Martensitic transformation and shape memory behavior of Fe-Mn-Si based shape memory alloy under quasi-static and impact compressive loading

Relatively poor shape memory effect (SME) of iron-based shape memory alloys (Fe-SMAs) limits their further applications. Although recent studies have demonstrated significant SME improvements in Fe‑SMAs using various tensile-based methods, their behavior under compressive loading remains underexplored. This study investigates the SME of Fe-SMAs under quasi-static and impact compressive loading, addressing the limitations of existing impact testing apparatuses and the unclear relationship between martensitic transformation and volume resistivity during unloading and subsequent heating. A modified split Hopkinson pressure bar (SHPB) apparatus, equipped with a double momentum trap structure, was developed to ensure accurate high strain rate testing by eliminating residual stress waves and multiple loadings. Simultaneously, real‑time volume resistivity monitoring to capture the martensitic transformation during single compressive unloading and cyclic compressive training process was performed. The results revealed that the SME of Fe‑SMAs improves with increasing strain rate and that cyclic compressive training further enhances shape recovery under both quasi‑static and impact conditions. Notably, the maximum shape recovery ratio η is observed under the quasi-static compressive loading after the fifth cycle, reaching about 94.6 %, which is larger than the impact tensile training after sixth cycle (η=93 %). The shape recovery under the impact was generally lower compared to tensile training due to coexistence of multiple and single variants, as confirmed by electron backscatter diffraction (EBSD) analyses. Larger grain size produced under quasi-static training results in a higher SME. This study provides insights into the compressive training mechanisms of Fe-SMAs, contributing to the optimization of SME for diverse loading applications.