A Study on Phase Transformation in FeMnAlNi Shape Memory Alloy by High-Energy X-ray Diffraction

Fe-based shape memory alloys have recently gained increasing interest in the scientific community due to their lower cost compared to the NiTi system and their unique properties, such as a wide phase transformation window. Among various compositions, the FeMnAlNi system has attracted particular attention for its potential to exhibit large superelastic strain in specific crystal orientations. However, its broader adoption is currently limited by its high sensitivity to heat treatment conditions, grain size, crystal orientation, and rapid degradation under cyclic loading. To enhance our understanding of these factors, this study investigates the mechanical response of coarse-grained FeMnAlNi specimens with varying orientations and heat treatments. The experimental approach integrates crystal orientation analysis via electron backscatter diffraction (EBSD), in situ strain measurements using digital image correlation (DIC), and in situ high-energy X-ray diffraction. The results quantify variations in the fraction of austenite and martensite phases during deformation, as well as distortions in the austenite phase. These analyses were also performed with cyclic loading providing a unique set of experimental results for a deeper understanding of the phase transformation of the FeMnAlNi system.