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Sample records for martensitic phase transformations

  1. Complexion-mediated martensitic phase transformation in Titanium

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Tasan, C. C.; Lai, M. J.; Dippel, A.-C.; Raabe, D.

    2017-02-01

    The most efficient way to tune microstructures and mechanical properties of metallic alloys lies in designing and using athermal phase transformations. Examples are shape memory alloys and high strength steels, which together stand for 1,500 million tons annual production. In these materials, martensite formation and mechanical twinning are tuned via composition adjustment for realizing complex microstructures and beneficial mechanical properties. Here we report a new phase transformation that has the potential to widen the application window of Ti alloys, the most important structural material in aerospace design, by nanostructuring them via complexion-mediated transformation. This is a reversible martensitic transformation mechanism that leads to a final nanolaminate structure of α'' (orthorhombic) martensite bounded with planar complexions of athermal ω (a-ω, hexagonal). Both phases are crystallographically related to the parent β (BCC) matrix. As expected from a planar complexion, the a-ω is stable only at the hetero-interface.

  2. Complexion-mediated martensitic phase transformation in Titanium.

    PubMed

    Zhang, J; Tasan, C C; Lai, M J; Dippel, A-C; Raabe, D

    2017-02-01

    The most efficient way to tune microstructures and mechanical properties of metallic alloys lies in designing and using athermal phase transformations. Examples are shape memory alloys and high strength steels, which together stand for 1,500 million tons annual production. In these materials, martensite formation and mechanical twinning are tuned via composition adjustment for realizing complex microstructures and beneficial mechanical properties. Here we report a new phase transformation that has the potential to widen the application window of Ti alloys, the most important structural material in aerospace design, by nanostructuring them via complexion-mediated transformation. This is a reversible martensitic transformation mechanism that leads to a final nanolaminate structure of α″ (orthorhombic) martensite bounded with planar complexions of athermal ω (a-ω, hexagonal). Both phases are crystallographically related to the parent β (BCC) matrix. As expected from a planar complexion, the a-ω is stable only at the hetero-interface.

  3. Complexion-mediated martensitic phase transformation in Titanium

    PubMed Central

    Zhang, J.; Tasan, C. C.; Lai, M. J.; Dippel, A. -C.; Raabe, D.

    2017-01-01

    The most efficient way to tune microstructures and mechanical properties of metallic alloys lies in designing and using athermal phase transformations. Examples are shape memory alloys and high strength steels, which together stand for 1,500 million tons annual production. In these materials, martensite formation and mechanical twinning are tuned via composition adjustment for realizing complex microstructures and beneficial mechanical properties. Here we report a new phase transformation that has the potential to widen the application window of Ti alloys, the most important structural material in aerospace design, by nanostructuring them via complexion-mediated transformation. This is a reversible martensitic transformation mechanism that leads to a final nanolaminate structure of α″ (orthorhombic) martensite bounded with planar complexions of athermal ω (a–ω, hexagonal). Both phases are crystallographically related to the parent β (BCC) matrix. As expected from a planar complexion, the a–ω is stable only at the hetero-interface. PMID:28145484

  4. 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.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

  7. 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.

  8. 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.

  9. 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.

  10. Molecular dynamics simulation of the martensitic phase transformation in NiAl alloys.

    PubMed

    Pun, G P Purja; Mishin, Y

    2010-10-06

    Using molecular dynamics simulations with an embedded-atom interatomic potential, we study the effect of chemical composition and uniaxial mechanical stresses on the martensitic phase transformation in Ni-rich NiAl alloys. The martensitic phase has a tetragonal crystal structure and can contain multiple twins arranged in domains and plates. The transformation is reversible and is characterized by a significant temperature hysteresis. The magnitude of the hysteresis depends on the chemical composition and stress. We show that applied compressive and tensile stresses reduce and can even eliminate the hysteresis. Crystalline defects such as free surfaces, dislocations and anti-phase boundaries reduce the martensitic transformation temperature and affect the microstructure of the martensite. Their effect can be explained by heterogeneous nucleation of the new phase in defected regions.

  11. Confined martensitic phase transformation kinetics and lattice dynamics in Ni–Co–Fe–Ga shape memory alloys

    SciTech Connect

    Cong, Daoyong; Rule, Kirrily Clair; Li, Wen-Hsien; Lee, Chi-Hung; Zhang, Qinghua; Wang, Haoliang; Hao, Yulin; Wang, Yandong; Huang, E-Wen

    2016-09-02

    Here we describe insights into the phase transformation kinetics and lattice dynamics associated with the newly discovered confined martensitic transformation, which are of great significance to the in-depth understanding of the phase transformation behavior responsible for the rich new physical phenomena in shape memory alloys and could shed light on the design of novel multifunctional properties through tuning the confined martensitic transformation.

  12. Computer Simulation of Martensitic Transformations.

    NASA Astrophysics Data System (ADS)

    Rifkin, Jonathan A.

    This investigation attempted to determine the mechanism of martensitic nucleation by employing computer molecular dynamics; simulations were conducted of various lattices defects to see if they can serve as nucleation sites. As a prerequisite to the simulations the relation between transformation properties and interatomic potential was studied. It was found that the interatomic potential must have specific properties to successfully simulate solid-solid transformations; in particular it needs a long range oscillating tail. We've also studied homogeneous transformations between BCC and FCC structures and concluded it is unlikely that any has a lower energy barrier energy than the Bain transformation. A two dimensional solid was modelled first to gain experience on a relatively simple system; the transformation was from a square lattice to a triangular one. Next a three dimensional system was studied whose interatomic potential was chosen to mimic sodium. Because of the low transition temperature (18K) the transformation from the low temperature phase to high temperature phase was studied (FCC to BCC). The two dimensional system displayed many phenomena characteristic of real martensitic systems: defects promoted nucleation, the martensite grew in plates, some plates served to nucleate new plates (autocatalytic nucleation) and some defects gave rise to multiple plates (butterfly martensite). The three dimensional system did not undergo a permanent martensitic transformation but it did show signs of temporary transformations where some martensite formed and then dissipated. This happened following the dissociation of a screw dislocation into two partial dislocations.

  13. 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

    2017-07-01

    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.

  14. Modeling the coupling between martensitic phase transformation and plasticity in shape memory alloys

    NASA Astrophysics Data System (ADS)

    Manchiraju, Sivom

    The thermo-mechanical response of NiTi shape memory alloys (SMAs) is predominantly dictated by two inelastic deformation processes---martensitic phase transformation and plastic deformation. This thesis presents a new microstructural finite element (MFE) model that couples these processes and anisotropic elasticity. The coupling occurs via the stress redistribution induced by each mechanism. The approach includes three key improvements to the literature. First, transformation and plasticity are modeled at a crystallographic level and can occur simultaneously. Second, a rigorous large-strain finite element formulation is used, thereby capturing texture development (crystal rotation). Third, the formulation adopts recent first principle calculations of monoclinic martensite stiffness. The model is calibrated to experimental data for polycrystalline NiTi (49.9 at% Ni). Inputs include anisotropic elastic properties, texture, and DSC data as well as a subset of pseudoelastic and load-biased thermal cycling data. This calibration process provides updated material values---namely, larger self-hardening between similar martensite plates. It is then assessed against additional pseudoelastic and load-biased thermal cycling experimental data and neutron diffraction measurements of martensite texture evolution. Several experimental trends are captured---in particular, the transformation strain during thermal cycling monotonically increases with increasing bias stress, reaching a peak and then decreasing due to intervention of plasticity---a trend which existing MFE models are unable to capture. Plasticity is also shown to enhance stress-induced martensite formation during loading and generate retained martensite upon unloading. The simulations even enable a quantitative connection between deformation processing and two-way shape memory effect. Some experimental trends are not captured---in particular, the ratcheting of macrostrain with repeated thermal cycling. This may

  15. Thermal stability and phase transformations of martensitic Ti–Nb alloys

    PubMed Central

    Bönisch, Matthias; Calin, Mariana; Waitz, Thomas; Panigrahi, Ajit; Zehetbauer, Michael; Gebert, Annett; Skrotzki, Werner; Eckert, Jürgen

    2013-01-01

    Aiming at understanding the governing microstructural phenomena during heat treatments of Ni-free Ti-based shape memory materials for biomedical applications, a series of Ti–Nb alloys with Nb concentrations up to 29 wt% was produced by cold-crucible casting, followed by homogenization treatment and water quenching. Despite the large amount of literature available concerning the thermal stability and ageing behavior of Ti–Nb alloys, only few studies were performed dealing with the isochronal transformation behavior of initially martensitic Ti–Nb alloys. In this work, the formation of martensites (α′ and α″) and their stability under different thermal processing conditions were investigated by a combination of x-ray diffraction, differential scanning calorimetry, dilatometry and electron microscopy. The effect of Nb additions on the structural competition in correlation with stable and metastable phase diagrams was also studied. Alloys with 24 wt% Nb or less undergo a transformation sequence on heating from room temperature to 1155 K. In alloys containing >24 wt% Nb α″ martensitically reverts back to β0, which is highly unstable against chemical demixing by formation of isothermal ωiso. During slow cooling from the single phase β domain α precipitates and only very limited amounts of α″ martensite form. PMID:27877611

  16. Thermal stability and phase transformations of martensitic Ti-Nb alloys

    NASA Astrophysics Data System (ADS)

    Bönisch, Matthias; Calin, Mariana; Waitz, Thomas; Panigrahi, Ajit; Zehetbauer, Michael; Gebert, Annett; Skrotzki, Werner; Eckert, Jürgen

    2013-10-01

    Aiming at understanding the governing microstructural phenomena during heat treatments of Ni-free Ti-based shape memory materials for biomedical applications, a series of Ti-Nb alloys with Nb concentrations up to 29 wt% was produced by cold-crucible casting, followed by homogenization treatment and water quenching. Despite the large amount of literature available concerning the thermal stability and ageing behavior of Ti-Nb alloys, only few studies were performed dealing with the isochronal transformation behavior of initially martensitic Ti-Nb alloys. In this work, the formation of martensites (α‧ and α″) and their stability under different thermal processing conditions were investigated by a combination of x-ray diffraction, differential scanning calorimetry, dilatometry and electron microscopy. The effect of Nb additions on the structural competition in correlation with stable and metastable phase diagrams was also studied. Alloys with 24 wt% Nb or less undergo a \\alpha '/\\alpha '' \\to \\alpha + \\beta \\to \\beta transformation sequence on heating from room temperature to 1155 K. In alloys containing >24 wt% Nb α″ martensitically reverts back to β0, which is highly unstable against chemical demixing by formation of isothermal ωiso. During slow cooling from the single phase β domain α precipitates and only very limited amounts of α″ martensite form.

  17. Thermal stability and phase transformations of martensitic Ti-Nb alloys.

    PubMed

    Bönisch, Matthias; Calin, Mariana; Waitz, Thomas; Panigrahi, Ajit; Zehetbauer, Michael; Gebert, Annett; Skrotzki, Werner; Eckert, Jürgen

    2013-10-01

    Aiming at understanding the governing microstructural phenomena during heat treatments of Ni-free Ti-based shape memory materials for biomedical applications, a series of Ti-Nb alloys with Nb concentrations up to 29 wt% was produced by cold-crucible casting, followed by homogenization treatment and water quenching. Despite the large amount of literature available concerning the thermal stability and ageing behavior of Ti-Nb alloys, only few studies were performed dealing with the isochronal transformation behavior of initially martensitic Ti-Nb alloys. In this work, the formation of martensites (α' and α″) and their stability under different thermal processing conditions were investigated by a combination of x-ray diffraction, differential scanning calorimetry, dilatometry and electron microscopy. The effect of Nb additions on the structural competition in correlation with stable and metastable phase diagrams was also studied. Alloys with 24 wt% Nb or less undergo a [Formula: see text] transformation sequence on heating from room temperature to 1155 K. In alloys containing >24 wt% Nb α″ martensitically reverts back to β0, which is highly unstable against chemical demixing by formation of isothermal ωiso. During slow cooling from the single phase β domain α precipitates and only very limited amounts of α″ martensite form.

  18. 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.

  19. Surface tension and energy in multivariant martensitic transformations: phase-field theory, simulations, and model of coherent interface.

    PubMed

    Levitas, Valery I; Javanbakht, Mahdi

    2010-10-15

    The Ginzburg-Landau theory for multivariant martensitic phase transformations is advanced in three directions: the potential is developed that introduces the surface tension at interfaces; a mixed term in gradient energy is introduced to control the martensite-martensite interface energy independent of that for austenite-martensite; and a noncontradictory expression for variable surface energy is suggested. The problems of surface-induced pretransformation, barrierless multivariant nucleation, and the growth of an embryo in a nanosize sample are solved to elucidate the effect of the above contributions. The obtained results represent an advanced model for coherent interface.

  20. Phase field approach to martensitic phase transformations with large strains and interface stresses

    NASA Astrophysics Data System (ADS)

    Levitas, Valery I.

    2014-10-01

    Thermodynamically consistent phase field theory for multivariant martensitic transformations, which includes large strains and interface stresses, is developed. Theory is formulated in a way that some geometrically nonlinear terms do not disappear in the geometrically linear limit, which in particular allowed us to introduce the expression for the interface stresses consistent with the sharp interface approach. Namely, for the propagating nonequilibrium interface, a structural part of the interface Cauchy stresses reduces to a biaxial tension with the magnitude equal to the temperature-dependent interface energy. Additional elastic and viscous contributions to the interface stresses do not require separate constitutive equations and are determined by solution of the coupled system of phase field and mechanics equations. Ginzburg-Landau equations are derived for the evolution of the order parameters and temperature evolution equation. Boundary conditions for the order parameters include variation of the surface energy during phase transformation. Because elastic energy is defined per unit volume of unloaded (intermediate) configuration, additional contributions to the Ginzburg-Landau equations and the expression for entropy appear, which are important even for small strains. A complete system of equations for fifth- and sixth-degree polynomials in terms of the order parameters is presented in the reference and actual configurations. An analytical solution for the propagating interface and critical martensitic nucleus which includes distribution of components of interface stresses has been found for the sixth-degree polynomial. This required resolving a fundamental problem in the interface and surface science: how to define the Gibbsian dividing surface, i.e., the sharp interface equivalent to the finite-width interface. An unexpected, simple solution was found utilizing the principle of static equivalence. In fact, even two equations for determination of the

  1. 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.

  2. 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)

  3. Martensitic transformation of the Ni[sub 2]Al phase in 63. 1 at. % NiAl

    SciTech Connect

    Murthy, A.S.; Goo, E. . Dept. of Materials Science and Engineering)

    1993-07-01

    Electron diffraction and high resolution electron microscopy of 63.1 at.% NiAl have shown that the metastable hexagonal Ni[sub 2]Al precipitate, coherent in the B2 matrix phase, transforms concurrently with the martensitic transformation of the B2 NiAl matrix to the L1[sub 0] phase. The Ni[sub 2]Al precipitate that is coherent with the L1[sub 0] phase in monoclinic.

  4. Radial Distribution of Martensitic Phase Transformation in a Metastable Stainless Steel under Torsional Deformation: A Synchrotron X-ray Diffraction Study

    SciTech Connect

    Cakmak, Ercan; Choo, Hahn; An, Ke; Ren, Yang

    2011-01-01

    The strain-induced martensitic phase transformation in a metastable 304 L stainless steel under torsional deformation was investigated using synchrotron X-ray diffraction. The measured radial distribution of the martensite phase fraction in a solid cylindrical specimen agrees well with the prediction based on a combination of transformation kinetics and a radial plastic strain distribution equation.

  5. Incorporation of plasticity into the Landau-Ginzburg theory of martensitic phase transformations

    NASA Astrophysics Data System (ADS)

    Gröger, Roman; Lookman, Turab

    2008-03-01

    The Landau-Ginzburg theory of martensitic phase transformations has been utilized to reproduce the evolution of elastic texture in defect-free materials undergoing structural phase transformations. Generalizations of this theory to phase transformations that are accompanied by significant plastic distortions (as in U6Nb) have been little studied. We propose a simple model that demonstrates how to incorporate plasticity into the Landau-Ginzburg theory. In the presence of topological defects such as dislocations, the usual Saint Venant compatibility constraint becomes an incompatibility constraint and this is represented by a tensor field ηij. In our case, the components of ηij are expressed as gradients of the components of the Nye tensor that represent the dislocation density. The presence of dislocations induces large internal stresses in certain regions of the material, and these act as initiation sites for plastic deformation. When the external loading is applied, dislocations moving from these regions cause strain hardening that is detectable in experimental uniaxial measurements. This model serves as a starting point for further development of the framework of three-dimensional rate-independent theory of plasticity within the Landau-Ginzburg formalism.

  6. 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.

  7. Linking simulations and experiments for the multiscale tracking of thermally induced martensitic phase transformation in NiTi SMA

    NASA Astrophysics Data System (ADS)

    Gur, Sourav; Frantziskonis, George N.

    2016-10-01

    Martensitic phase transformation in NiTi shape memory alloys (SMA) occurs over a hierarchy of spatial scales, as evidenced from observed multiscale patterns of the martensitic phase fraction, which depend on the material microstructure and on the size of the SMA specimen. This paper presents a methodology for the multiscale tracking of the thermally induced martensitic phase transformation process in NiTi SMA. Fine scale stochastic phase field simulations are coupled to macroscale experimental measurements through the compound wavelet matrix method (CWM). A novel process for obtaining CWM fine scale wavelet coefficients is used that enhances the effectiveness of the method in transferring uncertainties from fine to coarse scales, and also ensures the preservation of spatial correlations in the phase fraction pattern. Size effects, well-documented in the literature, play an important role in designing the multiscale tracking methodology. Molecular dynamics (MD) simulations are employed to verify the phase field simulations in terms of different statistical measures and to demonstrate size effects at the nanometer scale. The effects of thermally induced martensite phase fraction uncertainties on the constitutive response of NiTi SMA is demonstrated.

  8. International Conference on Martensitic Transformations (ICOMAT 92)

    DTIC Science & Technology

    1993-03-05

    of stress -induced (that is, occuring in the region ahead of a crack tip) t-ni martensitic transformation to fracture toughness Of ceramics is...discussed in detail. and considered that it is related to th differenet Initial stress iields Intr~odu4ed by the constrained- h 5tiR in the P"ent Phase...diffractometer, which makes the accurate determination of struc- tures possible for single crystal martensites produced by stress - induced transformation

  9. 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.

  10. A uniaxial constitutive model for superelastic NiTi SMA including R-phase and martensite transformations and thermal effects

    NASA Astrophysics Data System (ADS)

    Helbert, Guillaume; Saint-Sulpice, Luc; Arbab Chirani, Shabnam; Dieng, Lamine; Lecompte, Thibaut; Calloch, Sylvain; Pilvin, Philippe

    2017-02-01

    The well-known martensitic transformation is not always the unique solid-solid phase change in NiTi shape memory alloys (SMA). For this material, R-phase can occur from both austenite and martensite. In some applications, macroscopic strain of the material can be limited to 2%. In these cases, R-phase contribution can not be neglected anymore when compared with martensite. Furthermore, different thermomechanical couplings have to be taken into account to carefully predict strain rate effects and to better describe application conditions. In this paper, a new model taking into account various phase transformations with thermomechanical couplings is presented. This model is based on several transformation criteria. In most applications, SMA are used as wires, submitted to tensile-tensile loadings, in the superelasticity working range. Consequently, a uniaxial reduction of the model is presented for its simplicity. A thermodynamic framework is proposed. It enables to describe the internal variables evolution laws. The simple and fast identification process of model parameters is briefly presented. To verify the validity of the proposed model, simulation results are compared with experimental ones. The influences of testing temperature and strain amplitude on the material behavior is discussed. The damping capacity is also studied, using an energy-based criterion.

  11. Martensitic transformation between competing phases in Ti-Ta alloys: a solid-state nudged elastic band study.

    PubMed

    Chakraborty, Tanmoy; Rogal, Jutta; Drautz, Ralf

    2015-03-25

    A combined density functional theory and solid-state nudged elastic band study is presented to investigate the martensitic transformation between β → (α″, ω) phases in the Ti-Ta system. The minimum energy paths along the transformation are calculated and the transformation mechanisms as well as relative stabilities of the different phases are discussed for various compositions. The analysis of the transformation paths is complemented by calculations of phonon spectra to determine the dynamical stability of the β, α″, and ω phase. Our theoretical results confirm the experimental findings that with increasing Ta concentration there is a competition between the destabilisation of the α″ and ω phase and the stabilisation of the high-temperature β phase.

  12. TEM study of the martensitic phases in the ductile DyCu and YCu intermetallic compounds [The martensitic phase transformation in ductile DyCu and YCu intermetallic compounds

    DOE PAGES

    Cao, G. H.; Oertel, C. -G.; Schaarschuch, R.; ...

    2017-05-03

    DyCu and YCu are representatives of the family of CsCl-type B2 rare earth intermetallic compounds that exhibit high room temperature ductility. Structure, orientation relationship, and morphology of the martensites in the equiatomic compounds DyCu and YCu are examined using transmission electron microscopy (TEM). TEM studies show that the martensite structures in DyCu and YCu alloys are virtually identical. The martensite is of orthorhombic CrB-type B33 structure with lattice parameters a = 0.38 nm, b = 1.22 nm, and c = 0.40 nm. (021¯) twins were observed in the B33 DyCu and YCu martensites. The orientation relationship of B33 and B2more » phases is (111¯)[112]B33 || (110)[001]B2. The simulated electron diffraction patterns of the B33 phase are consistent with those of experimental observations. TEM investigations also reveal that a dominant orthorhombic FeB-type B27 martensite with lattice parameters a = 0.71 nm, b = 0.45 nm, and c = 0.54 nm exists in YCu alloy. (11¯ 1) twins were observed in the B27 YCu martensite. As a result, the formation mechanism of B2 to B33 and B2 to B27 phase transformation is discussed.« less

  13. Direct observation of martensitic phase-transformation dynamics in iron by 4D single-pulse electron microscopy.

    PubMed

    Park, Hyun Soon; Kwon, Oh-Hoon; Baskin, J Spencer; Barwick, Brett; Zewail, Ahmed H

    2009-11-01

    The in situ martensitic phase transformation of iron, a complex solid-state transition involving collective atomic displacement and interface movement, is studied in real time by means of four-dimensional (4D) electron microscopy. The iron nanofilm specimen is heated at a maximum rate of approximately 10(11) K/s by a single heating pulse, and the evolution of the phase transformation from body-centered cubic to face-centered cubic crystal structure is followed by means of single-pulse, selected-area diffraction and real-space imaging. Two distinct components are revealed in the evolution of the crystal structure. The first, on the nanosecond time scale, is a direct martensitic transformation, which proceeds in regions heated into the temperature range of stability of the fcc phase, 1185-1667 K. The second, on the microsecond time scale, represents an indirect process for the hottest central zone of laser heating, where the temperature is initially above 1667 K and cooling is the rate-determining step. The mechanism of the direct transformation involves two steps, that of (barrier-crossing) nucleation on the reported nanosecond time scale, followed by a rapid grain growth typically in approximately 100 ps for 10 nm crystallites.

  14. SEM Technique Development for Exploring Martensitic Phase Transformations in Multi-Variant Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Chapman, Michael G.

    The purpose of this work is to validate that the martensitic transformations predicted by the model from Xian Chen and Dick James from the University of Minnesota. This model uses multiple criteria for compatibility between the austenite and martensite lattices including limitations of the middle eigenvalue of the transformation stretch matrix and what are called the "cofactor conditions." An alloy satisfying these criteria was found, (Au30Cu25Zn 45) but the traditional methods for verifying the shape and crystallographic orientation relationships of the transformation could not be used (serial sectioning and 3D Electron Backscatter Diffraction (EBSD)). The first method developed in this work uses the intensity peak of the background of EBSD patterns to extract surface topography measurements. Monte Carlo simulations were used to calculate the deviation from specular reflection for electrons on different materials at varying voltages. The geometric setup of the EBSD camera and the sample were then used with the experimentally measured intensity peak location on the camera to calculate the surface normal vectors for each point on a sample. A proof of concept experiment was first performed on the Tin sphere calibration standard, in which the surface normal vectors were found within around 0:5ffi error near the standard EBSD sample orientation. This technique was then used to measure the surface relief caused by the martensitic transformation of the AuCuZn alloy which can be matched to predicted surface shearing values to confirm the Chen/James model. The second method developed in this thesis measures the out-of-plane grain boundary inclination angle using 2D EBSD. This utilizes the penetration depth of the electron interaction volume, and is measured by calculating the proportion of the pattern that is created from each grain. This is completed by performing dot products between an EBSD line scan across the grain boundary and reference patterns taken from the bulk

  15. 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.

  16. Defect-induced incompatibility of elastic strains: Dislocations within the Landau theory of martensitic phase transformations

    NASA Astrophysics Data System (ADS)

    Gröger, R.; Lookman, T.; Saxena, A.

    2008-11-01

    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.

  17. 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.

  18. Phase transformation and long-term service of high-temperature martensitic chromium steels

    NASA Astrophysics Data System (ADS)

    Kalashnikov, I. S.; Tarasenko, L.; Acselrad, O.; Pereira, L. C.; Shalkevich, A.; Soboleva, G.

    2000-02-01

    Martensitic high Cr (10 - 16%) steels alloyed with Ni (Co), Mo, W, V, and N are widely used in constructions subjected to cyclic loads at temperatures up to 600 degrees Celsius, in general after quenching from 1100 - 1150 degrees Celsius followed by tempering at 650 - 690 degrees Celsius. Due to long term service exposure at high temperatures, different microstructural changes take place, such as second-phases precipitation, formation of low-angle grain boundaries, as well as internal damage caused by cyclic loads and creep. Specific phase diagrams are presented that can be used to define time periods for reliable operation of parts with given composition, based on the time required for the appearance of second phase particles known to be detrimental to mechanical strength and performance. Restoring thermal treatments to be applied after long time exposure at service conditions, aiming at increasing service life, are also presented and discussed. The combined use of the diagrams and the restoring treatment ensures prediction of a reliable service-life period for components made of these steels.

  19. Phase transformation and long-term service of high-temperature martensitic chromium steels

    NASA Astrophysics Data System (ADS)

    Kalashnikov, I. S.; Tarasenko, L.; Acselrad, O.; Pereira, L. C.; Shalkevich, A.; Soboleva, G.

    2001-02-01

    Martensitic high Cr (10 - 16%) steels alloyed with Ni (Co), Mo, W, V, and N are widely used in constructions subjected to cyclic loads at temperatures up to 600 degrees Celsius, in general after quenching from 1100 - 1150 degrees Celsius followed by tempering at 650 - 690 degrees Celsius. Due to long term service exposure at high temperatures, different microstructural changes take place, such as second-phases precipitation, formation of low-angle grain boundaries, as well as internal damage caused by cyclic loads and creep. Specific phase diagrams are presented that can be used to define time periods for reliable operation of parts with given composition, based on the time required for the appearance of second phase particles known to be detrimental to mechanical strength and performance. Restoring thermal treatments to be applied after long time exposure at service conditions, aiming at increasing service life, are also presented and discussed. The combined use of the diagrams and the restoring treatment ensures prediction of a reliable service-life period for components made of these steels.

  20. Martensitic transformations in laser processed coatings

    SciTech Connect

    Burg, M. van den; De Hosson, J.T.M. . Dept. of Applied Physics)

    1993-09-01

    This paper concentrates on laser coating of Fe-22 wt% Cr and a duplex steel SAF2205 by injecting Cr[sub 2]O[sub 3] powder into the melt pool. In particular the work focuses on the stabilization of high temperature distorted spinel phases due to the high quench rates involved as well as on the a quantitative crystallographic analysis of the resulting morphologies. The microstructure observed in TEM indicates that the material does not solidify in the distorted spinel structure. The presence of a small amount of cubic (Fe, Cr)-spinel suggests that the distorted spinel in fact might be nucleated from the cubic spinel phase. The plate like morphology of the distorted spinel phase in combination with the twinned internal structure of the plates put forward the idea that the transformation might be martensitic. Martensitic calculations executed with the lattice parameters of the cubic and distorted (Fe, Cr)-spinel phases are in excellent agreement with the experimental data confirming that the transformation might be martensitic indeed.

  1. A comparative first-principles study of martensitic phase transformations in TiPd2 and TiPd

    SciTech Connect

    Krcmar, Maja; Morris, James R

    2014-01-01

    Martensitic phase transformations in TiPd2 and TiPd alloys are studied employing density-functional, first-principles calculations. We examine the transformation of tetragonal C11b TiPd2 to the low-temperature orthorhombic phase (C11b oI6), and the transformation of cubic B2 TiPd under orthorhombic (B2 B19) and subsequent monoclinic transformations (B19 B19 ) as the system is cooled. To evaluate the transition temperature for TiPd2 we employ a theoretical approach based on a phenomenological Landau theory of the structural phase transition and a mean-field approximation for the free energy, utilizing first-principles calculations to obtain the deformation energy as a function of strains and to deduce parameters for constructing the free energy. The predicted transition temperature for the TiPd2 C11b oI6 transition temperature is in good agreement with reported experimental results. To investigate the TiPd B2 B19 transformation, we employ both the Cauchy-Born rule and a soft-mode- based approach, and elucidate on the importance of coupling of lattice distortion and atomic displacements (i.e., shuffling) in the formation of the final structure. The estimated B2 B19 transition temperature for TiPd system agrees well with the experimental results. We also find that there exists a very small but finite (0.0005 eV/atom) energy barrier of B19 TiPd under monoclinic deformation for B19 B19 structural phase transformation.

  2. A comparative first-principles study of martensitic phase transformations in TiPd2 and TiPd intermetallics.

    PubMed

    Krcmar, M; Morris, James R

    2014-04-02

    Martensitic phase transformations in TiPd2 and TiPd alloys are studied employing density-functional, first-principles calculations. We examine the transformation of tetragonal C11b TiPd2 to the low-temperature orthorhombic phase (C11b → oI6), and the transformation of cubic B2 TiPd under orthorhombic (B2→B19) and subsequent monoclinic transformations (B19→B19') as the system is cooled. We employ a theoretical approach based on a phenomenological Landau theory of the structural phase transitions and a mean-field approximation for the free energy, utilizing first-principles calculations to obtain the deformation energy as a function of strains and to deduce parameters for constructing the free energy. The predicted transition temperature for the TiPd2 C11b → oI6 transition is in good agreement with reported experimental results. To investigate the TiPd B2→B19 transformation, we employ both the Cauchy-Born rule and a soft-mode-based approach, and elucidate the importance of the coupling between lattice distortion and atomic displacements (i.e. shuffling) in the formation of the final structure. The calculated B2→B19 transition temperature for TiPd alloy agrees well with the experimental results. We also find that there exists a very small but finite (0.0005 eV/atom) energy barrier of B19 TiPd under monoclinic deformation for B19→B19' structural phase transformation.

  3. Structure, phase transformations, mechanical characteristics, and cold resistance of low-carbon martensitic steels

    NASA Astrophysics Data System (ADS)

    Kozvonin, V. A.; Shatsov, A. A.; Ryaposov, I. V.; Zakirova, M. G.; Generalova, K. N.

    2016-08-01

    Temper-resistant low-carbon Cr-Mn-Ni-Mo-V-Nb steels with concentrations of carbon of 0.15 and 0.27 wt % have been studied. It has been shown that, upon quenching, various morphological types of the α phase can be formed. The structure of the steels is stable in the course of heating below critical temperatures and remains a lath-type structure in the intercritical temperature range. Specific features of structural and phase transformations, as well as the dependence of the mechanical characteristics of the steels, on the tempering temperature have been determined.

  4. 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.

  5. Influences of cyclic loading on martensite transformation of TRIP steels

    NASA Astrophysics Data System (ADS)

    Dan, W. J.; Hu, Z. G.; Zhang, W. G.

    2013-03-01

    While austenite transformation into martensite induces increasing of the crack initiation life and restraining of the growth of fatigue cracks in cyclic-loading processes, TRIP-assisted steels have a better fatigue life than the AHSS (Advance High Strength Steels). As two key parameters in the cyclic loading process, strain amplitude and cyclic frequency are used in a kinetic transformation model to reasonably evaluate the phase transformation from austenite into martensite with the shear-band intersections theory, in which strain amplitude and cyclic frequency are related to the rate of shear-band intersection formation and the driving force of phase transformation. The results revealed that the martensite volume fraction increased and the rate of phase transformation decrease while the number of cycles increased, and the martensite volume fraction was almost constant after the number of cycles was more than 2000 times. Higher strain amplitude promotes martensite transformation and higher cyclic frequency impedes phase transformation, which are interpreted by temperature increment, the driving force of phase transformation and the rate of shearband intersection formation.

  6. Effect of N on Phase Transformations During Martensite Thermomechanical Processing of the Nano/Ultrafine-Grained 201L Steel

    NASA Astrophysics Data System (ADS)

    Saeedipour, S.; Kermanpur, A.; Najafizadeh, A.

    2016-12-01

    Effect of N addition on microstructural evolutions and mechanical properties of a 201L austenitic stainless steel during the martensite thermomechanical treatment was investigated. The as-homogenized samples were cold-rolled by 90% thickness reduction followed by reversion annealing at 800-900 °C for different times of 15-1800 s. The microstructures were characterized by optical and scanning electron microscopy and magnetic measurement, while mechanical properties were determined by hardness and shear punch tests. It was found that N addition retards the kinetics of strain-induced martensitic transformation, but accelerates the martensite reversion. The hardness, yield and ultimate shear strengths were increased by N alloying at the expense of elongation in both solution-annealed and reversion-annealed specimens.

  7. Influence of Ni on Martensitic Phase Transformations in NiTi Shape Memory Alloys

    SciTech Connect

    Frenzel, J.; George, Easo P; Dlouhy, A.; Somsen, Ch.; Wagner, M. F.-X; Eggeler, G.

    2010-01-01

    High-precision data on phase transformation temperatures in NiTi, including numerical expressions for the effect of Ni on M{sub S}, M{sub F}, A{sub S}, A{sub F} and T{sub 0}, are obtained, and the reasons for the large experimental scatter observed in previous studies are discussed. Clear experimental evidence is provided confirming the predictions of Tang et al. 1999 regarding deviations from a linear relation between the thermodynamic equilibrium temperature and Ni concentration. In addition to affecting the phase transition temperatures, increasing Ni contents are found to decrease the width of thermal hysteresis and the heat of transformation. These findings are rationalized on the basis of the crystallographic data of Prokoshkin et al. 2004 and the theory of Ball and James. The results show that it is important to document carefully the details of the arc-melting procedure used to make shape memory alloys and that, if the effects of processing are properly accounted for, precise values for the Ni concentration of the NiTi matrix can be obtained.

  8. Stability of crystalline solids—II: Application to temperature-induced martensitic phase transformations in a bi-atomic crystal

    NASA Astrophysics Data System (ADS)

    Elliott, Ryan S.; Shaw, John A.; Triantafyllidis, Nicolas

    2006-01-01

    This paper applies the stability theory of crystalline solids presented in the companion paper (Part I) to the study of martensitic transformations found in shape memory alloys (SMA's). The focus here is on temperature-induced martensitic transformations of bi-atomic crystals under stress-free loading conditions. A set of temperature-dependent atomic potentials and a multilattice description are employed to derive the energy density of a prototypical SMA ( B2 cubic austenite crystal). The bifurcation and stability behavior are then investigated with respect to two stability criteria (Cauchy-Born (CB) and phonon). Using a 4-lattice description five different equilibrium crystal structures are predicted: B2 cubic, L10 tetragonal, B19 orthorhombic, Cmmm orthorhombic, and B19' monoclinic. For our chosen model only the B2 and B19 equilibrium paths have stable segments which satisfy both the CB- and phonon-stability criteria. These stable segments overlap in temperature indicating the possibility of a hysteretic temperature-induced proper martensitic transformation. The B2 and B19 crystal structures are common in SMA's and therefore the simulated jump in the deformation gradient at a temperature for which both crystals are stable is compared to experimental values for NiTi, AuCd, and CuAlNi. Good agreement is found for the two SMA's which have cubic to orthorhombic transformations (AuCd and CuAlNi).

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

    DOE PAGES

    Bhatti, Kanwal Preet; El-Khatib, S.; Srivastava, Vijay; ...

    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

  10. Suppression of Martensitic Transformation in Co2Cr(Ga,Si) Heusler Alloys by Thermal Cycling

    NASA Astrophysics Data System (ADS)

    Liang, Xiao; Xiao, Fei; Jin, Xuejun; Fukuda, Takashi; Kakeshita, Tomoyuki

    2017-05-01

    We have investigated the influence of thermal cycles on martensitic transformation of a Co2Cr(Ga,Si) ferromagnetic Heusler alloy. The as-quenched specimen exhibits successive L21(L)- D022- L21(H) martensitic transformation in the cooling process, which is known as reentrant martensitic transformation. However, heating to 800 K (527 °C) for reverse D022- L21 transformation with a rate of 10 K/min (10 °C/min) stabilizes the parent phase, meaning that the martensitic transformation is suppressed by the thermal cycles. We found precipitate after thermal cycles, and it will be the reason for the stabilization of parent phase.

  11. Suppression of Martensitic Transformation in Co2Cr(Ga,Si) Heusler Alloys by Thermal Cycling

    NASA Astrophysics Data System (ADS)

    Liang, Xiao; Xiao, Fei; Jin, Xuejun; Fukuda, Takashi; Kakeshita, Tomoyuki

    2017-03-01

    We have investigated the influence of thermal cycles on martensitic transformation of a Co2Cr(Ga,Si) ferromagnetic Heusler alloy. The as-quenched specimen exhibits successive L21(L)-D022-L21(H) martensitic transformation in the cooling process, which is known as reentrant martensitic transformation. However, heating to 800 K (527 °C) for reverse D022-L21 transformation with a rate of 10 K/min (10 °C/min) stabilizes the parent phase, meaning that the martensitic transformation is suppressed by the thermal cycles. We found precipitate after thermal cycles, and it will be the reason for the stabilization of parent phase.

  12. Crystal symmetry and the reversibility of martensitic transformations

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Kaushik; Conti, Sergio; Zanzotto, Giovanni; Zimmer, Johannes

    2004-03-01

    Martensitic transformations are diffusionless, solid-to-solid phase transitions, and have been observed in metals, alloys, ceramics and proteins. They are characterized by a rapid change of crystal structure, accompanied by the development of a rich microstructure. Martensitic transformations can be irreversible, as seen in steels upon quenching, or they can be reversible, such as those observed in shape-memory alloys. In the latter case, the microstructures formed on cooling are easily manipulated by loads and disappear upon reheating. Here, using mathematical theory and numerical simulation, we explain these sharp differences in behaviour on the basis of the change in crystal symmetry during the transition. We find that a necessary condition for reversibility is that the symmetry groups of the parent and product phases be included in a common finite symmetry group. In these cases, the energy barrier to lattice-invariant shear is generically higher than that pertaining to the phase change and, consequently, transformations of this type can occur with virtually no plasticity. Irreversibility is inevitable in all other martensitic transformations, where the energy barrier to plastic deformation (via lattice-invariant shears, as in twinning or slip) is no higher than the barrier to the phase change itself. Various experimental observations confirm the importance of the symmetry of the stable states in determining the macroscopic reversibility of martensitic transformations.

  13. Influence of the Martensitic Transformation on the Microscale Plastic Strain Heterogeneities in a Duplex Stainless Steel

    NASA Astrophysics Data System (ADS)

    Lechartier, Audrey; Martin, Guilhem; Comby, Solène; Roussel-Dherbey, Francine; Deschamps, Alexis; Mantel, Marc; Meyer, Nicolas; Verdier, Marc; Veron, Muriel

    2017-01-01

    The influence of the martensitic transformation on microscale plastic strain heterogeneity of a duplex stainless steel has been investigated. Microscale strain heterogeneities were measured by digital image correlation during an in situ tensile test within the SEM. The martensitic transformation was monitored in situ during tensile testing by high-energy synchrotron X-ray diffraction. A clear correlation is shown between the plasticity-induced transformation of austenite to martensite and the development of plastic strain heterogeneities at the phase level.

  14. Effect of yttrium on martensite-austenite phase transformation temperatures and high temperature oxidation kinetics of Ti-Ni-Hf high-temperature shape memory alloys

    NASA Astrophysics Data System (ADS)

    Kim, Jeoung Han; Kim, Kyong Min; Yeom, Jong Taek; Young, Sung

    2016-03-01

    The effect of yttrium (< 5.5 at%) on the martensite-austenite phase transformation temperatures, microstructural evolution, and hot workability of Ti-Ni-Hf high-temperature shape memory alloys is investigated. For these purposes, differential scanning calorimetry, hot compression, and thermo-gravimetric tests are conducted. The phase transformation temperatures are not noticeably influenced by the addition of yttrium up to 4.5 at%. Furthermore, the hot workability is not significantly affected by the yttrium addition up to 1.0 at%. However, when the amount of yttrium addition exceeds 1.0 at%, the hot workability deteriorates significantly. In contrast, remarkable improvement in the high temperature oxidation resistance due to the yttrium addition is demonstrated. The total thickness of the oxide layers is substantially thinner in the Y-added specimen. In particular, the thickness of (Ti,Hf) oxide layer is reduced from 200 µm to 120 µm by the addition of 0.3 at% Y.

  15. Field induced martensitic phase transition in nonstoichoimetric Ni45Mn44Sn11 Heusler alloy

    NASA Astrophysics Data System (ADS)

    Chabri, T.; Venimadhav, A.; Nath, T. K.

    2017-05-01

    Nonstoichiometric high-Mn content Mn45Ni44Sn11 ferromagnetic shape memory alloys (FSMAs) were prepared by arc melting technique. First order transition near the martensitic transition (austenitic → martensitic) has been observed from magnetization, differential scanning calorimetry and resistivity measurements upon heating and cooling run. The austenitic phase was transformed into the martensitic phase, which means that these alloys have potential as FSMA applications. The shift of martensitic transition to the lower temperature with the magnetic field confirms the field induced martensitic transition. This signifies that the highly ordered austenitic phase can be arrested to the lower temperature with the application of magnetic field.

  16. 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.

  17. 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.

  18. 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.

  19. The Investigation of Strain-Induced Martensite Reverse Transformation in AISI 304 Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Cios, G.; Tokarski, T.; Żywczak, A.; Dziurka, R.; Stępień, M.; Gondek, Ł.; Marciszko, M.; Pawłowski, B.; Wieczerzak, K.; Bała, P.

    2017-07-01

    This paper presents a comprehensive study on the strain-induced martensitic transformation and reversion transformation of the strain-induced martensite in AISI 304 stainless steel using a number of complementary techniques such as dilatometry, calorimetry, magnetometry, and in-situ X-ray diffraction, coupled with high-resolution microstructural transmission Kikuchi diffraction analysis. Tensile deformation was applied at temperatures between room temperature and 213 K (-60 °C) in order to obtain a different volume fraction of strain-induced martensite (up to 70 pct). The volume fraction of the strain-induced martensite, measured by the magnetometric method, was correlated with the total elongation, hardness, and linear thermal expansion coefficient. The thermal expansion coefficient, as well as the hardness of the strain-induced martensitic phase was evaluated. The in-situ thermal treatment experiments showed unusual changes in the kinetics of the reverse transformation (α' → γ). The X-ray diffraction analysis revealed that the reverse transformation may be stress assisted—strains inherited from the martensitic transformation may increase its kinetics at the lower annealing temperature range. More importantly, the transmission Kikuchi diffraction measurements showed that the reverse transformation of the strain-induced martensite proceeds through a displacive, diffusionless mechanism, maintaining the Kurdjumov-Sachs crystallographic relationship between the martensite and the reverted austenite. This finding is in contradiction to the results reported by other researchers for a similar alloy composition.

  20. The Investigation of Strain-Induced Martensite Reverse Transformation in AISI 304 Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Cios, G.; Tokarski, T.; Żywczak, A.; Dziurka, R.; Stępień, M.; Gondek, Ł.; Marciszko, M.; Pawłowski, B.; Wieczerzak, K.; Bała, P.

    2017-10-01

    This paper presents a comprehensive study on the strain-induced martensitic transformation and reversion transformation of the strain-induced martensite in AISI 304 stainless steel using a number of complementary techniques such as dilatometry, calorimetry, magnetometry, and in-situ X-ray diffraction, coupled with high-resolution microstructural transmission Kikuchi diffraction analysis. Tensile deformation was applied at temperatures between room temperature and 213 K (-60 °C) in order to obtain a different volume fraction of strain-induced martensite (up to 70 pct). The volume fraction of the strain-induced martensite, measured by the magnetometric method, was correlated with the total elongation, hardness, and linear thermal expansion coefficient. The thermal expansion coefficient, as well as the hardness of the strain-induced martensitic phase was evaluated. The in-situ thermal treatment experiments showed unusual changes in the kinetics of the reverse transformation (α' → γ). The X-ray diffraction analysis revealed that the reverse transformation may be stress assisted—strains inherited from the martensitic transformation may increase its kinetics at the lower annealing temperature range. More importantly, the transmission Kikuchi diffraction measurements showed that the reverse transformation of the strain-induced martensite proceeds through a displacive, diffusionless mechanism, maintaining the Kurdjumov-Sachs crystallographic relationship between the martensite and the reverted austenite. This finding is in contradiction to the results reported by other researchers for a similar alloy composition.

  1. Influence of grain growth on the martensitic transformation in. beta. -Cu-Zn-Al memory alloys

    SciTech Connect

    Muntasell, J.; Tamarit, J.L. ); Cesari, E. ); Guilemany, J.M. )

    1989-04-01

    The effect of grain size on martensitic transformation in Cu-Zn-Al shape memory alloys subjected to two thermal treatments in order to retain {beta} phase has been studied by means of calorimetry and acoustic emission. The dependence of transformation temperatures and thermal hysteresis on grain size is interpreted from a thermodynamic model in terms of elastic enthalpy and frictional work contributions; these are non-chemical terms present in thermoelastic martensitic transformation.

  2. Thermally activated martensitic transformations in Mg-PSZ

    SciTech Connect

    Behrens, G.; Heuer, A.H.

    1996-04-01

    The thermally activated, stress-assisted martensitic tetragonal {yields} monoclinic (t {yields} m) and tetragonal {yields} orthorhombic (t {yields} o) transformations in a high-toughness Mg-PSZ were investigated by monitoring the phase assemblage with Raman spectroscopy after a variety of heat treatments and loading conditions. After a short anneal at 1,000 C, which transforms m- and o-ZrO{sub 2} to the t polymorph, isothermal t {yields} m and t {yields} o transformations occur at room temperature during the months following the anneal. The transformation rates in the annealed samples are greatly enhanced under external stress. Alternatively, samples containing regions of significant residual stress, introduced by indentation for example, and then annealed at relatively low temperatures, underwent additional thermally activated transformation in the stressed regions. The thermodynamics and kinetics of this complex transformation ``plasticity,`` and its effect on mechanical properties, are discussed.

  3. Shock-induced martensitic transformations in near-equiatomic NiTi alloys

    SciTech Connect

    Thakur, A.M.; Thadhani, N.N.; Schwarz, R.B.

