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

A suite of solid solutions of zirconium diboride, formulated (Zr1-xTix)B-2 (x = 0, 1, 2 and 5 mol%), was prepared by borothermal reduction at 1550 degrees C starting from ZrO2, TiO2 and B. Solid solutions of (Zr1-xTix)B-2 were heat-treated at 1900 degrees C to evaluate the influence of the substitution of TiB2 on the high-temperature stability. Moreover, (Zr1-xTix)B-2-20 vol% SiC ceramics were fabricated by spark plasma sintering at 2000 degrees C and the corresponding microstructure and Vickers hardness were characterised. The results revealed that the solid solution of TiB2 (>= 1 mol%) could suppress the coarsening effect of by-product B2O3, resulting in particle refinement of ZrB2-based powder, and the average particle size was reduced from 0.75 mu m to 0.40 mu m. Whereas, (Zr1-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 ZrB2. ZrB2-SiC and (Zr0.99Ti0.01)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 TiB2-substitution was limited, and hardness decreased gradually.