The improved SiC joints prepared by pressureless braze joining using Ti–Si interlayer with metallic infiltration

In this study, braze joining of SiC ceramics using a Ti-Si as the interlayer was first obtained at 1500 degrees C under pressureless condition in a conventional graphite heater furnace, and the shear strength of the resulted SiC joint was only 2.7 +/- 1.2 MPa. Results showed that the joining condition could be improved by adding metallic infiltration of Fe, Co, and Ni to Ti-Si interlayer and the shear strength was significantly increased to 73.7 +/- 11.7 MPa under the same processing conditions employed in this study. The joining mechanism was then proposed based on thermodynamics calculation, elements mapping as well as the microstructural analysis. In a graphite vapor environment, decomposition of the interlayer (Ti3SiC2) was readily promoted as compared to tungsten or molybdenum vapor environment. The decomposed products (Si) would easily dissolve into the liquid phase of Fe, Co, and Ni. Therefore, the infiltration of the above metallic elements would promote the decomposition of the Ti3SiC2 phase by decreasing the partial pressure of Si. However, the pores, which was produced by the graphite environment as well as the infiltration of the above metallic elements, provided a route for the diffusion of Fe, Co, and Ni elements. Results of this study showed that a robust SiC joint could be obtained by the decomposition of the interlayer first and then the densification of the interlayer under the same process with the metallic infiltration.