is considered in more detail and the results of corresponding magnetic measurements are described.

  7. Shock wave induced martensitic transformations and morphology changes in Fe-Pd ferromagnetic shape memory alloy thin films

    NASA Astrophysics Data System (ADS)

    Bischoff, A. J.; Arabi-Hashemi, A.; Ehrhardt, M.; Lorenz, P.; Zimmer, K.; Mayr, S. G.

    2016-04-01

    Combining experimental methods and classical molecular dynamics (MD) computer simulations, we explore the martensitic transformation in Fe70Pd30 ferromagnetic shape memory alloy thin films induced by laser shock peening. X-ray diffraction and scanning electron microscope measurements at shock wave pressures of up to 2.5 GPa reveal formation of martensitic variants with preferred orientation of the shorter c-axis of the tetragonal unit cell perpendicular to the surface plane. Moreover, consequential merging of growth islands on the film surface is observed. MD simulations unveil the underlying physics that are characterized by an austenite-martensite transformation with a preferential alignment of the c-axis along the propagation direction of the shock wave, resulting in flattening and in-plane expansion of surface features.

  8. Effects of transformed ferrite growth on the tensile fracture characteristics of a dual-phase steel

    NASA Astrophysics Data System (ADS)

    Jeong, W. C.; Kim, C. H.

    1988-02-01

    The effects of transformed ferrite growth on the tensile fracture characteristics of a dual-phase steel were investigated by observing crack initiation, propagation, and fracture behaviors. Crack initiation occurred by decohesion between martensite and ferrite. However, cracks propagated along the ferrite-martensite interface in a high temperature quenched specimen, whereas in specimens quenched from lower temperature cracks propagated into the martensite particle. Tensile fracture behaviors were not strongly influenced by the cooling rate. At both cooling rates of 5.6 and 0.1 °C/sec, specimens quenched from high temperature fractured by partially brittle fracture mode, but fracture mode changed to ductile mode as the quenching temperature decreased. The effect of transformed ferrite on the fracture mode was not substantially different from that of retained ferrite. However, the crack initiation and propagation was influenced by the variation in martensite distribution caused by different growth behavior of transformed ferrite.

  9. Orientation relationship, plasticity, twin relationship, and interfacial structure of the ???' isothermal martensitic transformation in Pu-Ga alloys

    SciTech Connect

    Moore, K; Krenn, C; Wall, M; Schwartz, A

    2006-01-24

    The orientation relationship, habit plane, parent-product interface at the atomic level, twin relationship, and plastic deformation resulting from the {delta} {yields} {alpha}{prime} isothermal martensitic transformation in Pu-Ga alloys are examined using optical microscopy, transmission electron microscopy, and finite element calculations. The {delta} {yields} {alpha}{prime} transformation exhibits a {approx}20% volume collapse when the face-centered cubic {delta} phase transforms to the monoclinic {alpha}{prime} phase, which results in unique and intriguing crystallography and morphology. Here, we show that the orientation relationship is very close to that previously reported by Zocco et al. (1990), but has small rotational misalignments between the two phases both parallel and perpendicular to the [110]{sub {delta}} {parallel}[100]{sub {alpha}{prime}} direction. The amount of plastic deformation is exceedingly large due to the {approx}20% volume collapse and transmission electron microscopy is used to quantify the difference in dislocation density between untransformed {delta}-matrix and regions of {delta} adjacent to the transformed {alpha}{prime}. The twins contained in {alpha}{prime} plates are shown to have a (205){sub {alpha}} orientation as the lattice invariant deformation and are found to be composed of two alternating variants that share a common <020>{sub {alpha}{prime}} direction, but differ by a 60 degree rotation about <020>{sub {alpha}{prime}}. A combination of electron diffraction and optical microscopy has been employed to examine the macroscopic habit plane and the analysis suggests that a large fraction of the observed habit planes are on or near {l_brace}111{r_brace}{sub {delta}}. Finally, high resolution transmission electron microscopy reveals that the interface is faceted on {l_brace}111{r_brace}{sub {delta}}, exhibiting a series of terrace and ledges.

  10. Martensitic transformation of FeNi nanofilm induced by interfacial stress generated in FeNi/V nanomultilayered structure

    PubMed Central

    2014-01-01

    FeNi/V nanomultilayered films with different V layer thicknesses were synthesized by magnetron sputtering. By adjusting the thickness of the V layer, different interfacial compressive stress were imposed on FeNi layers and the effect of interfacial stress on martensitic transformation of the FeNi film was investigated. Without insertion of V layers, the FeNi film exhibits a face-centered cubic (fcc) structure. With the thickness of V inserted layers up to 1.5 nm, under the coherent growth structure in FeNi/V nanomultilayered films, FeNi layers bear interfacial compressive stress due to the larger lattice parameter relative to V, which induces the martensitic transformation of the FeNi film. As the V layer thickness increases to 2.0 nm, V layers cannot keep the coherent growth structure with FeNi layers, leading to the disappearance of interfacial compressive stress and termination of the martensitic transformation in the FeNi film. The interfacial compressive stress-induced martensitic transformation of the FeNi nanofilm is verified through experiment. The method of imposing and modulating the interfacial stress through the epitaxial growth structure in the nanomultilayered films should be noticed and utilized. PMID:25232296

  11. Calorimetric and acoustic emission study of martensitic transformation in single-crystalline Ni2MnGa alloys

    NASA Astrophysics Data System (ADS)

    Tóth, László Z.; Szabó, Sándor; Daróczi, Lajos; Beke, Dezső L.

    2014-12-01

    The jerky character of austenite-martensite phase transformation in Ni2MnGa single crystals (with 10M martensite structure) has been investigated by thermal cycling using a differential scanning calorimeter (DSC) and by detection of acoustic emissions (AEs) at low cooling and heating rates (0.1 K/min and below). It is illustrated that, besides the low cooling and heating rate, mass and surface roughness are also important parameters in optimizing the best signal/noise ratio in order to obtain individual peaks suitable for statistical analysis. Three types of samples, differing in the twin structure and twin boundary behavior, were investigated with and without surface roughening made by electro-erosion. The statistical analysis, carried out for both (thermal and acoustic) types of signals, provided power-law behavior. In calorimetric measurements the energy exponents, obtained in cooling, were the same within the experimental errors (ɛ =1.7 ±0.2 ) for the three samples investigated. In acoustic emission experiments the energy and amplitude, α , exponents were determined both for cooling and heating. The exponents for cooling and heating runs are slightly different. They are larger for heating for both α and ɛ , in accordance with the asymmetric acoustic activity: we observed higher acoustic activity (higher number of hits) during cooling. The effect of the surface roughness is negligible in the exponents (but higher acoustic activity corresponds to higher roughness) and the following values were obtained: ɛ =1.5 ±0.1 and α =2.1 ±0.1 for cooling as well as ɛ =1.8 ±0.1 and α =2.6 ±0.1 for heating. Our results are in accordance with the results of Gallardo et al. [Phys. Rev. B 81, 174102 (2010), 10.1103/PhysRevB.81.174102] obtained in Cu based alloys: the exponents of the energy distributions, for both DSC and AE signals, were the same within the experimental errors. Furthermore, our exponents obtained from the AE measurements are close to the values

  12. On the Effect of Manganese on Grain Size Stability and Hardenability in Ultrafine-Grained Ferrite/Martensite Dual-Phase Steels

    NASA Astrophysics Data System (ADS)

    Calcagnotto, Marion; Ponge, Dirk; Raabe, Dierk

    2012-01-01

    Two plain carbon steels with varying manganese content (0.87 wt pct and 1.63 wt pct) were refined to approximately 1 μm by large strain warm deformation and subsequently subjected to intercritical annealing to produce an ultrafine grained ferrite/martensite dual-phase steel. The influence of the Mn content on microstructure evolution is studied by scanning electron microscopy (SEM). The Mn distribution in ferrite and martensite is analyzed by high-resolution electron backscatter diffraction (EBSD) combined with energy dispersive X-ray spectroscopy (EDX). The experimental findings are supported by the calculated phase diagrams, equilibrium phase compositions, and the estimated diffusion distances using Thermo-Calc (Thermo-Calc Software, McMurray, PA) and Dictra (Thermo-Calc Software). Mn substantially enhances the grain size stability during intercritical annealing and the ability of austenite to undergo martensitic phase transformation. The first observation is explained in terms of the alteration of the phase transformation temperatures and the grain boundary mobility, while the second is a result of the Mn enrichment in cementite during large strain warm deformation, which is inherited by the newly formed austenite and increases its hardenability. The latter is the main reason why the ultrafine-grained material exhibits a hardenability that is comparable with the hardenability of the coarse-grained reference material.

  13. Phase transformations in superconducting and non-superconducting perovskites

    SciTech Connect

    Mitchell, T.E.

    1992-01-01

    Most of the high {Tc} superconductors and other perovskite-related cuprates exhibit some kind of structural instability. For example, tetragonal-to-orthorhombic phase transformations occur in the Y-Ba-Cu-O and La-Sr-Cu-O systems while crystal structures in the Bi-Ca-Sr-Cu-O and Tl-Ba-Ca-Cu-O systems have incommensurate periodicities associated with displacements of the heavy cations. In YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}, the transformation is due to the ordering of oxygen vacancies while in La{sub 2-x}Sr{sub x}CuO{sub 4} the transformation is accompanied by tilting of the (CuO{sub 6}) octahedra. Such tilting and distortion of the co-ordination octahedra commonly occur in perovskite-related compounds and transformations between the structures are frequently martensitic. Phase transformations in the superconducting cuprates have been investigated by transmission electron microscopy but none of them appear to be martensitic. The phase transformations are accompanied by twinning and the resulting configurations are used to calculate twin boundary energies.

  14. Phase transformations in superconducting and non-superconducting perovskites

    SciTech Connect

    Mitchell, T.E.

    1992-07-01

    Most of the high {Tc} superconductors and other perovskite-related cuprates exhibit some kind of structural instability. For example, tetragonal-to-orthorhombic phase transformations occur in the Y-Ba-Cu-O and La-Sr-Cu-O systems while crystal structures in the Bi-Ca-Sr-Cu-O and Tl-Ba-Ca-Cu-O systems have incommensurate periodicities associated with displacements of the heavy cations. In YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}, the transformation is due to the ordering of oxygen vacancies while in La{sub 2-x}Sr{sub x}CuO{sub 4} the transformation is accompanied by tilting of the [CuO{sub 6}] octahedra. Such tilting and distortion of the co-ordination octahedra commonly occur in perovskite-related compounds and transformations between the structures are frequently martensitic. Phase transformations in the superconducting cuprates have been investigated by transmission electron microscopy but none of them appear to be martensitic. The phase transformations are accompanied by twinning and the resulting configurations are used to calculate twin boundary energies.

  15. Plasticity-improved Zr-Cu-Al bulk metallic glass matrix composites containing martensite phase

    NASA Astrophysics Data System (ADS)

    Sun, Y. F.; Wei, B. C.; Wang, Y. R.; Li, W. H.; Cheung, T. L.; Shek, C. H.

    2005-08-01

    Zr48.5Cu46.5Al5 bulk metallic glass matrix composites with diameters of 3 and 4mm were produced through water-cooled copper mold casting. Micrometer-sized bcc based B2 structured CuZr phase containing martensite plate, together with some densely distributed nanocrystalline Zr2Cu and plate-like Cu10Zr7 compound, was found embedded in a glassy matrix. The microstructure formation strongly depends on the composition and cooling rate. Room temperature compression tests reveal significant strain hardening and plastic strains of 7.7% and 6.4% before failure are obtained for the 3-mm- and 4-mm-diam samples, respectively. The formation of the martensite phase is proposed to contribute to the strain hardening and plastic deformation of the materials.

  16. Determination of the vibrational contribution to the entropy change at the martensitic transformation in Ni-Mn-Sn metamagnetic shape memory alloys: a combined approach of time-of-flight neutron spectroscopy and ab initio calculations.

    PubMed

    Recarte, V; Zbiri, M; Jiménez-Ruiz, M; Sánchez-Alarcos, V; Pérez-Landazábal, J I

    2016-05-25

    The different contributions to the entropy change linked to the austenite-martensitic transition in a Ni-Mn-Sn metamagnetic shape memory alloy have been determined by combining different experimental techniques. The vibrational contribution has been inferred from the vibrational density of states of both the martensitic and austenite phases. This has been accomplished by combining time-of-flight neutron scattering measurements and ab initio calculations. Further, the electronic part of the entropy change has also been calculated. Since the martensitic transformation takes place between two paramagnetic phases, the magnetic contribution can be neglected and the entropy change can be reduced to the sum of two terms: vibrational and electronic. The obtained value of the vibrational contribution ([Formula: see text]) nearly provides the total entropy change measured by calorimetry ([Formula: see text]), the difference being the electronic contribution within the experimental error. PMID:27120315

  17. Different structures of monoclinic martensitic phases in titanium nickelide

    NASA Astrophysics Data System (ADS)

    Voronin, V. I.; Naish, V. E.; Novoselova, T. V.; Pushin, V. G.; Sagaradze, I. V.

    2000-03-01

    The detailed theoretical and experimental analysis has been undertaken to bring to light the true structure of the monoclinic phase in titanium nickelide (NiTi). Theoretical models for such a phase have been proposed to describe the experimental data. In addition to the well-known B19‧ phase two more structures - new monoclinic M phase with Cm space group and triclinic phase with P1 space group - have been produced and analyzed in detail. Diffraction patterns have been obtained from different NiTi samples by using the neutron diffractometer IVV2 at different temperatures. From the refinement by DBWS-9411 program all these neutron patterns have been decoded successfully. The proposed new structures and stereotype B19‧ one agree with correspondent experimental data and the agreement is quite good.

  18. Interaction between phase transformations and dislocations at the nanoscale. Part 1. General phase field approach

    NASA Astrophysics Data System (ADS)

    Levitas, Valery I.; Javanbakht, Mahdi

    2015-09-01

    Thermodynamically consistent, three-dimensional (3D) phase field approach (PFA) for coupled multivariant martensitic transformations (PTs), including cyclic PTs, variant-variant transformations (i.e., twinning), and dislocation evolution is developed at large strains. One of our key points is in the justification of the multiplicative decomposition of the deformation gradient into elastic, transformational, and plastic parts. The plastic part includes four mechanisms: dislocation motion in martensite along slip systems of martensite and slip systems of austenite inherited during PT and dislocation motion in austenite along slip systems of austenite and slip systems of martensite inherited during reverse PT. The plastic part of the velocity gradient for all these mechanisms is defined in the crystal lattice of the austenite utilizing just slip systems of austenite and inherited slip systems of martensite, and just two corresponding types of order parameters. The explicit expressions for the Helmholtz free energy and the transformation and plastic deformation gradients are presented to satisfy the formulated conditions related to homogeneous thermodynamic equilibrium states of crystal lattice and their instabilities. In particular, they result in a constant (i.e., stress- and temperature-independent) transformation deformation gradient and Burgers vectors. Thermodynamic treatment resulted in the determination of the driving forces for change of the order parameters for PTs and dislocations. It also determined the boundary conditions for the order parameters that include a variation of the surface energy during PT and exit of dislocations. Ginzburg-Landau equations for dislocations include variation of properties during PTs, which in turn produces additional contributions from dislocations to the Ginzburg-Landau equations for PTs. A complete system of coupled PFA and mechanics equations is presented. A similar theory can be developed for PFA to dislocations and other

  19. Neutron Scattering Studies of Pre-Transitional Effects in Solid-Solid Phase Transformations

    SciTech Connect

    Shapiro, S. M.

    1999-06-30

    Neutron scattering studies have played a fundamental role in understanding solid-solid phase transformations, particularly in studying the lattice dynamical behavior associated with precursor effects. A review of the studies performed on solids exhibiting Martensitic transformations is given below. The mode softening and associated elastic diffuse scattering, previously observed in NiAl alloys, will be discussed as well as more recent work on Ni{sub 2}MnGa, a system exhibiting magnetic order as well as a Martensitic transformation. Also, new results on the precursor effects in ordered and disordered FePt alloys will be presented.

