Processing and mechanical properties of Al2O3–5 vol.% Cr nanocomposites

The use of chromium (III) acetylacetonate as a source of nanometre sized chromium particles for the production of Al2O3–5 vol.% Cr nanocomposites has been investigated. The details of the processing procedure are crucial in determining the mechanical properties of the composite. The highest strength and fracture toughness, 736±29 MPa and 4.0±0.2 MPa m1/2, respectively, were obtained for the nanocomposite hot pressed at 1450 °C. It is shown that the strengthening in Al2O3–5% Cr nanocomposites mainly results from microstructure refinement in that the mean alumina matrix grain size in the optimum composite was 0.68 μm compared with a grain size of 3.6 μm in the monolithic alumina hot pressed under identical conditions. Crack bridging and crack deflection by the nano-sized Cr particles did not occur to any significant extent. The slight improvement in fracture toughness may result from the observed change in fracture mode from intergranular fracture for monolithic alumina to transgranular failure for the nanocomposites.