Comprehensive study of strain hardening behavior of CrCoNi medium-entropy alloy

Abstract

The influence of strain rate on strain hardening behavior of CrCoNi medium-entropy alloy (MEA) was investigated by performing hot compression tests at strain rates in the range of 0.001 s−1 to 1 s−1 under temperatures ranging from 700 ℃ to 1000 ℃. In general, flow stress and peak stress of CrCoNi MEA decrease with decreasing strain rate and increasing temperature. The strain rate sensitivity factor (m) increases with increasing deformation temperature. Strong dependence of strain hardening behavior on strain rate was observed at high temperatures ranging from 900 °C to 1000 °C. When CrCoNi MEA deformed at 900–1000 °C, an increased strain hardening rate was observed at high strain rate of 1–0.1 s−1, and such phenomenon is absent when the strain rate is lower than 0.1 s−1. Microstructural characterization via electron backscatter diffraction (EBSD) technique indicates that the effect of strain rate on microstructure is different from that for samples deformed at 700 ℃ to those at 900 ℃ and 1000 ℃. The fractions of recrystallized grains decrease with increasing strain rate for the samples deformed under 900–1000 °C. When samples deformed at 700 °C, recrystallized grains only form at high strain, i.e., 1 s−1. Finally, the mechanism for the high strain rate dependence of strain hardening behavior and microstructure was discussed.