  20. Mössbauer studies of a martensitic transformation and of cryogenic treatments of a D2 tool steel

    NASA Astrophysics Data System (ADS)

    Costa, B. F. O.; Blumers, M.; Kortmann, A.; Theisen, W.; Batista, A. C.; Klingelhöfer, G.

    2013-04-01

    A D2 tool steel X153CrVMo12 with composition C1.53 Cr12 V0.95 Mo0.80 Mn0.40(wt% Fe balanced) was studied by use of Mössbauer spectroscopy and X-ray diffraction. It was observed that the study of carbides by X-ray diffraction was difficult while Mössbauer spectroscopy gives some light on the process occurring during cryogenic treatment. With the increase of the martensitic phase the carbides decrease and are dissolved in solid solution of martensite as well as the chromium element.

  1. Martensitic transformation behaviors of rapidly solidified Ti–Ni–Mo powders

    SciTech Connect

    Kim, Yeon-wook

    2012-10-15

    For the fabrication of bulk near-net-shape shape memory alloys and porous metallic biomaterials, consolidation of Ti–Ni–Mo alloy powders is more useful than that of elemental powders of Ti, Ni and Mo. Ti{sub 50}Ni{sub 49.9}Mo{sub 0.1} shape memory alloy powders were prepared by gas atomization, and transformation temperatures and microstructures of those powders were investigated as a function of powder size. XRD analysis showed that the B2–R–B19 martensitic transformation occurred in powders smaller than 150 μm. According to DSC analysis of the as-atomized powders, the B2–R transformation temperature (T{sub R}) of the 25–50 μm powders was 18.4 °C. The T{sub R} decreased with increasing powder size, however, the difference in T{sub R} between 25–50 μm powders and 100–150 μm powders is only 1 °C. Evaluation of powder microstructures was based on SEM examination of the surface and the polished and etched powder cross sections and the typical images of the rapidly solidified powders showed cellular morphology. Porous cylindrical foams of 10 mm diameter and 1.5 mm length were fabricated by spark plasma sintering (SPS) at 800 °C and 5 MPa. Finally these porous TiNi alloy samples are heat-treated for 1 h at 850 °C, and then quenched in ice water. The bulk samples have 23% porosity and 4.6 g/cm{sup 3} density and their T{sub R} is 17.8 °C.

  2. Microstructure and properties of pipeline steel with a ferrite/martensite dual-phase microstructure

    SciTech Connect

    Li Rutao Zuo Xiurong Hu Yueyue Wang Zhenwei Hu, Dingxu

    2011-08-15

    In order to satisfy the transportation of the crude oil and gas in severe environmental conditions, a ferrite/martensite dual-phase pipeline steel has been developed. After a forming process and double submerged arc welding, the microstructure of the base metal, heat affected zone and weld metal was characterized using scanning electron microscopy and transmission electron microscopy. The pipe showed good deformability and an excellent combination of high strength and toughness, which is suitable for a pipeline subjected to the progressive and abrupt ground movement. The base metal having a ferrite/martensite dual-phase microstructure exhibited excellent mechanical properties in terms of uniform elongation of 7.5%, yield ratio of 0.78, strain hardening exponent of 0.145, an impact energy of 286 J at - 10 deg. C and a shear area of 98% at 0 deg. C in the drop weight tear test. The tensile strength and impact energy of the weld metal didn't significantly reduce, because of the intragranularly nucleated acicular ferrites microstructure, leading to high strength and toughness in weld metal. The heat affected zone contained complete quenching zone and incomplete quenching zone, which exhibited excellent low temperature toughness of 239 J at - 10 deg. C. - Research Highlights: {yields}The pipe with ferrite/martensite microstructure shows high deformability. {yields}The base metal of the pipe consists of ferrite and martensite. {yields}Heat affected zone shows excellent low temperature toughness. {yields}Weld metal mainly consists of intragranularly nucleated acicular ferrites. {yields}Weld metal shows excellent low temperature toughness and high strength.

  3. Neutron diffraction study of the martensitic transformation and chemical order in Heusler alloy Ni1.91Mn1.29Ga0.8

    SciTech Connect

    Ari-Gur, Pnina; Garlea, Vasile O.; Cao, Huibo; Ge, Y.; Aaltio, I.; Hannula, S. P.; Koledov, V.

    2015-11-05

    In this study, Heusler alloys of Ni-Mn-Ga compositions demonstrate ferromagnetic shape memory effect in the martensitic state. The transformation temperature and the chemical order depend strongly on the composition. In the current work, the structure and chemical order of the martensitic phase of Ni1.91Mn1.29Ga0.8 were studied using neutron diffraction; the diffraction pattern was refined using the FullProf software. It was determined that the structural transition occurs around 330 K. At room temperature, 300 K, which is below the martensite transformation temperature, all the Bragg reflections can be described by a monoclinic lattice with a symmetry of space group P 1 2/m 1 and lattice constants of a = 4.23047(7) [Å], b = 5.58333(6) [Å], c = 21.0179(2) [Å], beta = 90.328(1). The chemical order is of critical importance in these alloys, and it was previously studied at 363 K. Analysis of the neutron diffraction in the monoclinic phase shows that the chemical order is maintained during the martensitic transformation.

  4. In-situ phase transformation in the field ion microscope.

    NASA Astrophysics Data System (ADS)

    Miller, M. K.; Russell, K. F.

    1991-04-01

    Many materials undergo an athermal martensite transformation when cooled. This transformation has been observed in the Tishomingo meteorite during cooling to cryogenic temperatures. The meteorite is unstable when cooled to the cryogenic temperatures (40 - 85K) suitable for field ion imaging since the martensite start temperature of this material (Fe-32.5 wt%Ni) is approximately 235K.

  5. Effects of Forming Induced Phase Transformation on Crushing Behavior of TRIP Steel

    SciTech Connect

    Liu, Wenning N.; Choi, Kyoo Sil; Soulami, Ayoub; Sun, Xin; Khaleel, Mohammad A.

    2010-04-15

    In this paper, results of finite element crash simulation are presented for a TRIP steel side rail with and without considering the phase transformation during forming operations. A homogeneous phase transformation model is adapted to model the mechanical behavior of the austenite-to-martensite phase. The forming process of TRIP steels is simulated with the implementation of the material model. The distribution and volume fraction of the martensite in TRIP steels may be greatly influenced by various factors during forming process and subsequently contribute to the behavior of the formed TRIP steels during the crushing process. The results indicate that, with the forming induced phase transformation, higher energy absorption of the side rail can be achieved. The phase transformation enhances the strength of the side rail

  6. Zig-zag twins and helical phase transformations.

    PubMed

    Ganor, Yaniv; Dumitrică, Traian; Feng, Fan; James, Richard D

    2016-04-28

    We demonstrate the large bending deformation induced by an array of permanent magnets (applied field ∼0.02 T) designed to minimize poles in the bent state of the crystal. Planar cantilevers of NiMnGa (5M modulated martensite) ferromagnetic shape memory alloy deform into an arched shape according to theory, with a zig-zag microstructure that complies with the kinematic and magnetic compatibility between adjacent twin variants. A general theory of bent and twisted states is given, applicable to both twinning and austenite/martensite transformations. Some of these configurations achieve order-of-magnitude amplification of rotation and axial strain. We investigate also atomistic analogues of these bent and twisted configurations with perfect interfaces between phases. These mechanisms of large deformation, induced by small magnetic fields or temperature changes, have potential application to the development of new actuation technologies for micro-robotic systems. PMID:27002072

  7. Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires

    PubMed Central

    Wang, Liqiang; Wang, Cong; Zhang, Lai-Chang; Chen, Liangyu; Lu, Weijie; Zhang, Di

    2016-01-01

    NiTi wires were brazed together via eutectic reaction between NiTi and Nb powder deposited at the wire contact region. Phase transformation and deformation behavior of the NiTi-Nb eutectic microstructure were investigated using transmission electron microscopy (TEM) and cyclic loading-unloading tests. Results show that R phase and B19′ martensite transformation are induced by plastic deformation. R phase transformation, which significantly contributes to superelasticity, preferentially occurs at the interfaces between NiTi and eutectic region. Round-shaped Nb-rich phase with rod-like and lamellar-type eutectics are observed in eutectic regions. These phases appear to affect the deformation behavior of the brazed NiTi-Nb region via five distinct stages in stress-strain curves: (I) R phase reorientation, (II) R phase transformation from parent phase, (III) elastic deformation of reoriented martensite accompanied by the plastic deformation of Nb-rich phase and lamellar NiTi-Nb eutectic, (IV) B19′ martensitic transformation, and (V) plastic deformation of the specimen. PMID:27049025

  8. Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires.

    PubMed

    Wang, Liqiang; Wang, Cong; Zhang, Lai-Chang; Chen, Liangyu; Lu, Weijie; Zhang, Di

    2016-01-01

    NiTi wires were brazed together via eutectic reaction between NiTi and Nb powder deposited at the wire contact region. Phase transformation and deformation behavior of the NiTi-Nb eutectic microstructure were investigated using transmission electron microscopy (TEM) and cyclic loading-unloading tests. Results show that R phase and B19' martensite transformation are induced by plastic deformation. R phase transformation, which significantly contributes to superelasticity, preferentially occurs at the interfaces between NiTi and eutectic region. Round-shaped Nb-rich phase with rod-like and lamellar-type eutectics are observed in eutectic regions. These phases appear to affect the deformation behavior of the brazed NiTi-Nb region via five distinct stages in stress-strain curves: (I) R phase reorientation, (II) R phase transformation from parent phase, (III) elastic deformation of reoriented martensite accompanied by the plastic deformation of Nb-rich phase and lamellar NiTi-Nb eutectic, (IV) B19' martensitic transformation, and (V) plastic deformation of the specimen. PMID:27049025

  9. Atomistic simulation of martensite-austenite phase transition in nanoscale nickel-titanium crystals

    NASA Astrophysics Data System (ADS)

    Kexel, Christian; Schramm, Stefan; Solov'yov, Andrey V.

    2015-09-01

    Shape-memory (SM) alloys can, after initial inelastic deformation, reconstruct their pristine lattice structure upon heating. The underlying phenomenon is the structural solid-solid phase transition from low-temperature lower-symmetry martensite to the high-temperature higher-symmetry austenite. Conventional nickel-titanium (NiTi) with near-equiatomic concentration already possesses an eminent importance for many applications, whereas the nanostructured equivalent can exhibit yet enhanced thermomechanical properties. However, no plausible microscopic theory of the SM effect in NiTi exists, especially for nanoscale systems. We investigate the thermally induced martensite-austenite phase transition in free equiatomic nanocrystals, comprising up to approximately 40 000 atoms, by means of molecular-dynamics simulations (MD) using a classical Gupta-type many-body scheme. Thereby we complement and extend a previously published study [D. Mutter, P. Nielaba, Eur. Phys. J. B 84, 109 (2011)]. The structural transition, revealing features of a first-order phase transition, is demonstrated. It is contrasted with the melting phase transition, a quantum solid model and bulk experimental findings. Moreover, a nucleation-growth process is observed as well as the irreversibility of the transition upon cooling.

  10. Stress-induced martensitic transformation during tensile test of full-size TF conductor jacket tube at 4.2 K

    SciTech Connect

    Yang, H. H.; Li, S. P.; Wu, Z. X.; Huang, C. J.; Huang, R. J.; Li, L. F.

    2014-01-27

    The toroidal-field (TF) conductor jacket of International Thermonuclear Experimental Reactor (ITER) is made of modified 316LN stainless steel, which is influenced by heat treatment at approximately 650 °C for 200 h to produce Nb{sub 3}Sn superconducting materials at the final stage. Due to the high electromagnetic forces arising during magnet operation, higher mechanical properties of the jacket materials at cryogenic temperatures are required. In our work, mechanical properties of the full-size TF conductor jacket tube were investigated, which satisfied the ITER requirements. Stress-induced martensitic transformation mechanism during tensile test of the conductor jacket material at 4.2 K was characterized by means of in-situ temperature dependent XRD, vibrating sample magnetometer (VSM) and in conjunction with transmission electron microscopy (TEM). The tensile behavior related to the amount of stress-induced phase transformation at cryogenic temperature was also discussed.

  11. The HCP To BCC Phase Transformation in Ti Characterized by Nanosecond Electron Microscopy

    SciTech Connect

    Campbell, G; LaGrange, T; King, W; Colvin, J; Ziegler, A; Browning, N; Kleinschmidt, H; Bostanjoglo, O

    2005-06-21

    The general class of martensitic phase transformations occurs by a rapid lattice-distortive mechanism, where kinetics and morphology of the transformation are dominated by the strain energy. Since transformation is diffusionless, phase fronts propagate through a crystal with great speed that can approach the speed of sound. We have observed a particular example of this class of phase transformation, the hexagonal close packed (HCP) to body centered cubic (BCC) transformation in titanium that is driven by a rapid increase in temperature. We have used a novel nanosecond electron microscope (the dynamic transmission electron microscope, DTEM) to acquire diffraction and imaging information on the transformation, which is driven in-situ by nanosecond laser irradiation. Using nanosecond exposure times that are possible in the DTEM, data can be collected about the transient events in these fast transformations. We have identified the phase transformation with diffraction patterns and correlated the time of the phase transformation with calculated conditions in the sample.

  12. Atomic Structure and Phase Transformations in Pu Alloys

    SciTech Connect

    Schwartz, A J; Cynn, H; Blobaum, K M; Wall, M A; Moore, K T; Evans, W J; Farber, D L; Jeffries, J R; Massalski, T B

    2008-04-28

    Plutonium and plutonium-based alloys containing Al or Ga exhibit numerous phases with crystal structures ranging from simple monoclinic to face-centered cubic. Only recently, however, has there been increased convergence in the actinides community on the details of the equilibrium form of the phase diagrams. Practically speaking, while the phase diagrams that represent the stability of the fcc {delta}-phase field at room temperature are generally applicable, it is also recognized that Pu and its alloys are never truly in thermodynamic equilibrium because of self-irradiation effects, primarily from the alpha decay of Pu isotopes. This article covers past and current research on several properties of Pu and Pu-(Al or Ga) alloys and their connections to the crystal structure and the microstructure. We review the consequences of radioactive decay, the recent advances in understanding the electronic structure, the current research on phase transformations and their relations to phase diagrams and phase stability, the nature of the isothermal martensitic {delta} {yields} {alpha}{prime} transformation, and the pressure-induced transformations in the {delta}-phase alloys. New data are also presented on the structures and phase transformations observed in these materials following the application of pressure, including the formation of transition phases.

  13. Characterization of the carbides and the martensite phase in powder-metallurgy high-speed steel

    SciTech Connect

    Godec, Matjaz; Batic, Barbara Setina; Mandrino, Djordje; Nagode, Ales; Leskovsek, Vojteh; Skapin, Sreco D.; Jenko, Monika

    2010-04-15

    A microstructural characterization of the powder-metallurgy high-speed-steel S390 Microclean was performed based on an elemental distribution of the carbide phase as well as crystallographic analyses. The results showed that there were two types of carbides present: vanadium-rich carbides, which were not chemically homogeneous and exhibited a tungsten-enriched or tungsten-depleted central area; and chemically homogeneous tungsten-rich M{sub 6}C-type carbides. Despite the possibility of chemical inhomogenities, the crystallographic orientation of each of the carbides was shown to be uniform. Using electron backscatter diffraction the vanadium-rich carbides were determined to be either cubic VC or hexagonal V{sub 6}C{sub 5}, while the tungsten-rich carbides were M{sub 6}C. The electron backscatter diffraction results were also verified using X-ray diffraction. Several electron backscatter diffraction pattern maps were acquired in order to define the fraction of each carbide phase as well as the amount of martensite phase. The fraction of martensite was estimated using band-contrast images, while the fraction of carbides was calculated using the crystallographic data.

