An evaluation of optimized grain boundary character distribution in hot-worked GH4698 superalloy

Microstructures, especially grain boundary character distributions (GBCDs), are characterized in specimens of GH4698 alloy submitted to hot compression and subsequent solution annealing. This investigation quantifies and provides a detailed description of the generation and growth of twins during annealing to evaluate the applicability of optimized GBCDs in hot-worked Ni-based superalloys. The grain size and number of twin boundaries depend on the processing parameters. Significant optimization of the GBCD can be achieved by a coupled process of hot compression conducted at small strain ( ε = 0.1) and prolonged solution treatment at low temperature ( T = 1070 °C, t = 60 min), as shown by the high values of N Ave (the average number of Σ3 grain boundaries in a single grain) and R (the ratio of the area-weighted average grain size without considering twins as the boundary with respect to the grain size with twins). The key to optimizing the GBCD is to activate strain-induced boundary migration (SIBM) while inhibiting dynamic recrystallization and recrystallization, thus resulting in the formation of microstructures with a high proportion (74%) of Σ3 n ( n = 1, 2, 3) boundaries. The SIBM process includes the formation of new Σ3 boundaries through accidental growth mechanisms behind the migrated grain boundaries and interfacial reactions between Σ3 n boundaries to interrupt the connectivity of random high-angle grain boundary networks. Graphical Abstract