Microstructure characteristic and its influence on the strength of SiC ceramic joints diffusion bonded by spark plasma sintering

The interfacial microstructure evolution and shear strength of SiC joints for high temperature applications diffusion bonded by spark plasma sintering with a Ta-5W interlayer in the temperature range of 1500 °C to 1700 °C were investigated. The interfacial microstructure analysis indicated that (Ta,W)C phase formed initially and (Ta,W)-Si intermetallic compounds subsequently at SiC/Ta-5W interface. Bonding temperature had a significant effect on the reaction layer thickness, which increased with increasing the bonding temperature, and holding time also has an influence on reaction layer thickness. Calculation of diffusion kinetics for the SiC/Ta-5W interface showed that the diffusion constant was about two orders of magnitude larger than that obtained by hot-pressing bonding, and the activation energy was almost one-tenth that of hot-pressing bonding. Both the reaction layer thickness and the interfacial defects had a great effect on the robustness of the joint, and the maximum shear strength of 122 ± 15 MPa was obtained for the joint bonded at 1600 °C for 5 min.