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

Abstract The elasto-plastic properties and contact damage evolution of ZrB 2 ultra-high-temperature ceramics (UHTCs) pressureless sintered at 1900 °C with MoSi 2 , TaSi 2 , or ZrSi 2 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 TaSi 2 and ZrSi 2 additives and extensive formation of (Zr 1− m Si m )B 2 solid-solutions in the case of the ZrSi 2 additive. Furthermore, ZrB 2 sintered with ZrSi 2 underwent severe peptization at 800 °C, raising questions as to its utility as a UHTC. It was also found that ZrB 2 sintered with MoSi 2 exhibits the best combination of contact-mechanical properties, being harder, stiffer, and more resistant to quasiplastic damage and radial cracking than ZrB 2 sintered with TaSi 2 or ZrSi 2 , as well as equally resistant to ring/cone cracking from ∼600 °C onwards. Implications of interest for the UHTC community are discussed.