E. Laarz et al / Journal of the European Ceramic Society 21(2001)1027-1035 1 Fig 9. SEM micrographs of thermally etched cross-sections parallel to the pressure direction of hot-pressed Al2Or-TiNnano composites (0.5 wt% PAA):(a)AlO3-5 vol TiNnano(the dark vertical line is a grain boundary between two large alumina grains); (b)Al2Ox-10 vol % TiNnano:(c) AO-20 vol %TIN systems, which can be used for preparation of composites 100% of the theoretical density was accomplished after with dense and homogeneous microstructures Compo- sintering. The homogeneity of Tic containing compo sites containing micron-sized TIN and TiC, nano-sized site microstructures was not affected by pH variations in TiN (30 nm mean size), TiC whiskers and Ti(C, N) the alkaline range during wet processing. For Al2O3 whiskers were investigated. By characterizing the sur- TiN composite materials, highly alkaline processing face chemistry of micron-sized TiN and Tic powders we conditions are preferred in order to prevent agglomera were able to define appropriate conditions for the wet- tion of TiN particulates. varying the content of Tinnano processing step. By first dispersing alumina with 0.5 revealed that there is an optimum concentration below wt% PAA and then adding the tiN or TiC phase, well which excessive alumina grain growth occurs whereas at dispersed and colloidally stable composite suspensions higher concentrations Tin particles tend to form with 20 vol. solids loading could be obtained. The agglomerates at the grain boundaries. The location of good colloidal stability relates to repulsive electrostatic the optimum concentration probably depends on the forces between the alumina particles with adsorbed hot pressing conditions. The role of processing para- PAA layers(pHien 3)and the TiN or TiC particles meters in the high-temperature densification step and (pHiep4.)at or above the inherent pH=9 of the sus- their influence on mechanical composite properties is pension. After freeze-granulation of the composite sus- the subject of ongoing investigations pension and freeze-drying of the granules, the organic content could be burned out by heating for 15 min at 600C in a graphite furnace Sintering was accomplished Acknowledgements in a hot-press furnace with flowing argon at 1700C and 28 MPa for 1.5 h. The assessment of composite micro- This work has been performed within the framework structures showed that the used processing scheme is of the Brinell Centre(thematic network"Ceramics and applicable to all investigated composite materials. In all nanocrystalline materials"and"The Brinell Centre- cases it is possible to obtain well-dispersed secondary Inorganic Interfacial Engineering). Financing by the TiN and TiC phases in the alumina matrix phase by Swedish Foundation for Strategic Research(SSF), the controlling suspension pH and added amount PAA. 98 Swedish National board for Industrial and Technical)                        2
         
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