Sylvie Demouchy, Manuel Thieme, Fabrice Barou , Benoit Beausir, Vincent Taupin, Patrick Cordier

We report a comprehensive dataset characterizing and quantifying the dislocation density in the crystallographic frame (ρ_α^c) and disclination density (ρ_θ) in fine-grained polycrystalline olivine deformed in uniaxial compression or torsion, at 1000 °C and 1200 °C, under a confining pressure of 300 MPa. Finite strains range from 0.11 up to 8.6 % and stresses reach up to 1073 MPa. The data set is a selection of 19 electron backscatter diffraction maps acquired with conventional angular resolution (0.5°), but at high spatial resolution (step size from 0.05 to 0.1 µm). Thanks to analytical improvement for data acquisition and treatment with notably the use ATEX software, we report spatial distribution of both geometrically necessary dislocation (GND) and disclination densities. Area with the highest GND densities define subgrain boundaries. The type of GND densities involved also indicate that most olivine subgrain boundaries have mixed character. Moreover, strategy for visualization also permit to identify a population of minor GND, not well organized. Low temperature and high stress sample displays a higher, but less organized GND density than sample deformed at high temperature for similar finite strain and identical strain rate, confirming the action of dislocation creep in these samples, even for small grain (2 m). Furthermore, disclination dipoles along grain boundaries are identified in every undeformed and deformed EBSD maps, mostly at the triple junction of a grain boundary with a subgrain, but also along sub-grain boundaries, and at subgrain boundary tips. Nevertheless, for the range of parameters investigated, there is no notable correlation of the disclination density with stress, strain, or temperature. However, a positive correlation between average disclination density and average GND density per grain is found confirming their similar role as defects producing intragranular misorientation. Furthermore, a negative correlation between the disclination density and the grain size or perimeter is found, providing a first rule of thumb on the distribution of disclinations. Field Disclination and Dislocation Mechanics simulations of the elastic fields due to experimentally measured dislocations and disclinations (e.g. strains/rotations and stresses), provide further evidence of the interplay between both types of defects. At last, our results also support that disclinations act as a plastic deformation mechanism, by allowing rotation of a very small crystal volume.