Martensitic Transformation Characteristics Research Articles

Active interlocking metasurfaces enabled by shape memory alloys

Interlocking metasurfaces (ILMs) are a newly developed joining technology that relies on arrays of interlocking features that transmit force and constrain motion between adjoining bodies in one or more directions. This study explores harnessing the shape memory effect (SME) in Nickel-Titanium shape memory alloys (NiTi SMAs) in structures fabricated using additive manufacturing (AM) to advance the development of active ILMs by creating unit cells that open or close at specific temperatures. The study encompasses designing and fabricating two distinct interlocking array configurations using near-equiatomic NiTi powder and the laser powder bed fusion (L-PBF) AM technique, following a previously developed AM process optimization framework to manufacture defect-free parts. To guide the design process, finite element analysis (FEA) was employed to predict strain values during engage-disengage cycles. The martensitic transformation characteristics of the ILMs were characterized. Thermomechanical testing revealed that the ILMs demonstrate high locking force once engaged, coupled with complete shape recovery and good cyclic stability. Digital image correlation (DIC) was also employed to validate the FEA predictions during the engage-disengage cycles. The results indicate that NiTi SMA-based ILMs can be designed and fabricated into complex shapes using L-PBF. By leveraging the SME, the functionality of an ILM can be improved upon. The combination of computational modeling, additive manufacturing, and thermomechanical and physical property characterization provides a framework for designing future ILMs out of active materials.

The mechanism for the superior isotropic mechanical properties attained in a cross rolling TiNb alloy

In the present study, the Ti–41Nb (wt.%) alloy featuring a microstructure composed of β and α″ phases have been prepared through the application of the Cross Rolling (CSR) technique to achieve a near-isotropic superior mechanical behavior. The experimental findings revealed that the CSR sample exhibits a uniform β matrix, randomly dispersed α″ martensite and a high density of dislocations and grain boundaries. Subsequent experiments unveiled that the CSR sample displays an almost isotropic mechanical response across three typical directions, Rolling Direction (RD), a 45° deviation from RD, and Transverse Direction (TD), evidenced by comparable stress-strain curve profiles and ultimate tensile strength (UTS) values. Due to the randomly distributed textures and high density of dislocations and grain boundaries, the stress-induced martensitic (SIM) transformation exhibits a similar characteristic in three typical directions, that is, the SIM transformation took place homogeneously and continuously. Consequently, the CSR sample can achieve a near-isotropic and outstanding mechanical performance due to the similar characteristics of martensitic phase transformation and the strengthening effect brought by the high density of dislocations and grain boundaries.

Martensite transformation characteristics in the heat affected zone of laser cladding on rail

This paper studied the macroscopic morphology and properties of the heat affected zone (HAZ) in multi-layer multi-track cladding layers on rail. The results showed that in the two-layer laser cladding, there are martensitic structures and cracks in the HAZ. With the increase of the number of laser cladding layers, the tempering structure in the HAZ expands gradually from the bottom to the top, from the middle to the edge, and no cracks appear in the HAZ. At ten-layer laser cladding, the martensitic structure has been completely eliminated and transformed into tempered sorbite. Finally, the hardness test shows that the hardness of cladding layer, HAZ and substrate are basically the same, which meets the performance requirements of rail repair.

Ultrasonic scattering behavior in austenitic NiTi with varying grain size and precipitate characteristics

Shape memory alloys like NiTi exhibit high strain recovery due to a reversible martensitic transformation when cooled or stressed, enabling actuation and biomedical applications. The characteristics of the stress-induced martensitic transformation in Ni-rich NiTi depend on the heat treatment. For example, aging induces the precipitation of Ni;4Ti;3 and lowers the critical stress needed for martensitic transformation. However, comprehensive characterization of these nanoscale precipitates is challenging as only small areas can be inspected efficiently. Ultrasonic immersion testing may assist in developing linkages between structure and transformation behavior as ultrasonic scattering is sensitive to the microstructure and easily mapped on the bulk scale. To this end, the ability of scattering behavior to discern between different precipitation characteristics must be probed to establish the sensitivity of ultrasonic parameters to changes in precipitation. This work explores the dependence of wave speed, attenuation, and backscattered energy on varying annealing and aging heat treatments of Ni-rich NiTi. The annealing treatments result in a gradient of grain sizes, while the aging treatments result in nucleation and growth of precipitate phases with increasing hold time. Variations in the ultrasonic parameters elucidate the sensitivity to changes in the microstructure, which are more quantitatively explored through existing analytical scattering models.

