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.

马氏体相变 (MT) 在决定形状记忆合金 (SMA) 的机械和功能特性方面起着关键作用。MT 的行为在很大程度上取决于材料的微观结构，两级或多级 MT 就是典型的例子。然而，尽管已经做出了很多努力，但两级或多级 MT 的物理起源仍然存在争议。在这项研究中，在具有纳米级浓度调制的基于 TiNb 的 SMA 中观察到了一种新型的两级 MT。这种化学异质性诱导的两阶段 MT 的物理起源是贫铌和富铌区域之间母相和马氏体相的热力学稳定性差异。