Effects of Co/CoNi ratio on elemental occupancy tendencies and lattice misfit of γ/γ′ phases in precipitation-strengthened alloys

Occupancy tendencies of elements significantly differ in precipitation-strengthened Ni-based, CoNi-based, and Co-based alloys, which further affect the γ/γ′ lattice misfit and mechanical properties, but relevant research is lacking. In this work, occupancy tendencies of doping elements (Ta, W, Cr, Fe, Mo, Re, Ti, V) and lattice misfit of γ and γ′ phases in precipitation-strengthened alloys dependent on Co/CoNi ratios have been systematically studied through first-principles calculations. The results show that the tendency of all eight elements to occupy the γ′-Al sublattice site increases with the increase of the Co/CoNi ratio, and the tendency to occupy the γ-Ni/Co site all decreases. The occupancy tendencies of these elements exhibit a strong correlation with the Co/CoNi ratio. Lattice misfit gradually increases as the Co/CoNi ratio is raised. Notably, element Ta has the greatest influence on lattice misfit. The appropriate Co/CoNi ratio is conducive to synergistically enhancing high entropy effects and lattice distortion effects for matrix and Ni₃Al precipitate phase, and regulating reasonable lattice misfit, which is beneficial for the design of precipitation-strengthened alloys with excellent strength-ductility balance.