Effect of ZrO ₂ impurity on promoting reactive sintering of ZrB ₂–SiC–ZrC composites

Abstract

ZrO ₂ impurity phase was examined by means of X-ray diffraction and scanning electron microscopy in reactive-sintered ZrB ₂–SiC–ZrC composites hot-pressed at 1600°C and 1800°C. An analytical electron microscopy study further revealed solid-solution of both Zr and O in the β-SiC phase: Zr:Si ratios were measured to be 1.83 ± 0.17 × 10 ⁻² and 1.91 ± 0.16 × 10 ⁻² respectively for each sample, while O:Si ratios were in the range of 2.3 ∼ 2.8 × 10 ⁻². Common co-existence of ZrO ₂ grains and SiC grains containing Zr–O solutes indicates that this oxide plays a significant role in the sintering process, which substantially modifies the reactive phase relations. Observation of an intergranular Si–Zr–C–O glassy phase suggests the presence of a similar sintering liquid as a fast or even dominant diffusion path to promote the reactive sintering.