Martensitic transformation characteristics, mechanical properties and damping behavior of Cu–Al–Ni shape memory alloys: A review of their modifications and improvements

Copper-based shape memory alloys (SMAs) have recently been introduced as a viable alternative to Ni–Ti SMAs. This is attributed to the fact that Cu-based SMAs are cheaper than Ni–Ti SMAs and exhibit satisfactory shape memory properties. Of these materials, Cu–Al–Ni SMAs have been widely used as they possess high thermal resistance and good mechanical properties. The concentration of Al and Ni is the most important factor determining the martensite type and transformation temperatures of these SMAs. Furthermore, thermal treatment, including quenching and aging, significantly affects the microstructural evolution and martensitic transformation (MT) temperatures of Cu–Al–Ni SMAs. Modifying the formed martensite phases and MT temperatures is possible by controlling the quenching rate and ageing temperature. Damping ability is one of the distinct advantages of these Cu-based SMAs, which has been modified and improved by many researchers. Plastic deformation is an effective method of evolving the microstructure of Cu–Al–Ni SMAs and improving their mechanical properties. Therefore, this present study examines the effect of alloy composition and thermal treatment on the MT temperatures and the microstructural evolution of Cu–Al–Ni SMAs. It also discusses the solutions to control the damping behavior of Cu-based SMAs, as well as the role of plastic deformation in improving the different properties Cu–Al–Ni SMAs. Lastly, additive manufacturing (AM) is proposed as a modern method of producing porous Cu–Al–Ni SMAs since it grants the possibility of controlling the porosities more efficiently.

Coexistence of strain glass transition and martensitic transformation in highly nickel-rich ferroelastic alloy with large elastocaloric effect

Strain glass transition attracts increasing attention in ferroelastic alloys in the context that martensitic transformation serves as the dominant mechanism for shape memory alloys. However, observing the coexistence of strain glass transition and martensitic transformation has not been reported. In this work, we introduce the strain glass transition by doping element to form highly nickel-rich Ni55Ti45 at.% alloys and in the meantime attain the characteristics of martensitic transformation in the alloys. We confirm the existence of strain glass transition by 1) no exothermic/endothermic peaks in heat flow curves, 2) two deviations in electric resistivity curves, 3) two frequency-dependent dips of storage modulus, and 4) successive formation and constrained growth of nanodomains over a wide temperature range. We observe the martensitic transformation characterized by 1) two pronounced exothermic peaks upon cooling and one endothermic peak upon heating in heat flow curves, 2) thermal hysteresis in electric resistivity curves, and 3) macroscopic martensitic twins in transmission electron microscopy images. With these two phase transformations, the quasilinear superelasticity, high strength, and large elastocaloric ΔTad of up to 9.7 K are achieved. By designing the strain maps and microstructural evolution pathways, we have provided a temperature-composition transformation path diagram to offer mechanistic insights and tuning strategies for the development of advanced alloys.

Influence of laser treatment on the characteristics of martensitic transformation in Fe–Ni–Ti–Al alloy

Influence of laser treatment on the characteristics of martensitic transformation in Fe–Ni–Ti–Al alloy

High-pressure quenching effect on martensitic transformation characteristics and mechanical properties of low-alloy medium-carbon steel

