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

Fabrication of a preliminary continuous Sigma 1140 + SiC fibre reinforced M oSi2 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 mater ial with porosity < 5%. Matrix cracking occurred between fibres and was att ributed primarily to differences in the coefficient of thermal expansion of MoSi2, SiC and the steel substrate. Evidence for the formation of SiC by i nterfacial reaction between the fibre C coating and the MoSi2 matrix has be en observed, although this reaction was not uniform at all points on the in terface. SIC formation has been suggested to affect the bonding between the fibre and the matrix and the subsequent mechanical properties of consolida ted material. Pest oxidation bf the MoSi2 matrix has been used to extract t he SiC fibres after plasma spraying to assess the effect of process induced damage on the fiber properties in the matrix. However, the extraction proc ess itself caused some changes to fibre properties which made analysis prob lematical. The similar to 3.1 GPa as-supplied mean tensile fibre strength w as 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 respective ly. The fibre surface integrity was affected by both oxidation effects duri ng extraction and by the impact of MoSi2 droplets during spraying. (C) 1999 Elsevier Science S.A. All rights reserved.