Mária Orolínová

Preparation and microstructure evolution of nanocomposite powder copper

The paper is aimed at preparing the nanocrystalline Cu-Al2O3 and Cu-MgO powders with 1-10 vol.% of the dispersoid by a combination of mechanical milling and phase precursor transformations. The secondary particles were prepared in situ within CuO powder. The nanometric Cu matrix was obtained by different reduction methods of the CuO precursor. The influence of dispersoid quantity and different technological parameters on the Cu microstructure was estimated. The study compares the microstructural evolution of Cu-3 vol.% MgO and Cu-3 vol.% Al2O3 composites. The effects of both oxides on the preservation of the initial powder nanostructure after consolidation and the thermal structural stability, as well as the tensile properties, are analysed. The results indicate that an alumina dispersoid is more suitable for nanostructure stabilisation of a Cu matrix compared to an MgO one, due to good coherency at the Cu/Al2O3interface.

Structural Analysis of Dispersion Strengthened Materials and Processes

Dispersion strengthened materials are characterized by high strength properties and good temperature stability of structure until to temperatures of 0.9 melting temperature of aluminium. Dispersion strengthened Al A14C3 materials are prepared by powder metallurgy way and the raw powder mixtures are generally consolidated by hot extrusion obtaining a fully dense material. This work is focused on a study of the microstructure in AI A14C3 materials containing 4 and 12 vol. % A14C3. The microstructure was analyzed by transmission electron microscopy and X-ray diffraction methods. The several microstructural features: morphology, size and distribution of particles of dispersoid, grain size and crystallite size of aluminium matrix, micro strain and dislocations density in materials were determined. The aim is an analysis of the effect of A14C3 amount on the microstructure formation during hot extrusion and analysis of the microstructure evolution at temperature loading and after cooling to ambient temperature. After hot extrusion the Al 12 vol. % A14C3 alloy is characterized by finer grains, higher micro strain and dislocations density and by a very low intensity of aluminium matrix deformation texture in comparison to Al 4 vol. % A14C3 material. In the hot extruded system with 4 vol. % A14C3 a strong deformation texture was observed. Therefore the amount of dispersoid strongly affects the formation of microstructures. The higher volume of A14C3 particles provides effective hindrance of the dislocations motion in Al matrix by the attractive interaction between dislocations and particles during extrusion. Both amounta of A14C3 dispersoid insure the thermal stability of microstructure of analyzed materials to 773 K.

Microstructure Analysis of Carbonization Kinetics of Al-C System

Dispersion strengthened aluminium compacts have been prepared by powder metallurgy. Microstructure is based on the aluminium matrix strengthened with dispersed A14C3 particles. The strengthening is direct by dislocation movement retardation, and indirect by deformation induced microstructure modification in the next technological steps. The method of mechanical alloying process is described. Carbon transformation to carbide A14C3 can be characterised with different heat treatment schedules and nine different types of commercial carbon powders.