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

TaB2-based ceramics were hot pressed in low vacuum with addition of 5-10vol% MoSi2. Temperatures in the range of 1680-1780°C led to relative density around 90-95%. The hardness was about 18GPa, the fracture toughness 4.6 MPam1/2 and the room temperature flexural strength was around 630MPa, but abruptly decreased above 1200°C to 220MPa. The composite containing 10vol% of MoSi2 was tested in a bottom-up furnace in the temperature range 1200-1700°C for 30min. 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.