Fatigue stability of residual stress in shot peened alloys

Abstract

Fatigue specimens of Ni-20 pct Co and Ni-60 pct Co alloys were shot peened to an Almen intensity of 0.008N2 and cycled at two levels of alternating stress. The surface residual stress was monitored during cycling by the two exposure X-ray method. Microhardness surveys were made across cross sections of specimens representing each test condition. It was found that the surface residual stress decayed partially during the plastic cycling of the lower strength-higher stacking fault energy (SFE) 20 pct Co alloy and that little such decay occurred in either the plastic or elastic cycling of the higher strength-lower SFE 60 pct Co alloy. There was virtually no change of microhardness during cycling in either alloy, hence the residual stress relaxation in the 20 pct Co alloy is interpreted as a dynamic recovery process.