Precipitation Behaviors in the Diffusion Affected Zone of TLP Bonded Single Crystal Superalloy Joint

The single crystal superalloys were joined by transient liquid phase (TLP) bonding. The precipitating behavior in the diffusion affected zone (DAZ) was studied and the hardness across the DAZ was analyzed. Results have shown that there existed M3B2, M5B3 and M23B6 borides in the DAZ. With increasing bonding time, fine M3B2 precipitates formed first near the isothermal solidification zone (ISZ)/matrix interface. Then, the dendritic M5B3 precipitates formed with an obvious orientation relationship with the substrate. The acicular precipitates were constituted by M23B6 and M5B3 phases with continuous or discontinuous morphologies. The hardness of the DAZ reached a summit in the fine M3B2 region and decreased with the increase of the distance away from the ISZ/matrix interface.