Microstructure and properties of ZrB2-SiC and HfB₂-SiC composites fabricated by spark plasma sintering (SPS) using TaSi₂ as sintering aid

Dense ZrB₂SiC and HfB₂SiC composites were fabricated at 1800° by spark plasma sintering (SPS) using TaSi₂ as sintering aid. The volume content of SiC was 530% and that of TaSi₂ was 5% in the initial compositions. The additive of TaSi₂ contributed to the densification of composites by the decomposition and simultaneous solid solution of Ta atoms into boride grains which was probably associated with the decrease of activation energy of boride grain boundaries. With increasingSiC content, the electrical conductivity of ZrB₂SiC and HfB₂SiC composites decreased from 19.89 to 11.99 and 22.29 to 13.42 × 10⁵ω ^-1.m^-1 respectively. Generally, the thermal conductivity of composites showed an increasing tendency with increasing SiC content, indicating the maximum values of 49.93 and 118.39W/m.K respectively for ZrB ₂SiC nd HfB₂SiC composites produced with 30 vol% SiC content in the initial compositions. Additionally, the Vickers hardness of composites increased with the increment of SiC content from 16.9 to 20.2 and 24.0 to 28.5 GPa for ZrB₂SiC and HfB₂SiC composites respectively. The fracture toughness of ZrB₂SiC composites showed an increasing tendency from 3.70 to 4.44 MPa.m^1/2 with increasing SiC content while those of HfB₂SiC composites did not show a changing tendency and was in a range of 3.283.54 MPa.m^1/2. The elastic moduli of composites declined from 464.8 to 453.2 and 494.4 to 481.9 GPa for ZrB ₂SiC and HfB₂SiC composites respectively with increasing SiC content.