Effects of Ni addition on abnormal grain growth in superelastic CuAlMnCoNi alloy

Large-size grain is one of the effective parameters to determine the superelasticity of Cu-based alloys. In this study, the effects of Ni addition on abnormal grain growth (AGG) and microstructure evolution of CuAlMnCoNi alloys are systematically investigated. The activation energy and driving force of grain boundary (GB) migration during AGG are evaluated. The results reveal that Ni significantly promotes AGG. Average grain size reaches 6.0 cm after three cyclic heat treatments (CHTs) in a CuAlMnCoNi alloy containing 2 at.% Ni. A maximum superelastic strain of 11.8 % can be obtained at 15 % applied strain. The addition of 2 at.% Ni increases the solvus temperature of the alpha-phase to about 818 degrees C and raises alpha-phase volume fraction at phase equilibrium. The precipitation of alpha-phase with high volume fraction causes high number density of dislocations. The misorientation angle of subgrain is increased by the addition of Ni, contributing to the AGG in CuAlMnCoNi alloys. The addition of Ni reduces the activation energy of GB migration and increases the GB migration driving force.