SiC/SiC(N) Composites: Manufacture and potential UHT Applications

Kurzfassung

State-of-the-art, highly porous oxide based CMCs with intrinsic oxidation stability and no need to fibre coating, suffer from enhanced chemical attack due to high surface areas as well as from grain coarsening and strength reduction under UHT loading conditions. Dense oxide/oxide and especially non-oxide CMCs in combination with integrated oxidation and environmental protection systems have a real chance to overcome this problem, due to much lower attack surface area. Therefore, it is, of inevitable necessity to provide a suitable weak fibre/matrix bonding by fibre coating for both, oxide/oxide and non-oxide/non-oxide CMCs, which will be reliable for a limited time, in case of protection system failure. For PIP-processing, lanthanum phosphate is a prime candidate for this challenge due to inherent oxidation stability, high thermal resistance (m.p. 2058 °C) and chemical inertness to oxide as well as some non-oxide materials based on silicon carbide based materials. At DLR fundamental research based on commercial fabrics of alumina type (Nextel 610) as well as silicon carbide type (Tyranno Type SA3) was performed. According to effectiveness and performance of coating (number of cycles) fibre coatings applied by Foulard technique were further developed and evaluated. It turned out that an important factor is the surface roughness of the fibre. In addition, first results of mechanical properties before and after annealing at high temperature will be addressed. Moreover first results on plasma torch tests will be presented. In case of LSI-processing, providing pretty dense CMCs in one cycle, however, requiring severe processing conditions (>1410°C, Si-vapour conditions) new fibre coatings are under development in basic research programs and assessed to typical test conditions.