Surface integrity and its influence on fatigue life when turning nickel alloy GH4169

Fatigue life of a machined part strongly depends on its surface condition. This research investigated the machining induced surface integrity after turning the nickel based superalloy GH4169 standard fatigue test specimens by using different cutting parameters. Surface roughness, residual stress and the metamorphic layer influenced by applying different cutting parameters were studied. The specimens' fatigue lifes were obtained by high frequency fatigue test. The fracture and crack initiation analysis, the mechanism of cutting parameters influences on the fatigue life have been investigated as well. The results showed that using appropriate cutting parameters can lead to an optimal surface with the proper surface integrity indexes when turning by using the coated carbide tools. Finally, he high frequency fatigue tests with 0.1 stress ratio have been carried out. The results proved that the specimens which surface was with larger compressive residual stress and thinner metamorphic layer have stronger abilities to resist fatigue crack initiation.