Post-bond heat treatment effects on the wide gap transient liquid phase bonding of Inconel 718 with BNi-2 paste filler metal

Abstract

Wide gap transient liquid phase (TLP) bonding could be used for repairing large cracks or worn areas on aerospace components. Unfortunately, the residual borides in the joints after bonding might deteriorate their mechanical properties. Increasing bonding time or temperature could effectively reduce the fraction of borides and strengthen the joints. However, significant adverse heating might coarsen the grains, weakening the mechanical properties of joints. To improve the mechanical properties of joints without inducing much adverse heating, post-bond heat treatments (PBHT) with different cycles (solution treatment, aging, and combined solution treatment and aging) were applied to study the effects of PBHT on the wide gap TLP bonding of Inconel 718 with BNi-2 paste filler metal. The ultimate tensile strengths (UTS) and nanohardness of bonded joints with and without PBHT were analysed and compared in this study. The PBHT effects on the phase evolution of the bonded filler metal, grain size distributions and the diffusion process were investigated. The results indicated that PBHT improved the UTS of the TLP bonded joints without inducing much adverse heating, and the strongest joint with a UTS of 453 MPa was obtained after the combined solution treatment and aging. The improvement of the bonding strengths of joints was mainly attributed to the decrease in the fraction of Ni3B type borides during PBHT and the increased formation of γ' and γ" type strengthening phases during aging. In addition, the combined solution treatment and aging improved both the isotropy of Ni3B type borides and the local plasticity of the bonded joints.