Comparison of ZrB2-ZrC-SiC composites fabricated by spark plasma sintering and hot-pressing

Ultra-high-temperature-ceramic (UHTC) composites with the starting composition (vol. %) ZrB2+30ZrC+10SiC were fabricated by spark plasma sintering (SPS) and by hot pressing (HP). A fully dense material was produced by SPS, heating up to 2100°C in about 20 minutes and 30 MPa of applied pressure. In the HP case (1870°C for 40 minutes and 30 MPa of applied pressure), the incorporation of a sintering aid like silicon nitride was useful for reaching near full density. The total processing time was drastically lower, about one order of magnitude, for the SPS procedure compared to that necessary for HP.
The microstructure of both the composites was uniform and similar in grain size (< 3 mm) and shape. However, the phase chemistry and distribution changed little: secondary phases like zirconia and other Si-containing compounds were revealed only in the HP composite. A comparison of the SPS and HP techniques applied to ultra-refractory ceramics showed the former to be a rapid fabrication process leading to a refined microstructure depleted of secondary phase.