Influence of grain size in the near-micrometre regime on the deformation microstructure in aluminium

The effect of grain size on deformation microstructure formation in the near-micrometre grain size regime has been studied using samples of aluminium prepared using a spark plasma sintering technique. Samples in a fully recrystallized grain condition with average grain sizes ranging from 5.2 to 0.8 mu m have been prepared using this technique. Examination in the transmission electron microscope of these samples after compression at room temperature to approximately 20% reduction reveals that grains larger than 7 gm are subdivided by cell block boundaries similar to those observed in coarse-grained samples, with a similar dependency on the crystallographic orientation of the grains. With decreasing grain size down to approx. 1 mu m there is a gradual transition from cell block structures to cell structures. At even smaller grain sizes of down to approx. 0.5 mu m the dominant features are dislocation bundles and random dislocations, although at a larger compressive strain of 30% dislocation rotation boundaries may also be found in the interior of grains of this size. A standard < 1 1 0 > fibre texture is found for all grain sizes, with a decreasing sharpness with decreasing grain size. The structural transitions with decreasing grain size are discussed based on the general principles of grain subdivision by deformation-induced dislocation boundaries and of low-energy dislocation structures as applied to the not hitherto explored near-micrometre grain size regime. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.