Degradation kinetics of Ti-Cu compound layer in transient liquid phase bonded graphite/copper joints.

The continuous Ti-Cu compound layer produced in brazing of graphite to copper with Ti foil is found to be seriously detrimental to joint properties due to its brittleness. In this work, a transient liquid phase (TLP) bonding method with a diffusion process below melting point is developed to realize a Ti-Cu compound layer free joint. The degradation of Ti-Cu compound layer depends on two simultaneously occurring processes, namely flow of titanium atoms to copper substrate and that to TiC layer on graphite. The latter is determined by growth kinetics of TiC layer based on carbon diffusion process. A degradation model is proposed and applied to optimize the TLP bonding. The improved graphite/copper joints without Ti-Cu compound layer show 20.8% higher in shear strength compared with that of brazing joints.