Fe-Mn-Al-Ni based shape memory alloys exhibit an extremely low temperature dependence of the critical stress for martensitic transformation and display an ultra-wide superelastic temperature range （from -263 ℃ to 240 ℃）. Therefore， these shape memory alloys show promising applications in aerospace， space exploration， vibration and seismic damping， and other environments with variable working conditions. In this work， the main factors affecting the superelasticity of Fe-Mn-Al-Ni based shape memory alloys are reviewed and prospected. Since the precipitation of the coherent B2 nano-phase plays a key role in the martensitic transformation from non-thermoelastic to thermoelastic in Fe-Mn-Al-Ni-based shape memory alloys. The mechanism by which the coherent B2 nano-phase modulates the martensitic transformation of Fe-Mn-Al-Ni-based shape memory alloys and the related progress of its size regulation are firstly discussed. Since the superelasticity of Fe-Mn-Al-Ni-based shape memory alloys is known to be positively correlated with the grain size， the preparation of single crystals is a prerequisite for achieving excellent superelasticity. Therefore， the single-crystal growth studies of Fe-Mn-Al-Ni-based shape memory alloys in recent years are reviewed. Then， the functional properties of single-crystal Fe-Mn-Al-Ni-based shape memory alloys are summarized. Finally， the further research and development of the Fe-Mn-Al-Ni based shape memory alloys， such as the regulation mechanism of the coherent B2 nano-phase for martensitic transformation， the further development of large-size single crystals， and the improvement of the natural aging and cyclic superelasticity stability， are prospected.

Chromium (Cr) alloying is demonstrated to serve as a key compositional lever to engineer the microstructure and deformation mechanisms of CoNiV-based multi-principal element alloys (MPEAs). Increasing the Cr content from 5 to 15 atomic percent (at.%) modulates both κ-phase formation and stacking fault energy (SFE) in CoNiV-based MPEAs, thereby enabling controlled cooperative deformation between the κ phase and face-centered cubic (FCC) matrix. Thermodynamic simulations and first-principles calculations reveal that Cr addition suppresses κ-phase precipitation while significantly lowering the SFE, which enhances κ-phase shearability and promotes planar slip within the FCC matrix. Transmission electron microscopy indicates that the 10Cr alloy possesses deformable κ precipitates and abundant stacking faults, leading to enhanced hetero-deformation-induced (HDI) strengthening. The resulting heterogeneous κ/FCC architecture achieves an exceptional combination of yield strength (∼0.93 GPa) and elongation (∼41%), surpassing most reported Co-based MPEAs. Quantitative analysis of back stress and effective stress further suggests that HDI strengthening contributes significantly to the strain-hardening response. This work proposes a compositional–mechanical coupling pathway, i.e., Cr-mediated modulation of κ-phase shearability and SFE, that provides a mechanistic foundation and design implication for overcoming the intrinsic strength–ductility trade-off in advanced MPEAs.

Fe-Mn damping alloys, which integrate high strength with superior damping capacity, are particularly suitable for manufacturing components with complex lattice or topological structures via additive manufacturing, enabling integrated lightweight and high-damping designs for load-bearing parts. In this work, Fe-20 Mn damping alloy was fabricated by selective laser melting (SLM), and its mechanical and damping properties were investigated. The as-SLMed alloy exhibits a fine microstructure, offering a tensile strength of 750 MPa, a yield strength of 505 MPa, and a damping performance Q -1 of 0.023 (at 6 x 10-4 strain). Annealing further improves both properties, achieving a yield strength of 621 MPa and Q -1 of 0.03. The enhancement is attributed to recrystallization, which transforms the high-defect, non-equilibrium SLMed state into a more stable structure strengthened by grain refinement and homogenized phase boundaries. Moreover, the increased stacking fault probability in epsilon and gamma phases, along with a higher density of epsilon-martensite variant boundaries and epsilon/gamma interfaces after annealing, raises the density of mobile interfaces, thereby directly boosting damping energy dissipation. This study systematically reveals the synergistic regulation of mechanical and damping properties in SLM-formed Fe-Mn alloys through heat treatment.

