High temperature fatigue behavior of wrought nickel-base superailoy GH4049

Abstract

Push-pull total strain-controlled fatigue tests without and with a hold period were carried at elevated temperatures for wrought nickel base superalloy GH4049. The influence of the testing temperature and strain hold period on fatigue behavior was determined. The alloy would exhibit either cyclic strain hardening, softening or stability during cyclic straining. Fatigue life depends strongly on the testing temperature and the introduction of the strain hold period. Observations on fatigue specimens using transmission electron microscopy (TEM) showed that the dislocations were distributed mostly in the "y matrix. It was observed by scanning electron microscopy (SEM) that cracks initiated always in a transgranular mode, but their propagation mode was closely related to the testing temperature. In addition, the fatigue life was predicted by linear damage summation (LDS), strain range partitioning (SRP) and the strain energy partitioning (SEP) method. The results of life prediction indicated that the SRP and SEP methods were in a good agreement as to the measured and predicted life at lower temperatures, while the LDS method showed better predictability at higher temperature as compared to the SRP and SEP methods.