On the Extension of Processing Time with Increase in Temperature during Transient-Liquid Phase Bonding

Transient-liquid phase (TLP) bonding of a nickel-based superalloy, IN 738, was performed. Contrary to conventional TLP bonding analytical models, which assume a parabolic relationship between liquid/solid interface migration and holding time, deviation from this law was observed experimentally and by numerical simulation. The deviation, which is caused by reduction in solute concentration gradient below a critical value, is suggested as an alternate phenomenon responsible for anomalous extension of processing time required to produce an eutectic-free joint with increase in bonding temperature. A decrease in the filler gap size and the use of a melting-point depressant (MPD) solute with higher solubility in the base material could reduce the occurrence of the anomalous behavior during a high-temperature TLP joining process.