STRUCTURES AND STRENGTH OF SIC NB BONDING INTERFACE/

Pressureless-sintered (PLS) SiC was joined to Nb by solid state bondin g at 1790 K for 0.6 similar to 144 ks and 7.26 MPa in vacuum. Interfac ial reaction layers and microstructures were investigated by an electr on probe microanalyser and X-ray diffractometry. The hexagonal Nb2C ph ase in the Nb side and the mixture of hexagonal Nb5Si3C and tetragonal Nb5Si3 phases in the interface of Nb2C and SiC were formed at 1790 K for 0.6 similar to 7.2 ks. With increasing joining time, the Nb2C cont aining small amounts of NbC changed to NbC. At the long joining time o f 72 ks, the hexagonal NbSi2 phase appeared at the interface between N bC adjacent to SiC and Nb5Si3C. The fracture shear strength of SiC/Nb/ SiC couples showed the maximum of 187 MPa at room temperature, where a uniform thin layer of NbC at the interface adjacent SiC at 1790 K for 36 ks was formed. The couples exhibited the stable strength at temper atures up to 973 K.