Solidification and solid state phenomena during TLP bonding of IN718 superalloy using Ni-Si-B ternary filler alloy

This paper addresses solidification and solid state precipitation phenomena during transient liquid phase (TLP) bonding of wrought IN718 nickel base superalloy using Ni-4.5Si-3.2B (wt.%) ternary filler alloy. The solidification sequence of the residual liquid in the joint centerline was found to be (1) formation of proeutectic gamma, followed by (2) gamma/Ni3B eutectic reaction, followed by (3) ternary eutectic of gamma/Ni3B/Ni6Si2B. Extensive fine Ni3Si formed within the eutectic-gamma via solid state precipitation during cooling. Extensive Cr-Mo-Nb rich boride precipitates were formed in the substrate region due to boron diffusion into the base metal during bonding process. The implications of the phase transformations on the mechanical properties, corrosion resistance and aging behavior of the joint, which are pertinent to the development of an optimum post bond heat treatment, are highlighted. (C) 2013 Elsevier B.V. All rights reserved.