In-situ characterization of phase interfaces in CuAlNi during mechanical cycling using dark-field X-ray microscopy

The interfacial stress fields play a critical role in determining the hysteresis and functional fatigue of shape memory alloys. These stress fields manifest at phase boundaries as a consequence of geometric incompatibility between the austenite and martensite phases. As the material approaches transformation, these interfacial stress fields act as an energy barrier, requiring extra energy to be driven into the system to overcome it, resulting in a hysteresis. In addition, increasing the energy in the system also increases dislocation generation, resulting in functional fatigue. In this research, we employ dark-field X-ray microscopy (DFXM), a high-resolution diffraction microstructure imaging technique, to characterize these phase interfaces and interfacial stress fields during mechanical cycling in a CuAlNi shape memory alloy. The results show the 3D emergence and evolution of individual phase interfaces and spatially-mapped orientation and elastic strain, including the interfacial elastic strain fields at the phase interfaces. These findings will contribute to a better understanding of the origins of hysteresis and functional fatigue by investigating interfacial stress fields and dislocation generation at phase interfaces and their effects on macroscopic behavior.