TaB2-based ceramics: Microstructure, mechanical properties and oxidation resistance

TaB2-based ceramics were hot pressed in low vacuum with addition of 5–10 vol% MoSi2. Temperatures in the range of 1680–1780 °C led to relative density around 90–95%. The hardness was about 18 GPa, the fracture toughness 4.6 MPa m1/2 and the room temperature flexural strength was around 630 MPa, but abruptly decreased above 1200 °C to 220 MPa. The composite containing 10 vol% of MoSi2 was tested in a bottom-up furnace in the temperature range 1200–1700 °C for 30 min. The microstructure appeared covered by a SiO2 layer, whose thickness increased with the temperature, but the bulk remained unaltered up to 1600 °C. At 1700 °C the specimen vaporized. Nanoindentation was employed on the oxidized cross sections in order to detect eventual mechanical properties modification associated to chemical/microstructural change, like formation of Ta–B–O solid solutions.