Brazing of SiC and SiCf/SiC composites performed with 84Si-16Ti eutectic alloy: microstructure and strength

The microstructure and strength of brazed joints for monolithic SiC and SiCf/SiC composites are presented and discussed; the brazing technique is based on the use of the 84Si-16Ti (at%) eutectic alloy. The rather low melting point of the used alloy allows to avoid a degradation of the fibre/matrix-interfaces in the composite materials. All the joints did not show any discontinuities and defects at the interface and revealed a fine eutectic structure. Moreover, in the case of composites, the joint layer appeared well adherent both to the matrix and the fibre interphase, and the brazing alloy infiltration looked sufficiently controlled. High resolving electron microscopic investigations of the microstructure and of the nanochemistry (HREM, EELS, esp. ELNES) revealed atomically sharp interfaces without interdiffusion or phase formation at the interlayer leading to the conclusion that direct chemical bonds are responsible for the adhesion. The joints of SiCf/SiC composites showed 71 ± 10 MPa shear strength at RT and nearly the same values at 600°C.