Martensitic Transformation Behavior Research Articles

Improvement in the superelasticity of a Ti–35.5Ni–15Cu (at.%) alloy using Ti(Ni,Cu)2 phase

In this study, microstructures, martensitic transformation behavior and superelasticity of a (Ni,Cu)-rich Ti-35.5Ni–15Cu (at.%) alloy were investigated by means of scanning electron microscopy, differential scanning calorimetry, tensile tests and transmission electron microscopy. As-cast Ti-35.5Ni–15Cu alloy ingot fabricated by arc melting was hot-rolled without cracking into a sheet with a thickness of 1.2 mm, which was ascribed to the introduction of ductile Ti(Ni,Cu)2 phase beneficial for improving ductility of the alloy. Ti(Ni,Cu)2 phase remained after 1123 K solution treatment, while it dissolved into the matrix during 1273 K solution treatment. Dissolution of Ti(Ni,Cu)2 phase rendered matrix supersaturated with Ni and the subsequent annealing of the Ni-supersaturated matrix at 673 K induced precipitation of very fine C11b-type Ti(Ni,Cu)2 phase. The specimen annealed at 673 K showed transformation temperatures comparable to those of a Ti–35Ni–15Cu (at.%) alloy and almost complete superelasticity, which were ascribed to precipitation of C11b-type Ti(Cu,Ni)2 phase that made the (Ni + Cu) content of matrix close to 50 at.% and strengthened the matrix. The utilization of Ti(Ni,Cu)2 phase for improving workability and superelasticity without lowering transformation temperatures and increasing transformation hysteresis in this study was considered to be a good strategy for putting the Ti–Ni–Cu alloys with high Cu-content to practical use.

Insights into the martensitic transformation kinetics and mechanical properties of quaternary Ti–Ni–Nb–V shape memory alloys

The effect of V addition on the microstructural evolution, martensitic transformation behaviors and mechanical performances of Ti–Ni–Nb shape memory alloys was systematically investigated. The results reveal that the phase remains almost equal in Ti–Ni–Nb–V shape memory alloys, irrespective of the V content. With increasing V content, the amount of β-Nb phase is increased, which further leads to a reduction in the interspace and width of the β-Nb phase. When the V content changes, Ti–Ni–Nb–V shape memory alloys possess a single stage B2⇌B19´ martensitic transformation. In addition, the martensitic transformation temperatures first increase and then decrease owing to the variation in the chemical composition of the TiNi matrix and microstructural features as the V content increases. The higher yield strength of Ti–Ni–Nb shape memory alloys can be obtained by adding a moderate V content. In conclusion, the lower martensitic transformation temperature and the higher yield strength can be tailored by optimizing the V content in Ti–Ni–Nb shape memory alloys, which would further widen their application fields.

Austenitic Stability and Strain-Induced Martensitic Transformation Behavior of Nanocrystalline FeNiCrMoC HSLA Steels

Austenitic Stability and Strain-Induced Martensitic Transformation Behavior of Nanocrystalline FeNiCrMoC HSLA Steels

Electron beam freeform fabrication of NiTi shape memory alloys: Crystallography, martensitic transformation, and functional response

In this work, NiTi shape memory alloys parts were additively manufactured using electron beam freeform fabrication (EBF3) under different processing parameters, including the beam current, travel speed, and wire feeding speed. The forming quality, phase composition, microstructure change, crystallography, martensitic transformation, shape memory and superelastic responses were systematically investigated. All deposits mainly consisted of B2-austenite at room temperature, and a handful of B19′-martensite and submicron-sized Ti4Ni2Ox precipitates were also detected. The martensitic transformation of NiTi alloys prepared by EBF3-technique possessed an individual reversible path between B2 and B19′ upon heating/cooling. The optimized deposit possessed the best comprehensive properties, where the values of the relative density, shape memory recovery and superelastic recovery ratios were 99.6%, 98.95%, and 55.78%, respectively. Furthermore, the dependence of the martensitic transformation behavior on the thermomechanical condition and the relationship between plastic deformation and phase transformation during superelastic deformation are discussed in detail. Our work details that the EBF3 provides a suitable way for the complex fabrication of large-scaled parts based on shape memory alloys.

