Microstructure and Properties of C/HfC-SiC Composites Prepared by Slurry Impregnation Assisted Precursor Infiltration Pyrolysis

In response to the urgent demand for ultra-high temperature ceramic matrix composites with integrated thermal protection and load-bearing capabilities for high-speed aircrafts, this study prepared stable ceramic slurry from submicron HfC ceramic powder, and utilized the slurry pressure impregnation-assisted precursor infiltration pyrolysis (PIP) process to fabricate C/HfC-SiC composites with uniformly distributed HfC matrix to overcome the shortcomings of the existing reaction-derived HfC precursor, such as high cost, low efficiency, and poor densification effect. The influence of HfC content on the microstructure, mechanical properties, and ablation resistance of composites was investigated. Results showed that the composites had density of 2.20-2.58 g center dot cm(-3) and open porosity of approximately 5% when the actual volume fraction of HfC was in range of 13.1%-20.3%. Utilizing a single layer of carbon cloth to impregnate the ceramic slurry with pressure, HfC particles were able to disperse into the interior of the fiber bundle and distributed relatively evenly in the composites. Increasing the HfC content resulted in reducted fiber content, and decreased mechanical properties of composites. Specifically, when HfC volume fraction was 20.3%, the composites exhibited density, tensile strength and fracture toughness of 2.58 g center dot cm(-3), 147 MPa and 9.3 MPa center dot m(1/2), respectively. Following 60 s of ablation under an oxygen acetylene flame, the composites demonstrated linear ablation rate of 0.0062 mm/s and mass ablation rate of 0.005 g/s. The molten phase HfxSiyOz formed during the ablation process could effectively cover the composites surface and provide protection.