Wettability of silicon nitride ceramic composites by silver, copper and silver copper titanium alloys

The sessile drop method under vacuum (10-2 Pa) has been chosen to study the contact behaviour between ceramic composites and liquid metals (silver or copper) or alloys (silver-copper or silver-copper-titanium).With the help of a CCD camera, on-line observations were done and the contact angle evolution was followed as a function of temperature or time. Finally X-Ray diffraction analysis and electron micrographs (SEM, BSE, EDX) were used to analyze the ceramic-metal interfacial zone. A Si3 N4 powder was mixed with an electro-conductive secondary phase (TiN, TiB2, HfB2, MoSi2) and sintered by either hot isostatic pressing (HIP) or hot pressing (HP). The hipped and hot pressed samples contained at least 27 vol.% of the electroconductive secondary phase to allow electrodischarge machining (EDM). Low amounts of sintering aids were used to reduce the consolidation temperature in order to avoid decomposition of the silicon nitride phase and reactions between the powders. All composites are close to full density (relative density greater than 98%). Non-wetting was observed with silver, copper and the silver-copper alloy on all ceramic composites but the addition of 3 wt.% titanium to the silver-copper alloy induces wetting. In the reaction zone, the presence of a high amount of titanium due to the formation of TiNx and Ti5Si3 is noticed.