Grain growth in ultrafine grained aluminium processed by hydrostatic extrusion
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Ultrafine grained materials can be produced by a number of techniques among which one can distinguish hydrostatic extrusion. In aluminium, this method can be used to obtain a structure with the grain size of 300 nm and high fraction of HAGBs (more than 70%). During annealing this structure undergoes significant changes which were evaluated quantitatively. Annealing for 1 h at temperatures up to 200 °C results in normal grain growth whereas at higher temperatures or for longer annealing times a transition from normal to abnormal growth is observed. The activation energy for low temperature regime is 43 kJ/mol whereas for high temperature annealing—128 kJ/mol. The former corresponds to grain boundary diffusion whereas the latter is close to activation energy of self diffusion in aluminium. The change in activation energy well corresponds to the transition in grain growth mechanism from normal to abnormal.
KeywordsSevere Plastic Deformation Boundary Diffusion Equal Channel Angular Pressing Misorientation Angle Accumulative Roll Bonding
This work was supported by Polish Ministry of Science and Higher Education (Grant No 3 T08A 06430). Hydrostatic extrusion experiment was carried out at the Institute of High Pressure Physics of Polish Academy of Sciences which is gratefully acknowledged.
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