Microstructural Evolution and Functional Response of a FeMnSiCr Shape Memory Alloy Module Processed by High-Speed High-Pressure Torsion

In this study, a functional truncated-conical module made of the Fe57Mn27Si11Cr5 (at.%) shape memory alloy was investigated. The module was obtained by the severe plastic deformation process, High-Speed High-Pressure Torsion (HSHPT). It was processed in a single step, with the logarithmic strain estimated at ε = 1.10, and the correlation among the microstructure, structural state, and functional behavior was analyzed by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and mechanical testing. HSHPT processing replaced the initial dendritic structure with a severely deformed and refined microstructure characterized by deformation bands, fibrous regions, and lamellar features associated with ε-martensite. XRD analysis revealed that γ-FCC austenite remained the dominant crystalline phase and that the γ(111) reflection shifted from 2θ = 43.47° to 43.12°. AFM analysis, performed over an area of 1600 µm2, revealed an arithmetic mean roughness (Ra) of 14.59 nm and a root mean square roughness (Rq) of 19.77 nm. Segmentation of the scanned area using the Flooding procedure revealed a mean Equivalent Circular Diameter (ECD) of 253.39 nm. Mechanical tests demonstrated stable functional behavior and progressive cyclic stabilization. The module exhibited a superelastic-like load–displacement response, accompanied by an increase in energy storage efficiency and a decrease in dissipated energy during repeated compression cycles.