In this study, the effect of high-pressure quenching at 2, 3 GPa on the martensitic transformation characteristics and mechanical properties of 40Cr steel was examined using EBSD, Mössbaue, and TEM. The results reveal that the microstructure following high-pressure quenching is a mixture of lath martensite and plate martensite, with plate martensite content increasing steadily as pressure is increased. Plate martensite exhibits distinct characteristics in the 2 GPa-sample, either crossing the prior austenite grain (PAG) or growing from the grain boundary into the interior. In 3 GPa-sample, the lath and plate martensite are distributed in clusters, with the majority of adjacent laths exhibiting {112} <111> twinning orientation relationship (OR). The number of variants was decreased from 24 for conventional quenching to 15 and the PAG size was refined to 15 μm. The percentage of M2 martensite increased from 67.71% at atmospheric pressure to 72.59% at 3 GPa, resulting in a decrease in the solid solution C content, which appears to incorporate with Cr to form fine, dispersed Cr23C6 particles. The hardness of the 3 GPa sample (807 HV) enhanced by 40%, and the compressive yield strength reached 3.5 GPa, which was three times that of conventional quenching.

Application of Biocompatible Noble Metal Film Materials to Medical Implants: TiNi Surface Modification

Recently, film materials based on the combination of noble metals have showed promising results for surface modification of medical implants, allowing both to improve biocompatibility and to acquire the increased antibacterial effect. An important challenge here is to combine the developed coating morphology, which is favorable for biological response, with a high protective function, which, on the contrary, requires a compact coating microstructure. In this work, we aimed to solve this problem with respect to the TiNi implant material. We have tested two types of compact thin sublayers: Iridium (Ir’), formed by metal-organic chemical vapor deposition (MOCVD), and gold (Au), formed by physical vapor deposition (PVD). Subsequently these sublayers were coated with a developed-columnar-iridium (Ir) by MOCVD. Features of the microstructure, chemical and phase composition of all these film materials were studied using powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The changes in the characteristics of TiNi martensitic transformation due to MOCVD experiments were also studied by differential scanning calorimetry (DSC). The biocompatibility of Ir’/TiNi, Au/TiNi, Ir/Ir’/TiNi, Ir/Au/TiNi samples was assessed by cytoxicity testing (Man-1 cells) and measuring of nickel content in the biological extracts. The application of both sublayers effectively reduces the release of nickel, which was previously shown for Ir/TiNi samples. This prevents the toxic effect. Note that the Ir’ sublayer better protects against nickel release, while the Au sublayer promotes cell proliferation.

Martensitic Transformation Temperatures and Hall Effect in Ni47-xMn41+xIn12 (x = 0, 1, 2) Alloys.

At present, the question of the relationship between the characteristic martensitic transformation temperatures (MTT) and the electronic parameters of a system has not been fully studied. In the present work, an attempt to establish a similar relationship using the example of the concentration of charge carriers, n, was made. The field dependences of Hall resistivity ρH and magnetization M of the magnetocaloric Ni47-xMn41+xIn12 (x = 0, 1, 2) alloys were measured at T = 4.2 K and in magnetic fields of up to 80 kOe. The MTT were obtained from the temperature dependences of electrical resistivity and magnetization. It was observed that the MTT correlate strongly with both the valence electron concentration e/a and the electronic transport characteristics, which are the coefficient of the normal (NHE) R0 and anomalous (AHE) RS Hall effect and the concentration of charge carriers n.

Martensitic Transformation, Magnetic and Mechanical Characteristics in Unidirectional Ni–Mn–Sn Heusler Alloy

A textured structure of Ni–Mn–Sn Heusler alloy with [001] preferred orientation has been grown by the directional solidification method. The crystal exhibits a single austenite phase L21 cubic structure (a = 5.997 Å) at room temperature. Magnetization and electronic transport measurements reveal the phase transformation characteristics. The maximum values of magnetic entropy change determined by Maxwell’s thermodynamic relation during the structural and magnetic phase transformations are 3.5 J/kg·K and −4.1 J/kg·K, and the total effective refrigerant capacity reaches about 314 J/kg (5 T). The evident reduction in hysteresis loss and broad operating temperature window provide a greater prospect for improving the cyclic stability of refrigeration and optimizing the application of such a magnetic refrigeration material. Both magnetoresistance (−18%, 5 T) and exchange bias field (302 Oe, 2 K) have also been investigated to understand the nature of phase transformations and exchange interactions. Furthermore, as the material exhibits excellent mechanical properties (1068 MPa, 9.0%), our experimental results provide a new reference for the application of Ni–Mn–Sn Heusler alloys.