    1997-07-01

    Shock-impact generated tensile-stress pulses were used to induce B2-to-monoclinic martensitic transformations in two near-equiatomic NiTi alloys having different martensite transformation start (M{sub s}) temperatures. The NiTi-I alloy (M{sub s} {approx} +27 C) impacted at room temperature at 2.0 and 2.7 GPa tensile stress-pulse magnitude, showed acicular martensite morphology. These martensite needles had a substructure containing microtwins, typical of stress-assisted martensite. The NiTi-II alloy (M{sub s} {approx} {minus}45 C) showed no martensite formation when shocked with tensile-stress pulses of 2 GPa. For tensile stresses of 4.1 GPa, the alloy showed spall initiation near the region of maximum tensile-stress duration. In addition, monoclinic martensite needles, with a well-defined dislocation substructure, typical of strain-induced martensite, were seen clustering around the spall region. No stress-assisted martensite was formed in this alloy due to its very low M{sub s} temperature. The present article documents results of the use of a metallurgical technique for generating large-amplitude tensile stress pulses of finite duration for studies of phase transformations involving changes from a high density to a low density state.

  4. 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.

  5. 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.

  6. Acoustic emission and shape memory effect in the martensitic transformation.

    PubMed

    Sreekala, S; Ananthakrishna, G

    2003-04-04

    Acoustic emission signals are known to exhibit a high degree of reproducibility in time and show correlations with the growth and shrinkage of martensite domains when athermal martensites are subjected to repeated thermal cycling in a restricted temperature range. We show that a recently introduced two dimensional model for the martensitic transformation mimics these features. We also show that these features are related to the shape memory effect where near full reversal of morphological features are seen under these thermal cycling conditions.

  7. 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.

  8. Transition temperature of martensitic transformations in hafnia and zirconia

    NASA Astrophysics Data System (ADS)

    Luo, Xuhui; Demkov, A. A.

    2008-03-01

    Transition metal oxides find applications in ceramics, catalysis and semiconductor technology. In particular, hafnium dioxide or hafnia will succeed silica as a gate dielectric in advanced transistors. However, thermodynamic properties of thin hafnia films are not well understood, despite their technological importance. We use density functional theory to investigate the tetragonal to monoclinic phase transition in hafnia and zirconia. We find that unlike the case of the cubic to tetragonal transition, this phase transition is not driven by a soft mode. We use transition state theory to identify the minimum energy path (MEP) employing first principle calculations for hafnia and zirconia, sow that both transformations are martensitic, and obtain the transition barriers. Martensitic transformations include both the internal coordinate transformation and deformation of the cell lattice vectors (``strain and shuffle''), therefore the potential energy surface and MEP are function not only of the internal atomic coordinates but also of the unit cell lattice vectors. Considering the simplest case of uniform strain the transition temperatures we then relate the barrier height to the transition temperature. As a self-consistency check, assuming the equality of thermodynamics potentials of the tetragonal and monoclinic phases during the transition, and using the difference in the internal energy calculated from first principles we estimate the entropy change associated with the transition which is found in good agreement with that calculated form the phonon spectra.

  9. Crystallographic analysis of the martensitic transformation in medium-carbon steel with packet martensite

    NASA Astrophysics Data System (ADS)

    Gundyrev, V. M.; Zel'dovich, V. I.; Schastlivtsev, V. M.

    2016-10-01

    Based on X-ray diffraction studies of the martensite texture in a single martensite packet, exact orientation relationships between the orientations of martensite crystallites and the original austenite single crystal in medium-carbon steel 37KhN3A have been determined to be as follows: (011)α||(1; 0.990; 1.009)γ to an accuracy of ± 0.15°, [ {01overline 1 } ]_α ||{[ {1;1.163; - 2.133} ]_γ } to an accuracy of ±0.15°. It has been shown that the orientation relationships proved to be almost the same as in the Fe-31% Ni alloy with a twinned martensite with close lattice parameters. Therefore, the conclusion has been drawn that the mechanism of the lattice deformation upon the martensitic transformation is the same in both alloys. It is described as follows. The lattice deformation occurs by shear on the (111) plane in the {[ {11overline 2 } ]_{_γ }} direction and is accompanied by an additional change in the dimensions in the mutually perpendicular directions {[ {11overline 2 } ]_{_γ }},[ {111} ],and{[ {1overline 1 0} ]_{_γ }}. The invariantlattice deformation is implemented by slip in martensite on the planes of the (112)α type in the direction {[ {overline 1 overline 1 1} ]_α }. One of the 24 crystallographically equivalent variants of the transformation mechanism has been considered. Apart from this type of deformation, an additional deformation of martensite is possible that does not change its orientation. It has been shown that the orientation of the martensite crystallite calculated via the phenomenological theory of the martensitic transformations (PTMT) differs by approximately 1° from the experimentally determined orientation. This refers to both the lath and twinned martensite. In the twinned martensite, the invariant plane obtained in the PTMT calculations and the habit plane coincide. In lath martensite of 37KhN3A steel, the invariant plane of the martensite crystal obtained in PTMT calculations deviates by 25° from the orientation of the

  10. 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.

  11. 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.

  12. 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.

  13. Martensitic and magnetic transformation in Mn50Ni50-xSnx ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Ma, L.; Wang, S. Q.; Li, Y. Z.; Zhen, C. M.; Hou, D. L.; Wang, W. H.; Chen, J. L.; Wu, G. H.

    2012-10-01

    A martensitic transformation (MT) from a body-centered-cubic austenitic phase to a tetragonal martensitic phase has been found in Mn50Ni50-xSnx (0 ≤ x ≤ 11) alloys. The martensitic transformation temperature can be decreased by about 71.6 K by increasing the Sn concentration by 1 at. %. For 9 ≤ x ≤ 11, Mn50Ni50-xSnx ferromagnetic shape memory alloys are obtained. Due to the large magnetization difference (ΔM = 60 emu/g) and small thermal hysteresis (ΔT = 6 K) in the Mn50Ni40Sn10 alloy, a two-way magnetic-field-induced martensitic transformation is observed with dT/dH = 2 K/T.

  14. Microstructure and martensitic transformation of Ni-Ti-Pr alloys

    NASA Astrophysics Data System (ADS)

    Zhao, Chunwang; Zhao, Shilei; Jin, Yongjun; Guo, Shaoqiang; Hou, Qingyu

    2017-09-01

    The effect of Pr addition on the microstructure and martensitic transformation behavior of Ni50Ti50- x Pr x ( x = 0, 0.1, 0.3, 0.5, 0.7, 0.9) alloys were investigated experimentally. Results show that the microstructures of Ni-Ti-Pr alloys consist of the NiTi matrix and the NiPr precipitate with the Ti solute. The martensitic transformation start temperature decreases gradually with the increase in Pr fraction. The stress around NiPr precipitates is responsible for the decrease in martensitic transformation temperature with the increase in Pr fraction in Ni-Ti-Pr alloys.

  15. Martensitic transformation in ZrO 2-based ceramics at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Li, L.-F.; Hong, C.-S.; Li, Y.-Y.; Zhang, Z.

    The microstructural changes associated with the tetragonal to monoclinic martensitic transformation at cryogenic temperatures in sintered CeO2-ZrO2 ceramics containing 15.5-16.5 mol% CeO2 have been studied by means of TEM observations. X-ray diffraction analysis indicates that the stress-induced martensitic phase increases with decreases in both temperature and CeO2 content. The effects of martensitic morphologies, anti-phase boundaries (APBs) and various dislocation features on mechanical properties are also discussed in the paper.

  16. Martensitic transformation of NiTi nanocrystals embedded in an amorphous matrix

    SciTech Connect

    Waitz, T. . E-mail: waitz@ap.univie.ac.at; Karnthaler, H.P.

    2004-11-08

    The influence of the size on the martensitic phase transformation of spherical NiTi nanocrystals embedded in an amorphous matrix was studied by transmission electron microscopy. The transformation from B2 austenite to B19' martensite is suppressed by a transformation barrier that increases with increasing transformation strains and decreasing diameter of the nanocrystals. Minimizing the strain and interface energy yields a two step transformation from B2 to the R-phase and finally to B19'. The transformation starts at the crystalline/amorphous interface by heterogeneous nucleation. In the case of the R-phase to B19' transformation large strains occur causing after a certain point fine compound twinning during growth that finally leads to a complete transformation right up to the interface. In the isolated nanocrystals a lack of collective transformation effects yields larger transformation barriers and causes larger critical diameters than those observed in the grains of nanocrystalline NiTi.

  17. 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.

  18. Study of the {alpha}{double_prime} phase texture obtained by martensitic {beta}-{alpha}{double_prime} phase transformation induced by tensile test in a sheet of Ti5Al2Sn4Zr4Mo2Cr1Fe

    SciTech Connect

    Pionnier, D.; Humbert, M.; Philippe, M.J.; Combres, Y.

    1998-10-09

    The purpose was to investigate the texture development of the {alpha}{double_prime} orthorhombic martensite phase induced by stress within a commercial sheet of Ti5Al2Sn4Zr4Mo2Cr1Fe. First, the experimental textures of the initial b.c.c. phase, then of the b.c.c. phase and the {alpha}{double_prime} martensite phase after a uniaxial deformation were determined from pole figures. Comparison of the {alpha}{double_prime} experimental texture with a {alpha}{double_prime} texture, simulated with no variant selection from the b.c.c. texture of the initial {beta} matrix clearly shows that a strong variant selection was induced by stress. In order to better understand the formation of this {alpha}{double_prime} orthorhombic texture, texture transformations were simulated according to different variant selection assumptions. As a result, it was shown that the {alpha}{double_prime} orthorhombic texture is formed by the variants favorably oriented with respect to stresses induced during tensile test.

  19. 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.

  20. Martensitic phase transition involving dislocations

    NASA Astrophysics Data System (ADS)

    Le, K. C.; Günther, C.

    2015-06-01

    A model of solid-solid phase transition involving dislocations in crystals is proposed within the nonlinear continuum dislocation theory (CDT). The co-existence of phases having piecewise constant plastic slip in laminates is possible for the two-well free energy density. The jumps of the plastic slip across the phase interfaces determine the surface dislocation densities at those incoherent boundaries. The number of phase interfaces should be determined by comparing the energy of dislocation arrays and the relaxed energy minimized among uniform plastic slips.

  1. Large-strain cyclic response and martensitic transformation of austenitic stainless steel at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Hamasaki, H.; Nakano, T.; Ishimaru, E.; Yoshida, F.

    2016-08-01

    Cyclic tension-compression tests were carried out for austenitic stainless steel (SUS304) at elevated temperatures. The significant Bauschinger effect was found in the obtained stress-strain curve. In addition, stagnation of deformation induced martensitic transformation was observed just after stress reversal until the equivalent stress reached the maximum value in the course of experiment. The constitutive model for SUS304 at room temperature was developed, in which homogenized stress of SUS304 was expressed by the weighed summation of stresses of austenite and martensite phases. The calculated stress-strain curves and predicted martensite volume fraction were well correlated with those experimental results.

  2. An energy criterion for the stress-induced martensitic transformation in a ductile system

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, A.; Weng, G. J.

    1994-11-01

    An energy criterion is developed to calculate the stress-strain behavior of a ductile system involving martensitic transformation under the application of stress. The martensitic inclusions are taken to develop from the ductile austenitic matrix due to the reduction in the Gibbs free energy, which consists of the chemical free energy and the surface energy of the parent and product phases, and the mechanical potential energy of the nonlinear system. The inclusions thus formed are assumed to be thin spheroidal platelets, randomly oriented in the matrix, each possessing a normal and shear component of transformation strain. A micromechanical theory is established to determine the nonlinear potential energy and the change in Gibbs free energy of the two-phase system at a given stage of transformation. It is found that the stressstrain behavior of the metastable system is the outcome of two competing effects, one from the ductility due to the plastic deformation of the ductile matrix and the phase transformation strain of the martensite inclusions, and the other from the stiffness due to the purely elastic response of the transformed martensites. While the ductility prevails in the early stage of deformation the stiffening effect later becomes more dominant with increasing amount of transformation. The resulting stress-strain curve then exhibits the familiar sigmoidal shape, characteristically different from that of an ordinary ductile phase. The theory does not assume any a priori law for the evolving volume fraction of the martensite ; it is calculated incrementally based on the change of Gibbs free energy between the current and the transformed state. Nor does the theory assume any a priori flow rule for the transformation strains, which are calculated strictly from the lattice parameters of the parent and transformed phase. Comparison with some available experimental data for the stress-strain behavior of a TRIP steel and the corresponding evolution of the

  3. Martensitic transformations and morphology studies of NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Murari, M. S.; Pattabi, Manjunatha

    2017-05-01

    The forward transformation temperatures Martensite Start (Ms) and Martensite Finish (Mf) during cooling, reverse transformation temperatures Austenite Start (As) and Austenite Finish (Af) during heating are very sensitive to the thermal and mechanical history of the Shape Memory Alloy (SMA). Heat treatments, cold and hot roll, thermal and mechanical cycling have great influence on the transformation temperatures. Different characterizing techniques like Differential Scanning Calorimeter (DSC), X-Ray Diffractometer (XRD), Electrical Resistivity (ER) and Thermo Mechanical Analyzer (TMA) were employed to study the phase transformation temperatures of NiTi alloy. The microstructure of the samples was studied with Atomic Force Microscope (AFM), Optical Microscope (OM) and Field Emission Scanning Electron Microscope (FESEM).

  4. Martensitic transformation of NiTi studied at the nanometer scale by local mechanical spectroscopy

    SciTech Connect

    Oulevey, F.; Gremaud, G.; Mari, D.; Kulik, A.J.; Burnham, N.A.; Benoit, W.

    1999-12-17

    Near-stoichiometric NiTi alloys exhibit a martensitic phase transformation between a low-temperature monoclinic phase, called martensite, and a high temperature cubic phase with B2 structure, called austenite. This transformation is responsible for the shape memory and pseudo-elastic effects in deformed NiTi alloys. Optical microscopy observation suggests that the transformation occurs very suddenly inside an austenite grain. This has led to the concept of military transformation. The width of the globally measured transformation would then be a sum of different narrow contributions coming from different places inside the sample. this image is, however, not universally accepted. A measurement inside one single grain of a polycrystal would be a way to address these questions. Both the special scale of the R phase distribution and the military character of the transformation will have an effect on the result of such a measurement. The martensitic transformation of such alloys has already been observed on bulk samples by mechanical spectroscopy, i.e., measurement of the inelastic part of the deformation induced by a cyclic stress. Such measurements, also called Internal Friction measurements, give access to the mechanical energy dissipation during the phase transition. However, they give an average behavior of all parts of the sample. This paper reports the first local (i.e., at a submicron scale) mechanical spectroscopy measurement of the martensitic transformation in thermally cycled NiTi alloys.

  5. Mesoscale martensitic transformation in single crystals of topological defects.

    PubMed

    Li, Xiao; Martínez-González, José A; Hernández-Ortiz, Juan P; Ramírez-Hernández, Abelardo; Zhou, Ye; Sadati, Monirosadat; Zhang, Rui; Nealey, Paul F; de Pablo, Juan J

    2017-09-19

    Liquid-crystal blue phases (BPs) are highly ordered at two levels. Molecules exhibit orientational order at nanometer length scales, while chirality leads to ordered arrays of double-twisted cylinders over micrometer scales. Past studies of polycrystalline BPs were challenged by the existence of grain boundaries between randomly oriented crystalline nanodomains. Here, the nucleation of BPs is controlled with precision by relying on chemically nanopatterned surfaces, leading to macroscopic single-crystal BP specimens where the dynamics of mesocrystal formation can be directly observed. Theory and experiments show that transitions between two BPs having a different network structure proceed through local reorganization of the crystalline array, without diffusion of the double-twisted cylinders. In solid crystals, martensitic transformations between crystal structures involve the concerted motion of a few atoms, without diffusion. The transformation between BPs, where crystal features arise in the submicron regime, is found to be martensitic in nature when one considers the collective behavior of the double-twist cylinders. Single-crystal BPs are shown to offer fertile grounds for the study of directed crystal nucleation and the controlled growth of soft matter.

  6. Small-angle Neutron Scattering Study of Magnetic Ordering and Inhomogeneity Across the Martensitic Phase Transformation in Ni50-xCoxMn40Sn10 Alloys

    DTIC Science & Technology

    2012-04-27

    of ∼16 Å. Literal interpretation of these data thus suggests a dense assembly of approximately 20 Å F nanoparticles in a non-F matrix . It must be...λ2 = 1, where λ1, λ2, andλ3 are the ordered eigenvalues of the transformation stretch matrix (U) describing the austenite→martensite transforma- tion...formation of F clusters in a P or AF matrix , leading to superparmagnetic phenomena. Although such a picture is capable of explaining the basic behavior

  7. Nanoscale martensitic phase transition at interfaces in shape memory materials

    NASA Astrophysics Data System (ADS)

    Dar, Rebecca D.; Chen, Ying

    2017-01-01

    In polycrystalline shape memory materials, mechanical interactions between martensitic transformation and grain boundaries at small scales play a critical role. Using a cobalt-based shape memory alloy, instrumented nanoindentation that probes nanoscale behavior reveals that grain boundary regions are resistant to transformation and have an adverse effect on shape memory possibly because an increase in strain energy outweighs reduction in interface energy. When grain boundaries are replaced by a thin, intergranular layer of a ductile and more malleable phase, grain boundary constraints are greatly alleviated, and transformation nearby can be well accommodated. Statistical analysis of results from a large number of nanoindents shows a decrease in shape recovery near grain boundaries and an increase in shape recovery near the new grain boundary phase, compared to grain interior. This is corroborated by analysis of nanoscale hardness and energy dissipation. Nanoscale martensitic transformation near interfaces depends largely on how the material across the interface accommodates transformation displacement. Engineering interfaces and enhancing local compatibility could drastically alter the energetics for phase transition at interfaces favorable for shape memory.

  8. Two-phase ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Golovanenko, S. A.; Fonshtein, N. M.

    1984-11-01

    The results of laboratory and production experiments showed that the main condition for providing the necessary combination of properties of two-phase ferritic-martensitic steels (high tensile strength, low yield strength, high plasticity and work hardenability) is obtaining the specified quantity of the hardening phase (martensite) in the structure (20-28% M to obtain σt ≥ 550 MPa or 10-18% M for σt ≥ 450 MPa). The specified ratio of the structural constituents under conditions of mass production of two-phase ferritic-martensitic steels may be guaranteed only with the use of steels containing carbon and alloy elements within the necessary limits and also with strict observance of the heat-treatment cycle. Without the use of metallographic measurements as the criteria for obtaining the optimum structural condition in addition to the required values of strength and plasticity it is necessary to use the σ0.2/σt ratio, which must not be greater than 0.5-0.6 with the absence of yield points on the tensile curve (without special temper rolling). As the result of the combination of work done in the Central Scientific-Research Institute of Ferrous Metallurgy together with plants of the Ministries of Ferrous Metallurgy and of the Automobile Industry at present the production is being introduced and experimental production lots of heat-treated two-phase steels of the following types with guaranteed mechanical properties are being supplied: At the Novolipetsk Metallurgical Combine cold-rolled 0.7-2.0-mm sheet of 06KhG(S)Yu and 06G2SYu steels with σ0.2 = 260-320 MPa, σt ≥ 550 MPa, δ4 ≥ 30%, and σ0.2/σt ≤ 0.5-0.6. At the Cherepovets Metallurgical Combine hot-rolled 2-6-mm sheet of 09G2(S) steel with σ0.2 = 260-320 MPa, σt ≥ 550 MPa, δ4 ≥ 25%, and σ0.2/σt ≤ 0.5-0.6. At the Beloretsk Metallurgical Combine (billets melted and rolled at the Cherepovets Metallurgical Combine) heat-treated cold-drawn wire up to 10.5 mm in diameter of 06KhGR steel with

  9. Martensitic transformation during coalescence of Fe-Ni nanoparticles. Atomistic simulation

    NASA Astrophysics Data System (ADS)

    Karkina, L. E.; Karkin, I. N.; Kuznetsov, A. R.

    2017-09-01

    Martensitic transformation during coalescence of two Fe-20 at.% Ni nanoparticles of size d ∼3-7 nm has been studied using molecular dynamics. Orientation relationship analysis showed that Kurdyumov-Sachs orientation relationship was observed between the initial γ-phase and the final α phase (at T = 0 K) for all of the studied cases of misorientation. A significant change in the type of contact boundaries between the two nanoparticles was obtained after the completion of the martensitic transformation, which was caused by a change in the indices of the misorientation axis of the particles and in the number of symmetry elements for it.

  10. Crystallographic Features of The Martensitic Transformation in PbTiO3 Compound

    NASA Astrophysics Data System (ADS)

    Navruz, N.

    2010-01-01

    Martensitic transformations are displacive in nature and occur in the solid state in a wide variety of metallic and non metallic materials. Although the occurrence of martensitic transformations in inorganic and ceramic compounds has been well recognized for many years, it is only in the last decade that they have achieved prominence. An important group of materials in which martensitic transformations play a significant role in determining microstructure and thus properties are the perovskite-type oxides such as PbTiO3. In this study, emphasis is given to the crystallography of the paraelectric cubic to ferroelectric tetragonal phase transformation in PbTiO3 compound. A detailed crystallographic analysis is performed in Lead Titanate (PbTiO3) and the crystallographic parameters are calculated. The predictions of the crystallographic analysis are compared with the experimental results available.

  11. 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%.

  12. 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.

  13. Investigation on microstructure and martensitic transformation of neodymium-added NiTi shape memory alloys

    NASA Astrophysics Data System (ADS)

    Maashaa, Dovchinvanchig; Dorj, Ulzii-Orshikh; Lee, Malrey; Lee, Min Hi; Zhao, Chunwang; Dashjav, Munguntsetseg; Woo, Seon-Mi

    2016-10-01

    The effect of rare earth element neodymium (Nd) addition on the microstructure and martensitic transformation behavior of Ni50Ti50-xNdx (x = 0, 0.1, 0.3, 0.5 and 0.7 at.%) shape memory alloy was investigated by scanning electronic microscope, X-ray diffraction and differential scanning calorimetry. The results show that the microstructure of Ni-Ti-Nd ternary alloy consists of NiNd phase, NiTi2 and the NiTi matrix. A one-step martensitic transformation is observed in the alloys. The martensitic transformation temperature Ms increases sharply increasing 0.1-0.7 at.% Nd content is added.

  14. Martensitic fcc-to-hcp transformations in solid xenon under pressure: a first-principles study.

    PubMed

    Kim, Eunja; Nicol, Malcolm; Cynn, Hyunchae; Yoo, Choong-Shik

    2006-01-27

    First-principles calculations reveal that the fcc-to-hcp pressure-induced transformation in solid xenon proceeds through two mechanisms between 5 and 70 GPa. The dynamics of the phase transition involves a sluggish stacking-disorder growth at lower pressures (path I) that changes to a path involving an orthorhombic distortion at higher pressures (path II). The switchover is governed by a delicate interplay of energetics (enthalpy of the system for the structural stability) and kinetics (energy barrier for the transition). The two types of martensitic transformations involved in this pressure-induced structural transformation are a twinned martensitic transition at lower pressures and a slipped martensitic transition at higher pressures.

  15. Magnetic properties and martensitic transformation in quaternary Heusler alloy of NiMnFeGa

    NASA Astrophysics Data System (ADS)

    Liu, Z. H.; Zhang, M.; Wang, W. Q.; Wang, W. H.; Chen, J. L.; Wu, G. H.; Meng, F. B.; Liu, H. Y.; Liu, B. D.; Qu, J. P.

    2002-11-01

    Quaternary Heusler alloy Ni2)(Mn,FeGa has been studied systematically for the structure, martensitic transformation, and magnetic properties in two systems of Ni50.5Mn25-xFexGa24.5 and Ni50.4Mn28-xFexGa21.6. Substituting Fe for Mn up to about 70%, the pure L21 phase and the thermoelastic martensitic transformation still can be observed in these quaternary systems. Iron doping dropped the martensitic transformation temperature from 220 to 140 K, increased the Curie temperature from 351 to 429 K, and broadened the thermal hysteresis from about 7 to 18 K. Magnetic analysis revealed that Fe atoms contribute to the net magnetization of the material with a moment lower than that of Mn. The temperature dependence of magnetic-field-induced strains has been improved by this doping method.

  16. In-situ investigations of the martensitic transformation in TiNi by synchrotron radiation

    SciTech Connect

    Kulkov, S.N.; Mironov, Yu.P.

    1999-01-01

    By means of synchrotron X-ray diffraction method the stress-induced martensite transformation in TiNi (with two different phase compositions) at room temperature was investigated in situ. It has been shown that in the alloys with temperature-induced martensite in the initial state a nonperiodic fluctuation of intensity of the X-ray reflexes appeared due to anomalous transformation B2 + B19{prime}{sub T} {r_arrow} B2 {r_arrow} B19{prime}{sub Si}.

  17. Possible martensitic transformation in Heusler alloy Mn2PdSn from first principles

    NASA Astrophysics Data System (ADS)

    Feng, L.; Feng, X.; Liu, E. K.; Wang, W. H.; Wu, G. H.; Hu, J. F.; Zhang, W. X.

    2016-12-01

    The tetragonal distortion, electronic structure and magnetic property of Mn2PdSn have been systematically investigated by first-principles calculations. The results indicate that the total energy of tetragonal martensitic phase is lower than cubic austenitic phase for Mn2PdSn. The corresponding c/a ratio and energy difference are 1.23 and 41.62 meV/f.u., respectively. This suggests that there is a great possibility for martensitic transformation to occur in Mn2PdSn with temperature decreasing. The electronic structure shows that there are sharp DOS peaks originating from p-d hybridization in the vicinity of Fermi level in the cubic phase. And these peaks disappear or become more flat in the martensitic phase.

  18. Martensitic transformation and magnetic properties of Heusler alloy Ni-Fe-Ga ribbon

    NASA Astrophysics Data System (ADS)

    Liu, Z. H.; Liu, H.; Zhang, X. X.; Zhang, M.; Dai, X. F.; Hu, H. N.; Chen, J. L.; Wu, G. H.

    2004-08-01

    The martensitic transformation and magnetic properties of ferromagnetic shape memory alloy Ni 50+ xFe 25- xGa 25 ( x=-1, 0, 1, 2, 3, 4) ribbons have been systematically studied. It has been found that with the increase of Ni concentration, the martensitic transformation temperature increases, but the Curie temperature decreases. Both the two-step thermally induced structural transformation and the one-step transition have been observed in NiFeGa alloys with different compositions. It is found that the two-step transition became the one-step transition after the ribbon being heat treated at 873 K or higher. X-ray diffraction patterns show that only L2→B2 transition occurs in the samples treated at 873 K, while the γ phase will form in the samples treated at higher temperature. Transmission electron microscopy (TEM) studies show that the alloys with martensitic transformation temperature above the room temperature are non-modulated martensite with the large domain size, being different from the stoichiometric Ni 2FeGa alloy that is a modulated martensite with small domain size. The influences of Fe substitution for Ni in Ni 2FeGa on the saturation magnetization and exchange interaction are also discussed.

  19. 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.

  20. 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.

  1. Influence of Plastic Deformation on Martensitic Transformation During Hot Stamping of Complex Structure Auto Parts

    NASA Astrophysics Data System (ADS)

    Shen, Yuhan; Song, Yanli; Hua, Lin; Lu, Jue

    2017-04-01

    The ultra-high strength steel auto parts manufactured by hot stamping are widely applied for weight reduction and safety improvement. During the hot stamping process, hot forming and quenching are performed in one step wherein plastic deformation and phase transformation simultaneously take place and affect each other. Thereinto, the influence of deformation on martensitic transformation is of great importance. In the present paper, the influence of plastic deformation on martensitic transformation during hot stamping of complex structure auto parts was investigated. For this purpose, a B-pillar reinforced panel in B1500HS steel was manufactured by hot stamping, and the process was simulated by finite element software based on a thermo-mechanical-metallurgical coupled model. Considering various deformation degrees, the microstructures and mechanical properties at four typical locations of the hot stamped B-pillar reinforced panel were detected. The results show that the martensitic content and the microhardness increase with the increase in the deformation amount. There are two reasons causing this phenomenon: (1) the increase in mechanical driving force and (2) the increased probability of the martensitic nucleation at crystal defects. The x-ray diffraction analysis indicates the carbon enrichment in retained austenite which results from the carbon diffusion during the low-carbon martensite formation. Furthermore, the carbon content decreases with the increase in the deformation amount, because the deformation of austenite suppresses the carbon diffusion.

  2. Influence of Plastic Deformation on Martensitic Transformation During Hot Stamping of Complex Structure Auto Parts

    NASA Astrophysics Data System (ADS)

    Shen, Yuhan; Song, Yanli; Hua, Lin; Lu, Jue

    2017-02-01

    The ultra-high strength steel auto parts manufactured by hot stamping are widely applied for weight reduction and safety improvement. During the hot stamping process, hot forming and quenching are performed in one step wherein plastic deformation and phase transformation simultaneously take place and affect each other. Thereinto, the influence of deformation on martensitic transformation is of great importance. In the present paper, the influence of plastic deformation on martensitic transformation during hot stamping of complex structure auto parts was investigated. For this purpose, a B-pillar reinforced panel in B1500HS steel was manufactured by hot stamping, and the process was simulated by finite element software based on a thermo-mechanical-metallurgical coupled model. Considering various deformation degrees, the microstructures and mechanical properties at four typical locations of the hot stamped B-pillar reinforced panel were detected. The results show that the martensitic content and the microhardness increase with the increase in the deformation amount. There are two reasons causing this phenomenon: (1) the increase in mechanical driving force and (2) the increased probability of the martensitic nucleation at crystal defects. The x-ray diffraction analysis indicates the carbon enrichment in retained austenite which results from the carbon diffusion during the low-carbon martensite formation. Furthermore, the carbon content decreases with the increase in the deformation amount, because the deformation of austenite suppresses the carbon diffusion.

  3. 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.

  4. Local strain evolution due to athermal γ→ε martensitic transformation in biomedical CoCrMo alloys.

    PubMed

    Yamanaka, Kenta; Mori, Manami; Koizumi, Yuichiro; Chiba, Akihiko

    2014-04-01

    Locally developed strains caused by athermal γ face-centered cubic (fcc)→ε hexagonal close-packed (hcp) martensitic transformation were investigated for the γ matrix of Ni-free Co-29Cr-6Mo (wt%) alloys prepared with or without added nitrogen. Electron-backscatter-diffraction-(EBSD)-based strain analysis revealed that in addition to ε-martensite interiors, the N-free alloy that had a duplex microstructure consisting of the γ matrix and athermal ε-martensite plates showed larger magnitudes of both elastic and plastic strains in the γ phase matrix than the N-doped counterpart that did not have a ε-martensite phase. Transmission electron microscopy (TEM) results indicated that the ε-martensite microplates were aggregates of thin ε-layers, which were formed by three different {111}γ〈112¯〉γ Shockley partial dislocations in accordance with a previously proposed mechanism (Putaux and Chevalier, 1996) that canceled the shear strains of the individual variants. The plastic strains are believed to have originated from the martensitic transformation itself, and the activity of dislocations is believed to be the origin of the transformation. We have revealed that the elastic strains in the γ matrix originate from interactions among the ε-martensite phase, extended dislocations, and/or thin ε-layers. The dislocations highly dissociated into stacking faults, making stress relaxation at intersections difficult and further introducing local strain evolution. Copyright © 2013 Elsevier Ltd. All rights reserved.

  5. 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

  6. Magnetic field and atomic order effect on the martensitic transformation of a metamagnetic alloy.

    PubMed

    Barandiaran, J M; Chernenko, V A; Cesari, E; Salas, D; Gutierrez, J; Lazpita, P

    2013-12-04

    The martensitic transformation (MT) of metamagnetic shape memory alloys is very sensitive to the applied magnetic field and atomic order. We analyze the alloy Ni50Mn34.5In15.5 in magnetic fields up to 13 T. The alloy has been prepared both in an ordered state by slow cooling, and in a disordered state by rapid quenching. In both cases the dependence of the martensitic transition temperature on the field is highly nonlinear. Such departure from linearity is due to a decrease of the entropy change at the transition, ΔS, with the applied field. This can be explained by the ordering effect of the magnetic field on the frustrated magnetic structure of the alloy in the martensitic phase. Compliance with a recent model, relying on the strong magnetoelastic interactions in these compounds, is very satisfactory.

  7. Suppression of martensitic transformation in Fe50Mn23Ga27 by local symmetry breaking

    NASA Astrophysics Data System (ADS)

    Ma, Tianyu; Liu, Xiaolian; Yan, Mi; Wu, Chen; Ren, Shuai; Li, Huiying; Fang, Minxia; Qiu, Zhiyong; Ren, Xiaobing

    2015-05-01

    Defects-induced local symmetry breaking has led to unusual properties in nonferromagnetic ferroelastic materials upon suppressing their martensitic transformation. Thus, it is of interest to discover additional properties by local symmetry breaking in one important class of the ferroelastic materials, i.e., the ferromagnetic shape memory alloys. In this letter, it is found that local symmetry breaking including both tetragonal nano-inclusions and anti-phase boundaries (APBs), suppresses martensitic transformation of a body-centered-cubic Fe50Mn23Ga27 alloy, however, does not affect the magnetic ordering. Large electrical resistivity is retained to the low temperature ferromagnetic state, behaving like a half-metal ferromagnet. Lower ordering degree at APBs and local stress fields generated by the lattice expansion of tetragonal nanoparticles hinder the formation of long-range-ordered martensites. The half-metal-like conducting behavior upon suppressing martensitic transformation extends the regime of ferromagnetic shape memory materials and may lead to potential applications in spintronic devices.

  8. Power-law statistics for avalanches in a martensitic transformation.

    PubMed

    Ahluwalia, R; Ananthakrishna, G

    2001-04-30

    We devise a two-dimensional model that mimics the recently observed power-law distributions for the amplitudes and durations of the acoustic emission signals observed during martensitic transformation [Vives et al., Phys. Rev. Lett. 72, 1694 (1994)]. We include a threshold mechanism, long-range interaction between the transformed domains, inertial effects, and dissipation arising due to the motion of the interface. The model exhibits thermal hysteresis and, more importantly, it shows that the energy is released in the form of avalanches with power-law distributions for their amplitudes and durations. Computer simulations also reveal morphological features similar to those observed in real systems.

  9. In- Situ Synchrotron Diffraction Studies on Transformation Strain Development in a High-Strength Quenched and Tempered Structural Steel—Part II. Martensitic Transformation

    NASA Astrophysics Data System (ADS)

    Dutta, R. K.; Huizenga, R. M.; Petrov, R. H.; Amirthalingam, M.; King, A.; Gao, H.; Hermans, M. J. M.; Richardson, I. M.

    2014-01-01

    In-situ synchrotron diffraction studies on the kinetics of phase transformation and transformation strain development during bainitic transformation were presented in part I of the current article. In the current article, in-situ phase transformation behavior of a high-strength (830 MPa yield stress) quenched and tempered S690QL1 [Fe-0.16C-0.2Si-0.87Mn-0.33Cr-0.21Mo (wt. pct)] structural steel, during continuous cooling and under different mechanical loading conditions to promote martensitic transformation, has been studied. Time-temperature-load resolved 2D synchrotron diffraction patterns were recorded and used to calculate the phase fractions and lattice parameters of the phases during heating and cooling cycles under different loading conditions. In addition to the thermal expansion behavior, the effects of the applied stress on the elastic strains during the martensitic transformation were calculated. The results show that small tensile stresses applied at the transformation temperature do not change the kinetics of the phase transformation. The start temperature for the martensitic transformation increases with the increasing applied tensile stress. The elastic strains are not affected significantly with the increasing tensile stress. The variant selection during martensitic transformation under small applied loads (in the elastic region) is weak.

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

    NASA Astrophysics Data System (ADS)

    Sugimoto, Koh-Ichi; Hojo, Tomohiko

    2016-11-01

    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.

  11. 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.

  12. Strain-induced martensite to austenite reverse transformation in an ultrafine-grained Fe-Ni-Mn martensitic steel

    NASA Astrophysics Data System (ADS)

    Ghasemi-Nanesa, H.; Nili-Ahmadabadi, M.; Koohdar, H. R.; Habibi-Parsa, M.; Nedjad, S. Hossein; Alidokht, S. A.; Langdon, Terence G.

    2014-05-01

    Research was conducted to evaluate the effect of heavy cold rolling on microstructural evolution in an Fe-10Ni-7Mn (wt.%) martensitic steel. The chemical driving force for the strain-induced martensite to austenite reverse transformation was calculated using thermodynamic principles and a model was developed for estimating the effect of applied stress on the driving force of the martensite to austenite reverse transformation through heavy cold rolling. These calculations show that, in order to make a reverse transformation feasible, the applied stress on the material should supply the total driving force, both chemical and non-chemical, for the transformation. It is demonstrated that after 60% cold rolling the required driving force for the reverse transformation may be provided. Experimental results, including cold rolling and transmission electron microscopy images, are utilized to verify the thermodynamic calculations.

  13. Martensitic transformation of austenitic stainless steel orthodontic wires during intraoral exposure.

    PubMed

    Izquierdo, Paula P; de Biasi, Ronaldo S; Elias, Carlos N; Nojima, Lincoln I

    2010-12-01

    Our purpose was to study the mechanical properties and phase transformations of orthodontic wires submitted to in-vivo exposure in the mouth for different periods of time. Stainless steel wires were tied to fixed orthodontic appliances of 30 patients from the orthodontics clinic of Universidade Federal do Rio de Janeiro School of Dentistry in Brazil. According to the duration of the clinical treatment, the patients were divided into 3 groups. After in-vivo exposure, the samples were studied by mechanical testing (torsion) and ferromagnetic resonance. Statistical analyses were carried out to evaluate the correlation between time of exposure, mechanical properties, and austenite-to-martensite transformation among the groups. The results were compared with as-received control samples. The torque values increased as time in the mouth increased. The increase in torque resistance showed high correlations with time of exposure (P = 0.005) and austenite-martensite phase transformation. The resistance of stainless steel orthodontic wires increases as the time in the mouth increases; this effect is attributed to the austenite-to-martensite transformation. Copyright © 2010 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

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

    NASA Technical Reports Server (NTRS)

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

    2016-01-01

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

  15. Ab initio simulations of phase stability and martensitic transitions in NiTi

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  16. Stress Induce Martensitic Transformations in Hydrogen Embrittlement of Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Rozenak, Paul

    2013-04-01

    In austenitic type stainless steels, hydrogen concentration gradients formed during electrochemical charging and followed by hydrogen loss during aging, at room temperature, surface stresses, and martensitic phases α'-BCC and ɛ-HCP developed. The basic relationship between the X-ray diffraction peak broadening and the hydrogen gradients, formed during charging and aging at room temperature in such austenitic stainless steels, were analyzed. The results demonstrate that the impact of stresses must be considered in the discussion of phase transformations due to hydrogenation. Austenitic stainless steels based on iron-nickel-chromium, have relatively low stacking fault energy γSFE and undergo: quenching to low temperatures, plastic deformation, sensitization heat treatments, high pressure (≥3-5 × 109 Pa) by hydrogen or other gases, electrochemical charging (when the sample is cathode) and when is irradiation by various ions the samples in vacuum. All the above mentioned induce formation of ɛ and α' in the face-centered cubic (FCC) austenite γ matrix. The highest stresses cause formation of mainly α' phase and ɛ-martensite, and both are involved in plastic deformation processes and promoting crack propagation at the surface. In 310 steel, the crack propagation is based on deformation processes following ɛ-martensitic formation only. Formations of ɛ- and α'-martensites were noted along the fracture surfaces and ahead of the crack tip. The cracks propagated through the ɛ-martensitic plates, which formed along the active slip planes, while α' phase was always found in the high-stress region on the ends of the ligaments from both sides of the crack surfaces undergoing propagation.

  17. Stress Induce Martensitic Transformations in Hydrogen Embrittlement of Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Rozenak, Paul

    2014-01-01

    In austenitic type stainless steels, hydrogen concentration gradients formed during electrochemical charging and followed by hydrogen loss during aging, at room temperature, surface stresses, and martensitic phases α'-BCC and ɛ-HCP developed. The basic relationship between the X-ray diffraction peak broadening and the hydrogen gradients, formed during charging and aging at room temperature in such austenitic stainless steels, were analyzed. The results demonstrate that the impact of stresses must be considered in the discussion of phase transformations due to hydrogenation. Austenitic stainless steels based on iron-nickel-chromium, have relatively low stacking fault energy γSFE and undergo: quenching to low temperatures, plastic deformation, sensitization heat treatments, high pressure (≥3-5 × 109 Pa) by hydrogen or other gases, electrochemical charging (when the sample is cathode) and when is irradiation by various ions the samples in vacuum. All the above mentioned induce formation of ɛ and α' in the face-centered cubic (FCC) austenite γ matrix. The highest stresses cause formation of mainly α' phase and ɛ-martensite, and both are involved in plastic deformation processes and promoting crack propagation at the surface. In 310 steel, the crack propagation is based on deformation processes following ɛ-martensitic formation only. Formations of ɛ- and α'-martensites were noted along the fracture surfaces and ahead of the crack tip. The cracks propagated through the ɛ-martensitic plates, which formed along the active slip planes, while α' phase was always found in the high-stress region on the ends of the ligaments from both sides of the crack surfaces undergoing propagation.

  18. 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.

  19. 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.

  20. 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.

  1. Martensitic transformations and the evolution of the defect microstructure of metastable austenitic steel during severe plastic deformation by high-pressure torsion

    NASA Astrophysics Data System (ADS)

    Litovchenko, I. Yu.; Tyumentsev, A. N.; Akkuzin, S. A.; Naiden, E. P.; Korznikov, A. V.

    2016-08-01

    It has been shown that, in metastable austenitic Fe-18Cr-10Ni-Ti steel, under conditions of torsion under pressure, local reversible (forward plus reverse) (γ → α' → γ) martensitic transformations can occur, which are one of the mechanisms of the formation of nanostructured states. An increase in the rotation rate, which leads to an increase in the deformation temperature, stimulates the reverse (α' → γ) transformation. The evolution of the structural and phase states is represented as the following sequence: (1) mechanical twinning; (2) nucleation of martensitic plates in the microtwinned structure of the austenite with the formation of two-phase (γ + α') structures, packet α' martensite, and structural states with a high curvature of the crystal lattice; (3) reverse (α' → γ)-transformations; and (4) the fragmentation of nanosized crystals via the formation of a nanotwinned structure in the austenite and of a nanoscale banded structure of the ɛ martensite in the α' martensite.

  2. 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.

  3. Ab initio Prediction of Martensitic and Intermartensitic Phase Boundaries in Ni-Mn-Ga.

    PubMed

    Dutta, B; Çakır, A; Giacobbe, C; Al-Zubi, A; Hickel, T; Acet, M; Neugebauer, J

    2016-01-15

    Despite the importance of martensitic transformations of Ni-Mn-Ga Heusler alloys for their magnetocaloric and shape-memory properties, the martensitic part of their phase diagrams is not well determined. Using an ab initio approach that includes the interplay of lattice and vibrational degrees of freedom we identify an intermartensitic transformation between a modulated and a nonmodulated phase as a function of excess Ni and Mn content. Based on an evaluation of the theoretical findings and experimental x-ray diffraction data for Mn-rich alloys, we are able to predict the phase diagram for Ni-rich alloys. In contrast to other mechanisms discussed for various material systems in the literature, we herewith show that the intermartensitic transformation can be understood solely using thermodynamic concepts.

  4. Electric field control of Martensitic Phase Transitions in Thin Films of Ni-Mn-In

    NASA Astrophysics Data System (ADS)

    Al-Aqtash, Nabil; Sokolov, Andrei; Sabirianov, Renat

    2015-03-01

    We propose the electric field control of martensite transformation of Ni-Mn-In thin films deposited on ferroelectric (FE) substrate. DFT- based calculations indicate that the off-stochiometric Ni2Mn1.5In0.5 alloy shows that the ferromagnetic (FM) cubic phase undergoes transformation to tetragonal ferromagnetic (FiM) martensite phase at low temperature. The presence of FE substrate changes the relative stability of FM austenite and FiM martensite phases. (SrZrO3/PbZrO3) superlattices were considered as FE substrates with polarization perpendicular to the interface. The relative stability of two phases of the thin films can be tuned by polarization reversal in FE due to the change in sign of induced charges at the interface. The energetically favorable structures of the FE/Ni2Mn1.5In0.5 systems depend on interface structure between FE and Ni2Mn1.5In0.5 layers, e.g Ni-(Pb-O) interface. The energy difference (per NiMnIn f.u) between FM austenite and FiM martensite states of the film on FE substrate is ΔE = 0.22 eV with polarization away from interface, upon polarization reversal ΔE = 0.75 eV, compared to (ΔE = 0.24 eV) in the bulk. Additionally Pb atoms in PbO3 planes shifted in opposite direction with respect to oxygen planes and alter the chemical bonding of Pb with Ni atoms of the thin films. These changes possibly cause the shift of the martensite transition temperature. These results clearly indicate the possibility of control of martensitic transition in Ni-Mn-In thin films by FE substrate.

  5. First-principles study of martensitic transformation and magnetic properties of carbon doped Ni-Mn-Sn Heusler alloys

    NASA Astrophysics Data System (ADS)

    Xiao, Haibo; Yang, Changping; Wang, Ruilong; Xu, Linfang; Liu, Guozhen; Marchenkov, V. V.

    2016-10-01

    The magnetic properties, structural stabilities and martensitic transformation of carbon doped Ni-Mn-Sn Heusler alloys are investigated by means of ab initio calculations in framework of the density functional theory. The results of calculations have shown that the martensitic transformation can be realized in all series of carbon doped Ni2Mn1.5Sn0.5 - xCx alloys with tetragonal ratio of 1.34, 1.40,1.42 and 1.44, respectively for x = 0.125 , 0.25 , 0.375 and 0.5. The DOS peak at the Fermi level almost disappearing in the tetragonal phase near the Fermi level is the evidence of triggering martensitic transformation which is due to the structural Jahn-Teller effect. We have also found that the difference between the austenitic and martensitic phases increases with increasing carbon content, which implies an enhancement of the martensitic phase transition temperature (TM). Besides, the electron density difference shows the enhancement of bonding between Mn and carbon atoms with the distortion taken place.

  6. Stress-induced martensitic transformation in Ni-Ti(-Cu) interlayers controlling stress distribution in functional coatings during sliding

    NASA Astrophysics Data System (ADS)

    Callisti, M.; Polcar, T.

    2015-01-01

    The stress-induced martensitic transformation occurring in sputter-deposited Ni48.1Ti51.9 and Ni43.4Ti49.6Cu7 interlayers, integrated in a W-S-C/Ni-Ti(-Cu) bilayer design, was investigated by transmission electron microscopy, after these bilayers were subjected to different sliding conditions. Martensitic bands across the interlayers were formed depending on the sliding direction with their shape and distribution a function primarily of both applied normal load and grain size. The Ni48.1Ti51.9 interlayer (lateral grain size of ∼3 μm) showed well oriented and ordered martensitic bands extended through the interlayer thickness under low load (5 N). At a higher load (18 N) the growth of these bands was limited by the stabilised martensite formed as a consequence of the high compressive stress, at the interface with the substrate. The Ni43.4Ti49.6Cu7 interlayer (lateral grain size of ∼650 nm) exhibited no significant evidence of stabilised martensite under different loading conditions. The martensitic transformation was limited by the smaller grain size and most of the stress was relaxed by elastic and, to some extent, pseudo-elastic deformation of the austenitic phase. Grain boundaries were found to stop the growth of martensitic bands, thus limiting the activation of the martensitic transformation into the neighbouring grains during sliding. The grain refinement caused a change in the capability of the interlayer to relax shear and compressive stresses. Such a change was found to affect the formation of the WS2-rich tribolayer on the W-S-C sliding surface, and consequently the shear stress transmitted down throughout the bilayers thickness. Accordingly, different levels of deformation were observed on the top layer.

