Abstract
This research presents the influence of Al addition on microstructure and mechanical behavior of ZrB2–SiC ultra-high temperature ceramic matrix composite (UHTCMC) fabricated by spark plasma sintering (SPS). A 2.5 wt% Al-doped ZrB2–20 vol% SiC UHTCMC was produced by SPS method at 1900 °C under a pressure of 40 MPa for 7 min. The microstructural and phase analysis of the composite showed that aluminum-containing compounds were formed in-situ during the SPS as a result of chemical reactions between Al and surface oxide films of the raw materials (i.e. ZrO2 and SiO2 on the surfaces of ZrB2 and SiC particles, respectively). The Al dopant was completely consumed and converted to the intermetallic Al3Zr and Al4Si compounds as well as Al2O3 and Al2SiO5. A relative density of 99.8%, a hardness (HV5) of 21.5 GPa and a fracture toughness (indentation method) of 6.3 MPa m1/2 were estimated for the Al-doped ZrB2–SiC composite. Crack bridging, branching, and deflection were identified as the main toughening mechanisms.
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