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Bulk, polycrystalline (Co, Cu, Mg, Ni, Zn)O was synthesized using solid-state sintering. Micropillars were prepared and mechanically deformed along three crystallographic orientations: (001), (101), and (111). Pillars (001) and (111) cracked, while Pillar (101) remained intact. Pillars (001) and (101) exhibited activated slip systems, confirmed by a large stress drop, and the presence of slip bands, respectively. Schmid factor (SF) analysis was performed to examine the effect of grain orientations on dislocation activity and slip behavior. SF values range from 0 to 0.5, with non-zero values indicating potential for slip. Six slip systems exist in the (Co, Cu, Mg, Ni, Zn)O rock salt crystal structure: 1/2⟨110⟩11¯0. For the (001) orientation, four slip systems are potentially active (SF = 0.5). For the (101) orientation, there are four potentially active slip systems (SF = 0.25). For the (111) orientation, no potentially active slips systems exist (SF = 0). Dislocation structures, which were observed post-compression via transmission electron microscopy, demonstrated variations in size, number, and distribution across the pillar, depending on micropillar orientation. Entangled dislocations created misorientation in Pillar (001), which led to the possible formation of subgrains, while singular dislocations were observed in Pillar (101), and a lack of dislocations was observed in Pillar (111). Zener–Stroh type dislocation entanglement-mediated cracking is the proposed cause of the transgranular-type cracks in Pillar (001). The possible subgrain formation, or lack of formation, respectively, caused intergranular-type cracks to additionally form in Pillar (001), while Pillar (111) only exhibited transgranular-type brittle fracture. In combination, these findings highlight the importance of dislocation activity, without the need for elevated temperature, and grain orientation in controlling the mechanical deformation response in single-phase (Co, Cu, Mg, Ni, Zn)O.
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Evolution of texture and internal stresses within polycrystalline rock salt using in situ 3D synchrotron computed tomography and 3D X-ray diffraction
Rock salt caverns have been extensively used as reliable repositories for hazardous waste such as nuclear waste, oil or compressed gases. Undisturbed rock salt deposits in nature are usually impermeable and have very low porosity. However, rock salt formations under excavation stresses can develop crack networks, which increase their porosities; and in the case of a connected crack network within the media, rock salt may become permeable. Although the relationship between the permeability of rock salt and the applied stresses has been reported in the literature, a microscopic study that investigates the properties influencing this relationship, such as the evolution of texture and internal stresses, has yet to be conducted. This study employs in situ 3D synchrotron micro-computed tomography and 3D X-ray diffraction (3DXRD) on two small-scale polycrystalline rock salt specimens to investigate the evolution of the texture and internal stresses within the specimens. The 3DXRD technique measures the 3D crystal structure and lattice strains within rock salt grains. The specimens were prepared under 1D compression conditions and have shown an initial {111} preferred texture, a dominant {110}〈1 1 0〉 slip system and no fully connected crack network. The {111} preferred texture under the unconfined compression experiment became stronger, while the {111}〈1 1 0〉 slip system became more prominent. The specimens did not have a fully connected crack network until applied axial stresses reached about 30 MPa, at a point where the impermeability of the material becomes compromised due to the development of multiple major cracks.
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- Award ID(s):
- 1641054
- PAR ID:
- 10310988
- Date Published:
- Journal Name:
- Journal of Applied Crystallography
- Volume:
- 54
- Issue:
- 5
- ISSN:
- 1600-5767
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1107/S1600576721007809
