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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Unravelling the sintering temperature-induced phase transformations in Ba(Fe 0.7 Ta 0.3 )O 3-δ ceramics

This work reports on the fundamental details of the crystal structure and phase transformations in Ba(Fe 0.7 Ta 0.3 )O 3-δ , the best known temperature-independent oxygen-sensing ceramic material for applications in extreme environments. Ba(Fe 0.7 Ta 0.3 )O 3-δ ceramics were synthesized using conventional solid-state ceramic reaction under variable sintering temperatures (T s = 1200–1350 °C). Combined X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM) measurements revealed the T s -induced phase transformations and their origin in Ba(Fe 0.7 Ta 0.3 )O 3-δ . Associated with phase transformations, pseudo-cubic (PC) reflections, such as {200} PC , {211} PC , and {220} PC , exhibited distinct anomalies with increasing T s . At T s = 1200 °C, Ba(Fe 0.7 Ta 0.3 )O 3-δ stabilized in mixed orthorhombic + rhombohedral phases (Amm2 + R3m). With increasing T s (≥1250 °C), Ba(Fe 0.7 Ta 0.3 )O 3-δ ceramics stabilized in tetragonal/rhombohedral [P4mm + R3m] mixed phases, while variations in the quantity of the respective phases were observed. Because both structure and crystal chemistry play key roles in achieving enhanced performance in chemical sensing and catalytic converters, detailed understanding of the phase transformations and crystal structure of Ba(Fe 0.7 Ta 0.3 )O 3-δ ceramics, as derived in this work, will be useful to develop chemical sensors with optimum performance for high-temperature and corrosive environments.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Morphology and phase transformations of tin oxide nanostructures synthesized by the hydrothermal method in the presence of dicarboxylic acids

A new approach to the synthesis of non-stoichiometric tin oxide structures with different morphologies and the phase compositions has been evaluated. The nanostructures were synthesized by hydrothermal treatment of the mixtures of dicarboxylic acids ― aminoterephthalic or oxalic ― with nanocrystalline SnO{sub 2} powder, which was obtained via the sol-gel technology. The products were characterized by Raman and IR spectroscopy, SEM, HRTEM, and XRD analysis. It was shown that the controlled addition of a dicarboxylic acid leads not only to a change in the morphology of the nanostructures, but also to SnO{sub 2}–SnO{sub 2}/Sn{sub 3}O{sub 4}–Sn{sub 3}O{sub 4}–SnO phase transformations. A single-phase Sn{sub 3}O{sub 4} in the form of the well-separated hexagonal nanoplates and mixed SnO{sub 2}/Sn{sub 3}O{sub 4} phases in the form of hierarchical flower-like structures were obtained in the presence of organic additives. The effects of concentration, redox activity of the acids and heat treatment on the basic characteristics of the synthesized tin oxide nanostructures and phase transformations in the synthesized materials are discussed. - Graphical abstract: The controlled addition of aminoterephthalic or oxalic acid leads not only to a change in the morphology of the nanostructures, but also to SnO{sub 2}–SnO{sub 2}/Sn{sub 3}O{sub 4}–Sn{sub 3}O{sub 4}–SnO phase transformations. - Highlights: • A new approach to the synthesis of non-stoichiometric tin oxide structures is studied. • Tin oxide structures are synthesized via hydrothermal method with dicarboxylic acids. • Morphology and phase composition are changed with redox activity and dosage of acid. • The redox activity of acid has an effect on ratio of SnO and SnO{sub 2} in crystal structure. • A pure phase Sn{sub 3}O{sub 4} nanoplates and SnO{sub 2}/Sn{sub 3}O{sub 4} hierarchical structures are formed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Interplay of Mechanochemistry and Material Processes in the Graphite to Diamond Phase Transformation

The manifestation of intramolecular strains in covalent systems is widely known to accelerate chemical reactions and open alternative reaction paths. This process is moderately well understood for isolated molecules and unimolecular processes. However, in condensed matter processes such as phase transformations, material properties and structure may influence typical mechanochemical effects. Therefore, we utilize steered molecular dynamics to induce out of plane strains in graphite and compress the system under a constant strain rate to induce phase transformation. We show that the out of plane strain allows phase transformations to initiate at small amounts of compressive strain. Yet, in contrast to typical mechanochemical results, the sum of compressive and out of plane work needed to form a diamond has a local minimum due to altered defect formation processes during phase transformation. Additionally, these altered processes slow the kinetics of the phase transformation, taking longer from initiation to total material transformation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1976

Phase transformation and stabilization of a high strength austenite

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.