The effect of reversed austenite on mechanical properties of 13Cr4NiMo steel: a CPFEM study

In order to investigate the effect of reversed austenite on the mechanical properties of 13Cr4NiMo steel, a meso scale crystal plasticity finite element model (CPFEM) was established to simulate the deformation induced martensitic transformation (DIMT) and micromechanical behavior during tensile deformation. The results demonstrate that the mechanical stability of the film-like austenite embedded in the martensite lath boundary is greater than blocky austenite within the martensite lath. The film-like austenite will preferentially undergo DIMT during initial plastic deformation prior to blocky austenite. After deformation, the tempered martensite yields and deforms plastically, while adjacent new martensite is elastically deformed. The incompatible deformation leads to the introduction of dislocations in the tempered martensite and increases the work hardening rate. The new martensite, that is transformed from film-like austenite, significantly increases the true strain of the adjacent martensite matrix, which is beneficial to the plasticity and toughness, but has little contribution to the increase of matrix stress. New martensite, transformed from blocky austenite, increases the von Mises stress of the adjacent martensite matrix, which improves the tensile strength and strain hardening capacity, but makes little contribution to the increase of matrix strain.

Constitutive modeling and finite element analysis of metastable medium entropy alloy

In this study, the constitutive model of metastable ferrous Fe60Co15Ni15Cr10 (at%) medium entropy alloy (FeMEA) was constructed based on deformation-induced martensitic transformation (DIMT) behavior under cryogenic temperature. The crystal structure of the FeMEA gradually transformed from a single face-centered cubic (FCC) phase to a body-centered cubic (BCC) phase during deformation. The critical initiation stress criterion and the volumetric fraction evolution model were employed to describe the DIMT kinetics during uniaxial tensile testing. The flow stress model of the FCC phase as a function of the applied strain was developed using the dislocation-based hardening model, and the BCC phase behavior was evaluated based on the macroscopic behavior of the multiphase material and phase transformation kinetics. The decline in the dislocation mean free path for the FCC phase was associated with the grain refinement of the FCC phase due to the transformed BCC islands. To verify its applicability, the model was compared to the experimental data describing phase transformation kinetics and the mechanical behavior.

Effects of cooling rate on martensitic transformation behavior and shape memory property for Ni-rich NiTiHf-Nb high-temperature shape memory alloy

The NiTiHf-Nb alloy exhibits good workability as well as high-temperature shape memory property. In this work, effects of cooling rate on martensitic transformation behavior and shape memory property for Ni-rich (Ni 50.1 Ti 34.9 Hf 15 ) 85 Nb 15 alloy were investigated. For comparison, the martensitic transformation behavior and shape memory property of Ni 50.1 Ti 34.9 Hf 15 alloy were also investigated. As the cooling rate decreased from water cooling to furnace cooling after solution treatment, the martensitic transformation temperatures (TTs) of (Ni 50.1 Ti 34.9 Hf 15 ) 85 Nb 15 alloy decreased gradually, whereas the decrease was not obvious for Ni 50.1 Ti 34.9 Hf 15 alloy. The increased valence electron concentration (c v ) should account for the decrease in TTs of (Ni 50.1 Ti 34.9 Hf 15 ) 85 Nb 15 alloy. The shape memory effect strain increased with the decrease in the cooling rate for both two alloys, and the largest shape memory effect strain of 2.6% can be obtained in furnace-cooled (Ni 50.1 Ti 34.9 Hf 15 ) 85 Nb 15 alloy. This enhancement in the shape memory property should be ascribed to the precipitation of H-phase in furnace-cooled (Ni 50.1 Ti 34.9 Hf 15 ) 85 Nb 15 alloy. • Higher shape memory effect strain could be obtained by slow cooling after solution treatment. • Higher martensitic transformation temperatures could be obtained by fast cooling after solution treatment. • The martensitic start transformation temperatures were c v dependent. • Precipitation of H-phase could be improved by addition of Nb.

Effect of Hf on the Microstructure and Martensitic Transformation Behavior in Ti–Pd–Hf Alloy

Effect of Hf on the Microstructure and Martensitic Transformation Behavior in Ti–Pd–Hf Alloy

Effects of Curvature of the Cross-section on the Buckling Characteristics and Buckling Shape of the Convex Tape-shaped Ti-Ni Shape Memory Alloy Element

The negative stiffness exhibited by shape memory alloys (SMA) during buckling can be applied to passive vibration isolators and force-limiting mechanisms. However, to apply the negative stiffness of SMA, it is necessary to calculate the negative tangential stiffness value and buckling load of the shape memory alloy after buckling by design. In our previous study, we have shown that it is possible to increase the negative tangential stiffness and buckling load after buckling by increasing the curvature of a plate-like SMA material in the form of a convex tape with a given cross-sectional curvature. In this study, it is considered that the cause of the negative tangential stiffness after buckling is the change in martensitic phase transformation behavior during buckling deformation due to the addition of curvature to the cross-section. The results showed that the phase transformation behavior of a flat SMA element and a convex tape SMA element with curvature in its cross section changed. As a result, it was found that the flat SMA element does not exhibit negative stiffness immediately after buckling because martensitic phase transformation does not occur in the center of the specimen immediately after buckling, while the convex-tape SMA element tends to exhibit negative stiffness from immediately after buckling due to martensitic phase transformation in the center of the specimen.