  14. Self-trapping of carbon atoms in α'-Fe during the martensitic transformation: A qualitative picture from ab initio calculations

    NASA Astrophysics Data System (ADS)

    Ruban, A. V.

    2014-10-01

    Strain-induced and chemical interactions of interstitial carbon atoms in bcc or α-Fe are obtained in first-principles calculations. Subsequent Monte Carlo simulations show that at low temperatures, carbon atoms prefer to occupy at least two different octahedral sublattices, which is due to quite strong attractive interactions of carbon atoms at the corresponding coordination shells. The direct total-energy calculations of one of the obtained ordered structures with composition Fe16C2, show that it is more stable than the predicted earlier structure with the same composition but carbon atoms occupying only one octahedral sublattice. This indicates that the long-existing thermodynamic mean-field theory of ordering of carbon in α-Fe assuming strong preference of carbon atoms to occupy only one octahedral sublattice is deficient. It is shown that the presence of carbon atoms only at one octahedral sublattice in the experimentally observed martensitic phase, α'-Fe, is a self-trapping effect. It occurs during a displacive martensitic transformation from γ- to α-Fe, which kinematically transfers the carbon atoms from a single fcc octahedral sublattice to one of three octahedral sublattices, where they appear to be locked by a consequent tetragonal distortion minimizing elastic energy of the phase. The latter creates a strong preference for carbon atoms to be only at one already occupied octahedral sublattice preventing them from further distribution over the other sublattices.

  15. Shape Memory effect and Superelasticity in the [001] Single crystals of a FeNiCoAlTa Alloy with γ-α'-Thermoelastic Martensitic Transformations

    NASA Astrophysics Data System (ADS)

    Chumlyakov, Yu. I.; Kireeva, I. V.; Kretinina, I. V.; Keinikh, K. S.; Kuts, O. A.; Kirillov, V. A.; Karaman, I.; Maier, H.

    2013-12-01

    Using single crystals of a Fe - 28% Ni - 17% Co - 11.5% Al - 25% Ta (аt.%) alloy, oriented for tensile loading along the [001] direction, the shape-memory (SME) and superelasticity (SE) effects caused by reversible thermoelastic martensitic transformations (MTs) from a high-temperature fcc-phase into a bctmartensite are investigated. It is demonstrated that the conditions necessary for the thermoelastic MTs to occur are achieved by aging at 973 K within the time interval (t) from 0.5 to 7.0 hours, which is accompanied by precipitation of the γ'-phase particles, (FeNiCo)3(AlTa), whose d < 8-12 nm. When the size of the γ'-precipitates becomes as large as d ≥ 8-12 nm, the MT becomes partially reversible. The physical causes underlying the kinetics of thermoelstic reversible fcc-bct MTs are discussed.

  16. The Impact of Martensite Deformation on Shape Memory Effect Recovery Strain Evolution

    NASA Astrophysics Data System (ADS)

    Lanba, Asheesh; Hamilton, Reginald F.

    2015-08-01

    The one-way shape memory effect of polycrystalline NiTi is investigated after differential levels of martensite deformation. Martensite naturally forms an energy-minimizing configuration, referred to as self-accommodated, of differently oriented martensite variants, which are internally twinned. Stress preferentially orients a select variant that eventually detwins and plastically deforms at the highest stress levels. In this work, the underlying morphology is ascertained based on the evolution of micro-scale deformation measurements using digital image correlation analysis of three characteristic material responses. An initial martensitic structure is deformed at constant temperature. The forward austenite-to-martensite and reverse martensite-to-austenite phase transformations take place during temperature cycling under a constant stress. The austenite-to-martensite transformation is tensile stress induced at a constant temperature and initiates via a localized strain band. For the conversion of self-accommodated martensite to orientated morphology and further deformation, spatially heterogeneous strains accrue over the entire specimen surface. Shape memory recovery during heating, on the other hand, culminates with a centralized strain localization that persists as recovery approaches completion. The recovery temperature differential ( A f - A s) depends on the extent of deformation. This work characterizes the influence of stress on phase transformation and martensite deformation morphology for deformation in the martensitic state compared to the stress-induced phase transformation.

  17. Phase separation and superparamagnetism in the martensitic phase of N i50 -xC oxM n40S n10

    NASA Astrophysics Data System (ADS)

    Yuan, S.; Kuhns, P. L.; Reyes, A. P.; Brooks, J. S.; Hoch, M. J. R.; Srivastava, V.; James, R. D.; Leighton, C.

    2016-03-01

    N i50 -xC oxM n40S n10 shape memory alloys in the approximate range 5 ≤x ≤8 display desirable properties for applications as well as intriguing magnetism. These off-stoichiometric Heusler alloys undergo a martensitic phase transformation at a temperature TM of 300-400 K, from ferromagnetic (FM) to nonferromagnetic, with unusually low thermal hysteresis and a large change in magnetization. The low temperature magnetic structures in the martensitic phase of such alloys, which are distinctly inhomogeneous, are of great interest but are not well understood. Our present use of spin echo nuclear magnetic resonance in the large hyperfine fields at 55Mn sites provides compelling evidence that nanoscale magnetic phase separation into FM and antiferromagnetic (AFM) regions occurs below TM in alloys with x in the range 0 to 7. At finite Co substitution, the FM regions are found to be of two distinct types, corresponding to high and low local concentrations of Co on Ni sites. Estimates of the size distributions of both the FM and AFM nanoregions have been made. At x =7 , the AFM component is not long-range ordered, even below 4 K, and is quite different from the AFM component found at x =0 ; by x =14 , the FM phase is completely dominant. Of particular interest, we find for x =7 that field cooling leads to dramatic changes in the AFM regions. These findings provide insight into the origins of magnetic phase separation and superparamagnetism in these complex alloys, particularly their intrinsic exchange bias, which is of considerable current interest.

  18. Effect of Prior Athermal Martensite on the Isothermal Transformation Kinetics Below M s in a Low-C High-Si Steel

    NASA Astrophysics Data System (ADS)

    Navarro-López, A.; Sietsma, J.; Santofimia, M. J.

    2016-03-01

    Thermomechanical processing of Advanced Multiphase High Strength Steels often includes isothermal treatments around the martensite start temperature ( M s). It has been reported that the presence of martensite formed prior to these isothermal treatments accelerates the kinetics of the subsequent transformation. This kinetic effect is commonly attributed to the creation of potential nucleation sites at martensite-austenite interfaces. The aim of this study is to determine qualitatively and quantitatively the effect of a small volume fraction of martensite on the nucleation kinetics of the subsequent transformation. For this purpose, dilatometry experiments were performed at different temperatures above and below the M s temperature for athermal martensite in a low-carbon high-silicon steel. Microstructural analysis led to the identification of the isothermal decomposition product formed above and below M s as bainitic ferrite. The analysis of the transformation processes demonstrated that the initial stage of formation of bainitic ferrite at heat treatments below M s is at least two orders of magnitude faster than above M s due to the presence of martensite.

  19. Phase Transformations in Confined Nanosystems

    SciTech Connect

    Shield, Jeffrey E.; Belashchenko, Kirill

    2014-04-29

    This project discovered that non-equilibrium structures, including chemically ordered structures not observed in bulk systems, form in isolated nanoscale systems. Further, a generalized model was developed that effectively explained the suppression of equilibrium phase transformations. This thermodynamic model considered the free energy decrease associated with the phase transformation was less than the increase in energy associated with the formation of an interphase interface, therefore inhibiting the phase transformation. A critical diameter exists where the system transitions to bulk behavior, and a generalized equation was formulated that successfully predicted this transition in the Fe-Au system. This provided and explains a new route to novel structures not possible in bulk systems. The structural characterization was accomplished using transmission electron microscopy in collaboration with Matthew Kramer of Ames Laboratory. The PI and graduate student visited Ames Laboratory several times a year to conduct the experiments.

  20. A micromechanical modelling of the hysteretic behavior in thermally induced martensitic phase transitions: Application to Cu-Zn-Al shape memory alloys

    SciTech Connect

    Agouram, S.; Bensalah, M.O.; Ghazali, A.

    1998-12-11

    The hysteretic behavior of Cu-Zn-Al shape memory alloys (SMAs) in thermally induced martensitic phase transition is dealt with. The problem is studied by means of a kinematic analysis where the internal variables describing the material`s microstructure are regarded as implicit functions of the applied thermomechanical loading parameters ({Sigma}{sub ij}, {Tau}). On the other hand, a thermodynamic approach is used in which the local balance formalism is based on the thermoelastic equilibrium concept. Considering that thermoelastic equilibrium temperatures between phases, in the forward and reverse transformation, are dependent on the location in the transformation path enables the hysteretic behavior to be determined. Hence, a set of non-linear equations is deduced simulating the complete and partial cycles. Results obtained in this way, in the thermally induced phase transition with no applied stress, are in good agreement with experimental observations performed on Cu-based SMAs.

  1. Irreversible deformation and the superplasticity of a TN-1 alloy during thermal cycling through the martensitic transformations ranges under loading

    NASA Astrophysics Data System (ADS)

    Andronov, I. N.; Ryabkov, Yu. I.; Bogdanov, N. P.; Severova, N. A.; Danilov, A. N.; Churilina, I. V.

    2015-10-01

    The influence of the thermal cycling conditions on the thermal-cycling creep of a TN-1 alloy and the related irreversible deformations is studied. The conditions under which an anomalous increase in the irreversible deformations begins are determined. The structural mechanism of the irreversible deformations of an equiatomic alloy is shown to be analogous to the structural mechanism of metal creep at high temperatures: it predominantly has a dislocation character. It is proposed to use the effect of anomalous increase in the deformation of materials with reversible martensitic transformations for forming parts made of these materials at low temperatures.

  2. Interaction between phase transformations and dislocations at the nanoscale. Part 2: Phase field simulation examples

    NASA Astrophysics Data System (ADS)

    Javanbakht, Mahdi; Levitas, Valery I.

    2015-09-01

    The complete system of phase field equations for coupled martensitic phase transformations (PTs), dislocation evolution, and mechanics at large strains is presented. Finite element method (FEM) is utilized to solve this system for two important problems. The first one is related to the simulation of shear strain-induced PT at the evolving dislocation pile-ups in a nanosized bicrystal. Plasticity plays a dual part in the interaction with PT. Dislocation pile-ups produce strong stress tensor concentrators that lead to barrierless martensite (M) nucleation. On the other hand, plasticity in the transforming grain relaxes these stress concentrators suppressing PT. The final stationary M morphology is governed by the local thermodynamic equilibrium, either at the interfaces or in terms of stresses averaged over the martensitic region or the entire grain. This is very surprising because of strong heterogeneity of stress fields and is in contrast to previous statements that phase equilibrium conditions do not enter the description of strain-induced PTs. The second problem is devoted to martensitic plate propagation through a bicrystal during temperature-induced PT. For elastic growth (without dislocations) and a large thermal driving force, a complex transformation path with plate branching and direct and reverse PTs is observed, which still ends with the same stationary nanostructure as for a smaller driving force and a traditional transformation path. Sharp grain boundary arrests plate growth at a relatively small driving force, exhibiting an athermal friction. For elastoplastic growth, the generation of dislocations produces athermal friction and arrests the plate below some critical driving force, leading to a morphological transition from plate to lath M. The width of the martensitic plate increases in comparison with elastic growth due to internal stress relaxation. Plate growth is accompanied by the nucleation of dislocations within M and remaining in M, the

  3. The mathematical modeling of phase transformation of steel during quenching

    SciTech Connect

    Jahanian, S.; Mosleh, M.

    1999-02-01

    In the heat treatment of steel, uneven cooling invariably introduces residual stresses in the workpiece. These residual stresses can combine with the thermomechanical stresses encountered in operation to cause premature fatigue failure of the material. A prediction of the residual and thermoelastoplastic stresses developed during heat treatment would be beneficial for component design. In this article a numerical model is developed to predict the thermoelastoplastic and residual stresses during rapid cooling of a long solid cylinder. The total strains developed during cooling of the cylinder comprise elastic, thermal, and plastic strains and strains due to phase transformation. For plastic deformation an extension of Jiang`s constitutive equations developed by Jahanian is adopted. The properties of the material are assumed to be temperature dependent and characterized by nonlinear strain hardening. For phase transformation two parts are considered: nucleation according to Scheil`s method and phase growth according to Johnson and Mehl`s law. For martensitic transformation, a law established by Koisteinin and Marburger is used. Non-additivity of pearlitic and bainitic nucleation suggested by Manning and Lorig is taken into account by means of a correction factor to Scheil`s summation of the transition from pearlitic to bainitic. The effect of phase transformation and temperature dependence of material properties is investigated. It is shown that by neglecting the temperature dependency and phase transformation in numerical calculations, the results are underestimated. The numerical results are compared with the available experimental data in the literature, and good agreement is observed.

  4. Phase Transformation in Tantalum under Extreme Laser Deformation

    SciTech Connect

    Lu, C. -H.; Hahn, E. N.; Remington, B. A.; Maddox, B. R.; Bringa, E. M.; Meyers, M. A.

    2015-10-19

    The structural and mechanical response of metals is intimately connected to phase transformations. For instance, the product of a phase transformation (martensite) is responsible for the extraordinary range of strength and toughness of steel, making it a versatile and important structural material. Although abundant in metals and alloys, the discovery of new phase transformations is not currently a common event and often requires a mix of experimentation, predictive computations, and luck. High-energy pulsed lasers enable the exploration of extreme pressures and temperatures, where such discoveries may lie. The formation of a hexagonal (omega) phase was observed in recovered monocrystalline body-centered cubic tantalum of four crystallographic orientations subjected to an extreme regime of pressure, temperature, and strain-rate. This was accomplished using high-energy pulsed lasers. The omega phase and twinning were identified by transmission electron microscopy at 70 GPa (determined by a corresponding VISAR experiment). It is proposed that the shear stresses generated by the uniaxial strain state of shock compression play an essential role in the transformation. Lastly, molecular dynamics simulations show the transformation of small nodules from body-centered cubic to a hexagonal close-packed structure under the same stress state (pressure and shear).

  5. Phase Transformation in Tantalum under Extreme Laser Deformation.

    PubMed

    Lu, C-H; Hahn, E N; Remington, B A; Maddox, B R; Bringa, E M; Meyers, M A

    2015-01-01

    The structural and mechanical response of metals is intimately connected to phase transformations. For instance, the product of a phase transformation (martensite) is responsible for the extraordinary range of strength and toughness of steel, making it a versatile and important structural material. Although abundant in metals and alloys, the discovery of new phase transformations is not currently a common event and often requires a mix of experimentation, predictive computations, and luck. High-energy pulsed lasers enable the exploration of extreme pressures and temperatures, where such discoveries may lie. The formation of a hexagonal (omega) phase was observed in recovered monocrystalline body-centered cubic tantalum of four crystallographic orientations subjected to an extreme regime of pressure, temperature, and strain-rate. This was accomplished using high-energy pulsed lasers. The omega phase and twinning were identified by transmission electron microscopy at 70 GPa (determined by a corresponding VISAR experiment). It is proposed that the shear stresses generated by the uniaxial strain state of shock compression play an essential role in the transformation. Molecular dynamics simulations show the transformation of small nodules from body-centered cubic to a hexagonal close-packed structure under the same stress state (pressure and shear). PMID:26478106

  6. Phase transformation in tantalum under extreme laser deformation

    DOE PAGESBeta

    Lu, C. -H.; Hahn, E. N.; Remington, B. A.; Maddox, B. R.; Bringa, E. M.; Meyers, M. A.

