MICROSTRUCTURE CHARACTERISTICS AND CRYSTALLOGRAPHIC ORIENTATION OF TRANSIENT LIQUID PHASE JOINT OF NI-BASE SINGLE CRYSTAL SUPERALLOY

The Ni-based single crystal superalloy was bonded by the transient liquid phase (TLP) bonding using Ni-15Cr-3.5B amorphous ribbon as an insert alloy. The microstructure characteristics in the joint during TLP process were evaluated by OM, SEM and TEM. The electron back scattering diffraction (EBSD) method was applied to determine the crystallographic orientation between the bonded interlayer and substrates. The results indicated that the joint consists of a bond, diffusion and base zones, in the meantime M23B6 +γ and MB+γ eutectics formed in the bond center and the fine M3B2 phases occurred in the diffusion zone. The γ' phases both in the bonded interlayer and in the superalloy substrate are almost identical after homogenization treatment. Due to the epitaxial growth of the isothermal solidification fronts from each mating surface, the crystallographic orientation between the bonded interlayer and the bonded substrate has a good match.