An ultra-strength SiC ceramic joint with an in-situ formed high-entropy carbide interlayer via diffusion bonding by spark plasma sintering

Abstract

A novel Ta0.5HfZrTi refractory high-entropy alloy instead of the traditional single refractory metal was chosen as an interlayer for diffusion bonding of silicon carbide (SiC) ceramics by spark plasma sintering. The microstructural evolution and mechanical properties of SiC joints processed at 1400–1700 °C for 5–20 min under a pressure of 30 MPa were investigated. The phase constitutes in the reaction layer varied with the joining conditions and mainly consisted of (TaHfZrTi)C, (TaHfZrTi)xSiyCz, and (TaHfZrTi)xSiy. The initial reaction phases exhibited metallic element segregation owing to the different Gibbs free energies of the interfacial reactions. The crystalline structure of the diffusion-formed (TaHfZrTi)C was identified as face-centered cubic sphalerite. A near-full (TaHfZrTi)C reaction layer was successfully achieved at 1700 °C for 20 min due to the fast formation of a relatively dense (TaHfZrTi)C layer and the decomposition of (TaHfZrTi)xSiyCz at elevated temperatures. The maximum joint hardness and shear strength at the same conditions were significantly improved to 2552.1 ± 357.1 HV and 326.2 ± 9.9 MPa, respectively.