Fabrication of a composite powder and its application as an active brazing alloy

A copper-based active brazing alloy containing a high titanium content was produced by an electroless coating technique. Particles with a narrow density distribution were produced by deposition of nano-copper on a fine titanium powder. Both conventional titanium powder and sponge titanium were studied. The effects of pH and time on copper deposition were investiguated. Higher pH was found to increase the quantity of copper deposited. Using multiple depositions, a copper-titanium ratio of 75 wt% copper-25 wt% titanium could be achieved after several platings for pH varying between 12 and 12.8. The particle size distribution of the composite powder shows uniform growth of the copper shell and no agglomeration under pH 12. Major agglomeration of the final powder was observed for a bath pH of 12.8. Complete melting of the composite powder has been studied by DSC and the sessile drop technique. Melting began within the diffusion zone formed at the interface through the Cu4Ti→Cu(s) + L peritectic reaction that occurs at 885◦C. The melting process continued by successive peritectic reactions and dissolution of the remaining elements of the diffusion couple. The wetting behavior of this alloy was evaluated on different ceramic substrates (Al2O3, Si3N4) and found to be similar to literature observations. C 2005 Springer Science + Business Media, Inc.