The Evolution of Compatible Microstructures in Shape Memory Alloys

Shape memory alloys (SMAs) have been extensively used in sensors and actuators. Their behavior is dominated by the microstructures. Observations show that martensite twins usually form laminated patterns with interfaces that satisfy the compatibility equation to minimize the total energy. However, due to high nonlinearity of the material, the relationship between the overall response and microstructure has not yet been revealed. In this study, we identify the set of possible twin structures and the paths along which the microstructure evolves continuously between austenite and martensite phases under loads. The variational principle is used to capture the dissipative nature of interface motion in microstructures when phase transformation occurs. The model is applied to study superelasticity effect in Cu-Al-Ni single crystals. Many subtle features are explained.