Decomposition kinetics of carbon-doped FeCoCrNiMn high-entropy alloy at intermediate temperature

Phase decomposition kinetics and the corresponding mechanical properties of the severe cold-rolled (SCRed) carbon-doped (1.3 at.%) equimolar FeCoCrNiMn high-entropy alloy (HEA) after being annealed at 500 degrees C were investigated. This single face-centered cubic (FCC) solid-solution HEA decomposed to M23C6+L1(0), B2, and sigma in chronological order. The formation kinetics of the L1(0), B2, and sigma phases followed the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. The yield strength of the HEA was 1520 MPa and increased to 1920 MPa after being annealed at 500 degrees C for 1 h, as a result of the formation of nanosized M23C6 and L1(0). Both strength and ductility decreased after 2 d of annealing due to the increase of volume fractions and the coarsening of the M23C6 and L1(0) precipitates. From 4 to 32 d, the hardness was found to increase, which is ascribed to the rapid formation of the B2 and sigma phases. From 32 to 64 d, the hardness increased further to finally reach about HV 760, with the FCC matrix almost exhausted to form the M23C6, L1(0), B2, and sigma phases. The results of this work may serve as a guide for the heat-treatment of carbon-doped HEAs.