Grain Size Dependence of Hardness in Dense Submicrometer Alumina

Pressureless sintered alumina compacts with a submicrometer microstructure exhibit a hardness that approaches or even exceeds the level of advanced hotpressed composites of Al₂O₃+ 35 vol% 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. Quasiconventional powder processing is used to produce these outstanding alumina bodies.