First evidence of grain boundary serration in a specifically heat treated wrought Alloy 625 Ni-based superalloy

Grain boundary serration is an effective way to increase the high temperature resistance of superalloys and steels. The popular Alloy 625 Ni-based superalloy was until now believed not to form serrated grain boundaries based on previous considerations of serrability criteria. Following the recent strain-induced serration mechanism, a special heat treatment involving continuous slow cooling between the solution and aging temperature was designed. As a result, significant serration was observed for the first time for Alloy 625 promoted by slow cooling. Grain boundary carbides were systematically detected from either degenerescence of solidification C carbides or heterogeneous nucleation. Upon aging, serration amplitude increased and precipitation of the δ phase proliferated.