Assessment of melting behavior of Cu-coated Ti powders using thermal analysis

The sequence of intermetallic formation and growth, and melting behavior of a Cu-coated Ti powder, used as active brazing alloy (ABA) for joining ceramic was studied. The experiments show that melting starts at around 885 °C, regardless of the heating rate. Prior to the onset of melting, a series of intermetallic layers was observed (Cu/TiCu4/Ti3Cu4/Ti2Cu3/Ti) with their relative thickness depending on the heating rate. A heating rate of 10 °C/min gives a final melting temperature of 900 °C as opposed to 915 °C for a sample heated at 40 °C/min. The utilization of N2 as a “protective” gas has shown the instantaneous formation of TiN from the reaction between Ti and N2 when the first liquid appears, indicating N diffusion through the copper shell. The remainder of the powder still contains Ti in copper as a TiN diffusion barrier was formed. Mixtures of ABA and Si3N4 powder have demonstrated that the surface of the powder becomes liquid at 894 °C as an intense exothermic peak from the reaction between Ti and Si3N4 is observed.