Extraordinary high-temperature mechanical properties in binder-free nanopolycrystalline WC ceramic

Abstract

• The binder-free nanopolycrystalline WC ceramic with an average grain size of 103 nm was fabricated through high-pressure sintering. • The binder-free nanopolycrystalline WC ceramic exhibits excellent mechanical properties at both room temperature and high temperature up to 1000 °C. • Ultrahigh hardness at 1000 °C is mainly from the nanocrystalline microstructure and numerous low-energy, highly stable Σ2 grain boundaries. From the perspective of high-temperature applications, materials with excellent high-temperature mechanical properties are always desirable. The present work demonstrates that the binder-free nanopolycrystalline WC ceramic with an average grain size of 103 nm obtained by high-pressure and high-temperature sintering exhibits excellent mechanical properties at both room temperature and high temperature up to 1000 °C. Specifically, the binder-free nanopolycrystalline WC ceramic still maintains a considerably high Vicker hardness H V of 23.4 GPa at 1000 °C, which is only 22% lower than the room temperature H V . This outstanding thermo-mechanical stability is superior to that of typical technical ceramics, e.g. SiC, Si 3 N 4 , Al 2 O 3 , etc. Nanocrystalline grains with many dislocations, numerous low-energy, highly stable Σ2 grain boundaries, and a relatively low thermal expansion coefficient, are responsible for the observed outstanding high-temperature mechanical properties.