CORRELATION BETWEEN THE OXIDATION-STATE OF ALPHA-SIC AND ITS WETTABILITY WITH NONREACTIVE (SN) OR REACTIVE (NI) METALLIC COMPONENTS AND THEIR BINARY SI-ALLOYS

Wetting experiments were performed on alpha-SiC/Sn (505 K < T < 1873 K ) and alpha-SiC/Ni (T = 1773 K) in an argon atmosphere with 700 vpm mo isture. Wettability and reactivity of alpha-SiC with both metallic com ponents were affected by the oxidation state of alpha-SiC. Under the e xperimental conditions, passive to active transition of alpha-SiC occu rs at similar to 1600 K. Up to 1600 K, wettability between liquid Sn a nd alpha-SiC is governed by a passive SiO2-film overlaying alpha-SiC, while at higher temperatures an increased carbon surface concentration , leads to higher contact angle values. Under the present experimental conditions the start of reactivity between Ni and alpha-SiC coincides with the passive to active transition of alpha-SiC. The presence of s ilicon at the ceramic-metal interface, in the form of alloying element into both Sn or Ni, was found to decrease the temperature of passive to active transition of alpha-SiC, to improve the wettability for both alpha-SiC/Sn and alpha-SiC/Ni, and to suppress the interfacial reacti on between Ni and alpha-SiC. (C) 1997 Acta Metallurgica Inc.