Measuring the microscale origins of functional fatigue in materials with martensitic transformations

The aim of this experiment is to measure the interfacial stress fields that lead to functional fatigue in materials that undergo martensitic phase transformations (MPTs) such as shape memory alloys (SMAs). MPT is a diffusionless, often reversible phase transformation between a high-symmetry and a low-symmetry phase. It is the enabling mechanism behind the novel properties of SMAs, switchable multiferroics, and TRIP steels, but functional fatigue continues to be a major barrier. Functional fatigue is caused by stress fields that form at the phase interface and lead to dislocation generation. We plan to use dark-field X-ray microscopy (DFXM) to measure these interfacial stress fields during stress-induced MPT for the first time, using a mechanical load frame. CuAlNi SMAs will be mechanically cycled to observe how dislocations develop in connection with these interfacial stress fields and influence the functional fatigue behavior.