Cold expansion technology has been widely used in aviation industries as an effective method of improving the fatigue performance of fastener holes. It can improve the fatigue life several times over without adding weight, meeting the growing demand for lightweight and durable aircraft structures. In recent years, it has been extensively studied through extensive experiments and finite element simulations to analyze the residual stresses around the fastener hole. Appropriate process parameters lead to the generation of beneficial residual stresses that influence the material microstructure, thereby improving the fatigue life of the component. This paper summarized factors influencing residual stresses in cold expansion and their effects on fatigue life, and the strengthening mechanism, parameter optimization, and effect of anti-fatigue are discussed from the point of view of the residual stress and microstructure. The development of new cold expansion technologies and the research directions that can realize anti-fatigue technology efficiently are proposed.

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.