  7. Kinetics of martensitic transformations in magnetic field or under hydrostatic pressure.

    PubMed

    Kakeshita, Tomoyuki; Nam, Jung-Min; Fukuda, Takashi

    2011-02-01

    We have recently constructed a phenomenological theory that provides a unified explanation for athermal and isothermal martensitic transformation processes. On the basis of this theory, we predict some properties of martensitic transformation and confirm them experimentally using some Fe-based alloys and a Ni-Co-Mn-In magnetic shape memory alloy.

  8. Martensitic transformation thermodynamic calculation of ZrO2-MgO system

    NASA Astrophysics Data System (ADS)

    Li, Jing; Peng, Jinhui; Guo, Shenghui; Qv, Wenwen; Chen, Guo; Li, Wei; Zhang, Libo

    2012-11-01

    The phase transformation of different polymorphs in zirconia is very important for the processing and mechanical properties of zirconia ceramics. In this work, thermodynamic description of ZrO2-MgO system is investigated using the related thermodynamic parameters. Special attention is paid to the calculation of the Gibbs free energy change between tetragonal and monoclinic phases in ZrO2-MgO, namely t → m phase transformation driving force, as a function of composition and temperature. Furthermore, in 8.7 mol% MgO-ZrO2, the equilibrium temperature between tetragonal and monoclinic phases, T0, was obtained as 1107.8 K and martensitic transformation start temperature (Ms) for t → m of this ceramic with a mean grain size of 1.15 mm was also calculated to be as 737.7 K, which is in good agreement with experiment one of 689.5 K with 7.0% residual.

  9. 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.

  10. 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.

  11. Electronic structure and ferromagnetism in the martensitic-transformation material Ni2FeGa

    NASA Astrophysics Data System (ADS)

    Liu, Z. H.; Hu, H. N.; Liu, G. D.; Cui, Y. T.; Zhang, M.; Chen, J. L.; Wu, G. H.; Xiao, Gang

    2004-04-01

    We calculated the electronic structures of the Heusler alloy Ni2FeGa for both the cubic and the orthorhombic structures by self-consistent full-potential linearized-augmented plane-wave method. The localized moment of Fe atom is interpreted based on the electronic structure and the popular explanation of the localized moment of Mn in Heusler alloy X2MnY. Comparing the density of states of cubic and orthorhombic structures, we observed that a Ni peak near the density of states of d band for the cubic structure splits for the orthorhombic structure, indicating a band Jahn-Teller mechanism should be responsible for the structural transition. Accompanied by this transformation, an increase of Ni moment and magnetization redistribution occurred. Temperature-dependence anisotropy field shows an evidence of martensitic transformation between 125 and 190 K. The magnetic behavior seems to contain a transition from Heisenberg-like at temperature below 70 K to itinerant magnetism at temperature higher than 160 K upon martensitic transformation. Temperature dependence of saturation magnetization reveals the spontaneous magnetization at martensite and parent phase are 3.170μB and 3.035μB, respectively. The calculated magnetic moment at martensite is 3.171μB, which is quite consistent with the experimental value. The magnetic moment of Fe and Ni atom in Heusler alloy Ni2FeGa is analyzed based on the computational results and the experimental magnetization curves. It is found that the magnetic moment of Fe atoms is about 10 43% larger than that of α-Fe.

  12. AFM/MFM hybrid nanocharacterization of martensitic transformation and degradation for Fe-Pd shape memory alloy

    NASA Astrophysics Data System (ADS)

    Suzuki, Takayuki; Nagatani, Kohei; Hirano, Kazumi; Teramoto, Tokuo; Taya, Minoru

    2003-07-01

    Martensitic transformation and degradation characteristics for Fe-Pd ferromagnetic shape memory alloy were investigated by the developed AFM (Atomic Force Microscope)/MFM (Magnetic Force Microscope) hybrid nano-characterization technique. In AFM martensitic transformation was detected by the changes of surface topography of martensite plates. In MFM martensitic transformation was detected by the changes of magnetic domain structures. This technique has an advantage that martensitic transformation characteristics such as martensitic transformation temperature and reverse transformation temperature can be measured at microscopic and nanoscopic small area. Degradation characteristics of martensitic transformation under cyclic loading were also detected by the changes of AFM and MFM images. In AFM images surface topography of martensite plates became flat and in MFM images the morphology of magnetic domain structures became unfocused under cyclic loading. Then it was found that the hybrid nano-characterization was very high sensitive technique to evaluate degradation for Fe-Pd ferromagnetic shape memory alloy.

  13. 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%.

  14. 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.

  15. 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.

  16. Stress-induced martensitic transformation and impact toughness of cast irons and high-carbon Fe-Ni-C steel

    NASA Astrophysics Data System (ADS)

    Zhang, M.-X.; Kelly, P. M.

    2001-11-01

    The relationship between the impact toughness and stress-induced martensitic transformation, which occurs during the impact process, has been studied in white cast irons and an Fe-Ni-C alloy at different temperatures. The experimental results have shown that in the brittle white cast irons, the stress-induced martensitic transformation makes a positive contribution to the impact toughness, and lowering the stability of austenite increases the toughness. In contrast, the transformation makes a negative contribution to the toughness of high-carbon austenitic steels, and lowering the stability of austenite decreases the toughness. The present work supports the early theory[1] that the magnitude of the toughness change depends on the fracture properties of the new phase and the energy being dissipated during the transformation process. Using the crystallographic model for the stress-induced martensitic transformation, which was originally developed in ceramics and was then refined and extended to irons and steels, the effect of the stress-induced martensitic transformation on the impact toughness can be predicted.

  17. Low-temperature criticality of martensitic transformations of Cu nanoprecipitates in α-Fe.

    PubMed

    Erhart, Paul; Sadigh, Babak

    2013-07-12

    Nanoprecipitates form during nucleation of multiphase equilibria in phase segregating multicomponent systems. In spite of their ubiquity, their size-dependent physical chemistry, in particular, at the boundary between phases with incompatible topologies, is still rather arcane. Here, we use extensive atomistic simulations to map out the size-temperature phase diagram of Cu nanoprecipitates in α-Fe. The growing precipitates undergo martensitic transformations from the body-centered cubic (bcc) phase to multiply twinned 9R structures. At high temperatures, the transitions exhibit strong first-order character and prominent hysteresis. Upon cooling, the discontinuities become less pronounced and the transitions occur at ever smaller cluster sizes. Below 300 K, the hysteresis vanishes while the transition remains discontinuous with a finite but diminishing latent heat. This unusual size-temperature phase diagram results from the entropy generated by the soft modes of the bcc-Cu phase, which are stabilized through confinement by the α-Fe lattice.

  18. Trigger Stress for Stress-Induced Martensitic Transformation during Tensile Deformation in Ti-Al-Nb Alloys: Effect of Grain Size

    NASA Astrophysics Data System (ADS)

    Paradkar, Archana; Kamat, S. V.; Gogia, A. K.; Kashyap, B. P.

    2008-03-01

    The effect of β grain size on trigger stress for stress-induced martensitic transformation during tensile deformation in Ti-Al-Nb alloys was investigated. The trigger stress for stress-induced martensitic transformation (SIMT) in Ti-Al-Nb alloys exhibited a U-shaped behavior with variation in grain size. The variation of trigger stress with grain size was explained qualitatively, in terms of the contrasting change in the internal elastic energy stored in matrix due to formation of martensite (Δ E el ) and the irreversible work done in overcoming the internal frictional resistance to phase boundary movement (∂ E irr) with β grain size.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    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 ɛ-martensite were analyzed.

  1. First-principles study of martensitic transformation of IrTi alloy

    NASA Astrophysics Data System (ADS)

    Chen, Wen-Zhou; Jiang, Zhen-Yi; Si, Liang; Li, Li-Sha; Zhou, Bo

    2011-10-01

    Ab initio phonon calculations were performed to probe the martensitic transformation of IrTi. The details of the orthorhombic structure were obtained by the soft-phonon approach. We demonstrate that the tetragonal (L10)→ orthorhombic ( Cmmm) transition is driven by the softening of a phonon at the R point (0 1/2 1/2) of the Brillouin zone. The energy landscapes between the various phases of IrTi show that the structural behaviors of IrTi alloy are from cubic to tetragonal, then to orthorhombic and thus the original thought of cubic to monoclinic transition is modified.

  2. 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

  3. 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.

  4. Reversible Martensitic Transformation under Low Magnetic Fields in Magnetic Shape Memory Alloys

    PubMed Central

    Bruno, N. M.; Wang, S.; Karaman, I.; Chumlyakov, Y. I.

    2017-01-01

    Magnetic field-induced, reversible martensitic transformations in NiCoMnIn meta-magnetic shape memory alloys were studied under constant and varying mechanical loads to understand the role of coupled magneto-mechanical loading on the transformation characteristics and the magnetic field levels required for reversible phase transformations. The samples with two distinct microstructures were tested along the [001] austenite crystallographic direction using a custom designed magneto-thermo-mechanical characterization device while carefully controlling their thermodynamic states through isothermal constant stress and stress-varying magnetic field ramping. Measurements revealed that these meta-magnetic shape memory alloys were capable of generating entropy changes of 14 J kg−1 K−1 or 22 J kg −1 K−1, and corresponding magnetocaloric cooling with reversible shape changes as high as 5.6% under only 1.3 T, or 3 T applied magnetic fields, respectively. Thus, we demonstrate that this alloy is suitable as an active component in near room temperature devices, such as magnetocaloric regenerators, and that the field levels generated by permanent magnets can be sufficient to completely transform the alloy between its martensitic and austenitic states if the loading sequence developed, herein, is employed. PMID:28091551

  5. Reversible Martensitic Transformation under Low Magnetic Fields in Magnetic Shape Memory Alloys.

    PubMed

    Bruno, N M; Wang, S; Karaman, I; Chumlyakov, Y I

    2017-01-16

    Magnetic field-induced, reversible martensitic transformations in NiCoMnIn meta-magnetic shape memory alloys were studied under constant and varying mechanical loads to understand the role of coupled magneto-mechanical loading on the transformation characteristics and the magnetic field levels required for reversible phase transformations. The samples with two distinct microstructures were tested along the [001] austenite crystallographic direction using a custom designed magneto-thermo-mechanical characterization device while carefully controlling their thermodynamic states through isothermal constant stress and stress-varying magnetic field ramping. Measurements revealed that these meta-magnetic shape memory alloys were capable of generating entropy changes of 14 J kg(-1) K(-1) or 22 J kg (-1) K(-1), and corresponding magnetocaloric cooling with reversible shape changes as high as 5.6% under only 1.3 T, or 3 T applied magnetic fields, respectively. Thus, we demonstrate that this alloy is suitable as an active component in near room temperature devices, such as magnetocaloric regenerators, and that the field levels generated by permanent magnets can be sufficient to completely transform the alloy between its martensitic and austenitic states if the loading sequence developed, herein, is employed.

  6. Reversible Martensitic Transformation under Low Magnetic Fields in Magnetic Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Bruno, N. M.; Wang, S.; Karaman, I.; Chumlyakov, Y. I.

    2017-01-01

    Magnetic field-induced, reversible martensitic transformations in NiCoMnIn meta-magnetic shape memory alloys were studied under constant and varying mechanical loads to understand the role of coupled magneto-mechanical loading on the transformation characteristics and the magnetic field levels required for reversible phase transformations. The samples with two distinct microstructures were tested along the [001] austenite crystallographic direction using a custom designed magneto-thermo-mechanical characterization device while carefully controlling their thermodynamic states through isothermal constant stress and stress-varying magnetic field ramping. Measurements revealed that these meta-magnetic shape memory alloys were capable of generating entropy changes of 14 J kg‑1 K‑1 or 22 J kg ‑1 K‑1, and corresponding magnetocaloric cooling with reversible shape changes as high as 5.6% under only 1.3 T, or 3 T applied magnetic fields, respectively. Thus, we demonstrate that this alloy is suitable as an active component in near room temperature devices, such as magnetocaloric regenerators, and that the field levels generated by permanent magnets can be sufficient to completely transform the alloy between its martensitic and austenitic states if the loading sequence developed, herein, is employed.

  7. A Thermo-Plastic-Martensite Transformation Coupled Constitutive Model for Hot Stamping

    NASA Astrophysics Data System (ADS)

    Bin, Zhu; WeiKang, Liang; Zhongxiang, Gui; Kai, Wang; Chao, Wang; Yilin, Wang; Yisheng, Zhang

    2017-03-01

    In this study, a thermo-plastic-martensite transformation coupled model based on the von Mises yield criterion and the associated plastic flow rule is developed to further improve the accuracy of numerical simulation during hot stamping. The constitutive model is implemented into the finite element program ABAQUS using user subroutine VUMAT. The martensite transformation, transformation-induced plasticity and volume expansion during the austenite-to-martensite transformation are included in the constitutive model. For this purpose, isothermal tensile tests are performed to obtain the flow stress, and non-isothermal tensile tests were carried out to validate the constitutive model. The non-isothermal tensile numerical simulation demonstrates that the thermo-plastic-martensite transformation coupled constitutive model provides a reasonable prediction of force-displacement curves upon loading, which is expected to be applied for modeling and simulation of hot stamping.

  8. A Thermo-Plastic-Martensite Transformation Coupled Constitutive Model for Hot Stamping

    NASA Astrophysics Data System (ADS)

    Bin, Zhu; WeiKang, Liang; Zhongxiang, Gui; Kai, Wang; Chao, Wang; Yilin, Wang; Yisheng, Zhang

    2017-01-01

    In this study, a thermo-plastic-martensite transformation coupled model based on the von Mises yield criterion and the associated plastic flow rule is developed to further improve the accuracy of numerical simulation during hot stamping. The constitutive model is implemented into the finite element program ABAQUS using user subroutine VUMAT. The martensite transformation, transformation-induced plasticity and volume expansion during the austenite-to-martensite transformation are included in the constitutive model. For this purpose, isothermal tensile tests are performed to obtain the flow stress, and non-isothermal tensile tests were carried out to validate the constitutive model. The non-isothermal tensile numerical simulation demonstrates that the thermo-plastic-martensite transformation coupled constitutive model provides a reasonable prediction of force-displacement curves upon loading, which is expected to be applied for modeling and simulation of hot stamping.

  9. Magnetic indication of the stress-induced martensitic transformation in ferromagnetic Ni Mn Ga alloy

    NASA Astrophysics Data System (ADS)

    Heczko, O.; L'vov, V. A.; Straka, L.; Hannula, S.-P.

    2006-07-01

    A quantitative study of the stress-induced martensitic transformation in Ni 49.7Mn 29.1Ga 21.2 magnetic shape memory alloy has been carried out in two different ways: the first way is based on the measurements of saturation magnetization under variable mechanical stress and the second one is founded on the quantitative theoretical treatment of experimental stress-strain loops. A functional dependence between the volume fraction of transformed martensite and applied stress has been determined from both magnetization and strain values. A quantitative agreement between the functions determined in two different ways has been observed, and hence, the effectiveness of the magnetic indication of the stress-induced martensitic transformations has been proved. This method can be used to monitor stress-induced transformations in martensitic films, needles and small specimens.

  10. 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.

  11. The founder of the theory of diffusionless (martensite) transformations in metallic alloys

    NASA Astrophysics Data System (ADS)

    Vintaikin, E. Z.; Nosova, G. I.

    1997-02-01

    In February 1997 G. V. Kurdyumov is to celebrate his 95th birthday. Doing justice to this wonderful scientist, we publish an article by his disciples (colleagues at the Bardin Central Research Institute of Ferrous Metallurgy) devoted to his achievements in the field of martensite transformations. We also present one of his fundamental works on martensite transformations published in 1948 in Reports of the Academy of Sciences of the USSR, Vol. 60, No. 9.

  12. 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.

  13. 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.

  14. Dynamic behaviour and shock-induced martensite transformation in near-beta Ti-5553 alloy under high strain rate loading

    NASA Astrophysics Data System (ADS)

    Wang, Lin; Wang, Yangwei; Xu, Xin; Liu, Chengze

    2015-09-01

    Ti-5553 alloy is a near-beta titanium alloy with high strength and high fracture toughness. In this paper, the dynamic behaviour and shock-induced martensite phase transformation of Ti-5553 alloy with alpha/beta phases were investigated. Split Hopkinson Pressure Bar was employed to investigate the dynamic properties. Microstructure evolutions were characterized by Scanning Electronic Microscopy and Transmission Electron Microscope. The experimental results have demonstrated that Ti-5553 alloy with alpha/beta phases exhibits various strain rate hardening effects, both failure through adiabatic shear band. Ti-5553 alloy with Widmannstatten microstructure exhibit more obvious strain rate hardening effect, lower critical strain rate for ASB nucleation, compared with the alloy with Bimodal microstructures. Under dynamic compression, shock-induced beta to alpha" martensite transformation occurs.

  15. Magnetocaloric effect in Ni2MnGa single crystal in the vicinity of the martensitic phase transition

    NASA Astrophysics Data System (ADS)

    Radelytskyi, I.; Pękała, M.; Szymczak, R.; Gawryluk, D. J.; Berkowski, M.; Fink-Finowicki, J.; Diduszko, R.; Dyakonov, V.; Szymczak, H.

    2017-05-01

    The magnetocaloric effect in the vicinity of the martensitic transformation for a single crystalline alloy with a composition close to the stoichiometric Ni2MnGa has been determined indirectly by M(T,H) magnetization measurements. It has an inverse character. The magnetocaloric parameters, i.e., the magnetic entropy change, refrigeration capacity and various hysteretic effects have been calculated from the M(T,H) dependences. Besides the martensitic transition a weak entirely separated intermartensitic transition was observed. These two successive magneto-structural transformations give contributions to the observed magnetocaloric effect. Unusual dependence of entropy change as a function of magnetic field has been explained as arising because of two different mechanisms. Additionally, to confirm that studied martensitic transformation is a first order phase transition electrical resistivity and thermoelectric power measurements have been performed.

  16. Martensitic transformation in a B2-containing CuZr-based BMG composite revealed by in situ neutron diffraction

    DOE PAGES

    Song, Gian; Lee, Chanho; Hong, Sung Hwan; ...

    2017-06-27

    Here, CuZr-based bulk-metallic-glass (BMG) composites reinforced by a B2-type CuZr crystalline-phase (CP) have been widely studied, and exhibit that the plastic deformation of the CP induces martensitic transformation from the B2 to B19', which plays a dominant role in the deformation behavior and mechanical properties. In the present study, 2.0% Co containing CuZr-based BMG composites were investigated using in-situ neutron-diffraction technique. The in-situ neutron-diffraction results reveal the continuous load transfer from the glass matrix to B2 CP and martensitic transformation from the B2 CP to B19' during the deformation of the composite. Moreover, it was found that the martensitic transformationmore » is initiated at the applied stress higher than 1500 MPa, and is significantly suppressed during the deformation, as compared to other 0.5% Co-containing CuZr-based BMG composites. Based on these in-situ neutron-diffraction results, the martensitic transformation is strongly affected by the amount of the addition of Co, which determines the mechanical properties of CP-reinforced BMG composites, such as ductility and hardening capability.« less

  17. Martensitic transformation of pure iron at a grain boundary: Atomistic evidence for a two-step Kurdjumov-Sachs–Pitsch pathway

    SciTech Connect

    Meiser, Jerome; Urbassek, Herbert M.

    2016-08-15

    Using classical molecular dynamics simulations and the Meyer-Entel interaction potential, we study the martensitic transformation pathway in a pure iron bi-crystal containing a symmetric tilt grain boundary. Upon cooling the system from the austenitic phase, the transformation starts with the nucleation of the martensitic phase near the grain boundary in a plate-like arrangement. The Kurdjumov-Sachs orientation relations are fulfilled at the plates. During further cooling, the plates expand and merge. In contrast to the orientation relation in the plate structure, the complete transformation proceeds via the Pitsch pathway.

  18. The atomistic mechanism of hcp-to-bcc martensitic transformation in the Ti-Nb system revealed by molecular dynamics simulations.

    PubMed

    Li, Yang; Li, JiaHao; Liu, BaiXin

    2015-02-14

    Applying the constructed Ti-Nb potentials, molecular dynamics simulations were conducted to investigate the martensitic transformation of Ti100-xNbx alloys (x = 5, 10…25) from the α' phase (hcp) to the β phase (bcc). It is found that the transformation involved four phases, i.e. α', α'', fco (face-centered orthorhombic), and β phases. The structures of the obtained phases exhibit consistency with experimental data, verifying the validity of atomic simulations. The simulations not only revealed the processes of atomic displacements during the transformation, but also elucidated the underlying mechanism of the martensitic transformation at the atomic level. The martensitic transformation incorporates three types of coinstantaneous deformations i.e. slide, shear as well as extension, and the subsequent lattice constant relaxation. Furthermore, according to the proposed mechanism, the crystallographic correlation between the initial α' phase and the final β phase has been deduced. The simulation results provide a clear landscape on the martensitic transformation mechanism, facilitating our comprehensive understanding on the phase transition in the Ti-Nb system.

  19. 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.

  20. 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.

  1. 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.

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

    PubMed

    Bondar, Volodimir I; Danilchenko, Vitalij Ie; Dzevin, Ievgenij M

    2014-02-24

    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.

  3. Martensitic transformation in a Cu-Zn-Al alloy studied by 63Cu and 27Al NMR

    NASA Astrophysics Data System (ADS)

    Rubini, S.; Dimitropoulos, C.; Gotthardt, R.; Borsa, F.

    1991-08-01

    27Al and 63Cu line shape, Knight shift, and relaxation rates over a wide range of temperature and external magnetic field are reported for a Cu-Zn-Al alloy displaying a martensitic phase transformation (MPT) at MS=152 K. Changes in line shape, linewidth, and T-12 at the MPT are detected for both nuclei, and are found to be consistent with the local atomic rearrangement occurring at the transformation. A double structure for the 27Al NMR line is observed in a small range of temperature below MS, and interpreted as the superposition of the signals arising from the two coexisting phases. It is shown that the growth of the martensitic phase during the cooling can be monitored by means of the deconvolution of the 27Al spectrum into the two components. From the analysis, it is inferred that a sudden formation of extensive regions in the martensitic phase occurs at the transition. The Knight shift and the Korringa term (T1T)-1 are slightly different in the two phases, indicating a small increase of the density of s electrons at the Fermi surface at the nuclear sites. The enhancement factors of the susceptibility and of the spin-lattice relaxation rate do not seem to be affected by the MPT but are different when measured at the Al or Cu site, indicating a local nonuniform charge-density distribution in the unit cell. A small enhancement of T-11 is observed for both nuclei in the temperature interval in which the growth of the martensite within the austenite is detected. The anomalous contribution to the relaxation is interpreted as due to strong local charge-density fluctuations caused by atomic motion at the interfaces between the two phases. No precursor effects were detected on the NMR parameters above MS, indicating the absence of a static or long-lived microstructure of the product phase and of a static short-wavelength modulation of the lattice.

  4. 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.

  5. Martensitic transformation and shape memory effect in ferromagnetic Heusler alloy Ni2FeGa

    NASA Astrophysics Data System (ADS)

    Liu, Z. H.; Zhang, M.; Cui, Y. T.; Zhou, Y. Q.; Wang, W. H.; Wu, G. H.; Zhang, X. X.; Xiao, Gang

    2003-01-01

    We have synthesized ferromagnetic Heusler alloy Ni2FeGa using the melt-spinning technique. The Ni2FeGa ribbon, having a high chemical ordering L21 structure, exhibits a thermoelastic martensitic transformation from cubic to orthorhombic structure at 142 K and a premartensitic transformation. The alloy has a relatively high Curie temperature of 430 K, a magnetization of 73 Am2/kg, and a low saturated field of 0.6 T. The textured samples with preferentially oriented grains show a completely recoverable two-way shape memory effect with a strain of 0.3% upon the thermoelastic martensitic transformation.

  6. Effects of ternary additions on Young's modulus and the martensitic transformation of Nb/sub 3/Sn

    SciTech Connect

    Bussiere, J.F.; Faucher, B.; Snead, C.L. Jr.; Suenaga, M.

    1982-01-01

    Recent measurements on bronze-processed Nb/sub 3/Sn using a vibrating reed technique have shown that Young's modulus at low temperatures decreases to 0.4 of its room temperature value, and that the internal friction increases dramatically below 50 K, the martensitic transformation temperature. In this study, this technique was used to study softening and the occurrence of the martensitic transformation in bronze-processed Nb/sub 3/Sn samples which contained additions of Ta, Ti, and Zr. Sample preparations and characteristics of the compositions are given. Internal friction and dynamic Young's modulus were measured using electronics based on a phase-locked loop and frequency mode developed by Simpson and Sosin. Softening of Young's modulus and occurrence of the martensitic transformation were found to be strongly affected by the presence of relatively small amounts (0-4 at .%) of Ta, Ti, or Zr. Additions incorporating 2 at .% Ti in the Nb/sub 3/Sn increased Young's modulus by a factor of 2 at 10 K and also suppressed the transformation.

  7. Effect of martensitic transformation on springback behavior of 304L austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Fathi, H.; Mohammadian Semnani, H. R.; Emadoddin, E.; Sadeghi, B. Mohammad

    2017-09-01

    The present paper studies the effect of martensitic transformation on the springback behavior of 304L austenitic stainless steel. Martensite volume fraction was determined at the bent portion under various strain rates after bending test. Martensitic transformation has a significant effect on the springback behavior of this material. The findings of this study indicated that the amount of springback was reduced under a situation of low strain rate, while a higher amount of springback was obtained with a higher strain rate. The reason for this phenomenon is that higher work hardening occurs during the forming process with the low strain rate due to the higher martensite volume fraction, therefore the formability of the sheet is enhanced and it leads to a decreased amount of springback after the bending test. Dependency of the springback on the martensite volume fraction and strain rate was expressed as formulas from the results of the experimental tests and simulation method. Bending tests were simulated using LS-DYNA software and utilizing MAT_TRIP to determine the martensite volume fraction and strain under various strain rates. Experimental result reveals good agreement with the simulation method.

  8. 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.

  9. Physical properties of Fe-Co-Ni-Ti alloy in the vicinity of martensitic transformation

    SciTech Connect

    Cesari, E.; Pons, J.; Segui, C.; Chernenko, V.A.; Kokorin, V.V.

    1999-01-08

    The shape memory steels have recently received much attention, from which a considerable progress has been achieved in understanding the factors which are of particular importance for their development. Among these steels, a special interest has been paid to the ferromagnetic Fe-Ni- and Fe-Co-based alloys mainly because of the thermoelastic character of the fcc ({gamma})-bct ({alpha}) martensitic transformation that they exhibit under the action of temperature (shape memory effect), stress (superelasticity) and magnetic field (magnetoelasticity). In the present work the authors report the results of the experimental investigation about the {gamma}-{alpha} thermoelastic martensitic transformation in Fe-Co-Ni-Ti alloy using different techniques (notably DSC, DMA, dilatometry, TEM and magnetic susceptibility). One of the objectives was to find the appropriate thermal treatments in order to increase the martensitic transformation temperatures up to room temperature.

  10. How to enable bulk-like martensitic transformation in epitaxial films

    NASA Astrophysics Data System (ADS)

    Wodniok, Marius; Teichert, Niclas; Helmich, Lars; Hütten, Andreas

    2017-05-01

    The present study is dedicated to the influence of different substrate and buffer layer materials on the martensitic transformation in sputter deposited epitaxial shape memory Heusler alloys. For this, the magnetocaloric Heusler alloy Ni-Co-Mn-Al [N. Teichert et al., Phys. Rev. B 91, 184405 (2015)] is grown on MgO(001), MgAl2O4(001), and MgO(001)/V substrates, which exhibit a lattice misfit to the Ni-Co-Mn-Al between -1.2% and 3.6%. By temperature dependent X-ray diffraction measurements it is shown that the optimum buffer layer for shape memory Heusler films is not one with minimum lattice misfit, but one with minimum Young's modulus and moderate misfit because an elastic buffer layer can deform during the martensitic transformation of the Heusler layer. Furthermore, epitaxial strain caused by a moderate lattice misfit does not significantly change the martensitic transformation temperatures.

  11. On the Micromechanisms of Shock-Induced Martensitic Transformation in Tantalum

    SciTech Connect

    Hsiung, L L

    2005-12-07

    Shock-induced twinning and martensitic transformation in tantalum, which exhibits no solid-state phase transformation under hydrostatic pressures up to 100 GPa, have been further investigated. Since the volume fraction and size of twin and phase domains are small in scale, they are considered foming by heterogeneous nucleation that is catalyzed by high density lattice dislocations. A dynamic dislocation mechanism is accordingly proposed based upon the observation of dense dislocation clustering within shock-recovered tantalum. The dense dislocation clustering can cause a significant increase of strain energy in local regions of {beta} (bcc) matrix, which renders mechanical instability and initiates the nucleation of twin and phase domains through the spontaneous reactions of dislocation dissociation within the dislocation clusters. That is, twin domains can be nucleated within the clusters through the homogeneous dissociation of 1/2<111> dislocations into 1/6<111> partial dislocations, and {omega} phase domains can be nucleated within the closters through the inhomogeneous dissociation of 1/2<111> dislocations into 1/12<111>, 1/3<111> and 1/12<111> partial dislocations.

  12. 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.

  13. A Stress-Induced Martensitic Transformation in Aged Ti49Ni51 Alloy after High-Velocity Impact

    PubMed Central

    Zhu, Yingying; Wang, Haizhen; Gao, Zhiyong; Cai, Wei

    2016-01-01

    The effects of a high-velocity impact on the microstructure, phase transformation and mechanical property of aged Ti49Ni51 alloy are investigated. The transformation behavior and microstructure along the impact direction after impact emerge with regionalization characteristics, including a deformed region near the crater (0–4 mm) and an un-deformed region of the distal crater (5–6 mm). Stress-induced martensite is the main deformation mechanism in the deforming region of aged Ti49Ni51 alloy under high-velocity impact. PMID:28773622

  14. A Stress-Induced Martensitic Transformation in Aged Ti49Ni51 Alloy after High-Velocity Impact.

    PubMed

    Zhu, Yingying; Wang, Haizhen; Gao, Zhiyong; Cai, Wei

    2016-06-23

    The effects of a high-velocity impact on the microstructure, phase transformation and mechanical property of aged Ti49Ni51 alloy are investigated. The transformation behavior and microstructure along the impact direction after impact emerge with regionalization characteristics, including a deformed region near the crater (0-4 mm) and an un-deformed region of the distal crater (5-6 mm). Stress-induced martensite is the main deformation mechanism in the deforming region of aged Ti49Ni51 alloy under high-velocity impact.

  15. Nature of the effect of magnetic fields on the starting temperature of martensitic transformation in iron alloys

    NASA Astrophysics Data System (ADS)

    Schastlivtsev, V. M.; Mirzaev, D. A.; Kaletina, Yu. V.; Fokina, E. A.

    2016-02-01

    The effect of a magnetic field on martensitic transformations, which is satisfactorily described by the Krivoglaz-Sadovskii formula, has been analyzed taking into account the nonequilibrium of the martensitic transformation, the possible adiabatic conditions, and the magnetostriction of the paraprocess in ferromagnetic austenite.

  16. The martensitic transformation, magnetocaloric effect, and magnetoresistance in high-Mn content Mn47+xNi43-xSn10 ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Xuan, H. C.; Zheng, Y. X.; Ma, S. C.; Cao, Q. Q.; Wang, D. H.; Du, Y. W.

    2010-11-01

    A series of high-Mn content Mn47+xNi43-xSn10 (x=0, 1, 2, 3, 4, and 5) ferromagnetic shape memory alloys were prepared by arc melting method. The martensitic transformation were observed in these alloys, even the content of Mn is higher than 50 at. %. The phase transition temperature of these alloys can be adjusted by tuning the compositions of Ni and Mn. Large positive magnetic entropy change and negative magnetoresistance which originate from the magnetic-field-induced martensitic transformation are obtained in these alloys.

  17. THE EFFECT OF REPEATED COMPRESSIVE DYNAMIC LOADING ON THE STRESS-INDUCED MARTENSITIC TRANSFORMATION IN NiTi SHAPE MEMORY ALLOYS

    SciTech Connect

    D. MILLER; W. THISSELL; ET AL

    2000-08-01

    It has been shown that quasi-static, cyclic, isothermal mechanical loading influences the mechanical response of the stress-induced martensitic transformation in fully annealed NiTi Shape Memory Alloys (SMAs). As the cycle number increases, hardening of the stress-strain response during the martensitic phase transformation is seen along with a decrease in the threshold stress for initiation of stress-induced martensite. Also, the amount of plastic strain and detwinned martensitic strain decreases as the cycle number increases. However, NiTi SMAs have not been experimentally explored under high compressive strain rates. This research explores the cyclic near-adiabatic stress-induced martensitic loading using a Split Hopkinskin Pressure Bar (SHPB). The results of the dynamic loading tests are presented with emphasis on the loading rate, stress-strain response, specimen temperature and post-test microstructural evaluation. The results from the high strain rate tests show similarities with the quasi-static results in the hardening of the stress-strain response and shifting of the threshold stress for initiation of stress-induced martensite.

  18. 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)

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

    DOE PAGES

    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

  20. Crystallography of the Delta to Alpha Martensitic Transformation in Plutonium Alloys

    SciTech Connect

    Jin, Y; Wang, Y; Khachaturyan, A; Krenn, C; Schwartz, A

    2004-07-15

    A new stress-accommodating crystallographic mechanism of the {delta} {yields} {alpha} martensitic transformation in plutonium alloys is proposed. According to this mechanism, an orientation variant of the {alpha} phase is produced by a combination of a homogeneous strain and shuffling of the alternating close-packed (111){sub {delta}} planes. It is shown that the formation of stable transformation-induced twins whose twin plane orientations and twin shear directions do not depend on the small variations of the crystal lattice parameters is the preferred stress-accommodating mode. Only these stable twins have dislocation-free twin boundaries while the twin boundaries of all others are decorated by ultra-dense distribution of partial dislocations. The theory predicts a crystal lattice rearrangement mechanism involving the (205){sub {alpha}} ((01{bar 1}){sub {delta}}) stable twins. The corresponding Invariant Plane Strain solutions, with special emphasis on two simplest shuffling modes, the single and double elementary modes, are presented and compared with the existing experimental observations. It is shown that the habit plane orientation is highly sensitive to the input values of the crystal lattice parameters and especially to the accuracy of the measured volume change in the {delta}{yields}{alpha} transformation. An analysis of these effects on the habit plane orientation and orientation relations is also presented.

  1. Magnetic Study of Martensitic Transformation in Austenitic Stainless Steel by Low Field Hysteresis Loops Analysis

    SciTech Connect

    Zhang Lefu; Takahashi, Seiki; Kamada, Yasuhiro; Kikuchi, Hiroaki; Mumtaz, Khalid; Ara, Katsuyuki; Sato, Masaya

    2005-04-09

    Magnetic method has been used to evaluate the volume percentage of {alpha}' martensitic phase in austenitic stainless steels by measuring saturation magnetization, and it is said to be a candidate NDE method. However, nondestructive detection of saturation magnetization without high magnetic field is difficult. In the current work, we present a NDE method for evaluating the magnetic properties of strain induced {alpha}' martensitic phase. Low field hysteresis loops of an austenitic stainless steels type SUS 304 after cold rolling were measured by using a yoke sensor. The results show that the initial permeability {mu}i and the relative coercive field Hcl calculated by low field hysteresis loop analysis keep monotonic relation with saturation magnetization and coercive force measured by VSM, respectively. By this method, it is possible to characterize the volume content and particle properties of {alpha}' martensitic phase in stainless steels.

  2. New mechanism for the alpha to omega martensitic transformation in pure titanium.

    PubMed

    Trinkle, D R; Hennig, R G; Srinivasan, S G; Hatch, D M; Jones, M D; Stokes, H T; Albers, R C; Wilkins, J W

    2003-07-11

    We propose a new direct mechanism for the pressure driven alpha-->omega martensitic transformation in pure titanium. A systematic algorithm enumerates all possible pathways whose energy barriers are evaluated. A new, homogeneous pathway emerges with a barrier at least 4 times lower than other pathways. The pathway is shown to be favorable in any nucleation model.

  3. Comparative study on microstructure and martensitic transformation of aged Ni-rich NiTi and NiTiCo shape memory alloys

    NASA Astrophysics Data System (ADS)

    El-Bagoury, Nader

    2016-05-01

    In this article the influence of aging heat treatment conditions of 250, 350, 450 and 550 °C for 3 h on the microstructure, martensitic transformation temperatures and mechanical properties of Ni51Ti49Co0 and Ni47 Ti49Co4 shape memory alloys was investigated. This comparative study was carried out using X-ray diffraction analysis, scanning electron microscope, energy dispersive spectrometer, differential scanning calorimeter and Vickers hardness tester. The results show that the microstructure of both aged alloys contains martensite phase and Ti2Ni in addition to some other precipitates. The martensitic transformation temperature was increased steadily by increasing the ageing temperature and lowering the value of valence electron number (ev/a) and concentration. Moreover, the hardness measurements were gradually increased at first by increasing the aging temperature from 250 to 350 °C. Further elevating in aging temperature to 450 and 550 °C decreases the hardness value.

  4. 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

  5. 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.

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

    PubMed

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

    2014-08-21

    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.

  7. Dependence of the enthalpy of the direct martensitic transformation in titanium nickelide on the stress

    NASA Astrophysics Data System (ADS)

    Egorov, S. A.; Volkov, A. E.

    2017-02-01

    An original technique of differential thermal analysis for studying thermal properties of samples loaded with a tangential stress has been created. In a series of experiments studying the direct martensitic transformation B2 → B19' in titanium nickelide during cooling under constant stress, it has been found that the enthalpy of transformation linearly decreases with an increase in stress and, at a stress of 100 MPa, it is 30% less than that of the sample in a free state.

  8. Probing the isothermal (delta)->(alpha)' martensitic transformation in Pu-Ga with in situ x-ray diffraction

    SciTech Connect

    Jeffries, J R; Blobaum, K M; Schwartz, A J; Cynn, H; Yang, W; Evans, W J

    2010-03-11

    The time-temperature-transformation (TTT) curve for the {delta} {yields} {alpha}{prime} isothermal martensitic transformation in a Pu-1.9 at. % Ga alloy is peculiar because it is reported to have a double-C curve. Recent work suggests that an ambient temperature conditioning treatment enables the lower-C curve. However, the mechanisms responsible for the double-C are still not fully understood. When the {delta} {yields} {alpha}{prime} transformation is induced by pressure, an intermediate {gamma}{prime} phase is observed in some alloys. It has been suggested that transformation at upper-C temperatures may proceed via this intermediate phase, while lower-C transformation progresses directly from {delta} to {alpha}{prime}. To investigate the possibility of thermally induced transformation via the intermediate {gamma}{prime} phase, in situ x-ray diffraction at the Advanced Photon Source was performed. Using transmission x-ray diffraction, the {delta} {yields} {alpha}{prime} transformation was observed in samples as thin at 30 {micro}m as a function of time and temperature. The intermediate {gamma}{prime} phase was not observed at -120 C (upper-C curve) or -155 C (lower-C curve). Results indicate that the bulk of the {alpha}{prime} phase forms relatively rapidly at -120 C and -155 C.

  9. Geometrical model for martensitic phase transitions: Understanding criticality and weak universality during microstructure growth

    NASA Astrophysics Data System (ADS)

    Torrents, Genís; Illa, Xavier; Vives, Eduard; Planes, Antoni

    2017-01-01

    A simple model for the growth of elongated domains (needle-like) during a martensitic phase transition is presented. The model is purely geometric and the only interactions are due to the sequentiality of the kinetic problem and to the excluded volume, since domains cannot retransform back to the original phase. Despite this very simple interaction, numerical simulations show that the final observed microstructure can be described as being a consequence of dipolar-like interactions. The model is analytically solved in 2D for the case in which two symmetry related domains can grow in the horizontal and vertical directions. It is remarkable that the solution is analytic both for a finite system of size L ×L and in the thermodynamic limit L →∞ , where the elongated domains become lines. Results prove the existence of criticality, i.e., that the domain sizes observed in the final microstructure show a power-law distribution characterized by a critical exponent. The exponent, nevertheless, depends on the relative probabilities of the different equivalent variants. The results provide a plausible explanation of the weak universality of the critical exponents measured during martensitic transformations in metallic alloys. Experimental exponents show a monotonous dependence with the number of equivalent variants that grow during the transition.

  10. Boron's effect on martensitic transformation and magnetocaloric effect in Ni43Mn46Sn11Bx alloys

    NASA Astrophysics Data System (ADS)

    Xuan, H. C.; Wang, D. H.; Zhang, C. L.; Han, Z. D.; Gu, B. X.; Du, Y. W.

    2008-03-01

    The most used method for changing the martensitic transformation temperatures in the ferromagnetic shape memory alloys is tuning the valence election concentration e /a. In this paper, we report an alternative way, i.e., introducing few interstitial boron atoms in Ni43Mn46Sn11 alloy. The experimental results show that the martensitic transformation temperatures increase with the increasing boron content remarkably and large magnetic entropy changes can be obtained in these alloys. A possible origin of the enhanced martensitic transformation temperatures and large magnetic entropy changes is discussed in this paper.

  11. Influence of martensitic transformation on the magnetic transition in Ni-Mn-Ga

    NASA Astrophysics Data System (ADS)

    Kokorin, V. V.; Konoplyuk, S. M.; Dalinger, A.; Maier, H. J.

    2017-06-01

    The magnetic transition with a temperature hysteresis of about 7 K was observed in the martensitic phase of Ni51.9Mn27Ga211. The measurements of AC magnetic susceptibility in constant magnetic fields up to 570 kA/m have proved its magnetic origin. The transport and caloric measurements were used to gain better understanding of the nature of this phenomenon. The variation of the martensite lattice parameters with temperature is suggested to account for the hysteresis of the magnetic transition.

  12. Temperature dependence of magnetic susceptibility in the vicinity of martensitic transformation in ferromagnetic shape memory alloys.

    PubMed

    Zablotskii, V; Pérez-Landazábal, J I; Recarte, V; Gómez-Polo, C

    2010-08-11

    Temperature dependences of low-field quasistatic magnetic susceptibility in the vicinity of martensitic transitions in an NiFeGa alloy are studied both by experiment and analytically. Pronounced reversible jumps of the magnetic susceptibility were observed near the martensitic transition temperature. A general description of the temperature dependences of the susceptibility in ferromagnetic austenite and martensite phases and the susceptibility jump at the transition is suggested. As a result, the main factors governing the temperature dependences of the magnetic susceptibility in the magnetic shape memory alloys are revealed. The magnetic susceptibility jump value is found to be related to changes of: (i) magnetic anisotropy; (ii) magnetic domain wall geometrical constraints (those determined by the alignment and size of twin variants) and (iii) mean magnetic domain spacing.

  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. Thermal-expansion anisotropy of orthorhombic martensite in the two-phase (α + β) titanium alloy

    NASA Astrophysics Data System (ADS)

    Demakov, S. L.; Stepanov, S. I.; Illarionov, A. G.; Ryzhkov, M. A.

    2017-03-01

    Anisotropy of the thermal expansion coefficient (TEC) has been revealed along the axes of the crystal lattice of the α″ titanium martensite in the two-phase (α + β) titanium alloy of grade VT16 (Ti-3Al-5V-4.5Mo, wt %). It has been established by the method of in situ X-ray diffraction analysis that the lattice parameter b of the orthorhombic martensite obtained by quenching from different temperatures decreases upon heating. The TECs along the axes of the crystal lattice of the martensite obtained by quenching from different temperatures have been calculated. It has been shown that the uniaxial extension of bars of the VT16 alloy quenched for the metastable β phase with relative deformations of 0.7, 1, 2, 3, 4, 5, 6, and 8% leads to the formation of the deformation-induced martensite with an axial texture along the b direction of the martensite lattice. In the course of dilatometric studies of the deformed bars, it has been established that there are two temperature intervals (from-100 to +70°C and from 150 to 300°C) with a low TEC. In the first interval, the value of the TEC varies from-2 × 10-6 to +8 × 10-6 K-1 and is determined by the volume fraction of the oriented α″ martensite. This Invar effect is one-dimensional and is manifested along the b axis of the martensite.

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

    DOE PAGES

    Ari-Gur, Pnina; Garlea, Vasile O.; Cao, Huibo; ...

    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

  16. Deformation behavior of duplex austenite and ε-martensite high-Mn steel.

    PubMed

    Kwon, Ki Hyuk; Suh, Byeong-Chan; Baik, Sung-Il; Kim, Young-Woon; Choi, Jong-Kyo; Kim, Nack J

    2013-02-01

    Deformation and work hardening behavior of Fe-17Mn-0.02C steel containing ε-martensite within the austenite matrix have been investigated by means of in situ microstructural observations and x-ray diffraction analysis. During deformation, the steel shows the deformation-induced transformation of austenite → ε-martensite → α'-martensite as well as the direct transformation of austenite → α'-martensite. Based on the calculation of changes in the fraction of each constituent phase, we found that the phase transformation of austenite → ε-martensite is more effective in work hardening than that of ε-martensite → α'-martensite. Moreover, reverse transformation of ε-martensite → austenite has also been observed during deformation. It originates from the formation of stacking faults within the deformed ε-martensite, resulting in the formation of 6H-long periodic ordered structure.

  17. 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.

  18. 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.

  19. Magnetic properties and martensitic transformation of Ni-Mn-Ge Heusler alloys from first-principles and Monte Carlo studies

    NASA Astrophysics Data System (ADS)

    Sokolovskiy, V. V.; Zagrebin, M. A.; Buchelnikov, V. D.

    2017-05-01

    In the present study, the magnetic properties and possibility of martensitic transformation in a series of off-stoichiometric Ni2+x Mn1-x Ge and Ni2Mn1+x Ge1-x Heusler alloys have been studied by using both first-principles and Monte Carlo methods. It is shown that in both cases an increase in chemical disorder stimulates the austenite-martensite transformation and leads to an increase in transition temperature. Moreover, the calculated formation energies confirm that these compounds are stable chemically. By using the exchange coupling constants obtained from ab initio calculations in combination with the Heisenberg model and Monte Carlo methods, the temperature-dependent magnetizations as well as Curie temperatures of the cubic and tetragonal Ni2+x Mn1-x Ge and Ni2Mn1+x Ge1-x have been determined. The phase diagrams of alloys studied showing the compositions with magnetostructural transformation are obtained. Calculated results demonstrate a similar trend to the previous experimental and theoretic results for Ni-Mn-(Ga, In, Sn, Sb) alloys that makes them possible promising magnetic materials in technological applications.

  20. 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.

  1. Computer simulation of martensitic transformations in constrained, two-dimensional crystals under external stress

    NASA Astrophysics Data System (ADS)

    Xu, Ping; Morris, J. W.

