Microstructure and mechanical properties of a dual phase transformation induced plasticity Fe-Mn-Co-Cr high entropy alloy

Abstract

The multicomponent alloys, also known as High Entropy Alloys (HEAs), have been the subject of intense exploration for over a decade now for a wide range of potential applications. To investigate microstructure and mechanical property correlation in a transformation-induced plasticity dual-phase high entropy alloy (DP-HEA) Fe50Mn30Co10Cr10 (at%), microstructural analysis, mechanical testing, and fractography were performed on the DP-HEA. The microstructural state of the alloy was analyzed by optical microscope, scanning electron microscope (SEM), energy dispersive spectroscopy, and electron backscatter diffraction (EBSD). The plastic deformation behavior of the alloy was assessed using uniaxial tensile tests. The digital image correlation (DIC) was used during the tensile test to evaluate the Young’s modulus and localized strain values at different points in the gauge section of the tensile specimens as a function of time. An insight into the micromechanism of plastic deformation was gleaned from a stress relaxation test (SRT). The alloy consisted of ~ 12% (by area) of γ-FCC and rest ε-HCP phases. The yield strength (YS), ultimate tensile strength, and elongation were 315 MPa, 755 MPa, and 62%, respectively. For this alloy, the plastic strain ratio was estimated to be ~ 0.75 using the DIC. The curve fitting of true stress/true strain curve using Ludwik’s equation revealed the strain hardening exponent to be 0.76. The flow stress changed from 315 MPa at YS to ~ 1200 MPa at necking. From the DIC data, the maximum strain in uniformly deformed and necked regions were determined to be 0.44 and 0.68, respectively. The DIC data analysis revealed the Young’s modulus of the alloy to be 180 GPa. The true activation volume of the alloy ranged from 300b3 to 450b3 and decreased with increase in flow stress. Overall, a good combination of strength, ductility, and work hardening behavior was noted in the HEA predominantly consisting of ε-HCP phase.