Distorted crystals carry useful information on processes involved in their formation, deformation and growth. The distortions are accommodated by geometrically necessary dislocations, and therefore characterising those dislocations is an informative task, to assist in, for example, deducing the slip systems that produced the dislocations. Electron Backscatter Diffraction (EBSD) allows detailed quantification of distorted crystal orientations and we summarise here a method for extracting information on dislocations from such data. The Weighted Burgers Vector (WBV) method calculates a vector at each point on an EBSD map, or an average over a region. The vector is a weighted average of the Burgers vectors of dislocation lines intersecting the map surface. It is weighted towards dislocation lines at a high angle to the map but that can be accounted for in interpretation. The method is fast and does not involve specific assumptions about dislocation types. It can be used, with care, to analyse subgrain walls (sharp orientation changes) as well as gradational orientation changes within individual grains. We describe new and published examples of the use of the technique to illustrate its potential; case studies to date mainly use the WBV direction not the magnitude. EBSD orientation data have angular errors, and so does the WBV. We present an analysis of these angular errors, showing there is a trade-off between directional accuracy and area sampled. In summary the technique is fast, free from assumptions, and errors can be taken into account to allow testing of hypotheses about dislocation types.

Seismic observations of the Earth’s inner-core testify to it being both a complex and dynamic part of the Earth. It exhibits significant variation in seismic attenuation and velocity with position, depth and direction. Interpretation of which is difficult without knowledge of the anelastic processes active in the inner-core is difficult. To address this, we used zinc, a low-pressure analogue of the hexagonal close pack (hcp) structured iron that forms the inner-core, to provide first-order constraints on the anelasticity of hcp-metals at high pressure, seismic frequencies (∼0.003-0.1Hz), homologous temperatures (T/Tm) up to ∼0.8. Measurements were made in a deformation-DIA combined with X-radiography. The data was analysed using an improved image processing method that reduces systematic errors and improves strain measurement precision by up to 3 orders of magnitude. Using this algorithm significant dissipation and softening of zinc’s Young’s modulus is observed. The softening occurs in the absence of significant impurities or a fluid phase and is caused by grain boundary sliding coupled with dynamic recrystallisation.The recrystallisation results in a steady-state grain-size and low dislocation density. A softened Young’s modulus predicts a reduction in shear wave speed 2-3 times greater than that for compressional waves, which is consistent with anelasticity playing a significant role in the seismic velocity of the inner-core. Comparison of elastic wave speeds from experimental or computed material properties with anelastically-retarded inner-core seismic velocities will tend to over-estimate the light element budget of the inner-core. Therefore anelastic effects in hcp-iron must be considered in the interpretation of the inner-core.

Strain weakening during plastic deformation can be achieved via strain energy reduction due to intragranular boundary development and grain boundary formation. To examine intragranular boundary formation at high temperatures (Th≈0.9), we analysed electron backscatter diffraction (EBSD) data of coarse-grained ice deformed at -30°C. Misorientation and weighted Burgers vector (WBV) statistics were calculated along planar intragranular boundaries. Neighbour-pair and random-pair misorientation distributions intersect at misorientation angles of 10–30°, indicating an upper limit to the misorientation threshold angle at which neighbouring grains begin to interact, e.g., rotate relative to each other. Misorientation angles change markedly along each analysed intragranular boundary, linking low- (<10°) and high-angle (10–38°) segments, with each segment exhibiting distinct misorientation axes and WBV directions. We suggest that these boundaries might be produced by the growth and intersection of individual boundary segments comprised of dislocations with distinct slip systems. This new kinematic model does not require a change in the boundary geometry after its formation, as required by the other models, to modify the crystallographic geometry of a planar boundary. Misorientation axis distributions are fundamentally different between intragranular boundaries (mostly confined to the ice basal plane) and grain boundaries (largely dispersed). This observation suggests a strong crystallographic control of intragranular boundary development via subgrain rotation. The apparent lack of crystallographic control for grain boundaries, on the other hand, suggests that misorientation axes become randomized upon grain boundary formation, likely due to the operation of other mechanisms/processes that can modify misorientation axes.