    1993-06-01

    This article reports a computer simulation study of the microstructures produced by martensitic transformations. In the present work, the transformation strain is dyadic, and the transformation is athermal and irreversible. The transformation occurs in a two-dimensional crystal that is constrained in a matrix that has no net transformation strain and may be subject to external stress. The crystal is divided into elementary cells. The transformation is simulated by computing the elastic strain energy in the linear elastic approximation and transforming the most-favored cell in each step to generate the minimum-energy transformation path. The simulation generates the microstructure at each step of the transformation and plots a temperature-transformation (TT) curve by computing the chemical driving force required to maintain the transformation and assuming that it is proportional to the undercooling. The results show that the matrix constraint causes complex, multivariant microstructures and separates M sand M f. Multiple variants partly relax the shear part of transformation strain but interfere so that the transformation is difficult to maintain. The dilational part of the transformation strain produces interesting microstructures, such as “butterfly martensite,” in partially transformed crystals. It also increases Δ M since it produces a hydrostatic stress that cannot be compensated by mixing variants. The applied stress can be divided into hydrostatic and deviatoric components. The hydrostatic component changes M swithout altering the microstructure or Δ M. The deviatoric stress changes the relative energies of the variants and produces a microstructure that is rich in the favored variant. It also increases Δ M, since single-variant transformations must be sustained against an accumulating, uncompensated shear. The thermal resistance (Δ M) increases with the magnitude of the deviatoric stress until a high-stress limit is reached and only one variant

  2. Computer simulation of martensitic transformations in constrained, two-dimensional crystals under external stress

    NASA Astrophysics Data System (ADS)

    Xu, Ping; Morris, J. W.

    1993-06-01

    This article reports a computer simulation study of the microstructures produced by martensitic transformations. In the present work, the transformation strain is dyadic, and the transformation is athermal and irreversible. The transformation occurs in a two-dimensional crystal that is constrained in a matrix that has no net transformation strain and may be subject to external stress. The crystal is divided into elementary cells. The transformation is simulated by computing the elastic strain energy in the linear elastic approximation and transforming the most-favored cell in each step to generate the minimum-energy transformation path. The simulation generates the microstructure at each step of the transformation and plots a temperature-transformation (TT) curve by computing the chemical driving force required to maintain the transformation and assuming that it is proportional to the undercooling. The results show that the matrix constraint causes complex, multivariant microstructures and separates M sand M f. Multiple variants partly relax the shear part of transformation strain but interfere so that the transformation is difficult to maintain. The dilational part of the transformation strain produces interesting microstructures, such as "butterfly martensite," in partially transformed crystals. It also increases Δ M since it produces a hydrostatic stress that cannot be compensated by mixing variants. The applied stress can be divided into hydrostatic and deviatoric components. The hydrostatic component changes M swithout altering the microstructure or Δ M. The deviatoric stress changes the relative energies of the variants and produces a microstructure that is rich in the favored variant. It also increases Δ M, since single-variant transformations must be sustained against an accumulating, uncompensated shear. The thermal resistance (Δ M) increases with the magnitude of the deviatoric stress until a high-stress limit is reached and only one variant appears

  3. Unraveling the composition dependence of the martensitic transformation temperature: A first-principles study of Ti-Ta alloys

    NASA Astrophysics Data System (ADS)

    Chakraborty, Tanmoy; Rogal, Jutta; Drautz, Ralf

    2016-12-01

    The martensitic start temperature Ms is one of the key characteristics of shape memory materials. High-temperature shape memory alloys are a special class of materials where transformation temperatures between the martensite and austenite phase above 373 K are desirable. For the design of new high-temperature shape memory alloys it is therefore important to understand and predict the dependence of Ms on the composition of the material. Using density functional theory in combination with the quasiharmonic Debye model, we evaluate the different contributions to the free energy to determine the transition temperature T0 over a wide range of compositions in Ti-Ta alloys. Our approach provides physical insight into the various contributions that explain the strong composition dependence of Ms that is observed experimentally. Based on our calculations, we identify the relative phase stability at T =0 K and the vibrational entropy difference between the involved phases as critical parameters to predict changes in T0. We propose a simple, one-dimensional descriptor to estimate the transition temperature that can be used in the identification of new alloys suitable for high-temperature shape memory applications.

  4. Magnetically controlled thermoelastic martensite transformations and properties of a fine-grained Ni54Mn21Ga25 alloy

    NASA Astrophysics Data System (ADS)

    Pushin, V. G.; Marchenkova, E. B.; Korolev, A. V.; Kourov, N. I.; Belosludtseva, E. S.; Pushin, A. V.; Uksusnikov, A. N.

    2017-07-01

    Comparative studies of physical characteristics (the electrical resistivity, the magnetic susceptibility, the magnetization, the bending deformation, and the degree of shape recovery during subsequent heating) of the Ni54Mn21Ga25 ferromagnetic alloy as-cast and rapidly quenched from melt have been performed in the temperature range 2-400 K. The results are compared to the results of studying the structural-phase transformations by transmission and scanning electron microscopy and X-ray diffraction. It is found that the rapid quenching influences the microstructure, the magnetic state, the critical temperatures, and the specific features of thermoelastic martensite transformations in the alloy. It is found that the resource of the alloy plasticity and thermomechanical bending cyclic stability demonstrates a record-breaking increase in the intercritical temperature range and during subsequent heating.

  5. 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.

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

    PubMed

    Zarkevich, N A; Johnson, D D

    2014-12-31

    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 nudged elastic band method implemented via density-functional theory, we detail the structural transformations in NiTi relevant to shape memory: those between a body-centered orthorhombic (bco) ground state 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. These high- and low-temperature structures and structural transformations provide much needed atomic-scale detail for transitions responsible for NiTi shape-memory effects.

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

    DOE PAGES

    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. 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.

  9. Phase composition and hardening of steels of the Fe-Cr-Ni-Co-Mo system with martensite-austenite structure

    NASA Astrophysics Data System (ADS)

    Tarasenko, L. V.; Shal'kevich, A. B.

    2007-03-01

    The phase composition and mechanical properties of maraging steels of the Fe-Cr-Ni-Co-Mo system are studied as a function of the alloying and of the temperatures of quenching and aging. The intermetallic phases strengthening martensite in different aging stages are determined. The degree of the hardening and the variation of the impact toughness at cryogenic temperatures are compared for steels with different structures (martensite and martensite-austenite) in the stages of maximum hardening and overaging. The effect of retained and reverted austenite on the resistance to crack propagation under impact loading is determined for steels with martensite of a different nature and amount of hardening phases.

  10. Buckling of a circular plate made of a shape memory alloy due to a reverse thermoelastic martensite transformation

    NASA Astrophysics Data System (ADS)

    Movchan, A. A.; Sil'chenko, L. G.

    2008-02-01

    We solve the axisymmetric buckling problem for a circular plate made of a shape memory alloy undergoing reverse martensite transformation under the action of a compressing load, which occurs after the direct martensite transformation under the action of a generally different (extending or compressing) load. The problem was solved without any simplifying assumptions concerning the transverse dimension of the supplementary phase transition region related to buckling. The mathematical problem was reduced to a nonlinear eigenvalue problem. An algorithm for solving this problem was proposed. It was shown that the critical buckling load under the reverse transition, which is obtained by taking into account the evolution of the phase strains, can be many times lower than the same quantity obtained under the assumption that the material behavior is elastic even for the least (martensite) values of the elastic moduli. The critical buckling force decreases with increasing modulus of the load applied at the preliminary stage of direct transition and weakly depends on whether this load was extending or compressing. In shape memory alloys (SMA), mutually related processes of strain and direct (from the austenitic into the martensite phase) or reverse thermoelastic phase transitions may occur. The direct transition occurs under cooling and (or) an increase in stresses and is accompanied by a significant decrease (nearly by a factor of three in titan nickelide) of the Young modulus. If the direct transition occurs under the action of stresses with nonzero deviator, then it is accompanied by accumulation of macroscopic phase strains, whose intensity may reach 8%. Under the reverse transition, which occurs under heating and (or) unloading, the moduli increase and the accumulated strain is removed. For plates compressed in their plane, in the case of uniform temperature distribution over the thickness, one can separate trivial processes under which the strained plate remains plane

  11. Martensitic transformation of Ni2FeGa ferromagnetic shape-memory alloy studied via transmission electron microscopy and electron energy-loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, H. R.; Ma, C.; Tian, H. F.; Wu, G. H.; Li, J. Q.

    2008-06-01

    The structural properties of Ni2FeGa Heusler alloy synthesized by melt-spinning technique have been systematically studied by means of in situ heating and cooling transmission electron microscopy. It was found that the Ni2FeGa alloy was annealed into a well-defined L21 structure at around 980 K, and complex microstructural domains appeared along with lowering temperature. At room temperature (293 K), a rich variety of micromodulated domains were observed. The domain structures were aligned along the ⟨110⟩ or ⟨100⟩ directions resulting to complex tweed structures. Below martensitic transformation (MT) temperature (Ms,˜142K) , the cubic parent phase transformed into unmodulated martensitic variants and modulated martensitic variants. The variants were alternated along the ⟨100⟩ direction with various arrangements and steplike incommensurate boundaries. The modulated martensitic variants were composed of lamellar structures that have predominately a 5M modulation structure along the ⟨110⟩ directions. The electron energy-loss spectroscopy analysis of the low-loss region and the electron energy-loss near-edge fine structure revealed a visible change of the electronic structure along with MT, which can be well interpreted by means of intra-atomic or intraband charge redistribution due to spd orbital hybridization among the Ni-Fe-Ga atoms.

  12. Martensitic fcc-to-hcp transformation observed in xenon at high pressure.

    PubMed

    Cynn, H; Yoo, C S; Baer, B; Iota-Herbei, V; McMahan, A K; Nicol, M; Carlson, S

    2001-05-14

    Angle-resolved x-ray diffraction patterns of Xe to 127 GPa indicate that the fcc-to-hcp transition occurs martensitically between 3 and 70 GPa in diamond-anvil cells without an intermediate phase. These data also reveal that the transition occurs by the introduction of stacking disorder in the fcc lattice at low pressure, which grows into hcp domains with increasing pressure. The small energy difference between the hcp and the fcc structures may allow the two phases to coexist over a wide pressure range. Evidence of similar stacking disorder and incipient growth of an hcp phase are also observed in solid Kr.

  13. Phase transformation and stabilization of a high strength austenite

    NASA Technical Reports Server (NTRS)

    Jin, S.; Huang, D.

    1976-01-01

    An investigation of the phase transformation and the austenite stabilization in a high strength austenite has been made. An Fe-29Ni-4.3Ti austenite age-hardened by gamma-prime (Ni3Ti) precipitates showed a further increase of strength after martensitic and reverse martensitic phase transformations. The stability of ausaged austenite as well as ausaged and transformation-strengthened austenite was improved significantly through an isothermal treatment at 500 C. The Ms temperature of the strengthened austenite was restored to nearly that of annealed austenite while the austenite was hardened to R(C) 41 through precipitation and phase transformations. The observed austenite stabilization is attributed to the formation of GP zones or short-range order of less than about 10A in size.

  14. Development of Stress-Induced Martensitic Transformation in TiNi Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Pieczyska, Elzbieta Alicja; Staszczak, Maria; Dunić, Vladimir; Slavković, Radovan; Tobushi, Hisaaki; Takeda, Kohei

    2014-07-01

    TiNi shape memory alloy (SMA) was subjected to tension at strain-controlled test on quasistatic testing machine. The nucleation, development, and saturation of the stress-induced martensitic transformation were investigated, taking into account the obtained dependency of mechanical parameters and the specimen temperature changes measured by an infrared camera (IR). Three kinds of data obtained by the IR system were analyzed: the temperature distribution on the SMA sample surface, the temperature changes derived as average from the chosen sample area, and the temperature profiles obtained along the sample length. The temperature distribution shows nucleation of the transformation process and a creation of the transformation bands. The average temperature reflects the effects of thermomechanical coupling, accompanying exothermic martensitic forward and endothermic reverse transformation. The temperature profiles revealed the temperature difference between the band and the rest of the sample. The experimental results were supported with finite element method numerical analysis (FEM). The FEM software components for structural and heat transfer problems, coupled in partitioned approach, were used for thermomechanical analysis.

  15. The Formation of Martensitic Austenite During Nitridation of Martensitic and Duplex Stainless Steels

    NASA Astrophysics Data System (ADS)

    Zangiabadi, Amirali; Dalton, John C.; Wang, Danqi; Ernst, Frank; Heuer, Arthur H.

    2017-01-01

    Isothermal martensite/ferrite-to-austenite phase transformations have been observed after low-temperature nitridation in the martensite and δ-ferrite phases in 15-5 PH (precipitation hardening), 17-7 PH, and 2205 (duplex) stainless steels. These transformations, in the region with nitrogen concentrations of 8 to 16 at. pct, are consistent with the notion that nitrogen is a strong austenite stabilizer and substitutional diffusion is effectively frozen at the paraequilibrium temperatures of our experiments. Our microstructural and diffraction analyses provide conclusive evidence for the martensitic nature of these phase transformations.

  16. The effect of cyclic martensitic transformations on diffusion of cobalt atoms in Fe-18wt.%Mn-2wt.%Si alloy

    NASA Astrophysics Data System (ADS)

    Danilchenko, Vitaliy E.; Mazanko, Vladimir F.; Filatov, Alexander V.; Iakovlev, Viktor E.

    2015-04-01

    Diffusion characteristics of cobalt atoms were investigated using radioactive isotope method in phase-hardened Fe-18wt.%Mn-2wt.%Si alloy. The observed significant increase of diffusion coefficient of cobalt atoms under the cyclic γ-ɛ-γ martensitic transformations was due to the action of two independent mechanisms - an athermal one and a thermally activated one. The first one arose from the direct γ-ɛ and the reverse ɛ-γ transformations with corresponding direct and reverse lattice shears during alternating stresses and simultaneous lattice restructuring. Another mechanism arose under the diffusion annealing of the phase-hardened alloy.

  17. The effect of cyclic martensitic transformations on diffusion of cobalt atoms in Fe-18wt.%Mn-2wt.%Si alloy.

    PubMed

    Danilchenko, Vitaliy E; Mazanko, Vladimir F; Filatov, Alexander V; Iakovlev, Viktor E

    2015-01-01

    Diffusion characteristics of cobalt atoms were investigated using radioactive isotope method in phase-hardened Fe-18wt.%Mn-2wt.%Si alloy. The observed significant increase of diffusion coefficient of cobalt atoms under the cyclic γ-ε-γ martensitic transformations was due to the action of two independent mechanisms - an athermal one and a thermally activated one. The first one arose from the direct γ-ε and the reverse ε-γ transformations with corresponding direct and reverse lattice shears during alternating stresses and simultaneous lattice restructuring. Another mechanism arose under the diffusion annealing of the phase-hardened alloy.

  18. 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.

  19. Reason for high strength and good ductility in dual phase steels composed of soft ferrite and hard martensite

    NASA Astrophysics Data System (ADS)

    Terada, Daisuke; Ikeda, Gosuke; Park, Myeong-heom; Shibata, Akinobu; Tsuji, Nobuhiro

    2017-07-01

    Dual phase (DP) steels in which the microstructures are composed of a soft ferrite phase and a hard martensite phase are known to show good strain-hardening, high strength and large elongation, but reasons for their superior mechanical properties are still unclear. In the present study, two types of DP structures, having either networked martensite or isolated martensite were fabricated in a low-carbon steel by different heat treatment routes, and their tensile deformation behavior was analyzed using the digital image correlation (DIC) technique. It was revealed that the DP specimens having networked martensite microstructures showed a better strength-ductility balance than the DP specimens with isolated martensite structures. The microscopic DIC analysis of identical areas showed that the strain distribution within the DP microstructures was not uniform and the plastic strain was localized in soft ferrite grains. The strain localized regions tended to detour around hard martensite but eventually propagated across the martensite. It was found also from the DIC analysis that the degree of strain partitioning between ferrite and martensite in the networked DP structure was lower than that in the isolated DP structure. The deformation became more homogeneous when the hard phase (martensite) was connected to form a network structure, which could be one of the reasons for the better strength-ductility balance in the networked DP structure compared to that in the isolated DP structure.

  20. The features of microstructure and mechanical properties of austenitic steel after direct and reverse martensitic transformations

    NASA Astrophysics Data System (ADS)

    Litovchenko, I. Yu.; Akkuzin, S. A.; Polekhina, N. A.; Tyumentsev, A. N.; Naiden, E. P.

    2015-10-01

    The features of structural states of metastable austenitic steel after thermomechanical treatments, including low-temperature deformation, warm deformation and subsequent annealing are investigated. It is shown that under these conditions the direct (γ → α') and reverse (α' → γ) martensitic transformations occur and submicrocrystalline structural states are formed. The proposed thermomechanical treatment allows varying the strength and plastic properties of austenitic steel in a wide range. The strength of steel in submicrocrystalline state is 4-6 times higher than its original value.

  1. Stress-induced martensitic transformation in high-strength [236]-oriented Ni51Ti36.5Hf12.5 single crystals

    NASA Astrophysics Data System (ADS)

    Surikov, N. Y.; Eftifeeva, A. S.; Panchenko, E. Yu; Chumlyakov, Yu I.

    2015-10-01

    The effects of heat treatment on the stress-induced B2-B19' martensitic transformations in the Ni51.0Ti36.5Hf12.5 single crystals oriented along [236] direction are studied. It is shown that in the annealed at 1323K for 4 h crystals, the temperature range of superelasticity increase almost twofold from 75K up to 135K as compared to the as-grown single crystal contained disperse particles of H-phase. The [236]-oriented Ni51.0Ti36.5Hf12.5 single crystals are characterized with high levels of applied compressive stress up to 1700 MPa in the as-grown state and 1900 MPa in annealed crystals for the completely reversible stress- induced B2-B19' martensitic transformation with reversible strain up to |εSE| =1.4%.

  2. 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.

  3. Thermal and magnetic field-induced martensitic transformation in Ni50Mn25-x Ga25Cu x (0  ⩽  x  ⩽  7) melt-spun ribbons

    NASA Astrophysics Data System (ADS)

    Li, Zongbin; Zou, Naifu; Sánchez-Valdés, C. F.; Sánchez Llamazares, J. L.; Yang, Bo; Hu, Yong; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang

    2016-01-01

    We have studied the phase transformation behavior of \\text{N}{{\\text{i}}50}\\text{M}{{\\text{n}}25}-x\\text{G}{{\\text{a}}25}\\text{C}{{\\text{u}}x} melt-spun ribbons with x  =  0, 1, 2, …, 7 (at%). It is shown that Cu substitution simultaneously increases and decreases the martensitic transformation temperature T M and the magnetic transition temperature of austenite T\\text{C}\\text{A} , respectively. In Ni50Mn18Ga25Cu7 ribbons, the magnetic and structural transformations are coupled. The field-induced martensitic transformation from a paramagnetic austenite with lower magnetization to a ferromagnetic martensite with higher magnetization has been studied. The critical field μ o H cr above which the magnetic field can induce the martensitic transition is well defined and decreases linearly with the decrease of the temperature at a reduction rate of 1 T K-1. Under a magnetic field of 5 T, the starting temperature of martensitic transformation (M s) increases by ~9 K. Such a magnetic field-induced transformation is irreversible and temperature dependent, giving rise to the maximum magnetic entropy change of 17.8 J kg-1 K-1 and hysteresis losses of 43.6 J kg-1 under the magnetic field change of 5 T, respectively.

  4. Characterization of the thermoelastic martensitic transformation in a NiTi alloy driven by temperature variation and external stress

    NASA Astrophysics Data System (ADS)

    Liang, K. F.; Lin, Z. C.; Fung, P. C. W.; Zhang, J. X.

    1997-08-01

    In order to test the concept of the physics of dissipation during first-order phase transitions in solids, we measured the internal friction (Q-1) and the relative shear modulus (μ) during a thermoelastic martensitic transformation in a NiTi alloy. We adopted two approaches: temperature variation and application of external stress. This investigation of internal friction was carried out with various vibration frequencies ω, temperature variation rates T˙, and strain variation rates ɛ˙. The index l (coupling factor between phase interface and oscillating stress) and index n (rate exponent for the effective phase transformation driving force) have been calculated from the experimental data for each case and the values of l and n are about the same in the two (doped) NiTi samples, irrespective of whether the phase transition is driven by a temperature variation or stress induced process. We compare the values of n and l for the NiTi samples with that of the other samples (VO2 ceramics and FeMn alloys), reinforcing the previous physical interpretations of these indices. We believe the indices n and l are indeed fingerprints of first-order phase transitions in solids.

  5. Microstructural studies of 35 degrees C copper Ni-Ti orthodontic wire and TEM confirmation of low-temperature martensite transformation.

    PubMed

    Brantley, William A; Guo, Wenhua; Clark, William A T; Iijima, Masahiro

    2008-02-01

    Previous temperature-modulated differential scanning calorimetry (TMDSC) study of nickel-titanium orthodontic wires revealed a large exothermic low-temperature peak that was attributed to transformation within martensitic NiTi. The purpose of this study was to use transmission electron microscopy (TEM) to verify this phase transformation in a clinically popular nickel-titanium wire, identify its mechanism and confirm other phase transformations found by TMDSC, and to provide detailed information about the microstructure of this wire. The 35 degrees C Copper nickel-titanium wire (Ormco) with cross-section dimensions of 0.016 in. x 0.022 in. used in the earlier TMDSC investigation was selected. Foils were prepared for TEM analyses by mechanical grinding, polishing, dimpling, ion milling and plasma cleaning. Standard bright-field and dark-field TEM images were obtained, along with convergent-beam electron diffraction patterns. A cryo-stage with the electron microscope (Phillips CM 200) permitted the specimen to be observed at -187, -45, and 50 degrees C, as well as at room temperature. Microstructures were also observed with an optical microscope and a scanning electron microscope. Room temperature microstructures had randomly oriented, elongated grains that were twinned. Electron diffraction patterns confirmed that phase transformations took place over temperature ranges previously found by TMDSC. TEM observations revealed a high dislocation density and fine-scale oxide particles, and that twinning is the mechanism for the low-temperature transformation in martensitic NiTi. TEM confirmed the low-temperature peak and other phase transformations observed by TMDSC, and revealed that twinning in martensite is the mechanism for the low-temperature peak. The high dislocation density and fine-scale oxide particles in the microstructure are the result of the wire manufacturing process.

  6. Multi-stage martensitic transformation in Ni-rich NiTi shape memory alloys

    NASA Astrophysics Data System (ADS)

    Wang, Xiebin; Verlinden, Bert; Kustov, Sergey

    Precipitation hardening is an effective way to improve the functional stability of NiTi shape memory alloys. The precipitates, mainly Ni4Ti3, could be introduced by aging treatment in Ni-rich NiTi alloys. However, the presence of Ni4Ti3 precipitates could disturb the transformation behavior, resulting in the multi-stage martensitic transformation (MMT). With the presence of MMT, it is difficult to control the transformation behavior, and thus limits the applicability of NiTi alloys. In this work, previous efforts on explaining the observed MMT are summarized. The difficulties in developing a unified explanation are discussed, and a possible way to avoid the MMT is proposed.

  7. Phase diagram of Ti50-xNi50+x : Crossover from martensite to strain glass

    NASA Astrophysics Data System (ADS)

    Zhang, Zhen; Wang, Yu; Wang, Dong; Zhou, Yumei; Otsuka, Kazuhiro; Ren, Xiaobing

    2010-06-01

    We systematically investigated the variation in transition behavior and physical properties over a wide excess Ni (acting as defect) concentration range (x=0-2.5) in Ti50-xNi50+x alloys. This enables the establishment of an updated quantitative phase diagram for this important system. The phase diagram shows not only the well-known parent phase and martensite phase but also a premartensitic state and a strain glass state. Our experiments were able to determine quantitatively the borders of these states, the latter two having been unclear so far. The new phase diagram shows that a crossover from martensite to strain glass occurs at x=1.3 , and the appearance of a “premartensitic phase” below a critical temperature Tnd for defect-containing compositions (x>0) . We propose that point defects (excess Ni here) play two roles in a ferroelastic/martensitic system: (i) changing the thermodynamic driving force for the formation of long-range strain order (martensite) and (ii) creating random local stress that favors a premartensitic nanostructure and strain glass. Our work enables a simple explanation for several long-standing puzzles, such as the appearance of premartensitic nanostructure, the vanishing of transition latent heat with increasing Ni content and the anomalous negative temperature coefficient of electrical resistivity in Ni-rich Ti-Ni alloys.

  8. 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.

  9. Magnetostructural martensitic transformations with large volume changes and magneto-strains in all-d-metal Heusler alloys

    NASA Astrophysics Data System (ADS)

    Wei, Z. Y.; Liu, E. K.; Li, Y.; Han, X. L.; Du, Z. W.; Luo, H. Z.; Liu, G. D.; Xi, X. K.; Zhang, H. W.; Wang, W. H.; Wu, G. H.

    2016-08-01

    The all-d-metal Mn2-based Heusler ferromagnetic shape memory alloys Mn50Ni40-xCoxTi10 (x = 8 and 9.5) are realized. With a generic comparison between d-metal Ti and main-group elements in lowering the transformation temperature, the magnetostructural martensitic transformations are established by further introducing Co to produce local ferromagnetic Mn-Co-Mn configurations. A 5-fold modulation and (3, -2) stacking of [00 10] of martensite are determined by X-ray diffraction and HRTEM analysis. Based on the transformation, a large magneto-strain of 6900 ppm and a large volume change of -2.54% are observed in polycrystalline samples, which makes the all-d-metal magnetic martensitic alloys of interest for magnetic/pressure multi-field driven applications.

  10. Kinetic model of thermoelastic martensite transformation in NiTi and NiMn based shape memory alloys

    SciTech Connect

    Wu, K.H.; Shi, J.D.; Yang, F.; Pu, Z.J.

    1996-12-31

    A new, quantitative model was developed to describe the martensite transformation kinetics of thermoelastic shape memory alloys (SMAs). In addition, a series of experiments were conducted to study the kinetics of thermoelastic martensite transformation in four SMA systems: NiTi, NiTi-15at%Hf, NiTi-20at%Zr and NiMn-7.5at%Ti alloys. Comparisons between data of the kinetic of martensite transformation with the present theoretic models show that the proposed model is in good agreement and concurs with the experimental data. Also, a comparison of data from the proposed model with data from existing kinetic models, such as Liang`s and Magee`s indicates that the proposed model can better describe the experimental data, including the relationship between d{xi}(T)/dT and {xi}, and d{xi}(T)/dT and T.

  11. Magnetostructural martensitic transformations with large volume changes and magneto-strains in all-d-metal Heusler alloys

    SciTech Connect

    Wei, Z. Y.; Liu, E. K. Xi, X. K.; Zhang, H. W.; Wang, W. H.; Wu, G. H.; Li, Y.; Han, X. L.; Du, Z. W.; Luo, H. Z.; Liu, G. D.

    2016-08-15

    The all-d-metal Mn{sub 2}-based Heusler ferromagnetic shape memory alloys Mn{sub 50}Ni{sub 40−x}Co{sub x}Ti{sub 10} (x = 8 and 9.5) are realized. With a generic comparison between d-metal Ti and main-group elements in lowering the transformation temperature, the magnetostructural martensitic transformations are established by further introducing Co to produce local ferromagnetic Mn-Co-Mn configurations. A 5-fold modulation and (3, −2) stacking of [00 10] of martensite are determined by X-ray diffraction and HRTEM analysis. Based on the transformation, a large magneto-strain of 6900 ppm and a large volume change of −2.54% are observed in polycrystalline samples, which makes the all-d-metal magnetic martensitic alloys of interest for magnetic/pressure multi-field driven applications.

  12. 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.

  13. 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.

  14. 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.

  15. On the Stability of Reversely Formed Austenite and Related Mechanism of Transformation in an Fe-Ni-Mn Martensitic Steel Aided by Electron Backscattering Diffraction and Atom Probe Tomography

    NASA Astrophysics Data System (ADS)

    Koohdar, Hamidreza; Nili-Ahmadabadi, Mahmoud; Habibi-Parsa, Mohammad; Jafarian, Hamid Reza; Bhattacharjee, Tilak; Tsuji, Nobuhiro

    2017-08-01

    The stability of reversely formed austenite and related mechanism of transformation were investigated against temperature and time in an Fe-9.6Ni-7.1Mn (at. pct) martensitic steel during intercritical annealing at a dual-phase (α + γ) region. Dilatometry, electron backscattering diffraction (EBSD), atom probe tomography (APT), and X-ray diffraction (XRD) were used to characterize the mechanism of reverse transformation. It was found that under intercritical annealing at 853 K (580 °C), when the heating rate is 20 K/s (20 °C/s), reverse transformation takes place through a mixed diffusion control mechanism, i.e., controlled by bulk diffusion and diffusion along the interface, where Ni controls the diffusion as its diffusivity is lower than that of Mn in the martensite and austenite. Increasing the intercritical annealing to 873 K (600 °C) at an identical heating rate of 20 K/s (20 °C/s) showed that reverse transformation occurs through a sequential combination of both martensitic and diffusional mechanisms. The transition temperature from diffusional to martensitic transformation was obtained close to 858 K (585 °C). Experimental results revealed that the austenite formed by the diffusional mechanism at 853 K (580 °C) mainly remains untransformed after cooling to ambient temperature due to the enrichment with Ni and Mn. It was also found that the stability of the reversely formed austenite by martensitic mechanism at 873 K (600 °C) is related to grain refinement.

  16. 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.

  17. The Z-Phase in 9Cr Ferritic/martensitic Heat Resistant Steel

    NASA Astrophysics Data System (ADS)

    Yin, Fengshi; Chen, Fuxia; Jiang, Xuebo; Xue, Bing; Zhou, Li; Jung, Woosang

    The precipitation behavior of Z-phase was investigated during long-term aging at 650°C in an ultra low carbon 9Cr ferritic/martensitic heat resistant steel. The steel was prepared by vacuum induction melting followed by hot forging and rolling into a plate. The plate was normalized at 1100°C for 1h, cooled in air and tempered at 700°C for 1h. Bimodal nano-sized MX precipitates distribute densely and homogeneously in the matrix within martensitic lath after normalizing-and-tempering heat treatment. After aging at 650°C for 1200h, the Z-phase was found to nucleate on the larger nano-sized MX. The Z-phase and MX have the following orientation relationship: <112>Z-phase//<001>MX and (1bar 10){Z-phase}//(200){MX} .

  18. Effect of atomic order on the martensitic and magnetic transformations in Ni-Mn-Ga ferromagnetic shape memory alloys.

    PubMed

    Sánchez-Alarcos, V; Pérez-Landazábal, J I; Recarte, V; Rodríguez-Velamazán, J A; Chernenko, V A

    2010-04-28

    The influence of long-range L2(1) atomic order on the martensitic and magnetic transformations of Ni-Mn-Ga shape memory alloys has been investigated. In order to correlate the structural and magnetic transformation temperatures with the atomic order, calorimetric, magnetic and neutron diffraction measurements have been performed on polycrystalline and single-crystalline alloys subjected to different thermal treatments. It is found that both transformation temperatures increase with increasing atomic order, showing exactly the same linear dependence on the degree of L2(1) atomic order. A quantitative correlation between atomic order and transformation temperatures has been established, from which the effect of atomic order on the relative stability between the structural phases has been quantified. On the other hand, the kinetics of the post-quench ordering process taking place in these alloys has been studied. It is shown that the activation energy of the ordering process agrees quite well with the activation energy of the Mn self-diffusion process.

  19. Magnetic influence on the martensitic transformation entropy in Ni-Mn-In metamagnetic alloy

    NASA Astrophysics Data System (ADS)

    Barandiaran, J. M.; Chernenko, V. A.; Cesari, E.; Salas, D.; Lazpita, P.; Gutierrez, J.; Orue, I.

    2013-02-01

    We study the martensitic transformation (MT) of metamagnetic shape memory alloy Ni50Mn34.5In15.5 in the magnetic fields up to 12 T. The observed dependence of the MT temperature, Tm, on the field is highly nonlinear. As far as magnetization change, ΔM, remains field-independent, a depart from linearity of Tm(H) function is attributed to a decrease of the transformation entropy, ΔS. This decrease correlates with the parameter (TC-Tm), controlled by magnetic field, where TC is the Curie temperature of austenite, and with the dependence of ΔS on the width of the MT temperature interval deduced from a ferroelastic model of MT.

  20. The anomalous expansion of lattice parameter as a function of temperature for an Fe-24Mn alloy during {gamma}{yields}{epsilon} martensitic transformation

    SciTech Connect

    Lu, X.; Qin, Z.; Zhang, Y.; Ding, B.; Hu, Z.

    2000-02-14

    In the present letter, the authors will report their experiment on an Fe-24Mn alloy using high temperature XRD and dilation. A relation between the lattice parameter of austenite and temperature during {gamma}{yields}{epsilon} martensitic transformation was determined. It is expected to be helpful in the understanding of {gamma}{yields}{epsilon} martensitic transformation in Fe-Mn based alloys.

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

    SciTech Connect

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

    2016-04-11

    Combining experimental methods and classical molecular dynamics (MD) computer simulations, we explore the martensitic transformation in Fe{sub 70}Pd{sub 30} 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.

  2. Martensite transformations in Mn2NiGa thin films grown on GaAs substrates

    NASA Astrophysics Data System (ADS)

    Schaefer, D. M.; Neckel, I. T.; Mazzaro, I.; Graff, I. L.; Varalda, J.; Schreiner, W. H.; Mosca, D. H.

    2016-11-01

    The purpose of this work is to investigate the correlation between magnetism and crystallographic structures of Mn2NiGa thin films grown by molecular beam epitaxy on GaAs(1 1 1) and GaAs(0 0 1) surfaces. The films present themselves with thermoelastic martensitic transformations upon cooling, and heating with high-temperature leads to austenite structures exhibiting a preferable (1 1 0) texture. X-ray diffraction measurements performed as a function of temperature reveal three different types of domain variants in the films within a large interval of temperatures. The austenite structures with lattice parameters ranging from 0.574 nm to 0.601 nm undergo volume conserving structural transitions to martensite with a c/a ratio of 1.2. The coexistence of variants with different domain configurations is induced on each GaAs substrate. Although the Curie temperatures (~360 K) are similar for films grown on GaAs(1 1 1) and GaAs (0 0 1) substrates, their saturation magnetizations are respectively 18 kA m-1 and 8 kA m-1 at room temperature and exhibit quite different magnetic irreversibility behaviors. Our results indicate that a multiplicity of possible equivalent variant domains on the GaAs surfaces makes it difficult to stabilize epitaxial films on these substrates.

  3. In-situ studies of the TGO growth stresses and the martensitic transformation in the B2 phase in commercial Pt-modified NiAl and NiCoCrAlY bond coat alloys.

    SciTech Connect

    Hovis, D.; Hu, L.; Reddy, A.; Heuer, A. H.; Paulikas, A. P.; Veal, B. W.

    2007-12-01

    Oxide growth stresses were measured in situ at 1100 C on commercial Pt-modified NiAl and NiCoCrAlY bond coat alloys using synchrotron X-rays. Measurements were taken on samples that had no preoxidation, as well as on samples that had experienced 24 one-hour thermal exposures at 1150 C, a condition known to induce rumpling in the Pt-modified NiAl alloy, but not in the NiCoCrAlY alloy. The NiCoCrAlY alloy showed continuous stress relaxation under all conditions, whereas the Pt-modified NiAl alloys would typically stabilize at a fixed (often non-zero) stress suggesting a higher creep strength in the 'Thermally Grown Oxide' on the latter alloy, though the precise behavior was dependent on initial surface preparation. The formation of martensite in the Pt-modified NiAl alloys was also observed upon cooling and occurred at temperatures below 200 C for all of the samples observed. Based on existing models, this M{sub s} temperature is too low to account for the rumpling observed in these alloys.

  4. γ→α‧ Martensitic transformation and magnetic property of cold rolled Fe-20Mn-4Al-0.3C steel

    NASA Astrophysics Data System (ADS)

    Ma, Biao; Li, Changsheng; Han, Yahui; Wang, Jikai

    2016-12-01

    Direct γ→α‧ martensitic transformation during cold rolling deformation was investigated for a high-Mn non-magnetic steel. Its influence on magnetic property was also analyzed. The magnetization under rolling reduction less than 50% almost presents a linear increase with the applied magnetic field. With deformation up to 73% and 93% thickness reductions, strain induced α‧-martensite transformation starts to occur, causing the steel to be slightly magnetized. The α‧-martensite prefers to nucleate directly at either microband-microband or microband-twin intersections without participation of intermediate ε-martensite. The volume fraction of α‧-martensite is estimated as 0.070% and 0.17%, respectively, based on the magnetic hysteresis loops. Such a small fraction of ferromagnetic α‧-martensite shows little influence on the magnetic induction intensity and low relative permeability.

  5. 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.

  6. Martensitic transformation in as-grown and annealed near-stoichiometric epitaxial Ni2MnGa thin films

    NASA Astrophysics Data System (ADS)

    Machain, P.; Condó, A. M.; Domenichini, P.; Pozo López, G.; Sirena, M.; Correa, V. F.; Haberkorn, N.

    2015-08-01

    Magnetic shape memory nanostructures have a great potential in the field of the nanoactuators. The relationship between dimensionality, microstructure and magnetism characterizes the materials performance. Here, we study the martensitic transformation in supported and free-standing epitaxial Ni47Mn24Ga29 films grown by sputtering on (0 0 1) MgO using a stoichiometric Ni2MnGa target. The films have a Curie temperature of ~390 K and a martensitic transition temperature of ~120 K. Similar transition temperatures have been observed in films with thicknesses of 1, 3 and 4 μm. Thicker films (with longer deposition time) present a wider martensitic transformation range that can be associated with small gradients in their chemical concentration due to the high vapour pressure of Mn and Ga. The magnetic anisotropy of the films shows a strong change below the martensitic transformation temperature. No features associated with variant reorientation induced by magnetic field have been observed. Annealed films in the presence of a Ni2MnGa bulk reference change their chemical composition to Ni49Mn26Ga25. The change in the chemical composition increases the martensitic transformation temperature, being closer to the stoichiometric compound, and reduces the transformation hysteresis. In addition, sharper transformations are obtained, which indicate that chemical inhomogeneities and defects are removed. Our results indicate that the properties of Ni-Mn-Ga thin films grown by sputtering can be optimized (fixing the chemical concentration and removing crystalline defects) by the annealing process, which is promising for the development of micromagnetic shape memory devices.

  7. The elastic properties and martensitic transformation behaviour of Ti50Pt50-xCox shape memory alloy

    NASA Astrophysics Data System (ADS)

    Chauke, Hasani; Mahlangu, Rosinah; Ngoepe, Phuti

    2014-03-01

    Ti-based shape memory alloys (SMAs) such as PdTi, AuTi and PtTi are important in the design for high temperature alloys due to their high martensitic transformation (Ms) of above 673 K. PtTi is the most attractive for the development of high temperature shape memory alloys (HTSMAs) since it has the highest Ms of about 1273 K. Above 1273 K The crystal structure is the ordered cubic B2 phase, and transforms to an orthorhombic B19 phase at lower temperature. The supercell approach method was used to investigate the effect of partial substitution of Pt with Co on the TiPt potential shape memory alloy. The first-principles calculations were carried out within the generalized gradient approximation to determine the stability of the Ti50Pt50-xCo for x=6.25, 18.75 and 25. We found that the calculated heats of formation and density of states predicted the 6.25 at.% Co to be the most stable structures compared. The elastic properties and the phonon dispersion results suggest that the partial substitution of Pt with Co increases the Ms of TiPt with the softening of the ' shear moduli.

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

    NASA Astrophysics Data System (ADS)

    Li, Wei; Liu, Ping; Zhang, Ke; Ma, Fengcang; Liu, Xinkuan; Chen, Xiaohong; He, Daihua

    2014-08-01

    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.

  9. 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

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

    PubMed

    Li, Wei; Liu, Ping; Zhang, Ke; Ma, Fengcang; Liu, Xinkuan; Chen, Xiaohong; He, Daihua

    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.

  11. Martensite transformation and shape memory effect on NiTi-Zr high temperature shape memory alloys

    SciTech Connect

    Pu, Z.; Tseng, H.; Wu, K.

    1995-10-17

    NiTi-Zr high temperature alloys possess relatively poor shape memory properties and ductility in comparison with NiTi-Hf and NiTi-Pd alloys. During martensite transformation of the newly-developed NiTi-Zr high temperature shape memory alloys (SMAs) the temperature increases along with Zr content when the Zr content is more than 10 at%. As the Zr content increases, the fully reversible strain of the alloys decreases. However, complete strain recovery behavior is exhibited by all the alloys studied in this paper, even those with a Zr content of 20 at%. Stability of the NiTi-Zr alloys during thermal cycling was also tested and results indicate that the NiTi-Zr alloys have poor stability against thermal cycling. The reasons for the deterioration of the shape memory effect and stability have yet to be determined.

  12. An approach to developing a force field for molecular simulation of martensitic phase transitions between phases with subtle differences in energy and structure.

    PubMed

    Tuble, Sigrid C; Anwar, Jamshed; Gale, Julian D

    2004-01-14

    d,l-Norleucine is one of only a few molecules whose crystals exhibit a martensitic or displacive-type phase transformation where the emerging phase shows a topotaxial relationship with the parent phase. The molecular mechanism for such phase transformations, particularly in molecular crystals, is not well understood. Crystalline phases that exhibit displacive phase transitions tend to be very similar in structure and energy. Consequently, the development of a force field for such phases is challenging as the phase behavior is determined by subtle differences in their lattice energies and entropies. We report an approach for developing a force field for such phases with an application to d,l-norleucine. The proposed procedure includes calculation of the phase diagram of the crystalline phases as a function of temperature to identify the best force field. d,l-Norleucine also presents an additional problem since in the solid state it exists as a zwitterion that is unstable in vacuo and therefore cannot be characterized using high-level ab initio calculations in the gas phase. However, a stable zwitterion could be obtained using Onsager's reaction-field continuum model for a solvent (SCRF) using both Hartree-Fock and density functional theory. A number of force fields and the various sets of partial charges obtained from the SCRF calculations were screened for their ability to reproduce the crystal structures of the two known phases, alpha and beta, of d,l-norleucine. Selected parameter sets were then employed in free energy minimizations to identify the best set on the basis of a correct prediction of the alpha-beta phase transition. The Williams' nonbonded parameters combined with partial charges from SCRF-Polarized Continuum Model calculation were found to reproduce the structures of the phases accurately and also maintained their stability in extended molecular dynamics simulations in the Parrinello-Rahman constant stress ensemble. Moreover, we were also able to

  13. Phase transformation analysis of varied nickel-titanium orthodontic wires.

    PubMed

    Ren, Chao-chao; Bai, Yu-xing; Wang, Hong-mei; Zheng, Yu-feng; Li, Song

    2008-10-20

    The shape memory effect of nickel-titanium (NiTi) archwires is largely determined by the phase transition temperature. It is associated with a reversible transformation from martensite to austenite. The aim of this study was to characterize austenite, martensite and R phase temperatures as well as transition temperature ranges of the commonly used clinical NiTi orthodontic arch wires selected from several manufacturers. Differential scanning calorimetry (DSC) method was used to study the phase transformation temperatures and the phase transition processes of 9 commonly used clinical NiTi alloys (types: 0.40 mm (0.016 inch), 0.40 mm x 0.56 mm (0.016 inch x 0.022 inch)). The austenite finish temperatures (Af) of 0.40 mm Smart, Ormco and 3M NiTi wires were lower than the room temperature, and no phase transformation was detected during oral temperature. Therefore, we predicted that these types of NiTi did not possess shape memory property. For 0.40 mm and 0.40 mm x 0.56 mm Youyan I NiTi wires, no phase transformation was detected during the scanning temperature range, suggesting that these two types of wires did not possess shape memory either. The Af of 0.40 mm x 0.56 mm Smart, L&H, Youyan II Ni-Ti wires were close to the oral temperature and presented as martensitic-austenitic structures at room temperature, suggesting the NiTi wires listed above have good shape memory effect. Although the 0.40 mm x 0.56 mm Damon CuNiTi wire showed martensitic-austenitic structures at oral temperature, its Af was much higher than the oral temperature. It means that transformation from martensite to austenite for this type of NiTi only finishes when oral temperature is above normal. The phase transformation temperatures and transformation behavior varied among different commonly used NiTi orthodontic arch wires, leading to variability in shape memory effect.

  14. Magnetostrain and magnetocaloric effect by field-induced reverse martensitic transformation for Pd-doped Ni45Co5Mn37In13 Heusler alloy

    NASA Astrophysics Data System (ADS)

    Li, Z.; Xu, K.; Yang, H. M.; Zhang, Y. L.; Jing, C.

    2015-06-01

    In the present work, polycrystalline Ni45Co5-xPdxMn37In13 (x = 0, 0.5, 1, and 3) Heusler alloys were prepared. The influences of Pd substitution for Co on crystal structure, martensitic transformation (MT), and magnetic properties have been carefully investigated for these quinary alloys. The structure measurement indicates that every sample possesses L10 martensitic structure at room temperature. With increasing of Pd content, it is found that the MT region shifts towards higher temperature, but the Curie transition region of austenitic state moves to lower temperature. Owing to the fact that the MT gradually approaches Curie point, the magnetization of austenitic phase is significantly decreased, while the one of martensitic phase almost remains unchanged. In addition, the functional properties associated with the field-induced reverse MT have been also studied in Ni45Co5-xPdxMn37In13 (x = 0, 0.5, and 1) alloys. In comparison to quaternary parent alloy, both of enhanced magnetostrain (0.3%) and isothermal entropy change (25 J/kg K) are observed in quinary Ni45Co4.5Pd0.5Mn37In13 alloy under an applied magnetic field up to 3 T. The implication of such results has been discussed in detail.

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

    SciTech Connect

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

    2005-08-01

    Zr{sub 48.5}Cu{sub 46.5}Al{sub 5} bulk metallic glass matrix composites with diameters of 3 and 4 mm 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 Zr{sub 2}Cu and plate-like Cu{sub 10}Zr{sub 7} 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. 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.

  17. 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

  18. Aspects of thermal martensite in a FeNiMnCo alloy.

    PubMed

    Güler, M; Güler, E; Kahveci, N

    2010-07-01

    Thermal martensite characteristics in Fe-29%Ni-2%Mn-2%Co alloy were investigated with scanning electron microscopy (SEM) and Mössbauer spectroscopy characterization techniques. SEM observations obviously revealed the lath martensite morphology in the prior austenite phase of examined alloy. As well, the martensitic transformation kinetics was found to be as athermal type. On the other hand, Mössbauer spectroscopy offered the paramagnetic austenite phase and ferromagnetic martensite phase with their volume fractions. Also, the internal magnetic field of the martensite was measured as 32.9T from the Mössbauer spectrometer.

  19. 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.

  20. Principles of Phase Transformations

    DTIC Science & Technology

    1945-05-12

    weight per cent. Thereafter the lattice changes to a cubic structure with the same car- bon content (0.2fo) as the prior slightly tetragonal...exists below which the stable structure is tetragonal, above which the cubic structure is stable. When the car- bon content is 0,8 weight per cent, this...tetragonallty Is gradually lost upon aging at room temperature, is rapidly lost upon heating to^lOO0^ the martensite acquiring a cubic structure . Two

  1. Lattice instability and martensitic transformation in LaAg predicted from first-principles theory.

    PubMed

    Vaitheeswaran, G; Kanchana, V; Zhang, Xinxin; Ma, Yanming; Svane, A; Kaul, S N

    2012-02-22

    The electronic structure, elastic constants and lattice dynamics of the B(2) type intermetallic compound LaAg are studied by means of density functional theory calculations with the generalized gradient approximation for exchange and correlation. The calculated equilibrium properties and elastic constants agree well with available experimental data. From the ratio between the bulk and shear moduli, LaAg is found to be ductile, which is unusual for B(2) type intermetallics. The computed band structure shows a dominant contribution from La 5d states near the Fermi level. The phonon dispersion relations, calculated using density functional perturbation theory, are in good agreement with available inelastic neutron scattering data. Under pressure, the phonon dispersions develop imaginary frequencies, starting at around 2.3 GPa, in good accordance with the martensitic instability observed above 3.4 GPa. By structural optimization the high pressure phase is identified as orthorhombic B(19).

