Understanding the role of microstructural repeatability in the functional fatigue behavior of shape memory alloys

Martensitic phase transformation (MPT), a diffusionless solid-to-solid phase transformation, is the enabling mechanism behind the novel behaviors of shape memory alloys (SMAs). However, functional fatigue—changes to the material during cyclic loading that diminish its exploitative properties—continues to be a major technological barrier. Functional fatigue is caused by dislocations that generate as a result of the MPT. Here, we plan to test a new hypothesis on the role of "microstructural repeatability" of the MPT. We propose a multiscale, multimodal experiment during stress-induced MPT cycling using novel lightweight Mg-Sc SMAs as a model material. The initial microstructure will be measured using DCT. The increase in dislocation density will be characterized in individual grains using XRTT, and these functional fatigue related quantities will be correlated with microstructural repeatability using 3DXRD.

马氏体相变（Martensitic Phase Transformation，MPT）是一类无扩散型固-固相变，亦是形状记忆合金（Shape Memory Alloys，SMAs）展现独特新型性能的核心调控机制。然而，功能疲劳——即循环加载过程中材料发生劣化其可利用性能的现象——仍是制约其工程应用的重大技术壁垒。功能疲劳由马氏体相变过程中产生的位错所诱发。本研究拟针对马氏体相变的"微观结构可重复性"作用机制提出全新假说并开展验证工作。我们计划以新型轻质Mg-Sc系形状记忆合金作为模型材料，开展应力诱导马氏体相变循环过程中的多尺度、多模态实验研究。将采用DCT表征材料的初始微观结构；通过XRTT对单个晶粒内的位错密度增量进行表征，并借助3DXRD将上述与功能疲劳相关的特征量与微观结构可重复性进行关联分析。