Microstructure and mechanical behavior of CrCoNi medium entropy alloys in 1000 MPa grade

Abstract

The ultrafine-grained (UFG) CrCoNi medium entropy alloys (MEAs) with excellent mechanical and tribological performances were fabricated by combining rolling deformation and annealing treatment. The microstructures of CrCoNi MEAs were characterized by electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). The results show that the materials annealed at 650 ℃ for 10 min after cryogenic rolling display a yield strength as high as 1135 MPa and a graceful uniform ductility of 14.1%. Another group of materials rolled at room temperature followed by annealing at 650 ℃ for 20 min exhibit a yield strength of 987 MPa and an improved ductility of 18.6%. In addition, the grains of CrCoNi medium entropy alloys after above treatment are greatly refined to an average grain size of 0.81 μm and 0.92 μm respectively. The ultra-high strength is due to the grain boundary strengthening of high angle boundaries and dislocation strengthening of low angle boundaries. Remarkably, such UFG MEAs exhibit high wear resistance.

Keywords

• medium entropy alloy
• strength and ductility
• wear resistance
• ultrafine-grained microstructure
• recrystallization