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 M23C6 carbides were systematically detected from either degenerescence of solidification MC carbides or heterogeneous nucleation. Upon aging, serration amplitude increased and precipitation of the delta phase proliferated.