Abstract:
The character distribution of interfaces in polycrystalline materials, including phase and grain boundaries, influences macroscopic properties, such as bulk viscosity. Olivine is the dominant phase of the upper mantle and has been considered as a material for implants in the human body. Until recently, the grain boundary network and its anisotropic frequency distribution nor its dependence on chemical composition where known for any rock forming mineral. Therefore, we characterized interfaces in different aggregates of olivine. The different aggregates where synthesized with varying chemical compositions ranging from Mg2SiO4 forsterite to Mg1.8Fe0.2SiO4 and Mg1.0Fe1.0 SiO4 olivine and different additions of incompatible elements that are known to segregate to the interfaces. We characterized the grain boundary character and plane distribution (GBCD and GBPD) in doped aggregates in diffusion creep and in the dislocation assisted grain boundary sliding regime using a torsion deformation setup. Thus we extract the influence of the GBPD on bulk viscosity.
Because the geometry of the grain boundary network geometry controls percolation during melting, we constrained how the interfacial network geometry changes during melting.
We used high end electron microscopy techniques to characterize the geometrically varying interfaces. Grain orientation data from over 4×104 grains, corresponding to more than 6000 mm grain boundary length per sample were used to stereologically extract the geometry of the interfacial network.
We found that the interfacial network geometry is affected by segregation, deformation and strongly by melting. We provide a first description of the grain boundary network geometry. We implement the network geometry into first phase-field models. These show a remarkable effect of the network geometry on grain growth.