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

Starting from ZrN and amorphous boron, dense ZrB2 ceramics with 37 vol% 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. ZrB2-37 vol%BN ceramics densified at 1700 °C exhibited attractive mechanical performance: a three-point bending strength of 353 MPa, a Vicker’s hardness of 6.7 GPa and a Young’s modulus of 197.5 GPa. Note that its strength dropped sharply to 191 MPa measured at 1300 °C. The combination of low sintering temperature (1100–1550 °C), low Young’s modulus (180–200 GPa) and relatively high strength (200–350 MPa) make reactively sintered ZrB2-BN composites as promising matrix for continuous fiber reinforced composites.