Low-Temperature Densification of Zirconium Diboride Ceramics by Reactive Hot Pressing

Zirconium diboride–silicon carbide ceramics with relative densities in excess of 95% were produced by reactive hot pressing (RHP) at temperatures as low as 1650°C. The ZrB₂ matrix was formed by reacting elemental zirconium and boron. Attrition milling of the starting powders produced nanosized (<100 nm) Zr particulates that reacted with B below 600°C. The reaction resulted in the formation of nanoscale ZrB₂ crystallites that could be densified more than 250°C below the temperatures required for conventional ZrB₂ powder. Because of the low-temperature densification, the resulting ZrB₂ grain sizes were as small as 0.5±0.30 μm for specimens densified at 1650°C and 1.5±1.2 μm for specimens densified at 1800°C. Vickers hardness, elastic modulus, and flexure strength of fully dense materials produced by RHP were 27, 510, and 800 MPa, respectively.