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The evolution of microstructure and microhardness was studied in a commercial 5483Al-5Mg alloy processed by high pressure torsion (HPT) under a pressure of 6.0 GPa up to 10 turns. Significant grain size refinement was observed even after 1/4 turn and additional processing led to a further grain size reduction and a shift in the distribution of grain boundary misorientation angles towards higher values.An essentially fully homogeneous microstructure was reached after 10 turns with a final grain size of ~70 nm, a saturation Vickers microhardness of Hv  240 which was attained at and above equivalent strains of ~150, a relatively narrow grain size distribution and a fraction of ~80% of high-angle grain boundaries. Analysis shows the Hall-Petch plot deviates from the conventional linear relationship for samples processed through small numbers of turns but after 3 or more turns there is a direct correlation between the results obtained in HPT processing and coarsegrained samples.

The aim of this work was to investigate the influence of different types of carbon filler on the thermal stability and flammability of rigid polyurethane foams. As a filler, multi-walled carbon nanotubes and graphite fakes were used. Scanning electron microscopy was used to observe the structure of foam and dispersion of nanofiller in polymer matrix. Thermal stability of these composites was determined by thermogravimetry analysis. Test was carried out under both nitrogen and air atmosphere. The degradation products were evaluated by thermogravimetry (TG) combined with infrared spectroscopy (TG-IR) measurements. The activation energy was measured by the Flynn-Wall-Ozawa method from the TG curves. Flammability tests like limiting oxygen index and smoke density were also measured. No significant changes in the thermal stability of the composites were observed. The activation energy of sample containing carbon filler increased. Based on TG-IR, one can notice that there were no differences in the emitted volatile products during thermal degradation. Carbon filler enhanced fire retardancy of polyurethane foam; however, graphite gives better results.

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