Structures and Strength of SiC/Nb Bonding Interface

Pressureless-sintered (PLS) SiC was joined to Nb by solid state bonding at 1790 K for 0.6∼144 ks and 7.26 MPa in vacuum. Interfacial reaction layers and microstructures were investigated by an electron probe microanalyser and X-ray diffractometry. The hexagonal Nb2C phase 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∼7.2 ks. With increasing joining time, the Nb2C containing small amounts of NbC changed to NbC. At the long joining time of 72 ks, the hexagonal NbSi2 phase appeared at the interface between NbC 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 temperatures up to 973 K.