Processing, microstructure and mechanical properties of Al2O3–Cr nanocomposites

Alumina–chromium composites are well known for their good mechanical properties in comparison with pure alumina or metals. The composites have high hardness, high mechanical strength and because of their strong resistance to abrupt changes of temperature within the 25–1300 °C range or high temperature resistance to oxidation, they can be used at temperatures exceeding 1000 °C. Most of earlier works tended to use particles in the micrometer range. In this work, Al2O3–Cr nanocomposites with 25, 50 and 75 vol.% Cr were made by pressureless sintering and hot pressing of aluminium oxide nanopowder (∼80 nm) and chromium particles in the micrometer range. The presented paper concerns the examination of the microstructure and mechanical properties (hardness, bending strength, wear resistance) of Al2O3–Cr nanocomposites. The microstructural examinations (optical, scanning and transmission microscopy) show that almost fully dense materials can be obtained (typically 98–99% of theoretical density), when pressureless sintering at 1600 °C or hot pressing at 1400 °C. Moreover, the sintering process did not cause any major changes in the structure of the composite, although it was stated significant growth of the Al2O3 nanograins.