Ceramic processing of nanometric powders obtained by reactive milling

The conventional sintering of nanometric powders compacts is one of the simpler routes to produce ceramic matrix nanocomposites. The reactive milling is one interesting alternative synthesis process for nanocomposites precursor powders. In reactive milling, the reaction in a powder mixture is mechanically activated by high-energy milling producing single or mixed (including ceramic-ceramic) compounds materials. The high-energy milled powders products present some peculiar characteristics, particularly the presence of strong agglomerates. Depending on materials properties such as hardness and toughness, these reaction products also present very small crystallite size, high deformation and high density of crystalline defects, partial or total amorphization, and high specific surface area. Most of these characteristics are troublesome in ceramic processing. In the present work, we report on the reactive milling synthesis and subsequent ceramic processing of powders mixtures aiming the production of alumina matrix nanocomposites with inclusions of TiC, TiB2, NbC, Nb and Ni3Al. The precursor powders were synthesized as strong agglomerates with nanometric crystallite size. The introduction of additional high-energy milling after reaction and conventional ball or planetary milling was considered as a necessary processing step for better dispersion of the powders and homogeneous inclusions distribution in the alumina matrix. It is also discussed the behavior and microstructural evolution during pressureless sintering of the powder compacts of different compositions.