    2015-10-19

    The structural and mechanical response of metals is intimately connected to phase transformations. For instance, the product of a phase transformation (martensite) is responsible for the extraordinary range of strength and toughness of steel, making it a versatile and important structural material. Although abundant in metals and alloys, the discovery of new phase transformations is not currently a common event and often requires a mix of experimentation, predictive computations, and luck. High-energy pulsed lasers enable the exploration of extreme pressures and temperatures, where such discoveries may lie. The formation of a hexagonal (omega) phase was observed in recovered monocrystalline body-centeredmore » cubic tantalum of four crystallographic orientations subjected to an extreme regime of pressure, temperature, and strain-rate. This was accomplished using high-energy pulsed lasers. The omega phase and twinning were identified by transmission electron microscopy at 70 GPa (determined by a corresponding VISAR experiment). It is proposed that the shear stresses generated by the uniaxial strain state of shock compression play an essential role in the transformation. In conclusion, molecular dynamics simulations show the transformation of small nodules from body-centered cubic to a hexagonal close-packed structure under the same stress state (pressure and shear).« less

  7. Phase transformation in tantalum under extreme laser deformation

    SciTech Connect

    Lu, C. -H.; Hahn, E. N.; Remington, B. A.; Maddox, B. R.; Bringa, E. M.; Meyers, M. A.

    2015-10-19

    The structural and mechanical response of metals is intimately connected to phase transformations. For instance, the product of a phase transformation (martensite) is responsible for the extraordinary range of strength and toughness of steel, making it a versatile and important structural material. Although abundant in metals and alloys, the discovery of new phase transformations is not currently a common event and often requires a mix of experimentation, predictive computations, and luck. High-energy pulsed lasers enable the exploration of extreme pressures and temperatures, where such discoveries may lie. The formation of a hexagonal (omega) phase was observed in recovered monocrystalline body-centered cubic tantalum of four crystallographic orientations subjected to an extreme regime of pressure, temperature, and strain-rate. This was accomplished using high-energy pulsed lasers. The omega phase and twinning were identified by transmission electron microscopy at 70 GPa (determined by a corresponding VISAR experiment). It is proposed that the shear stresses generated by the uniaxial strain state of shock compression play an essential role in the transformation. In conclusion, molecular dynamics simulations show the transformation of small nodules from body-centered cubic to a hexagonal close-packed structure under the same stress state (pressure and shear).

  8. Phase Transformation in Tantalum under Extreme Laser Deformation

    DOE PAGESBeta

    Lu, C. -H.; Hahn, E. N.; Remington, B. A.; Maddox, B. R.; Bringa, E. M.; Meyers, M. A.

    2015-10-19

    The structural and mechanical response of metals is intimately connected to phase transformations. For instance, the product of a phase transformation (martensite) is responsible for the extraordinary range of strength and toughness of steel, making it a versatile and important structural material. Although abundant in metals and alloys, the discovery of new phase transformations is not currently a common event and often requires a mix of experimentation, predictive computations, and luck. High-energy pulsed lasers enable the exploration of extreme pressures and temperatures, where such discoveries may lie. The formation of a hexagonal (omega) phase was observed in recovered monocrystalline body-centeredmore » cubic tantalum of four crystallographic orientations subjected to an extreme regime of pressure, temperature, and strain-rate. This was accomplished using high-energy pulsed lasers. The omega phase and twinning were identified by transmission electron microscopy at 70 GPa (determined by a corresponding VISAR experiment). It is proposed that the shear stresses generated by the uniaxial strain state of shock compression play an essential role in the transformation. Lastly, molecular dynamics simulations show the transformation of small nodules from body-centered cubic to a hexagonal close-packed structure under the same stress state (pressure and shear).« less

  9. Phase Transformation in Tantalum under Extreme Laser Deformation

    PubMed Central

    Lu, C.-H.; Hahn, E. N.; Remington, B. A.; Maddox, B. R.; Bringa, E. M.; Meyers, M. A.

    2015-01-01

    The structural and mechanical response of metals is intimately connected to phase transformations. For instance, the product of a phase transformation (martensite) is responsible for the extraordinary range of strength and toughness of steel, making it a versatile and important structural material. Although abundant in metals and alloys, the discovery of new phase transformations is not currently a common event and often requires a mix of experimentation, predictive computations, and luck. High-energy pulsed lasers enable the exploration of extreme pressures and temperatures, where such discoveries may lie. The formation of a hexagonal (omega) phase was observed in recovered monocrystalline body-centered cubic tantalum of four crystallographic orientations subjected to an extreme regime of pressure, temperature, and strain-rate. This was accomplished using high-energy pulsed lasers. The omega phase and twinning were identified by transmission electron microscopy at 70 GPa (determined by a corresponding VISAR experiment). It is proposed that the shear stresses generated by the uniaxial strain state of shock compression play an essential role in the transformation. Molecular dynamics simulations show the transformation of small nodules from body-centered cubic to a hexagonal close-packed structure under the same stress state (pressure and shear). PMID:26478106

  10. The effect of multiple martensitic transformations on diffusion of Fe and Ni atoms in Fe-31.7%Ni-0.06%C alloy

    PubMed Central

    2014-01-01

    Diffusion characteristics of iron and nickel atoms were investigated using radioactive isotopes method in phase-hardened metastable iron-nickel Fe-31.7%Ni-0.06%C alloy with nanofragmented structure. It has been found that diffusion mobility of nickel and iron atoms in reverted austenite of Fe-31.7%Ni-0.06%C alloy significantly increases as the result of multiple γ-α-γ martensitic transformations. The diffusion coefficients of nickel and iron in the austenite at 400°C corresponded to the stationary diffusion coefficients at the temperatures above 900°C. The revealed diffusion acceleration at low temperatures is caused by high-density dislocations and additional low-angle subboundaries of disoriented nanofragments of reverted austenite and deformation twin subboundaries formed during multiple γ-α-γ cycles. PMID:25024684

  11. Simultaneous investigation of thermal, acoustic, and magnetic emission during martensitic transformation in single-crystalline Ni2MnGa

    NASA Astrophysics Data System (ADS)

    Tóth, László Z.; Daróczi, Lajos; Szabó, Sándor; Beke, Dezső L.

    2016-04-01

    Simultaneous thermal, acoustic, and magnetic emission (AE and ME) measurements during thermally induced martensitic transformation in Ni2MnGa single crystals demonstrate that all three types of the above noises display many coincident peaks and the same start and finish temperatures. The amplitude and energy distribution functions for AE and ME avalanches satisfy power-law behavior, corresponding to the symmetry of the martensite. At zero external magnetic field asymmetry in the exponents was obtained: their value was larger for heating than for cooling. Application of constant, external magnetic fields (up to B =722 mT) leads to the disappearance of the above asymmetry, due to the decrease of the multiplicity of the martensite variants. Time correlations (i.e., the existence of nonhomogeneous temporal processes) within AE as well as ME emission events are demonstrated by deviations from the uncorrelated behavior on probability distributions of waiting times as well as of a sequence of number of events. It is shown that the above functions collapse on universal master curves for cooling and heating as well as for AE and ME noises. The analysis of the existence of temporal correlations between AE and ME events revealed that at short times the acoustic signals show a time delay relative to the magnetic one, due to the time necessary for the propagation of the ultrasound. At intermediate times, as expected, the magnetic signal is delayed, i.e., the magnetic domain rearrangement followed the steps of structural transformation. At much longer times the deviation from an uncorrelated (Poisson-type) behavior is attributed to the nonhomogeneity of the avalanche statistics.

  12. Precipitate phases in normalized and tempered ferritic/martensitic steel P92

    NASA Astrophysics Data System (ADS)

    Shen, Yinzhong; Liu, Huan; Shang, Zhongxia; Xu, Zhiqiang

    2015-10-01

    Ferritic/martensitic steel P92 is a promising candidate for cladding and duct applications in Sodium-Cooled Fast Reactor. The precipitate phases of the P92 steel normalized at 1323 K (1050 °C) for 30 min and tempered at 1038 K (765 °C) for 1 h have been investigated using transmission electron microscopes. Four types of phases consisting of M23C6, MX, M2X and sigma-FeCr were identified in the steel. MX phases consist of Nb-rich M(C,N) carbonitride, Nb-rich MC carbide, V-rich M(C,N) carbonitride, V-rich MC carbide, V-rich MN nitride, and complex MC carbides with Nb-rich MC core and V-rich MC wings. M2X phases consist of Cr-rich M2(C,N) carbonitride, Cr-rich M2C carbide and M2N nitride. Sigma-FeCr has a simple tetragonal lattice and a typical chemical formula of Fe0.45Cr0.45W0.1. M23C6 and MX are the dominant phases, while the sigma-FeCr has the lowest content. The formation of sigma-FeCr and M2X phases in the steel is also discussed.

  13. Influence of annealing on martensitic transformation and magnetic entropy change in Ni37.7Co12.7Mn40.8Sn8.8 magnetic shape memory alloy ribbon

    NASA Astrophysics Data System (ADS)

    Chen, F.; Liu, W. L.; Shi, Y. G.; Müllner, P.

    2015-03-01

    The microstructure, martensitic transformation and magnetic properties of Ni37.7Co12.7Mn40.8Sn8.8 high temperature magnetic shape memory ribbon subjected to different annealing temperature were investigated. Annealing up to 1073 K slightly raised the transformation temperatures and the transformation interval, while annealing at 1173 K considerably decreased the transformation temperature and strongly widened the transformation interval due to the formation of a second phase. The as-spun and annealed ribbon at 973 K exhibited giant magnetic entropy changes of around 15 J/kg K under 15 kOe magnetic field above 400 K. Further increasing annealing temperature caused a decrease of the magnetic entropy change. To achieve a large magnetocaloric effect while keeping an elevated transformation temperature, an appropriate annealing parameter should be carefully considered.

  14. Drastic influence of minor Fe or Co additions on the glass forming ability, martensitic transformations and mechanical properties of shape memory Zr-Cu-Al bulk metallic glass composites

    NASA Astrophysics Data System (ADS)

    González, Sergio; Pérez, Pablo; Rossinyol, Emma; Suriñach, Santiago; Baró, Maria Dolors; Pellicer, Eva; Sort, Jordi

    2014-06-01

    The microstructure and mechanical properties of Zr48Cu48 - x Al4M x (M ≡ Fe or Co, x = 0, 0.5, 1 at.%) metallic glass (MG) composites are highly dependent on the amount of Fe or Co added as microalloying elements in the parent Zr48Cu48Al4 material. Addition of Fe and Co promotes the transformation from austenite to martensite during the course of nanoindentation or compression experiments, resulting in an enhancement of plasticity. However, the presence of Fe or Co also reduces the glass forming ability, ultimately causing a worsening of the mechanical properties. Owing to the interplay between these two effects, the compressive plasticity for alloys with x = 0.5 (5.5% in Zr48Cu47.5Al4Co0.5 and 6.2% in Zr48Cu47.5Al4Fe0.5) is considerably larger than for Zr48Cu48Al4 or the alloys with x = 1. Slight variations in the Young’s modulus (around 5-10%) and significant changes in the yield stress (up to 25%) are also observed depending on the composition. The different microstructural factors that have an influence on the mechanical behavior of these composites are investigated in detail: (i) co-existence of amorphous and crystalline phases in the as-cast state, (ii) nature of the crystalline phases (austenite versus martensite content), and (iii) propensity for the austenite to undergo a mechanically-driven martensitic transformation during plastic deformation. Evidence for intragranular nanotwins likely generated in the course of the austenite-martensite transformation is provided by transmission electron microscopy. Our results reveal that fine-tuning of the composition of the Zr-Cu-Al-(Fe,Co) system is crucial in order to optimize the mechanical performance of these bulk MG composites, to make them suitable materials for structural applications.

  15. The correlation of local deformation and stress-assisted local phase transformations in MMC foams

    SciTech Connect

    Berek, H.; Ballaschk, U.; Aneziris, C.G.; Losch, K.; Schladitz, K.

    2015-09-15

    Cellular structures are of growing interest for industry, and are of particular importance for lightweight applications. In this paper, a special case of metal matrix composite foams (MMCs) is investigated. The investigated foams are composed of austenitic steel exhibiting transformation induced plasticity (TRIP) and magnesia partially stabilized zirconia (Mg-PSZ). Both components exhibit martensitic phase transformation during deformation, thus generating the potential for improved mechanical properties such as strength, ductility, and energy absorption capability. The aim of these investigations was to show that stress-assisted phase transformations within the ceramic reinforcement correspond to strong local deformation, and to determine whether they can trigger martensitic phase transformations in the steel matrix. To this end, in situ interrupted compression experiments were performed in an X-ray computed tomography device (XCT). By using a recently developed registration algorithm, local deformation could be calculated and regions of interest could be defined. Corresponding cross sections were prepared and used to analyze the local phase composition by electron backscatter diffraction (EBSD). The results show a strong correlation between local deformation and phase transformation. - Graphical abstract: Display Omitted - Highlights: • In situ compressive deformation on MMC foams was performed in an XCT. • Local deformation fields and their gradient amplitudes were estimated. • Cross sections were manufactured containing defined regions of interest. • Local EBSD phase analysis was performed. • Local deformation and local phase transformation are correlated.

  16. Phase Stability and Stress-Induced Transformations in Beta Titanium Alloys

    NASA Astrophysics Data System (ADS)

    Kolli, R. Prakash; Joost, William J.; Ankem, Sreeramamurthy

    2015-06-01

    In this article, we provide a brief review of the recent developments related to the relationship between phase stability and stress-induced transformations in metastable body-centered-cubic β-phase titanium alloys. Stress-induced transformations occur during tensile, compressive, and creep loading and influence the mechanical response. These transformations are not fully understood and increased understanding of these mechanisms will permit future development of improved alloys for aerospace, biomedical, and energy applications. In the first part of this article, we review phase stability and discuss a few recent developments. In the second section, we discuss the current status of understanding stress-induced transformations and several areas that require further study. We also provide our perspective on the direction of future research efforts. Additionally, we address the occurrence of the hcp ω-phase and the orthorhombic α″-martensite phase stress-induced transformations.

  17. Internal friction measurements of phase transformations during the process of deep cryogenic treatment of a tool steel

    NASA Astrophysics Data System (ADS)

    Li, Shaohong; Min, Na; Li, Junwan; Wu, Xiaochun

    2013-10-01

    This paper reports internal friction measurements in die steel with the aim of clarifying phase transformation mechanisms during deep cryogenic treatment (DCT). Internal friction peaks appeared in the quenched sample and the DCT treated material during the process of cooling down to -160 °C from room temperature (20 °C) and then heating up to room temperature for multiple cycles in high vacuum. However, internal friction peaks do not appear in annealed material. It is concluded that the internal friction peaks are attributed to stress-induced martensite formation based on thermal hysteresis phenomena. That is, retained austenite is mostly transformed into martensite during the DCT.

  18. The role of the martensite transformation for the mechanical amorphization of NiTi

    SciTech Connect

    Ewert, J.C.; Boehm, I.; Haider, F.; Peter, R.

    1997-05-01

    Mechanical amorphization by cold rolling and uniaxial deformation of the intermetallic compound NiTi was studied by TEM and DSC. In cold rolled samples it could be clearly shown that amorphization occurs and that the amorphous regions recrystallize at T {approx} 350 C. In uniaxially deformed material a microstructure similar to that of cold rolled samples and a DSC-peak at the same temperature was found. In the TEM, extended amorphous regions could only be identified after a moderate heat treatment at 250 C. After deformation at temperatures above room temperature, a considerably lower degree of amorphization was found, and the fraction of amorphous volume was found to depend on the martensite transition temperature of the material.

  19. Effect of niobium addition on the martensitic transformation and magnetocaloric effect in low hysteresis NiCoMnSn magnetic shape memory alloys

    SciTech Connect

    Emre, Baris; Bruno, Nickolaus M.; Yuce Emre, Suheyla; Karaman, Ibrahim

    2014-12-08

    The effect of Nb substitution for Ni in Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} magnetic shape memory alloys on their magnetic properties, martensitic transformation characteristics, transformation hysteresis, and magnetocaloric properties was studied using wavelength-dispersive X-ray spectroscopy, differential scanning calorimetry, and the temperature and field dependence of the magnetization. Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} alloy has a very low transformation hysteresis; however, the martensitic transformation temperatures are notably above room temperature, which is not desirable for magnetic refrigeration applications. In this study, small quantities of Nb substitution were shown to drastically shift the transformation temperatures to lower temperatures, at a rate of 68 K/at. % Nb, which is needed for household refrigeration. The austenite Curie temperature also decreased with increasing Nb content. However, a decrease in the latent heat of the martensitic transition was observed, which negatively affects the magnetic field-induced adiabatic temperature change capability. Still, the relatively large transformation entropy and the low transformation hysteresis make the Nb-doped Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} alloys potential candidates for solid state refrigeration near room temperature.