Achieving great comprehensive elastocaloric cooling performances of superelastic NiTi by grain size engineering

Elastocaloric materials, as cutting-edge alternatives to hazardous refrigerants utilized in vapor-compression systems, are promising for eco-friendly solid-state cooling, but their various refrigeration metrics still lack reconciliation. Here, we investigate the grain size (GS) dependence of elastocaloric effect of NiTi with average GSs of 11, 22, 30, 45, and 70 nm and eventually find a suitable GS yielding great comprehensive cooling properties. Adiabatic temperature variation (|ΔTad|), isothermal entropy change (ΔS), and energy dissipation (ΔW) increase monotonically with GS, while cyclic stability and working temperature span (Tspan) exhibit an opposite trend, showing inevitable compromises among these criteria. The closer to 11 or 70 nm the GS is, the more intense conflicts are, due to the extreme natures of second-order-like and first-order transformation. The conflicts are significantly relaxed in the 30 nm-GS specimen with robust mechanical properties and mild martensitic transformation characteristics. The reconciled large |ΔTad| and low ΔW, benefiting from appreciable transformation strain and small hysteresis, make its coefficient of performance 3.7 and 2.32 times that in 11 and 70 nm-GS counterparts, respectively. High repeatability manifested as negligible degradation by 1.2% in the magnitude of |ΔTad| after 200 tensile cycles is also achieved owing to its high strength and good crystallographic compatibility, which contrasts sharply to that of the 70 nm-GS one decayed by 15%. Furthermore, a superior combination of wide Tspan (64 K) and large ΔS (31 J kg−1 K−1) results in a high refrigeration capacity of 1.7 kJ kg−1. The work demonstrates a concrete strategy for designing efficient and reliable elastocaloric refrigerants.

Effect of electron irradiation defects on the martensitic transformation characteristics and microstructure of Ni45Co5Mn37In13 alloys

Ni-Co-Mn-In based alloys with magnetically driven shape memory effect have shown its huge potential for applying as the intelligent driver in the spacecrafts. However, the numerous cosmic radiations, especially the electron irradiation with large penetration depth, could seriously harm its' serving stability. Herein, the Ni45Co5Mn37In13 alloys are exposed to the high energy electron irradiation with different fluence to study the phase transition behavior and microstructure evolution in the irradiation process. As a result, we reveal that the electron irradiation could induce dense crystal defects which not only reduce the transition temperature and thus retain the residual austenite in the martensitic matrix, but also destroy the continuity of martensitic laths and the atom arrangement in the twin boundaries. This work has important theoretical significance for understanding the electron irradiation's effect on the martensitic transformation and microstructure of Ni-Co-Mn-In alloys, and is conducive to expand martensitic transformation theory.

Investigation of the complex magnetic behavior of Ni46.86Co2.91Mn38.17Sn12.06 (at%) magnetic shape memory alloy at low temperatures

The magnetic properties, martensitic transformation characteristics, the magnetic field-induced transformation characteristics, and super spin-glass behaviour at low temperature of Ni46.86Co2.91Mn38.17Sn12.06 (at%) magnetic shape memory alloys (MSMAs) were investigated under various magnetic field levels over temperature intervals from 400 K to 10 K. We observe a small magnetization difference during the martensitic transition evidenced with a visible thermal hysteresis. To investigate the magnetic field induced phase fraction, the minimum magnetic field required to start and complete the magnetostructural phase transition is computed. Super-spin glass features in magnetic data are observed that interacting magnetic clusters are frozen below a critical temperature. Magnetization is computed as a function of temperature at various constant fields using molecular field theory. The critical exponent, β is deduced for the temperature-induced magnetization, which indicates that the MSMA exhibited ferromagnetic ordering during field-cooling and on heating an antiferromagnetic ordering at low temperatures and in low applied magnetic fields. These observations are consistent within the framework of an Ising or Heisenberg model.

