Phase diagram of the Ni-Fe-Mn-Ti martensitic alloy.

A research team led by Professor Ma Tianyu from the Frontier Institute of Science and Technology (FIST) at Xi'an Jiaotong University (XJTU), in collaboration with Professor Ren Xiaobing, chair professor at XJTU and chief researcher at Yongjiang Laboratory, has discovered Ni-Fe-Mn-Ti, a special martensitic alloy whose elastic modulus remains nearly constant during continuous cooling below the martensite finish temperature, in contrast to the low-temperature modulus hardening typically observed in normal martensitic alloys.

Within the large micro-domains of this Elinvar martensite, two types of nanoscale configurations (nano-domains) coexist. During cooling, a slow transformation occurs between these two types of nano-domains, compensating for the intrinsic modulus hardening effect caused by enhanced atomic bonding, thereby producing the Elinvar effect.

Stress can also drive a displacive phase transformation between these two nano-domains, which not only endows this Elinvar martensitic alloy with a wide-temperature-range superelastic effect, but also grants it favorable low-temperature plasticity.

This work represents the first discovery of the Elinvar effect in a first-order martensitic phase transformation system, breaking through the theoretical limitations of low-temperature hardening in traditional metallic materials and providing a new mechanism for designing Elinvar alloys and solving the low-temperature brittleness problem of metals.

The related work was published in Physical Review Letters (2026, 137, 016101) under the title Elinvar Effect by Nanoscale Displacive Phase Transformation in Martensites.