Microstructural characteristics and mechanical response of diffusion bonding Inconel 617 superalloy

This study focuses on the microstructural characteristics and mechanical response of the diffusion-bonded joints of Inconel 617 superalloy. The joints exhibited two types of interfacial microstructure involving the straight interface (i.e., bond line) and the interface with partial migration of grain boundaries (GB). The straight interface was composed of the GB of γ-Ni, M₂₃C₆ carbide and α-Al₂O₃ oxide. The M₂₃C₆ carbide was precipitated with a semi-coherence of 33̅3_M23C6//111̅_γ−Ni, and an amorphous interface was detected between the α-Al₂O₃ and γ-Ni phase. The migration of GB across the interface was mainly caused by dynamic recrystallization and strain-induced GB migration. In addition, the α-Al₂O₃ oxide was remained inside the migrated grain. The formation of the M₂₃C₆ and α-Al₂O₃ was governed by diffusion mechanism, and the γ′-Ni₃Al phase was formed surrounding the α-Al₂O₃ due to the abundant diffusion of Al. The straight interface, particularly embedded with the hard particles (i.e., the M₂₃C₆ carbide and α-Al₂O₃ oxide), restricted GND slipping, resulting in concentration of stresses and initiation of cracks. The migrated interface, in contrast, effectively prevented crack propagation and induced crack deflection, supporting more continuous and uniform plastic deformation. The elongation of 51.2 % was obtained for the joint with partial migrated interface, reaching 71 % of the base metal. Nevertheless, the optimum impact toughness of the joints (20.38 J/cm²) was merely 24 % of the base metal, mainly affected by the remained straight interface.