ZrB2-SiC-WC coating with SiC diffusion bond coat on graphite by spark plasma sintering process

A dense, crack free and well bonded ZrB2-SiC-WC top coating with silicon carbide diffusion bond coat was successfully prepared on graphite substrate by spark plasma sintering (SPS) at 1900 degrees C under 20 MPa pressure for 5 min. The thickness of top coat and diffusion bond coat was about 800 mu m and 3 mm, respectively. The bonding strength was evaluated by bending test. In the bending specimens the fracture occurred not at the interface, but at the graphite substrate which indicates that the bonding strength of coating and substrate is higher than strength of graphite substrate. Phase continuity of silicon carbide from top coat to interface and diffusion zone led to high adhesion of coating to graphite.