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Abstract: A detailed investigation of the microstructure and mechanical properties has been conducted in pure nickel deformed to high strains using accumulative roll bonding (ARB). Samples have been investigated after different numbers of ARB cycles and the results have been compared with data for nickel processed by other deformation techniques, with particular focus on conventional rolling. It is found that the structural evolution in ARB-processed nickel is rapid at low strains followed by a slower evolution as the strain approaches ultrahigh levels. Comparing samples processed by ARB and by conventional rolling to an identical nominal strain, the microstructure after ARB is more refined and contains a greater fraction of high angle boundaries. This enhanced refinement is attributed to the geometric accumulation of shear-strain influenced volumes as a result of the ARB process and large-draught rolling conditions. Based on the observations, it is suggested that the key strengthening mechanisms in deformed nickel are grain boundary and dislocation boundary strengthening, and that the strength–microstructure relationship can be expressed by a single parameter equation: σ−σ 0=k 2 d av −0.5, where k 2 is a constant and d av is the average boundary spacing in the deformed microstructure. [Copyright &y& Elsevier]

Abstract: Samples of the magnesium alloy AZ31 have been deformed by compression to strains of 5% and 10% and microstructural observations made to investigate the activation of specific extension twin variants. The twinning has been analyzed on a grain-by-grain basis for more than 260 grains to determine both the number of extension twin variants in each grain, and the volume fraction of each. At 5% strain approx. 30% of the grains contain twins corresponding to variants with the third or lower ranked Schmid factor, with the fraction increasing to 40% after 10% compression. A grain size effect is also observed in that smaller grains are less likely to contain lower ranked twin variants. For both 5% and 10% compression no clear relationship exists between the volume fraction of each twin variant in a given grain population and the Schmid factor for the twin variant. A positive linear relationship can be defined, however, between the maximum twinning fraction that a twin variant can reach and its Schmid factor. [Copyright &y& Elsevier]

Abstract: The twinning and slip system activities during compression testing at room temperature and 150°C have been investigated for an AZ31 magnesium alloy. The samples, which were cut from a rolled sheet, were compressed with the compression axis taken at different angles to the sheet normal direction. The electron backscatter diffraction technique in the scanning electron microscope was used to investigate the local texture and microstructure evolution. The plastic deformation of magnesium is controlled by both twinning and slip during deformation. Extensive twinning takes place when the sample is loaded perpendicular to the basal plane normals (BPNs). A high work-hardening rate, with very little twinning, is observed for samples loaded parallel to the BPNs. The main features of the stress–strain curves can be explained based on the microstructural and texture data. [Copyright &y& Elsevier]

Abstract: The relationship between crystallographic orientation and the deformation microstructure formed during cold-rolling to high strains (up to ɛ vM =4.5) has been investigated. The starting material was Ni (99.96% purity) with a coarse initial average grain size (approximately 500μm). Microstructural characterization was carried out using a combination of electron channeling contrast imaging and electron back-scatter diffraction orientation mapping. An orientation dependence of the deformation microstructure was observed even at the highest strain examined. A large increase in the average boundary misorientation is found at strains above ɛ vM =1.8 for regions with the {112}〈111〉 and {123}〈634〉 orientations. This increase accompanies the structural transition from a medium strain microstructure to a high strain lamellar microstructure. In contrast, the average misorientation in regions of {110}〈112〉 orientation increases only slowly even up to the highest strain examined. [Copyright &y& Elsevier]

Commercial purity aluminum (99.5%) was fabricated by equal channel angular pressing (ECAP) up to total accumulated strains of approx. 10. The annealing behavior of material deformed to total strains of approx. 1 and 10 was investigated, using heat treatments of 2 h at various temperatures from 100 to 500 °C. The microstructure of the annealed materials was characterized using the electron back-scatter pattern technique. A number of parameters were determined including the distribution and average values of both the boundary spacings and misorientations. For samples deformed to a total strain of 1, annealing resulted in discontinuous recrystallization. For samples deformed to a total strain of 10, annealing resulted in microstructures exhibiting characteristics of both uniform coarsening and, in a number of places, of discontinuous recrystallization. An attempt was made, based on the boundary spacing distributions, to separate these two components. The grain size after annealing was still however small, being just 6.4 μm after 2 h at 300 °C. [Copyright &y& Elsevier]