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. •The Co/CoNi ratio alters the occupancy tendency of doped alloying elements•Lattice misfit progressively increases with increasing Co/CoNi ratio•Synchronous entropy increment and lattice misfit manipulation of γ and γ′ via Co/CoNi