  20. Effect of niobium addition on the martensitic transformation and magnetocaloric effect in low hysteresis NiCoMnSn magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Emre, Baris; Bruno, Nickolaus M.; Yuce Emre, Suheyla; Karaman, Ibrahim

    2014-12-01

    The effect of Nb substitution for Ni in Ni45Co5Mn40Sn10 magnetic shape memory alloys on their magnetic properties, martensitic transformation characteristics, transformation hysteresis, and magnetocaloric properties was studied using wavelength-dispersive X-ray spectroscopy, differential scanning calorimetry, and the temperature and field dependence of the magnetization. Ni45Co5Mn40Sn10 alloy has a very low transformation hysteresis; however, the martensitic transformation temperatures are notably above room temperature, which is not desirable for magnetic refrigeration applications. In this study, small quantities of Nb substitution were shown to drastically shift the transformation temperatures to lower temperatures, at a rate of 68 K/at. % Nb, which is needed for household refrigeration. The austenite Curie temperature also decreased with increasing Nb content. However, a decrease in the latent heat of the martensitic transition was observed, which negatively affects the magnetic field-induced adiabatic temperature change capability. Still, the relatively large transformation entropy and the low transformation hysteresis make the Nb-doped Ni45Co5Mn40Sn10 alloys potential candidates for solid state refrigeration near room temperature.

  1. Determination of the vibrational contribution to the entropy change at the martensitic transformation in Ni–Mn–Sn metamagnetic shape memory alloys: a combined approach of time-of-flight neutron spectroscopy and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Recarte, V.; Zbiri, M.; Jiménez-Ruiz, M.; Sánchez-Alarcos, V.; Pérez-Landazábal, J. I.

    2016-05-01

    The different contributions to the entropy change linked to the austenite-martensitic transition in a Ni–Mn–Sn metamagnetic shape memory alloy have been determined by combining different experimental techniques. The vibrational contribution has been inferred from the vibrational density of states of both the martensitic and austenite phases. This has been accomplished by combining time-of-flight neutron scattering measurements and ab initio calculations. Further, the electronic part of the entropy change has also been calculated. Since the martensitic transformation takes place between two paramagnetic phases, the magnetic contribution can be neglected and the entropy change can be reduced to the sum of two terms: vibrational and electronic. The obtained value of the vibrational contribution (-36+/- 5 \\text{J} \\text{k}{{\\text{g}}-1} {{\\text{K}}-1} ) nearly provides the total entropy change measured by calorimetry (-41~+/- 3 \\text{J} \\text{k}{{\\text{g}}-1} {{\\text{K}}-1} ), the difference being the electronic contribution within the experimental error.

  2. Re-equilibration after quenches in athermal martensites: Conversion delays for vapor-to-liquid domain-wall phases

    NASA Astrophysics Data System (ADS)

    Shankaraiah, N.; Murthy, K. P. N.; Lookman, T.; Shenoy, S. R.

    2015-06-01

    Entropy barriers and aging states appear in martensitic structural-transition models, slowly re-equilibrating after temperature quenches, under Monte Carlo dynamics. Concepts from protein folding and aging harmonic oscillators turn out to be useful in understanding these nonequilibrium evolutions. We show how the athermal, nonactivated delay time for seeded parent-phase austenite to convert to product-phase martensite arises from an identified entropy barrier in Fourier space. In an aging state of low Monte Carlo acceptances, the strain structure factor makes constant-energy searches for rare pathways to enter a Brillouin zone "golf hole" enclosing negative-energy states, and to suddenly release entropically trapped stresses. In this context, a stress-dependent effective temperature can be defined, that re-equilibrates to the quenched bath temperature.

  3. Magnetic and magneto-transport studies of substrate effect on the martensitic transformation in a NiMnIn shape memory alloy

    NASA Astrophysics Data System (ADS)

    Sokolov, Andrei; Kirianov, Eugene; Zlenko, Albina; Quetz, Abdiel; Aryal, Anil; Pandey, Sudip; Dubenko, Igor; Stadler, Shane; Ali, Naushad; Al-Aqtash, Nabil; Sabirianov, Renat

    2016-05-01

    The effect of substrates on the magnetic and transport properties of Ni2Mn1.5In0.5 ultra-thin films were studied theoretically and experimentally. High quality 8-nm films were grown by laser-assisted molecular beam epitaxy deposition. Magneto-transport measurements revealed that the films undergo electronic structure transformation similar to those of bulk materials at the martensitic transformation. The temperature of the transformation depends strongly on lattice parameters of the substrate. To explain this behavior, we performed DFT calculations on the system and found that different substrates change the relative stability of the ferromagnetic (FM) austenite and ferrimagnetic (FiM) martensite states. We conclude that the energy difference between the FM austenite and FiM martensite states in Ni2Mn1.5In0.5 films grown on MgO (001) substrates is ΔE = 0.20 eV per NiMnIn f.u, somewhat lower compared to ΔE = 0.24 eV in the bulk material with the same lattice parameters. When the lattice parameters of Ni2Mn1.5In0.5 film have values close to those of the MgO substrate, the energy difference becomes ΔE = 0.08 eV per NiMnIn f.u. These results suggest the possibility to control the martensitic transition in thin films through substrate engineering.

  4. The effect of crystallographic texture on stress-induced martensitic transformation in NiTi: A computational analysis.

    PubMed

    Weafer, F M; Guo, Y; Bruzzi, M S

    2016-01-01

    NiTi׳s superelasticity is exploited in a number of biomedical devices, in particular self-expanding endovascular stents. These stents are often laser-cut from textured micro-tubing; texture is the distribution of crystallographic grain orientations in a polycrystalline material which has been experimentally shown to have a marked influence on mechanical properties. This study offers a computational examination into the effect of texture on the stress-induced martensite transformation (SIMT) in a micro-dogbone NiTi specimen subject to tensile loading. Finite Element Analysis (FEA) is employed to simulate the transformational behaviour of the specimen on a micro-scale level. To represent a realistic grain structure in the FEA model, grains present in a 200µm×290µm test site located at the centre edge of the specimen were identified using Scanning Electron Microscopy (SEM). Grains are assumed to have homogenous behaviour with properties varying according to their crystallographic orientation to the loading direction. Required material properties were extracted from uniaxial stress-strain curves of single crystals for each crystallographic orientation for input into the in-built UMAT/Nitinol. The orientation of each grain in the test site was identified using Electron Back-Scatter Diffraction (EBSD) techniques. In this way, a quantitative explanation is offered to the effect of crystallographic texture on SIMT. Finally, the evolution of grains in the specimen, during the transformation process, was experimentally investigated by means of an in-situ SEM tensile test. PMID:26334356

  5. Revealing martensitic transformation and α/β interface evolution in electron beam melting three-dimensional-printed Ti-6Al-4V

    NASA Astrophysics Data System (ADS)

    Tan, Xipeng; Kok, Yihong; Toh, Wei Quan; Tan, Yu Jun; Descoins, Marion; Mangelinck, Dominique; Tor, Shu Beng; Leong, Kah Fai; Chua, Chee Kai

    2016-05-01

    As an important metal three-dimensional printing technology, electron beam melting (EBM) is gaining increasing attention due to its huge potential applications in aerospace and biomedical fields. EBM processing of Ti-6Al-4V as well as its microstructure and mechanical properties were extensively investigated. However, it is still lack of quantitative studies regarding its microstructural evolution, indicative of EBM thermal process. Here, we report α‧ martensitic transformation and α/β interface evolution in varied printing thicknesses of EBM-printed Ti-6Al-4V block samples by means of atom probe tomography. Quantitative chemical composition analysis suggests a general phase transformation sequence. By increasing in-fill hatched thickness, elemental partitioning ratios arise and β volume fraction is increased. Furthermore, we observe kinetic vanadium segregation and aluminum depletion at interface front and the resultant α/β interface widening phenomenon. It may give rise to an increased α/β lattice mismatch and weakened α/β interfaces, which could account for the degraded strength as printing thickness increases.

  6. Revealing martensitic transformation and α/β interface evolution in electron beam melting three-dimensional-printed Ti-6Al-4V.

    PubMed

    Tan, Xipeng; Kok, Yihong; Toh, Wei Quan; Tan, Yu Jun; Descoins, Marion; Mangelinck, Dominique; Tor, Shu Beng; Leong, Kah Fai; Chua, Chee Kai

    2016-01-01

    As an important metal three-dimensional printing technology, electron beam melting (EBM) is gaining increasing attention due to its huge potential applications in aerospace and biomedical fields. EBM processing of Ti-6Al-4V as well as its microstructure and mechanical properties were extensively investigated. However, it is still lack of quantitative studies regarding its microstructural evolution, indicative of EBM thermal process. Here, we report α' martensitic transformation and α/β interface evolution in varied printing thicknesses of EBM-printed Ti-6Al-4V block samples by means of atom probe tomography. Quantitative chemical composition analysis suggests a general phase transformation sequence. By increasing in-fill hatched thickness, elemental partitioning ratios arise and β volume fraction is increased. Furthermore, we observe kinetic vanadium segregation and aluminum depletion at interface front and the resultant α/β interface widening phenomenon. It may give rise to an increased α/β lattice mismatch and weakened α/β interfaces, which could account for the degraded strength as printing thickness increases. PMID:27185285

  7. Revealing martensitic transformation and α/β interface evolution in electron beam melting three-dimensional-printed Ti-6Al-4V

    PubMed Central

    Tan, Xipeng; Kok, Yihong; Toh, Wei Quan; Tan, Yu Jun; Descoins, Marion; Mangelinck, Dominique; Tor, Shu Beng; Leong, Kah Fai; Chua, Chee Kai

    2016-01-01

    As an important metal three-dimensional printing technology, electron beam melting (EBM) is gaining increasing attention due to its huge potential applications in aerospace and biomedical fields. EBM processing of Ti-6Al-4V as well as its microstructure and mechanical properties were extensively investigated. However, it is still lack of quantitative studies regarding its microstructural evolution, indicative of EBM thermal process. Here, we report α′ martensitic transformation and α/β interface evolution in varied printing thicknesses of EBM-printed Ti-6Al-4V block samples by means of atom probe tomography. Quantitative chemical composition analysis suggests a general phase transformation sequence. By increasing in-fill hatched thickness, elemental partitioning ratios arise and β volume fraction is increased. Furthermore, we observe kinetic vanadium segregation and aluminum depletion at interface front and the resultant α/β interface widening phenomenon. It may give rise to an increased α/β lattice mismatch and weakened α/β interfaces, which could account for the degraded strength as printing thickness increases. PMID:27185285

  8. Phase transformations in some hafnium-tantalum-titanium-zirconium alloys

    SciTech Connect

    Ohriner, E.K.; Kapoor, D.

    1997-11-01

    Phase transformations in hafnium alloys are of interest as a means of achieving a material which exhibits flow softening and high localized strains during deformation at high strain rates. Hafnium transforms from a body-centered-cubic beta phase to a hexagonal alpha phase upon cooling below 1749{degrees}C. Hafnium-based alloys containing up to 17.5% Ti, up to 17.5% Ta, and up to 7.3% Zr by weight were button-arc melted and, in some cases, hot extruded to obtain a refined grain size. A number of alloys were shown to have beta solvus temperatures in the range of 1100 to 1300{degrees}C and showed evidence of a shear transformation upon water quenching. The Vickers microhardness of the quenched materials are typically above 350 HV as compared to 300 HV or less for materials with an alpha plus beta structure. Quenching dilatometry indicates a martensite start temperature of about 750{degrees}C for the Hf-7.5 Ta-10 Ti-1 Zr alloy and 800{degrees}C or more for the Hf-7.5 Ta-7.5 Ti-1 Zr alloy. Tensile tests at 1 s{sup {minus}1} strain rate show a constant ultimate tensile strength for temperatures up to 600{degrees}C for the above two alloys and a rapid decrease in strength with a further increase in temperature.

  9. Tuning avalanche criticality: Acoustic emission during the martensitic transformation of a compressed Ni-Mn-Ga single crystal

    NASA Astrophysics Data System (ADS)

    Niemann, R.; Baró, J.; Heczko, O.; Schultz, L.; Fähler, S.; Vives, E.; Mañosa, L.; Planes, A.

    2012-12-01

    The propagation of a phase front during a thermally induced martensitic transition is discontinuous due to pinning at various defects, an effect which results in acoustic emission. Here we analyze the consequences of an applied compressive stress exemplarily on a Ni50.4Mn27.9Ga21.7 single crystal. Our experiments show that the distribution of the energies of the acoustic emission events follows a power law for more than three decades. This indicates that the transition exhibits avalanche criticality. The exponent characterizing the distribution of energies depends on the applied stress, and decreases from 1.9±0.1 at zero stress to 1.5±0.2 at stress above 3MPa. This decrease could be attributed to the reduced multiplicity of variants possible under uniaxial compression.

  10. Phase field modeling of tetragonal to monoclinic phase transformation in zirconia

    NASA Astrophysics Data System (ADS)

    Mamivand, Mahmood

    Zirconia based ceramics are strong, hard, inert, and smooth, with low thermal conductivity and good biocompatibility. Such properties made zirconia ceramics an ideal material for different applications form thermal barrier coatings (TBCs) to biomedicine applications like femoral implants and dental bridges. However, this unusual versatility of excellent properties would be mediated by the metastable tetragonal (or cubic) transformation to the stable monoclinic phase after a certain exposure at service temperatures. This transformation from tetragonal to monoclinic, known as LTD (low temperature degradation) in biomedical application, proceeds by propagation of martensite, which corresponds to transformation twinning. As such, tetragonal to monoclinic transformation is highly sensitive to mechanical and chemomechanical stresses. It is known in fact that this transformation is the source of the fracture toughening in stabilized zirconia as it occurs at the stress concentration regions ahead of the crack tip. This dissertation is an attempt to provide a kinetic-based model for tetragonal to monoclinic transformation in zirconia. We used the phase field technique to capture the temporal and spatial evolution of monoclinic phase. In addition to morphological patterns, we were able to calculate the developed internal stresses during tetragonal to monoclinic transformation. The model was started form the two dimensional single crystal then was expanded to the two dimensional polycrystalline and finally to the three dimensional single crystal. The model is able to predict the most physical properties associated with tetragonal to monoclinic transformation in zirconia including: morphological patterns, transformation toughening, shape memory effect, pseudoelasticity, surface uplift, and variants impingement. The model was benched marked with several experimental works. The good agreements between simulation results and experimental data, make the model a reliable tool for

  11. Phase Transformation Hysteresis in a Plutonium Alloy System: Modeling the Resistivity during the Transformation

    SciTech Connect

    Haslam, J J; Wall, M A; Johnson, D L; Mayhall, D J; Schwartz, A J

    2001-11-14

    We have induced, measured, and modeled the {delta}-{alpha}' martensitic transformation in a Pu-Ga alloy by a resistivity technique on a 2.8-mm diameter disk sample. Our measurements of the resistance by a 4-probe technique were consistent with the expected resistance obtained from a finite element analysis of the 4-point measurement of resistivity in our round disk configuration. Analysis by finite element methods of the postulated configuration of {alpha}' particles within model {delta} grains suggests that a considerable anisotropy in the resistivity may be obtained depending on the arrangement of the {alpha}' lens shaped particles within the grains. The resistivity of these grains departs from the series resistance model and can lead to significant errors in the predicted amount of the {alpha}' phase present in the microstructure. An underestimation of the amount of {alpha}' in the sample by 15%, or more, appears to be possible.

