Molecular Dynamics Simulation on Compatibility and Microstructure Evolution During Stress-Induced Phase Transformation in NiTi Single Crystal

Understanding phase transformation behaviors is essential for the material design of shape memory alloys (SMAs). This paper studies stress-induced phase transformation in single-crystal NiTi SMAs with three orientations (i.e.,,, and) using molecular dynamics (MD) simulations. Microstructural evolutions and mechanical responses are analyzed. Results indicate that different orientations promote transformation into martensitic variants with greater atomic-scale transformation strain, resulting in larger phase transformation strains in the stress-strain responses. Subsequently, microstructure compatibility is studied. Patterns after transformation are classified into three types: parallel twins, twin-twin domains, and multiple-twin domains. The specific patterns formed depend on both loading mode and crystal orientation. Further analyses indicate that: (1) all the interfaces obtained in this study satisfy their corresponding twinning equations; (2) the global compatibility analysis shows the [1 0 1] compression model’s cross twinning matches one ideal case, while the [1 1 1] tension model’s triple junction corresponds to four possible cases. This work provides novel insights into microstructure compatibility in differently oriented NiTi single crystal, enhancing understanding of their phase transformation processes.