TLP bonding of cast IN718 nickel based superalloy: Process–microstructure–strength characteristics

This paper aims at addressing the microstructure–strength characteristics relationship during transient liquid phase (TLP) bonding of cast IN718 nickel based superalloy using Ni-7 Cr-4.5 Si-3 Fe-3.2 B (wt%) amorphous interlayer. The progress of the isothermal solidification at different temperatures for different times is analyzed using a Larson–Miller parameter (LMP). It was found that there is direct relationship between isothermal solidification zone (ISZ) size and LMP. Results showed that in situation where isothermal solidification has not been completed, the ratio of athermal solidification zone (ASZ) size to the width of the total solidified zone is the controlling factor for shear strength of the TLP bonds. After completion of isothermal solidification, the shear strength of the joint is controlled by the hardness of ISZ, which in turn is governed by transport of solid solution strengthening elements (more effectively Cr, Nb and Mo) via dissolution of the base metal and inter diffusion between base metal and bond region during isothermal solidification.