Influence of loading direction on tensile deformation behavior of a lean duplex stainless steel sheet: The role of martensitic transformation

In this work, the tensile deformation behavior of a hot-rolled lean duplex stainless steel with metastable austenite (named as present TLDX) was studied at 20 °C along the loading directions of 0°, 45° and 90° to the rolling direction (corresponding to the L-oriented, D-oriented and T-oriented specimens, respectively). The initial microstructure, martensitic transformation characteristics, damage and fracture behavior were clarified through microstructure observations. The intrinsic mechanism of anisotropy in tensile deformation behavior was comprehensively discussed referring to the microstructure characteristics. The present TLDX exhibited remarkable mechanical anisotropy at 20 °C, characterized by the highest values of ultimate tensile strength (σu = 853 MPa) and plasticity (et = 70.6%, eu = 62.3%) for the L-oriented specimen and the lowest values (i.e., σu = 790 MPa, et = 53.3%, eu = 50.4%) for the T-oriented specimen, although the yield strength is comparable (σs∼524 MPa) for different loading directions. Strain-induced martensitic transformation (SIMT) with a sequence of γ→ε→α′ was detected for all specimens. The L-oriented specimen is most favorable for SIMT, followed by the D-oriented specimen, and finally the T-oriented specimen, which, caused by the different strain partitioning response, is the main factor contributing to the mechanical anisotropy at 20 °C. Different damage and fracture characteristics for different loading directions were also identified, which are closely associated with the initial microstructure.

Microstructure, martensitic transformation, mechanical properties and shape memory effect of (TiBw+TiCp)/Ti-V-Al shape memory alloy composites

In the present investigation, the effect of the volume fraction of B4C ceramic particles on the microstructure, martensitic transformation, mechanical properties and strain recovery characteristics of Ti-V-Al shape memory alloy composites was explored. The results revealed that the addition of B4C ceramic particles resulted in the formation of in-situ TiB whiskers and TiC particles as well as grain refinement. Based on the introduction of in-situ reinforcement and grain refinement, the martensitic transformation temperature of Ti-V-Al shape memory alloy composites gradually increased, as the B4C ceramic particle content increased from 0.5 vol.% to 10.0 vol.%. In summary, a lightweight Ti-V-Al shape memory alloy composite with high performance, including a higher martensitic transformation temperature, improved thermal cycling stability, higher strength and larger elastic modulus, can be obtained by adjusting the volume fraction of B4C ceramic particles.

Regularities of Martensitic Transformations of Fe–Ni Alloys Rapidly Quenched from Melt

The regularities of formation of the grain structure of metastable iron–nickel alloys formed in conditions of high temperature gradients during the melt hardening (spinning) and its effect on the characteristics of martensitic transformations (MT) in local areas of thin ribbons are reviewed and studied. A comparison of the texture of the austenitic and martensitic phases on different sides of thin ribbons is carried out. The consequences of influence of relaxation processes in hardening of thin ribbons on regularities of formation of the grain structure are investigated. The proposed x-ray method of measuring the amount of martensite allows solving the problem of measuring the amount of martensite in the local areas of textured alloys. As established, the completeness of MT is different for the contact and free sides of the ribbon. The main factors, which determine the heterogeneous distribution of the martensitic phase in the local areas of the ribbon, are analysed. The size effects at MP, residual stresses, and changes in the chemical composition of the austenitic phase on the distribution of the martensitic phase in local sections of the ribbon are analysed. The influence of size effect on the direct γ–α- and reverse α–γ-MT in thin ribbons is studied. The role of ultradispersed component of austenitic grains in the stabilization of austenite of rapidly quenched alloys with cyclic γ–α–γ MT is revealed.

