Equal Channel Angular Extrusion in Stainless Shape Memory Alloys

Abstract

Several works, mainly of this group, have demonstrated that one of the main factors for the improvement of the shape memory in stainless shape memory alloy (SMA) is the decrease of the austenitic grain size. However, for the conventional methods of thermomechanical treatment, the smallest grain size obtained up to now was around 30 micron. This project has as objective to study the influence of the microstructure in the mechanical properties in stainless shape memory alloy when submitted to severe plastic deformation by equal channel angular extrusion (ECAE). Two compositions will be used, Fe-Mn-Si-(Cr-Ni) and Fe-Mn-Si-(Cr-Ni-Co) produced by vacuum induction melting furnace (VMI). Once in appropriate dimensions, they will be deformed by ECAE using a 120o die angle, in the sense to obtain grain size in smaller scale. The shape recovery related to grain size after ECAE processing will be investigated for each alloy. It will also be evaluated the microstructure evolution of those alloys submitted to different heat treatments after ECAE processing and the influence of resulting grain size increase in relation to SME. The microstructural characterization will be performed using optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron-backscatter diffraction (EBSD) and hardness measurement. The characterization of SME will be performed with tensile test, DSC (Differential Scanning Calolimetry), DMA (Dynamic Mechanical Analyzer) and X-ray diffraction. The determination of the grain size before and after ECAE deformed will be analyzed using the ASTM E112 standard.