Grain Size Dependence of Hardness in Dense Submicrometer Al2O3

Pressureless sintered alumina compacts with a submicron microstructure exhibit a hardness that approaches or even exceeds the level of advanced hot-pressed composites of Al2O3 plus 35 vol-percent TiC, whereas the strength of both ceramics is approximately the same. The combination of reduced dislocation mobility (due to the small grain size), high density and density homogeneity are the prerequisites for the surprisingly high hardness. Quasi-conventional powder processing is used to produce these outstanding alumina bodies.