Solidification characterization and its correlation with the mechanical properties and functional response of NiTi shape memory alloy manufactured by electron beam freeform fabrication

Compared with the common additive manufacturing techniques, the vacuum operating environment and high deposition efficiency of wire-based vacuum additive manufacturing are more expective in the preparation of NiTi shape memory alloys. In the present work, the strategy of interlaminar residence was adopted to deposit the dense wall-structure NiTi shape memory alloy on the commercially pure titanium substrate using the electron beam freeform fabrication (EBF 3 ) technique. The principle of phase constitution, microstructure evolution, martensitic transformation behavior, mechanical properties, and the functional response was studied in detail. The stable regions of as-deposited NiTi alloy were composed of B2 austenite at ambient temperature, and a small amount of B19′ martensite also was observed. Meanwhile, the nano-scaled Ti 4 Ni 2 O x precipitate existed in the interdendritic and grain interior of the EBF 3 -fabricated NiTi alloy. The stable regions of EBF 3 -fabricated NiTi alloy presented a single reversible martensitic transformation (B2 ↔ B19′) during the cooling and heating process. In addition, the solidification characterization, such as microstructure evolution and crystallographic orientation in the building direction and horizon direction, brought about certain differences in the mechanical properties and functional response, such as tensile strength, elongation, superelasticity, and damping capacity. The corresponding intrinsic mechanism has been discussed. Our work also provides a promising method for the flexible manufacture of dense shape memory alloys with large scale and complex geometry, which is beneficial to expanding their application fields. • The dense wall-structure slightly Ni-rich NiTi shape memory alloy was successfully deposited on the commercially pure titanium substrate using the electron beam freeform fabrication (EBF 3 ) additive manufacturing technique. • The stable regions of EBF 3 -fabricated NiTi alloy presented a single reversible martensitic transformation (B2 ↔ B19′) during the cooling and heating process. • The solidification characterization and its correlation with the mechanical properties and the functional response have been discussed.

Deformation-Induced Martensitic Transformation Behavior of Retained Austenite during Rolling Contact in Carburized SAE4320 Steel

Deformation-Induced Martensitic Transformation Behavior of Retained Austenite during Rolling Contact in Carburized SAE4320 Steel

Investigation on porous NiMnGa alloy and its composite with epoxy resin

This article investigated microstructure, phase transformation and mechanical property of porous NiMnGa alloy and its composite with epoxy resin. The porous NiMnGa alloys with large pores and different porosity exhibited a similar martensitic transformation behavior but with reduced martensitic transformation temperature as compared to that of the original powder. The porous alloys exhibited low mechanical strength and ductility due to the existence of large size pores. After compositing with epoxy resin, the mechanical strength and ductility of the porous alloy had been apparently enhanced due to the synergistic effect between the polymer and porous alloy. In addition, the composite demonstrated a martensitic transformation behavior similar with that of the porous alloy, indicating that the constraint effect of polymer matrix on the phase transformation of the porous alloy could be neglected. The combination of porous NiMnGa alloys with continuous structure and polymer could provide a promising way to make NiMnGa/polymer composites with better performance than the composites consisting of NiMnGa particles and polymer.

Martensite transformation behavior and magnetocaloric effect in annealed Ni-Co-Mn-Sn microwires

Effect of annealing on martensite transformation (MT) and magnetocaloric effect (MCE) in a Ni41.3Co6.3Mn42.4Sn10.0 microwire was investigated. After annealing at temperatures 723–1173 K, the MT temperatures and Curie points shifted to higher range; meanwhile, the thermal hysteresis (ΔThys) decreased. However, partial transition arrest appeared when annealed at temperatures > 1073 K, leading to decreased magnetization difference (ΔM) between martensite and austenite phases. The maxima ΔM and minima ΔThys were produced at an annealing temperature 1023 K. Consequently, a large magnetic entropy change (ΔSMmax) 20.1 J/kg·K, wide working temperature span (ΔTFWHM) 20 K and thus high effective refrigeration capacity (RCeff) 197 J/kg were obtained under a magnetic field 5.0 T after annealing at 1023 K for 1 h. These facts make Ni-Co-Mn-Sn microwires promising for miniature refrigeration devices due to their high specific surface area, low thermal hysteresis and markedly reduced annealing temperature and time.

