The role of grain boundaries in low-temperature plasticity of olivine revealed by nanoindentation

Abstract

Nanoindentation experiments on a high-angle grain boundary (60 * misorientation) in a pure forsterite bicrystal reveal that the interface acts as a source of dislocations. * Nanoindentation experiments on a high-angle grain boundary (60 * misorientation) in a pure forsterite bicrystal reveal that the interface acts as an obstacle to incoming dislocations, leading to pileups of dislocations.* Nanoindentation experiments on a subgrain boundary (13 * misorientation) in a pure forsterite bicrystal do not detect the impact of the interface on dislocations.

The Effect of Intracrystalline Water on the Mechanical Properties of Olivine at Room Temperature

“…As the value from FTIR is a volume‐averaged measurement of water concentration, we used a simple diffusion model to estimate the amount of water that remains in the outer 5 μm of the crystal (see supplement for additional detail). A depth of 5 μm covers the typical region over which olivine deforms during our nanoindentation experiments (∼3 times the maximum indent depth), with most strain occurring at even shallower depths (e.g., Avadanii et al., 2023; Wallis et al., 2020). We assume that diffusion along the [010] axis is the relevant dehydration mechanism given the orientation of M666.…”

“…The variability in hardness and yield stress for different crystal orientations at any given indentation depth (∼2–3 GPa at depths greater than 500 nm) is approximately the same as that measured previously using spherical nanoindentation (Kumamoto et al., 2017). Due to the complexity of the stress state beneath the indenter tip, many slip systems can be activated beneath an indent in a crystal of any orientation (e.g., Avadanii et al., 2023; Wallis et al., 2020). The (100)[001] and (110)[001] slip systems are generally the most active at room temperature (e.g., Avadanii et al., 2023; Gaboriaud et al., 1981; Wallis et al., 2020) due to their low critical resolved shear stresses (e.g., Hansen et al., 2019).…”

“…Due to the complexity of the stress state beneath the indenter tip, many slip systems can be activated beneath an indent in a crystal of any orientation (e.g., Avadanii et al., 2023; Wallis et al., 2020). The (100)[001] and (110)[001] slip systems are generally the most active at room temperature (e.g., Avadanii et al., 2023; Gaboriaud et al., 1981; Wallis et al., 2020) due to their low critical resolved shear stresses (e.g., Hansen et al., 2019). Thus the observed anisotropy in hardness and yield stress in our results is primarily due to different resolved shear stresses on these slip systems depending on the geometry of deformation under the indenter tip.…”

“…Recently, indentation methods have seen a rise in popularity in the geosciences due to their comparative ease of use, rapid data acquisition, and reproducibility (e.g., Kranjc et al., 2016; Kumamoto et al., 2017; Thom et al., 2022; Thom & Goldsby, 2019). Furthermore, the self‐confining nature of the technique allows LTP in olivine to be investigated at room temperature, generating clear microstructural evidence of dislocation activity (Avadanii et al., 2023; Kumamoto et al., 2017; Wallis et al., 2020). These low‐temperature experiments are well suited to distinguishing among different models for the influence of water in LTP.…”

The Role of Grain Boundaries in Low‐Temperature Plasticity of Olivine Revealed by Nanoindentation

“… • The nanoindentation data presented in Section 3.1, and the HR‐EBSD and TEM data presented in Section 3.2 in this study are available at the http://figshare.com repository via DOI http://10.6084/m9.figshare.21507060 with the CC BY 4.0 license (Avadanii et al., 2022). • The nanoindentation data have been analyzed using Matlab. …”