Thermal cycling of siliconized-SiC at high temperatures

Thermal cycling (between 1340 degreesC and 1480 degreesC) experiments were conducted using two types of reaction-bonded (siliconized) silicon carbide. A commercial material (Crystar(TM)) and various silicon carbide pieces tha t had been joined together using electrophoretic deposition (EPD) followed by reaction bonding were evaluated. During the thermal cycling, residual "f ree" silicon metal rapidly vaporized from the Crystar(TM) and cracks develo ped within its large SiC grains. In contrast, the EPD/reaction-bonded silic on carbide joints did not lose an observable amount of their residual silic on nor develop cracks. The reduced loss was attributed to reduced silicon c ontent with the silicon residing largely in closed pores of the EPD layer. Reduced vaporization of the silicon that resided in surface-connected pores was engineered by applying a thick SiC surface coating. The morphology of the resulting coating was microscopically evaluated and two sequential grow th mechanisms were postulated. An implication of this research is that herm etic (gas-tight) joints could be formed using EPD-derived SiC as a filler m aterial. (C) 2001 Kluwer Academic Publishers.