Large Elastocaloric Effect in Fe‐Doped Co–Fe–V–Ga Shape Memory Alloys

Herein, the impact of Fe substitution for Co on martensitic transformation (MT), crystal structure, elastocaloric effect (eCE), and mechanical characteristics in Co51V34Ga15 shape memory alloys (SMAs) is systematically investigated. The temperatures of MT are found to be properly adjusted by varying the Fe content in Co51−xFexV34Ga15 (x = 0, 0.3, and 0.6) alloys, shifting toward the lower values as the Fe concentration increases. Furthermore, alloying with Fe is shown to significantly improve the eCE and superelastic properties of these alloys. Under the uniaxial stress of 600 MPa, the Co50.7Fe0.3V34Ga15 alloy exhibits a significant adiabatic temperature drop of −9.5 K under adiabatic cooling conditions. Moreover, it demonstrates good stability during the cycling test with a stable temperature change of −6.6 K remaining nearly constant after 420 cycles under 500 MPa. Additionally, a maximum compressive strength of approximately 1500 MPa is achieved in the Co50.7Fe0.3V34Ga15 alloy, which makes it the promising candidate for multifunctional materials.

Toward tunable mechanical behavior and enhanced elastocaloric effect in NiTi alloy by gradient structure

Tailoring properties of engineering materials to meet various application requirements is a long-standing challenge in materials science. Here, we demonstrate an unprecedented strategy to achieve highly tunable mechanical behavior and significantly enhanced elastocaloric effect in superelastic NiTi via gradient structure fabricated by laser surface annealing on a severely deformed matrix. The gradient-structured (GS) NiTi sheet is characterized by a nanocrystalline core sandwiched between two coarse-grained layers with grain-size gradients enabled by progressive annealing within the thickness due to the natural degradation of heat penetration. Tailorable martensitic transformation characteristics, which gradually change from a uniform mode with quasi-linear stress-strain response to a nucleation and growth mode with plateau-type superelasticity, are readily realized through tuning the grain-size gradient. Furthermore, the GS NiTi exhibits more than 50% and 130% improvement in elastocaloric cooling capacity and efficiency compared to traditional nanocrystalline and coarse-grained NiTi with homogeneous microstructures, respectively. Such significant performance breakthroughs are attributed to the strong synergetic strengthening between fine and coarse grains in the GS NiTi, which cannot be offered by the freestanding components. The unique strengthening mechanism is activated, even in the absence of plastic deformation, by the high mechanical incompatibility among heterogeneous domains and the resultant pronounced strain gradient accommodated by martensite variants. The work opens a novel avenue for fabricating bulk GS materials with desired mechanical properties and inspires the microstructure optimization in a wide range of ferroelastic materials for giant caloric effects.

Effect of drawing and annealing on the microstructure and mechanical properties of 304 austenitic stainless steel wire

Plastic deformation at room temperature, and the proceeding heat treatments, are important processes for optimizing the microstructure and mechanical properties of austenitic stainless steel. The microstructure and mechanical properties of cold-drawn 304 austenitic stainless steel wire were investigated after annealing at 700 °C and 800 °C, with different times (20, 40 and 60 min) and drawing strain (0.4, 1.0 and 1.5). Electron backscattered diffraction (EBSD) techniques, transmission electron microscope (TEM) analysis, differential scanning calorimeter (DSC) and tensile tests were performed in order to study the microstructure evolution and mechanical properties during different annealing processes for the 304 austenitic stainless steel wire. The results showed that the quantity of α′ martensite and dislocations increased with an increase in the strain, which means that, while the ultimate tensile strength of the cold-drawn wires elevated, the elongation reduced. The mechanical properties of stainless steel wires also varied with the evolution of martensite transformation characteristics, density of stacking fault, dislocation and twin, as well as the recrystallization degree under various annealing conditions. The recrystallization temperature of steel wire was mainly determined by the magnitude of the strain, while the martensite reversal temperature was determined by the stacking fault energy and the deformation value. The temperature of recrystallization and martensite reverse in steel wire decreased with the increment of the strain. The balance of tensile strength and elongation of steel wire can be obtained by adopting the proper annealing process combined with cold-drawing deformation. In this paper, we showed that a good combination of strength and elongation in 304 austenitic stainless steel can be obtained with a strain of 1.5 annealed at 800 °C for 20 min.