Al2O3-SiC composites prepared by warm pressing and sintering of an organosilicon polymer-coated alumina powder

Al2O3/SiC micro/nano composites were prepared by axial pressing of poly(allyl)carbosilane-coated submicrometre alumina powder at elevated temperature (called also warm pressing, or plastic forming) with subsequent pressureless sintering in the temperature interval between 1700 and 1850 degrees C. Warm pressing at 350 degrees C and 50 MPa resulted in green bodies with high mechanical strength and with markedly higher density than in green bodies prepared by cold isostatic pressing of the same powder at 1000MPa. The sintering of warm pressed specimens moreover yielded the composites with higher final density (less than 4% of residual porosity) with the microstructure composed of micrometer-sized alumina grains (D-50 < 2 mu m) with inter- and intragranular SiC precipitates. High sintering temperatures (> 1800 degrees C) promoted the formation of intergranular platelets identified by TEM as 6H polytype of alpha-SiC. The maximum hardness (19.4 +/- 0.5 GPa) and fracture toughness (4.8 +/- 0.1 MPa m(1/2)) were achieved in the composites containing 8 vol.% of SiC, and sintered for 3 h at 1850 degrees C. These values are within the limits reported for nanocomposites Al2O3/SiC by other authors and do not represent any significant improvement in comparison to monolithic alumina. (c) 2006 Elsevier Ltd. All rights reserved.