Densification behavior of ZrB2 with Co–WC as additives

Abstract

Among ultra-high temperature ceramics (UHTCs), zirconium diboride (ZrB2) ceramics have high electrical/thermal conductivity, excellent corrosion resistance, and a chemically stable crystal structure. These properties make ZrB2 suitable for extreme chemical and thermal environments, such as atmospheric re-entry and hypersonic aircrafts. ZrB2 has low intrinsic sinterability due to its strong covalent bonds and low self-diffusion coefficients. In the ZrB2 sintering process, decreased ZrB2 particle size is an important factor for increasing the driving force of densification. SPEX mill, a type of high energy milling, was employed to decrease particle size. Co-bonded WC was used by jar and media in SPEX mill because Co?WC is hard enough to pulverize ZrB2 particles. During SPEX milling, ZrB2 powders were contaminated by Co?WC. Co?WC contaminant could be also used by sintering additives. This study investigated the effects of Co, WC, and Co?WC for the densification of ZrB2. The ZrB2 composites were sintered by spark plasma sintering (SPS). Microstructures were observed using scanning electron microscopy (SEM) and phases of sintered samples were characterized by X-ray diffraction (XRD).