This study was carried out to investigate the effect of heating rate on the phase transition between additive base metal powder and liquid insert metal during transient liquid phase (TLP) diffusion bonding of Ni-based superalloy GTD-111. Heating rates studied were 10, 1, 0.5 and 0.1°Cs-1 in high vacuum conditions (3×10-5 torr) by means of a high frequency induction furnace. When heated at lower than 0.5°Cs-1, the transition of dissolution to solidification occurred during heating. In the case of very slow heating, the dissolution quickly finished at a lower temperature, and solidification soon started. The separated grains of additive base metal powders supplied the lager interface area for the diffusion of boron. Solidification transition temperatures of liquid phase were affected by the increase of diffusion interface and of duration time during slow heating. A minimum heating rate required to heat insert materials to a normal TLP isothermal bonding temperature of GTD-111 (≈1150°C) without a dissolution-solidification transition during heating should be higher than 1°Cs-1.