Effect of surface finish on high temperature fatigue of a nickel based super alloy

The influence of residual stresses induced by machining, scratches and different processes of surface improvement, on fatigue resistance has been studied on Waspaloy at 426°C under load control. Tests were performed on single edge notched samples. Scratches on notched samples exhibited a much larger effect, reducing fatigue life by an order of magnitude. Surface improvement processes, like blending of scratches and shot peening, substantially improved fatigue resistance as compared to notched samples with scratches.SEM analysis shows multiple crack initiation. The information on striation spacing in the given set of surface conditions was used to estimate initiation/stage I period, growth up to 400μm deep crack and total fatigue life.