Effect of bonding temperatures on the transient liquid phase bonding of a directionally solidified Ni-based superalloy, GTD-111

The bonding phenomenon and the mechanism involved in the transient liquid phase bonding (TLP Bonding) of directionally solidified Ni-based superalloy GTD-111 was investigated. At a bonding temperature of 1403 K, the liquid insert metal was eliminated by isothermal solidification, which was controlled by the diffusion of B and Si into the base metal. The solids in the bonded interlayer simultaneously grew epitaxially from the mating base metal inward from the insert metal. The number of grain boundaries formed at the bonded interlayer corresponded with those of the base metal. Liquefaction at the grain boundary and dendrite boundary occurred at a temperature of 1433 K. At a bonding temperature of 1453 K which is higher than the liquefaction temperature of the grain boundary, liquids of the insert metal were connected with liquated grain boundaries; this connection extended as far as the grain boundary, which was approximately 1.5 mm from the interface. The composition of this liquid was a mixture of the insert metal and phase that existed at the grain boundary. At extended holding times, liquid phases gradually decreased, and liquids with a continuous band shape develop into distinct islands. However, the liquid phases did not disappear after a holding period of 7.2 ks at 1453K. The extended isothermal solidification process at the bonding temperature, which is higher than the liquefaction temperature for the grain boundary, was controlled by the diffusion of Ti. This resulted in its preferential liquefaction compared to B or Si in the insert metal.