THE MECHANICAL-PROPERTIES AND MICROSTRUCTURE OF SIC-ALN PARTICULATE COMPOSITE

Silicon carbide (SiC) and aluminium nitride (AlN) were found to form a solid solution at temperatures above 1800 degrees C. Based on this in teresting result, the composite was fabricated by mechanical mixing of the SiC and AlN powders, and hot pressed under 40 MPa at 1950 degrees C in an argon atmosphere. The objective was to achieve full density a nd minimize solid solution formation. During the sintering process, th e SiC-AlN system passed through three steps to form the solid solution at the end. First, the AlN particle is vaporized from its surface; ne xt, the evaporated AlN is deposited on the surface of the SiC grains a nd the AlN particle, accompanied by a reduction in its size, and final ly, partial SiC and AlN solid-solution formation on the boundary of th e SiC grains. Because of the AlN deposition and solid-solution formati on at the boundary of SiC grains, a barrier layer was present on the s urface of SiC grains. This leads to the formation of fine grains. The toughening mechanism is thought to be by thermal residual stresses, du e to the difference between the coefficients of thermal expansion of t he matrix SiC and that of the dispersed AlN particles, and crack defle ction around the SiC grains. Therefore, it is that which improves the mechanical properties of the SiC-AlN composite. (C) 1998 Chapman & Hal l.