Chemical bonding dictates alloying effect on inherent mechanical strength and plastic deformation mechanism in CoNiCr multicomponent alloy

The influence of 3 d transition elements and Al on the intrinsic mechanical properties of CoNiCr was investigated by a combined first-principles calculation and chemical bonding study. All alloying elements tend to reduce elastic moduli, hardness, and ideal tensile strength, with Ti, V, Cu, and Al causing the most pronounced weakening effects while Mn and Fe exerting minor influences. These changes stem from variations in electron band filling and orbital hybridization. Specifically, elements with valence electron concentration (VEC) that are significantly different from CoNiCr destabilize bonding by either depleting bonding states (Ti and V), reducing d-d hybridization and overpopulating antibonding states (Cu), or altering orbital hybridization from d-d to p-d (Al). In contrast, Mn and Fe with comparable VEC preserve the bonding strength. Regarding deformation mechanism, all dopants tend to increase stacking fault energy ( γ isf ). Most alloys exhibit the co-activation of slip and stacking fault, while Cu alloying favors twinning alongside dislocation slip. Notably, the competition between stacking fault and twinning is governed by 1/2 γ isf . VEC is identified as a critical parameter influencing γ isf , with alloys possessing high VEC typically showing larger γ isf . These findings establish a theoretical basis for designing high-performance fcc multicomponent alloys through composition-controlled chemical bonding engineering.