TU79. NEUROANATOMICAL AND GENETIC CORRELATES OF FACIAL SHAPE: POTENTIAL BIOMARKERS FOR SCHIZOPHRENIA

The Ti-Ni-Hf shape memory alloy powders were prepared by plasma rotating electrode process. And the powders were featured with the perfect sphericity and smooth surface. Moreover, the grain size was refined in the Ti-Ni-Hf alloy powders due to the rapid cooling rate during plasma rotating electrode process. It was found that the Ti-Ni-Hf alloy powders had the typical self-accommodation configuration including spear-like, mosaic-like and lath-like martensite. Various twins, such as (001) compound twin, (011) type I twin as well as {111} type I twin, were observed in Ti-Ni-Hf alloy powders. Differing from the bulk Ti-Ni-Hf alloy, two-stage transformation corresponding to B2⇌B19’ martensitic transformation was detected in the as-received Ti-Ni-Hf alloy powders. In addition, the martensitic transformation behaviors were closely related to the annealing temperatures. The Ti-Ni-Hf alloy powders with low annealing temperature of 500 ​°C still exhibited two-stage martensitic transformation, while two-stage martensitic transformation changed into single martensitic transformation in the Ti-Ni-Hf alloy powders with the higher annealing temperature of 900 ​°C. And finally the possible mechanisms for the evolution of martensitic transformation behaviors were discussed.

Mechanisms of two-stage martensitic transformation in Ti-Ni-Hf alloy powder

The Ti-Ni-Hf shape memory alloy powders were prepared by plasma rotating electrode process. And the powders were featured with the perfect sphericity and smooth surface. Moreover, the grain size was refined in the Ti-Ni-Hf alloy powders due to the rapid cooling rate during plasma rotating electrode process. It was found that the Ti-Ni-Hf alloy powders had the typical self-accommodation configuration including spear-like, mosaic-like and lath-like martensite. Various twins, such as (001) compound twin, (011) type I twin as well as {111} type I twin, were observed in Ti-Ni-Hf alloy powders. Differing from the bulk Ti-Ni-Hf alloy, two-stage transformation corresponding to B2⇌B19’ martensitic transformation was detected in the as-received Ti-Ni-Hf alloy powders. In addition, the martensitic transformation behaviors were closely related to the annealing temperatures. The Ti-Ni-Hf alloy powders with low annealing temperature of 500 ​°C still exhibited two-stage martensitic transformation, while two-stage martensitic transformation changed into single martensitic transformation in the Ti-Ni-Hf alloy powders with the higher annealing temperature of 900 ​°C. And finally the possible mechanisms for the evolution of martensitic transformation behaviors were discussed.

Martensitic transformation and elastocaloric effect of Co51.5+xV31.5-xGa17 (x = 0.1, 0.2, 0.3) alloys

Co-V-Ga alloy, a newly discovered multifunctional material based on martensitic transformation (MT), has promising application prospects in spintronics and solid-state refrigeration fields. In this work, we investigated the MT behaviors and the elastocaloric effect (eCE) of Co51.5+xV31.5-xGa17 (x = 0.1, 0.2, 0.3) alloys. The alloys undergo a MT from paramagnetic austenite to paramagnetic martensite, accompanying by a large latent heat (about 6–9 J g−1). The MT temperature increases with the increase of the ratio of Co to V. The digital image correlation (DIC) combined with infrared thermography (IR) techniques were utilized to in situ characterize the stress-induced MT and temperature change of the sample. For the sample of x = 0.2, at a testing temperature of 301 K, it heats with a giant adiabatic temperature change up to 13.4 K upon loading, while cools only 2.4 K when stress releasing, showing an irreversible eCE. Raising the test temperature (319, 327 and 333 K) can greatly improve the reversibility of the eCE. Such an asymmetric elastocaloric temperature change at 301 K is closely related to the irreversibility of stress-induced MT, which can be attributed to several factors including the self-cooling effect, heat dissipative mechanism and the valence bond structure of Co-V-Ga alloys.