Jin, S.↗
DOE OSTI2017

Thermal and magnetic hysteresis associated with martensitic and magnetic phase transformations in Ni 52 Mn 25 In 16 Co 7 Heusler alloy

Ni-Mn-In-Co Heusler alloys demonstrate promising magnetocaloric performance for use as refrigerants in magnetic cooling systems with the goal of replacing the lower efficiency, eco-adverse fluid-compression technology. The largest change in entropy occurs when the applied magnetic field causes a merged structural and magnetic transformation and the associated entropy changes of the two transformations works constructively. In this study, magnetic and crystalline phase transformations were each treated separately and the effects of the application of magnetic field on thermal hystereses associated with both structural and magnetic transformations of the Ni 52 Mn 25 In 16 Co 7 were studied. From the analysis of synchrotron diffraction data and thermomagnetic measurements, it was revealed that the alloy undergoes both structural (from cubic austenite to a mixture of 7M & 5M modulated martensite) and magnetic (ferromagnetic to a low-magnetization phase) phase transformations. Here, thermal hysteresis is associated with both transformations, and the variation of the thermal hystereses of the magnetic and structural transformations with applied magnetic field is significantly different. Because of the differences between the hystereses loops of the two transformations, they merge only upon heating under a certain magnetic field.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effects of phase transformation on the microstructures and magnetostriction of Fe-Ga and Fe-Ga-Zn ferromagnetic shape memory alloys

The phase transformation and magnetostriction of bulk Fe{sub 73}Ga{sub 27} and Fe{sub 73}Ga{sub 18}Zn{sub 9} (at. %) ferromagnetic shape memory alloys (FSMs) were investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD), and a magnetostrictive-meter setup. For the Fe{sub 73}Ga{sub 27} FSM alloy solution treated at 1100 °C for 4 h and quenched in ice brine, the antiphase boundary segments of the D0{sub 3} domain were observed in the A2 (disordered) matrix, and the Fe{sub 73}Ga{sub 27} FSM alloy had an optimal magnetostriction (λ{sub ‖}{sup s }= 71 × 10{sup −6} and λ{sub ⊥}{sup s }= −31 × 10{sup −6}). In Fe{sub 73}Ga{sub 27} FSM alloy as-quenched, aged at 700 °C for 24 h, and furnace cooled, D0{sub 3} nanoclusters underwent phase transformation to an intermediate tetragonal phase (i.e., L1{sub 0}-like martensite) via Bain distortion, and finally L1{sub 2} (Fe{sub 3}Ga) structures precipitated, as observed by TEM and XRD. The L1{sub 0}-like martensite and L1{sub 2} phases in the aged Fe{sub 73}Ga{sub 27} FSM alloy drastically decreased the magnetostriction from positive to negative (λ{sub ‖}{sup s }= −20 × 10{sup −6} and λ{sub ⊥}{sup s }= −8 × 10{sup −6}). However, in Fe{sub 73}Ga{sub 18}Zn{sub 9} FSM alloy as-quenched and aged, the phase transformation of D0{sub 3} to an intermediate tetragonal martensite phase and precipitation of L1{sub 2} structures were not found. The results indicate that the aged Fe{sub 73}Ga{sub 18}Zn{sub 9} FSM alloy maintained stable magnetostriction (λ{sub ‖}{sup s }= 36 × 10{sup −6} and λ{sub ⊥}{sup s }= −31 × 10{sup −6}). Adding Zn can improve the ferromagnetic shape memory effect of aged Fe{sub 73}Ga{sub 18}Zn{sub 9} alloy, which may be useful in application of the alloy in high temperature environments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Phase transformation in tantalum under extreme laser deformation

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).

