Role of base-metal composition in isothermal solidification during diffusion brazing of nickel-based superalloys

The key feature of diffusion brazing, also referred to as transient liquid phase bonding, is isothermal solidification which precludes the formation of intermetallic in the joint centreline. Analysing the available data published in the literature showed that the composition of the nickel-based superalloys plays a strong role in determining the required time for obtaining intermetallic-free joint during diffusion brazing. This effect is not predictable by the standard conventional models. It is proposed that increasing the boride-forming elements in the base superalloy which promotes in situ boride precipitation at the diffusion-affected zone can accelerate the diffusion flux of the boron into the base superalloy, leading to faster isothermal solidification. The higher the Cr?+?Mo?+?Nb?+?Ta?+?W content in base superalloy, the shorter the isothermal solidification time.