Transparent Alumina Nanoceramics Prepared under High Pressure and Low Temperature

Abstract

A transparent alumina ceramic with a transmittance of 71.7% at 640 nm is fabricated by sintering mixed metastable Al2O3 powder at 5.0 GPa/600 °C. The spherical starting particles are deformed and highly densified during compression, and transformed into α‐Al2O3 at 5.0 GPa/500 °C. High pressure suppresses the growth of transformed grains to produce alumina bulks with an average grain size of approximately 52 nm at 600 °C. In addition, the Hall–Petch effects combined with the pressure‐induced curvilinear grain boundary and Moiré fringe‐like defects enhance the transparent alumina sample to yield a Vickers hardness of 26.4 GPa (0.5 kgf). However, these microstructures do not enhance the fracture toughness of the transparent alumina ceramics.