36 MATERIALS SCIENCE↗
DOE OSTI2015

Phase-field modeling of the beta to omega phase transformation in Zr–Nb alloys

A three-dimensional elastoplastic phase-field model is developed, using the Finite Element Method (FEM), for modeling the athermal beta to omega phase transformation in Zr–Nb alloys by including plastic deformation and strain hardening of the material. The microstructure evolution during athermal transformation as well as under different stress states, e.g. uni-axial tensile and compressive, bi-axial tensile and compressive, shear and tri-axial loadings, is studied. The effects of plasticity, stress states and the stress loading direction on the microstructure evolution as well as on the mechanical properties are studied. The input data corresponding to a Zr – 8 at.% Nb alloy are acquired from experimental studies as well as by using the CALPHAD method. Our simulations show that the four different omega variants grow as ellipsoidal shaped particles. Our results show that due to stress relaxation, the athermal phase transformation occurs slightly more readily in the presence of plasticity compared to that in its absence. The evolution of omega phase is different under different stress states, which leads to the differences in the mechanical properties of the material. The variant selection mechanism, i.e. formation of different variants under different stress loading directions, is also nicely captured by our model.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Problem of Identification of Phase Transformation Models Used in Simulations of Steels Processing

Accuracy of phase transformation models depends on the correctness of coefficients evaluation, adequate to the investigated material. Dilatometric tests combined with the inverse analysis are used to perform identification. Since the problem is nonlinear, analytical approach is not possible and the inverse solution is transferred into the optimization task. It leads to difficulties typical for optimization of multivariable function such as local minima and lack of proof of the uniqueness. The problem of the effectiveness and uniqueness of the inverse algorithms used for identification of phase transformation models for steels was investigated for two models. The first was a modified JMAK (Johnson–Mehl–Avrami–Kolmogorov) equation. The second was an upgrade of the Leblond equation, in which second-order derivative of the volume fraction with respect to time was introduced. In classical identification, the result for one transformation depends on the coefficients for the remaining transformations and optimization has to be performed several times until the compatibility between transformations is reached. To avoid encountered problems, complex optimization simultaneously for all coefficients in the models was performed. This approach was based on nature-inspired optimization techniques. Models with identified coefficients for various steels were validated in simulations of industrial processes of laminar cooling and continuous annealing of strips.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Pulse current auxiliary forging of sintered TiAl alloys based on the investigation of dynamic recrystallization and phase transformation

Highlights: • DRX kinetics model of sintered near γ TiAl alloy was established. • DRX process was accompanied by twinning when compressed at 1125 °C/0.1 s{sup − 1}. • Hot deformation has a promotion to the phase transformation of γ → α. - Abstract: Pulse current auxiliary forging is a new and efficient way to fabricate high performance TiAl based alloys. Dynamic recrystallization (DRX) and phase transformation have a pronounced effect on the subsequent deformability of TiAl based alloys. Hence, the dynamic recrystallization kinetics were determined at the temperature range of 1125–1275 °C and strain rate range of 0.1–0.001 s{sup − 1}. In addition, the DRX mechanism and phase transformation of TiAl based alloys were investigated to model the microstructure evolution in order to provide guidance for the pulse current auxiliary forging process. When the specimens were compressed at 1125 °C/0.1 s{sup − 1}, twinning played an important role in the DRX process. With increasing deformation temperature, the microstructure transformed from near gamma into duplex microstructure. In addition, according to the kinetics of dynamic recrystallization and phase transformation, fully DRXed TiAl based alloys were fabricated through pulse current auxiliary forging. The as-forged TiAl-based alloys show good superplastic performance with an elongation over 410%.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Lattice distortion-induced phase transformations in La{sub 1-y}Pr{sub y}MnO{sub 3+{delta}} manganites