  2. Effect of annealing on the martensitic transformation and magnetocaloric effect in Ni44.1Mn44.2Sn11.7 ribbons

    NASA Astrophysics Data System (ADS)

    Xuan, H. C.; Xie, K. X.; Wang, D. H.; Han, Z. D.; Zhang, C. L.; Gu, B. X.; Du, Y. W.

    2008-06-01

    The Ni44.1Mn44.2Sn11.7 ribbons were prepared by melt spinning. A single-phase austenite with L21 structure was confirmed in the melt-spun ribbons at room temperature. After the heat treatment, the martensitic transformation temperature increases obviously in the annealed ribbons. This method may be an effective way to tune the characteristic temperatures in the ferromagnetic shape memory alloys. Giant magnetic entropy changes are observed in the annealed ribbons. The peak values at 10kOe are 32.1 and 20.1J /kgK, for the ribbons annealed at 1123 and 1173K, respectively.

  3. 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.

  4. Atomistically Informed Extended Gibbs Energy Description for Phase-Field Simulation of Tempering of Martensitic Steel

    PubMed Central

    Shchyglo, Oleg; Hammerschmidt, Thomas; Čak, Miroslav; Drautz, Ralf; Steinbach, Ingo

    2016-01-01

    In this study we propose a unified multi-scale chemo-mechanical description of the BCT (Body-Centered Tetragonal) to BCC (Body-Centered Cubic) order-disorder transition in martensitic steel by adding the mechanical degrees of freedom to the standard CALPHAD (CALculation of PHAse Diagrams) type Gibbs energy description. The model takes into account external strain, the effect of carbon composition on the lattice parameter and elastic moduli. The carbon composition effect on the lattice parameters and elastic constants is described by a sublattice model with properties obtained from DFT (Density Functional Theory) calculations; the temperature dependence of the elasticity parameters is estimated from available experimental data. This formalism is crucial for studying the kinetics of martensite tempering in realistic microstructures. The obtained extended Gibbs energy description opens the way to phase-field simulations of tempering of martensitic steel comprising microstructure evolution, carbon diffusion and lattice symmetry change due to the ordering/disordering of carbon atoms under multiaxial load. PMID:28773790

  5. PHASE TRANSFORMATIONS IN METALS AND ALLOYS (SELECTED ARTICLES),

    DTIC Science & Technology

    Contents: Stabilization of reverse martensite transformation under the influence of intraphase work hardening; and Structural changes during decomposition of supersaturated solid solution of tungsten in cobalt.

  6. 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.

  7. 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.

  8. 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

  9. Stress-induced martensitic transformation of a NiTi alloy in isothermal shear, tension and compression

    SciTech Connect

    Orgeas, L.; Favier, D.

    1998-09-18

    The thermomechanical behavior of stress-induced martensitic transformation in an equiatomic NiTi alloy was investigated with respect to different deformation modes including uniaxial tension, compression and shear of plate specimens at different temperatures above the M{sub s} temperature. Results showed that loading conditions have significant influences on the deformation behavior of the alloy. In particular, deformation behavior was observed to be asymmetric in tension and in compression. The physical origins of such an asymmetry ar explored. Comparison among the results obtained from the tension, compression and shear tests disproves the use of classical Von Mises equivalent in the modelling of the three-dimensional behavior of martensitic transformation in this alloy. Based on this analysis, another criterion for yielding, which involves the third stress invariant, is therefore suggested.

  10. Characterization of the martensitic transformation in melt-spun NiMnGa ribbons by magnetoinductive effect

    NASA Astrophysics Data System (ADS)

    Pérez-Landazábal, J. I.; Gomez-Polo, C.; Recarte, V.; Seguí, C.; Cesari, E.; Ochin, P.

    2005-04-01

    The magnetoinductance effect, in particular, the temperature dependence of the AC complex impedance, Z(T), has been employed in the characterization of the martensitic transformation (MT) in a melt-spun Ni 52.5Mn 24.5Ga 23 ribbon. While the resistive component shows the characteristic decrease associated with the martensite-to-austenite transformation, the inductive component reflects the temperature dependence of the magnetic permeability of the sample. These structural and magnetic changes associated with the characteristic MT were experimentally checked by differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The results indicate that the AC impedance technique can be employed as a very simple and versatile characterization technique in the analysis of MT in magnetic memory shape alloys.

  11. 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.

  12. Cyclic Martensitic Transformations Influence on the Diffusion Of Carbon Atoms in Fe-18 wt.%Mn-2 wt.%Si alloy

    NASA Astrophysics Data System (ADS)

    Danilchenko, Vitaliy E.; Filatov, Alexander V.; Mazanko, Vladimir F.; Iakovlev, Viktor E.

    2017-03-01

    A significant carbon diffusion mobility acceleration as a result of cyclic γ↔ɛ martensitic transformations in iron-manganese alloy is determined by one- and two-dimensional structure defects of ɛ-martensite with face-centered close-packed lattice. Such defects (dislocations, low angle sub-boundaries of dislocations, chaotic stacking faults) were formed during cyclic γ↔ɛ martensitic transformations. Peak carbon diffusion coefficient increase was observed under thermocycling when maximum quantity of lattice defects increase was fixed.

  13. Surface modification, martensitic transformation, and optical properties of hydrogenated ZrO2 nanocondensates via pulsed laser ablation in water

    NASA Astrophysics Data System (ADS)

    Wu, Chao-Hsien; Huang, Chang-Ning; Shen, Pouyan; Chen, Shuei-Yuan

    2011-12-01

    Pulsed laser ablation on Zr plate in water under Q-switch mode and a fluence of 700 and 800 mJ/pulse for a rather high power density of 1.5 and 1.7 × 1011 W/cm2, respectively, was employed to fabricate hydrogenated ZrO2 nanocondensates. X-ray diffraction and transmission electron microscopic observations indicated such nanocondensates are full of {111} and {100} facets and predominantly in monoclinic (m-) rather than cubic- and/or tetragonal (t-) crystal symmetry in particular when fabricated at 700 mJ/pulse. The hydrogenated ZrO2 nanocondensates underwent martensitic t → m transformation at a rather small critical size (ca. 20 nm) due to H+ signature and hence oxygen vacancy deficiency in the lattice. The resultant m-phase was free of twin and fault due to site saturation and rather limited growth of the nanosized particles. Spectroscopic characterizations indicated that the nanocondensates have a significant internal compressive stress, (H+, Zr2+, Zr3+) co-signature and hence a smaller band gap of 5.2-5.3 eV for potential applications in UV region.

  14. In-situ high-energy X-ray diffraction investigation on stress-induced martensitic transformation in Ti-Nb binary alloys

    SciTech Connect

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

    2016-01-10

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

  15. 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.

  16. Chemically Induced Phase Transformation in Austenite by Focused Ion Beam

    NASA Astrophysics Data System (ADS)

    Basa, Adina; Thaulow, Christian; Barnoush, Afrooz

    2013-11-01

    A highly stable austenite phase in a super duplex stainless steel was subjected to a combination of different gallium ion doses at different acceleration voltages. It was shown that contrary to what is expected, an austenite to ferrite phase transformation occurred within the focused ion beam (FIB) milled regions. Chemical analysis of the FIB milled region proved that the gallium implantation preceded the FIB milling. High resolution electron backscatter diffraction analysis also showed that the phase transformation was not followed by the typical shear and plastic deformation expected from the martensitic transformation. On the basis of these observations, it was concluded that the change in the chemical composition of the austenite and the local increase in gallium, which is a ferrite stabilizer, results in the local selective transformation of austenite to ferrite.

  17. Influence of Ti additions on martensitic transformation and magnetic properties of cast Ni51Fe22-xGa27Tix shape memory alloys

    NASA Astrophysics Data System (ADS)

    El-Bagoury, Nader; Mohsen, Q.; Kaseem, M. A.; Hessien, M. M.

    2013-09-01

    The effect of Ti addition on the microstructure, martensitic transformation, magnetic and mechanical properties of polycrystalline Ni51Fe22- x Ga27Ti x ( x=0, 2 and 4) ferromagnetic shape memory alloy was investigated by scanning electron microscope, differential scanning calorimetry and X-ray diffraction. The results showed that the martensitic transformation temperature increases monotonously with the increase of fraction of Ti substitution for Fe. The increase in the martensite transformation temperatures should be related to the change of the electron concentration after the addition of Ti to Ni51Fe22- x Ga27Ti x alloys. According to the results of X-ray diffraction and magnetic properties, Ti has significant effect the structure of Ni51Fe22- x Ga27Ti x . Adding of 4 at% Ti altered the structure of the matrix from five-layered tetragonal martensite of Ni51Fe22Ga27 and Ni51Fe20Ga27Ti2 alloys to non-modulated tetragonal martensite. Magnetic properties proved that the alloy transits from ferromagnetic, five-layered tetragonal martensite, to paramagnetic, non-modulated martensite structure, with increasing Ti content to 4 at.%. Saturation magnetization, remnant magnetization and coercivity of the alloy were significantly influenced by Ti additions. Hardness values of Ni51Fe22Ga27 increased by the addition of Ti.

  18. Enhanced reversibility and unusual microstructure of a phase-transforming material.

    PubMed

    Song, Yintao; Chen, Xian; Dabade, Vivekanand; Shield, Thomas W; James, Richard D

    2013-10-03

    Materials undergoing reversible solid-to-solid martensitic phase transformations are desirable for applications in medical sensors and actuators, eco-friendly refrigerators and energy conversion devices. The ability to pass back and forth through the phase transformation many times without degradation of properties (termed 'reversibility') is critical for these applications. Materials tuned to satisfy a certain geometric compatibility condition have been shown to exhibit high reversibility, measured by low hysteresis and small migration of transformation temperature under cycling. Recently, stronger compatibility conditions called the 'cofactor conditions' have been proposed theoretically to achieve even better reversibility. Here we report the enhanced reversibility and unusual microstructure of the first martensitic material, Zn45Au30Cu25, that closely satisfies the cofactor conditions. We observe four striking properties of this material. (1) Despite a transformation strain of 8%, the transformation temperature shifts less than 0.5 °C after more than 16,000 thermal cycles. For comparison, the transformation temperature of the ubiquitous NiTi alloy shifts up to 20 °C in the first 20 cycles. (2) The hysteresis remains approximately 2 °C during this cycling. For comparison, the hysteresis of the NiTi alloy is up to 70 °C (refs 9, 12). (3) The alloy exhibits an unusual riverine microstructure of martensite not seen in other martensites. (4) Unlike that of typical polycrystal martensites, its microstructure changes drastically in consecutive transformation cycles, whereas macroscopic properties such as transformation temperature and latent heat are nearly reproducible. These results promise a concrete strategy for seeking ultra-reliable martensitic materials.

  19. Thermoelastic martensitic transformations, mechanical properties, and shape-memory effects in rapidly quenched Ni45Ti32Hf18Cu5 alloy in the ultrafine-grained state

    NASA Astrophysics Data System (ADS)

    Pushin, V. G.; Pushin, A. V.; Kuranova, N. N.; Kuntsevich, T. E.; Uksusnikov, A. N.; Dyakina, V. P.; Kourov, N. I.

    2016-12-01

    Methods of transmission and scanning electron microscopy and chemical microanalysis, electron diffraction, and X-ray diffraction were used to study the structure and the chemical and phase composition of ribbons of the four-component quasi-binary alloy Ni45Ti32Hf18Cu5. The influence of the synthesis regimes and subsequent heat treatment of the alloy on the formation of the amorphized state and ultrafine-grained structure has been determined. The critical temperatures of the devitrification and of the B2 ↔ B19' thermoelastic martensitic transformation have been established based on the data of the temperature dependences of the electrical resistivity. The lattice parameters of the B2 and B19' phases and the (Ti,Hf)2Ni phase have been determined by X-ray diffraction. The mechanical properties of the alloy were determined in tensile tests, and the shape-memory effects in the ribbons of the alloy were measured using bending tests.

  20. 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.

  1. 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.

  2. Energy Barriers and Hysteresis in Martensitic Phase Transformations

    DTIC Science & Technology

    2008-08-01

    I) ∂F2 (Gλ,Gλ) + ω(|λGλ|)|Gλ|2 ] Jλdt1dt2 (93) Since Gλ is bounded uniformly in L2(Ω`) and ω(|λGλ|)→ 0 uniformly, then the error term can be...small hysteresis width. Nature Materials 5 (2006), 286-290. [9] E. De Giorgi and T. Franzoni, Su un tipo di convergenza variazionale. Atti Accad. Naz

  3. 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.

  4. On the Driving Forces of Magnetically Induced Martensitic Transformation in Directionally Solidified Polycrystalline Ni-Mn-In Meta-Magnetic Shape Memory Alloy with Structural Anisotropy

    NASA Astrophysics Data System (ADS)

    Hu, Qiaodan; Zhou, Zhenni; Yang, Liang; Huang, Yujin; Li, Jun; Li, Jianguo

    2017-08-01

    The magnetic anisotropy energy (MAE) in the ferromagnetic shape memory alloys (FSMAs) provides the driving forces to obtain large magnetic field induced strain (MFIS) by rearranging the martensitic variants. However, to date, no significant MAE was observed in the new class of Ni-Mn-Z (Z = In, Sn, Sb) metamagnetic shape memory alloys (MSMAs). Here, we report a significant magnetic anisotropy in Ni48Mn35In17 Heusler alloy with a [110]A fiber texture prepared by the directional solidification. In this case, when the applied magnetic field is along the [110]A direction, a larger magnetization change is obtained compared with that of the randomly oriented samples, which increases the driving forces for the magnetically induced martensitic transformation (MIMT). In contrast, along the [110]A direction, the magnetocaloric effect (MCE) is enhanced by 60 pct, the MFIS is improved by 20 pct, and the critical field for the MFIS is reduced by 0.5 T. Such a peculiar magnetic behavior could be well explained by a proposed model on the viewpoint of the transformation of ferromagnetic austenite phase. Furthermore, considering the thermodynamics aspects, we demonstrate that two main magnetic energies of the Zeeman energy and the MAE in the MSMAs assist each other to promote the MIMT, instead of opposing each other in the FSMAs. This discovery of the strong magnetic anisotropy in highly textured polycrystals provides a feasible route to enhance the MIMT, and new insights to design and prepare the Ni-Mn-based Heusler alloys for practical applications.

  5. On phase transformation behavior of porous Shape Memory Alloys.

    PubMed

    Liu, Bingfei; Dui, Guansuo; Zhu, Yuping

    2012-01-01

    This paper is concerned on the phase transformation mechanism of porous Shape Memory Alloys (SMAs). A unit-cell model is adopted to establish the constitutive relation for porous SMAs, the stress distributions, the phase distributions and the martensitic volume fractions for the model are then derived under both pure hydrostatic stress and uniaxial compression. Further, an example for the uniaxial response under compression for a porous Ni-Ti SMA material considering hydrostatic stress is supplied. Good agreement between the theoretical prediction of the proposed model and published experimental data is observed. Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.

  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.

  7. Effect of austenite on mechanical properties in high manganese austenitic stainless steel with two phase of martensite and austenite

    NASA Astrophysics Data System (ADS)

    Kim, Y. H.; Kim, J. H.; Hwang, T. H.; Lee, J. Y.; Kang, C. Y.

    2015-05-01

    The effect of the austenite phase on mechanical properties of austenitic stainless steels was investigated using specimens with different volume fractions of retained and reversed austenite. Stainless steels with dual-phase coexisting martensite and austenite were successfully synthesized by deformation and reverse transformation treatment in the cold-rolled high manganese austenitic stainless steel and the ultrafine reverse austenite with less than 0.5 µm in size was formed by reverse transformation treatment in the temperature range of 500-750 °C for various times. With the increase of deformation degree, the volume fraction of retained austenite decreased, while that of the reversed austenite increased as the annealing time increased. From the results of the mechanical properties, it was obvious that as the volume fraction of retained and reversed austenite increased, hardness and strength rapidly decreased, while elongation increased. With regard to each austenite, reversed austenite indicated higher value of hardness and strength, while elongation suggested a lower value because of strengthening owing to grain refinement.

  8. 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.

  9. Martensitic transformation B2-R in Ni-Ti-Fe: experimental determination of the Landau potential and quantum saturation of the order parameter.

    PubMed

    Salje, Ekhard K H; Zhang, Huali; Planes, Antoni; Moya, Xavier

    2008-07-09

    The Landau potential of the martensitic phase transformation in Ni(46.8)Ti(50)Fe(3.2) was determined using high resolution x-ray diffraction to measure the spontaneous strain and calorimetric measurements to determine the excess specific heat of the R phase. The spontaneous strain is proportional to the square of the order parameter which is tested by the relation of the excess entropy and the order parameter. The parameters of the Landau free energy were determined by fitting the temperature evolution of the order parameter and using the scaling between the excess entropy and the order parameter. The double well potential at absolute zero temperature was calculated and the interface energy and domain wall thickness were estimated.

  10. 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

  11. 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

    2016-04-06

    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.

  12. Effect of martensitic transformation on magnetoelectric properties of Ni2MnGa/PbZr0.52Ti0.48O3 composite

    NASA Astrophysics Data System (ADS)

    Zhao, K.; Chen, K.; Dai, Y. R.; Wan, J. G.; Zhu, J. S.

    2005-10-01

    The magnetoelectric (ME) coefficient was measured as a function of temperature, from room temperature to 100°C, in a bilayer composite of Ni2MnGa/PbZr0.52Ti0.48O3. A distinct peak of the ME coefficient was observed near the martensitic transformation temperature of the Ni2MnGa alloy. The effect of martensitic transition on the ME coefficient and the multiferroic properties were discussed.

  13. Study of martensitic-ferritic dual phase steels produced by hot stamping

    NASA Astrophysics Data System (ADS)

    Erişir, E.; Bilir, O. G.

    2017-02-01

    The effects of heat treatment and initial microstructure on tensile properties of 22MnB5 and 30MnB5 high-strength hot stamping steels with martensite-ferrite matrix were investigated. Hot stamping steels possessed limited elongations of about 5% in a tensile strength ranging from 1300 to 1500 MPa when quenched at temperatures above A3 temperatures. The total elongations were tried to improve by partial austenization between Ac1 and Ac3 temperature and quenching. Ac1 and Ac3 temperatures were calculated via ThermoCalc. Microstructural characterization was made by using Light Microscope and Scanning Electron Microscope. Microstructure is composed of ferrite+martensite. It was seen that annealing temperature affects the volume fraction of phases. It was concluded that initial microstructure is an important parameter for the final microstructure. This method can be used for automobile parts which require higher TE with sufficient yield and tensile strength. Also this process may be a way of using Zn coated steel sheets in hot stamping process.

  14. Internal friction associated with the structural phase transformations in Ni-Mn-Ga alloys

    SciTech Connect

    Cesari, E.; Pons, J.; Segui, C.; Chernenko, V.A.; Kokorin, V.V.

    1997-03-01

    A double peak in the temperature dependence of internal friction (IF) and elastic modulus in some off-stoichiometric Ni{sub 2}MnGa shape memory alloys has been observed both on cooling and heating between the parent and martensite phases. Transmission electron microscopy (TEM) observations have shown that these anomalies are related to structural transformations from the parent cubic phase (P) to an intermediate cubic modulated phase (I) and from the I phase to the martensitic one (M). As for the IF results, the I to M transformation has the characteristics of a first-order phase transition, whereas the P to I transformation shows some distinctive features, such as no temperature-rate dependence.

  15. Interfacial Modulus Mapping during Structural Transformation in Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Wan, Jianfeng; Cui, Shushan; Zhang, Jihua; Rong, Yonghua

    2017-10-01

    Through the modified phase-field model the local soft mode mechanism of nucleation during martensitic transformation was confirmed in shape memory alloys. It was discovered that the modulus loss (8 pct) depended on the martensitic nucleation exceeding the loss (1 pct) during the martensitic growth. The elastic modulus and the stress across the martensite/parent interface differed from those across the martensitic twin boundary. The modulus losses in systems with three variants, two variants, and one variant were compared.

  16. Adaptive modulations of martensites.

    PubMed

    Kaufmann, S; Rössler, U K; Heczko, O; Wuttig, M; Buschbeck, J; Schultz, L; Fähler, S

    2010-04-09

    Modulated phases occur in numerous functional materials like giant ferroelectrics and magnetic shape-memory alloys. To understand the origin of these phases, we employ and generalize the concept of adaptive martensite. As a starting point, we investigate the coexistence of austenite, adaptive 14M phase, and tetragonal martensite in Ni-Mn-Ga magnetic shape-memory alloy epitaxial films. We show that the modulated martensite can be constructed from nanotwinned variants of the tetragonal martensite phase. By combining the concept of adaptive martensite with branching of twin variants, we can explain key features of modulated phases from a microscopic view. This includes metastability, the sequence of 6M-10M-14M-NM intermartensitic transitions, and the magnetocrystalline anisotropy.

  17. 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.

  18. Interplay between diffusive and displacive phase transformations: time-temperature-transformation diagrams and microstructures.

    PubMed

    Bouville, Mathieu; Ahluwalia, Rajeev

    2006-08-04

    Materials which can undergo extremely fast displacive transformations as well as very slow diffusive transformations are studied using a Ginzburg-Landau framework. This simple model captures the essential physics behind microstructure formation and time-temperature-transformation diagrams in alloys such as steels. It also predicts the formation of mixed microstructures by an interplay between diffusive and displacive mechanisms. The intrinsic volume changes associated with the transformations stabilize mixed microstructures such as martensite-retained austenite (responsible for the existence of a martensite finish temperature) and martensite-pearlite.

  19. 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.

  20. In-situ investigation of stress-induced martensitic transformation in Ti–Nb binary alloys with low Young's modulus [In-situ high-energy X-ray diffraction investigation on stress-induced martensitic transformation in Ti-Nb binary alloys

    SciTech Connect

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

    2015-11-04

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

  1. In-situ investigation of stress-induced martensitic transformation in Ti–Nb binary alloys with low Young's modulus [In-situ high-energy X-ray diffraction investigation on stress-induced martensitic transformation in Ti-Nb binary alloys

    DOE PAGES

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

    2015-11-04

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

  2. Validation and Analysis of the Parameters for Reconstructing the Austenite Phase from Martensite Electron Backscatter Diffraction Data

    NASA Astrophysics Data System (ADS)

    Sanz, L.; Pereda, B.; López, B.

    2017-08-01

    This work focuses on the validation of a method for reconstructing the fcc crystallographic data from martensite orientation electron backscatter diffraction (EBSD) maps based on the "γ nuclei identification" and "γ nuclei spreading strategy." To that end, an Fe-30Ni alloy was employed. The martensite transformation start temperature (M s ) of this material is close to or below room temperature; therefore, during hot deformation and after water quenching, it presents an fcc austenitic microstructure, while after subzero quenching, austenite-to-martensite transformation takes place. Accordingly, the reconstruction procedure can be applied to the martensitic EBSD crystallographic data, and the morphological and orientation results of the reconstruction can be validated by comparison with the original crystallographic fcc data. Torsion tests were performed to produce recrystallized and deformed austenite microstructures. Although applying the Kurdjumov-Sachs orientation relationship (OR) resulted in reconstructed area fractions larger than 75 pct, the reconstruction quality improved significantly when other ORs closer to the Greninger-Troiano OR were applied. The analysis carried out on the recrystallized microstructure shows that the method is robust against variation in the different parameters involved in the reconstruction. Good angular and morphological reconstruction results were obtained in both recrystallized and deformed microstructures, including the ability to reconstruct twins.

  3. Neodymium-rich precipitate phases in a high-chromium ferritic/martensitic steel

    NASA Astrophysics Data System (ADS)

    Shen, Yinzhong; Zhou, Xiaoling; Shang, Zhongxia

    2016-05-01

    Neodymium being considered as nitride forming element has been used in a design of advanced ferritic/martensitic (FM) steels for fossil fired power plants at service temperatures of 630 °C to 650 °C to effectively improve the creep strength of the steels. To fully understand the characteristics of neodymium precipitates in high-Cr FM steels, precipitate phases in an 11Cr FM steel with 0.03 wt% addition of Nd have been investigated by transmission electron microscopy. Three neodymium phases with a face-centered cubic crystal structure and different composition were observed in the steel. They consisted of neodymium carbonitride with an average lattice parameter of 1.0836 nm, Nd-rich carbonitride mainly containing Mn, and Nd-rich MN nitride mainly containing Mn and Co. Other three Nd-rich and Nd-containing phases, which appear to be Nd-Co-Cr/Nd-rich intermetallic compounds and Cr-Fe-rich nitride containing Nd, were also detected in the steel. Nd-relevant precipitates were found to be minor phases compared with M23C6 and Nb/V/Ta-rich MX phases in the steel. The content of Nd in other precipitate phases was very low. Most of added Nd is considered to be present as solid solution in the matrix of the steel.

  4. 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.

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

    PubMed

    Danilchenko, Vitaliy E; Mazanko, Vladimir F; Iakovlev, Viktor E

    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.

  6. 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

  7. Effect of Quenching and Partitioning with Hot Stamping on Martensite Transformation and Mechanical Properties of AHSS

    NASA Astrophysics Data System (ADS)

    Chang, Ying; Li, Guanzhong; Wang, Cunyu; Li, Xiaodong; Dong, Han

    2015-08-01

    Two-step quenching and partitioning treatment with hot stamping was applied to advanced high-strength steel (AHSS). The newly treated steel possesses a fine microstructure and typically curved micromorphology. The martensite start temperature of the newly treated steel is increased through the effect of plastic deformation on austenitic microstructure. However, the martensite volume fraction of this steel is deceased because of the enhanced stability of the untransformed austenite after plastic deformation. Consequently, the fraction of retained austenite is increased. The newly treated steel also shows excellent mechanical properties. The volume fraction of retained austenite reaches the highest value of 17.2% when hot stamping is performed at 750 °C. Hence, the steel displays favorable plasticity with an elongation of 14.5%. Moreover, the highest hardness value of 426 HV is obtained when hot stamping is performed at 650 °C. The newly developed process may be employed to develop a new generation of AHSSs.

  8. 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

  9. Effects of interstitial impurities on the high pressure martensitic α to ω structural transformation and grain growth in zirconium.

    PubMed

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

    2011-03-30

    Static high pressure diamond anvil cell experiments were performed on three polycrystalline Zr samples having varying interstitial impurity concentrations. Systematic increase in transition pressure with the increase in the amount of interstitial impurities is observed for the martensitic α →ω structural phase transition in Zr. Significant room temperature crystal grain growth is also observed for the two highest purity samples at the α →ω transition. In the case of the lowest purity sample interstitial impurities obstruct the α →ω transition, while possibly helping impede grain growth-even as the sample is heated to 1279 K.

  10. 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.

    PubMed

    González, Sergio; Pérez, Pablo; Rossinyol, Emma; Suriñach, Santiago; Dolors Baró, Maria; 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.

  11. Anisotropic kinetics of solid phase transition from first principles: alpha-omega phase transformation of Zr.

    PubMed

    Guan, Shu-Hui; Liu, Zhi-Pan

    2016-02-14

    Structural inhomogeneity is ubiquitous in solid crystals and plays critical roles in phase nucleation and propagation. Here, we develop a heterogeneous solid-solid phase transition theory for predicting the prevailing heterophase junctions, the metastable states governing microstructure evolution in solids. Using this theory and first-principles pathway sampling simulation, we determine two types of heterophase junctions pertaining to metal α-ω phase transition at different pressures and predict the reversibility of transformation only at low pressures, i.e. below 7 GPa. The low-pressure transformation is dominated by displacive Martensitic mechanism, while the high-pressure one is controlled by the reconstructive mechanism. The mechanism of α-ω phase transition is thus highly pressure-sensitive, for which the traditional homogeneous model fails to explain the experimental observations. The results provide the first atomic-level evidence on the coexistence of two different solid phase transition mechanisms in one system.

  12. 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.

  13. 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

    2015-10-19

    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. 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).

  14. 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).

  15. 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

  16. Phase transformation in tantalum under extreme laser deformation

    DOE PAGES

    Lu, C. -H.; Hahn, E. N.; Remington, B. 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

  17. Phase Transformation in Tantalum under Extreme Laser Deformation

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    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).

  18. Metastability of the martensitic transformation in a 12 mol% ceria-zirconia alloy; II, grinding studies

    SciTech Connect

    Swain, M.V.; Hannink, R.H.J. . Div. of Materials Science and Technology)

    1989-08-01

    Observations of the grinding-induced transformation in single-phase Ce-TZP materials, referred to in an earlier paper, are presented. Two techniques were used to grind the surface: by hand in a slurry of abrasive particles and with a high-speed diamond-impregnated wheel. Significant differences in X-ray diffraction profiles between the two grinding methods were observed. Limited monoclinic ZrO/sub 2/ was detected on the machine-ground surface, along with the reversal of the tetragonal ZrO/sub 2/ (200) peak intensities. On the hand-ground surface, considerable monoclinic phase was observed. Transmission electron microscope studies at various depths below the ground surface were undertaken to identify the differences between these surfaces and fractured surfaces. A simple explanation is proposed for the reversal of the tetragonal peak intensities.

  19. Influence of the microstructure on the resulting 18R martensitic transformation of polycrystalline Cu−Al−Zn thin films obtained by sputtering and reactive annealing

    SciTech Connect

    Domenichini, P.; Condó, A.M.; Soldera, F.; Sirena, M.; Haberkorn, N.

    2016-04-15

    We report the influence of the microstructure on the martensitic transformation in polycrystalline Cu−Zn−Al thin films with 18R structure. The films are grown in two steps. First, Cu−Al thin films are obtained by DC sputtering. Second, the Zn is introduced in the Cu−Al thin films by the annealing them together with a bulk Cu−Zn−Al reference. The crystalline structure of the films was analyzed by X-ray diffraction and transmission electron microscopy. The martensitic transformation temperature was measured by electrical transport using conventional four probe geometry. It was observed that temperatures above 973 K are necessary for zincification of the samples to occur. The resulting martensitic transformation and its hysteresis (barrier for the transformation) depend on the grain size, topology and films thickness. - Highlights: • Polycrystalline Cu−Al−Zn thin films with nanometric grain size are sintered. • Influence of thermal annealing process on the microstructure is analyzed. • Martensitic transformation of Cu−Al−Zn thin films is strongly affected by the microstructure.

  20. 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.

  1. Numerical simulation of martensitic transformations in magnetic transition-metal alloys

    NASA Astrophysics Data System (ADS)

    Entel, P.; Kadau, K.; Meyer, R.; Herper, H. C.; Acet, M.; Wassermann, E. F.

    1998-01-01

    We have performed molecular-dynamics (MD) simulations of martensitic nucleation processes in iron-based transition-metal alloys. In order to handle a sufficiently large number of atoms in the simulation process, use has been made of the embedded-atom method (EAM). Results for structural transition temperatures, superelastic behavior as well as tendential-shape memory effects compare qualitatively well with experimental results. Results are also compared with a zero-temperature stability analysis on the basis of full-potential band-structure calculations.

  2. Crystallization and phase transformations in amorphous NiTi thin films for microelectromechanical systems

    SciTech Connect

    Lee, Hoo-Jeong; Ramirez, Ainissa G.

    2004-08-16

    Amorphous sputtered nickel-titanium thin films were deposited onto micromachined silicon-nitride membranes and subjected to heating and cooling conditions. Their associated microstructure was monitored directly and simultaneously with in situ transmission electron microscopy. These electron-transparent membranes constrained the NiTi films and rendered it possible for observation of the complete transformation cycle, which includes: the crystallization of the amorphous phase to austenite phase (cubic B2 structure) with heating; and the conversion of austenite (B2) to martensite (monoclinic B19{sup '} structure) with cooling. Electron micrographs show the nucleation and growth of grains occurs at a temperature of 470 deg. C and at a rate that indicates a polymorphic transformation. The onset of martensitic transformation occurs between 25 and 35 deg. C. Calorimetric measurements are consistent with the observed crystallization.

  3. A new Framework for the Interpretation of Modulated Martensites in Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Jusuf, Vincent

    Shape memory alloys (SMAs) are a class of materials with unusual properties that have been attributed to the material undergoing a martensitic phase transformation (MPT). An MPT consists of the material's crystal structure evolving in a coordinated fashion from a high symmetry austenite phase to a low symmetry martensite phase. Often in SMAs, the austenite is a B2 cubic configuration that transforms into a Modulated Martensite (MM) phase. MMs are long-period stacking order structures consisting of cubic (110) basal planes. First-principles computational results have shown that the minimum energy phase for these materials is not a MM, but a short-period structure called the ground state martensite. It is commonly argued that energy contributions associated with kinematic compatibility constraints at the austenite-martensite interface explain the experimental observation of meta-stable MMs, as opposed to the expected ground state martensite phase. To date, a general approach for predicting the properties of the MM structure that will be observed for a particular material has not been available. In this work, we develop a new framework for the interpretation of MMs as natural features of the material's energy landscape (expressed as a function of the lattice parameters and individual atomic positions within a perfect infinite crystal). From this energy-based framework, a new understanding of MMs as a mixture of two short-period base martensite phases is developed. Using only a small set of input data associated with the two base martensites, this Modulated Martensite Mixture Model is capable of accurately predicting the energy, lattice constants, and structural details of an arbitrary modulated martensite phase. This is demonstrated by comparing the Modulated Martensite Mixture Model predictions to computational results from a particular empirical atomistic model.

  4. Vibrational and magnetic contributions to the entropy change associated with the martensitic transformation of Ni-Fe-Ga ferromagnetic shape memory alloys.

    PubMed

    Recarte, V; Pérez-Landazábal, J I; Gómez-Polo, C; Sánchez-Alarcos, V; Cesari, E; Pons, J

    2010-10-20

    Ferromagnetic shape memory alloys undergo a martensitic transformation accompanied by a change in the magnetic and vibrational properties. However, these property changes are not independent. In this paper, the interplay between magnetic and vibrational properties in the martensitic transformation entropy change has been analyzed for Ni-Fe-Ga ferromagnetic shape memory alloys. The martensitic transformation entropy change has a magnetic and a vibrational contribution, ΔS(p−>m)=ΔS(vib)(p−>m) + ΔS(mag)(p−>m). Using a mean field approximation for the magnetic entropy, the full entropy ΔS(p−>m) has been decomposed and the magnetic contribution ΔS(mag)(p−>m) calculated. Upon removing the magnetic term, the vibrational entropy ΔS(vib)(p−>m) does not change substantially in the composition range where T(M) is below T(C). This latter contribution to the martensitic transformation entropy change has been analyzed using a Debye distribution for the density of states and a proportion of Einstein modes that account for the anomalous phonon mode of the austenite.

  5. Fatigue properties of a metastable beta-type titanium alloy with reversible phase transformation.

    PubMed

    Li, S J; Cui, T C; Hao, Y L; Yang, R

    2008-03-01

    Due to recent concern about allergic and toxic effects of Ni ions released from TiNi alloy into human body, much attention has been focused on the development of new Ni-free, metastable beta-type biomedical titanium alloys with a reversible phase transformation between the beta phase and the alpha'' martensite. This study investigates the effect of the stress-induced alpha'' martensite on the mechanical and fatigue properties of Ti-24Nb-4Zr-7.6Sn (wt.%) alloy. The results show that the as-forged alloy has a low dynamic Young's modulus of 55GPa and a recoverable tensile strain of approximately 3%. Compared with Ti-6Al-4V ELI, the studied alloy has quite a high low-cycle fatigue strength because of the effective suppression of microplastic deformation by the reversible martensitic transformation. Due to the low critical stress required to induce the martensitic transformation, it has low fatigue endurance comparable to that of Ti-6Al-4V ELI. Cold rolling produces a beta+alpha'' two-phase microstructure that is characterized by regions of nano-size beta grains interspersed with coarse grains containing alpha'' martensite plates. Cold rolling increases fatigue endurance by approximately 50% while decreasing the Young's modulus to 49GPa along the rolling direction but increasing it to 68GPa along the transverse direction. Due to the effective suppression of the brittle isothermal omega phase, balanced properties of high strength, low Young's modulus and good ductility can be achieved through ageing treatment at intermediate temperature.

  6. 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.

  7. Phase transformation and its effect on mechanical characteristics in warm-deformed Ti-29Nb-13Ta-4.6Zr alloy

    NASA Astrophysics Data System (ADS)

    Lee, Taekyung; Nakai, Masaaki; Niinomi, Mitsuo; Park, Chan Hee; Lee, Chong Soo

    2015-01-01

    Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy has been extensively studied as it is promising for use in biomedical applications. Despite its potential, the effects of warm plastic deformation on the alloy have not yet been revealed. This study investigated the differences in phase constitution of two warm-deformed TNTZ alloys and revealed relevant mechanisms with particular attention to martensitic transformation. The influence of phase constituents on mechanical characteristics was discussed as well. The TNTZ alloy deformed at 823 K possessed α, β, and ω phases as well as α″ martensite, and demonstrated a low Young's modulus and double-yielding phenomenon. In contrast, the alloy deformed at 723 K had no martensite but more ω phase, leading to increased strength, hardness, and Young's modulus. The absence of α″ martensite in the alloy deformed at 723 K was interpreted in light of β-stability of the parent phase and reduced M s temperature.

  8. Microstructure and mechanical properties of dual phase steels, with different martensite morphology, produced during TLP bonding of a low C-Mn steel

    NASA Astrophysics Data System (ADS)

    Fazaeli, Abolfazl; Ekrami, Aliakbar; Kokabi, Amir Hossein

    2016-09-01

    In this research, production of ferrite - martensite dual phase Steels with different martensite morphology was considered during transient liquid phase bonding of a low carbon steel. The steel was bonded using an iron base interlayer with melting point of 1443 K and 40 μm thickness. Bonding process carried out at 1473 K, under pressure of 0.5 MPa, at different holding time of 10, 20, 30 and 40 minutes. Microstructural studies of joint region showed that isothermal solidification completed at the bonding time of 40 minutes. Microstructure of joints made at the bonding time of 10, 20, and 30 minutes consists of two distinct region, athermal and isothermal solidified zones. Microstructure of these zones was studied and chemical composition of these zones was determined by EDS. Joints made with bonding time of 40 minutes were homogenized at 1008 K and then cooled into cold water to produce dual phase ferrite and martensite microstructure with different martensite morphology. According to shear test results, it was found that the shear strength of ferrite - fibrous martensite microstructure is greater than those with ferrite - continuous martensite and ferrite - blocky martensite microstructure.

  9. Modeling thermally induced martensitic transformations in nickel titanium shape memory alloys

    NASA Astrophysics Data System (ADS)

    Jaeger, Stefanie; Eggeler, Gunther; Kastner, Oliver

    2015-05-01

    During stress-free thermal analysis with differential scanning calorimetry (DSC), nickel titanium (NiTi) shape memory alloys show a thermal hysteresis which is affected by cooling/heating rates. Moreover, the Ni content of near equiatomic alloys governs the phase transition temperatures. This contribution aims at establishing a constitutive equation which can account for these effects, building on earlier work by Müller, Achenbach and Seelecke (MAS). To be specific, we discuss our new method with a focus on NiTi alloys. As in the original MAS model, our approach is rooted in a non-convex free energy representation and rate equations are utilized to incorporate history dependence during non-equilibrium processes. The relaxation times of these rate equations are determined by characteristic transformation probabilities which in turn are governed by the free energy landscape of our system. We show how the model can be parameterized to rationalize experimental DSC data observed for NiTi samples of variable composition and measured at variable cooling/heating rates. The good agreement between model predictions and experimental results suggests that thermal hystereses are not only related to interfacial strain energy effects but also affected by the transient character of the transformation process incorporating specific thermal relaxation times. Our analysis shows that we observe strong hysteretic effects when the cooling/heating rates exceed these characteristic relaxation rates.

  10. 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.

  11. 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.

  12. 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.

  13. Phase transformation changes in thermocycled nickel-titanium orthodontic wires.

    PubMed

    Berzins, David W; Roberts, Howard W

    2010-07-01

    In the oral environment, orthodontic wires will be subject to thermal fluctuations. The purpose of this study was to investigate the effect of thermocycling on nickel-titanium (NiTi) wire phase transformations. Straight segments from single 27 and 35 degrees C copper NiTi (Ormco), Sentalloy (GAC), and Nitinol Heat Activated (3M Unitek) archwires were sectioned into 5mm segments (n=20). A control group consisted of five randomly selected non-thermocycled segments. The remaining segments were thermocycled between 5 and 55 degrees C with five randomly selected segments analyzed with differential scanning calorimetry (DSC; -100<-->150 degrees C at 10 degrees C/min) after 1000, 5000, and 10,000 cycles. Thermal peaks were evaluated with results analyzed via ANOVA (alpha=0.05). Nitinol HA and Sentalloy did not demonstrate qualitative or quantitative phase transformation behavior differences. Significant differences were observed in some of the copper NiTi transformation temperatures, as well as the heating enthalpy with the 27 degrees C copper NiTi wires (p<0.05). Qualitatively, with increased thermocycling the extent of R-phase in the heating peaks decreased in the 35 degrees C copper NiTi, and an austenite to martensite peak shoulder developed during cooling in the 27 degrees C copper NiTi. Repeated temperature fluctuations may contribute to qualitative and quantitative phase transformation changes in some NiTi wires. Copyright 2010 Academy of Dental Materials. All rights reserved.

  14. Mechanism of the gamma-beta phase transformation of Mg2SiO4 at high temperature and pressure

    NASA Technical Reports Server (NTRS)

    Rubie, D. C.; Brearley, A. J.

    1990-01-01

    The results of experiments on the phase transformation of Mg2SiO4 olivine at 15 GPa pressure in a multianvil cell are reported. At this pressure and a temperature of 900 C, early formed metastable gamma-spinel transforms partially to the beta-phase. The observed microstructures, which are similar to those in shocked meteorites, show that the gamma-to-beta transformation can occur either by diffusion-controlled growth or by a martensitic mechanism, depending on how far the pressure-temperature conditions deviate from their values at phase equilibrium. The results suggest that the diffusion-controlled mechanism is most likely to operate at the beta/gamma phase boundary in the mantle, but martensitic beta-to-gamma transformation might occur in subduction zones and could reduce the shear strength of the subducting slab.

  15. 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.

  16. Effect of uni- and biaxial strain on phase transformations in Fe thin films

    NASA Astrophysics Data System (ADS)

    Sak-Saracino, Emilia; Urbassek, Herbert M.

    2016-01-01

    Using molecular-dynamics simulation, we study the phase transformations in Fe thin films induced by uni- and biaxial strain. Both the austenitic transformation of a body-centered cubic (bcc) film at the equilibrium temperature of the face-centered cubic (fcc)-bcc transformation and the martensitic transformation of an undercooled fcc film are studied. We demonstrate that different strain states (uni- or biaxial) induce different nucleation kinetics of the new phase and hence different microstructures evolve. For the case of the austenitic transformation, the direction of the applied strain selects the orientation of the nucleated grains of the new phase; the application of biaxial strain leads to a symmetric twinned structure. For the martensitic transformation, the influence of the strain state is even more pronounced, in that it can either inhibit the transformation, induce the homogeneous nucleation of a fine-dispersed array of the new phase resulting in a single-crystalline final state, or lead to the more conventional mechanism of heterogeneous nucleation of grains at the free surfaces, which grow and result in a poly-crystalline microstructure of the transformed material.

  17. 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.

  18. 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.

  19. 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

    2016-05-17

    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.

  20. 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

  1. 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.

  2. Strain-rate-induced bcc-to-hcp phase transformation of Fe nanowires

    NASA Astrophysics Data System (ADS)

    Xie, Hongxian; Yu, Tao; Fang, Wei; Yin, Fuxing; Faraz Khan, Dil

    2016-12-01

    Using molecular dynamics simulation method, the plastic deformation mechanism of Fe nanowires is studied by applying uniaxial tension along the [110] direction. The simulation result shows that the bcc-to-hcp martensitic phase transformation mechanism controls the plastic deformation of the nanowires at high strain rate or low temperature; however, the plastic deformation mechanism will transform into a dislocation nucleation mechanism at low strain rate and higher temperature. Furthermore, the underlying cause of why the bcc-to-hcp martensitic phase transition mechanism is related to high strain rate and low temperature is also carefully studied. Based on the present study, a strain rate-temperature plastic deformation map for Fe nanowires has been proposed. Project supported by the National Natural Science Foundation of China (Grant No. 51571082) and China Postdoctoral Science Foundation (Grant No. 2015M580191).

  3. Large magnetoresistance in single-crystalline Ni50Mn50-xInx alloys (x=14-16) upon martensitic transformation

    NASA Astrophysics Data System (ADS)

    Yu, S. Y.; Liu, Z. H.; Liu, G. D.; Chen, J. L.; Cao, Z. X.; Wu, G. H.; Zhang, B.; Zhang, X. X.

    2006-10-01

    Variation of electrical resistance in single-crystalline Ni50Mn50-xInx alloys (x=14-16) upon martensitic transformation was investigated. In Ni50Mn35In15 with Tm˜295K, a negative magnetoresistance (MR) over 60% is attainable at moderate field strengths; in Ni50Mn34In16 with Tm˜190K, the MR can exceed 70% over a temperature of approximately 100K. The significant change in electric resistance upon martensitic transformation originates primarily from the altered electronic structure, while the large effect of a magnetic field follows its ability to manipulate the transformation in materials of low Tm and large ΔM /ΔS. The extremely large MR promises more innovative applications for these important alloys.

  4. Superstrength of nanograined steel with nanoscale intermetallic precipitates transformed from shock-compressed martensitic steel

    NASA Astrophysics Data System (ADS)

    Yu, Hailiang; Yan, Ming; Lu, Cheng; Tieu, Anh Kiet; Li, Huijun; Zhu, Qiang; Godbole, Ajit; Li, Jintao; Su, Lihong; Kong, Charlie

    2016-11-01

    An increasing number of industrial applications need superstrength steels. It is known that refined grains and nanoscale precipitates can increase strength. The hardest martensitic steel reported to date is C0.8 steel, whose nanohardness can reach 11.9 GPa through incremental interstitial solid solution strengthening. Here we report a nanograined (NG) steel dispersed with nanoscale precipitates which has an extraordinarily high hardness of 19.1 GPa. The NG steel (shock-compressed Armox 500T steel) was obtained under these conditions: high strain rate of 1.2 μs-1, high temperature rise rate of 600 Kμs-1 and high pressure of 17 GPa. The mean grain size achieved was 39 nm and reinforcing precipitates were indexed in the NG steel. The strength of the NG steel is expected to be ~3950 MPa. The discovery of the NG steel offers a general pathway for designing new advanced steel materials with exceptional hardness and excellent strength.

