Microstructural evolution, mechanical properties and corrosion resistance of CoCrFeNiW_0.5 high entropy alloys with various annealing heat treatment

High entropy alloys (HEAs) with excellent mechanical properties and corrosion resistance show promising potential for use in many fields including marine environment. In order to make a good tradeoff between the mechanical properties and corrosion resistance, the microstructure of HEA is adjusted by proper heat treatment. Herein, the non-equiatomic CoCrFeNiW_0.5 HEA with dual FCC and μ phase was prepared by using an electromagnetic levitation melting method, and the microstructure, mechanical properties and corrosion resistance of these alloys with annealing temperature range from 600 to 1200 °C for 3 h have been investigated. After annealing at 1000 °C, a large number of needle-like μ phase precipitates was firstly observed in the matrix, the volume fraction of the μ phase is 26.64 %, which is about twice as higher as under the as-cast conditions (13.35 %). This alloy exhibited the highest compression yield strength of 1253.9 MPa with a considerable fracture strain of 40.8 % and the highest Vickers hardness value of 369.6 HV. The decomposition of μ phase precipitates was observed when annealing temperature up to 1200 °C, which lead to the mechanical properties of the alloy decreased slightly. All the alloys were found to show excellent corrosion resistance in 3.5 wt% NaCl solution, and corrosion occurs preferentially on the FCC matrix and phase boundaries, the increase of μ phase volume fraction result in more severe galvanic corrosion of alloys. Our results offer insights into analyzing the evolution of both mechanical properties and corrosion resistance of HEAs caused by heat treatment.