Solute redistribution during transient liquid phase bonding of IN738LC with BNi-3 interlayer

Abstract

Redistribution of alloying elements in the transient liquid phase (TLP) bonding zone of IN738LC/BNi-3/IN738LC was studied to investigate microstructural evolution in this area. Wavelength dispersive spectrometry and electron probe microanalysis revealed that, during non-isothermal solidification in the TLP bonding zone, enrichment of residual liquid phase with the positive segregating elements caused formation of intermetallic in the bonding zone. Scanning electron microscopy observation indicated that the redistribution of alloying elements, between TLP bonding zone and base alloy, resulted in formation of a γ′ boundary layer, containing high density of fine γ′, around the bonding zone. Diffusion of γ′ promoting elements, from the base alloy inward the TLP zone, controlled the growth of this layer. Unlike TLP bonding at 1100–1150°C, isothermal solidification kinetic was reduced notably during TLP bonding at 1200–1250°C. Investigations demonstrated that the low isothermal solidification kinetic was not only due to the enrichment of liquid phase with the base alloying elements such as Ti and Zr, which was reported in the previous papers, but also the reduction of solid solubility limit of B in the base alloy contributed to the reduction of isothermal solidification kinetic.