Microstructure and Super-Elasticity of Fe-33Mn-17Al-8.5Ni (at. %) Alloy for Structural Applications

Abstract

The control of the residually stressed γ’-FCC phase in the grain boundaries that affects super-elasticity in the promising Fe-Mn-Al-Ni shape memory alloy (SMA) and grain size enhancement was an epitome for research in the current study. New composition Fe-33Mn-17Al-8.5Ni (at. %) was designed with the help of thermocalc software TCFE 11 database, produced in an electric arc furnace under an argon atmosphere and systematically investigated in the as-cast and heat-treated conditions. Characterization was performed using optical microscopy, X-ray diffraction measurements (XRD), and compression tests. Controlling the cooling conditions after heat treatment (HT) with high flowrate air cooling helped to reduce on the formation of the detrimental phase, γ’ at the grain boundaries as well as observed some grain growth in the microstructure without necessarily causing cracking as reported previously with quenching in cold water. The yield strength depicting the stress-induced martensitic transformation was 925 MPa for as cast and 909 MPa upon heat treatment. From cyclic compression loading/deloading training, a recovery strain of 2.1% and 2.3% was attained at 800 MPa maximum stress in the as-cast and heat treated-conditions, respectively.