ZrB2–MoSi2 Ceramics: kinetics of compaction during hot pressing in СО environment, phase interactions at interfaces and static fatigue

Ceramics in the ZrB2–MoSi2 system pass through different stages during hot pressing in CO-CO2 environment. The first stage follows a smooth parabolic curve up to 1600 °C, then, a sharp compaction to full density occurs by transient liquid-phase sintering in the 1610–1850 °C temperature range. Ceramics sintered in this range have the primary compounds, ZrB2 and MoSi2, disappeared and new phases, such as (ZrB2)SS, SiC, B4C and ZrC, formed. The high sintering rate are associated to exothermic phase transformations, which significantly increase the temperature in the diffusion zones. In the 1850–2150 °C range, complete homogenization of the solid solution based on ZrB2 occurs and the sintering curve follows that typical of solid-state densification, i.e. increases continuously and slowly. Materials sintered at 1370–1850 °C have matrix grain size around 0.6–1.8 µm, while those sintered at 1940–2150 °C have grain size around 8–10 µm. Hot compression tests showed that the ZrB2-MoSi2 ceramic sintered at 1870 °C had the highest creep resistance compared with a ZrB2-SiC baseline.