Microstructures and formation mechanism of continuous carbon fiber-reinforced (TiZrHfNbTa)C high-entropy ceramic composites fabricated via high-entropy alloy reactive melt infiltration

Using TiZrHfNbTa high-entropy alloys as cation sources and carbon matrix in carbon fiber-reinforced carbon (Cf/C) preforms as carbon sources, this study presents rapid construction of dense, continuous Cf-reinforced (TiZrHfNbTa)C high-entropy ceramic (Cf/HEC) composites based on reactive melt infiltration (referred to as Cf/HECRMI composites). The results consistently indicate the uniform distribution of elements in the ceramic phase. Based on X-ray diffraction patterns, the ceramic phase was inferred as a (TiZrHfNbTa)C HEC phase. Cf/HECRMI composites can form because the TiZrHfNbTa high-entropy alloy reacts with the carbon matrix to form uniform ceramic monomers, which spontaneously assemble into the (TiZrHfNbTa)C HEC phase under high-temperature conditions. Owing to the dense microstructures, the high strength of the (TiZrHfNbTa)C phase, high strength and toughness of the residual TiZrHfNbTa alloy phase, and Cf reinforcement, Cf/HECRMI composites exhibit excellent mechanical properties with a bending strength of 584.2 MPa. These composites also possess outstanding ablation resistance, with linear and mass rates of 0.6 μm s−1 and 0.9 mg s−1, respectively, under an ablation time of 180 s and ablation temperature maintained at ∼2000 °C. The high ablation resistance can be attributed to dense, stable, and highly viscous complex oxides (HfZrO4, TiNbTaO7, Hf6Ta2O17, Nb2Zr6O17, ZrO2, and HfO2) formed on the sample surfaces.