Abstract

SiC fibre reinforced SiAlON-MoSi2 composites have been manufactured by concurrent fibre winding and low pressure plasma spraying (LPPS), producing multi-layer, circumferentially fibre-reinforced composite rings. LPPS parameters for the powder used were optimised by a two-level experimental design method followed by additional tuning, achieving smooth sprayed surfaces with low matrix porosity and good deposition efficiency. The microstructure of the SiAlON-MoSi2 matrix consisted of a lamellar structure and uniformly distributed SiAlON splats throughout the MoSi2 matrix. The spray/wind composites exhibited 2% porosity and well controlled fibre distribution. Matrix cracking occurred after heat treatment at 1500°C and was attributed to the development of large tensile residual stresses during cooling due to CTE mismatch. Increasing the SiAlON to MoSi2 ratio in the composite solved the problem. Simulations based on residual stresses showed that the maximum permissible fibre volume fraction to avoid matrix cracking was 0.06 for SiC/MoSi2 and 0.23 for SiC/SiAlON(40v/o)-MoSi2.

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