Modeling High-Energy Ball Milling in the Alumina-Yttria System

Experimental results from high-energy ball milling of alumina-yttria powder mixtures have been analyzed with models collected from the literature. Depending on the milling conditions, either there is formation of an intermediate phase in the alumina-yttria system (yttrium aluminum perovskite, YAP), or the sample becomes mostly amorphous. Variations due to milling tool material can be accounted for by local models based on the Hertzian theory of elastic bodies, but the effects of changing mills are poorly accounted for by published models. Therefore, the concept of an impact frequency distribution over the energy spectrum is introduced as a tool for studying the characteristics of the mills. The pressure on the powder trapped between two colliding bodies has been found to be the factor deciding the outcome of the process. The threshold behavior of the system yields an amorphous structure for low pressures, and formation of YAP when impact pressures exceed the threshold value.