Fibre Reinforced Silicon Carbide: Effect of Densification Method and Parameters

The future fabrication of complex shaped structural components in fiber reinforced ceramic materials will require the densification of the composite by efficient but cost effective methods. In the present study the feasibility of liquid phase sintering (LPS) under low gas pressure, for the densification of silicon carbide as the matrix of a composite is examined. Monolithic and fiber reinforced silicon carbide, containing alumina and yttria as sintering aids, were densified by low pressure sintering and by hot pressing. The fiber examined was an intermediate modulus carbon fiber, both with and without pyrolytic carbon coating. The effects of varying the process parameters, temperature, sintering time, alumina and yttria concentration (the combined additve content was varied between 3-9 wt.% of the total powder mass) were determined at temperatures between 1750-1900 deg C under 10 bar argon pressure for hold times up to 2 h. Total alumina and yttria content was varied between 3-9 wt.% of the combined powder mass. Loss of sintering aids and interaction of fiber, fiber coating and matrix (specifically in relation to fiber/matrix interface formation) were monitored, through x-ray diffraction, scanning electron microscopy and transmission electron microscopy examination of samples, and density measurements of the monolithic silicon carbide. A maximum density figure of 2.97 Mg/m exp 3 91% of the theoretical figure) was obtained in a sample containing 9 wt.% of additives sintered at 1900 deg C for 120 min. However, evidence of the segregation and loss of sintering aids in the un-reinforced SiC and migration of the additive phase to monolithic sample edges and fibers matrix interfaces, prompted the shortening of sintering times.