Microstructure evolution of metastable dual-phase high-entropy alloy Fe50Mn30Co10Cr10 under Taylor impact tests: Experiments and constitutive modeling

Abstract

In order to investigate microstructure evolution after severe plastic deformation and calibrate the constitutive model, Taylor impact experiments are conducted on the metastable dual-phase high-entropy alloy (HEA) ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{30}{\mathrm{Co}}_{10}{\mathrm{Cr}}_{10}$. Two kinds of HEA projectiles (short-cylinder: diameter 6 mm, length 6 mm or long-cylinder: diameter 12 mm, length 40 mm) are launched. Parameters of the Johnson-Cook Cowper–Symonds constitutive model are optimized via the long-cylinder Taylor impact experiments. After cylinder Taylor impact tests, deformation microstructures at different regions are characterized, and finite element modelings (FEMs) based on the modified constitutive model are conducted to interpret deformation mechanisms. The face-centered cubic (FCC) to hexagonal close-packed (HCP) phase transformation is predominant. The distribution of the equivalent plastic strain obtained from the FEM analysis indicates pronounced deformation gradient along the impact direction, consistent with the gradient microstructure of the postmortem sample. The higher equivalent plastic strain promotes more intense phase transformation and leads to higher grain boundary densities in both phases. Moreover, at high impact velocity, the reverse HCP to FCC phase transformation and $\left\{111\right\}〈112〉$ deformation twinning at the impact surface is activated, primarily due to the increase in stacking fault energy caused by impact temperature rise.