Co-reinforcing of mullite-TiN-CNT composites with ZrB2 and TiB2 compounds
In this study, the microstructural and mechanical properties of three different mullite matrix composites were investigated. Accordingly, Mullite-TiN-CNT, Mullite-TiN-TiB2-CNT and Mullite-TiN-TiB2-ZrB2-CNT composites with 10?wt % of each TiN, TiB2 and ZrB2 reinforcement particles as well as 1?wt % CNT were prepared by the spark plasma sintering (SPS) technique. The sintering processes were conducted at 1350?°C for 5?min with a mean heating rate of 60?°C/min. The relative densities of the composites achieved were higher than 97% of theoretical density. The results of mechanical properties of the fabricated composites showed that Mul-TiN-TiB2-ZrB2-CNT composites obtained the highest hardness and fracture toughness values. XRD results confirmed the presence of mullite, TiN, TiB2 and ZrB2 phases without any additional reactions between reinforcement and matrix phases. Microstructural studies demonstrated the uniform distribution of reinforcing phases in the matrix for all composites. The fracture surface micrographs revealed the dominating transgranular fracture mode indicated the strong adhesion of the reinforcing particles to the matrix. Pulling out of CNTs was also observed in the fracture surface of composites, which plays a vital role in the fracture energy absorption and joining of interfaces.