Development of Joining and Coating Technique for SiC and SiC/SiC Composites Utilizing Nite Processing

For joining, the same SiC nano-powder and sintering additive with NITE processing to fabricate SiC were used. Silicon carbide or SiC/SiC plates were joined by hot-pressing at 1700-1900 °C for 1 hour under 20 MPa. The joined bars were evaluated by tensile test and asymmetric four point flexural test. For the coating, W is used considering the application. Starting materials were both fine powders and by lay-up two zones of powders (slurry) followed by hot pressing, two layers of W and SiC were produced with strong bonding. The joint thickness was controlled to approximately 10 m̈m. The tensile strength for the joint of monolithic SiC was approximately 40 MPa with 40% porosity at the interface. The shear strength of the joint of monolithic SiC could not be obtained, since the crack at joint propagated into the substrate, but it was more than 90 MPa. After improving the technique, the dense joint was formed and then, the tensile strength increased to more than 250 MPa. For W coated SiC, SiC, W and their interface reaction layers can be controlled to make acceptable bonding by optimizing the materials used and process condition. Using the optimized condition, W coated SiC/SiC composites were developed, although the optimization of processing for the composites is still required.