Relationship of isothermal solidification completion and precipitate formation with mechanical properties of Inconel 939 joints vacuum TLP bonded by an amorphous Ni–Cr–Fe–Si–B filler alloy

Abstract

In this research, vacuum transient liquid phase bonding of Inconel 939 superalloy was performed using an amorphous Ni–Cr–Fe–Si–B filler alloy at different temperatures from 1060 °C to 1180 °C, and the microstructure and mechanical properties of the joints were investigated. The results showed that the bonding region can be categorized into three athermal solidification, isothermal solidification, and diffusion affected zones. The ASZ region consisted of a eutectic phase while the ISZ region included a Ni-rich gamma single-phase solid solution. Also, the DAZ involved cubic-shaped, needle-like and grain boundary-shaped borides. The width of DAZ increased with increasing the bonding temperatures, and it also led to a decrease in the ASZ/joint ratio. The ASZ was disappeared at 1180 °C. The highest hardness value was obtained for the DAZ region of the sample bonded at 1180 ᵒC, and a direct relationship was detected between the bonding temperature and ISZ hardness. The addition of bonding temperature also led to the improvement of the shear strength and joint efficiency. It was also found that an inverse relationship can be detected between the shear strength and the ASZ/joint ratio. A joint efficiency of ∼79% was obtained for the bonding temperature of 1180 °C.