OXIDE FIBER COATINGS FOR SILICON CARBIDE CERAMIC MATRIX COMPOSITES

摘要

The y-polymorph of the rare-earth disilicates (RE_2Si_2O_7) is a potential oxidation-resistant alternative to carbon or BN for CMC fiber-matrix interphases. The formation of γ-Y_2Si_2O_7 and 7-Ho_2Si_2O_7 at different temperatures and processing environments was investigated. Silica -yttrium hydroxide and silica - holmium hydroxide dispersions were made and heat-treated at 1200° - 1400°C for 8 h in air. Dense pellets of Y_2Si_2O_7 and Ho_2Si_2O_7 were made and indented. Sections below Vickers indents were analyzed for evidence of plastic deformation. SCS-0 fibers were put in γ-Re_2Si_2O_7 matrix (RE = Y and Ho) and densified at 1200°C/1 h using the field assisted sintering technique (FAST). Fiber push-out experiments were then conducted on these fibers. Preliminary results for characterization of deformation of γ-RE_2Si_2O_7 after indentation, and sliding stress values from fiber push-out are reported.