Hardness-gradient reversion in FeMnSiCr shape memory alloy modules produced by high-speed high pressure torsion

Abstract

High pressure torsion (HPT) processing technology, consisting in the obtainment of (ultra)fine bulk metallic structure during 2–3 complete rotations of the superior anvil at low speed (~10-1 rpm) under high applied pressure (~ GPa) applied on the lower anvil, has been modified as to allow the application of elevated number of rotation numbers (~102 rpm). By high-speed high pressure torsion (HS-HPT), coned-disk spring shape modules were processed from an as cast Fe-28Mn-6Si-5Cr (mass %) shape memory alloy (SMA). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies revealed that the modules became nanostructured as an effect of HS-HPT processing. After processing, a hardness gradient was obtained along the truncated cone generator, increasing from inner to outer areas, due to different deformation degrees in these zones. After complete flattening, the measurements revealed that the hardness gradient maintained its value but reversed its variation sense.