Effect of Ni content and crystallographic orientation on mechanical properties of single-crystal (CoCr)100-x Ni x medium-entropy alloy

Nanoindentation analyses of (CoCr)(100-x )Ni (x) medium-entropy alloys with different Ni contents and crystal orientations were carried out by molecular dynamics simulations. Analyses show that the force-displacement curves during elastic deformation are in good accordance with the Hertz contact theory and the elastic modulus is closely related to the Ni contents and crystal orientations. The elastic-plastic transition point appears later in (CoCr)(67)Ni-33 than in other alloys. The plastic deformation was studied by exploring the instantaneous microstructure, which was found to be dominated by homogeneous nucleation of Shockley partial dislocations and the accumulation of stacking faults, and different levels of dislocation density were produced in the alloys with different Ni contents and crystal orientations. By analyzing the evolution of dislocation density and hardness, a linear relationship between the square root of dislocation density and hardness can be revealed, which agrees well with the classical Taylor hardening model, and the empirical constant is found closely related to crystal orientations.