Microevolution of grain boundary character distribution in Hastelloy C-276 during the annealing process

Grain boundary character distribution and disconnectivity of random boundaries were observed in-situ in the Hastelloy C-276 alloy sample through thermomechanical processing. The role of X3 boundaries in microstructural evolution of grain boundary character distribution was analyzed by electron back-scattered diffraction (EBSD) and the mechanisms of grain boundary engineering (GBE) during annealing were elucidated. The results showed that the fraction of X3n boundaries (including X3 boundaries) consistently increased in number with annealing time; however, the X3 boundaries had different effects on the disconnectivity of random boundaries because of their variants, i.e., coherent and incoherent X3 boundaries. At the initial annealing stage, new incoherent X3 boundaries were generated, according to the X3 regeneration mechanism model; X9 and X27 boundaries appeared and increased in number with increasing X3 boundary interactions. These incoherent X3 boundaries could disrupt the connectivity of the random grain boundaries and form large clusters. However, at the annealing stage, some incoherent X3 boundaries were annihilated, and new coherent ones emerged. As a result, the random grain boundary network evolved by obtaining significant connectivity with larger clusters, attributed to the reduction of the incoherent X3 boundaries. This implies that the incoherent X3 boundaries play an important role in the optimization of grain boundary engineering. (c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC

Automated summary

Grain boundary character distribution and disconnectivity of random boundaries were observed in-situ in the Hastelloy C-276 alloy sample through thermomechanical processing. The role of X3 boundaries in microstructural evolution of grain boundary character distribution was analyzed by electron back-scattered diffraction (EBSD) and the mechanisms of grain boundary engineering (GBE) during annealing were elucidated. The results showed that the fraction of X3n boundaries consistently increased in number with annealing time; however, the X3 boundaries had different effects on the disconnectivity of random boundaries because of their variants, i.e., coherent and incoherent X3 boundaries. At the initial annealing stage, new incoherent X3 boundaries were generated, according to the X3 regeneration mechanism model; X9 and X27 boundaries appeared and increased in number with increasing X3 boundary interactions. These incoherent X3 boundaries could disrupt the connectivity of the random grain boundaries and form large clusters. However, at the annealing stage, some incoherent X3 boundaries were annihilated, and new coherent ones emerged. As a result, the random grain boundary network evolved by obtaining significant connectivity with larger clusters, attributed to the reduction of the incoherent X3 boundaries. This implies that the incoherent X3 boundaries play an important role in the optimization of grain boundary engineering.