Intragranular deformation mechanisms in calcite deformed by high-pressure torsion at room temperature

Abstract

Polycrystalline calcite was deformed to high strain at room-temperature and confining pressures of 1-4 GPa using high-pressure torsion. The high confining pressure suppresses brittle failure and allows for shear strains >100. The post-deformation microstructures show inter-and intragranular cataclastic deformation and a high density of mechanical e 011 À 8 È É twins and deformation lamellae in highly strained porphyroclasts. The morphologies of the twins resemble twin morphologies that are typically associated with substantially higher deformation temperatures. Porphyroclasts oriented unfavorably for twinning frequently exhibit two types of deformation lamellae with characteristic crystallographic orientation relationships associated with calcite twins. The misorientation of the first deformation lamella type with respect to the host corresponds to the combination of one r 101 À 4 È É twin operation and one specific f 011 À 2 È É or e 011 À 8 È É twin operation. Boundary sections of this lamella type often split into two separated segments, where one segment corresponds to an incoherent r 101 À 4 È É twin boundary and the other to an f 011 À 2 È É or e 011 À 8 È É twin boundary. The misorientation of the second type of deformation lamellae corresponds to the combination of specific r 101 À 4 È É and f 011 À 2 È É twin operations. The boundary segments of this lamella type may also split into the constituent twin boundaries. Our results show that brittle failure can effectively be suppressed during room-temperature deformation of calcite to high strains if confining pressures in the GPa range are applied. At these conditions, the combination of successive twin operations produces hitherto unknown deformation lamellae.

Calcite Twin Formation, Measurement and Use as Stress–Strain Indicators: A Review of Progress over the Last Decade

“…This can occur by climb or cross-slip [12], which are both thermally activated processes. Twin boundary migration, which may give birth to lamellae with irregular shapes, is driven by the heterogeneity of the lattice defect energy associated with dislocations and vacancies in twin and host grains and is also considered to be thermally activated [14,15].…”

“…This last approach only provides access to the final deformation state and unfortunately does not provide information at the onset of, or during twinning. For example, Schuster et al [15,16] analysed post-mortem microstructures of high P-T deformed samples by Electron Backscatter Diffraction (EBSD) in a scanning electron microscope or using X-ray line profile analysis.…”

“…Schuster et al [15] carried out experimental deformation of polycrystalline calcite to high strain at room temperature and confining pressures of 1-4 GPa using high-pressure torsion. The authors report that the experimentally produced mechanical e-twins are significantly thicker than 1 µm and have a moderate lenticular shape.…”

“…The formation of thick, lens-shaped twins requires that the dislocations that propagate the twin can move out of their glide plane by climb or cross-slip [12]. Although this process is usually considered to be thermally activated, the results by [15] show that high lattice strain produced during the deformation under a confining pressure in excess of 1 GPa can lead to substantial twin thickening even at room temperature. Thus, although such confining pressure conditions largely exceed those under which deformation twinning considered in this paper may occur, this effect is possibly not as negligible as previously thought [51] and should not be neglected when calcite twin morphologies are used as geothermometers.…”

In Situ Synchrotron X‐Ray Diffraction during High‐Pressure Torsion Deformation of Ni and NiTi

“…[2] Furthermore, within the past years, the interest of researchers also turned to the application of SPD methods to materials with functional and tunable properties (thermoelectrics, hydrogen storage, magnetic, biomedical) [3][4][5][6] and even geomaterials. [7] However, the characterization of the microstructure and other properties is always conducted after the complete SPD processing, whereas the dynamic evolution of the microstructure can only be presumed. The exact pathway to the final microstructure remains unclear as accessible in situ parameters are very limited.…”