Improved microstructure and fracture properties of short carbon fiber-toughened ZrB2-based UHTC composites via colloidal process

•A novel colloidal processing was firstly applied to fabricate carbon fiber-toughened ZrB2-based UHTC composites.•The microstructure homogeneity and fracture properties were improved significantly.•colloidal processing route avoids the fiber agglomeration and alleviates the fiber damage•Structural defects and fiber degradation are minimized.

Ultra-high temperature ceramics are potential materials for a variety of high temperature applications because of excellent thermo-mechanical properties and oxidation resistance. To further improve their fracture properties, a novel colloidal process was proposed to fabricate the short carbon fiber-toughened ZrB2–ZrSi2 composites. Microstructure analysis found that the colloidal processing route could avoid the fibers' agglomeration and alleviate the fibers' damage, which minimizes the structural defects and retains the fibers' strength. The relative density of composites achieves 98.35% and the distribution of fibers in matrix is homogeneous. Mechanical tests indicate that the flexural strength is 458 MPa and the fracture toughness is 6.9 MPa·m1/2. In comparison to the composite obtained by conventional processing route, the fracture toughness increases by 47%. The main mechanisms for improved fracture properties could be attributed to the crack deflection, fiber sliding and fiber bridging.

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