Effect of Surface Integrity on High-temperature Low-cycle Fatigue of FGH96 Powder Metallurgy Superalloy

Ceramic shot and ceramic shot+cast-iron shot were employed to peen the turning surface of FGH96 powder metallurgy superalloy to induce 3 surface integrity statues. Surface topography, residual stress profile and high-temperature low-cycle fatigue performance were investigated of single shot peening (SSP), double shot peening (DSP) and turning statues. The results show that DSP removes turning marks, increases the average roughness Ra, and induces the crater with smooth bottom, which makes the Kurtosis parameter approach 3. Moreover as contrast, SSP with low intensity could only partially eliminate marks. Meanwhile, surface compressive residual stress values are from -1000 MPa to -1100 MPa by SSP and DSP compared with -446 MPa by turning; furthermore, the depth of DSP residual stress profile is 250 mu m from 100 mu m of turning. By the effect of perfect DSP surface integrity statue, fatigue cycles increase to 108% compared with turning, and the SSP edges up only 21% in the fatigue condition of 650 degrees C/epsilon(t)=1.2%. The fatigue life dispersion decreases after peening. The results of macro/microscopic observation and analysis show the fatigue propagation lives are close among three surface integrity statues while the fatigue initiation lives vary greatly. The initiation life of DSP is 221% of SSP and 216% of turning. It is important and necessary to optimize the shot peening method for surface integrity promotion and high temperature low-cycle fatigue performance improvement.