  12. Observation on Formation of Fresh Martensite from the Reversed Austenite During Water-Quenching Process in Fe-0.2C-5Mn Steel

    NASA Astrophysics Data System (ADS)

    Zhao, Chuan; Zhang, Chi; Cao, Wen-Quan; Yang, Zhi-Gang; Weng, Yu-Qing

    2015-09-01

    Phase transformation behavior during intercritical annealing in Fe-0.2C-5Mn was studied. Austenite lath formed and transformed at martensite lath during annealing. XRD revealed that retained austenite amount did not always increase with time. TEM result may firstly demonstrate that reversed austenite partly changed into fresh martensite during quenching while the remained part was retained as retained austenite. The final structure consisted of ferrite, retained austenite and fresh martensite. Simulation was done by DICTRA to support TEM result.

  13. Phase transformation theory: A powerful tool for the design of advanced steels

    NASA Astrophysics Data System (ADS)

    Caballero, F. G.; Miller, M. K.; Garcia-Mateo, C.; Capdevila, C.; Garcia de Andrés, C.

    2008-12-01

    An innovative design procedure based on phase transformation theory alone has been successfully applied to design steels with a microstructure consisting of a mixture of bainitic ferrite, retained austenite, and some martensite. An increase in the amount of bainitic ferrite is needed in order to avoid the presence of large regions of untransformed austenite, which under stress decompose to brittle martensite. The design procedure addresses this diffi culty by adjusting the T'o curve to greater carbon concentrations with the use of substitutional solutes such as manganese and chromium. The concepts of bainite transformation theory can be exploited even further to design steels with strength in excess of 2.5 GPa and considerable toughness.

  14. Influence of structural-phase state of ferritic-martensitic steels on the helium porosity development

    NASA Astrophysics Data System (ADS)

    Chernov, I. I.; Staltsov, M. S.; Kalin, B. A.; Bogachev, I. A.; Guseva, L. Yu; Dzhumaev, P. S.; Emelyanova, O. V.; Drozhzhina, M. V.; Manukovsky, K. V.; Nikolaeva, I. D.

    2016-04-01

    Transmission electron microscopy (TEM) has been used to study the effect of the initial structural-phase state (SPhS) of ferritic-martensitic steels EK-181, EP-450 and EP-450- ODS (with 0.5 wt.% nanoparticles of Y2O3) on the of helium porosity formation and gas swelling. Different SPhS of steel EK-181 was produced by water quenching, annealing, normalizing plus tempered, intensive plastic deformation by torsion (HPDT). Irradiation was carried out by He+-40 keV ions at 923 K up to fluence of 5-1020 He+/m2. It is shown that the water quenching causes the formation of uniformly distributed small bubbles (d¯ ∼ 2 nm) of the highest density (ρ∼ 1025 m-3). After normalization followed by tempering as well as after annealing bubbles distribution is highly non-uniform both by volume and in size. Very large faceted bubbles (pre-equilibrium gas-filled voids) are formed in ferrite grains resulting in high level of gas swelling of the irradiated layer with S = 4,9 ± 1,2 and 3.8 ± 0.9% respectively. Nano- and microcrystalline structure created by HPDT completely degenerate at irradiation temperature and ion irradiation formed bubbles of the same parameters as in the annealed steel. Bubbles formed in EP-450-ODS steel are smaller in size and density, which led to a decrease of helium swelling by 4 times (S = 0.8 ± 0.2%) as compared to the swelling of the matrix steel EP-450 (S = 3.1 ± 0.7%).

  15. Effect of heat treatment on the crystal structure, martensitic transformation and magnetic properties of Mn53Ni25Ga22 ferromagnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Dong, G. F.; Gao, Z. Y.

    2016-02-01

    In this study, the effect of heat treatment on crystal structure, martensitic transformation, thermodynamic behavior and magnetic properties of polycrystalline Mn53Ni25Ga22 ferromagnetic shape memory alloy was systematically investigated. The results show that the heat treatment has obvious effect on martensitic transformation temperatures, crystal structure and hysteresis loops. Heat treatment greatly effects on transformation temperatures due to modified composition of the matrix. Martensitic transformation temperature, saturation magnetization decreased with the increase heat treatment temperature, reaching their minimum values at the heat treatment temperature of 1173 K for 12 h. Curie temperature of maximum values obtained at solution-treated of 1173 K for 12 h. In other word, increasing heat treatment temperature and time has an effect on Curie temperature. In addition, the annealed alloy Mn53Ni25Ga22 may completely dissolve in vacuum tubes at 1173 K for 12 h. It is found that the studied alloys have some (Mn,Ni)4 Ga-type compound precipitates, which can be seen dispersing both in grain interiors and on grain boundaries at other heat treatment process. Lastly, Rietveld analysis shows the good agreement between experiment and calculated data of XRD patterns.

  16. Phase transformations coupled to deformation processes

    NASA Astrophysics Data System (ADS)

    Lookman, Turab

    2013-06-01

    Phase transformation processes have a substantial impact on the inelastic and damage response of materials. Yet, our understanding of how different loading conditions affect volume fractions of transformed phases, microstructure and transformation pathways is very much in its infancy. With an emphasis on distilling single crystal physics that can, in principle, be incorporated into higher length scale models, I will discuss how recent atomistic simulations on Ti are beginning to provide insights into transformation pathways and the interplay of phase transformations and deformation processes. These simulations are complemented by shock experiments on Zr, Ti together with characterization studies at the Advanced Photon Source.

  17. Formation of a SMC Structure Upon Warm Isothermal Deformation and its Influence on Martensitic Transformations in Titanium-Nickelide Based Alloys

    NASA Astrophysics Data System (ADS)

    Lotkov, A. I.; Grishkov, V. N.; Kashin, O. A.; Baturin, A. A.; Timkin, V. N.; Zhapova, D. Yu.

    2015-10-01

    The evolution of the microstructure and the change in the martensitic transformation temperatures of the Ti49.2Ni50.8 (at.%) alloy with increase of the magnitude of deformation upon isothermal rolling in channel rollers (T = 723 K) have been investigated. It is found that the grain size grows in the initial stages of deformation. It has been shown that for e > 0.2 a change in the grain structure takes place over the entire bulk of the specimen via the mechanism of continuous dynamic recrystallization. It has been established that up to a deformation of e ~ 0.2 the martensitic transformation temperatures vary nonmonotonically and remain practically constant thereafter, which is explained by the occurrence of processes of dynamic recrystallization.

  18. Reversible nanodiamond-carbon onion phase transformations.

    PubMed

    Xiao, J; Ouyang, G; Liu, P; Wang, C X; Yang, G W

    2014-06-11

    Because of their considerable science and technical interest, nanodiamonds (3-5 nm) are often used as a model to study the phase transformation between graphite and diamond. Here we demonstrated that a reversible nanodiamond-carbon onion phase transformation can become true when laser irradiates colloidal suspensions of nanodiamonds at the ambient temperature and pressure. Nanodiamonds are first transformed to carbon onions driven by the laser-induced high temperature in which an intermediary bucky diamond phase is observed. Sequentially, carbon onions are transformed back to nanodiamonds driven by the laser-induced high temperature and high pressure from carbon onions as nanoscaled temperature and pressure cell upon the laser irradiation process in liquid. Similarly, the same bucky diamond phase serving as an intermediate phase is found during the carbon onion-to-nanodiamond transition. To have a clear insight into the unique phase transformation the thermodynamic approaches on the nanoscale were proposed to elucidate the reversible phase transformation of nanodiamond-to-carbon onion-to-nanodiamond via an intermediary bucky diamond phase upon the laser irradiation in liquid. This reversible transition reveals a series of phase transformations between diamond and carbon allotropes, such as carbon onion and bucky diamond, having a general insight into the basic physics involved in these phase transformations. These results give a clue to the root of meteoritic nanodiamonds that are commonly found in primitive meteorites but their origin is puzzling and offers one suitable approach for breaking controllable pathways between diamond and carbon allotropes. PMID:24823241

  19. The effect of Pd on martensitic transformation and magnetic properties for Ni50Mn38-xPdxSn12Heusler alloys

    NASA Astrophysics Data System (ADS)

    Jing, C.; Zheng, D.; Li, Z.; Yu, L. J.; Zhang, Y. L.; Liu, Y.; Sun, J. K.; Liu, C. Q.; Deng, D. M.; Yang, W. T.

    2016-05-01

    In the past decade, Mn rich Ni-Mn based alloys have attained considerable attention due to their abundant physics and potential application as multifunctional materials. In this paper, polycrystalline Ni50Mn38-xPdxSn12 (x = 0, 2, 4, 6) Heusler alloys have been prepared, and the martensitic phase transformation (MPT) together with the shape memory effect and the magnetocaloric effect has been investigated. The experimental result indicates that the MPT evidently shifts to a lower temperature with increase of Pd substitution for Mn atoms, which can be attributed to the weakness of the hybridization between the Ni atom and excess Mn on the Sn site rather than the electron concentration. The physics properties study focused on the sample of Ni50Mn34Pd4Sn12 shows a good two-way shape memory behavior, and the maximum value of strain Δ L/L reaches about 0.13% during the MPT. The small of both entropy change Δ ST and magnetostrain can be ascribed to the inconspicuous influence of magnetic field induced MPT.

  20. Anomalous magnetic configuration of Mn{sub 2}NiAl ribbon and the role of hybridization in the martensitic transformation of Mn{sub 50}Ni{sub 50−x}Al{sub x} ribbons

    SciTech Connect

    Zhao, R. B.; Zhao, D. W.; Li, G. K.; Ma, L. E-mail: houdenglu@mail.hebtu.edu.cn; Zhen, C. M.; Hou, D. L. E-mail: houdenglu@mail.hebtu.edu.cn; Wang, W. H.; Liu, E. K.; Chen, J. L.; Wu, G. H.

    2014-12-08

    The magnetic configuration of Mn{sub 2}NiAl ribbon has been investigated. In contrast to Ni{sub 2}MnAl, the compound Mn{sub 2}NiAl with considerable disorder does exhibit ferromagnetism and, due to exchange interaction competition, both ferromagnetic and antiferromagnetic moment orientations can coexist between nearest neighbor Mn atoms. This is unexpected in Heusler alloys. Regarding the mechanism of the martensitic transformation in Mn{sub 50}Ni{sub 50−x}Al{sub x}, it is found that increasing the Al content results in an unusual change in the lattice constant, a decrease of the transformation entropy change, and enhancement of the calculated electron localization. These results indicate that the p-d covalent hybridization between Mn (or Ni) and Al atoms gradually increases at the expense of the d-d hybridization between Ni and Mn atoms. This leads to an increased stability of the austenite phase and a decrease of the martensitic transformation temperature. For 11 ≤ x ≤ 14, Mn{sub 50}Ni{sub 50−x}Al{sub x} ferromagnetic shape memory alloys are obtained.

  1. Investigation of Phase Transformations in High-Alloy Austenitic TRIP Steel Under High Pressure (up to 18 GPa) by In Situ Synchrotron X-ray Diffraction and Scanning Electron Microscopy

    NASA Astrophysics Data System (ADS)

    Ackermann, Stephanie; Martin, Stefan; Schwarz, Marcus R.; Schimpf, Christian; Kulawinski, Dirk; Lathe, Christian; Henkel, Sebastian; Rafaja, David; Biermann, Horst; Weidner, Anja

    2016-01-01

    In order to clarify the difference between the deformation-induced ɛ-martensite ( ɛ 1) and the pressure-induced ɛ-iron ( ɛ 2), high-pressure quasi-hydrostatic experiments were performed on a low-carbon, high-alloy metastable austenitic steel. In situ synchrotron X-ray diffraction measurements as well as post-mortem investigations of the microstructure by electron backscatter diffraction were carried out to study the microstructural transformations. Three processes were observed during compression experiments: first, the formation of deformation-induced hexagonal ɛ 1-martensite, as well as small nuclei of deformation-induced bcc α'-martensite ( α 1') within the fcc γ-matrix due to non-hydrostaticity in the experiments; second, the onset of the phase transformation from the metastable fcc γ-austenite into the hexagonal pressure-induced ɛ 2-iron phase occurred at around 6 GPa; third, during decompression, the hexagonal pressure-induced ɛ 2-iron transformed partially into bcc α'-martensite ( α 2'). Completely different characteristics with regard to habitus as well as to orientation relationships were observed between the pressure-induced phases ( ɛ 2-iron phase and α 2'-martensite) and the deformation-induced martensites ( ɛ 1- and α 1'-martensite).

  2. 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.

  3. In Situ TEM Nanoindentation Studies on Stress-Induced Phase Transformations in Metallic Materials

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Wang, H.; Zhang, X.

    2016-01-01

    Although abundant phase transformations are in general thermally driven processes, there are many examples wherein stresses can induce phase transformations. Numerous in situ techniques, such as in situ x-ray diffraction and neutron diffraction, have been applied to reveal phase transformations. Recently, an in situ nanoindentation technique coupled with transmission electron microscopy demonstrated the capability to directly correlating stresses with phase transformations and microstructural evolutions at a submicron length scale. Here we briefly review in situ studies on stress-induced diffusional and diffusionless phase transformations in amorphous CuZrAl alloy and NiFeGa shape memory alloy. In the amorphous CuZrAl, in situ nanoindentation studies show that the nucleation of nanocrystals (a diffusional process) occurs at ultra-low stresses manifested by a prominent stress drop. In the NiFeGa shape memory alloy, two distinctive types of martensitic (diffusionless) phase transformations accompanied by stress plateaus are observed, including a reversible gradual phase transformation at low stress levels, and an irreversible abrupt phase transition at higher stress levels.

  4. In Situ TEM Nanoindentation Studies on Stress-Induced Phase Transformations in Metallic Materials

    DOE PAGESBeta

    Liu, Y.; Wang, H.; Zhang, X.

    2015-11-30

    Though abundant phase transformations are in general thermally driven processes, there are many examples wherein stresses can induce phase transformations. We applied numerous in situ techniques, such as in situ x-ray diffraction and neutron diffraction in order to reveal phase transformations. Recently, an in situ nanoindentation technique coupled with transmission electron microscopy demonstrated the capability to directly correlating stresses with phase transformations and microstructural evolutions at a submicron length scale. We briefly review in situ studies on stress-induced diffusional and diffusionless phase transformations in amorphous CuZrAl alloy and NiFeGa shape memory alloy. Moreover, in the amorphous CuZrAl, in situ nanoindentationmore » studies show that the nucleation of nanocrystals (a diffusional process) occurs at ultra-low stresses manifested by a prominent stress drop. In the NiFeGa shape memory alloy, two distinctive types of martensitic (diffusionless) phase transformations accompanied by stress plateaus are observed, including a reversible gradual phase transformation at low stress levels, and an irreversible abrupt phase transition at higher stress levels.« less

  5. In Situ TEM Nanoindentation Studies on Stress-Induced Phase Transformations in Metallic Materials

    SciTech Connect

    Liu, Y.; Wang, H.; Zhang, X.

    2015-11-30

    Though abundant phase transformations are in general thermally driven processes, there are many examples wherein stresses can induce phase transformations. We applied numerous in situ techniques, such as in situ x-ray diffraction and neutron diffraction in order to reveal phase transformations. Recently, an in situ nanoindentation technique coupled with transmission electron microscopy demonstrated the capability to directly correlating stresses with phase transformations and microstructural evolutions at a submicron length scale. We briefly review in situ studies on stress-induced diffusional and diffusionless phase transformations in amorphous CuZrAl alloy and NiFeGa shape memory alloy. Moreover, in the amorphous CuZrAl, in situ nanoindentation studies show that the nucleation of nanocrystals (a diffusional process) occurs at ultra-low stresses manifested by a prominent stress drop. In the NiFeGa shape memory alloy, two distinctive types of martensitic (diffusionless) phase transformations accompanied by stress plateaus are observed, including a reversible gradual phase transformation at low stress levels, and an irreversible abrupt phase transition at higher stress levels.

