Improvement of high-temperature fatigue performance in the nickel-based alloy by LSP-induced surface nanocrystallization

Abstract

High-temperature fatigue performance of turbine blades (material: nickel-based alloy) is improved by a surface nanocrystallization technology. Surface nanocrystallization characterized by XRD, SEM and TEM, can be achieved by laser shock peening (LSP). Different microstructures are observed at the depths along the direction of propagation of the shock wave. A layer of isometric 30–500 nm nanocrystalline (1-μm-thick) is formed homogeneously at the surface of materials after LSP. With a heat treatment at 600 °C, the surface nanocrystals remain, while most of the residual compressive stresses are relaxed. The nanohardness of the deformed plastic layer (surface) is improved by a single laser shock impact, and an increase in the number of impacts improves the nanohardness amplitude. This nanohardness exhibits good stability against temperature, because of dislocation strengthening after thermal effect. The results of combined high-and-low cycle fatigue tests at 530 °C reveal that fatigue life of the turbine blades increased significantly by LSP, which are primarily associated with the effects such as surface nanocrystallization, high-density dislocation and residual compressive stress after thermal relaxation.