Interfacial and thermomechanical characterization of reaction formed joints in silicon carbide-based materials

The microstructure and mechanical properties of reaction formed joints of RefelTM reaction bonded SiC (RB-SiC) and HexoloyTM sintered SiC were studied in order to achieve a better understanding of the influence of base materials and joining process parameters on the high temperature strength of reaction formed joints. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and optical microscopy were used to characterize the joints prior to mechanical tests. The microstructural analysis indicated that the joints consist of silicon carbide (SiC) grains (with grain sizes ranging from 0.1 to 2 μm) and crystalline silicon as an intergranular phase. Most of the silicon carbide grains in the joint have hexagonal crystal structure with certain preferential orientations related to the silicon matrix. The high temperature strength of joints was measured by constant strain rate experiments in compression where joints were forming 45° with the compression axe. The strength of the joined Refel RB-SiC has been found to be at least equal to that of the bulk materials (550 MPa at 1235°C and 400 MPa at 1385°C). The joined Hexoloy specimens had strengths (1.4 GPa at 1290°C and 750 MPa at 1420°C) lower than the bulk material but higher than the joints of RB-SiC.