Microstructural characteristics and mechanical response of diffusion bonding Inconel 617 superalloy

Abstract

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 33̅3M23C6//111̅γ−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.