Dislocation-grain boundary interactions in columnar aluminum

While the relatively straightforward classical theory of plasticity has been widely adopted as a first order approximation of material behavior during deformation, it has only been adequate in explaining very few of the observed plastic deformation phenomena. Previous studies at the sub-micron level have shown that the classical theory cannot predict the complex dislocation behavior that had been experimentally observed. Further, classical plasticity could not predict other observed phenomena that display size effects, since it does not account for length scales in any way.; In this thesis we set out to experimentally observe and connect geometrically necessary dislocation (GND) behavior near grain boundaries with the general predicted plastic behavior of the material, as well as the crystallographic geometry of the grain boundary. The crystallographic orientation field was measured near a set of high angle boundaries in a pseudo two-dimensional (columnar grained) Aluminum polycrystal that had been deformed in compression using automated electron backscatter diffraction, and the continuum theory of dislocations was applied in order to extract the GND densities. A study of the characterization method concluded that values of the GND densities were accurate to better than 5%.; Observation of spatial plots of the measured GND densities illustrated that only certain grains exhibited dislocation pileups at the grain boundaries. By linking portions of the orientation field near grain boundaries by means of rank correlations to both the slip systems predicted active and the local crystallographic compatibility between slip systems across the boundary, it was also observed that grains with large observed pileups near the grain boundary are those whose most active slip systems are the systems least favored to transmit through the grain boundary.; Lastly, by studying the average displacement vectors for fixed sizes of Burger's circuits in the measured orientation fields, it was seen that the net vector magnitudes were large for multiple circuit sizes in the grains that exhibited dislocation pileup behavior. This indicated that the length scales associated with plastic deformation cannot be assumed fixed for a given material or deformation stage, and may vary depending on the local crystallographic attributes.