ZrB2–SiC composites prepared by reactive pulsed electric current sintering

Fully densified ZrB2–20 vol% SiC composites were produced by reactive pulsed electric current sintering (PECS) of a powder mixture containing ZrH2, B, SiC and B4C within a total thermal cycle time of only 50 min. During the combined synthesis and sintering process, the ZrH2 powder decomposed gradually from ZrH2 into ZrHm and finally metal Zr that reacted with elemental B to form the ZrB2 matrix. Reducing the ZrH2 particle size by attritor milling significantly enhanced densification and allowed initiation of self-propagating high temperature synthesis (SHS) during PECS. The PECS grades exhibited a slightly textured structure, with ≤17% of the ZrB2 grains oriented with their (0 0 1) planes perpendicular to the direction of pressure and DC current. Because of the ZrB2 grain orientation, anisotropic mechanical properties were observed. Ceramics prepared from attritor milled powders and PECS with a pressure applied after 5 min upon reaching 1900 °C achieved excellent flexural strengths of 901–937 MPa. The hardness and fracture toughness were respectively 19.7–19.8 GPa and 4.0–4.7 MPa m1/2 in the direction parallel and 20.2–21.3 GPa and 3.8–3.9 MPa m1/2 in the direction perpendicular to the applied pressure.