Microstructure evolution and interfacial healing mechanism of heterogeneous interfaces in NiCo based superalloys during hot compression bonding

This study focuses on the microstructural evolution of heterogeneous interfaces and healing mechanism of bonding interfaces of NiCo based superalloys during hot compression bonding. The coarse and fine grain sides show distinct refinement mechanisms during hot deformation. The coarse grain side refines the grains mainly through deformation twins and deformation microbands, and the residual primary γ' phase also facilitates the recrystallization through particle-stimulated nucleation mechanism. Continuous dynamic recrystallization through in-situ transformation of dislocation cells into high angle grain boundaries also contributes to the formation of necklace-like recrystallization on coarse grain side. The grains on the fine-grain side are further refined mainly by strain-induced discontinuous dynamic recrystallization. Dislocation density gradients induced by heterogeneous deformation drive migration of bonding interfaces across interfacial oxides from fine to coarse grain side during hot deformation. As the deformation strain increases, the migrating interfaces form the first layer of necklace-like recrystallization on coarse grain side due to deformation uncoordinated. Further increasing the deformation strain, the local deformation leads to continuous expansion of necklace-like recrystallized grains in deformed grains and refined recrystallized grains. The testing of mechanical properties indicate that the heterogeneous interface achieves complete healing, which provides a new idea for fabrication of dual microstructure turbine disks.