Comparative study of the effects of conventional shot peening and ultrasonic shot peening on very high cycle fatigue properties of GH4169 superalloy

This study investigates the effects of two different shot peening techniques, conventional shot peening (CSP) and ultrasonic shot peening (USP), on the very high cycle fatigue (VHCF) properties of the GH4169 superalloy. The study evaluates and compares surface roughness, X-ray diffraction patterns, microhardness, and residual stress in specimens treated with CSP and USP. The VHCF tests reveal that both CSP and USP treatments improve the VHCF properties of the GH4169 superalloy. However, while the USP-treated specimens have deeper work hardening and compress residual stress layers, their VHCF lives are significantly shorter than those of the CSP-treated specimens. Additionally, the study finds that the stress triaxiality, which inhibits dislocations at the crack tip, is higher closer to the center of the specimen. The transmission electron microscopy (TEM) results further confirm that the reduced dislocation density and increased stress concentration in the plastic zone of the high stress triaxiality region promote fatigue short crack propagation and reduce the fatigue properties of the material.