Microstructural refinement of ceramic powders under mechanical processing conditions

The present work discusses the preparation of nanostructured ceramics by mechanical processing. Coarse-grained powders of different oxides, carbides, borides and silicides have been subjected to mechanical treatment inside a commercial ball mill under controlled experimental conditions. Ceramic powders underwent a microstructural refinement process down to the nanometer range, accompanied by the accumulation of structural disorder. The analysis of X-ray diffraction patterns according to the Rietveld method permitted the estimation of both the average crystallite size and strain content as a function of the milling time. Opposite trends are observed, the decrease of the crystallite size being paralleled by the increase of the strain content. The processes of crystallite size decrease and strain accumulation were then phenomenologically characterized in terms of apparent rate constants and asymptotic final values of crystallite size and strain. It has been thus possible to point out an intimate connection between the processes of crystallite size decrease and strain accumulation.