  6. Fracture mechanisms in dual phase steels based on the acicular ferrite + martensite/austenite microstructure

    NASA Astrophysics Data System (ADS)

    Poruks, Peter

    The fracture mechanisms of low carbon microalloyed plate steels based on the acicular ferrite + marten site/austenite microstructure (AF + M/A) are investigated. The final microstructure consists of a dispersed phase of submicron equi-axed martensite particles with a bainitic ferrite matrix. A series of plates with M/A volume fractions of 0.076--0.179 are studied. Brittle fracture is investigated by Instrumented Charpy impact testing of samples at -196°C and subsequent metallography. The M/A particles are identified as the crack nucleation sites and the cleavage fracture stress calculated to be 2400 MPa in a complete AF microstrucuture. This value is significantly larger than in steels that contain significant proportions of conventional bainite. Standard Charpy and Instrumented Charpy impact testing is conducted through a temperature range from -80 to + 22°C to study ductile fracture behaviour. The total absorbed energy is separated into energies of crack nucleation and of crack propagation. It is found that the energy of crack nucleation is weakly dependent on the volume fraction of M/A and completely independent of temperature over the range studied. The crack propagation energy varies significantly with both variables, decreasing with increased volume fraction of M/A and with decreasing temperature. The peak load in the instrumented Charpy data is used to calculate the dynamic fracture toughness, KId, which is found to be 105--120 MPa-m1/2. The void nucleation and void growth stages of ductile fracture are studied by metallographic examination of tensile bars. The sites of void nucleation are identified as inclusions and M/A particles. Voids nucleate at the M/A particles by decohesion of the particle-matrix interface. A constant void nucleation strain of epsilon = 0.90 +/- 0.05 is measured for all of the samples independent of the volume fraction of M/A. A stress-based criterion is used to predict void nucleation and the interface strength is determined to be

  7. Martensitic transformation behaviors of Ti49+xNi21-xCu30 (x=0,1,2,3) shape memory alloy strips

    NASA Astrophysics Data System (ADS)

    Kim, Yeon-Wook; Kim, Hyun-Jin; Nam, Tae-Hyun

    2010-05-01

    Four batches of Ti-Ni-Cu strips (Ti49Ni21Cu30, Ti50Ni20Cu30, Ti51Ni19Cu30 and Ti52Ni18Cu30) were prepared by an arc melt overflow technique. The microstructure of as-cast strips exhibited columnar grains normal to the strip surface. XRD analysis showed that B2-B19 martensitic transformation occurred in all alloy strips. The martensitic transformation start temperature (Ms) of the Ti49Ni21Cu30 strip was 54.6 °C and continued to increase with increasing Ti-content. During cycle deformation with an applied stress of 120 MPa, transformation hysteresis and elongation associated with the B2-B19 transformation were observed to be 4.1 °C and 1.84% in the Ti49Ni21Cu30 strip. The transformation hysteresis associated with the B2-B19 transformation increased with increasing Ti-content, while the elongation decreased with increasing Ti-content. Even though it is known that Ti-Ni-Cu alloys with high Cu-content (more than 13 at % Cu) are too brittle to deform plastically, the rapidly solidified Ti-Ni-Cu alloy strips, which contain 30 at % Cu, have excellent shape memory characteristics and mechanical properties.

  8. Computational Modeling and Experimental Characterization of Martensitic Transformations in Nicoal for Self-Sensing Materials

    NASA Technical Reports Server (NTRS)

    Wallace, T. A.; Yamakov, V. I.; Hochhalter, J. D.; Leser, W. P.; Warner, J. E.; Newman, J. A.; Purja Pun, G. P.; Mishin, Y.

    2015-01-01

    Fundamental changes to aero-vehicle management require the utilization of automated health monitoring of vehicle structural components. A novel method is the use of self-sensing materials, which contain embedded sensory particles (SP). SPs are micron-sized pieces of shape-memory alloy that undergo transformation when the local strain reaches a prescribed threshold. The transformation is a result of a spontaneous rearrangement of the atoms in the crystal lattice under intensified stress near damaged locations, generating acoustic waves of a specific spectrum that can be detected by a suitably placed sensor. The sensitivity of the method depends on the strength of the emitted signal and its propagation through the material. To study the transition behavior of the sensory particle inside a metal matrix under load, a simulation approach based on a coupled atomistic-continuum model is used. The simulation results indicate a strong dependence of the particle's pseudoelastic response on its crystallographic orientation with respect to the loading direction and suggest possible ways of optimizing particle sensitivity. The technology of embedded sensory particles will serve as the key element in an autonomous structural health monitoring system that will constantly monitor for damage initiation in service, which will enable quick detection of unforeseen damage initiation in real-time and during onground inspections.

  9. Kinetic arrest of the first order austenite to martensite phase transition in Ni50Mn34In16 : dc magnetization studies

    NASA Astrophysics Data System (ADS)

    Sharma, V. K.; Chattopadhyay, M. K.; Roy, S. B.

    2007-10-01

    We report results of dc magnetization studies focusing particularly on the austenite-martensite phase transition in Ni50Mn34In16 . We show that the nature of this phase transition depends significantly on the temperature (T) and magnetic field (H) history of the sample. In the presence of high magnetic field, this austenite to martensite first order phase transition is kinetically arrested. The low-temperature and high-field magnetic state shows a typical nonergodic glasslike dynamical response. Comparisons are made with similar phenomena observed recently in various classes of magnetic materials including CMR manganites.

  10. Reverse-Martensitic Hardening of Austenitic Stainless Steel upon Up-quenching

    NASA Astrophysics Data System (ADS)

    Sato, Kiminori; Guo, Defeng; Li, Xiaohong; Zhang, Xiangyi

    2016-08-01

    Reverse-martensitic transformation utilizing up-quenching was demonstrated for austenitic stainless steel. Up-quenching was done following the stress-induced phase modification to martensite and then enrichment of the body-centered-cubic ferrite. Transmission-electron-microscopy observation and Vickers hardness test revealed that the reverse-martensitic transformation yields quench hardening owing to an introduction of highly-concentrated dislocation. It is furthermore found that Cr precipitation on grain boundaries caused by isothermal aging is largely suppressed in the present approach.

  11. Machining and Phase Transformation Response of Room-Temperature Austenitic NiTi Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Kaynak, Yusuf

    2014-09-01

    This experimental work reports the results of a study addressing tool wear, surface topography, and x-ray diffraction analysis for the finish cutting process of room-temperature austenitic NiTi alloy. Turning operation of NiTi alloy was conducted under dry, minimum quantity lubrication (MQL) and cryogenic cooling conditions at various cutting speeds. Findings revealed that cryogenic machining substantially reduced tool wear and improved surface topography and quality of the finished parts in comparison with the other two approaches. Phase transformation on the surface of work material was not observed after dry and MQL machining, but B19' martensite phase was found on the surface of cryogenically machined samples.

  12. Phase transformation studies in unirradiated and proton beam irradiated Ni-Ti alloy between 25 and 100°C

    NASA Astrophysics Data System (ADS)

    Ayub, Rana; Afzal, Naveed; Ahmad, R.

    2012-06-01

    The stress-induced phase transformation characteristics of unirradiated and proton beam irradiated NiTi alloy were investigated at different tests temperatures. The wire-shaped NiTi specimens were irradiated by 2 MeV proton beam for 30 min at room temperature to a flux of 1019 protons/m2 s. Engineering stress-strain (S-S) curves of both unirradiated and irradiated specimens were obtained using a materials testing machine at 25, 50, 75 and 100°C. The results indicate a single-stage phase transformation from austenite to martensite (B2-B19‧) in unirraidated specimens at all the test temperatures. In contrast, in the case of the irradiated specimens, a two-stage austenite-rhombohedral-martensite (B2-R-B19‧) phase transformation is observed at 25 and 50°C. The B2-R-B19‧ phase transformation, however, is found to change into B2-B19‧ transformation at 75 and 100°C. The stress required to initiate the B19‧ phase transformation (σMS) and the plateau range are found to be lower in irradiated specimens compared with those of the unirradiated specimens. The results obtained are discussed on the basis of the formation of Ni4Ti3 precipitates in irradiated specimens and their consequences on the phase transformations.

  13. A three-phase cylinder model for residual and transformational stresses in SMA composites

    SciTech Connect

    Berman, J.B.; White, S.R.

    1994-12-31

    SMA composites are a class of smart materials in which shape memory alloy (SMA) actuators are embedded in a polymer matrix composite. The difference in thermal expansion between the SMA and the host material leads to residual stresses during processing. Similarly, the SMA transformations from martensite to austenite, or the reverse, also generate stresses. These stresses acting in combination can lead to SMA/epoxy interfacial debonding. In this study the residual and transformational stresses are investigated for an SMA wire embedded in a graphite/epoxy composite. A three phase micromechanical model is developed. The SMA wire is assumed to behave as a thermoelastic material. Nitinol{trademark} SMA austenitic and martensitic transformations are modeled using linear piecewise interpolation of the experimental data. The interphase is modeled as a thermoelastic polymer. A transversely isotropic thermoelastic composite is used for the outer phase. Stress-free conditions are assumed immediately before cool down from the cure temperature. The effect of SMA and coating properties on residual and transformational stresses are evaluated. A decrease in stresses at the composite/coating interface is predicted through the use of thick, compliant coatings. Reducing the recovery strain and moving the transformation to higher temperatures are also effective in reducing residual stresses.

  14. Microstructural Evidence for Conditioning-dependent (delta) -> (alpha)' Transformations in Retained (delta)-phase Pu-Ga

    SciTech Connect

    Jeffries, J R; Blobaum, K M; Wall, M A; Schwartz, A J

    2008-06-16

    The retained {delta} phase of a Pu-1.9 at.% Ga alloy is metastable with respect to the martensitic {delta} {yields} {alpha}{prime} transformation that occurs at low temperatures. This transformation has been shown to proceed by means of an isothermal martensitic mode, but the kinetics of the transformation are atypical. The transformation exhibits a 'double-C' in a time-temperature-transformation diagram, wherein there exist two temperatures where a given amount of transformation occurs in a minimum amount of time. The cause of the double-C kinetics remains uncertain, eliciting proposals of multiple mechanisms, multiple paths, or different morphologies as possible origins. Recently, a 'conditioning' treatment was found to affect the {delta} {yields} {alpha}{prime} transformation, but the underlying mechanism by which the conditioning treatment influences the transformation has not yet been resolved. In this study, microstructural characterization as a function of temperature, time, and conditioning has been employed to illuminate the role of conditioning in the {delta} {yields} {alpha}{prime} transformation. Conditioning is found to enhance transformation in the upper-C and to enable transformation in the lower-C. The data garnered from these experiments suggest that conditioning is intimately linked to nucleation processes and of little consequence to the growth and morphology of the {alpha}{prime} product phase.

  15. Impact Toughness of 0.2 Pct C-1.5 Pct Si-(1.5 to 5) Pct Mn Transformation-Induced Plasticity-Aided Steels with an Annealed Martensite Matrix

    NASA Astrophysics Data System (ADS)

    Tanino, Hikaru; Horita, Masaomi; Sugimoto, Koh-Ichi

    2016-05-01

    The impact properties of 0.2 pct C-1.5 pct Si-(1.5 to 5) pct Mn transformation-induced plasticity (TRIP)-aided steels with an annealed martensite matrix which had been subjected to isothermal transformation after inter-critical annealing were investigated for potential automotive applications. The impact properties are related to the retained austenite characteristics of the steels. The products of tensile strength (TS) and Charpy impact absorbed value (CIAV) were the same for the 1.5 and 5 pct Mn steels, although the ductile-brittle transition temperature was higher for the latter. The impact properties of the 3 pct Mn steel were worse than these two steels. The high TS × CIAV value for the 5 pct Mn steel at 293 K (25 °C) was mainly caused by the TRIP effect of a larger amount of retained austenite (36 vol pct) and the hardened matrix structure; low retained austenite stability and/or a hard martensite-austenite phase reduced this value. The higher ductile-brittle transition temperature of the 5 pct Mn steel was associated with Mn segregation, a large amount of unstable retained austenite on prior austenitic grain boundaries, and decreased cleavage fracture stress owing to the high Mn content.

  16. Calorimetric Study of Phase Stability and Phase Transformation in U- xZr ( x = 2, 5, 10 wt pct) Alloys

    NASA Astrophysics Data System (ADS)

    Rai, Arun Kumar; Subramanian, Raju; Hajra, Raj Narayan; Tripathy, Haraprasanna; Rengachari, Mythili; Saibaba, Saroja

    2015-11-01

    A comprehensive calorimetric study of high-temperature phase equilibria and phase transformation characteristics in U- xZr ( x = 2, 5, 10 wt pct) alloys has been undertaken, as a function of heating and cooling rates. It is found that the following sequence of phase transformation takes place upon slow heating in annealed U-2 wt pct Zr alloy: α + α' + δ-UZr2 → α + γ 2 → β + γ 2 → β + γ 1 → γ. For alloys of 5 and 10 wt pct Zr, the additional presence of a miscibility gap ( γ 1 U-rich bcc + γ 2 Zr-rich bcc) in the high-temperature γ(bcc) phase region resulted in the following transformation sequence: α + α' + δ-UZr2 → α + γ 2 → β + γ 2 → γ 1 + γ 2 → γ. Further, it has been demonstrated that depending on the nature of starting microstructure, namely whether it is α eq + δ-UZr2, or a mix of α' + α eq + δ-UZr2 phases, the relative extents of two possible co-occurring modes of the first on-heating phase transformation step differ. In case of starting microstructure having mixture of three phases α' + α eq + δ-UZr2, it is found that α'-martensite relaxation via α' + α eq + δ-UZr2 → α eq + δ-UZr2 constitutes the first on-heating thermal response. The α'-martensitic relaxation is very closely followed by the dissolution of δ-UZr2. The co-occurrence of these two events gives rise to a composite thermal arrest in a normal dynamic calorimetry profile. However, if the starting microstructure is the one having the equilibrium mix of α eq and δ-UZr2, then only the peritectoidal dissolution of δ-UZr2 is found in the calorimetry profile. Unless, a very slow cooling rate of the order of 0.1 K min-1 is adopted from high-temperature γ(bcc) phase, it is not possible to obtain 100 pct of α eq phase along with equilibrium amount of δ-UZr2. At normal and high cooling rates, it is possible to suppress the diffusional decomposition of γ to varying extents. The direct γ → α'-martensite transformation has been observed at

  17. On pressure-shear plate impact for studying the kinetics of stress-induced phase transformations

    NASA Astrophysics Data System (ADS)

    Escobar, Joanne C.; Clifton, Rodney J.

    1992-07-01

    Pressure-shear plate impact experiments are proposed for studying the kinetics of stress-induced phase transformations. The purpose of this paper is to determine loading conditions and specimen orientations which can be expected to activate a single habit plane variant parallel to the impact plane, thereby simplifying the study of the kinetics of the transformation through monitoring the wave profiles associated with the propagating phase boundary. The Wechsler Lieberman-Read phenomenological theory was used to determine habit plane indices and directions of shape deformation for a Cu-Al-Ni shape memory alloy which undergoes a martensitic phase transformation under stress. Elastic waves generated by pressure-shear impact were analyzed for wave propagation in the direction of the normal to a habit plane. A critical resolved shear stress criterion was used to predict variants which are expected to be activated for a range of impact velocities and relative magnitudes of the normal and transverse components of the impact velocity.

  18. Influence of Laser Peening on Phase Transformation and Corrosion Resistance of AISI 321 steel

    NASA Astrophysics Data System (ADS)

    Karthik, D.; Swaroop, S.