  5. Superstrength of nanograined steel with nanoscale intermetallic precipitates transformed from shock-compressed martensitic steel

    PubMed Central

    Yu, Hailiang; Yan, Ming; Lu, Cheng; Tieu, Anh Kiet; Li, Huijun; Zhu, Qiang; Godbole, Ajit; Li, Jintao; Su, Lihong; Kong, Charlie

    2016-01-01

    An increasing number of industrial applications need superstrength steels. It is known that refined grains and nanoscale precipitates can increase strength. The hardest martensitic steel reported to date is C0.8 steel, whose nanohardness can reach 11.9 GPa through incremental interstitial solid solution strengthening. Here we report a nanograined (NG) steel dispersed with nanoscale precipitates which has an extraordinarily high hardness of 19.1 GPa. The NG steel (shock-compressed Armox 500T steel) was obtained under these conditions: high strain rate of 1.2 μs−1, high temperature rise rate of 600 Kμs−1 and high pressure of 17 GPa. The mean grain size achieved was 39 nm and reinforcing precipitates were indexed in the NG steel. The strength of the NG steel is expected to be ~3950 MPa. The discovery of the NG steel offers a general pathway for designing new advanced steel materials with exceptional hardness and excellent strength. PMID:27892460

  6. 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%).

  7. Ion-irradiation-assisted tuning of phase transformations and physical properties in single crystalline Fe7Pd3 ferromagnetic shape memory alloy thin films

    NASA Astrophysics Data System (ADS)

    Arabi-Hashemi, A.; Witte, R.; Lotnyk, A.; Brand, R. A.; Setzer, A.; Esquinazi, P.; Hahn, H.; Averback, R. S.; Mayr, S. G.

    2015-05-01

    Control of multi-martensite phase transformations and physical properties constitute greatly unresolved challenges in Fe7Pd3-based ferromagnetic shape memory alloys. Single crystalline Fe7Pd3 thin films reveal an austenite to martensite phase transformation, continuously ranging from the face-centered cubic (fcc) to the face-centered tetragonal (fct) and body-centered cubic (bcc) phases upon irradiation with 1.8 MeV Kr+ ions. Within the present contribution, we explore this scenario within a comprehensive experimental study: employing atomic force microscopy (AFM) and high resolution transmission electron microscopy (HR-TEM), we first clarify the crystallography of the ion-irradiation-induced austenite \\Rightarrow martensite and inter-martensite transitions, explore the multi-variant martensite structures with c-a twinning and unravel a very gradual transition between variants at twin boundaries. Accompanying magnetic properties, addressed locally and globally, are characterized by an increasing saturation magnetization from fcc to bcc, while coercivity and remanence are demonstrated to be governed by magnetocrystalline anisotropy and ion-irradiation-induced defect density, respectively. Based on reversibility of ion-irradiation-induced materials changes due to annealing treatment and a conversion electron Mößbauer spectroscopy (CEMS) study to address changes in order, a quantitative defect-based physical picture of ion-irradiation-induced austenite ⇔ martensite transformation in Fe7Pd3 is developed. The presented concepts thus pave the way for ion-irradiation-assisted optimization strategies for tailored functional alloys.

  8. The role of coherent precipitates in martensitic transformations in single crystal and polycrystalline Ti-50.8at%Ni

    SciTech Connect

    Gall, K.; Sehitoglu, H.; Karaman, I.; Chumlyakov, Y.I.; Zuev, Y.L.

    1998-08-11

    In the mid 80`s Miyazaki and colleagues discovered that there was a significant difference in the recoverable strain levels of solutionized versus aged NiTi single crystals. More recent research efforts have focused on understanding both thermal and stress-induced martensitic transformations in solutionized versus aged NiTi. Several researchers have determined that only a specific range of heat treatments (for example T {approximately} 673--773 K, t {approximately} 1--1.5 h for 50.8 at% Ni) are capable of precipitating coherent or semi-coherent particles in NiTi. Heat treatments that fall into the aforementioned range will be referred to as peak aging treatments since they lead to a drastic change in mechanical properties. The modeling of recoverable strain levels in peak aged samples has proven consistent with experimental observations. The purpose of the present study is to model the orientation dependence of the critical stress levels required to induce the transformation in peak aged specimens.

  9. A micromechanics constitutive model for pure dilatant martensitic transformation of ZrO2-containing ceramics

    NASA Astrophysics Data System (ADS)

    Qingping, Sun; Shouwen, Yu; Kehchih, Hwang

    1990-05-01

    A new micromechanics constitutive model for pure dilatant transformation plasticity of structure ceramics is proposed in this paper. Based on the thermodynamics, micromechanics and microscale t→m transformation mechanism analysis of the TZP and PSZ ZrO2-containing ceramics, an analytic expressions of the Helmholtz and complementary free energy of the constitutive element for the case of pure dilatant transformation is derived for the first time in a self-consistent manner. By the analysis of energy dissipation in the forward and reverse transformations, the micromechanics constitutive law is derived in the framework of Hill-Rice's internal variable constitutive theory.

  10. A scanning Hall probe imaging study of the field induced martensite-austenite phase transition in Ni50Mn34In16 alloy.

    PubMed

    Sharma, V K; Moore, J D; Chattopadhyay, M K; Morrison, Kelly; Cohen, L F; Roy, S B

    2010-01-13

    The martensite to austenite phase transition in the off-stoichiometric Heusler alloy Ni(50)Mn(34)In(16) can be induced both by temperature change and by application of a magnetic field. We have used scanning Hall probe imaging to study the magnetic field induced martensite-austenite phase transition. The study provides clear visual evidence of the coexistence of the martensite and austenite phases across this field induced transition in both increasing and decreasing magnetic fields. Clear evidence of thermomagnetic history effects associated with the martensite-austenite phase transition is also obtained. Quantitative analysis of the magnetic field dependence of the volume fraction of the austenite phase in Ni(50)Mn(34)In(16) shows evidence of a nucleation and growth mechanism across the field induced martensite-austenite phase transition. The local M-H loops constructed from the Hall images indicate the presence of a landscape of the critical magnetic field (for the field induced transition) distributed over the sample volume and thus confirm the disorder influenced nature of this first-order magnetic phase transition.

  11. A study of stress-induced phase transformation and micromechanical behavior of CuZr-based alloy by in-situ neutron diffraction

    DOE PAGES

    Wang, Dongmei; Mu, Juan; Chen, Yan; ...

    2017-03-01

    The stress-induced phase transformation and micromechanical behavior of CuZr-based alloy were investigated by in-situ neutron diffraction. The pseudoelastic behavior with a pronounced strain-hardening effect is observed. The retained martensite nuclei and the residual stress obtained from the 1st cycle reduce the stress threshold for the martensitic transformation. A critical stress level is required for the reverse martensitic transformation from martensite to B2 phase. An increase of intensity for the B2 (110) plane in the 1st cycle is caused by the twinning along the {112}<111> twinning system. The convoluted stress partitioning influenced by the elastic and transformation anisotropy along with themore » newly formed martensite determines the microstress partitioning of the studied CuZr-based alloy. The reversible martensitic transformation is responsible for the pseudoelasticity. The macro mechanical behavior of the pure B2 phase can be divided into 3 stages, which are mediated by the evolvement of the martensitic transformation. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).« less

  12. 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.

  13. Two internal-friction peaks related to thermoelastic martensitic transformations in CuAlNiMnTi shape-memory alloy

    SciTech Connect

    Gong, C.L.; Han, F.S.; Li, Z.; Wang, M.P.

    2004-09-01

    A partial phase transition method was used in internal friction measurements to study the motion of phase interface in martensitic transition of CuAlNiMnTi polycrystalline shape memory alloy. It is found that the IF peak arisen from the reversible martensitic transition is in fact composed of two independent IF peaks that relate to different motion modes of the interface. The low-temperature peak corresponds to the minimum of relative dynamic modulus and is attributed to an elastic modulus softening effect caused by the viscous motion of the phase interface. The high-temperature peak corresponds to the inflection point of the relative dynamic modulus and the volume change produced by the normal motion of the phase interface is responsible for the peak.

  14. Reversible Characteristics and Cycling Effects of the ɛ ↔ γ Martensitic Transformations in Fe-Mn-Cr Twip/Trip Steels

    NASA Astrophysics Data System (ADS)

    Mertinger, V.; Benke, M.; Nagy, E.; Pataki, T.

    2014-07-01

    The variation of thermal characteristics of the ɛ ↔ γ transformation during thermal cycling and the effect of Cr content was studied in two Fe-Mn-Cr steels through cyclic DSC examinations. It was found that the martensite start temperature decreased and the austenite start temperature increased in the first cycles, then both stabilized after several cycles. The latent heat of the transformations increased first and then also stabilized. The Cr content pushed the ɛ ↔ γ transformations to lower temperatures, decreased the thermal hysteresis and the latent heat. It is experimentally shown that 6.53 m/m% Cr content increases the stacking fault energy in this alloy.

  15. 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.

  16. Effect of warm rolling on the martensite transformation temperatures, shape memory effect, and superelasticity in Ti49.2Ni50.8 alloy

    NASA Astrophysics Data System (ADS)

    Lotkov, Aleksander; Zhapova, Dorzhima; Grishkov, Victor; Cherniavsky, Alexander; Timkin, Victor

    2016-11-01

    The paper presents research data demonstrating the effect of warm caliber rolling on the martensite transformation temperatures, shape memory effect, and superelasticity in Ti49.2Ni50.8 (at %). The experimental values of inelastic strain in coarse-grained and microcrystalline Ti49.2Ni50.8 (at %) specimens exceed the theoretical limit of recoverable strain or maximum lattice strain for TiNi-based alloys.

  17. 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.

  18. Correlation of martensitic transformation temperatures of Ni- Mn-Ga/Al-X alloys to non-bonding electron concentration

    NASA Astrophysics Data System (ADS)

    Ramudu, M.; Satish Kumar, A.; Seshubai, V.; Rajasekharan, T.

    2015-02-01

    The martensitic transformation TM of the alloys of Ni-Mn-Ga and Ni-Mn-Al show a general trend of increase with electron per atom ratio (e/a) calculated from the total number of electrons outside the rare gas shell of the atoms. However prediction of TM fails among iron substituted Ni-Mn-Ga alloys and those with In doped for Ga, due to the absence of a useful trend. A scheme of computing modified electron concentration is presented considering only the non-bonding electrons per atom Ne/a of the compounds, based on Pauling's ideas on the electronic structure of metallic elements. Systematic variation of TM with Ne/a is reproduced for a large number of alloys of Ni-Mn-Ga and the anomaly observed for Fe containing alloys with e/a disappears. The non-bonding electron concentration is thus demonstrated to be effective in predicting TM of shape memory alloys of Ni-Mn-Ga-X system including the isoelectronic compounds of Ni-Mn-Ga-In.

  19. The influence of aging on critical transformation stress levels and martensite start temperatures in NiTi. Part 2: Discussion of experimental results

    SciTech Connect

    Gall, K.; Sehitoglu, H.; Chumlyakov, Y.I.; Kireeva, I.V.; Maier, H.J.

    1999-01-01

    An experimental study was performed to determine the effect of aging on martensitic transformations in NiTi. Polycrystalline and single crystal NiTi ([100], [110], and [111] orientations) were both considered. Stress-induced transformations in single crystals of the [110] and [111] orientations. Solutionized and over-aged single crystals exhibited a strong orientation dependence of the critical stress required to trigger the transformation, {sigma}{sub cr}. The Schmid law was able to accurately predict the orientation dependence of {sigma}{sub cr} in the solutionized and over-aged single crystals. Peak-aged single crystals demonstrated a much weaker orientation dependence of {sigma}{sub cr} and in general, the Schmid law was not obeyed. By considering the local stress fields outside of the semi-coherent precipitates, the decrease in the orientation dependence of {sigma}{sub cr} was accounted for. The martensite start temperatures, M{sub s}, in aged single crystal and polycrystalline NiTi were much higher than in solutionized samples. In peak-aged NiTi the increase was primarily attributed to the local stress fields outside the coherent precipitates which create preferential nucleation sites for the martensite. In the over-aged NiTi the increase in M{sub s} was primarily attributed to the decrease in the average Ni concentration of the matrix surrounding the coarsened precipitates.

  20. 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).

  1. 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

  2. Elastic model of a dislocation center for martensite nucleation

    SciTech Connect

    Vereshchagin, V.P.; Kashchenko, M.P.

    1995-01-01

    The possibility of spontaneous nucleation of a crystal of new phase when the original structure is metastable is usually connected with the catalyzing effect of defects playing the role of nucleation centers. In the case of the {gamma}{r_arrow}{alpha} martensite transformation in iron alloys, even individual dislocations can act as such defects, based on analysis of long-range elastic fields of isolated linear dislocations in a linearly elastic anisotropic continuum, the authors established the existence of a correlation between the geometric characteristics of the elastically deformed state in the vicinity of 60-degree and 30-degree dislocations and the structure and morphological characteristics of {alpha}-martensite observed in massive iron alloy samples. These results suggest that the dislocation affects the pathway of the martensite reaction and allows the authors to say that the specific characteristics of heterogeneous nucleation of new phase for the martensite mechanism of the {gamma}{r_arrow}{alpha} transformation involves singling out a single structural rearrangement variant which is suitable from the standpoint of adapation of the transforming lattice to the characteristic features of the elastically deformed state created by the dislocation. The possibilities for such adaption are limited by the crystallography of the transformation and the reactions of the surrounding austenite occurring when regular connections exist with the morphological characteristics of the martensite crystal, and are not necessarily compatible with the individual features of the elastic field of each dislocation. Considering this, the authors can introduce the concept of a dislocation center for nucleation of a martensite crystal about the region of the dislocation where conditions are realized which are favorable for the formation of a nucleus of martensite crystal of a certain shape and orientation, and they can develop an elastic model corresponding to this concept.

  3. 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

  4. Martensite stabilization in Ni{sub 50}Ti{sub 32.2}Hf{sub 17.7}

    SciTech Connect

    Santamarta, R.; Segui, C.; Pons, J.; Cesari, E.

    1999-09-10

    Thermal martensite stabilization, that is, the transient shift of the reverse transformation temperatures either after direct quench to martensite from parent phase, or after ageing in the martensitic state, has been studied for many years in Cu-based alloys, and mechanisms to explain this phenomenon as well as thermomechanical treatments to avoid it have been proposed. In this paper, results on martensite aging behavior in a Ni-Ti-Hf melt-spun ribbon are reported, confirming the occurrence of the above mentioned possibility of thermal stabilization in the Ni-Ti alloy system.

  5. 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

    PubMed Central

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

    2014-01-01

    The microstructure and mechanical properties of Zr48Cu48 − xAl4Mx (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. PMID:27877691

  6. ELASTIC AND ANELASTIC BEHAVIOR DURING THE MARTENSITIC TRANSFORMATION IN INDIUM-THALLIUM ALLOYS,

    DTIC Science & Technology

    originate from the stress-assisted motion of twin boundaries that are known to spontaneously coalesce immediately below the transformation temperature...proposed for this relaxation, invoking an interaction between twin boundaries and solute, whereby reordering of solute is effected in differently orientated tetragonal regions by twin-boundary motion. (Author)

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

    SciTech Connect

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

    2016-05-15

    The effect of substrates on the magnetic and transport properties of Ni{sub 2}Mn{sub 1.5}In{sub 0.5} 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 Ni{sub 2}Mn{sub 1.5}In{sub 0.5} 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 Ni{sub 2}Mn{sub 1.5}In{sub 0.5} 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.

  8. Self-accommodation of crystals of martensitic phases in titanium and zirconium based alloys

    NASA Astrophysics Data System (ADS)

    Khundzhua, A. G.; Ptitsyn, A. G.; Brovkina, E. A.; Chzhen, S.

    2012-11-01

    The orientation relationships between austenite and α' and α″ martensite lattices in titanium and zirconium alloys is performed in view of the possibility of the formation of self-accommodating complexes, which is an important component of the shape memory effect. Different diffraction patterns calculated for various matrices of the orientation relationship were compared with the experimental patterns for Ti45Zr45Nb10 alloy using a formula developed for the optimal expression of the orientation relationship for α″. The generalization and analysis of the literature data for titanium- and zirconium-based solid solutions performed using the developed algorithm lead us to conclusions regarding the tendency of α' martensite in titanium-based solid solutions to self-accommodate, which occurred more strongly than that in zirconium-based alloys, and the best results in shape memory realization should be expected in Ti-Ta and Ti-Nb systems. Possible reasons for the absence of the shape memory effect for α' martensite in titanium- and zirconium-based alloys, with regard to the necessary crystallographic conditions for the formation of self-accommodating processes are analyzed.

  9. Length scale effects and multiscale modeling of thermally induced phase transformation kinetics in NiTi SMA

    NASA Astrophysics Data System (ADS)

    Frantziskonis, George N.; Gur, Sourav

    2017-06-01

    Thermally induced phase transformation in NiTi shape memory alloys (SMAs) shows strong size and shape, collectively termed length scale effects, at the nano to micrometer scales, and that has important implications for the design and use of devices and structures at such scales. This paper, based on a recently developed multiscale model that utilizes molecular dynamics (MDs) simulations at small scales and MD-verified phase field (PhF) simulations at larger scales, reports results on specific length scale effects, i.e. length scale effects in martensite phase fraction (MPF) evolution, transformation temperatures (martensite and austenite start and finish) and in the thermally cyclic transformation between austenitic and martensitic phase. The multiscale study identifies saturation points for length scale effects and studies, for the first time, the length scale effect on the kinetics (i.e. developed internal strains) in the B19‧ phase during phase transformation. The major part of the work addresses small scale single crystals in specific orientations. However, the multiscale method is used in a unique and novel way to indirectly study length scale and grain size effects on evolution kinetics in polycrystalline NiTi, and to compare the simulation results to experiments. The interplay of the grain size and the length scale effect on the thermally induced MPF evolution is also shown in this present study. Finally, the multiscale coupling results are employed to improve phenomenological material models for NiTi SMA.

  10. Microstructures and martensitic transformation behavior of superelastic Ti-Ni-Ag scaffolds

    SciTech Connect

    Li, Shuanglei; Kim, Eun-soo; Kim, Yeon-wook; Nam, Tae-hyun

    2016-10-15

    Highlights: • The B2-R-B19′ transformation occurred in 49Ti-50.3Ni-0.7Ag alloy fibers. • Annealing treated alloy fibers showed superelastic recovery ratio of 93%. • Ageing treated scaffold had an elastic modulus of 0.67 GPa. • Ageing treated scaffold exhibited good superelasticity at human body temperature. - Abstract: Ti-Ni-Ag scaffolds were prepared by sintering rapidly solidified alloy fibers. Microstructures and transformation behaviors of alloy fibers and scaffolds were investigated by means of electron probe micro-analyzer (EPMA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The B2-R-B19′ transformation occurs in alloy fibers. The alloy fibers have good superelasticity with superelastic recovery ratio of 93% after annealing heat treatment. The as-sintered Ti-Ni-Ag scaffolds possess three-dimensional and interconnected pores and have the porosity level of 80%. The heat treated Ti-Ni-Ag scaffolds not only have an elastic modulus of 0.67 GPa, which match well with that of cancellous bone, but also show excellent superelasticity at human body temperature. In terms of the mechanical properties, the Ti-Ni-Ag scaffolds in this study can meet the main requirements of bone scaffold for the purpose of bone replacement applications.

  11. Phase Transformations and Microstructural Evolution: Part II

    SciTech Connect

    Clarke, Amy Jean

    2015-10-30

    The activities of the Phase Transformations Committee of the Materials Processing & Manufacturing Division (MPMD) of The Minerals, Metals & Materials Society (TMS) are oriented toward understanding the fundamental aspects of phase transformations. Emphasis is placed on the thermodynamic driving forces for phase transformations, the kinetics of nucleation and growth, interfacial structures and energies, transformation crystallography, surface reliefs, and, above all, the atomic mechanisms of phase transformations. Phase transformations and microstructural evolution are directly linked to materials processing, properties, and performance. In this issue, aspects of liquid–solid and solid-state phase transformations and microstructural evolution are highlighted. Many papers in this issue are highlighted by this paper, giving a brief summary of what they bring to the scientific community.

  12. Phase Transformations and Microstructural Evolution: Part I

    SciTech Connect

    Clarke, Amy Jean

    2015-08-29

    The activities of the Phase Transformations Committee of the Materials Processing & Manufacturing Division (MPMD) of The Minerals, Metals & Materials Society (TMS) are oriented toward understanding the fundamental aspects of phase transformations. Emphasis is placed on the thermodynamic driving forces for phase transformations, the kinetics of nucleation and growth, interfacial structures and energies, transformation crystallography, surface reliefs, and, above all, the atomic mechanisms of phase transformations. Phase transformations and microstructural evolution are directly linked to materials processing, properties, and performance, including in extreme environments, of structural metal alloys. In this paper, aspects of phase transformations and microstructural evolution are highlighted from the atomic to the microscopic scale for ferrous and non-ferrous alloys. Many papers from this issue are highlighted with small summaries of their scientific achievements given.

  13. Phase Transformations and Microstructural Evolution: Part II

    DOE PAGES

    Clarke, Amy Jean

    2015-10-30

    The activities of the Phase Transformations Committee of the Materials Processing & Manufacturing Division (MPMD) of The Minerals, Metals & Materials Society (TMS) are oriented toward understanding the fundamental aspects of phase transformations. Emphasis is placed on the thermodynamic driving forces for phase transformations, the kinetics of nucleation and growth, interfacial structures and energies, transformation crystallography, surface reliefs, and, above all, the atomic mechanisms of phase transformations. Phase transformations and microstructural evolution are directly linked to materials processing, properties, and performance. In this issue, aspects of liquid–solid and solid-state phase transformations and microstructural evolution are highlighted. Many papers in thismore » issue are highlighted by this paper, giving a brief summary of what they bring to the scientific community.« less

  14. Phase Transformations and Microstructural Evolution: Part I

    DOE PAGES

    Clarke, Amy Jean

    2015-08-29

    The activities of the Phase Transformations Committee of the Materials Processing & Manufacturing Division (MPMD) of The Minerals, Metals & Materials Society (TMS) are oriented toward understanding the fundamental aspects of phase transformations. Emphasis is placed on the thermodynamic driving forces for phase transformations, the kinetics of nucleation and growth, interfacial structures and energies, transformation crystallography, surface reliefs, and, above all, the atomic mechanisms of phase transformations. Phase transformations and microstructural evolution are directly linked to materials processing, properties, and performance, including in extreme environments, of structural metal alloys. In this paper, aspects of phase transformations and microstructural evolution aremore » highlighted from the atomic to the microscopic scale for ferrous and non-ferrous alloys. Many papers from this issue are highlighted with small summaries of their scientific achievements given.« less

  15. Elastic-like deformation and elastocaloric effect of a partly ordered iron-platinum alloy exhibiting a weak first-order martensitic transformation

    NASA Astrophysics Data System (ADS)

    Fukuda, Takashi; Kakeshita, Tomoyuki

    2017-10-01

    We have studied the temperature dependencies of elastic-like deformation and the elastocaloric effect in an L12-type Fe3Pt alloy with degree of order S  =  0.75, which exhibits a weak first-order martensitic transformation (MT) near 85 K (T M). The stress–strain curve under a compressive stress applied in the [0 0 1] direction shows a small stage in the vicinity of T M due to the stress-induced MT. The transformation strain is 0.17% at T M; it decreases linearly as temperature decreases and disappears at 130 K. Thereseems to be a critical point of the MT in the stress–temperature phase diagram at (20 MPa, 130 K). The latent heat of the MT is estimated to be 0.52 J mol‑1 from the Clausius–Clapeyron equation. The adiabatic temperature change ΔT adi caused by the latent heat is 0.04 K at 90 K. In contrast, experimentally obtained ΔT is approximately 1 K at 90 K when the applied stress is 100 MPa. The main contribution to ΔT is the temperature dependence of elastic strain caused by softening; the Young’s modulus at 288 K is 55 GPa and it decreases linearly with a slope of 0.28 GPa K‑1 as temperature decreases.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Tensile Residual Stress Mitigation Using Low Temperature Phase Transformation Filler Wire in Welded Armor Plates

    SciTech Connect

    Feng, Zhili; Bunn, Jeffrey R; Tzelepis, Demetrios A; Payzant, E Andrew; Yu, Xinghua

    2016-01-01

    Hydrogen induced cracking (HIC) has been a persistent issue in welding of high-strength steels. Mitigating residual stresses is one of the most efficient ways to control HIC. The current study develops a proactive in-process weld residual stress mitigation technique, which manipulates the thermal expansion and contraction sequence in the weldments during welding process. When the steel weld is cooled after welding, martensitic transformation will occur at a temperature below 400 C. Volume expansion in the weld due to the martensitic transformation will reduce tensile stresses in the weld and heat affected zone and in some cases produce compressive residual stresses in the weld. Based on this concept, a customized filler wire which undergoes a martensitic phase transformation during cooling was developed. The new filler wire shows significant improvement in terms of reducing the tendency of HIC in high strength steels. Bulk residual stress mapping using neutron diffraction revealed reduced tensile and compressive residual stresses in the welds made by the new filler wire.

  1. 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.

  2. 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.

  3. 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.

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

    DOE PAGES

    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. 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.

  6. A Shear Strain Route Dependency of Martensite Formation in 316L Stainless Steel.

    PubMed

    Kang, Suk Hoon; Kim, Tae Kyu; Jang, Jinsung; Oh, Kyu Hwan

    2015-06-01

    In this study, the effect of simple shearing on microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. Two different shear strain routes were obtained by twisting cylindrical specimens in the forward and backward directions. The strain-induced martensite phase was effectively obtained by alteration of the routes. Formation of the martensite phase clearly resulted in significant hardening of the steel. Grain-size reduction and strain-induced martensitic transformation within the deformed structures of the strained specimens were characterized by scanning electron microscopy - electron back-scattered diffraction, X-ray diffraction, and the TEM-ASTAR (transmission electron microscopy - analytical scanning transmission atomic resolution, automatic crystal orientation/phase mapping for TEM) system. Significant numbers of twin networks were formed by alteration of the shear strain routes, and the martensite phases were nucleated at the twin interfaces.

  7. 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.

  8. 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.

  9. Fundamental Development on Utilizing the R-phase Transformation in NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Wang, Xiebin; Kustov, Sergey; Verlinden, Bert; Van Humbeeck, Jan

    2015-06-01

    In near equiatomic NiTi alloys, the reversible thermoelastic transformation between B2-structured austenite phase and the R-phase is attracting increasing interest for practical applications. However, the following two issues limit the widespread utilization of the R-phase transformation: (1) there is no effective approach to control the R-phase transformation temperatures; (2) it is not easy to largely separate the temperature domain of the R-phase and the B19' martensite phase transformation, especially in the presence of an external force. This article reviews concisely the work of the present authors on solving the above two problems. The effect of grain size on the aging microstructure and related transformation behavior is first discussed. Inspired by these findings, an approach to solve the above two problems has been developed by introducing nanoscaled Ni4Ti3 precipitates in the samples with micron-sized grains. The performance of alloys associated with the R-phase transformation, which shows controllable transformation temperatures, is summarized.

  10. 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.

  11. 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.

  12. Evolution of Intergranular Stresses in a Martensitic and an Austenitic NiTi Wire during Loading-unloading Tensile Deformation

    SciTech Connect

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

    2015-06-01

    In situ synchrotron X-ray diffraction testing was carried out on a martensitic and an austenitic NiTi wire to study the evolution of internal stresses and the stress-induced martensite (SIM) phase transformation during room temperature tensile deformation. From the point of lattice strain evolution, it is concluded that (1) for the martensitic NiTi wire, detwinning of the [011](B19') type II twins and the {010}(B19') compound twins is responsible for internal strains formed at the early stage of deformation. (2) The measured diffraction moduli of individual martensite families show large elastic anisotropy and strong influences of texture. (3) For the austenitic NiTi wire, internal residual stresses were produced due to transformation-induced plasticity, which is more likely to occur in austenite families that have higher elastic moduli than their associated martensite families. (4) Plastic deformation was observed in the SIM at higher stresses, which largely decreased the lower plateau stresses.

  13. Phase Transformations and Microstructural Evolution of Mo-Bearing Stainless Steels

    NASA Astrophysics Data System (ADS)

    Anderson, T. D.; Dupont, J. N.; Perricone, M. J.; Marder, A. R.

    2007-01-01

    The good corrosion resistance of superaustenitic stainless steel (SASS) alloys has been shown to be a direct consequence of high concentrations of Mo, which can have a significant effect on the microstructural development of welds in these alloys. In this research, the microstructural development of welds in the Fe-Ni-Cr-Mo system was analyzed over a wide variety of Cr/Ni ratios and Mo contents. The system was first simulated by construction of multicomponent phase diagrams using the CALPHAD technique. Data from vertical sections of these diagrams are presented over a wide compositional range to produce diagrams that can be used as a guide to understand the influence of composition on microstructural development. A large number of experimental alloys were then prepared via arc-button melting for comparison with the diagrams. Each alloy was characterized using various microscopy techniques. The expected δ-ferrite and γ-austenite phases were accompanied by martensite at low Cr/Ni ratios and by σ phase at high Mo contents. A total of 20 possible phase transformation sequences are proposed, resulting in various amounts and morphologies of the γ, δ, σ, and martensite phases. The results were used to construct a map of expected phase transformation sequence and resultant microstructure as a function of composition. The results of this work provide a working guideline for future base metal and filler metal development of this class of materials.

  14. Thickness dependent exchange bias in martensitic epitaxial Ni-Mn-Sn thin films

    SciTech Connect

    Behler, Anna; Teichert, Niclas; Auge, Alexander; Hütten, Andreas; Dutta, Biswanath; Hickel, Tilmann; Waske, Anja; Eckert, Jürgen

    2013-12-15

    A thickness dependent exchange bias in the low temperature martensitic state of epitaxial Ni-Mn-Sn thin films is found. The effect can be retained down to very small thicknesses. For a Ni{sub 50}Mn{sub 32}Sn{sub 18} thin film, which does not undergo a martensitic transformation, no exchange bias is observed. Our results suggest that a significant interplay between ferromagnetic and antiferromagnetic regions, which is the origin for exchange bias, is only present in the martensite. The finding is supported by ab initio calculations showing that the antiferromagnetic order is stabilized in the phase.

  15. Low temperature stability of 4O martensite in Ni49.1Mn38.9Sn12 metamagnetic Heusler alloy ribbons

    NASA Astrophysics Data System (ADS)

    Czaja, P.; Przewoźnik, J.; Gondek, Ł.; Hawelek, L.; Żywczak, A.; Zschech, E.

    2017-01-01

    The structural transformation sequence in Ni49.1Mn38.9Sn12 ribbons is studied using calorimetric, thermomagnetic, resistivity and in-situ XRD measurements. It is confirmed that the ferromagnetic L21 austenite phase transforms into 4O martensite at 242 K. The austenite phase persists in the sample to well below the TC of martensite. Upon further cooling the 4O martensite phase is stable down to the low temperature range, what is ascribed to its limited Ni/Mn and e/a ratios. On heating lattice constants assume lower values resulting from stress relief upon thermal cycling.

  16. Transformation Toughening of Ceramics

    DTIC Science & Technology

    1991-02-01

    34Metastabiits of Martensitic Trans- (-50 Am in diameter) of cubic phase, whereas the Ce- TZP formation in a 12 moll, Ceria- Zirconia Alloy I. Deformation and...ceria-partially-stablized zirconia (Ce- TZP ) that undergoes martensitic transformation from tetragonal to monoclinic phase. 1- 7 However, the shapes...Stabilized Tetragonal Zirconia Polycrystals (Ce- TZP )," . Mat. Sci. 204[4], 1178-84 (1985). 8. D.B. Marshall, "Crack Shielding in Ceria-Partially-Stabilized

  17. Thermodynamics of entropy-driven phase transformations.

    PubMed

    Radosz, A; Ostasiewicz, K; Magnuszewski, P; Damczyk, J; Radosiński, Ł; Kusmartsev, F V; Samson, J H; Mituś, A C; Pawlik, G

    2006-02-01

    Thermodynamic properties of one-dimensional lattice models exhibiting entropy-driven phase transformations are discussed in quantum and classical regimes. Motivated by the multistability of compounds exhibiting photoinduced phase transitions, we consider systems with asymmetric, double, and triple well on-site potential. One finds that among a variety of regimes, quantum versus classical, discrete versus continuum, a key feature is asymmetry distinguished as a "shift" type and "shape" type in limiting cases. The behavior of the specific heat indicates one phase transformation in a "shift" type and a sequence of two phase transformations in "shape"-type systems. Future analysis in higher dimensions should allow us to identify which of these entropy-driven phase transformations would evolve into phase transitions of the first order.

  18. 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.

  19. Interface Propagation and Microstructure Evolution in Phase Field Models of Stress-Induced Martensitic Phase Transformations

    DTIC Science & Technology

    2010-01-01

    simulation, the initial conditions are g1 ¼ g2 ¼ 0:1 in a circle of radius 2 nm (an embryo ) at the center of the sample and zero elsewhere. The boundary...in narrow bands around the interfaces if the driving force is less than a critical value, K: Fig. 10. Evolution of an embryo , gi ¼ 0:1, in a circle...concentration curve does not exhibit a hysteresis loop and energy dissipation. 4. In Fig. 22 we display the evolution of an embryo with gi ¼ 0:1 as in

  20. 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.

  1. Fatigue crack propagation in dual-phase steels: Effects of ferritic-martensitic microstructures on crack path morphology

    NASA Astrophysics Data System (ADS)

    Dutta, V. B.; Suresh, S.; Ritchie, R. O.

    1984-06-01

    microstructures with maximum resistance to fatigue crack extension while maintaining high strength levels. A wide range of crack growth rates has been examined, from ~10-8 to 10-3 mm per cycle, in a series of duplex microstructures of comparable yield strength and prior austenite grain size where intercritical heat treatments were used to vary the proportion, morphology, and distribution of the ferrite and martensite phases. Results of fatigue crack propagation tests, conducted on “long cracks” in room temperature moist air environments, revealed a very large influence of microstructure over the entire spectrum of growth rates at low load ratios. Similar trends were observed at high load ratio, although the extent of the microstructural effects on crack growth behavior was significantly less marked. Specifically, microstructures containing fine globular or coarse martensite in a coarse-grained ferritic matrix demonstrated exceptionally high resistance to crack growth without loss in strength properties. To our knowledge, these microstructures yielded the highest ambient temperature fatigue threshold stress intensity range ΔK0 values reported to date, and certainly the highest combination of strength and ΔK0 for steels ( i.e., ΔK0 values above 19 MPa√m with yield strengths in excess of 600 MPa). Such unusually high crack growth resistance is attributed primarily to a tortuous morphology of crack path which results in a reduction in the crack driving force from crack deflection and roughness-induced crack closure mechanisms. Quantitative metallography and experimental crack closure measurements, applied to currently available analytical models for the deflection and closure processes, are presented to substantiate such interpretations.

  2. 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

  3. Mechanisms of transformation toughening

    SciTech Connect

    Olson, G.B.

    1992-02-01

    Modelling the thermodynamics and kinetics of isothermal martensitic transformation under stress, transformation toughening in austenitic steels, and dispersed phase transformation plasticity in low alloy steels are discussed briefly in this progress report for Doe Grant DE-FG02-88ER45365.

  4. 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.

  5. Effects of Quenching Media on Phase Transformation Characteristics and Hardness of Cu-Al-Ni-Co Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Saud, Safaa N.; Hamzah, E.; Abubakar, T.; Farahany, S.; Bakhsheshi-Rad, H. R.

    2015-04-01

    This paper presents the investigation on the effects of various thermal treatments and quenching media on the phase transformation behaviour of Cu-Al-Ni-Co shape memory alloys (SMAs). The transformation temperatures were determined using a differential scanning calorimeter. The variation of cooling rates had a consequential effect on the phase transformation characteristics of the Cu-Al-Ni-Co SMAs. Nevertheless, the transformation temperature peaks were varied in terms of location as well as heat flow. The results indicated that there was an improvement in transformation temperatures whenever ice water was used as quenching medium. It was also observed that the forward transformation temperatures were higher than the reverse transformation. It was verified that the required heat for the transformation of martensite into austenite was more than the transformation of austenite into martensite. Moreover, thermodynamic parameters, such as enthalpy and entropy, tended to decrease and increase as a result of the changes in the cooling rates of each medium. To clarify the variations of the structures and properties of Cu-Al-Ni-Co SMA quenched samples, x-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, and Vickers hardness were used.

  6. Phase and structural transformations in U and U-Nb alloy upon severe deformation and heat treatments

    NASA Astrophysics Data System (ADS)

    Zuev, Yu. N.; Sagaradze, V. V.; Pecherkina, N. L.; Kabanova, I. I.; Svyatov, I. L.; Bondarchuk, S. V.; Belyaev, D. V.

    2013-12-01

    Transmission electron microscopy was used to analyze the twin and dislocation structure of samples of commercial uranium in the initial (undeformed) state and after severe deformation using explosive loading by plane and spherical waves of various intensity. It has been shown that an increase in the intensity of explosive loading by a plane wave leads, first, to an increase in the density of randomly distributed dislocations and twins and, then, to the development of polygonization processes with the formation of a subgrain structure of the α phase. Crystallographic analysis of the initial and deformation-induced twins in uranium has shown the presence of predominantly {130} twins of mixed type and, in singular cases, {172} and {176} twins of the second kind. It has been established that the retained spherical shells have a distinctly pronounced zonal structure, which contains information on the forward and reverse martensitic phase transformations of uranium (α ↔ β(γ) ↔ L, etc.) that occur under shock-wave loading by spherical waves. Conditions are determined for the manifestation of structural heredity in the U-6 wt % Nb alloy with recovery of the size and shape of grains of the initial high-temperature γ phase during the forward γ → α″ martensitic transformation upon cooling and during reverse α″ → γ transformation upon heating. Elimination of the structural heredity with significant grain refinement of the high-temperature γ phase occurs in the process of repeated quenching from 700°C after one type of preliminary treatments (cold deformation of α″ martensite, recrystallization of the deformed α″ phase, high-temperature aging of the initial α″ martensite, and eutectoid decomposition).

  7. Role of magnetic and atomic ordering in the martensitic transformation of Ni-Mn-In from a first-principles study

    NASA Astrophysics Data System (ADS)

    Li, Chun-Mei; Luo, Hu-Bin; Hu, Qing-Miao; Yang, Rui; Johansson, Börje; Vitos, Levente

    2012-12-01

    The composition-dependent lattice parameters, crystal structure, elastic properties, magnetic moment, and electronic structure of Ni2Mn1+xIn1-x (0≤x≤0.6) are studied by using first-principles calculations. It is shown that the martensitic phase transition (MPT) from cubic L21 to tetragonal L10 accompanies the MnMn-MnIn ferromagnetic (FM) to antiferromagnetic (AFM) transition, at around the critical composition x=0.32, in agreement with the experimental measurement. The Mn-In atomic disorder leads to decreasing stability of the martensite relative to the austenite, which depresses the MPT. The shear elastic constant C' of the parent phase first decreases slightly with increasing x and then remains almost unchanged above x=0.32, indicating C' alone cannot account for the increase of the MPT temperature with x. The total magnetic moments for the L21 phase are in good agreement with those determined by experiments, whereas for the L10 phase they are slightly larger than the experimental data due to the possible Mn-In atomic disorder in the sample. The calculated density of states demonstrate that the covalent bonding between the minority spin states of Ni and In plays an important role in both the magnetic and structural stability.

  8. The influence of phase transformation hardening on continuous laser processing of notches for fracture splitting of a C70S6 connecting rod

    NASA Astrophysics Data System (ADS)

    Kou, S. Q.; Gao, Y.; Shi, Z.

    2017-01-01

    The dynamic process of local material microstructure and hardness of continuous laser grooving for fracture splitting of a C70S6 connecting rod was studied. According to the phase transformation characteristics of C70S6 steel during laser processing, the coupling calculation between the transient temperature field and phase transformation process of continuous laser grooving was carried out, and then the phase transformation process and phase compositions in the heat affected zone (HAZ) was obtained. The research results showed that the HAZ was composed of martensite and pearlite as well as residual austenite after continuous laser grooving, and the generation of the martensite in the HAZ is beneficial to the subsequent splitting process; meanwhile, the hardening effect of continuous laser grooving is remarkable on the HAZ, and the requirement for the cutting tool and technique used at the subsequent machining process for the fine boring of the big end hole should be higher.

  9. Phase Equilibria, Phase Diagrams and Phase Transformations - 2nd Edition

    NASA Astrophysics Data System (ADS)

    Hillert, Mats

    2006-03-01

    Computational tools allow material scientists to model and analyze increasingly complicated systems to appreciate material behavior. Accurate use and interpretation however, requires a strong understanding of the thermodynamic principles that underpin phase equilibrium, transformation and state. This fully revised and updated edition covers the fundamentals of thermodynamics, with a view to modern computer applications. The theoretical basis of chemical equilibria and chemical changes is covered with an emphasis on the properties of phase diagrams. Starting with the basic principles, discussion moves to systems involving multiple phases. New chapters cover irreversible thermodynamics, extremum principles, and the thermodynamics of surfaces and interfaces. Theoretical descriptions of equilibrium conditions, the state of systems at equilibrium and the changes as equilibrium is reached, are all demonstrated graphically. With illustrative examples - many computer calculated - and worked examples, this textbook is an valuable resource for advanced undergraduates and graduate students in materials science and engineering. Fully revised and updated edition covering the fundamentals of thermodynamics with a view to modern computer applications such as Thermo-Calc Emphasis is placed on phase diagrams, the key application of thermodynamics Contains numerous illustrative examples, many computer-calculated and some for real systems, and worked examples to help demonstrate the principles

  10. In-situ characterization of highly reversible phase transformation by synchrotron X-ray Laue microdiffraction

    NASA Astrophysics Data System (ADS)

    Chen, Xian; Tamura, Nobumichi; MacDowell, Alastair; James, Richard D.

    2016-05-01

    The alloy Cu25Au30Zn45 undergoes a huge first-order phase transformation (6% strain) and shows a high reversibility under thermal cycling and an unusual martensitc microstructure in sharp contrast to its nearby compositions. This alloy was discovered by systematically tuning the composition so that its lattice parameters satisfy the cofactor conditions (i.e., the kinematic conditions of compatibility between phases). It was conjectured that satisfaction of these conditions is responsible for the enhanced reversibility as well as the observed unusual fluid-like microstructure during transformation, but so far, there has been no direct evidence confirming that these observed microstructures are those predicted by the cofactor conditions. To verify this hypothesis, we use synchrotron X-ray Laue microdiffraction to measure the orientations and structural parameters of variants and phases near the austenite/martensite interface. The areas consisting of both austenite and multi-variants of martensite are scanned by microLaue diffraction. The cofactor conditions have been examined from the kinematic relation of lattice vectors across the interface. The continuity condition of the interface is precisely verified from the correspondent lattice vectors between two phases.

  11. In-situ characterization of highly reversible phase transformation by synchrotron X-ray Laue microdiffraction

    SciTech Connect

    Chen, Xian; Tamura, Nobumichi; MacDowell, Alastair; James, Richard D.

    2016-05-23

    The alloy Cu{sub 25}Au{sub 30}Zn{sub 45} undergoes a huge first-order phase transformation (6% strain) and shows a high reversibility under thermal cycling and an unusual martensitc microstructure in sharp contrast to its nearby compositions. This alloy was discovered by systematically tuning the composition so that its lattice parameters satisfy the cofactor conditions (i.e., the kinematic conditions of compatibility between phases). It was conjectured that satisfaction of these conditions is responsible for the enhanced reversibility as well as the observed unusual fluid-like microstructure during transformation, but so far, there has been no direct evidence confirming that these observed microstructures are those predicted by the cofactor conditions. To verify this hypothesis, we use synchrotron X-ray Laue microdiffraction to measure the orientations and structural parameters of variants and phases near the austenite/martensite interface. The areas consisting of both austenite and multi-variants of martensite are scanned by microLaue diffraction. The cofactor conditions have been examined from the kinematic relation of lattice vectors across the interface. The continuity condition of the interface is precisely verified from the correspondent lattice vectors between two phases.

  12. In-situ characterization of highly reversible phase transformation by synchrotron X-ray Laue microdiffraction

    DOE PAGES

    Chen, Xian; Tamura, Nobumichi; MacDowell, Alastair; ...

    2016-05-23

    The alloy Cu 25 Au 30 Zn 45 undergoes a huge first-order phase transformation (6% strain) and shows a high reversibility under thermal cycling and an unusual martensitc microstructure in sharp contrast to its nearby compositions. We discovered this alloy by systematically tuning the composition so that its lattice parameters satisfy the cofactor conditions (i.e., the kinematic conditions of compatibility between phases). It was conjectured that satisfaction of these conditions is responsible for the enhanced reversibility as well as the observed unusual fluid-like microstructure during transformation, but so far, there has been no direct evidence confirming that these observed microstructuresmore » are those predicted by the cofactor conditions. In order to verify this hypothesis, we use synchrotron X-ray Laue microdiffraction to measure the orientations and structural parameters of variants and phases near the austenite/martensite interface. The areas consisting of both austenite and multi-variants of martensite are scanned by microLaue diffraction. The cofactor conditions have been examined from the kinematic relation of lattice vectors across the interface. The continuity condition of the interface is precisely verified from the correspondent lattice vectors between two phases.« less

  13. Effect of tensile pre-strain at different orientation on martensitic transformation and mechanical properties of 316L stainless steel

    NASA Astrophysics Data System (ADS)

    Wibowo, F.; Zulfi, F. R.; Korda, A. A.

    2017-01-01

    Deformation induced martensite was studied in 316L stainless steel through tensile pre-strain deformation in the rolling direction (RD) and perpendicular to the rolling direction (LT) at various %pre-strain. The experiment was carried out at various given %pre-strain, which were 0%, 4.6%, 12%, 17.4%, and 25.2% for the RD, whereas for LT were 0%, 4.6%, 12%, 18%, and 26% for LT. Changes in the microstructure and mechanical properties were observed using optical microscope, tensile testing, hardness testing, and X-ray diffraction (XRD) analysis. The experimental results showed that the volume fraction of martensite was increased as the %pre-strain increased. In the same level of deformation by tensile pre-strain, the volume of martensite for RD was higher than that with LT direction. The ultimate tensile strength (UTS), yield strength (YS), and hardness of the steel were increased proportionally with the increases in %pre-strain, while the value of elongation and toughness were decreased with the increases in %pre-strain.

  14. Phase transformations upon doping in WO3

    NASA Astrophysics Data System (ADS)

    Wang, Wennie; Janotti, Anderson; Van de Walle, Chris G.

    2017-06-01

    High levels of doping in WO3 have been experimentally observed to lead to structural transformation towards higher symmetry phases. We explore the structural phase diagram with charge doping through first-principles methods based on hybrid density functional theory, as a function of doping the room-temperature monoclinic phase transitions to the orthorhombic, tetragonal, and finally cubic phase. Based on a decomposition of energies into electronic and strain contributions, we attribute the transformation to a gain in energy resulting from a lowering of the conduction band on an absolute energy scale.

  15. Origins of asymmetric stress-strain response in phase transformations

    SciTech Connect

    Sehitoglu, H.; Gall, K.

    1997-12-31

    It has been determined that the transformation stress-strain behavior of CuZnAl and NiTi shape memory alloys is dependent on the applied stress state. The uniaxial compressive stress necessary to macroscopically trigger the transformation is approximately 34% (CuZnAl) and 26% (NiTi) larger than the required uniaxial tensile stress. For three dimensional stress states, the response of either alloy system is dependent on the directions of the dominant principal stresses along with the hydrostatic stress component of the stress state. The stress state effects are dominated by the favored growth and nucleation of more martensite plates in tension versus compression. The effect of different hydrostatic pressure levels between stress states on martensite plates volume change is considered small.

