Investigation of residual stress influence on fatigue crack growth in remanufactured titanium alloy with inhomogeneous microstructure

Laser remanufacturing technology is now the top choice for remanufacturing key components of aero-engines because of its cost-effectiveness, resource utilization, and performance recovery. Yet, the non-uniform microstructure and residual stress in the remanufacturing process of titanium alloy blades continue to be the primary technical challenges hindering the advancement of product quality and service performance. This paper systematically revealed the mechanism of Ti6Al4V laser remanufacturing interface residual stress on fatigue crack propagation behavior of inhomogeneous microstructure through stress relief methods such as deep cryogenic treatment (−196 °C/48h), stress-relief annealing (650 °C/1h), and ASTM E647 compact tension tests. The results indicate that interfacial residual stresses serve as additional loads, effectively increasing crack growth resistance (31 % decrease in m-value) while restricting plastic deformation at crack sub-surfaces, reducing the plasticity and toughness of inhomogeneous structures and speeding up crack propagation (40 % increase in crack growth rate), leading to the coexistence of high da/dN and low m-value phenomena in HAZ regions. Additionally, residual stresses heighten plastic mismatch effects by impacting crack closure behavior, with residual stress gradients notably prolonging the interfacial plastic mismatch effects. This study provides the first quantitative characterization of the synergistic interaction mechanisms between inhomogeneous interfacial residual stresses and microstructural evolution, establishing a theoretical foundation for residual stress gradient optimization and fatigue-resistant design in laser remanufacturing of critical aerospace components.