Enhanced low temperature toughness of Al2O3-ZrO2 nano/nano composites

There are reports in the literature that dense nanocrystalline ceramics may be ductile at room temperature, leading to enhanced processibility and reliability. However, in spire of vigorous scientific and commercial developments in the field for the last decade, there is still controversy regarding enhanced low temperature toughness in dense ceramics with nanocrystalline grain size. This is due to lack of control over static and dynamic grain growth at high sintering temperatures as well as proper testing methods. In this paper we report that it is possible to obtain enhanced room temperature toughness in dense Al2O3-ZrO2 nano/nano composites without any contribution from phase transformation toughening. Nano/nano in situ mixed composite powders in the Al2O3-ZrO2 binary system were produced with a homogeneous distribution of the two phases utilizing the ''Combustion Synthesis'' or ''Auto Ignition'' process. The microstructure was stable even at a temperature of 1200 degrees C because of the homogeneous distribution of two phases. Therefore, the powders could be hot isostatically pressed at that temperature to 98% of the theoretical density. The average room temperature hardness value was 4.45 GPa, which is one quarter of the value of a comparable conventional material. The average toughness value, as determined using the indentation method, was 8.38 Mpa.m(1/2). Since we could not detect any evidence of phase transformation in ZrO2, the present results are interpreted as evidence of enhanced ductility. In view of these results, it is believed that in some nanoceramics, it may be possible to have enhanced toughness at the room temperature. (C) 1997 Acta Metallurgica Inc.