Contact-mechanical properties at intermediate temperatures of ZrB2 ultra-high-temperature ceramics pressureless sintered with Mo, Ta, or Zr disilicides

The elasto-plastic properties and contact damage evolution of ZrB2 ultra-high-temperature ceramics (UHTCs) pressureless sintered at 1900 °C with MoSi2, TaSi2, or ZrSi2 additive were evaluated by Hertzian indentation tests in air up to 800 °C. It was found that liquid-phase sintering occurred in the three cases, but with severe decomposition of the TaSi2 and ZrSi2 additives and extensive formation of (Zr1−mSim)B2 solid-solutions in the case of the ZrSi2 additive. Furthermore, ZrB2 sintered with ZrSi2 underwent severe peptization at 800 °C, raising questions as to its utility as a UHTC. It was also found that ZrB2 sintered with MoSi2 exhibits the best combination of contact-mechanical properties, being harder, stiffer, and more resistant to quasiplastic damage and radial cracking than ZrB2 sintered with TaSi2 or ZrSi2, as well as equally resistant to ring/cone cracking from ∼600 °C onwards. Implications of interest for the UHTC community are discussed.