The structural and magnetic phase transformations that occur in the system of self-doped La{sub 1-y}Pr{sub y}MnO{sub 3+{delta}} ({delta} Almost-Equal-To 0.1, 0 {<=} y {<=} 1) manganites in the temperature range 4.2-300 K are studied by X-ray diffraction and measuring the temperature and field dependences of dc magnetization. The low-temperature magnetic phase transformations induced by the substitution of Pr for La correlate well with the structural phase transformations at T = 300 K, which indicates a strong coupling of the electronic and magnetic subsystems of La{sub 1-y}Pr{sub y}MnO{sub 3+{delta}} manganites with the crystal lattice. The anomalies of the magnetic and structural properties detected in this work in the form of peaks and inflection points in the concentration dependences of the magnetization and lattice parameters of the pseudocubic phase of La{sub 1-y}Pr{sub y}MnO{sub 3+{delta}} (0.1 {<=} y {<=} 0.7) in the temperature range 4.2-300 K are explained in terms of the existing concepts of the effect of Fermi surface nesting on the renormalization of the density of states and the hole dispersion near E{sub F} in the presence of a strong coupling of holes with low-frequency optical phonons, which results in their transformation into quasiparticles. The narrow peak in the magnetization curve M(y) of La{sub 1-y}Pr{sub y}MnO{sub 3+{delta}} that is detected near y = 0.3 at T = 4.2 K is assumed to correspond to the peak of coherence of quasiparticles with a low energy of coupling with the crystal lattice near E{sub F}, which was found earlier in the photoelectron emission spectra of manganites. The disappearance of the narrow magnetization peak with increasing Pr concentration is explained by the transition of charge carriers from the mode of 'light' holes weakly coupled to one of the soft phonons to the mode of 'heavy' holes strongly coupled to several phonons. The transition between phases with strongly different effective quasiparticle masses proceeds jumpwise; that is, it has features of the metal-insulator Mott transition and is accompanied by the transition from 3D to 2D quasiparticle motion in planes ab.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Recordings and Analysis of Atomic Ledge and Dislocation Movements in InGaAs to Nickelide Nanowire Phase Transformation

The formation of low resistance and self‐aligned contacts with thermally stable alloyed phases is a prerequisite for realizing reliable functionality in ultrascaled semiconductor transistors. Detailed structural analysis of the phase transformation accompanying contact alloying can facilitate contact engineering as transistor channels approach a few atoms across. Original in situ heating transmission electron microscopy studies are carried out to record and analyze the atomic scale dynamics of contact alloy formation between Ni and In 0.53 Ga 0.47 As nanowire channels. It is observed that the nickelide reacts on the In 0.53 Ga 0.47 As (111) || Ni 2 In 0.53 Ga 0.47 As (0001) interface with atomic ledge propagation along the Ni 2 In 0.53 Ga 0.47 As direction. Ledges nucleate as a train of strained single‐bilayers and propagate in‐plane as double‐bilayers that are associated with a misfit dislocation of . The atomic structure is reconstructed to explain this phase transformation that involves collective gliding of three Shockley partials in In 0.53 Ga 0.47 As lattice to cancel out shear stress and the formation of misfit dislocations to compensate the large lattice mismatch in the newly formed nickelide phase and the In 0.53 Ga 0.47 As layers. This work demonstrates the applicability of interfacial disconnection (ledge + dislocation) theory in a nanowire channel during thermally induced phase transformation that is typical in metal/III–V semiconductor reactions.

Chen, Renjie↗
DOE OSTI2024

Phase Transformations Driving Biaxial Stress Reduction During Wake-Up of Ferroelectric Hafnium Zirconium Oxide Thin Films

Biaxial stress is identified to play an important role in the polar orthorhombic phase stability in hafnium oxide-based ferroelectric thin films. However, the stress state during various stages of wake-up has not yet been quantified. In this work, the stress evolution with field cycling in hafnium zirconium oxide capacitors is evaluated. The remanent polarization of a 20 nm thick hafnium zirconium oxide thin film increases from 9.80 to 15.0 µC cm –2 following 10 6 field cycles. This increase in remanent polarization is accompanied by a decrease in relative permittivity that indicates that a phase transformation has occurred. The presence of a phase transformation is supported by nano-Fourier transform infrared spectroscopy measurements and scanning transmission electron microscopy that show an increase in ferroelectric phase content following wake-up. The stress of individual devices field cycled between pristine and 10 6 cycles is quantified using the sin 2 (ψ) technique, and the biaxial stress is observed to decrease from 4.3 ± 0.2 to 3.2 ± 0.3 GPa. The decrease in stress is attributed, in part, to a phase transformation from the antipolar Pbca phase to the ferroelectric Pca2 1 phase. This work provides new insight into the mechanisms controlling and/or accompanying polarization wake-up in hafnium oxide-based ferroelectrics.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Operando real-space imaging of a structural phase transformation in the high-voltage electrode LixNi0.5Mn1.5O4

