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Abstract Dislocations, linear defects in a crystalline lattice characterized by their slip systems, can provide a record of grain internal deformation. Comprehensive examination of this record has been limited by intrinsic limitations of the observational methods. Transmission electron microscopy reveals individual dislocations, but images only a few square$$\upmu$$ m of sample. Oxidative decoration requires involved sample preparation and has uncertainties in detection of all dislocations and their types. The possibility of mapping dislocation density and slip systems by conventional (Hough-transform based) EBSD is investigated here with naturally and experimentally deformed San Carlos olivine single crystals. Geometry and dislocation structures of crystals deformed in orientations designed to activate particular slip systems were previously analyzed by TEM and oxidative decoration. A curvature tensor is calculated from changes in orientation of the crystal lattice, which is inverted to calculate density of geometrically necessary dislocations with the Matlab Toolbox MTEX. Densities of individual dislocation types along with misorientation axes are compared to orientation change measured on the deformed crystals. After filtering (denoising), noise floor and calculated dislocation densities are comparable to those reported from high resolution EBSD mapping. For samples deformed in [110]c and [011]c orientations EBSD mapping confirms [100](010) and [001](010), respectively, as the dominant slip systems. EBSD mapping thus enables relatively efficient observation of dislocation structures associated with intracrystalline deformation, both distributed, and localized at sub-boundaries, over substantially larger areas than has previously been possible. This will enable mapping of dislocation structures in both naturally and experimentally deformed polycrystals, with potentially new insights into deformation processes in Earth’s upper mantle.
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Localized Defects in Cold Die-Compacted Metal Powders
In powder metallurgy (PM), the compaction step is fundamental to determining the final properties of the sintered components. The deformation and defectiveness introduced in the powder material during uniaxial die compaction can be correlated to the activation and enhancement of the dislocation pipe diffusion, a lattice diffusion mechanism during the sintering process. Its coefficient depends on the dislocation density. The powder particles are mostly deformed along the direction of the compaction (longitudinal direction) rather than along the compaction plane; consequently, the contact areas perpendicular to the direction of the compaction present a higher density of dislocations and lattice defects. This high density intensifies the shrinkage along the direction of compaction. To demonstrate the influence of uniaxial cold compaction on the material’s stress state the powder particles and their contacts were modeled using spheres made of pure copper. These spheres are compacted in a die at different pressures to better analyze the system’s response at the grade of deformation and the consequent influence on the material’s behavior during the sintering. In the different zones of the sphere, the micro-hardness was measured and correlated to the concentration of dislocations using the model for indentation size effect (ISE). After the compaction, the spheres were more deformed along the longitudinal than the transversal direction. The results obtained using hardness indentation show differences in the dislocation density between the undeformed and deformed spheres and, in the case of the compacted sphere, between the contact area along the longitudinal and the transversal direction.
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- Award ID(s):
- 2119832
- PAR ID:
- 10543626
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Journal of Manufacturing and Materials Processing
- Volume:
- 6
- Issue:
- 6
- ISSN:
- 2504-4494
- Page Range / eLocation ID:
- 155
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/jmmp6060155