    2016-07-01

    The objective of this study is to investigate the influence of laser peening without coating (LPwC) on austenitic to martensitic (γ → α') phase transformation and corrosion behavior of austenitic stainless steel AISI 321 in 3.5% NaCl environment. Results indicate that LPwC induces a large compressive residual stresses of nearly -854 MPa and γ → α' phase transformation of about 18% (volume fraction). Microstructures of peened surface confirmed the γ → α' phase transformation and showed no grain refinement. Hardness increased slightly with a case depth of 900 μm. Despite the smaller surface roughness introduced, corrosion resistance improved after peening due to compressive residual stresses.

  19. Influence of Laser Peening on Phase Transformation and Corrosion Resistance of AISI 321 steel

    NASA Astrophysics Data System (ADS)

    Karthik, D.; Swaroop, S.

    2016-06-01

    The objective of this study is to investigate the influence of laser peening without coating (LPwC) on austenitic to martensitic (γ → α') phase transformation and corrosion behavior of austenitic stainless steel AISI 321 in 3.5% NaCl environment. Results indicate that LPwC induces a large compressive residual stresses of nearly -854 MPa and γ → α' phase transformation of about 18% (volume fraction). Microstructures of peened surface confirmed the γ → α' phase transformation and showed no grain refinement. Hardness increased slightly with a case depth of 900 μm. Despite the smaller surface roughness introduced, corrosion resistance improved after peening due to compressive residual stresses.

  20. Phase transformations and phase relations in Ti{sub 50}Pd{sub (50-x)}TM{sub x} alloys

    SciTech Connect

    Schwartz, A.J.; Sluiter, M.H.; Harmon, B.N.; Tanner, L.E.

    1994-07-15

    The effect of transition metal (TM) substitution for Pd in Ti{sub 5O}Pd{sub (50-x}TM{sub x} alloys with x between 5 and 37.5 at.% and TM = V, Cr, Mn and Fe are being characterized by transmission electron microscopy and First-Principles Alloy Theory modeling. The goal is to obtain detailed structural information related to the ternary phase relations and transformations that are necessary for effective shape-memory alloy development. Thus far, the authors have found that the tend to have pseudobinary eutectoid-like configurations with a terminal TiPd and a non-close-packed long period ordered structure type crystal structure) based on the stoichiometry Ti{sub 2}PdTM. The systems exhibit a conventional martensitic transformation, as well as a new type of displacive transformation that shear-modulates B2 to produce a periodically distorted, but non-close-packed metastable product phase.

  1. An in-situ neutron diffraction study of a multi-phase transformation and twinning-induced plasticity steel during cyclic loading

    SciTech Connect

    Saleh, Ahmed A.; Brown, Donald W.; Clausen, Bjørn; Tomé, Carlos N.; Pereloma, Elena V.; Davies, Christopher H. J.; Gazder, Azdiar A.

    2015-04-27

    In-situ neutron diffraction during cyclic tension-compression loading (∼+3.5% to −2.8%) of a 17Mn-3Al-2Si-1Ni-0.06C steel that exhibits concurrent transformation and twinning -induced plasticity effects indicated a significant contribution of intragranular back stresses to the observed Bauschinger effect. Rietveld analysis revealed a higher rate of martensitic transformation during tension compared to compression. Throughout cycling, α′-martensite exhibited the highest phase strains such that it bears an increasing portion of the macroscopic load as its weight fraction evolves. On the other hand, the ε-martensite strain remained compressive as it accommodated most of the internal strains caused by the shape misfit associated with the γ→ε and/or ε→α′ transformations.

  2. An in-situ neutron diffraction study of a multi-phase transformation and twinning-induced plasticity steel during cyclic loading

    NASA Astrophysics Data System (ADS)

    Saleh, Ahmed A.; Brown, Donald W.; Pereloma, Elena V.; Clausen, Bjørn; Davies, Christopher H. J.; Tomé, Carlos N.; Gazder, Azdiar A.

    2015-04-01

    In-situ neutron diffraction during cyclic tension-compression loading (˜+3.5% to -2.8%) of a 17Mn-3Al-2Si-1Ni-0.06C steel that exhibits concurrent transformation and twinning -induced plasticity effects indicated a significant contribution of intragranular back stresses to the observed Bauschinger effect. Rietveld analysis revealed a higher rate of martensitic transformation during tension compared to compression. Throughout cycling, α'-martensite exhibited the highest phase strains such that it bears an increasing portion of the macroscopic load as its weight fraction evolves. On the other hand, the ɛ-martensite strain remained compressive as it accommodated most of the internal strains caused by the shape misfit associated with the γ→ɛ and/or ɛ→α' transformations.

  3. Residual stress induced stabilization of martensite phase and its effect on the magnetostructural transition in Mn-rich Ni-Mn-In/Ga magnetic shape-memory alloys

    NASA Astrophysics Data System (ADS)

    Singh, Sanjay; Kushwaha, Pallavi; Scheibel, F.; Liermann, Hanns-Peter; Barman, S. R.; Acet, M.; Felser, C.; Pandey, Dhananjai

    2015-07-01

    The irreversibility of the martensite transition in magnetic shape memory alloys (MSMAs) with respect to the external magnetic field is one of the biggest challenges that limits their application as giant caloric materials. This transition is a magnetostructural transition that is accompanied with a steep drop in magnetization (i.e.,Δ M ) around the martensite start temperature (Ms) due to the lower magnetization of the martensite phase. In this Rapid Communication, we show that Δ M around Ms in Mn-rich Ni-Mn-based MSMAs gets suppressed by two orders of magnitude in crushed powders due to the stabilization of the martensite phase at temperatures well above Ms and the austenite finish (Af) temperatures due to residual stresses. Analysis of the intensities and the FWHM of the x-ray powder-diffraction patterns reveals stabilized martensite phase fractions as 97 % , 75 % , and 90 % with corresponding residual microstrains as 5.4 % , 5.6 % , and 3 % in crushed powders of the three different Mn-rich Ni-Mn alloys, namely, M n1.8N i1.8I n0.4 , M n1.75N i1.25Ga , and M n1.9N i1.1Ga , respectively. Even after annealing at 773 K, the residual stress stabilized martensite phase does not fully revert to the equilibrium cubic austenite phase as the magnetostructural transition is only partially restored with a reduced value of Δ M . Our results have a very significant bearing on the application of such alloys as inverse magnetocaloric and barocaloric materials.

  4. Isothermal martensitic transformation in a 12Cr-9Ni-4Mo-2Cu stainless steel in applied magnetic fields

    NASA Astrophysics Data System (ADS)

    San Martín, D.; Aarts, K. W. P.; Rivera-Díaz-del-Castillo, P. E. J.; van Dijk, N. H.; Brück, E.; van der Zwaag, S.

    This work concerns an in situ study of the isothermal formation of martensite in a stainless steel under the influence of magnetic fields up to 9 T at three different temperatures (213, 233 and 253 K). It is shown that the presence of a constant applied magnetic field promotes the formation of martensite significantly. The activation energy for the nucleation of martensite has been derived using a semi-empirical kinetic model. The experimental results have been analyzed using the Ghosh and Olson model. While this model describes the time and field dependences of the experimental data well, the thermal frictional energy and the defect size values are much lower than those expected from earlier work.

  5. Experimental and computational investigation of the effect of phase transformation on fracture parameters of an SMA

    NASA Astrophysics Data System (ADS)

    Haghgouyan, Behrouz; Shafaghi, Nima; Aydıner, C. Can; Anlas, Gunay

    2016-07-01

    A comprehensive, multi-method experimental characterization of fracture is conducted on shape memory alloy NiTi that exhibits superelasticity due to austenite-to-martensite stress induced phase transformation. This characterization includes (i) load-based measurement of critical stress intensity factor (K max) using ASTM standard E399, (ii) measurement of crack tip opening displacement (CTOD) per ASTM standard E1290, (iii) the digital image correlation (DIC) characterization of the transformation zone as well as the displacement-field based measurement of K max from the DIC data. Samples have also been tested at T = 100 °C to suppress the martensitic transformation to investigate transformation toughening. The experimental investigation is complemented with finite element (FE) analysis that uses Auricchio–Taylor–Lubliner constitutive model. A direct observation with DIC revealed a small scale transformation (K-dominance). K max of the transforming material is higher than that of the transformation-suppressed material tested at 100 °C, suggesting transformation toughening. At 100 °C, the material becomes quite brittle with a very small crack-tip plastic zone when the transformation mechanism is blocked. By measures of critical CTOD, the gap widens even more between the superelastic and transformation-suppressed cases, particularly because of the side effect that, in this very interesting material, material modulus increases with temperature. Evaluating the transformation zone from the DIC strains with reference to the uniaxial stress–strain curve, an equivalent strain form is proposed in conjunction with the plane stress FE prediction.

  6. FEM simulations of a multi stage forming process on Sandvik maraging steel 1RK91 describing the stress assisted and the strain induced martensite transformation

    NASA Astrophysics Data System (ADS)

    Post, J.; Huétink, J.; Geijselaers, H. J. M.; Voncken, R. M. J.

    2003-10-01

    Sandvik steel IRK91 combines good corrosion resistance with high strength. The steel has good deformability in austenitic conditions. This material belongs to the group of metastable austenites, so during deformation a strain-induced transformation into martensite takes place. After deformation, transformation ccontinues as a resuit of internai stresses. Depending on the heat treatment, this stress-assisted transformation is more or less atitocatalytic. Both transformations are stress-state and temperature dependent. This article presents a constitutive model for this steel, based on the macroscopic material behaviour measured by inductive measurements. Both the stress-assisted and the strain-induced transformation to martensite are incorpomted in this model. Path-dependent work hardening is also taken into account. The model is implemented in the commercial FEM code MARC for doing simulations. In the simulations thé tools are treated as rigid bodies, friction is taken into account beeause it inflnences the stress state during metal forming. The material properties after a calculation step are mapped to the next step to incorporate the cumulative effect of the transformation and work hardening during the different steps. A multi-stage metal-forming process is simulated. The process consists of different forming steps with intervals between them to simulate the waiting time between the different metal-forming steps. Results of the transformation behaviour are presented together with the shape of the product during and after metal forming. Finally, this article shows the results of the calculation in which the material transforms autocatalytic, as a resuit of a specific heat treatment.

  7. Phase selection during laser surface melting of martensitic stainless tool steels

    SciTech Connect

    Colaco, R.; Vilar, R.

    1997-01-15

    Laser surface melting (LSM) of tool steels allows for the complete dissolution of large brittle carbides, leading to homogeneous and extremely fine microstructures. Due to its characteristics, LSM allows improvement of the performance of tool steels by increasing their resistance to erosive and abrasive wear. Nevertheless, when DIN X42Cr13 and DIN X100Cr18 martensitic stainless steels are submitted to LSM, considerable amounts of austenite and {delta}-ferrite formed during the first stage of solidification can be retained in metastable condition at room temperature by mechanisms which are not yet fully understood. The purpose of the present work is to establish the influence of solidification conditions on the primary solidification mode of these two martensitic stainless tool steels, aimed to optimize the LSM operating conditions. Accordingly, samples of DIN X40Cr13 and DIN X100Cr18 were submitted to LSM with a wide range of solidification speeds. The microstructures were analyzed in order to identify the primary solidification mode. The experimental results were compared with theoretical predictions, based on comparison of the dendrite tip temperatures of austenite and {delta}-ferrite as function of the solidification speed.

  8. Martensitic transformation behavior in Ti–Ni–X (Ag, In, Sn, Sb, Te, Tl, Pb, Bi) ternary alloys

    SciTech Connect

    Jang, Jai-young; Chun, Su-jin; Kim, Nam-suk; Cho, Jeung-won; Kim, Jae-hyun; Yeom, Jong-taek; Kim, Jae-il; Nam, Tae-hyun

    2013-12-15

    Graphical abstract: - Highlights: • Ag, In and Sn were soluble in TiNi matrix, while Sb, Te, Tl, Pb and Bi were not. • The B2-R-B19′transformation occurred in Ti-Ni-(Ag, In, Sn) alloys. • Solid solution hardening was essential for inducing the B2-R transformation. - Abstract: The microstructures and transformation behaviors of Ti–Ni–X (Ag, In, Sn, Sb, Te, Tl, Pb, Bi) ternary alloys were investigated using electron probe micro-analysis (EPMA), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Micro Vickers hardness tests. All specimens consisted of Ti–Ni matrices and second phase particles. Ag, In and Sn were soluble in Ti–Ni matrices with a limited solubility (≤1.0 at%), while Sb, Te, Tl, Pb and Bi were not soluble. Two-stage B2-R-B19′ transformation occurred in Ti–48.8Ni–1.2Ag, Ti–49.0Ni–1.0In and Ti–49.0Ni–1.0Sn alloys, while one-stage B2-B19′ transformation occurred in Ti–49.0Ni–1.0Ag, Ti–49.0Ni–1.0Sb, Ti–49.0Ni–1.0Te, Ti–49.0Ni–1.0Pb and Ti–49.0Ni–1.0Bi alloys. Micro Vickers hardness of the alloys displaying the B2-R-B19′ transformation (Hv 250–368) was much larger than that (transformation. Solid solution hardening was an important factor for inducing the B2-R transformation in Ti–Ni–X (X = non-transition elements) alloys.

  9. The mechansims by which solute nitrogen affects phase transformations and mechanical properties of automotive dual-phase sheet steel

    NASA Astrophysics Data System (ADS)

    Brown, Tyson W.

    Dual-phase steels have seen increased use in automotive applications in recent years, in order to meet the goals of weight reduction and occupant safety. Variations in nitrogen content that may be encountered in steel sourced from a basic oxygen furnace process compared to an electric arc furnace process require that dual-phase steel producers understand the ways that nitrogen affects processing and properties. In the current work, the distribution of nitrogen was investigated in a dual-phase steel with a base chemistry of 0.1 C, 2.0 Mn, 0.2 Cr, 0.2 Mo (wt pct) across a range of nitrogen contents (30-159 ppm) with Al (0.2 and 0.08 wt pct), and Ti (0.02 wt pct) additions used for precipitation control of nitrogen amounts. The distribution of nitrogen amongst trapping sites, including precipitates, grain boundaries, dislocations, and interstitial sites (away from other types of defects) was determined from a combination of electrolytic dissolution, internal friction, and three-dimensional atom probe tomography experiments. Various mechanisms by which different amounts and locations of nitrogen affect phase transformations and mechanical properties were identified from quantitative metallography, dilatometric measurement of phase transformations, tensile testing, and nanoindentation hardness testing. Results indicate nitrogen that is not precipitated with Ti or Al (free nitrogen) partitions to austenite (and thus martensite) during typical intercritical annealing treatments, and is mostly contained in Cottrell atmospheres in martensite. Due to the austenite stabilizing effect of nitrogen, the presence of free nitrogen during intercritical annealing leads to a higher austenite fraction in certain conditions. Thus, the presence of free nitrogen in a dual-phase microstructure will lead to an increase in tensile and yield strengths from both an increase in martensite fraction, and an increase in martensite hardness due to solid solution strengthening. Despite the presence

  10. Deformation and Phase Transformation Processes in Polycrystalline NiTi and NiTiHf High Temperature Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Benafan, Othmane

    2012-01-01

    The deformation and transformation mechanisms of polycrystalline Ni49.9Ti50.1 and Ni50.3Ti29.7Hf20 (in at.%) shape memory alloys were investigated by combined experimental and modeling efforts aided by an in situ neutron diffraction technique at stress and temperature. The thermomechanical response of the low temperature martensite, the high temperature austenite phases, and changes between these two states during thermomechanical cycling were probed and reported. In the cubic austenite phase, stress-induced martensite, deformation twinning and slip processes were observed which helped in constructing a deformation map that contained the limits over which each of the identified mechanisms was dominant. Deformation of the monoclinic martensitic phase was also investigated where the microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were compared to the bulk macroscopic response. When cycling between these two phases, the evolution of inelastic strains, along with the shape setting procedures were examined and used for the optimization of the transformation properties as a function of deformation levels and temperatures. Finally, this work was extended to the development of multiaxial capabilities at elevated temperatures for the in situ neutron diffraction measurements of shape memory alloys on the VULCAN Diffractometer at Oak Ridge National Laboratory.