Breaking the strength-ductility trade-off requires microstructural designs that sustain work hardening while avoiding early damage initiation. Here we show that ultralow-nitrogen control offers a practical processing window to tune the precipitation interplay among kappa, L12, and VN in a CoNiV-based multi-principal-element alloy, thereby promoting heterostructure-assisted strengthening. Annealing at 800-1000 degrees C systematically alters kappa-phase stability and FCC recrystallization: partial recrystallization at 800 degrees C evolves into a fully recrystallized FCC matrix with increased kappa fraction at 900 degrees C, followed by reduced kappa fraction and marked grain coarsening at 950-1000 degrees C. The N950 condition, featuring a balanced kappa distribution together with fine L12 precipitation, achieves a yield strength of 787 MPa, an ultimate tensile strength of 1231 MPa, and an elongation of 32.8%, demonstrating an excellent strength-ductility synergy. In contrast, upon kappa dissolution at 1000 degrees C, VN-containing precipitates and microstructural coarsening correlate with diminished work hardening and ductility. Loading-unloading tensile analysis further indicates that the optimized heterostructure in N950 promotes sustained strain hardening through an enhanced back-stress contribution, consistent with cooperative deformation between kappa and the FCC matrix. These results establish a practical ultralow-N processing window for maximizing strength-ductility synergy by controlling kappa-L12-VN precipitation competition in CoNiV-based alloys.

Fe-Mn-Al-Ni based shape memory alloys (SMAs) are able to exhibit superelasticity in a wide range of temperatures, and their superelastic stresses are extremely low temperature dependent, which holds potential applications in inclement fields such as deep space. However, the difficulty in obtaining large single crystals and the shortcoming of natural aging in this alloy system are hindering their practical application. Based on this, an ultra-large Fe-Mn-Al-Ni-Mo single-crystal SMA with nearly zero natural aging effect was successfully fabricated in this work via bifunctional Mo-segregation engineering. Firstly, at elevated temperatures, the grain boundary segregation of Mo atoms in this alloy effectively facilitated the abnormal grain growth during cyclic heat treatment. Based on this, a large-scale Fe-Mn-Al-Ni-Mo single-crystal bar with a diameter of approximately 15.5 mm and a length of approximately 95 mm was obtained. Meanwhile, the Mo atoms with a low diffusion coefficient effectively hindered the coarsening of coherent B2 nanoprecipitates during natural aging. This led to the Fe-Mn-Al-Ni-Mo single crystals close to [001] orientation to exhibit a huge superelastic strain of 8.5% even after 1.5 years of natural aging. In contrast, B2 nanoprecipitates in the Mo-free Fe-Mn-Al-Ni SMA grew from similar to 7.7 to similar to 10.1 nm after natural aging for 1.5 years. This study provides a unique insight into the development of high-performance functional alloys using elemental segregation engineering. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

The mechanical incompatibility between the alpha and beta phases could deteriorate the ductility of alpha + beta dual-phase Ti alloys at cryogenic temperatures. In this study, stress-induced alpha ' martensite was intentionally tailored by alloying 3 wt% Mo into the alpha-type Ti-5Al-2.5Zr base alloy to introduce a bifunctional prior beta phase, which refined the alpha grains and transformed into hcp alpha ' martensite during deformation at liquid nitrogen temperature to accommodate the plastic strain. The strain partitioning between the softer prior beta grains and harder alpha grains elevated local stress at the prior beta/alpha interfaces, which activated additional stress-induced alpha ' martensite transformation and < c+a >- and < a >-type dislocations in the adjacent alpha grains. These mechanisms mitigated strain localization and promoted compatible deformation between the prior beta and alpha grains, thereby leading to simultaneously enhanced cryogenic strength and ductility in the Ti-5Al-2.5Zr-3Mo alloy, which exhibits a superior combination of cryogenic yield strength of 1010 MPa, ultimate tensile strength of 1181 MPa, and ductility of 16.9 %. This work demonstrates a promising pathway for designing strong yet ductile cryogenic Ti alloys through regulating stress-induced alpha ' martensitic transformation.

