Processing of high hardness-high toughness alumina matrix nanocomposites

Ceramic-matrix composites with nanocrystalline (grain size less than ∼100 nm) matrix provide new opportunities, both scientific and technological. Fully dense nanocrystalline alumina matrix composites with grain size as fine as 40 nm has been synthesized. The results show significantly higher hardness and toughness in nanocomposites. The hardness values of fully dense nanocrystalline Al2O3-10 vol.% Nb composite range from 20 to 23 GPa. The indentation toughness of Al2O3-10 vol.% Nb sintered at 900°C and 2 GPa for 60 min is >8 MPa m1/2. The present results show an increase in fracture toughness by more than 250% while retaining the hardness as compared with microcrystalline single-phase alumina.