POLYMER-DERIVED CERAMIC COATINGS ON C C-SIC COMPOSITES/

A protective coating has been developed to enhance the oxidation stabi lity of C fibre reinforced SiC (C/C-SiC). The coating was prepared by pyrolysis of a polysilazane layer, which was obtained by dip-coating. Silicon powder was added to the polysilazane solution to prevent shrin kage during pyrolysis. The ceramic coating was characterized regarding layer thickness, adhesion, and oxidation protection for C-fibres. Und er the prevailing conditions the thickness of the ceramic layer was de termined to be up to 5 mu m after one coating-pyrolysis cycle and coul d be increased by further coating. Additionally, the thickness could b e varied by changing the viscosity of the polymer solution as well as the withdrawal speed. The highest values measured for the adhesion of the ceramic coating on the substrate were 14 MPa. The lifetime of the composite material at high temperatures in air could be increased by u p to 120% with the coating, compared with the uncoated samples. (C) 19 96 Elsevier Science Limited.