Ultra-low temperature reactive spark plasma sintering of ZrB₂-hBN ceramics

Starting from ZrN and amorphous boron, dense ZrB₂ ceramics with 37vol% hexagonal BN were consolidated by spark plasma sintering. Benefiting from the moderate exothermic reaction between ZrN and B and the resultant fine powder generated, ZrB₂-BN ceramics with relative density of 94% could be reached at 1100°C, further improved to 97% by 1550°C. The effects of sintering temperature and holding time on the densification behavior, microstructural evolution and mechanical properties of ZrB₂-BN ceramics were investigated. ZrB₂-37vol%BN ceramics densified at 1700°C exhibited attractive mechanical performance: a three-point bending strength of 353MPa, a Vicker's hardness of 6.7GPa and a Young's modulus of 197.5GPa. Note that its strength dropped sharply to 191MPa measured at 1300°C. The combination of low sintering temperature (1100-1550°C), low Young's modulus (180-200GPa) and relatively high strength (200-350MPa) make reactively sintered ZrB₂-BN composites as promising matrix for continuous fiber reinforced composites.