Abstract Discontinuous solid-solid phase transformations play a pivotal role in determining the properties of rechargeable battery electrodes. By leveraging operando Bragg Coherent Diffractive Imaging (BCDI), we investigate the discontinuous phase transformation in Li x Ni 0.5 Mn 1.5 O 4 within an operational Li metal coin cell. Throughout Li-intercalation, we directly observe the nucleation and growth of the Li-rich phase within the initially charged Li-poor phase in a 500 nm particle. Supported by the microelasticity model, the operando imaging unveils an evolution from a curved coherent to a planar semi-coherent interface driven by dislocation dynamics. Our data indicates negligible kinetic limitations from interface propagation impacting the transformation kinetics, even at a discharge rate of C/2 (80 mA/g). This study highlights BCDI’s capability to decode complex operando diffraction data, offering exciting opportunities to study nanoscale phase transformations with various stimuli.

Sun, Yifei (ORCID:0000000295625120)↗
DOE OSTI2013

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

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)

36 MATERIALS SCIENCE↗
DOE OSTI2016

Phase transformations in a Cu−Cr alloy induced by high pressure torsion

Phase transformations induced by high pressure torsion (HPT) at room temperature in two samples of the Cu-0.86 at.% Cr alloy, pre-annealed at 550 °C and 1000 °C, were studied in order to obtain two different initial states for the HPT procedure. Observation of microstructure of the samples before HPT revealed that the sample annealed at 550 °C contained two types of Cr precipitates in the Cu matrix: large particles (size about 500 nm) and small ones (size about 70 nm). The sample annealed at 1000 °C showed only a little fraction of Cr precipitates (size about 2 μm). The subsequent HPT process resulted in the partial dissolution of Cr precipitates in the first sample and dissolution of Cr precipitates with simultaneous decomposition of the supersaturated solid solution in another. However, the resulting microstructure of the samples after HPT was very similar from the standpoint of grain size, phase composition, texture analysis and hardness measurements. - Highlights: • Cu−Cr alloy with two different initial states was deformed by HPT. • Phase transformations in the deformed materials were studied. • SEM, TEM and X-ray diffraction techniques were used for microstructure analysis. • HPT leads to formation the same microstructure independent of the initial state.

36 MATERIALS SCIENCE↗
DOE OSTI2016

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

Here, 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 ZrH 2-2c . 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.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Plane Strain Compression and Subsequent Recrystallization Annealing on Microstructures and Phase Transformation of NiTiFe Shape Memory Alloy

The effect of plane strain compression and subsequent recrystallization annealing on microstructures and phase transformation of NiTiFe shape memory alloy (SMA) is investigated. Inhomogeneous plastic deformation at various deformation degrees occurs in NiTiFe SMA during plane strain compression. Nanocrystalline phase and amorphous phase increase as the deformation degree increases. B2 austenite, B19′ martensite, nanocrystalline and amorphous phases coexist in the NiTiFe samples subjected to large plastic strain. The static recrystallization mechanisms depend on the microstructures of the deformed NiTiFe samples. The static recrystallization mechanisms deal with nucleation and growth of the recrystallized grains, growth of nanocrystalline phase and crystallization of amorphous phase. Grain size, subgrain boundaries, geometrically necessary dislocation density and Schmid factor are captured on the basis of electron backscattered diffraction data. The process of recrystallization annealing cannot eliminate the deformation texture completely. The slip direction [110] is the most favorable slip direction in the recrystallized NiTiFe sample. Plane strain compression along with subsequent recrystallization annealing changes the phase transformation path of as-rolled NiTiFe SMA, and it results in the decreasing martensite transformation start temperature. The three annealed NiTiFe samples exhibit the similar phase transformation behavior since complete recrystallization annealing leads to the similar microstructures.

36 MATERIALS SCIENCE↗