Joining of oxide/oxide composites by a preceramic polymer

Le résumé fourni par la source

Ceramic matrix composites (CMC), particularly oxide fiber-reinforced oxide matrix (ox/ox) composites, offer a viable alternative to traditional materials, due to their high temperature thermo-mechanical stability, intrinsic oxidation resistance and low density compared to metals. However, a joining material having the same thermo-mechanical behavior and oxidation stability as the ox/ox composites is still an open issue. In this respect, joining by a preceramic polymer offers a unique option, in principle enabling the fabrication of robust ceramic joints; since the process can be done at lower temperatures in respect to traditional methods such as brazing, it can also be attractive from an energy saving point of view. This study investigated the use of a polysilazane-based preceramic polymer (Durazane 1800) filled with an increasing amount of alumina particles and 1 wt % chopped alumina fibers to join and coat ox/ox composites. The process was the same for joining and coatings: i.e. curing at 180°C and pyrolysis up to 1200°C in air, followed by microstructural and mechanical characterization on each sample. Lap-shear tests were done on joined samples at room temperature, at 300°C and at 600°C, in air. Fracture surfaces exhibited cohesive failure, indicating sound adhesion between the joining material and the ox/ox composites. However, residual porosity and incomplete covering of the joined area were identified as a limiting factor affecting the joint strength. X-ray computer tomography (CT) was used to measure the volume of residual porosity, cracks and lack of coating material after curing and pyrolysis on coated samples.

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