INFLUENCE OF SURFACE ROUGHNESS AND PREOXIDATION STATE ON THE WETTABILITY OF ALUMINIUM NITRIDE BY COMMERCIAL BRAZES

Aluminium nitride substrates were prepared with surface finishes (Ra) of 0.17-0.20 micron and 0.02-0.03 micron and annealed in vacuum at 800 C. The smoother samples were oxidised in air at 1250 C. The wettability of the prepared surfaces by commercial brazing alloys CB4 (70.5%Ag, 26.5%Cu, 3%Ti) and CB5 (64%Ag, 34.2%Cu, 1.8%Ti) was determined at temperatures of 810-950 C by the sessile drop method. Wettability and the time to reach the final contact angle were not significantly affected by the surface roughness. Preoxidation increased both the initial and final contact angles, but did not significantly affect the time to reach the final contact angle. The results are explained in terms of reaction between the braze metal and the substrate. 20 refs.