Preliminary characterisation of a plasma sprayed MoSi2/sigma SIC fibre monotape

Fabrication of a preliminary continuous Sigma 1140 + SiC fibre reinforced MoSi2 composite monotape by plasma spraying onto a ring shaped substrate has been successfully demonstrated without any SiC breakage. The MoSi2 matrix microstructure was typical of a splat quenched plasma spray processed material with porosity < 5%. Matrix cracking occurred between fibres and was attributed primarily to differences in the coefficient of thermal expansion of MoSi2, SiC and the steel substrate. Evidence for the formation of SiC by interfacial reaction between the fibre C coating and the MoSi2 matrix has been observed, although this reaction was not uniform at all points on the interface. SIC formation has been suggested to affect the bonding between the fibre and the matrix and the subsequent mechanical properties of consolidated material. Pest oxidation bf the MoSi2 matrix has been used to extract the SiC fibres after plasma spraying to assess the effect of process induced damage on the fiber properties in the matrix. However, the extraction process itself caused some changes to fibre properties which made analysis problematical. The similar to 3.1 GPa as-supplied mean tensile fibre strength was retained during plasma spraying, but the Weibull modulus reduced from 25 to 11, i.e. the spread of fibre strengths increased. Mean bend strain and Weibull modulus were reduced from 1.78 to 1.57 and from 25 to 10 respectively. The fibre surface integrity was affected by both oxidation effects during extraction and by the impact of MoSi2 droplets during spraying. (C) 1999 Elsevier Science S.A. All rights reserved