High-temperature stability and densification of Ti-substituted ZrB2-based ceramics

Abstract A suite of solid solutions of zirconium diboride, formulated (Zr 1-x Ti x )B 2 (x = 0, 1, 2 and 5 mol%), was prepared by borothermal reduction at 1550 °C starting from ZrO 2 , TiO 2 and B. Solid solutions of (Zr 1-x Ti x )B 2 were heat-treated at 1900 °C to evaluate the influence of the substitution of TiB 2 on the high-temperature stability. Moreover, (Zr 1-x Ti x )B 2 -20 vol% SiC ceramics were fabricated by spark plasma sintering at 2000 °C and the corresponding microstructure and Vickers hardness were characterised. The results revealed that the solid solution of TiB 2 (≥1 mol%) could suppress the coarsening effect of by-product B 2 O 3 , resulting in particle refinement of ZrB 2 -based powder, and the average particle size was reduced from 0.75 μm to 0.40 μm. Whereas, (Zr 1-x Ti x )B 2 grain grew after the high-temperature testing in all cases, mainly due to the enhanced surface diffusion at high temperature. Consequently, the particle size of solid solutions was slightly larger than that of pure ZrB 2 . ZrB 2 -SiC and (Zr 0.99 Ti 0.01 )B 2 -SiC specimens with the relatively fine microstructure were obtained after SPS sintering and possessed the relatively high hardness (23.5 GPa and 23.3 GPa). With x value further increasing (>1 mol%), the microstructure refinement as a consequence of TiB 2 -substitution was limited, and hardness decreased gradually.