High Temperature Fatigue of Mechanically Surface Treated Materials

Abstract

The most well known eSSect of mechanical surface treatments on metallic ~rlaterials is the improvement in fatigue properties. It is therefore not surprising that most of the archival literature on mechanical surface treatments, such as shot peening, deep rolling and laser shock peening, deals with the effect of near-surface properties on fatigue behavior. Most of these studies, however, are confined to room temperature fatigue behavior; in comparison, the effect of mechanical surface treatment on fatigue behavior at high temperatures has been rarely investigated [ I -51. The season for this disparity can be found in the popular belief that f~itigue strength irnprovement by mechanical surface treatments is mainly due to the presence of compressive residual stresses, and since such stsesses should anneal out at elevated tempesatures, mechanical surfice treatments for high temperature applications would appear questionable. However, this view may be over simplistic as there is always a possibility that the residual stresses may be at least partjally stable at elevated temperatures [6]; in addition, other factors may be involved, such as the nature of the near-surface microstructure. Accordingly, it is the objective of this study to examine the role of mechanical surface treatments on the high tcnlperature fatigue behavior of several metallic engineering materials. Moreover, it is the aim of this work to clarify what are the critical temperature thsesholds at which near-surface microstructures and residual stresses become unstable and whether this can explain the observed fatigue behavior.