Effect of temperature and strain rate on quasi-static and dynamic compressive behavior of forged CrMnFeCoNi high entropy alloy

Abstract

The equiatomic CrMnFeCoNi high entropy alloy (HEA) has attracted much attention due to the superior ductility. However, as a face-centered cubic (FCC) single-phase solid solution, the as-cast CrMnFeCoNi HEA is limited in many applications because of the low strength. The aim of this work is to improve the mechanical properties of CrMnFeCoNi HEA by forging. The forged CrMnFeCoNi HEA was prepared and the effect of temperature and strain rate on the deformation behavior and mechanism under quasi-static and dynamic compression was investigated. After hot forging, CrMnFeCoNi HEA still maintained FCC single-phase structure, the average grain size reduced to ∼40 μm, the distribution of elements was more uniform, and some defects were introduced into the material. The quasi-static (1 × 10−3 s−1) and dynamic (2 × 103, 7 × 103 and 1 × 104 s−1) compression tests of forged CrMnFeCoNi HEA were performed at temperatures ranging from −196 °C to 950 °C. The material exhibited excellent compressive strength and great plasticity, and showed significant temperature sensitivity and strain rate sensitivity of the yield strength. When the strain rate was up to 1 × 104 s−1, the yield strength was ∼1076 MPa at −100 °C and ∼80% higher than that under quasi-static compression. The strain hardening rate increased with the decrease of temperature under both quasi-static and dynamic conditions, while strain rate sensitivity was exhibited only at high temperatures. Discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX) and twinning-induced dynamic recrystallization (TDRX) were activated during hot compressions. DDRX was activated when the strain rate was low, and CDRX and TDRX were strengthened with the increase of strain rate. The influence of strain rate and temperature on the deformation mechanism was investigated. Low temperature and high strain rate were conducive to the formation of deformed twins.