Effect of bonding time on microstructure and completion of isotherm solidification during TLP bonding of dissimilar nickel base superalloys IN738LC and Nimonic 75

Joining of Inconel 738 and Nimonic 75 nickel base superalloys using Ni-Cr-B-containing interlayer, MBF-80, performed by transient liquid phase process (TLP) at 1080, 1120, 1150 and 1180°C and different times. Bonding microstructure was studied using a scanning electron microscope (SEM) and a light microscope. Microstructural studies showed that in short bonding time, the microstructure consists of continuous eutectic intermetallic phases in the center line of the joint and with increasing bonding time at constant temperature, eutectic intermetallic phases gradually decrease from the bonding and finally completely disappear. In order to predict the time required to isotherm solidification completion, Fick’s diffusion equations were used and it was observed that there is a good agreement between the predicted time of isotherm solidification completion and experimental results.