The role of cobalt in the high temperature creep of γ′-strengthened nickel-based superalloys

Abstract

High temperature creep tests in γ′-strengthened nickel-based superalloys with seven different cobalt contents from 0 to 25 wt.% were conducted; the dislocation structure of these alloys during creep was observed and the stacking fault energy of their matrix materials was measured. The results show that there is an optimum stacking fault energy for the alloy with 15 wt.% Co, and cobalt may increase the creep frictional stress when the creep rate is controlled by the mechanism in which dislocations either cut or climb around the γ′ particles. However, the contribution of the solid solution strengthening of matrices to the creep frictional stress may not vary monotonically with the cobalt content. Moreover, the stacking fault energy of matrices may affect the recovery of dislocations rather than their slip process in high temperature creep.