微裂纹与相变温度阀值对NiTi合金失效的影响

Effect of micro crack and transformation temperature threshold on failure of NiTi alloy

基于分子动力学方法探究微裂纹缺陷与相变温度阈值的耦合作用对NiTi合金在原子尺度上的相变和失效过程的影响。结果表明:在微裂纹扩展过程中,由于应力水平的变化,材料经历奥氏体线性阶段、奥氏体-马氏体塑性阶段、马氏体线性阶段和裂纹失稳扩展阶段与宏观应力诱导相变相似的微相变过程。当温度低于马氏体相变温度阈值时,裂纹扩展速率随温度的升高而升高,应力诱导相变在预制裂纹区域首先发生;当温度超过马氏体相变温度阈值时,裂纹扩展速率随温度的升高反而降低,应力诱导相变首先在裂尖前方区域发生。此结论为深入研究NiTi合金的微裂纹演化与相变温度阈值的耦合关系开启新思路。

The coupling effects of the micro crack and the transformation temperature threshold on transformation and failure process in atom scale were studied by the molecular dynamics method. The results show that there are four stages in crack propagation,namely the austenite linear stage,austenite-martensite plastic stage,martensite linear stage and crack propagation stage. These stages are similar with macro transformation processes. When the temperature is lower than the temperature threshold of martensitic transformation,crack propagation rate increases with temperature rising,and phase transformation induced by stress occurs first in pre-crack area. When temperature is higher than the temperature threshold of martensitic transformation,crack propagation rate decreases with temperature rising,and phase transformation induced by stress occurs first in crack tip. These conclusions provide a new way to further study the coupling relationship between the micro crack evolution and the transformation temperature threshold in NiTi alloy.