Synergistic strengthening at the γ / γ ′ interface: A pinning-to-network transition driven by trace Co

Precisely tuning interfacial properties with trace elements is a key challenge in alloy design, particularly for Ni-based superalloys where the role of trace Co at the γ/γ′ interface is unclear. This study addresses this challenge using atomistic simulations, uncovering a non-monotonic strengthening effect optimized at 0.25 at. % Co. A distinct double yielding behavior is observed in all samples, but the optimal concentration uniquely enhances the second yield strength. The origin of this enhanced strength is a remarkably stable Cottrell atmosphere. This stability fundamentally alters the deformation pathway by catalyzing the formation of a dense dislocation network while simultaneously suppressing premature shearing of the γ′ phase. This efficient transition to a network-hardening regime allows the system to sustain higher stresses before ultimate yield and successfully avoids the dynamic strain aging instabilities inherent to other concentrations. These findings therefore deepen the understanding of the pinning-to-network strengthening transition and provide a mechanistic pathway for designing advanced alloys via the precise engineering of interfacial deformation.