Microstructural and mechanical behavior of a CoCrFeNiCu4 non-equiatomic high entropy alloy

Abstract

Abstract High entropy alloy (HEA)-based alloy design is experiencing a conceptual broadening from equiatomic alloys to non-equiatomic alloys. To provide experimental basis for designing Cu-rich non-equiatomic HEAs, in the current study, a dual phase (Cu-rich and CoCrFeNi-rich phases) face-centered cubic CoCrFeNiCu4 alloy was systematically investigated. We provided initial and experiment-based understanding of the behavioral change of the alloy during a variety of thermal cycles and thermomechanical processing. The current results indicate that, during heating, preferred precipitation of Cu-rich particles occurs, leading to more pronounced compositional differences between the two constituent FCC phases and increased relative volume fraction of the Cu-rich phase. The Alloy exhibits a continuous melting and discontinuous solidification of the Cu-rich and CoCrFeNi-rich phases. After being cold-rolled to ∼90% thickness reduction, the alloy exhibits a recrystallization temperature higher than 800 °C. Annealing at 300 and 500\u2009°C led to strength reduction and/or ductility decrease; further increasing annealing temperature monotonically caused softening and ductilization due to decreased density of pre-existing dislocations. The yield-drop phenomena observed for the 900 °C- and 1000\u2009°C-annealed specimens are associated with the locking of pre-existing dislocations by some “atmosphere”, the nature of which warrants further elucidation.