Papers by Author: Woo Young Song

Abstract: In the case of transient liquid phase diffusion bonding with Ni base superalloy GTD-111, the bonding temperature was sustained at 1403K ~ 1453K. Thus, the microstructure of specimens heated at 1403K ~ 1453K was examined. In the raw material, γ-γ' eutectic phases, platelet η phases, MC carbide and PFZ were clearly observed in interdendritic regions or near the grain boundary and the size of primary γ' precipitates near the interdendritic regions were larger than the core. The primary γ' precipitated in the dendrite core dissolved early in the bonding process. γ' precipitated near the interdendritic regions were partially solubilized and their shape was changed. The dissolution rate increased with increasing temperature. Phases in the interdendritic regions or near the grain boundary changed continuously with time at the bonding temperature. At a bonding temperature of 1403K, the eutectic phases remained, but η phases were transformed from a platelet shape to a needle morphology and the PFZ region widened with time. The interdendritic region and near the grain boundary became partially liquid at 1423K and fully at 1453K by the reaction of η phases and PFZ. The interdendritic region and near grain the boundary became liquid and new phases which were mixed with η phases, PFZ and MC carbide crystallized during cooling at 1453K. Crystalline η phases were transformed from a rod shape to a platelet shape with increasing holding time.

Abstract: The effect of a mixed powder on the wide gap transient liquid phase diffusion bonding of a directionally solidified Ni base superalloy, GTD-111 was investigated. The mixed powder consisted of a mixture of a powdered Ni base filler (GNi-3) and powdered base metal (GTD-111). The range of the base metal powder was 40 to 70wt%. Bonding was performed at a temperature of 1463K, using various holding time. In the case of a lower 50wt%, the base metal powders completely melted and base metal mating at the interface dissolved at an early time, and extent of dissolution of base metal decreased with increasing mixing ratio. Liquid was eliminated by isothermal solidification, which was controlled by the diffusion of B into the base metal. The solids in the bonded interlayer grew epitaxially from the mating base metal inward from the insert metal and the number of grain boundaries formed at the bonded interlayer corresponded with those of the base metal. The finishing time for isothermal solidification was about 74ks. In the case 60wt% and higher, the base metal powders partially melted and remained in the vicinity of bonded interlayer. The solid was formed from the remaining powder and base metal mating at the interface. Finally, the bonded interlayer underwent the poly-crystallization when isothermal solidification was complete. The contents of Al and Ti in the bonded interlayer with a holding of 74ks were equal to that of the base metal.