  16. Characterization of strain-induced martensite phase in austenitic stainless steel using a magnetic minor-loop scaling relation

    SciTech Connect

    Kobayashi, Satoru; Saito, Atsushi; Takahashi, Seiki; Kamada, Yasuhiro; Kikuchi, Hiroaki

    2008-05-05

    We propose a combined magnetic method using a scaling power-law rule and initial permeability in magnetic minor hysteresis loops for characterization of ferromagnetic {alpha}{sup '} martensites in austenitic stainless steel. The scaling power law between the hysteresis loss and remanence is universal, being independent of volume fraction of strain-induced {alpha}{sup '} martensites. A coefficient of the power law largely decreases with volume fraction, while the initial permeability linearly increases, reflecting a change in the morphology and quantity of martensites, respectively. The present method is highly effective for integrity assessment of austenitic stainless steels because of the sensitivity and extremely low measurement field.

  17. Comprehensive School Transformation, Phase III. Program Evaluation.

    ERIC Educational Resources Information Center

    Prine, Donald; Wilkinson, David

    The Iowa Educational Excellence Act and its amendments provide for four types of Phase III programs: performance-based pay, supplemental pay, a combination of both, or comprehensive school transformation. In 1993, the Des Moines Phase III program, which originated as a combination of performance-based pay and supplemental pay, changed to a…

  18. Phase transformation and phonon anomalies in Ni{sub 2}MnGa

    SciTech Connect

    Zheludev, A.; Shapiro, S.M.; Wochner, P.; Schwartz, A.; Wall, M.; Tanner, L.E.

    1995-07-01

    Inelastic neutron scattering experiments and transmission electron microscopy have been used to study a single crystal of the Ni{sub 2}MnGa shape memory Hustler alloy in a wide temperature range covering the parent phase (T>T{sub 1}=265 K), a recently discovered pemartensitic (T{sub 1}T>T{sub M}) and martensitic (Tphase regions. A temperature-dependent anomaly in the TA{sub 2} phonon dispersion in the parent phase was observed and related to the phase transformations. The premartensitic phase involves a transverse modulation of the parent cubic structure with a simple periodicity of 1/3 [110]. The approximately tetragonal lattice of the low-temperature martensite is distorted by transverse modulations with incommensurate wave vectors [{zeta}M {zeta}M {sup 0}] and [{sup 2}{zeta}M {sup 2}{zeta}M {sup 0}], {zeta}M {approx}0.43. The observed phenomena are attributed to electron-phonon interactions and anharmonic effects.

  19. In Situ Observation of Phase Transformation and Structure Evolution of a 12 pct Cr Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Song, Changjiang; Guo, Yuanyi; Li, Kefeng; Sun, Fengmei; Han, Qingyou; Zhai, Qijie

    2012-10-01

    This work focuses on an in situ observation of phase transformation of a 12 pct Cr ferritic stainless steel using high-temperature laser scanning confocal microscopy. α→ γ→ δ phase transformation temperatures are determined to be approximately 1073 K and 1423 K (800 °C and 1150 °C), respectively. The onset of phase transformation is found to occur at grain boundaries. When the temperature is beyond 1518 K (1245 °C), the grain growth rate suddenly becomes very high, and the grain growth is related to the self-organizing of adjacent grains. δ→ γ phase transformation has been mostly restrained when cooling rates are in the range of 22.4 K/s to 13.3 K/s (22.4 °C/s to 13.3 °C/s) except for at grain boundaries. Martensitic phase transformation, rather than γ→ α phase transformation, occurs when the cooling rates are in the range of 8.5 K/s to 2.2 K/s (8.5 °C/s to 2.2 °C/s). The starting temperature of martensitic phase transformation is approximately 697 K to 728 K (424 °C to 455 °C) for specimens heated to 1373 K (1100 °C) ( i.e., γ phase field), which is 50 K to 100 K (50 °C to 100 °C) higher than that of specimens heated to 1723 K (1450 °C) ( i.e., δ phase field). Many bulges remain on the surfaces of the specimen heated to 1723 K (1450 °C), and their formation mechanism is analyzed.

  20. Lath martensites in low carbon steels

    SciTech Connect

    Sarikaya, M.; Thomas, G.

    1982-01-01

    The morphology and crystallography of lath martensite in low and medium carbon steels have been studied by transmission electron microscopy and diffraction. The steels have microduplex structures of dislocated lath martensite (a < b much less than c) with fairly straight boundaries and continuous interlath thin films of retained austenite. Stacks of laths (i.e., single crystals of martensite) form the packets which are derived from different (111) transformation variants of austenite. Microdiffraction experiments directly allow the determination of the orientation relationships between austenite and martensite. Relative orientations of adjacent individual laths cluster about common orientations from small to large angular differences all around a common <110>M direction. The overall microstructure and orientations result from minimization of the total strain and shape deformation. Considerable accommodation occurs by deformation of laths (sometimes twinned) and austenite (sometimes tripped to twin martensite). In the meantime, microchemical analyses have shown considerable carbon segregation to the martensite-austenite interface. 4 figures.

  1. Martensite aging effect in a Ti{sub 50}Pd{sub 50} high temperature shape memory alloy

    SciTech Connect

    Cai, W.; Otsuka, Kazuhiro

    1999-11-19

    Ti-Pd alloy system is one of the potential high temperature shape memory alloys due to its high martensitic transformation temperatures. Thus, many researches including shape memory characteristics, martensitic transformations and mechanical behavior of the alloys have been done in recent yeas. However, martensite aging effect in the alloy, which is an important issue as to the stability of martensite at high temperature, has not been reported yet. Ti{sub 50}Pd{sub 50} transforms from B2 parent phase to B19 martensite upon cooling, and M{sub s} is 823 K (25) and T{sub m} is 1,673 K (26). Thus M{sub s}/T{sub m} ratio of the alloy is about 0.49, and the alloy may show strong martensite aging effect according to the above proposal. It is now of interest to examine whether the Ti{sub 50}Pd{sub 50} alloy show martensite aging effect. As will be shown, the Ti{sub 50}Pd{sub 50} alloy indeed shows the aging effect, as expected; however, the aging effect of this alloy exhibits a unique feature, which is not found in other shape memory alloys.

  2. Modelling of Strains During SAW Surfacing Taking into Heat of the Weld in Temperature Field Description and Phase Transformations

    NASA Astrophysics Data System (ADS)

    Winczek, J.; Makles, K.; Gucwa, M.; Gnatowska, R.; Hatala, M.

    2017-08-01

    In the paper, the model of the thermal and structural strain calculation in a steel element during single-pass SAW surfacing is presented. The temperature field is described analytically assuming a bimodal volumetric model of heat source and a semi-infinite body model of the surfaced (rebuilt) workpiece. The electric arc is treated physically as one heat source. Part of the heat is transferred by the direct impact of the electric arc, while another part of the heat is transferred to the weld by the melted material of the electrode. Kinetics of phase transformations during heating is limited by temperature values at the beginning and at the end of austenitic transformation, while the progress of phase transformations during cooling is determined on the basis of TTT-welding diagramand JMA-K law for diffusive transformations, and K-M law for martensitic transformation. Totalstrains equal to the sum ofthermaland structuralstrainsinduced by phasetransformationsin weldingcycle.

  3. Z phase precipitation in martensitic 12CrMoVNb steels

    NASA Astrophysics Data System (ADS)

    Vodarek, V.; Strang, A.

    2003-10-01

    Precipitation of Z phase contributes significantly to degradation of creep properties of 12CrMoVNb steels because its precipitation is accompanied by dissolution offinely dispersed nitrides and carbonitrides of M2X and/or MX type. The orientation relationship between Z phase and the ferritic matrix was determined as: (001)_z// (001)_{α}, [010]_z // [010]_{α}. Prolonged thcrmal/creep exposure is accompanied by recrystallisation of the matrix and this orientation relationship is destroyed. Nevertheless Z phase particles preserve the form of thin plates. Z phase is a nitride which is rich in vanadium, niobium and chromium and its composition depends on both the temperature of precipitation and the initial chemical composition of steels. The composition of Z phase does not change during long term exposure at the original precipitation temperature. A relationship between the composition of Z phase and its temperature of formation may be able to be used as a temperature exposure indicator of steels. However it is also necessary to know the Z phase composition for a given cast of material.

  4. Martensitic transformation and magnetocaloric properties in Ni40.4Mn46.5Sn10.9Sb2.2 ribbons

    NASA Astrophysics Data System (ADS)

    Xuan, H. C.; Zhang, T.; Wu, Y. F.; Xu, Y. K.; Li, H.; Han, P. D.; Du, Y. W.; Zhang, C. L.

    2017-01-01

    The Ni40.4Mn46.5Sn10.9Sb2.2 ribbons were prepared by melt-spun method. The martensitic transformation (MT) and magnetocaloric effect in melt-spun and annealed Ni40.4Mn46.5Sn10.9Sb2.2 ribbons were investigated. After the heat treatment, the MT temperature increases obviously in the annealed ribbons. The large values of magnetic entropy changes and the effective refrigerant capacity around the MT and Curie temperature of the austenite are found to be 30.9 and -2.2 J/kg K, 70.6 and 132.6 J/kg, respectively, under the field change of 30 kOe for the annealed ribbons. The annealing effect on the MT and magnetocaloric effect, together with the origin of the large magnetic entropy changes, has been discussed in this paper.

  5. The Kinetics of Phase Transformation in Welds

    SciTech Connect

    Elmer, J W; Wong, J; Palmer, T

    2002-02-06

    The fundamentals of welding-induced phase transformations in metals and alloys are being investigated using a combination of advanced synchrotron based experimental methods and modem computational science tools. In-situ experimental methods have been developed using a spatially resolved x-ray probe to enable direct observations of phase transformations under the real non- isothermal conditions experienced during welding. These experimental techniques represent a major step forward in the understanding of phase transformations that occur during welding, and are now being used to aid in the development of models to predict microstructural evolution under the severe temperature gradients, high peak temperatures and rapid thermal fluctuations characteristic of welds. Titanium alloys, stainless steels and plain carbon steels are currently under investigation, and the phase transformation data being obtained here cannot be predicted or measured using conventional metallurgical approaches. Two principal synchrotron-based techniques have been developed and refined for in-situ investigations of phase transformation dynamics in the heat-affected zone (HAZ) and fusion zone (FZ) of welds: Spatially Resolved X-Ray Diffraction (SRXRD) and Time Resolved X-Ray Diffraction (TRXRD). Both techniques provide real-time observations of phases that exist during welding, and both have been developed at the Stanford Synchrotron Radiation Laboratory (SSRL) using a high flux wiggler beam line. The SRXRD technique enables direct observations of the phases existing in the HAZ of quasi-stationary moving arc welds, and is used to map the HAZ phases by sequentially jogging the weld with respect to the x-ray beam while taking x-ray diffraction (XRD) patterns at each new location. These spatially resolved XRD patterns are collected in linear traverses perpendicular to the direction of weld travel. The XRD data contained in multiple traverses is later compiled to produce an areal map of the phases

  6. Phase Transformation Study in Nb-Mo Microalloyed Steels Using Dilatometry and EBSD Quantification

    NASA Astrophysics Data System (ADS)

    Isasti, Nerea; Jorge-Badiola, Denis; Taheri, Mitra L.; Uranga, Pello

    2013-08-01

    A complete microstructural characterization and phase transformation analysis has been performed for several Nb and Nb-Mo microalloyed low-carbon steels using electron backscattered diffraction (EBSD) and dilatometry tests. Compression thermomechanical schedules were designed resulting in the undeformed and deformed austenite structures before final transformation. The effects of microalloying additions and accumulated deformation were analyzed after CCT diagram development and microstructural quantification. The resulting microstructures ranged from polygonal ferrite and pearlite at slow cooling ranges, to a combination of quasipolygonal ferrite and granular ferrite for intermediate cooling rates, and finally, to bainitic ferrite with martensite for fast cooling rates. The addition of Mo promotes a shift in the CCT diagrams to lower transformation start temperatures. When the amount of Nb is increased, CCT diagrams show little variations for transformations from the undeformed austenite and higher initial transformation temperatures in the transformations from the deformed austenite. This different behavior is due to the effect of niobium on strain accumulation in austenite and its subsequent acceleration of transformation kinetics. This article shows the complex interactions between chemical composition, deformation, and the phases formed, as well as their effect on microstructural unit sizes and homogeneity.

  7. Phase Transformation Behavior of Porous TiNi Alloys Produced by Powder Metallurgy Using Magnesium as a Space Holder

    NASA Astrophysics Data System (ADS)

    Aydoğmuş, Tarik; Bor, Elif Tarhan; Bor, Şakir

    2011-09-01

    Porous TiNi alloys with porosities in the range of 51 to 73 pct were prepared successfully applying a new powder metallurgy fabrication route in which magnesium was used as a space holder, resulting in either single austenite phase or a mixture of austenite and martensite phases dictated by the composition of the starting powders, but entirely free from secondary brittle intermetallics, oxides, nitrides, and carbonitrides. Since transformation temperatures are very sensitive to composition, deformation, and oxidation, for the first time, transformation temperatures of porous TiNi alloys were investigated using chemically homogeneous specimens in as-sintered and aged conditions eliminating secondary phase, contamination, and deformation effects. It was found that the porosity content of the foams has no influence on the phase transformation temperatures both in as-sintered and aged conditions, while deformation, oxidation, and aging treatment are severely influential.

  8. Multi-probe microstructure tracking during heat treatment without an in-situ setup: Case studies on martensitic steel, dual phase steel and β-Ti alloy

    SciTech Connect

    Zhang, Jiali Morsdorf, Lutz Tasan, Cemal Cem

    2016-01-15

    In-situ scanning electron microscopy observations of the microstructure evolution during heat treatments are increasingly demanded due to the growing number of alloys with complex microstructures. Post-mortem characterization of the as-processed microstructures rarely provides sufficient insight on the exact route of the microstructure formation. On the other hand, in-situ SEM approaches are often limited due to the arising challenges upon using an in-situ heating setup, e.g. in (i) employing different detectors, (ii) preventing specimen surface degradation, or (iii) controlling and measuring the temperature precisely. Here, we explore and expand the capabilities of the “mid-way” solution by step-wise microstructure tracking, ex-situ, at selected steps of heat treatment. This approach circumvents the limitations above, as it involves an atmosphere and temperature well-controlled dilatometer, and high resolution microstructure characterization (using electron channeling contrast imaging, electron backscatter diffraction, atom probe tomography, etc.). We demonstrate the capabilities of this approach by focusing on three cases: (i) nano-scale carbide precipitation during low-temperature tempering of martensitic steels, (ii) formation of transformation-induced geometrically necessary dislocations in a dual-phase steel during intercritical annealing, and (iii) the partial recrystallization of a metastable β-Ti alloy. - Highlights: • A multi-probe method to track microstructures during heat treatment is developed. • It enables the analysis of various complex phenomena, even those at atomistic scale. • It circumvents some of the free surface effects of classical in-situ experiments.

  9. X-ray diffraction study of the t-to-m phase transformation in 12-mol%-ceria-doped zirconia at low temperatures

    SciTech Connect

    Zhu, H.Y. . Dept. of Materials Science and Engineering)

    1994-09-01

    The t-to-m phase transformation in a 12-mol%-ceria-doped zirconia to subzero temperatures was studied in situ by XRD with a cryogenic sample stage. It was found that the t-to-m transformation continuously proceeded to 30 vol% as the temperature decreased to 125 K, when a burstlike transformation suddenly occurred with a transformation to 75 vol%. A preferred orientation of the ([bar 1]11)[sub m] plane parallel to the surface during the preburst transformation and XRD line broadening of both m and t phases after the burst were observed. The preburst transformation, which has not been revealed by previous dilatometry studies, is explained as surface martensitic transformation. This surface transformation occurs at higher temperature than the burstlike transformation due to less matrix constraint and the higher probability of nucleation.

  10. Phase Transformation in Cast Superaustenitic Stainless Steels

    SciTech Connect

    Lee Phillips, Nathaniel Steven

    2006-01-01

    Superaustenitic stainless steels constitute a group of Fe-based alloys that are compositionally balanced to have a purely austenitic matrix and exhibit favorable pitting and crevice corrosion resistant properties and mechanical strength. However, intermetallic precipitates such as sigma and Laves can form during casting or exposure to high-temperature processing, which degrade the corrosion and mechanical properties of the material. The goal of this study was to accurately characterize the solid-solid phase transformations seen in cast superaustenitic stainless steels. Heat treatments were performed to understand the time and temperature ranges for intermetallic phase formations in alloys CN3MN and CK3MCuN. Microstructures were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy and wavelength dispersive spectroscopy (EDS, WDS). The equilibrium microstructures, composed primarily of sigma and Laves within purely austenitic matrices, showed slow transformation kinetics. Factors that determine the extent of transformation, including diffusion, nucleation, and growth, are discussed.

  11. Structure and phase transformations in uranium metal

    NASA Astrophysics Data System (ADS)

    Axe, J. D.; Gruebel, G.; Lander, G. H.

    1994-10-01

    In common with other elemental actinides, metallic uranium exists in several allotropic forms, differing from one another by complex but subtle atomic rearrangements. This article reviews progress in understanding the successive phase transformations from the perspective of soft-mode instabilities.

  12. Structure and phase transformations in uranium metal

    SciTech Connect

    Axe, J.D.; Gruebel, G.; Lander, G.H.

    1993-12-01

    In common with other elemental actinides, metallic uranium exists in several allotropic forms, differing from one another by complex but subtle atomic rearrangements. This article reviews progress in understanding the successive phase transformations from the perspective of soft-mode instabilities.

  13. Effect of constituent phase on mechanical properties of 9Cr-1WVTa reduced activation ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Hoon; Moon, Joonoh; Park, Min-Gu; Lee, Tae-Ho; Jang, Min-Ho; Kim, Hyoung Chan; Suh, Dong-Woo

    2014-12-01

    Influence of the formation of ferrite and accompanying carbides in martensite matrix on the tensile and Charpy impact properties was investigated for reduced activation ferritic-martensitic (RAFM) 9Cr-1WVTa steel. As the fractions of ferrite and carbide adjacent to the ferrite grain boundary increase, both tensile and Charpy impact properties deteriorated in as-normalized condition. In particular, the tensile strength and elongation decreased simultaneously, which is believed to be led by the localized deformation in ferrite which is softer than martensite, promoting the formation and growth of voids. In addition, the formation of ferrite was also detrimental to the Charpy impact properties regarding to the absorbed energy because the precipitation of carbides around ferrite were vulnerable to the nucleation and propagation of cleavage cracks. The degradation of tensile properties can be recovered by tempering, but the DBTT temperature still increases with presence of ferrite.

  14. Influence of Addition of Nb on Phase Transformation, Microstructure and Mechanical Properties of Equiatomic NiTi SMA

    NASA Astrophysics Data System (ADS)

    Jiang, Shuyong; Liang, Yulong; Zhang, Yanqiu; Zhao, Yanan; Zhao, Chengzhi

    2016-10-01

    Three novel NiTiNb shape memory alloys, which possess a nominal chemical composition of Ni50- x/2-Ti50- x/2-Nb x (at.%) where x stands for 2, 4 and 6, respectively, were designed in order to investigate the influence of the addition of Nb on phase transformation, microstructure and mechanical properties of equiatomic NiTi shape memory alloy. All the three NiTiNb shape memory alloys contain B2 austenite phase, B19' martensite phase and β-Nb precipitate phase. Martensite type II twin can be observed in the case of Ni49Ti49Nb2 alloy. In the case of Ni48Ti48Nb4 alloy, there exists a boundary between Ti2Ni precipitate phase and β-Nb precipitate phase. As for Ni47Ti47Nb6 alloy, it can be observed that there exists an orientation relationship of [01bar{1}]_{{β{{ - Nb}}}} //[01bar{1}]_{{B2}} between β-Nb precipitate phase and B2 austenite matrix. The increase in Nb content contributes to enhancing the yield stress of NiTiNb shape memory alloy, but it leads to the decrease in compression fracture stress. The addition of Nb to equiatomic NiTi shape memory alloy does not have a significant influence on the transformation hysteresis of the alloy, which is attributed to the fact that NiTiNb shape memory alloy is not subjected to plastic deformation and hence β-Nb precipitate phase is unable to relax the elastic strain in the martensite interface.

  15. Modeling of Shape Memory Alloys: Phase Transformation/Plasticity Interaction at the Nano Scale and the Statistics of Variation in Pseudoelastic Performance

    NASA Astrophysics Data System (ADS)

    Paranjape, Harshad Madhukar

    Shape memory alloys (SMA) show two remarkable properties- pseudoelasticity and shape memory effect. These properties make them an attractive material for a variety of commercial applications. However, the mechanism of austenite to martensite phase transformation, responsible for these properties also induces plastic deformation leading to structural and functional fatigue. Micron scale experiments suggest that the plastic deformation is induced in part due to the local stress field of the fine martensite microstructure. However, the results are qualitative and the nature of transformation-plasticity interaction is dependent on factors like the width of the interfaces. This thesis presents a new modeling approach to study the interaction between martensite correspondence variant scale microstructure and plastic deformation in austenite. A phase field method based evolution law is developed for phase transformation and reorientation of martensite CVs. This is coupled with a crystal plasticity law for austenite plastic deformation. The model is formulated with finite deformation and rotations. The effect of local crystal orientation is incorporated. An explicit time integration scheme is developed and implemented in a finite element method (FEM) based framework, allowing the modeling of complex boundary conditions and arbitrary loading conditions. Two systematic studies are carried out with the model. First, the interaction between plasticity and phase transformation is studied for load-free and load-biased thermal cycling of single crystals. Key outcomes of this study are that, the residual martensite formed during thermal cycling provides nucleation sites for the phase transformation in the subsequent cycles. Further, the distribution of slip on different slip systems is determined by the martensite texture. This is a strong evidence for transformation induced plasticity. In the second study, experimentally informed simulations of NiTi micropillar compression are

  16. Magneto-structural transformations in Ni50Mn37.5Sn12.5-xInx Heusler powders

    NASA Astrophysics Data System (ADS)

    Maziarz, Wojciech; Wójcik, Anna; Czaja, Paweł; Żywczak, Antoni; Dutkiewicz, Jan; Hawełek, Łukasz; Cesari, Eduard

    2016-08-01

    The effect of ball milling and subsequently annealing of melt spun ribbons on magneto-structural transformations in Ni50Mn37.5Sn12.5-xInx (x=0, 2, 4, 6) ribbons is presented. Short time vibration milling allows to obtain chemically homogenous powders of angular particle shapes and size within 10-50 μm. Milling does not change the characteristic temperatures of martensitic transformation in comparison to the melt spun ribbons. The effect of In substitution for Sn on martensitic transformation has a complex mechanism, associated with electron density change. Substitution of Sn by In in both milled and annealed powders leads to decrease of Curie temperature of austenite and increase of martensitic transformation temperature, stabilizing martensitic phase. The coexistence of magnetic transformation of austenite and martensitic transformation at low magnetic field was observed. The intermartensitic transformation of 4O martensite to L10 martensite was observed during cooling at low magnetic field and this was confirmed by TEM microstructure observations. The annealing process of as-milled powders leads to the change of their martensitic structure due to relaxation of internal stresses associated with anisotropic columnar grain microstructure formed during melt spinning process. The level of stresses introduced during milling of ribbons has no significant influence on martensitic transformation. The annealing process of as milled powders leads to enhancement of their magnetic properties, decrease of Curie temperature of austenite, and marginal change of temperature of martenisitic transformation.

  17. Mechanochemical spinodal decomposition: a phenomenological theory of phase transformations in multi-component, crystalline solids

    NASA Astrophysics Data System (ADS)

    Rudraraju, Shiva; van der Ven, Anton; Garikipati, Krishna

    2016-06-01

    We present a phenomenological treatment of diffusion-driven martensitic phase transformations in multi-component crystalline solids that arise from non-convex free energies in mechanical and chemical variables. The treatment describes diffusional phase transformations that are accompanied by symmetry-breaking structural changes of the crystal unit cell and reveals the importance of a mechanochemical spinodal, defined as the region in strain-composition space, where the free-energy density function is non-convex. The approach is relevant to phase transformations wherein the structural order parameters can be expressed as linear combinations of strains relative to a high-symmetry reference crystal. The governing equations describing mechanochemical spinodal decomposition are variationally derived from a free-energy density function that accounts for interfacial energy via gradients of the rapidly varying strain and composition fields. A robust computational framework for treating the coupled, higher-order diffusion and nonlinear strain gradient elasticity problems is presented. Because the local strains in an inhomogeneous, transforming microstructure can be finite, the elasticity problem must account for geometric nonlinearity. An evaluation of available experimental phase diagrams and first-principles free energies suggests that mechanochemical spinodal decomposition should occur in metal hydrides such as ZrH2-2c. The rich physics that ensues is explored in several numerical examples in two and three dimensions, and the relevance of the mechanism is discussed in the context of important electrode materials for Li-ion batteries and high-temperature ceramics.

  18. Structural and phase transformations in quasi-binary TiNi-TiCu alloys with thermomechanical shape-memory effects

    NASA Astrophysics Data System (ADS)

    Pushin, V. G.; Kuranova, N. N.; Makarov, V. V.; Pushin, A. V.; Korolev, A. V.; Kourov, N. I.

    2015-12-01

    The structure, thermoelastic martensitic transformations, and physical properties of the usual microcrystalline and rapidly quenched submicrocrystalline ternary alloys of the quasi-binary TiNi-TiCu section with a copper content to 35 at % have been studied in a wide temperature range. The fine structure of the alloys has been investigated by the methods of the analytical transmission and scanning electron microscopy, and selected-area electron diffraction, including the in situ heating and cooling in the column of the microscope. The main specific features of the premartensitic state of the B2 austenite, the morphology, and the fine structure of the B19 and B19' martensitic phases have been established, and their evolution upon the alloying with copper and upon grain refinement and cooling and heating in situ have been studied. According to the data of the temperature measurements of electrical resistance, magnetic susceptibility, and XRD analysis, generalized complete diagrams of the B2 ↔ B19', B2 ↔ B19 ↔ B19' and B2↔ B19 martensitic transformations that occur upon cooling in these alloys with an increase in the copper concentration in the limits of 0-8, 8-15, and 15-35 at %, respectively, have been constructed.

  19. Luders-like deformation associated with martensite reorientation in NiTi

    SciTech Connect

    Liu, Y.; Liu, Y.; Van Humbeeck, J.

    1998-09-15

    It is known that near-equiatomic NiTi shape memory alloys may exhibit a Lueders-like deformation behavior under a variety of testing conditions. These conditions include the tensile deformation associated with the stress-induced martensitic transformation from the austenite, the reverse transformation of the stress-induced martensite to austenite in pseudoelasticity, and the deformation in martensitic state via a martensite variant reorientation process. The Lueders-like deformation behavior is characterized by a stress plateau and a stress-drop at the beginning of the process for the forward transformation upon loading and a stress minimum for the reverse transformation on unloading. Based largely on this observation in pseudoelasticity, it has been suggested that the stress peaks at the beginning of the stress plateau are associated with the nucleation of the product phase for the corresponding transformations and that the stress plateau corresponds to the process of the transformations. This common belief, however, is challenged by a number of experimental observations. This seems to suggest that the occurrence of the stress plateau on a stress-strain curve is mechanical in nature instead of being determined by the transformation. This uncertainty, however, needs to be clarified.

  20. Development of an interatomic potential for the simulation of defects, plasticity, and phase transformations in titanium

    NASA Astrophysics Data System (ADS)

    Mendelev, M. I.; Underwood, T. L.; Ackland, G. J.

    2016-10-01

    New interatomic potentials describing defects, plasticity, and high temperature phase transitions for Ti are presented. Fitting the martensitic hcp-bcc phase transformation temperature requires an efficient and accurate method to determine it. We apply a molecular dynamics method based on determination of the melting temperature of competing solid phases, and Gibbs-Helmholtz integration, and a lattice-switch Monte Carlo method: these agree on the hcp-bcc transformation temperatures to within 2 K. We were able to develop embedded atom potentials which give a good fit to either low or high temperature data, but not both. The first developed potential (Ti1) reproduces the hcp-bcc transformation and melting temperatures and is suitable for the simulation of phase transitions and bcc Ti. Two other potentials (Ti2 and Ti3) correctly describe defect properties and can be used to simulate plasticity or radiation damage in hcp Ti. The fact that a single embedded atom method potential cannot describe both low and high temperature phases may be attributed to neglect of electronic degrees of freedom, notably bcc has a much higher electronic entropy. A temperature-dependent potential obtained from the combination of potentials Ti1 and Ti2 may be used to simulate Ti properties at any temperature.

  1. Development of an interatomic potential for the simulation of defects, plasticity, and phase transformations in titanium.

    PubMed

    Mendelev, M I; Underwood, T L; Ackland, G J

    2016-10-21

    New interatomic potentials describing defects, plasticity, and high temperature phase transitions for Ti are presented. Fitting the martensitic hcp-bcc phase transformation temperature requires an efficient and accurate method to determine it. We apply a molecular dynamics method based on determination of the melting temperature of competing solid phases, and Gibbs-Helmholtz integration, and a lattice-switch Monte Carlo method: these agree on the hcp-bcc transformation temperatures to within 2 K. We were able to develop embedded atom potentials which give a good fit to either low or high temperature data, but not both. The first developed potential (Ti1) reproduces the hcp-bcc transformation and melting temperatures and is suitable for the simulation of phase transitions and bcc Ti. Two other potentials (Ti2 and Ti3) correctly describe defect properties and can be used to simulate plasticity or radiation damage in hcp Ti. The fact that a single embedded atom method potential cannot describe both low and high temperature phases may be attributed to neglect of electronic degrees of freedom, notably bcc has a much higher electronic entropy. A temperature-dependent potential obtained from the combination of potentials Ti1 and Ti2 may be used to simulate Ti properties at any temperature.

  2. Development of an interatomic potential for the simulation of defects, plasticity, and phase transformations in titanium

    SciTech Connect

    Mendelev, M. I.; Underwood, T. L.; Ackland, G. J.

    2016-10-17

    New interatomic potentials describing defects, plasticity, and high temperature phase transitions for Ti are presented. Fitting the martensitic hcp-bcc phase transformation temperature requires an efficient and accurate method to determine it. We apply a molecular dynamics method based on determination of the melting temperature of competing solid phases, and Gibbs-Helmholtz integration, and a lattice-switch Monte Carlo method: these agree on the hcp-bcc transformation temperatures to within 2 K. We were able to develop embedded atom potentials which give a good fit to either low or high temperature data, but not both. The first developed potential (Ti1) reproduces the hcp-bcc transformation and melting temperatures and is suitable for the simulation of phase transitions and bcc Ti. Two other potentials (Ti2 and Ti3) correctly describe defect properties and can be used to simulate plasticity or radiation damage in hcp Ti. The fact that a single embedded atom method potential cannot describe both low and high temperature phases may be attributed to neglect of electronic degrees of freedom, notably bcc has a much higher electronic entropy. As a result, a temperature-dependent potential obtained from the combination of potentials Ti1 and Ti2 may be used to simulate Ti properties at any temperature.

  3. Effect of prestrain on martensitic transformation in a Ti46.4Ni47.6Nb6.0 superelastic alloy and its application to medical stents.

    PubMed

    Takagi, T; Sutou, Y; Kainuma, R; Yamauchi, K; Ishida, K

    2006-01-01

    The effect of applied strain on martensitic transformation in a superelastic Ti(46.4)Ni(47.6)Nb(6.0) alloy at room temperature was investigated by tensile tests, differential scanning calorimetry measurements, and X-ray diffraction. Reverse transformation starting (A(s)) and finishing (A(f)) temperatures increased with the application of tensile-strain over 13%, the undeformed specimen showing A(s) = -29.2 degrees C and A(f) = 17.9 degrees C, while the 13% predeformed alloy exhibited A(s) = 37.1 degrees C and A(f) = 40.2 degrees C. Furthermore, the values of the A(s) and A(f) for the predeformed alloy almost recovered to those of the undeformed alloy when heated to about 42 degrees C and then showed superelasticity again at room temperature. This characteristic is significant for application in sensors, actuators, and medical devices. Especially, medical stents with such qualities show promise as a new class of self-expandable stents with both excellent mountability and deliverability.

  4. Pressure-magnetic field induced phase transformation in Ni{sub 46}Mn{sub 41}In{sub 13} Heusler alloy

    SciTech Connect

    Rama Rao, N. V. Manivel Raja, M.; Pandian, S.; Esakki Muthu, S.; Arumugam, S.

    2014-12-14

    The effect of hydrostatic pressure and magnetic field on the magnetic properties and phase transformation in Ni{sub 46}Mn{sub 41}In{sub 13} Heusler alloy was investigated. Pressure (P)-magnetic field (H)-temperature (T) phase diagram has been constructed from experimental results. In the P–T contour of the phase diagram, the slope of the austenite-martensite phase boundary line appears positive (dT/dP > 0), while it appears negative (dT/dH < 0) in the H–T contour. The results revealed that pressure and magnetic field have opposite effect on phase stabilization. The combined effect of pressure and magnetic field on martensitic transition has led to two important findings: (i) pressure dependent shift of austenite start temperature (A{sub s}) is higher when larger field is applied, and (ii) field dependent shift of A{sub s} is lowered when a higher pressure is applied. The pressure and magnetic field dependent shift observed in the martensitic transformation has been explained on the basis of thermodynamic calculations. Curie temperature of the phases was found to increase with pressure at a rate of 0.6 K/kbar.

  5. Enhancement in magnetocaloric properties of NiMnGa alloy through stoichiometric tuned phase transformation and magneto-thermal transitions

    NASA Astrophysics Data System (ADS)

    Dey, Sushmita; Roy, R. K.; Ghosh, M.; Basu Mallick, A.; Mitra, A.; Panda, A. K.

    2017-10-01

    The investigation is focussed on phase generation and magnetocaloric properties of a series of Ni77-XMnXGa23 (x = 22, 23, 24, 25, 27) alloys prepared through arc melting furnace. With increase in Mn content, the alloys showed systematic transition from a non-modulated martensite (NM) to a fully austenitic parent phase through an appearance and coexistence of modulated (M) structure. Intermediate Mn containing alloy (#Mn24) not only displayed high magnetic entropy change (ΔSM) of -7.7 J/kg-1K-1 but also large Refrigerant Capacity (RC) of 169 J.Kg-1 at magnetic field change of 3 T compared to other alloys. The coexisting martensite (NM, M) and parent austenite as well as overlapping thermomagnetic and structural transformation was deliverable through tuning of alloy chemistry wherein Ni was systematically substituted by Mn. Transmission electron microscopy (TEM) supported the proposition with existence of martensite plates of different morphology in Mn24 alloy exhibiting superior magnetocaloric properties.

  6. Phase transformation in AFM silicon tips.

    PubMed

    Kopycinska-Müller, M; Barth, M; Küttner, M; Köhler, B

    2017-09-01

    We confirmed the occurrence of phase transformations in an atomic force microscopy silicon tip during loading and unloading experiments performed on a polycrystalline Ti sample. The influence of the phase transformations on the effective mechanical and electrical properties of the tip was observed with the help of load-unload curves measured simultaneously for the tip-sample contact stiffness k (*) and the effective electrical resistance of the system R eff. We used the atomic force acoustic microscopy (AFAM) method to determine the values of k (*). To measure the changes in R eff, we combined a high voltage source/measure unit with the existing AFAM system. The data obtained showed that the phase transformation from Si-I to Si-II is preceded by other structural changes such as formation of distorted diamond structures and formation of Si-III. This conclusion was reached after observing a small hysteretic behavior in the load-unload stiffness curve accompanied by only very small changes in the resistance of the tip-sample system occurring on the unloading. The coinciding of a sudden increase in the values of the contact stiffness with a decrease in the resistance of the system indicated that the formation of metallic Si-II occurred in the subsequent measurements. The interpretation of our results found confirmation in the results of molecular dynamics and atomistic simulations performed for silicon under nanoindentation experiments.

  7. Phase transformation in AFM silicon tips

    NASA Astrophysics Data System (ADS)

    Kopycinska-Müller, M.; Barth, M.; Küttner, M.; Köhler, B.

    2017-09-01

    We confirmed the occurrence of phase transformations in an atomic force microscopy silicon tip during loading and unloading experiments performed on a polycrystalline Ti sample. The influence of the phase transformations on the effective mechanical and electrical properties of the tip was observed with the help of load-unload curves measured simultaneously for the tip-sample contact stiffness k * and the effective electrical resistance of the system R eff. We used the atomic force acoustic microscopy (AFAM) method to determine the values of k *. To measure the changes in R eff, we combined a high voltage source/measure unit with the existing AFAM system. The data obtained showed that the phase transformation from Si-I to Si-II is preceded by other structural changes such as formation of distorted diamond structures and formation of Si-III. This conclusion was reached after observing a small hysteretic behavior in the load-unload stiffness curve accompanied by only very small changes in the resistance of the tip-sample system occurring on the unloading. The coinciding of a sudden increase in the values of the contact stiffness with a decrease in the resistance of the system indicated that the formation of metallic Si-II occurred in the subsequent measurements. The interpretation of our results found confirmation in the results of molecular dynamics and atomistic simulations performed for silicon under nanoindentation experiments.

  8. Mossbauer and XRD characterization of the phase transformations in a Fe-Mn-Al-C-Mo-Si-Cu as cast alloy during tribology test

    NASA Astrophysics Data System (ADS)

    Ramos, J.; Piamba, J. F.; Sánchez, H.; Alcazar, G. A. Pérez

    2015-06-01

    In present study Fe-29.0Mn-6Al-0.9C-1.8Mo-1.6Si-0.4Cu (%w) alloy was obtained after melted in an induction furnace, and then molded as an ingot. From the as cast ingot it were cut samples for the different characterization measurements. The microstructure of the as-cast sample is of dendritic type and its XRD pattern was refined with the lines of the austenite, with a big volumetric fraction, and the lines of the martensite, with small volumetric fraction. The Mössbauer spectrum of the sample was fitted with a broad singlet which corresponds to disordered austenite. After the tribology test, its XRD pattern was refined with the lines of two austenite phases, one similar to the previous one and other with bigger lattice parameter. The total volumetric fraction of the austenite is smaller than that obtained for sample without wear. It was added the lines of the martensite phase with bigger volumetric fraction than that of the previous sample. The Mössbauer spectrum of the weared sample was fitted with two paramagnetic sites which correspond to the two Fe austenite phases and a hyperfine magnetic field distribution which is associated to the disordered original martensite and the new one which appears in the surface as a consequence of the wear process. These results show that during wear process the original austenite phase is transformed in martensite and in a new austenite phase. The increases of the martensitic phase improves mechanical properties and wear behavior.

  9. Materials Science and Technology, Volume 5, Phase Transformations in Materials

    NASA Astrophysics Data System (ADS)

    Haasen, Peter

    1996-12-01

    This volume covers phase transformations, a general phenomenon central to understanding the behavior of materials and to creating high-performance materials. From the Contents: Pelton: Thermodynamics and Phase Diagrams of Materials. Murch: Diffusion in Crystalline Solids. Binder: Statistical Theories of Phase Transitions/Spinodal Decomposition. Wagner/Kampmann: Homogeneous Second Phase Precipitation. Purdy: Transformations Involving Interfacial Diffusion. Delaey: Diffusionless Transformations. Ruoff: High Pressure Phase Transformations. Pitsch/Inden: Atomic Ordering. Müller- Krumbhaar/Kurz: Solidification.

  10. Phase Transformations in Cast Duplex Stainless Steels

    SciTech Connect

    Kim, Yoon-Jun

    2004-01-01

    Duplex stainless steels (DSS) constitute both ferrite and austenite as a matrix. Such a microstructure confers a high corrosion resistance with favorable mechanical properties. However, intermetallic phases such as σ and χ can also form during casting or high-temperature processing and can degrade the properties of the DSS. This research was initiated to develop time-temperature-transformation (TTT) and continuous-cooling-transformation (CCT) diagrams of two types of cast duplex stainless steels, CD3MN (Fe-22Cr-5Ni-Mo-N) and CD3MWCuN (Fe-25Cr-7Ni-Mo-W-Cu-N), in order to understand the time and temperature ranges for intermetallic phase formation. The alloys were heat treated isothermally or under controlled cooling conditions and then characterized using conventional metallographic methods that included tint etching, and also using electron microscopy (SEM, TEM) and wavelength dispersive spectroscopy (WDS). The kinetics of intermetallic-phase (σ + χ) formation were analyzed using the Johnson-Mehl-Avrami (MA) equation in the case of isothermal transformations and a modified form of this equation in the case of continuous cooling transformations. The rate of intermetallic-phase formation was found to be much faster in CD3MWCuN than CD3MN due mainly to differences in the major alloying contents such as Cr, Ni and Mo. To examine in more detail the effects of these elements of the phase stabilities; a series of eight steel castings was designed with the Cr, Ni and Mo contents systematically varied with respect to the nominal composition of CD3MN. The effects of varying the contents of alloying additions on the formation of intermetallic phases were also studied computationally using the commercial thermodynamic software package, Thermo-Calc. In general, σ was stabilized with increasing Cr addition and χ by increasing Mo addition. However, a delicate balance among Ni and other minor elements such as N and Si also exists. Phase equilibria in DSS can be affected by

  11. Transformation relaxation and aging in a CuZnAl shape-memory alloy studied by modulated differential scanning calorimetry

    SciTech Connect

    Wei, Z.G.

    1998-11-01

    The reverse martensitic transformation and aging processes in a polycrystalline Cu-23.52 at. pct Zn-9.65 at. pct Al shape-memory alloy have been studied using the recently developed modulated differential scanning calorimetry (MDSC) technique, and some new findings are obtained. By separating the nonreversing heat flow from the reversing heat flow, MDSC can better characterize the thermodynamic, kinetic, and hysteretic feature of thermoelastic martensitic transformations. Two kinds of exothermal relaxation peaks have been identified and separated from the endothermal reverse martensitic transformations: one is associated with the movement of twin interfaces or martensite-parent interfaces, and another is due to the atomic reordering in the parent phase via a vacancy mechanism. The martensite aging processes have been examined, and two stages of the aging process has been distinguished: the first stage of aging is characterized by the stabilization of martensite, as manifested in the increase in the reversing enthalpy of the reverse martensitic transformation and in the transformation temperatures, and the second stage, is in fact, the decomposition of the martensite on prolonged aging, accompanied by a decrease in the transformation enthalpy. The results suggest that the mechanisms of the relaxation in the martensite and in the parent phase may be quite different.

  12. Phase field simulations of plastic strain-induced phase transformations under high pressure and large shear

    NASA Astrophysics Data System (ADS)

    Javanbakht, Mahdi; Levitas, Valery I.

    2016-12-01

    Pressure and shear strain-induced phase transformations (PTs) in a nanograined bicrystal at the evolving dislocations pile-up have been studied utilizing a phase field approach (PFA). The complete system of PFA equations for coupled martensitic PT, dislocation evolution, and mechanics at large strains is presented and solved using the finite element method (FEM). The nucleation pressure for the high-pressure phase (HPP) under hydrostatic conditions near a single dislocation was determined to be 15.9 GPa. Under shear, a dislocation pile-up that appears in the left grain creates strong stress concentration near its tip and significantly increases the local thermodynamic driving force for PT, which causes nucleation of HPP even at zero pressure. At pressures of 1.59 and 5 GPa and shear, a major part of a grain transforms to HPP. When dislocations are considered in the transforming grain as well, they relax stresses and lead to a slightly smaller stationary HPP region than without dislocations. However, they strongly suppress nucleation of HPP and require larger shear. Unexpectedly, the stationary HPP morphology is governed by the simplest thermodynamic equilibrium conditions, which do not contain contributions from plasticity and surface energy. These equilibrium conditions are fulfilled either for the majority of points of phase interfaces or (approximately) in terms of stresses averaged over the HPP region or for the entire grain, despite the strong heterogeneity of stress fields. The major part of the driving force for PT in the stationary state is due to deviatoric stresses rather than pressure. While the least number of dislocations in a pile-up to nucleate HPP linearly decreases with increasing applied pressure, the least corresponding shear strain depends on pressure nonmonotonously. Surprisingly, the ratio of kinetic coefficients for PT and dislocations affect the stationary solution and the nanostructure. Consequently, there are multiple stationary solutions

  13. Chemical and mechanical stabilization of martensite

    SciTech Connect

    Kustov, S.; Pons, J.; Cesari, E.; Van Humbeeck, J

    2004-09-06

    An algorithm of quantitative analysis of two basic contributions to the stabilization of martensite - atomic reordering ('chemical' stabilization component) and pinning of interfaces ('mechanical' contribution) - has been developed. The algorithm uses data obtained by routine calorimetry measurements. The possibility to quantitatively separate contributions of 'chemical' and 'mechanical' stabilization components stems from the fact that they affect the first reverse transformation of stabilized martensite through thermodynamically reversible and irreversible factors, respectively. Analysis of the thermodynamics of the thermoelastic martensitic transformations allowed us to conclude that stabilization of martensite should be described in terms of pure shift and broadening of the reverse transformation. These parameters are shown to have a clear physical meaning. Namely, pure shift of the reverse transformation as a result of martensite stabilization provides an upper estimate for the atomic reordering or 'chemical' contribution to the stabilization, whereas broadening of the reverse transformation represents a lower limit for pinning-induced or 'mechanical' stabilization component. Experimental data on stabilization of a Cu-Zn-Al alloy are analyzed, indicating that contributions of 'chemical' and 'mechanical' stabilization components are comparable but depend on martensite ageing period and details of the initial heat treatment of samples.

  14. Characterization of Solid State Phase Transformation in Continuously Heated and Cooled Ferritic Weld Metal

    SciTech Connect

    Narayana, B; Mills, Michael J.; Specht, Eliot D; Santella, Michael L; Babu, Sudarsanam Suresh

    2010-12-01

    Arc welding processes involve cooling rates that vary over a wide range (1-100 K/s). The final microstructire is thus a product of the heating and cooling cycles experienced by the weld in addition to the weld composition. It has been shown that the first phase to form under weld cooling conditions may not be that predicted by equilibrium calculations. The partitioning of different interstitial/substitutional alloying elements at high temperatures can dramatically affect the subsequent phase transformations. In order to understand the effect of alloying on phase transformation temperatures and final microstructures time-resolved X-ray diffraction technique has been successfully used for characterization. The work by Jacot and Rappaz on pearlitic steels provided insight into austenitization of hypoeutectic steels using a finite volume model. However there is very little work done on the effect of heating and cooling rates on the phase transformation paths in bainitic/martensitic steels and weld metals. Previous work on a weld with higher aluminum content, deposited with a FCAW-S process indicated that even at aluminum levels where the primary phase to solidify from liquid should be delta ferrite, non-equilibrium austenite was observed. The presence of inhomogeneity in composition of the parent microstructure has been attributed to differences in transformation modes, temperatures and microstructures in dual-phase, TRIP steels and ferritic welds. The objectives of the work included the identification of the stability regions of different phases during heating and cooling, differences in the effect of weld heating and cooling rates on the phase transformation temperatures, and the variation in phase fractions of austenite and ferrite in the two phase regions as a function of temperature. The base composition used for the present work is a Fe-1%Al-2%Mn-1%Ni-0.04%C weld metal. A pseudo-binary phase diagram shows the expected solidification path under equilibrium

  15. Structural and phase transformations, mechanical properties, and shape-memory effects in quasibinary Ni50Ti38Hf12 alloy obtained by quenching from the melt

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    Methods of transmission and scanning electron microscopy and chemical microanalysis, electron diffraction, and X-ray diffraction were used to systematically study the structure and the chemical and phase composition of the Ni50Ti38Hf12 alloy synthesized by rapid quenching from the melt and subjected to various heat treatments. The critical temperatures of the devitrification of the initially amorphous rapidly quenched alloy and the B2 ↔ B19' thermoelastic martensitic transformations have been determined. The lattice parameters of the B2 austenite and thermoelastic B19' martensite have been measured. The main features of the formation of an ultrafine-grained structure in the alloy and the subsequent phase transformations (martensitic transformation and the decomposition with the formation of an intermetallic phase of the (Ti,Hf)2Ni type) have been studied depending on the regimes of heat treatment. Based on the results of measurements of mechanical properties upon tension (σM, σu, and δ) and the shape-memory effects (degree of shape recovery depending on the deformation by bending; and magnitude of the reversible strain ɛrev), regimes for obtaining high-strength and plastic states of the alloy with a shape-memory effect have been established.

