TaB_2-based ceramics: Microstructure, mechanical properties and oxidation resistance

摘要

TaB2-based ceramics were hot pressed in low vacuum with addition of 5-10 vol% MoSi_2- 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 MPam~(1/2) and the room temperature fiexural strength was around 630 MPa, but abruptly decreased above 1200 °C to 220 MPa. The composite containing 10vol% of MoSi_2 was tested in a bottom-up furnace in the temperature range 1200-1700 °C for 30 min. The microstructure appeared covered by a SiO_2 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.