3D in-situ characterization of individual grains in CuAlNi shape memory alloys during cyclic loading using X-ray topotomography

Due to the microstructural complexity of reversible martensitic phase transforming materials, elucidating the micromechanics of shape memory alloys (SMAs) necessitates the employment of novel high-resolution 3D in-situ characterization techniques. To facilitate advancements in both current and future SMA-based technologies, we must employ novel material characterization methods capable of unveiling the fundamental microstructural origins of, e.g., mechanical hysteresis and functional fatigue. This work will contribute to advancing this fundamental understanding. We employ a multi-modal approach combining X-ray topotomography, diffraction contrast tomography, and 3D X-ray diffraction during in-situ mechanical cycling in copper-aluminum-nickel (CuAlNi) SMAs. In particular, X-ray topotomography can be used to image the 3D morphology of austenite-martensite microstructures as a function of time as they interact with microstructure features like grain boundaries and precipitates. In this work, these techniques are used to spatially resolve the 3D morphology of stress-induced austenite-martensite microstructures during cyclic loading, including the resultant dislocation structures and retained martensite after unloading and how the martensite formation changes during multiple cycles.