Achieving a balance between high strength and high damping capacity in metallic alloys remains a significant challenge. This study demonstrated that a synergy of strength-damping could be achieved in a Mn15.4Cu5.4Ni2.4Fe alloy by aging after cold deformation. Compared to conventional aging without pre-deformation, the cold rolling followed by aging increased yield strength by above 40 % while reducing the damping capacity by below 10 %. The strengthening contributions from phase separation and dislocations acted independently in the aged alloy after the pre-deformation. The dislocations introduced by the pre-deformation hindered the martensitic transformation but promoted the growth of alpha-Mn during the aging. The aging after pre-deformation provides a pathway for preparing high strength Mn-Cu based damping alloys.

Previous work showed that a strong negative dependence of shape memory effect (SME) existed on annealing twin boundaries (ATBs) in Fe-Mn-Si-based shape memory alloys (SMAs). Microalloying is expected to improve the SME by inhibiting recrystallization and reducing the density of ATBs. In this study, the effects of 89 ppm B or 1 wt% Nb addition on the recrystallization, and the resultant evolutions of grain boundary character distributions and SME were studied in the cold-rolled and annealed Fe-Mn-Si-based alloys. The addition of B and Nb obviously improved the SME after annealing at temperatures above 973 K due to their impedance of recrystallization and the resultant lower density of ATBs. Independent of the B and Nb microalloying and recrystallization, there still existed a strong negative dependence of SME on the density of ATBs. These findings provide insight into improving the SME of Fe-Mn-Si-based SMAs through microalloying to impede the occurrence of recrystallization and reduce the density of ATBs.

Carbon gradient induced by high-temperature solution treatment in TWIP steel sheets significantly influences the mechanical behavior, primarily attributed to variations of stacking fault energy (SFE) across the decarburized layer. In this work, five through-thickness C gradients were successfully processed by annealing Fe-18Mn-1.5Si-1.1 C twinning induced plasticity (TWIP) steel sheets in air at different temperatures (900-1100 degrees C). The Cgradient steels exhibit inhomogeneous deformation mechanisms characterized by martensitic transformation at the low-carbon (<0.5 wt%) surface while twinning at the high-carbon (>0.9 wt%) core. The tensile properties of the C-gradient steel sheets became increasingly worser with the increased C gradient. The deteriorated mechanical properties could be ascribed to the reduced strain hardening rate (SHR) by the decreased carbon content and early crack initiation on the sheets surface due to the formation of brittle epsilon martensite during the tensile deformation. In engineering practice, attention must be paid to the deterioration in mechanical properties of thin-walled TWIP steel components by the carbon gradients when optimizing annealing technique.

Previous work has shown that the shape memory effect (SME) exhibited a strong negative dependence on the density of annealing twin boundaries (ATBs) in Fe-Mn-Si-based alloys. Reducing the density of ATBs has thus been an effective way to improve the SME of Fe-Mn-Si-based alloys. This study investigated the effects of trace B doping on the density of ATBs and the resultant SME in solution-treated Fe-Mn-Si-based alloys. Results indicated that doping 89 ppm B effectively reduced the density of ATBs in the solution-treated Fe-Mn-Si-based alloy. Consequently, its SME was remarkably improved. The maximum shape recovery strain reached 2.7 % in the Bdoped alloy, 1.3 % higher than in the alloy without B doping. This work demonstrates a new avenue to improve the SME by doping trace B, which is of significance for the fabrication of Fe-Mn-Si-based shape memory alloys in a more cost-effective manner.

For engineering applications that demand enduring durability, ultra-hard metallic alloys are essential. Yet, fabricating components with diverse hardness levels introduces complexities in alloy composition design, processing routes optimization, and the implementation of hardening methods across various alloy systems. In this study, we presented the achievement of an exceptionally adjustable hardness range, spanning from soft (229.6 HV) to ultra-hard (952.5 HV), in FeMnAlCu multi-principal element alloys (MPEAs) with varying Cu content. These adjustable hardness values were primarily tuned through routine short-term aging treatments to induce the formation of hard n-Mn phase. The ultra-hard Fe-37.5Mn-6.3Al-4.1Cu primarily consisted of near-equiaxed n-Mn and a small fraction of body-centered cubic (BCC) Mn-rich phase, with BCC Fe-rich and face-centered cubic (FCC) Cu-rich phases distributed at the interfaces of n-Mn. When the Cu content was increased to 6.2 wt%, the formation kinetics of n-Mn was significantly accelerated, resulting in an ultrahigh hardness of 952.5 HV after aging at 600 degrees C for 6 h. However, an excessive Cu content of 9.2 wt% dimished the hardening reponse due to the presence of a substantial quantity of thermally induced FCC gamma ' martensite in the solution-treated state. These results provide new insight into developing ultra-hard alloys through promoting the formation of hard n-Mn phase.