A novel two-stage martensitic transformation induced by nanoscale concentration modulation in a TiNb-based shape memory alloy

Martensitic transformation (MT) plays a critical role in determining both mechanical and functional properties of shape memory alloys (SMAs). The behavior of MT depends strongly on the microstructure of materials, and two- or multiple-stage MTs are typical examples of this. However, the physical origin of two- or multiple-stage MTs remains controversial although much effort has been made. In this study, a novel two-stage MT is observed in a TiNb-based SMA with nanoscale concentration modulation. The physical origin of this chemical-heterogeneity-induced two-stage MT is the difference in thermodynamic stability of the parent and martensitic phase between Nb-leaner and Nb-richer regions. The findings of this study not only expand the repertoire of mechanisms of two- or multiple-stage MT but also shed light on the long-standing controversy over the physical origin of multiple-stage MTs.

Martensitic phase transformation and shape memory properties of the as-cast NiCuTiHf and NiCuTiHfZr alloys

This study investigates the structure, martensitic phase transformation behavior, and shape memory properties of the quaternary Ni44.8Cu5Ti45.2Hf5 and quinary Ni44.8Cu5Ti40.2Hf5Zr5 and Ni45.5Cu5Ti39.5Hf5Zr5 shape memory alloys (SMAs) in the as-cast state. The alloys exhibited a dual-phase microstructure composed of matrix phase (austenite or martensite depending on the chemical composition) and Ti2Ni-type phase. The experimental results revealed that the alloys underwent a one-step B2↔B19′ transformation. The Ni44.8Cu5Ti45.2Hf5 alloy showed a maximum shape memory strain of 6.2% with a recovery ratio of 81% upon thermal cycling under a tensile stress of 300 MPa, while in the Ni44.8Cu5Ti40.2Hf5Zr5 alloy, a maximum shape memory strain of about 5% was obtained under 500 MPa with a recovery ratio of 86%. The as-cast Ni44.8Cu5Ti45.2Hf5 alloy showed superelastic response with 0.3% maximum transformation strain at 125℃. On the other hand, the Ni44.8Cu5Ti45.2Hf5 alloy showed the best superelastic response at 65℃ with a recoverable strain of about 1.9%. Two-way shape memory strains of 0.8% and 3.3% were obtained in the Ni44.8Cu5Ti45.2Hf5 and Ni44.8Cu5Ti40.2Hf5Zr5 alloys, respectively. The Ni45.5Cu5Ti39.5Hf5Zr5 alloy, however, did not reveal the shape memory effect. Results obtained from low-temperature X-ray diffraction (XRD) analysis indicated that the B2→B19′ transformation was considerably suppressed in this alloy and the volume fraction of B19′martensite did not exceed 8% even at an ultra-low temperature of − 150 °C.

Experimental Analysis of NiTi Alloy during Strain-Controlled Low-Cycle Fatigue.

The interaction between the stress-induced martensitic transformation and resistivity behavior of superelastic NiTi shape memory alloy (SMA) was studied. Strain-controlled low-cycle fatigue up to 6% was monitored by in situ electrical resistivity measurements. The experimental results show that a great motion of martensite fronts results in a significant accumulation of defects, as evidenced by transmission electron microscopy (TEM), before and after the tensile cycles. This gives rise to an overall increase of the resistivity values up to the maximum deformation. Therefore, the research suggests that shape memory alloy wire has great potential as a stress sensor inside bulk materials.

Microstructural evolution and phase transformation in proton-irradiated NiTi films

In the present work, the microstructural characteristics, martensitic transformation behavior, and mechanical performance of NiTi thin films irradiated with different proton fluences were investigated. Multiple-layer structures formed in the NiTi thin films owing to proton irradiation. As the proton fluences were 1.0 × 1015 p/cm2 and 5.0 × 1015 p/cm2, a two-layer structure containing a B2 phase and a B19’ martensite phase was introduced. In addition, thickness of B2 phase layer becomes larger and larger for irradiated NiTi thin films at room temperature, as the proton irradiation fluence increases. With further increasing proton irradiation fluence to 2.0 × 1016 p/cm2, an amorphous layer forms at the outmost layer of NiTi thin film. Moreover, an R phase and GP zones were detected in the interior of the B2 layer. The twin type of B19’ martensite also changed to release the stored elastic energy induced by proton irradiation. The martensite variant related (111‾) type I twins and the substructure of the <011> type II twins gradually evolved into (111) type I twins and (001) compound twins, respectively, with increasing proton irradiation fluence. The formation of a multiple-layer structure resulted in the presence of two endothermic and exothermic peaks corresponding to the B19’ ⇌ B2 martensitic transformation. The introduction of lattice defects was responsible for the reduction in the martensitic transformation temperature. The strength of the irradiated NiTi films was enhanced as a result of dislocation strengthening. However, the introduction of higher density of defects also leads to the deterioration of ductility.