THE WETTABILITY OF SILICON-CARBIDE BY LIQUID ALUMINUM - THE EFFECT OF FREE SILICON IN THE CARBIDE AND OF MAGNESIUM, SILICON AND COPPER ALLOY ADDITIONS TO THE ALUMINUM

Results from the sessile-drop method are reported for the effects on wetting angle, theta, of free silicon in the silicon carbide substrate and of alloy additions of silicon, copper or magnesium to the aluminium drop for the temperature range 700-960 or 1040-degrees-C in a titanium-gettered vacuum (10(-4)/10(-5) torr; 1 torr = 133.322 Pa). Wetting angle, theta, was reduced by a factor as large as 2.8 for pure aluminium on reaction-bonded, compared with sintered silicon carbide, attributable to partial dissolution by the aluminium of the 18 wt% free silicon present in the reaction-bonded material. For wetting of reaction-bonded silicon carbide, the addition of 5 wt% silicon, copper or magnesium to the aluminium gave contact angles that decreased in the sequence Si-->Cu-->Mg, with the magnesium addition being the only one to result in wetting (i.e. theta < 90-degrees) for all conditions studied. These results may have implications for design of conditions for joining or promotion of infiltration of silicon carbide parts, preforms or arrays with aluminium alloy melts.