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This study showed pronounced changes in the Raman scattering of silicon powder during high-energy ball milling. The powders were milled for 1–18 h in a steel ball mill in argon. The approximate pressure imposed on particles was 2 GPa. The spectra of the as-milled powders were compared with the initial silicon. It was found from the Raman peak position shifts that milling generated strains in the silicon lattice, bringing about a transformation of cubic silicon to tetragonal silicon and amorphization. The relative amount of new phases was determined from the area under the measured Raman peaks.

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.

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