Characterization and Modeling of Residual Stress and Cold Work Evolution in PM Nickel Base Disk Superalloy

Powder metal (PM) superalloys used for critical compressor and turbine disk applications are prone to fatigue failures in stress concentration features such as holes and radii, as well as from corrosion pits and inclusions. Residual stress and cold work will have a dramatic impact on the fatigue performance. Shot peening is widely used on PM disks to provide a fatigue benefit however, the relaxation due to thermal and mechanical loads can reduce or even eliminate the compressive residual stresses and increase the risk of a catastrophic disk failure. Up to now the evolution of the residual stress and cold work under typical operating conditions in PM disk superalloys is not well understood.In Phase I proprietary x-ray diffraction (XRD) techniques will be used to simultaneously measure the change in residual stress and cold work for fatigue specimens tested in a manner to approximate in-service conditions. XRD residual stress and cold work results will be used to establish the feasibility of applying analytical or empirically based modeling techniques to predict the residual stress and cold work evolution. The modeling technique will first be demonstrated on fatigue samples and further developed and proven on actual disk hardware in Phase II. The anticipated beginning and ending technology readiness levels (TRLs) for Phase I are 2 and 5, respectively.