The deformation after cooling from 1200 degrees C to 800 degrees C failed to produce ultrafine grains in M50NiL martensitic steel, whereas directly heating to 800 degrees C successfully fabricated ultrafine grains (0.39 mu m). This abnormality stemmed from the different initial microstructures before deformation-namely, austenite and tempered martensite. The ultrafine-grained M50NiL steel (1.4 mu m) prepared by forging at 800-850 degrees C exhibited markedly higher strength and toughness than the coarse-grained steel (75 mu m) produced by conventional forging, owing to significant grain refinement. Furthermore, forging as-cast M50NiL steel at 800-850 degrees C could simultaneously produce ultrafine grains and achieve compositional homogenization, offering great potential for substantially shortening the processing route for ultrafine-grained steels.

The effects of vanadium (V) content on the development of coherent L1(2) nanoprecipitates, and the resultant tensile mechanical properties and deformation mechanisms of non-equiatomic Co80-xNi20Vx (15 <= x <= 20, atomic percentage) medium-entropy alloys were systematically investigated. The results revealed that the L1(2) nanoprecipitates began to form when the V content reached 17 at.%, and their size increased progressively with further V addition. The L1(2) nanoprecipitates reached their maximum average size of similar to 9.3 nm at 19 at.% V. With increasing V content from 15 at.% to 19 at.%, the strength and strain hardening capability of the alloys were enhanced. The Co61Ni20V19 alloy exhibited the optimal strength-ductility synergy, achieving a yield strength of 644 MPa, an ultimate tensile strength of 1363 MPa, and a ductility of 28 %. This superior strength-ductility synergy is attributed to the strengthening effect of L1(2) nanoprecipitates and grain refinement. The formation of stacking faults and Lomer-Cottrell locks contributed primarily to the enhanced strain hardening ability during deformation. This study provides a theoretical basis for the optimizing the mechanical properties and guiding the design of medium-entropy alloys through the tailored precipitation of coherent L1(2) nanoprecipitates.

The severely suppressed deformation twinning in a pure titanium was reactivated through grain boundary engineering to construct uniformly distributed unrecrystallized grains with extensive low-angle grain boundaries. Twinning was promoted by coordinated deformation between unrecrystallized and recrystallized grains that generated high-density geometric necessary dislocations and local stress concentrations, thereby simultaneously improving strength, uniform elongation, and strain hardening.

The mechanical properties and deformation mechanisms of a newly developed Co-free FeMnSiNiAl high entropy alloy (HEA) at room and cryogenic temperatures were systematically investigated. The initial tensile deformation at room temperature was dominated by dislocation slipping, with modest strengthening from the Transformation-Induced Plasticity (TRIP) effect due to the deformation-induced FCC -> HCP martensitic transformation. Subsequently, the TRIP effect was markedly enhanced during the middle and later stages of deformation, leading to an excellent combination of yield strength (6y, 315.1 MPa), ultimate tensile strength (6u, 773.4 MPa), and fracture elongations (of, 78.3 %). The strengthening by the TRIP effect was significantly enhanced at cryogenic temperatures as a result of enhanced FCC -> HCP martensitic transformation. This resulted in a synergetic improvement in strength and ductility at 223 K, with 6 y of 363.6 MPa, 6 u of 832.1 MPa, and o f of 87.2 %. The enhanced ductility at 223 K was linked to the FCC -> HCP -> BCC sequential martensitic transformation during the middle and later stages of deformation, which acted as an additional way to accommodate plastic strain and delay strain localization. However, the rapid FCC -> HCP transformation at the early stage of deformation at 173 K and 77 K impeded the FCC -> HCP -> BCC sequential martensitic transformation during subsequent deformation stages, thus remarkably enhancing strength but reducing ductility. Our findings provide new insights into the design and development of TRIP-assisted single-phase FCC HEAs for cryogenic applications.

