Phase transformations during diffusion brazing of IN718/Ni–Cr–B/IN718

The production of robust joints after diffusion brazing necessitates the advanced understanding of phase transformations during the bonding process. This paper aims to investigate the solidification and the solid state precipitation during diffusion brazing of wrought IN718 nickel base superalloy using Ni–15Cr–4B (wt-) filler alloy. It was found that intermetallics containing eutectic type microconstituents were formed in the joint centreline by solidification which is controlled by segregation behaviour of B and its low solubility in Ni rich solid solution. In addition, extensive Cr–Mo–Nb rich precipitates were formed in the substrate region by solid state precipitation induced by B diffusion into base metal. The implications of the phase transformations on the joint properties are discussed.