Interphase Challenges in Dense Oxide and Non-oxide CMCs for Long Term Applications

Kurzfassung

Under long-term HT-loading conditions, highly porous all oxide fibre based CMCs as well as porous non-oxide CMCs suffer from enhanced chemical attack due to high surface area and due to microstructural degradation depending on phase composition. Additionally, fibre/matrix interaction may change due to internal oxidation resulting in brittle fracture behavior. Dense CMCs in combination with an integrated oxidation and environmental protection system have a real chance to overcome these problems. Furthermore a suitable weak fiber matrix interface must be provided which will be reliable for sufficient time in case of protection system failure. LaPO4 is a prime candidate for this challenge due to inherent oxidation stability, high thermal resistance and chemical inertness to oxide as well as non-oxide CMCs based on SiC. At DLR fundamental research based on commercial fabrics of alumina silicate, alumina as well as SiC type was performed. Coatings applied by Foulard technique as well as dip-coating were investigated and evaluated according to effectiveness and performance of coating. First results of mechanical as well as microstructural properties considering roughness of the fibres will be addressed before and after annealing at high temperature. Furthermore, a perspective of new fibre coatings suitable for the development of dense SiC/SiC materials via LPI processing will be given.