M. Orolínová’s research while affiliated with Slovak Academy of Sciences and other places

Nanocrystalline (nc) Cu powders with Al2O3 dispersoid (1-5 vol.% Al2O3) were prepared by combination of phase transformations with intensive milling and the following consolidation by pressing, sintering and hot extrusion. The electrical properties of the composites were analysed in relation to their microstructure and strength. The main contribution to the electrical resistivity was attributed to the grain/crystallite size of Cu matrix. The fraction of Fe impurities dissolved within the Cu matrix and the amount of Al2O3 particles in the Cu matrix affected the electrical resistivity remarkably. The optimal combination of electrical and strength properties can be achieved by cut-down of Al2O3 content and by optimization of dispersoid distribution in the matrix. © Institute of Materials and Machine Mechanics, Slovak Academy of Sciences, Bratislava, Slovak Republic.

Nanocrystalline (nc) Cu materials with Al2O3 dispersoid (1 and 5 vol.% Al2O3) were produced using the powder metallurgy (PM) techniques. The effect of reinforcement weight fraction, deformation temperature and annealing temperature (up to 800 C) on the strength properties and the microstructure was studied. Two strengthening mechanisms were considered at room temperature, strengthening by grain refinements and dispersion strengthening (DS). The strength properties of both nc Cu composites were strongly dependent on deformation temperature and material composition. The main contribution of nanometric Al2O3 particles to the strength of composites at elevated temperatures is probably the strong pinning effect on the grain/crystallite boundaries and preventing of recrystallization process. After annealing at 0.74 T-m both composites were characterized by an excellent stability of strength characteristics.

The objective of this work is study of the adsorption properties of magnetic clay composite under the ultrasound irradiation. First, the structural properties of the composite were characterized by X-ray diffraction method and Mössbauer spectroscopy. For the adsorption experiments, cadmium, as a heavy metal ion, was selected. The adsorption has been studied by a batch method using an ultrasound device and rotary shaker. The composite adsorption properties have been tested under different conditions such as pH of the solution, contact time, initial metal ions concentration and temperature. The sonication markedly influenced the adsorption properties of composite, the increase of the maximum adsorption capacity (about 35 %) was observed in comparison with the conventional method. No evident effect of temperature on the adsorption capacity of composite was proved. The maximum adsorption capacity at 298 K, 323 K and 343 K, calculated from the linearized Langmuir model, was 96, 99 and 100 mg Cd 2+ g-1 , respectively.

The study is focused on the microstructure and texture evolution in pure aluminium (prepared by the conventional casting technology) in comparison with the dispersion strengthened system Al-4vol.%Al4C3(prepared by the powder metallurgy method) during the ECAP deformation. The ECAP process of the pure aluminium led to the dislocation cell and subsequent subgrain structure formation with a mean subgrain of 2 µm. An application of ECAP method in the powdered alloy led to the transversal fragmentation of as-received elongated grains and mainly nanosized grains formation. The final size of the grains was approximately 100 nm. Pure aluminium after the ECAP contained a similar, but stronger, crystal orientation as-received Al (200) and in addition Al (311) orientation. In composite aluminium material the as-received Al (111) after the ECAP evolved into the dominating crystal orientation Al (220). K e y w o r d s : aluminium, dispersion strengthened Al, microstructure, texture, ECAP

The study investigates the influence of different fractions of particles (1, 2.5, 5, 8 and 10 vol.%) on microstructure of the as-extruded Al–Al4C3 composite as well as on the microstructure evolution at elevated temperatures and after cooling to room temperature. The results indicate that all the materials exhibit a stable microstructure up to 500 °C. The excellent thermal stability is secured by the dispersed nano-particles that strengthen crystallite/grain boundaries by direct interaction of the particles with moving dislocations. In addition, the higher particle contents (8 and 10 vol.%) help to suppress the deformation texture of the hot extruded solids and refine the matrix microstructure to a nanometric scale resulting in a marked enhancing of dislocation density and consequently hardness.

The aim of this study was to provide an insight into the texture formation during an extrusion process (at two different extrusion conditions) and into the texture evolution at thermal loading in temperature range from 298 K to 773 K and after cooling to ambient temperature. The texture was measured "in situ" by X-ray diffraction technique. The extrusion had induced the aluminium texture in both experimental AlSi26Ni8 alloys. Consequently the dominated crystal orientation in the radial direction was Al (111) and in the axial direction Al (110). This texture mode remained unchanged to the temperature 773 K as well as after cooling to ambient temperature. In this work it was undertaken to analyse the microstructure evolution from the AlSi28Ni6 powder particles to extruded bars in the view of the texture formation.

Microstructure of the dispersion strengthened aluminium compacts prepared by powder metallurgy technique consists of fine-grained matrix strengthened by dispersed nanometric ceramic particles. The study compares microstructural evolution of the as-extruded Al-Al4C3., materials containing 1 and 12 vol. % of Al4C3 at a temperature range from 293 to 773 K and after cooling to the room temperature. The results indicate that both materials exhibit a stable microstructure up to 773 K. The Al-12 vol. % Al4C3 compact shows finer microstructure than Al-1 vol. % Al4C3 resulting in markedly higher hardness and tensile strength.