  16. Phase Transformations upon Doping in Tungsten Trioxide

    NASA Astrophysics Data System (ADS)

    Wang, Wennie; Janotti, Anderson; van de Walle, Chris G.

    Tungsten trioxide (WO3) is an emerging semiconductor material, with a growing number of applications in Li-ion batteries, photocatalysis, gas sensors and electrochromic devices. As an electrochromic material, WO3 turns from transparent to blue upon doping with monovalent species. Due to it having an empty A-site in the ABO3 perovskite structure, high doping concentrations are possible through intercalation. Tungsten trioxide has been experimentally shown to transform from the ground-state monoclinic symmetry to cubic symmetry with increasing monovalent doping. We use first-principles calculations to understand this transformation. Our calculations show that the addition of electrons to the conduction band is a primary driver of the phase transformation. We quantify the energetics and structural aspects of this transformation using density functional theory, allowing us to elucidate the mechanism. Comparison with experiment, role of the dopant species, and implications of structural changes for device applications will be discussed. This work is supported by the DOE and NSF GRFP.

  17. In-situ characterization of highly reversible phase transformation by synchrotron X-ray Laue microdiffraction

    SciTech Connect

    Chen, Xian; Tamura, Nobumichi; MacDowell, Alastair; James, Richard D.

    2016-05-23

    The alloy Cu 25 Au 30 Zn 45 undergoes a huge first-order phase transformation (6% strain) and shows a high reversibility under thermal cycling and an unusual martensitc microstructure in sharp contrast to its nearby compositions. We discovered this alloy by systematically tuning the composition so that its lattice parameters satisfy the cofactor conditions (i.e., the kinematic conditions of compatibility between phases). It was conjectured that satisfaction of these conditions is responsible for the enhanced reversibility as well as the observed unusual fluid-like microstructure during transformation, but so far, there has been no direct evidence confirming that these observed microstructures are those predicted by the cofactor conditions. In order to verify this hypothesis, we use synchrotron X-ray Laue microdiffraction to measure the orientations and structural parameters of variants and phases near the austenite/martensite interface. The areas consisting of both austenite and multi-variants of martensite are scanned by microLaue diffraction. The cofactor conditions have been examined from the kinematic relation of lattice vectors across the interface. The continuity condition of the interface is precisely verified from the correspondent lattice vectors between two phases.

  18. Martensitic accommodation strain and the metal-insulator transition in manganites

    NASA Astrophysics Data System (ADS)

    Podzorov, V.; Kim, B. G.; Kiryukhin, V.; Gershenson, M. E.; Cheong, S.-W.

    2001-10-01

    In this paper, we report polarized optical microscopy and electrical transport studies of manganese oxides that reveal that the charge ordering transition in these compounds exhibits typical signatures of a martensitic transformation. We demonstrate that specific electronic properties of charge-ordered manganites stem from a combination of martensitic accommodation strain and effects of strong electron correlations. This intrinsic strain is strongly affected by the grain boundaries in ceramic samples. Consistently, our studies show a remarkable enhancement of low field magnetoresistance and the grain size effect on the resistivity in polycrystalline samples and suggest that the transport properties of this class of manganites are governed by the charge-disordered insulating phase stabilized at low temperature by virtue of martensitic accommodation strain. High sensitivity of this phase to strains and magnetic field leads to a variety of striking phenomena, such as unusually high magnetoresistance (1010%) in low magnetic fields.

  19. Development of an interatomic potential for the simulation of defects, plasticity, and phase transformations in titanium

    DOE PAGES

    Mendelev, M. I.; Underwood, T. L.; Ackland, G. J.

    2016-10-17

    New interatomic potentials describing defects, plasticity, and high temperature phase transitions for Ti are presented. Fitting the martensitic hcp-bcc phase transformation temperature requires an efficient and accurate method to determine it. We apply a molecular dynamics method based on determination of the melting temperature of competing solid phases, and Gibbs-Helmholtz integration, and a lattice-switch Monte Carlo method: these agree on the hcp-bcc transformation temperatures to within 2 K. We were able to develop embedded atom potentials which give a good fit to either low or high temperature data, but not both. The first developed potential (Ti1) reproduces the hcp-bcc transformationmore » and melting temperatures and is suitable for the simulation of phase transitions and bcc Ti. Two other potentials (Ti2 and Ti3) correctly describe defect properties and can be used to simulate plasticity or radiation damage in hcp Ti. The fact that a single embedded atom method potential cannot describe both low and high temperature phases may be attributed to neglect of electronic degrees of freedom, notably bcc has a much higher electronic entropy. As a result, a temperature-dependent potential obtained from the combination of potentials Ti1 and Ti2 may be used to simulate Ti properties at any temperature.« less

  20. Influence of Alloy Content and Prior Microstructure on Evolution of Secondary Phases in Weldments of 9Cr-Reduced Activation Ferritic-Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Thomas Paul, V.; Sudha, C.; Saroja, S.

    2015-08-01

    9Cr-Reduced Activation Ferritic-Martensitic steels with 1 and 1.4 wt pct tungsten are materials of choice for the test blanket module in fusion reactors. The steels possess a tempered martensite microstructure with a decoration of inter- and intra-lath carbides, which undergoes extensive modification on application of heat. The change in substructure and precipitation behavior on welding and subsequent thermal exposure has been studied using both experimental and computational techniques. Changes i.e., formation of various phases, their volume fraction, size, and morphology in different regions of the weldment due to prolonged thermal exposure was influenced not only by the time and temperature of exposure but also the prior microstructure. Laves phase of type Fe2W was formed in the high tungsten steel, on aging the weldment at 823 K (550 °C). It formed in the fine-grained heat-affected zone (HAZ) at much shorter durations than in the base metal. The accelerated kinetics has been understood in terms of enhanced precipitation of carbides at lath/grain boundaries during aging and the concomitant depletion of carbon and chromium and enrichment of tungsten in the vicinity of the carbides. Therefore, the fine-grained HAZ in the weldment was identified as a region susceptible for failure during service.

  1. Search for New Highly Energetic Phases under Compression and Shear

    DTIC Science & Technology

    2015-05-01

    propagation and microstructure evolution in phase field models of stress-induced martensitic phase transformations. International J. Plasticity , 2010...Zarechnyy O. M., Levitas V.I., and Ma, Y. Coupled plastic flow and phase transformation under compression of materials in a diamond anvil cell...Mechanically-Induced Phase Transformations and Chemical Reactions.” Advanced School “ Plasticity and Beyond: Microstructures , Crystal- Plasticity and

  2. Domain walls in ω-phase transformations

    NASA Astrophysics Data System (ADS)

    Sanati, Mahdi; Saxena, Avadh

    1998-11-01

    The β-phase (body-centered cubic: b.c.c.) to ω-phase transformation in certain elements (e.g. Zr) and alloys (e.g. ZrNb) is induced either by quenching or application of pressure. The ω-phase is a metastable state and usually coexists with the β-matrix in the form of small particles. To study the formation of domain walls in these materials we have extended the Landau model of Cook for the ω-phase transition by including a spatial gradient (Ginzburg) term of the scalar order parameter. In general, the Landau free energy is an asymmetric double-well potential. From the variational derivative of the total free energy we obtain a static equilibrium condition. By solving this equation for different physical parameters and boundary conditions, we obtained different quasi-one-dimensional soliton-like solutions. These solutions correspond to three different types of domain walls between the ω-phase and the β-matrix. In addition, we obtained soliton lattice (domain wall array) solutions, calculated their formation energy and the asymptotic interaction between the solitons.

  3. Phase amplitude conformal symmetry in Fourier transforms

    NASA Astrophysics Data System (ADS)

    Kuwata, S.

    2015-04-01

    For the Fourier transform ℑ : L2(R) → L2(R) of a complex-valued even or odd function ψ, it is found that the amplitude invariance |ℑψ| = |ψ| leads to a phase invariance or inversion as arg(ℑψ) = ±argψ + θ (θ = constant). The converse holds unless arg ψ = constant. The condition |ψ| = |ℑψ| is required in dealing with, for example, the minimum uncertainty relation between position and momentum. Without the evenness or oddness of ψ, |ℑψ| = |ψ| does not necessarily imply arg(ℑψ) = ±argψ + θ, nor is the converse.

  4. The Effect of Hardenability Variation on Phase Transformation of Spiral Bevel Gear in Quenching Process

    NASA Astrophysics Data System (ADS)

    Zhang, Yingtao; Shi, Wankai; Yang, Lin; Gu, Zhifei; Li, Zhichao

    2016-07-01

    The hardenability of gear steel is dependent on the composition of alloying elements and is one of important criteria to assess process of phase transformation. The variation of hardenability has to be considered in control of the microstructures and distortion during gear quenching. In this paper, the quantitative effect of hardenability has been investigated on phase transformations of spiral bevel gears in die quenching. The hardenability deviation of 22CrMoH steel was assessed by using Jominy test. The dilatometry experiments were conducted to build phase transformation kinetic models for steels with low and high hardenability, respectively. The complete die quenching process of spiral bevel gear was modeled to reveal the significant difference on microstructures and temperature history with variation of hardenability. The final microstructures of the gear are martensite in surface layer after quenching process. There are bainite inside the gear tooth and the mixture of bainite and ferrite inside gear for the gear with low hardenability. The microstructure is bainite inside the gear with high hardenability.

  5. Thermally Activated Martensite: Its Relationship to Non-Thermally Activated (Athermal) Martensite

    SciTech Connect

    Laughlin, D E; Jones, N J; Schwartz, A J; Massalski, T B

    2008-10-21

    The classification of martensitic displacive transformations into athermal, isothermal or anisothermal is discussed. Athermal does not mean 'no temperature dependence' as is often thought, but is best considered to be short for the notion of no thermal activation. Processes with no thermal activation do not depend on time, as there is no need to wait for sufficient statistical fluctuations in some specific order parameter to overcome an activation barrier to initiate the process. Clearly, this kind of process contrasts with those that are thermally activated. In the literature, thermally activated martensites are usually termed isothermal martensites, suggesting a constant temperature. Actually such martensites also typically occur with continuous cooling. The important distinctive feature of these martensites is that they are thermally activated and hence are distinguishable in principle from athermal martensites. A third type of process, anisothermal, has been introduced to account for those transformations which are thought to be thermally activated but which occur on continuous cooling. They may occur so rapidly that they do not appear to have an incubation time, and hence could be mistakenly called an athermal transformation. These designations will be reviewed and discussed in terms of activation energies and kinetic processes of the various martensitic transformations.

  6. Magnetic Properties and Phase Diagram of Ni50Mn_{50-x}Ga_{x/2}In_{x/2} Magnetic Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Xu, Xiao; Yoshida, Yasuki; Omori, Toshihiro; Kanomata, Takeshi; Kainuma, Ryosuke

    2016-12-01

    Ni50Mn50- x Ga x/2In x/2 magnetic shape memory alloys were systematically prepared, and the magnetic properties as well as the phase diagram, including atomic ordering, martensitic and magnetic transitions, were investigated. The B2- L21 order-disorder transformation showed a parabolic-like curve against the Ga+In composition. The martensitic transformation temperature was found to decrease with increasing Ga+In composition and to slightly bend downwards below the Curie temperature of the parent phase. Spontaneous magnetization was investigated for both parent and martensite alloys. The magnetism of martensite phase was found to show glassy magnetic behaviors by thermomagnetization and AC susceptibility measurements.

  7. Phase transformations in xerogels of mullite composition

    NASA Technical Reports Server (NTRS)

    Hyatt, Mark J.; Bansal, Narottam P.

    1988-01-01

    Monophasic and diphasic xerogels have been prepared as precursors for mullite (3Al2O3-2SiO2). Monophasic xerogel was synthesized from tetraethyl orthosilicate and aluminum nitrate nanohydrate and the diphasic xerogel from colloidal suspension of silica and boehmite. The chemical and structural evolutions, as a function of thermal treatment, in these two types of sol-gel derived mullite precursor powders have been characterized by DTA, TGA, X-ray diffraction, SEM and infrared spectroscopy. Monophasic xerogel transforms to an Al-Si spinel from an amorphous structure at approximately 980 C. The spinel then changes into mullite on further heating. Diphasic xerogel forms mullite at approximately 1360 C. The components of the diphasic powder react independently up to the point of mullite formation. The transformation in the monophasic powder occurs rapidly and yields strongly crystalline mullite with no other phases present. The diphasic powder, however, transforms rather slowly and contains remnants of the starting materials (alpha-Al2O3, cristobalite) even after heating at high temperatures for long times (1600 C, 6 hr). The diphasic powder could be sintered to high density but not the monophasic powder in spite of its molecular level homogeneity.

  8. Phase transformations in xerogels of mullite composition

    NASA Technical Reports Server (NTRS)

    Hyatt, Mark J.; Bansal, Narottam P.

    1990-01-01

    Monophasic and diphasic xerogels have been prepared as precursors for mullite (3Al203-2Si02). Monophasic xerogel was synthesized from tetraethyl orthosilicate and aluminum nitrate nanohydrate and the diphasic xerogel from colloidal suspension of silica and boehmite. The chemical and structural evolutions, as a function of thermal treatment, in these two types of sol-gel derived mullite precursor powders have been characterized by DTA, TGA, X-ray diffraction, SEM and infrared spectroscopy. Monophasic xerogel transforms to an Al-Si spinel from an amorphous structure at approximately 980 C. The spinel then changes into mullite on further heating. Diphasic xerogel forms mullite at approximately 1360 C. The components of the diphasic powder react independently up to the point of mullite formation. The transformation in the monophasic powder occurs rapidly and yields strongly crystalline mullite with no other phases present. The diphasic powder, however, transforms rather slowly and contains remnants of the starting materials (alpha-Al203, cristobalite) even after heating at high temperatures for long times (1600 C, 6 hr). The diphasic powder could be sintered to high density but not the monophasic powder in spite of its molecular level homogeneity.

  9. Relationships Between the Phase Transformation Kinetics, Texture Evolution, and Microstructure Development in a 304L Stainless Steel Under Biaxial Loading Conditions: Synchrotron X-ray and Electron Backscatter Diffraction Studies

    DOE PAGES

    Cakmak, Ercan; Choo, Hahn; Kang, Jun-Yun; ...

    2015-02-11

    Here we report that the relationships between the martensitic phase transformation kinetics, texture evolution, and the microstructure development in the parent austenite phase were studied for a 304L stainless steel that exhibits the transformation-induced plasticity effect under biaxial loading conditions at ambient temperature. The applied loading paths included: pure torsion, simultaneous biaxial torsion/tension, simultaneous biaxial torsion/compression, and stepwise loading of tension followed by torsion (i.e., first loading by uniaxial tension and then by pure torsion in sequence). Synchrotron X-ray and electron backscatter diffraction techniques were used to measure the evolution of the phase fractions, textures, and microstructures as a functionmore » of the applied strains. The influence of loading character and path on the changes in martensitic phase transformation kinetics is discussed in the context of (1) texture-transformation relationship and the preferred transformation of grains belonging to certain texture components over the others, (2) effects of axial strains on shear band evolutions, and (3) volume changes associated with martensitic transformation.« less

  10. Relationships Between the Phase Transformation Kinetics, Texture Evolution, and Microstructure Development in a 304L Stainless Steel Under Biaxial Loading Conditions: Synchrotron X-ray and Electron Backscatter Diffraction Studies

    SciTech Connect

    Cakmak, Ercan; Choo, Hahn; Kang, Jun-Yun; Ren, Yang

    2015-02-11

    Here we report that the relationships between the martensitic phase transformation kinetics, texture evolution, and the microstructure development in the parent austenite phase were studied for a 304L stainless steel that exhibits the transformation-induced plasticity effect under biaxial loading conditions at ambient temperature. The applied loading paths included: pure torsion, simultaneous biaxial torsion/tension, simultaneous biaxial torsion/compression, and stepwise loading of tension followed by torsion (i.e., first loading by uniaxial tension and then by pure torsion in sequence). Synchrotron X-ray and electron backscatter diffraction techniques were used to measure the evolution of the phase fractions, textures, and microstructures as a function of the applied strains. The influence of loading character and path on the changes in martensitic phase transformation kinetics is discussed in the context of (1) texture-transformation relationship and the preferred transformation of grains belonging to certain texture components over the others, (2) effects of axial strains on shear band evolutions, and (3) volume changes associated with martensitic transformation.

  11. Relationships between the Phase Transformation Kinetics, Texture Evolution, and Microstructure Development in a 304L Stainless Steel under Biaxial Loading Conditions: Synchrotron X-Ray and Electron Back-Scatter Diffraction Studies

    SciTech Connect

    Cakmak, Ercan; Choo, Hahn; Kang, Jun-Yun; Ren, Yang

    2015-05-01

    The relationships between the martensitic phase transformation kinetics, texture evolution, and the microstructure development in the parent austenite phase were studied for a 304L stainless steel that exhibits the transformation-induced plasticity effect under biaxial loading conditions at ambient temperature. The applied loading paths included: pure torsion, simultaneous biaxial torsion/tension, simultaneous biaxial torsion/compression, and stepwise loading of tension followed by torsion (i.e., first loading by uniaxial tension and then by pure torsion in sequence). Synchrotron X-ray and electron backscatter diffraction techniques were used to measure the evolution of the phase fractions, textures, and microstructures as a function of the applied strains. The influence of loading character and path on the changes in martensitic phase transformation kinetics is discussed in the context of (1) texture-transformation relationship and the preferred transformation of grains belonging to certain texture components over the others, (2) effects of axial strains on shear band evolutions, and (3) volume changes associated with martensitic transformation.

  12. Phase transformation and growth of hygroscopic aerosols

    SciTech Connect

    Tang, I.N.

    1995-09-01

    Ambient aerosols frequently contain large portions of hygroscopic inorganic salts such as chlorides, nitrates, and sulfates in either pure or mixed forms. Such inorganic salt aerosols exhibit the properties of deliquescence and efflorescence in air. The phase transformation from a solid particle to a saline droplet usually occurs spontaneously when the relative humidity of the atmosphere reaches a level specific to the chemical composition of the aerosol particle. Conversely, when the relative humidity decreases and becomes low enough, the saline droplet will evaporate and suddenly crystallize, expelling all its water content. The phase transformation and growth of aerosols play an important role in many atmospheric processes affecting air quality, visibility degradation, and climate changes. In this chapter, an exposition of the underlying thermodynamic principles is given, and recent advances in experimental methods utilizing single-particle levitation are discussed. In addition, pertinent and available thermodynamic data, which are needed for predicting the deliquescence properties of single and multi-component aerosols, are compiled. This chapter is useful to research scientists who are either interested in pursuing further studies of aerosol thermodynamics, or required to model the dynamic behavior of hygroscopic aerosols in a humid environment.

  13. Stressed microstructures in thermally induced M9R M18R martensites

    NASA Astrophysics Data System (ADS)

    Balandraud, Xavier; Zanzotto, Giovanni

    2007-01-01

    We revisit the phase transformation that produces 'long-period stacking' M9R-M18R martensites in Cu-based shape-memory alloys and analyze some associated microstructures, in particular, the typical wedge-shaped configuration. Our basic premise is that the cubic-to-monoclinic martensitic phase change in these alloys is, geometrically, but a slight modification of the well-known bcc-to-9R transformation occurring in various elemental crystals, whose lattice strain is, at the microlevel, the same Bain strain as for the bcc-to-fcc transformation. For the memory alloys we thus determine the 'near-Bain' microstrain, thereby analyzing the faulted, long-period stacking martensite as a mesoscale structure derived from compatibility with the austenite. We compute the transformation-twin systems, habit planes, average deformation and stacking-fault density of the 9R, 18R, M9R or M18R martensites, as they arise from the compatibility conditions between the parent and product lattices. We confirm earlier conclusions that a stress-free wedge is not kinematically compatible in these materials. However, we show that this microstructure is 'close enough' to compatibility, finding that its stress levels are low and should cause only minimal plastification and damage in the crystal. The wedge is therefore rationalized as a viable path for the transformation also in these substances. We verify this to hold for all the lattice parameters reported for Cu-based alloys. In general, we conclude that martensitic microstructures can be stressed to a degree also in good memory materials. Furthermore, we find that the lattice-parameter relations, guaranteeing the zero-stress compatibility of special configurations favoring the transformation and its reversibility, do not need to be strictly enforced in these crystals, because the residual stresses in microstructures are low regardless of lattice-parameter values.

  14. Phase diffusionless γ↔α transformations and their effect on physical, mechanical and corrosion properties of austenitic stainless steels irradiated with neutrons and charged particles

    NASA Astrophysics Data System (ADS)

    Maksimkin, O. P.

    2016-04-01

    The work presents relationships of γ→α' and α'→γ-transformations in reactor 12Cr18Ni10Ti and 08Cr16Ni11Mo3 austenitic stainless steels induced by cold work, irradiation and/or temperature. Energy and mechanical parameters of nucleation and development of deformation-induced martensitic α'-phase in the non-irradiated and irradiated steels are given. The mechanisms of localized static deformation were investigated and its effect on martensitic γ→α' transformation is determined. It has been shown that irradiation of 12Cr18Ni10Ti steel with heavy Kr ions (1.56MeV/nucleon, fluence of 1·1015 cm-2) results in formation of α'-martensite in near-surface layer of the sample. Results of systematic research on reversed α'→γ-transformation in austenitic metastable stainless steels irradiated with slow (VVR-K) and fast (BN-350) neutrons are presented. The effect of annealing on strength and magnetic characteristics was determined. It was found that at the temperature of 400 °C in the irradiated with neutrons samples (59 dpa) an increase of ferromagnetic α'-phase and microhardness was observed. The obtained results could be used during assessment of operational characteristics of highly irradiated austenitic steels during transportation and storage of Fuel Assemblies for fast nuclear reactors.

  15. Effect of pre-strain on mechanical properties and deformation induced transformation of 304 stainless steel

    NASA Astrophysics Data System (ADS)

    Zulfi, Fahri R.; Korda, Akhmad A.

    2016-08-01

    Effect of pre-strain on mechanical properties and deformation induced phase transformation of 304 stainless steel under tensile deformation has been studied. Pre-strain with the variation percentage of deformation was applied to the tensile test specimens. Tensile and hardness testing were carried out after pre-strain to study the mechanical properties change. Deformation induced phase transformation was investigated by using X-ray diffraction and optical microscope. XRD study indicates that metastable austenite transforms to martensite due to deformation. The martensite volume fraction increases with the increase in percentage of deformation. The increase in strength and hardness were associated with an increase in the volume fraction of martensite.

  16. Free energies of austenite and martensite Fe-C alloys: an atomistic study

    NASA Astrophysics Data System (ADS)

    Sak-Saracino, Emilia; Urbassek, Herbert M.

    2014-03-01

    We investigate the influence of C interstitials on the phase stability of Fe-C crystals. We employ the Meyer-Entel interatomic interaction potential which is able to reproduce the austenite-martensite phase transition for pure Fe, and supplement it by a simple pairwise Fe-C interaction potential. Using two different thermodynamic methods, we calculate the free energies of the martensite and austenite phases. We find that C destabilizes the ground-state bcc phase. The decrease in the equilibrium transformation temperature with increasing C content parallels the one found in the experiment. This destabilization is found even if C is added for a potential in which only the bcc phase is stable until the melting point; here, for sufficiently high C addition, a stable fcc phase is established in the phase diagram.

  17. Interplay of phase sequence and electronic structure in the modulated martensites of Mn2NiGa from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Kundu, Ashis; Gruner, Markus E.; Siewert, Mario; Hucht, Alfred; Entel, Peter; Ghosh, Subhradip

    2017-08-01

    We investigate the relative stability, structural properties, and electronic structure of various modulated martensites of the magnetic shape memory alloy Mn2NiGa by means of density functional theory. We observe that the instability in the high-temperature cubic structure first drives the system to a structure where modulation shuffles with a period of six atomic planes are taken into account. The driving mechanism for this instability is found to be the nesting of the minority band Fermi surface, in a similar way to that established for the prototype system Ni2MnGa . In agreement with experiments, we find 14M modulated structures with orthorhombic and monoclinic symmetries having energies lower than other modulated phases with the same symmetry. In addition, we also find energetically favorable 10M modulated structures which have not been observed experimentally for this system yet. The relative stability of various martensites is explained in terms of changes in the electronic structures near the Fermi level, affected mostly by the hybridization of Ni and Mn states. Our results indicate that the maximum achievable magnetic field-induced strain in Mn2NiGa would be larger than in Ni2MnGa . However, the energy costs for creating nanoscale adaptive twin boundaries are found to be one order of magnitude higher than that in Ni2MnGa .

  18. Ultrahigh Ductility, High-Carbon Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Qin, Shengwei; Liu, Yu; Hao, Qingguo; Zuo, Xunwei; Rong, Yonghua; Chen, Nailu

    2016-10-01

    Based on the proposed design idea of the anti-transformation-induced plasticity effect, both the additions of the Nb element and pretreatment of the normalization process as a novel quenching-partitioning-tempering (Q-P-T) were designed for Fe-0.63C-1.52Mn-1.49Si-0.62Cr-0.036Nb hot-rolled steel. This high-carbon Q-P-T martensitic steel exhibits a tensile strength of 1890 MPa and elongation of 29 pct accompanied by the excellent product of tensile and elongation of 55 GPa pct. The origin of ultrahigh ductility for high-carbon Q-P-T martensitic steel is revealed from two aspects: one is the softening of martensitic matrix due to both the depletion of carbon in the matensitic matrix during the Q-P-T process by partitioning of carbon from supersaturated martensite to retained austenite and the reduction of the dislocation density in a martensitic matrix by dislocation absorption by retained austenite effect during deformation, which significantly enhances the deformation ability of martensitic matrix; another is the high mechanical stability of considerable carbon-enriched retained austenite, which effectively reduces the formation of brittle twin-type martensite. This work verifies the correctness of the design idea of the anti-TRIP effect and makes the third-generation advanced high-strength steels extend to the field of high-carbon steels from low- and medium-carbon steels.

  19. Electron backscattered diffraction study of ɛ/α' martensitic variants induced by plastic deformation in 304 stainless steel

    NASA Astrophysics Data System (ADS)

    Gey, N.; Petit, B.; Humbert, M.

    2005-12-01

    The electron backscattered diffraction (EBSD) technique has been used to assess crystallographic features of the residual γ phase and the strain-induced ɛ/α' martensites in a 304 stainless steel, tensile tested to 10 pct strain at T=-60 °C. The martensitic transformation rate varies according to the γ-grain orientation against the applied stress and the γ-grain size. The α'-transformation textures as well as the γ-misorientation spreads observed in specific γ-grain orientations have been analyzed. Large misorientation spreads are observed in the less-transformed γ grains. This reveals an important crystallographic slip activity, even if less strain-induced martensite has been formed. A strong γ → α' variant selection was detected in the cube- and Goss-oriented γ grains for which the transformation is less developed. For the {110} <1-11> and copper-oriented γ grains, the amount of α' martensite is significantly higher and the γ → α' variant selection is less pronounced. This variant selection is then analyzed on at a local scale and is related to the presence of {111} γ localized deformation bands on which further ɛ/α' martensites have nucleated.

  20. Exceptional Resilience of Small-Scale Au30Cu25Zn45 under Cyclic Stress-Induced Phase Transformation.

    PubMed

    Ni, Xiaoyue; Greer, Julia R; Bhattacharya, Kaushik; James, Richard D; Chen, Xian

    2016-12-14

    Shape memory alloys that produce and recover from large deformation driven by martensitic transformation are widely exploited in biomedical devices and microactuators. Generally their actuation work degrades significantly within first a few cycles and is reduced at smaller dimensions. Further, alloys exhibiting unprecedented reversibility have relatively small superelastic strain, 0.7%. These raise the questions of whether high reversibility is necessarily accompanied by small work and strain and whether high work and strain is necessarily diminished at small scale. Here we conclusively demonstrate that these are not true by showing that Au30Cu25Zn45 pillars exhibit 12 MJ m(-3) work and 3.5% superelastic strain even after 100 000 phase transformation cycles. Our findings confirm that the lattice compatibility dominates the mechanical behavior of phase-changing materials at nano to micron scales and points a way for smart microactuators design having the mutual benefits of high actuation work and long lifetime.

  1. Phase transformation and growth of hygroscopic aerosols

    SciTech Connect

    Tang, I.N.

    1999-11-01

    Ambient aerosols play an important role in many atmospheric processes affecting air quality, visibility degradation, and climatic changes as well. Both natural and anthropogenic sources contribute to the formation of ambient aerosols, which are composed mostly of sulfates, nitrates, and chlorides in either pure or mixed forms. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. For pure inorganic salt particles with diameter larger than 0.1 micron, the phase transformation from a solid particle to a saline droplet occurs only when the relative humidity in the surrounding atmosphere reaches a certain critical level corresponding to the water activity of the saturated solution. The droplet size or mass in equilibrium with relative humidity can be calculated in a straightforward manner from thermodynamic considerations. For aqueous droplets 0.1 micron or smaller, the surface curvature effect on vapor pressure becomes important and the Kelvin equation must be used.

  2. Phase transformations in ion-irradiated silicides

    NASA Technical Reports Server (NTRS)

    Hewett, C. A.; Lau, S. S.; Suni, I.; Hung, L. S.

    1985-01-01

    The present investigation has three objectives. The first is concerned with the phase transformation of CoSi2 under ion implantation and the subsequent crystallization characteristics during annealing, taking into account epitaxial and nonepitaxial recrystallization behavior. The second objective is related to a study of the general trend of implantation-induced damage and crystallization behavior for a number of commonly used silicides. The last objective involves a comparison of the recrystallization behavior of cosputtered refractory silicides with that of the ion-implanted silicides. It was found that epitaxial regrowth of ion-irradiated CoSi2 occurred for samples with an epitaxial seed left at the Si/CoSi2 interface. A structural investigation of CoSi2 involving transmission electron microscopy (TEM) showed that after high-dose implantation CoSi2 is amorphous.

  3. First-principles computation of structural, elastic and magnetic properties of Ni2FeGa across the martensitic transformation.

    PubMed

    Sahariah, Munima B; Ghosh, Subhradip; Singh, Chabungbam S; Gowtham, S; Pandey, Ravindra

    2013-01-16

    The structural stabilities, elastic, electronic and magnetic properties of the Heusler-type shape memory alloy Ni(2)FeGa are calculated using density functional theory. The volume conserving tetragonal distortion of the austenite Ni(2)FeGa find an energy minimum at c/a = 1.33. Metastable behaviour of the high temperature cubic austenite phase is predicted due to elastic softening in the [110] direction. Calculations of the total and partial magnetic moments show a dominant contribution from Fe atoms of the alloy. The calculated density of states shows a depression in the minority spin channel of the cubic Ni(2)FeGa just above the Fermi level which gets partially filled up in the tetragonal phase. In contrast to Ni(2)MnGa, the transition metal spin-down states show partial hybridization in Ni(2)FeGa and there is a relatively high electron density of states near the Fermi level in both phases.

  4. First-principles computation of structural, elastic and magnetic properties of Ni2FeGa across the martensitic transformation

    NASA Astrophysics Data System (ADS)

    Sahariah, Munima B.; Ghosh, Subhradip; Singh, Chabungbam S.; Gowtham, S.; Pandey, Ravindra

    2013-01-01

    The structural stabilities, elastic, electronic and magnetic properties of the Heusler-type shape memory alloy Ni2FeGa are calculated using density functional theory. The volume conserving tetragonal distortion of the austenite Ni2FeGa find an energy minimum at c/a = 1.33. Metastable behaviour of the high temperature cubic austenite phase is predicted due to elastic softening in the [110] direction. Calculations of the total and partial magnetic moments show a dominant contribution from Fe atoms of the alloy. The calculated density of states shows a depression in the minority spin channel of the cubic Ni2FeGa just above the Fermi level which gets partially filled up in the tetragonal phase. In contrast to Ni2MnGa, the transition metal spin-down states show partial hybridization in Ni2FeGa and there is a relatively high electron density of states near the Fermi level in both phases.

  5. Transformation-Induced Creep and Creep Recovery of Shape Memory Alloy

    PubMed Central

    Takeda, Kohei; Tobushi, Hisaaki; Pieczyska, Elzbieta A.

    2012-01-01

    If the shape memory alloy is subjected to the subloop loading under the stress-controlled condition, creep and creep recovery can appear based on the martensitic transformation. In the design of shape memory alloy elements, these deformation properties are important since the deflection of shape memory alloy elements can change under constant stress. The conditions for the progress of the martensitic transformation are discussed based on the kinetics of the martensitic transformation for the shape memory alloy. During loading under constant stress rate, temperature increases due to the stress-induced martensitic transformation. If stress is held constant during the martensitic transformation stage in the loading process, temperature decreases and the condition for the progress of the martensitic transformation is satisfied, resulting in the transformation-induced creep deformation. If stress is held constant during the reverse transformation stage in the unloading process, creep recovery appears due to the reverse transformation. The details for these thermomechanical properties are investigated experimentally for TiNi shape memory alloy, which is most widely used in practical applications. The volume fraction of the martensitic phase increases in proportion to an increase in creep strain. PMID:28817016

  6. Transformation-Induced Creep and Creep Recovery of Shape Memory Alloy.

    PubMed

    Takeda, Kohei; Tobushi, Hisaaki; Pieczyska, Elzbieta A

    2012-05-22

    If the shape memory alloy is subjected to the subloop loading under the stress-controlled condition, creep and creep recovery can appear based on the martensitic transformation. In the design of shape memory alloy elements, these deformation properties are important since the deflection of shape memory alloy elements can change under constant stress. The conditions for the progress of the martensitic transformation are discussed based on the kinetics of the martensitic transformation for the shape memory alloy. During loading under constant stress rate, temperature increases due to the stress-induced martensitic transformation. If stress is held constant during the martensitic transformation stage in the loading process, temperature decreases and the condition for the progress of the martensitic transformation is satisfied, resulting in the transformation-induced creep deformation. If stress is held constant during the reverse transformation stage in the unloading process, creep recovery appears due to the reverse transformation. The details for these thermomechanical properties are investigated experimentally for TiNi shape memory alloy, which is most widely used in practical applications. The volume fraction of the martensitic phase increases in proportion to an increase in creep strain.

  7. Reversion of a Parent {130 }⟨310⟩ α'' Martensitic Twinning System at the Origin of {332 }⟨113⟩ β Twins Observed in Metastable β Titanium Alloys

    NASA Astrophysics Data System (ADS)

    Castany, P.; Yang, Y.; Bertrand, E.; Gloriant, T.

    2016-12-01

    In bcc metastable β titanium alloys, and particularly in superelastic alloys, a unique {332 }⟨113 ⟩ twinning system occurs during plastic deformation. However, in situ synchrotron x-ray diffraction during a tensile test shows that the β phase totally transforms into α'' martensite under stress in a Ti-27Nb (at. %) alloy. {332 }⟨113⟩ β twins are thus not formed directly in the β phase but are the result of the reversion of {130 }⟨310⟩ α'' parent twins occurring in martensite under stress. The formation of an interfacial twin boundary ω phase is also observed to accommodate strains induced during the phase reversion.

  8. Friction in ferroelastic and martensitic materials

    NASA Astrophysics Data System (ADS)

    Salje, E. K. H.

    2015-04-01

    Friction during ferroelastic and martensite phase transformations and under external elastic forcing is related to the appearance of jerks as fingerprint for avalanches of moving domain boundaries. It is argued that such avalanches can be observed if the time scale of the experiment is sufficiently long to allow a statistical evaluation and have a time resolution compatible with the characteristic duration of an avalanche. Typical experimental methods include the observation of acoustic emission, resonance elastic spectroscopy, calorimetry, and advanced phonon spectroscopy. The changes of the internal structure of mobile twin boundaries contribute to changes in their mobility and their friction. The local structures of jammed twin boundary patterns are elucidated by computer simulation, their time evolution is similar to that of observed avalanche dynamics.

  9. The effect of martensite plasticity on the cyclic deformation of super-elastic NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

    2014-01-01

    Based on stress-controlled cyclic tension-unloading experiments with different peak stresses, the effect of martensite plasticity on the cyclic deformation of super-elastic NiTi shape memory alloy micro-tubes is investigated and discussed. The experimental results show that the reverse transformation from the induced martensite phase to the austenite phase is gradually restricted by the plastic deformation of the induced martensite phase caused by an applied peak stress that is sufficiently high (higher than 900 MPa), and the extent of such restriction increases with further increasing the peak stress. The residual and peak strains of super-elastic NiTi shape memory alloy accumulate progressively, i.e., transformation ratchetting occurs during the cyclic tension-unloading with peak stresses from 600 to 900 MPa, and the transformation ratchetting strain increases with the increase of the peak stress. When the peak stress is higher than 900 MPa, the peak strain becomes almost unchanged, but the residual strain accumulates and the dissipation energy per cycle decreases very quickly with the increasing number of cycles due to the restricted reverse transformation by the martensite plasticity. Furthermore, a quantitative relationship between the applied stress and the stabilized residual strain is obtained to reasonably predict the evolution of the peak strain and the residual strain.

  10. Temperature-dependent quantitative 3omega scanning thermal microscopy: Local thermal conductivity changes in NiTi microstructures induced by martensite-austenite phase transition.

    PubMed

    Chirtoc, M; Gibkes, J; Wernhardt, R; Pelzl, J; Wieck, A

    2008-09-01

    We develop the theoretical description of 3omega signals from the resistive Wollaston thermal probe (ThP) of a scanning thermal microscope (SThM) in terms of an equivalent low-pass filter. The normalized amplitude and phase frequency spectra are completely characterized by a single parameter, the crossover frequency f(c)(k) depending on the sample thermal conductivity k. The application concerns polycrystalline NiTi shape memory alloy microstructured by focused Ga ion beam milling and implantation. The calibration of the ThP combined with a novel two-step normalization procedure allowed quantitative exploitation of 3omega signal variations as small as -1.75% in amplitude and 0.60 degrees in phase upon heating the sample from room temperature to 100 degrees C. This corresponds to k increase of 23.9% that is consistent with the expected thermal conductivity variation due to martensite-austenite structural phase transition. To our knowledge this is for the first time that SThM 3omega phase information is used quantitatively as well. The static, calibrated 3omega measurements are complementary to 3omega SThM images of the patterned sample surface. The local SThM measurement of temperature-dependent thermal conductivity opens the possibility to imaging structural phase transitions at submicron scale.

  11. Temperature-dependent quantitative 3{omega} scanning thermal microscopy: Local thermal conductivity changes in NiTi microstructures induced by martensite-austenite phase transition

    SciTech Connect

    Chirtoc, M.; Gibkes, J.; Wernhardt, R.; Pelzl, J.; Wieck, A.

    2008-09-15

    We develop the theoretical description of 3{omega} signals from the resistive Wollaston thermal probe (ThP) of a scanning thermal microscope (SThM) in terms of an equivalent low-pass filter. The normalized amplitude and phase frequency spectra are completely characterized by a single parameter, the crossover frequency f{sub c}(k) depending on the sample thermal conductivity k. The application concerns polycrystalline NiTi shape memory alloy microstructured by focused Ga ion beam milling and implantation. The calibration of the ThP combined with a novel two-step normalization procedure allowed quantitative exploitation of 3{omega} signal variations as small as -1.75% in amplitude and 0.60 deg. in phase upon heating the sample from room temperature to 100 deg. C. This corresponds to k increase of 23.9% that is consistent with the expected thermal conductivity variation due to martensite-austenite structural phase transition. To our knowledge this is for the first time that SThM 3{omega} phase information is used quantitatively as well. The static, calibrated 3{omega} measurements are complementary to 3{omega} SThM images of the patterned sample surface. The local SThM measurement of temperature-dependent thermal conductivity opens the possibility to imaging structural phase transitions at submicron scale.

  12. A new approach predicting the evolution of laminated nanostructures—martensite in NiTi as an example

    NASA Astrophysics Data System (ADS)

    Petersmann, M.; Antretter, T.; Waitz, T.; Fischer, F. D.

    2017-04-01

    A model for laminated nanostructures, combining classical energy minimization with full-field finite element calculations in a computationally fully automated manner, is set up and used to quantitatively analyse the interaction of grains via self-accommodation of their transformation strains. The well known Koistinenwell established B2-B19’ martensitic phase transformation in nanocrystalline NiTi is treated as an exemplary case to demonstrate our new framework. A systematic search for an optimal energy minimizing transformation path is employed within a full-field model, including crystallographic transformation strains and fully anisotropic elastic constants, by using the Python scripting language. The microstructure is updated based on previous calculation results. The underlying incremental free energy minimization criterion naturally reproduces the transformation kinetics. The sequence of grains subjected to transformation as well as the selection of martensitic variants within the grains are obtained yielding the evolution of the total interface energy as well as the strain energy, dominating our approach.

  13. On consistent micromechanical estimation of macroscopic elastic energy, coherence energy and phase transformation strains for SMA materials

    NASA Astrophysics Data System (ADS)

    Ziółkowski, Andrzej

    2017-01-01

    An apparatus of micromechanics is used to isolate the key ingredients entering macroscopic Gibbs free energy function of a shape memory alloy (SMA) material. A new self-equilibrated eigenstrains influence moduli (SEIM) method is developed for consistent estimation of effective (macroscopic) thermostatic properties of solid materials, which in microscale can be regarded as amalgams of n-phase linear thermoelastic component materials with eigenstrains. The SEIM satisfy the self-consistency conditions, following from elastic reciprocity (Betti) theorem. The method allowed expressing macroscopic coherency energy and elastic complementary energy terms present in the general form of macroscopic Gibbs free energy of SMA materials in the form of semilinear and semiquadratic functions of the phase composition. Consistent SEIM estimates of elastic complementary energy, coherency energy and phase transformation strains corresponding to classical Reuss and Voigt conjectures are explicitly specified. The Voigt explicit relations served as inspiration for working out an original engineering practice-oriented semiexperimental SEIM estimates. They are especially conveniently applicable for an isotropic aggregate (composite) composed of a mixture of n isotropic phases. Using experimental data for NiTi alloy and adopting conjecture that it can be treated as an isotropic aggregate of two isotropic phases, it is shown that the NiTi coherency energy and macroscopic phase strain are practically not influenced by the difference in values of austenite and martensite elastic constants. It is shown that existence of nonzero fluctuating part of phase microeigenstrains field is responsible for building up of so-called stored energy of coherency, which is accumulated in pure martensitic phase after full completion of phase transition. Experimental data for NiTi alloy show that the stored coherency energy cannot be neglected as it considerably influences the characteristic phase transition

  14. THERMODYNAMICS AND KINETICS OF PHASE TRANSFORMATIONS IN PLUTONIUM ALLOYS - PART I

    SciTech Connect

    Turchi, P A; Kaufman, L; Liu, Z; Zhou, S

    2004-08-18

    In this report we investigate order, stability, and phase transformations for a series of actinide-based alloys. The statics and kinetics of precipitation and ordering in this class of alloys are modeled with a scheme that couples fundamental information on the alloy energetics obtained from experimental and assessed thermo-chemical data to the CALPHAD approach commonly used in industry for designing alloys with engineering specificity with the help of the Thermo-Calc software application. The CALPHAD approach is applied to the study of the equilibrium thermodynamic properties of Pu-based alloys, Pu-X, where X=Al, Fe, Ga. The assessment of the equilibrium phase diagrams in the whole range of alloy composition has been performed with the PARROT module of the Thermo-Calc application software. Predictions are made on the low temperature and Pu-rich side of the phase diagrams of Pu-Ga and Pu-Al for which controversy has been noted in the past. The validity of the assessed thermo-chemical database will be discussed by comparing predicted heats of transformation for pure Pu with measured values from differential scanning calorimetry analysis. An overall picture for the stability properties of Pu-Ga and Pu-Al that reconciles the results of past studies carried out on these alloys is proposed. Results on phase stability in the ternary Fe-Ga-Pu and Al-Fe-Pu alloys are discussed. The information collected in this study is then used to model metastability, long-term stability and aging for this class of alloys by coupling Thermo-Calc with DICTRA, a series of modules that allow the analysis of DIffusion Controlled TRAnsformations. Kinetics information is then summarized in so-called TTT (temperature-time-transformations) diagrams for the most relevant phases of actinide alloys. Specifically, results are presented on kinetics of phase transformations associated with the eutectoid-phase decomposition reaction occurring at low temperature, and with the martensitic transformation

  15. Performance analysis of energy conversion via caloric effects in first-order ferroic phase transformations.

    PubMed

    Song, Yintao

    2014-07-07

    A finite-time thermodynamic model of ferroic refrigerators and generators, based on first order phase transformation, is given. We use this model to evaluate a novel method of converting heat directly into electricity based on the martensitic phase transformation accompanied by an abrupt change in magnetic ordering recently discovered [Srivastava et al., Adv. Energy Mater., 2011, 1, 97]. In this paper, we study the efficiency and power output of this method. The formulas of efficiency and power output in terms of material constants, design parameters, and working conditions are derived. The Clausius-Clapeyron coefficient is shown to be important to the efficiency. The figure of merit, as a dimensionless parameter, of energy conversion using the new method is introduced. It is shown that, as the figure of merit goes to infinity, the efficiency approaches the Carnot efficiency. Thermodynamic cycles of the new energy conversion method are optimized for a maximum power output. The matching criteria between materials and working temperatures of such optimized cycles are derived. Using these criteria, one can choose the most suitable materials under given working conditions, or decide the best working conditions for available materials.

  16. Crystal Level Continuum Modeling of Phase Transformations: The (alpha) <--> (epsilon) Transformation in Iron

    SciTech Connect

    Barton, N R; Benson, D J; Becker, R; Bykov, Y; Caplan, M

    2004-10-18

    We present a crystal level model for thermo-mechanical deformation with phase transformation capabilities. The model is formulated to allow for large pressures (on the order of the elastic moduli) and makes use of a multiplicative decomposition of the deformation gradient. Elastic and thermal lattice distortions are combined into a single lattice stretch to allow the model to be used in conjunction with general equation of state relationships. Phase transformations change the mass fractions of the material constituents. The driving force for phase transformations includes terms arising from mechanical work, from the temperature dependent chemical free energy change on transformation, and from interaction energy among the constituents. Deformation results from both these phase transformations and elasto-viscoplastic deformation of the constituents themselves. Simulation results are given for the {alpha} to {epsilon} phase transformation in iron. Results include simulations of shock induced transformation in single crystals and of compression of polycrystals. Results are compared to available experimental data.

  17. X-ray measurements of the self-organization of martensitic variants during thermal cycling

    NASA Astrophysics D