Doctor of Philosophy
Department of Materials Engineering
Stanford, Nicole, Effect of microstructural stability on the annealing behaviour of deformed aluminium single crystal, Doctor of Philosophy thesis, Department of Materials Engineering, University of Wollongong, 2002. http://ro.uow.edu.au/theses/1491
High purity aluminium single crystals of the Cube orientation (001), and a 45° rotated Cube orientation, (011)[01 1 ], have been deformed in plane strain compression. Deformation was carried out between room temperature and 600°C, over a range of strains, and at strain rates of up to 50 s-1. These deformed crystals were subsequently annealed in a muffle furnace for various times between 200°C and 400°C. The main objective was to compare texture development and structural evolution in the two crystal orientations in response to hot and cold deformation and subsequent annealing
The room temperature deformation behaviour of the Cube oriented crystals over strains of 0.06 to 1.2 was investigated by slip line analysis using atomic force microscopy (AFM). AFM was used to investigate quantitatively the development of slip lines and deformation bands at strains as low as 0.2. At the higher strains of 0.7 and 1.2 the mechanisms of deformation were analysed crystallographically using electron backscattered diffraction (EBSD), microstructurally using scanning electron microscopy and topographically using AFM. Coupling of these three techniques has demonstrated the irregular and localised nature of deformation at transition bands in deformed Cube oriented crystals.
For both the Cube and rotated Cube orientations, the deformation texture was investigated using EBSD and x-ray diffraction. The Cube orientation was found to increase in microstructural stability at higher deformation temperatures. However, the rotated Cube orientation was found to become less stable at higher deformation temperatures, a novel observation for aluminium and its dilute alloys
Hot deformation and annealing of crystals of the (01I) orientation produced a uniquely banded recrystallisation microstructure. Regularly spaced recrystallised grains grow within distinct bands confined between parallel regions of recovered subgrains. The subgrains are in fact contained within cylindrical or lath shaped volumes, and these volumes are not random, but are regularly spaced into an array. Even after full recrystallisation, the microstructure retained this banded appearance.
It is proposed that these banded microstructures are caused by periodic nucleation of recrystallisation, resulting from stored energy differentials present in the as-deformed microstructure. On annealing, nucleation of recrystallisation occurs in regularly spaced columns, but grain growth toward adjacent columns is inhibited by impingement with volumes of recovered subgrains, producing the banded microstructures that were observed. The small stored energy difference between the recrystallised grains and the volumes of recovered subgrains is considered to impede the completion of recrystallisation, and to result in the unusual banded microstructures found in hot deformed and annealed (011) crystals.
Deformation temperature was found to have a significant effect on recrystallisation texture. Annealing after cold deformation of the Cube orientation resulted in a random recrystallisation texture at all strains. Cold deformation and annealing of the (011) orientation produced a random texture at low strains, and at higher strains produced a recrystallisation texture lying at the periphery of the deformation texture. In contrast, annealing after hot deformation produced a recrystallisation texture close to the deformation texture, irrespective of microstructural stability, strain, or crystallographic orientation.