Strength–ductility synergy via dual-scale interlocking gradient dislocation architecture

Abstract

Forged GH5188 cobalt-based superalloy, owing to its exceptional high-temperature strength and oxidation resistance, has become the material of choice for critical components in aircraft engines. However, during service its subsurface layer is prone to stress relaxation and crack initiation, significantly limiting service life. Addressing the limitations of conventional surface-strengthening techniques such as shot peening and laser shock peening—whose reinforcement layers are shallower than 100 μm and whose post-processing costs are prohibitive—this study proposes an in-situ surface-strengthening strategy based on orthogonal cutting. During machining, a dual-scale interlocking network—an architecture consisting of 36 μm non-recrystallized coarse grains and 9.8 μm dynamically recrystallized fine grains—is formed on the GH5188 subsurface, and a dislocation density gradient from 2.39 × 10¹⁴ m⁻² at the surface to 1.22 × 10¹⁴ m⁻² at 400 μm depth is established. This in-situ approach increases the tensile strength from 739 MPa to 1214 MPa and the elongation from 41 % to 106 %, achieving deep-layer reinforcement without any subsequent treatments. For the first time, we reveal the core mechanisms by which gradient dislocations and dual-scale interlocked grains cooperate to optimize the synergy between strength and ductility, providing a new pathway for integrated surface functionalization of superalloys.