SiC/SiC and SiC/Kovar joining by Ni–Si and Mo interlayers

A composite joining technique, using a Ni–56Si filler alloy and Mo as interlayers, was used to join SiC to SiC and to Kovar. The wetting of the Ni–Si alloy on SiC ceramic was studied in a vacuum at 1,350 °C by the sessile drop technique as a function of time; the non-reactive wetting characteristics in the Ni–Si/SiC system were confirmed, with an equilibrium contact angle of about 23°. SiC/SiC joints were fabricated by two processes using a Ni–Si/Mo/Ni–Si structure as the interlayer. SiC/Kovar joints were produced by means of a multilayer structure: molybdenum, which is used as the interlayer, was joined to Kovar on one side by means of transient liquid phase bonding and to SiC on the other side, using a Ni–Si coating as a filler alloy. The resulting joints were analyzed and discussed in terms of joint morphology and microstructure, joint strength, and fracture behavior. Two interfacial layers form at the Kovar/Mo and the Mo/Ni–Si interfaces due to dissolution and interdiffusion phenomena between the metallic elements, without there being any observable reactions with the SiC component. The type of joining process and the experimental conditions used play a key role in determining the joint microstructure and composition, the joint strength and its fracture behavior.