Microstructure and excess free volume of severely cold shape rolled CoCrFeNiMn high entropy alloy

Abstract A CoCrFeNiMn high-entropy alloy (HEA) was subjected to shape rolling through equivalent strain of 0.5, 1.1, 1.4, 2.5, 3.7 and 4.2 at room temperature to study the microstructural evolution and formation of excess free volume during severe plastic deformation. The microstructure of the processed sample through the equivalent strain of 4.2 revealed a single fcc phase with an average grain size of ∼50 nm and an excess free volume of ∼0.96% due to formation of nano voids and defects after severe shape rolling. Microhardness measurements showed a saturation level but no nano voids were observed in the processed samples with equivalent strains of lower than 4.2. The results show precipitation and then dissolution of precipitates and also annihilation of defects due to recrystallization during heating between 700 and 900 °C. Density of processed samples reached to the initial condition after heating up to 1000 °C except the processed sample at the equivalent strain of 4.2 due to existence of stable nano voids in this sample.