Multi-stage strain-hardening and nano-twinning strengthening Co40Cr22Ni15Fe14Mo4Si3Mn2 multi-principal element alloy

CoCrNiFe multi-principal element alloy (MPEA) plates were prepared by melting and rolling. Thermomechanical treatment (cold rolling and aging) was developed to modify the formation of lattice defects and precipitates. The results show that the Co40Cr22Ni15Fe14Mo4Si3Mn2 MPEA have excellent room temperature ultimate tensile strength and hardness of 1946 MPa and 684 HV0.1. Electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) techniques were used to reveal the microstructure and provide insight into the mechanism. The strengthening mechanism comes from the multiple factors, and most notably, the interaction between nano-twins and Lomer-Cottrell locks. The presence of nano-twins and stacking faults has a significant impact on the strain hardening behavior of the alloy. At the same time, the occurrence and development of deformation substructure dominated by dislocation configuration is the reasons for the material to achieve multistage strain hardening (MSSH). This method of realizing MSSH behavior by adjusting microstructure is of great significance in the design and application of FCC MPEA and can be extended to other FCC alloys.