Interface healing mechanism of fine-grained Ni-Co-based superalloy during hot-compression bonding

The interface healing mechanism of fine-grained Ni-Co-based superalloy during hot-compression bonding(HCB)is investigated.During HCB,the incompatibility of deformation between theγand the primary γ′leads to a large number of dislocation pairs(DP),stacking faults(SF),and micro-twins(MT)in the primary γ′.These defects act as fast channels for elemental diffusion,leading to supersaturation of the primary γ′and promoting the growth of the γ-shell.On the one hand,the primary γ′with a γ-shell moves towards the bonding interface due to anomalous yielding phenomena of the primary γ′and plastic flow during HCB process.The increase in the number of defects leads to the growth of γ-γ′heterogeneous epitaxial recrystallization(HERX)grain with coherent structure at the bonding interface,which promotes the bulge of the interface grain boundaries(IGBs).On the other hand,the nucleation and growth of a necklace-like distribution of discontinuous dynamic recrystallization(DDRX)grain at the interface lead to the healing of IGBs.With the synergistic action of DDRX and HERX,the mechanical properties of Ni-Co-based superalloy joints through HCB achieve the same level as the base material.This finding further enriches the theory of interface healing in HCB.