Precipitation of ductile alpha phase can generally improve the ductility of Cu-based shape memory alloys but impair their shape memory effect (SME). An abnormal positive dependence on amount of the alpha phase was reported in both conventional Cu-Zn-Al and ductile Cu-Al-Mn alloys. To clarify reason for this abnormal dependence, we systematically investigated relationship between the martensitic transformation behavior and the amount of alpha phase in a ductile Cu-17.5Al-9.4Mn alloy. The results revealed that the occurrence of martensitic stabilization due to slow heating could rationalize the abnormal dependence. The reduced amount of stabilized martensites was proportional to the amount of alpha phase. An inverse dependence of SME on the Ms temperature existed in the ductile Cu-Al-Mn alloys, regardless of the intrusion of alpha phase.

To enhance the damping capacity at 350 K, the martensitic transformation temperatures must be increased. However, the increment in martensitic transformation temperatures can deteriorate the damping capacity. Whether good damping capacity can be obtained at elevated temperature is unknown to us. In this paper, we carefully investigated the evolution of damping capacity and vacancy behavior with the environmental temperature in ductile Cu-Al-Mn-Ni alloys with different Ms temperatures. Our results showed that the damping capacity in Cu-Al-Mn-Ni alloys subjected to 15 min step-quenching all showed an obvious degradation tendency with the increment in environmental temperature to above 313 K. The reduction of martensite amount and mobility of martensite boundaries could rationalize the degradation of damping capacity with the environmental temperature. The original number of vacancies on the martensite boundaries (Nvmb), which is positively dependent on the Ms temperature, controls the degradation rate of damping capacity in martensitic Cu-Al-Mn-Ni alloys. Among the experimental Cu-Al-Mn-Ni alloys, the Cu-18.0Al-8.4Mn-2.5Ni alloy with Ms = 360 K have the superior resistance to the degradation of damping capacity with the environmental temperature. In addition, we found that a critical temperature for vacancy diffusion exists at between 313 K and 333 K. With Ms temperature below the critical temperature, the alloy has a far lower original Nvmb than the one with Ms above the critical temperature. These findings highlight the importance of lowering the original Nvmb and increasing the critical temperature on improving the damping capacity at elevated temperatures.

This study investigated the effect of strain rates on the stress-induced martensitic transformation (SIMT) and mechanical properties of a Ti-15Nb-5Zr-4Sn-1Fe metastable (3-Ti alloy, with a focus on the role of the w phase on the initial activation of SIMT at the onset of yielding. The results demonstrated that increasing the strain rate from 5 x 10_ 4 s_ 1 to 1 x 10_ 1 s_ 1 enhanced the yield strength while reducing ultimate tensile strength and strain-hardening ability due to the slightly suppressed SIMT. The presence of dispersed w nanoparticles within the (3 matrix impeded the initial activation of long-range SIMT without preventing its occurrence, which partially contributed to the increased yield strength with increasing strain rate. Once the long-range SIMT was activated at higher stress levels, SIMT proceeded more readily, causing a more pronounced stress plateau and more homogeneous formation of martensite across different (3 grains at higher strain rates. These findings emphasize the significant influence of the w phase on the activation of SIMT under high strain rate deformation. Controlling the w phase could potentially regulate SIMT and optimize the mechanical properties of metastable (3-Ti alloy for high strain rate deformation.

Mechanical properties of cast FeMn binary damping alloys, especially their sensitivity to Mn content, are rarely studied, whereas numerous studies have focused on their hot-or cold-deformation processed counterparts. This work presented the first systematic investigation into the role of Mn content (15-21 %) on microstructure-mechanical property relationships in cast-state FeMn damping alloys, comparing as-cast (AC) and solution-treated (ST) conditions. Experimental results revealed that increasing Mn contents marginally enhanced yield strength while significantly compromising the total elongation of the AC alloys. The solution treatment could remarkably improve their total elongation but had little effect on their yield strength. The deformation induced gamma -> alpha' martensitic transformation, through the transformation-induced plasticity (TRIP) effect, governed the evolution of total elongation with the Mn content and solution treatment. The occurrence dependence of deformation induced gamma -> alpha' martensitic transformation on the Mn content could be rationalized by the driving force for gamma -> alpha' martensitic transformation.