Microstructural study of transient liquid phase bonded DD98 and K465 superalloys at high temperature

Microstructure of a transient liquid phase (TLP) bonded joint between single crystal DD98 and polycrystalline K465 superalloys was investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction techniques. After bonding at 1190 °C for 2 h, many phases formed in the centerline of the bonding zone due to an incompletely solidified liquid interlayer. There are script-like, tree-like and blocky compounds besides solid solution γ phase in this region. The script-like phase is CrB boride that is rich in Cr, the tree-like compound rich in Ni is M23B6 with FCC structure, and the blocky phase enriched in Ti, Ta, and Nb, is MC carbide that resulted from the interdiffusion of C atoms between dissimilar base metals. After TLP bonding, many blocky and fine M6C particles rich in Cr and W appeared in the diffusion zone of the K465 side. A number of blocky and platelet M3B2 borides rich in W, Cr and Mo precipitated in the diffusion zone of the DD98 side.