Microstructure and mechanical properties of SiC ceramics joints diffusion-bonded with a SiC-YF₃ interlayer via SPS

To address the issue of excessively high joining temperatures of silicon carbide (SiC) ceramics in the traditional nano-infiltrated transient eutectic (NITE) method, a method utilizing spark plasma sintering (SPS) diffusion bonding with a SiC-based interlayer containing YF₃ powder was proposed to reduce the joining temperature. The effects of joining temperature, holding time, and YF₃ content on the microstructure and mechanical properties of the joints were investigated. The results indicate that increasing the joining temperature and holding time significantly enhances the densification of the interlayer powder and improves the mechanical properties of the joints. The interlayer is primarily composed of 3C-SiC, along with phases such as Si-rich SiC_{1 − x}, C-rich SiC_{1 + x}, Y_xC_y, and Y_xSi_yC_z. The phase composition of the joints is influenced by the joining process. With increasing YF₃ content, Y_xSi_yC_z initially forms, followed by the precipitation of Y_xC_y and a decrease in the amount but an increase in the size of Y_xSi_yC_z. Consequently, the densification and strength of the joints first increase and then decrease, while the hardness gradually increases. Under the optimal joining process (1 750 °C/10 min/5% YF₃), the hardness of the interlayer reaches 2 013.1 HV ± 74.1 HV, comparable to that of the base material. The room-temperature shear strength is 181.9 MPa ± 55.2 MPa, and fracture occurs within the base material.