Fabrication, Microstructural Evolution, and Mechanical Properties of SiC/(Hf_0.25Ta_0.25Zr_0.25Nb_0.25)C/C Nanocomposites

A dense monolithic SiC/(Hf_0.25Ta_0.25Zr_0.25Nb_0.25)C/C high-entropy ceramic nanocomposite was prepared using a polymer-derived ceramic (PDC) method combined with spark plasma sintering (SPS). The microstructural evolution and mechanical properties of the obtained nanocomposites were characterized by X-ray diffractometer (XRD), transmission electron microscope (TEM), scanning-electron microscope (SEM), and nanoindentation. The results indicate that the phase composition of SiC/(Hf_0.25Ta_0.25Zr_0.25Nb_0.25)C/C can be adjusted by modifying the metal content of the single-source precursor (SSP) through molecular design. The resulting precursor exhibits an exceptionally high ceramic yield, with mass retention of over 90% at 1100 °C, which guarantees the densification of the final SiC/(Hf_0.25Ta_0.25Zr_0.25Nb_0.25)C/C composites. The PDC route facilitates the in situ formation of a high-entropy phase within the ceramic matrix under low temperature pyrolysis conditions. Combined with SPS, a dense monolithic SiC/(Hf_0.25Ta_0.25Zr_0.25Nb_0.25)C/C nanocomposite was obtained, exhibiting an open porosity of 0.41 vol%, nano-hardness of 27.47 ± 0.46 GPa, elastic modulus of 324.00 ± 13.60 GPa, and fracture toughness of 3.59 ± 0.24 MPa·m^0.5, demonstrating excellent mechanical properties.