Does flash sintering alter the deformation mechanisms of tungsten carbide?

Abstract

The study aims at unravelling the effect of fast and ultrafast electric current-assisted sintering on the plasticity of ultrahard binderless tungsten carbide. The small-scale deformation of polycrystalline micropillars obtained from samples consolidated by Spark Plasma Sintering (SPS) and Electrical Resistance Flash Sintering (ERFS) processes was studied. Micropillars, 3 µm in diameter, were prepared by focused ion beam and compressed ex and in-situ at room and high temperatures (700 °C). Electron-transparent lamellas were milled out from the pillars plastically deformed at different strain levels to carry out Transmission Kikuchi diffraction (TKD) and HRTEM analyses. At room temperature, the micropillars show similar mechanical responses under compression, reaching outstanding yield strengths (8–11 GPa) with plastic strain not exceeding 3–5% because of a dislocation-assisted toughening mechanism. At 700 °C, the pillar's yield strength drops to around 1.5–2 GPa accompanied by the relevant temperature-activated plasticity. However, only the pillars prepared from flash-sintered material can be homogeneously deformed up to ≈50%; conversely, those derived from SPS ceramics fail macroscopically at strains of ≈20–25% strain upon the localisation of plastic strain at shear bands.