Quantitative insights into the dislocation source behavior of twin boundaries suggest a new dislocation source mechanism

Abstract

Pop-in statistics from nanoindentation with spherical indenters are used to determine the stress required to activate dislocation sources in twin boundaries (TBs) in copper and its alloys. The TB source activation stress is smaller than that needed for bulk single crystals, irrespective of the indenter size, dislocation density and stacking fault energy. Because an array of pre-existing Frank partial dislocations is present at a TB, we propose that dislocation emission from the TB occurs by the Frank partials splitting into Shockley partials moving along the TB plane and perfect lattice dislocations, both of which are mobile. The proposed mechanism is supported by recent high resolution transmission electron microscopy images in deformed nanotwinned (NT) metals and may help to explain some of the superior properties of nanotwinned metals (e.g. high strength and good ductility), as well as the process of detwinning by the collective formation and motion of Shockley partial dislocations along TBs. Graphic abstract

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

“…Consequently, our observation of decreased stresses for the initiation of plasticity associated with the presence of the HAGB under the indent (Figure 3b) is an indicator that the HAGB acts as a source of dislocations in our spherical nanoindentation experiments. In metals, similar observations using spherical nanoindentation on twin boundaries have been attributed to generation of dislocations at the twin boundary (J. Li et al., 2021). In ceramics, similar experiments with a Berkovich indenter reveal decreased hardness and pop‐in load at grain boundaries in zirconia (Lian et al., 2007), or display no change in hardness with distance from grain boundaries in different oxides (Nakamura et al., 2023).…”

“…In metals, similar observations using spherical nanoindentation on twin boundaries have been attributed to generation of dislocations at the twin boundary (J. Li et al, 2021). In ceramics, similar experiments with a Berkovich indenter reveal decreased hardness and pop-in load at grain boundaries in zirconia (Lian et al, 2007), or display no change in hardness with distance from grain boundaries in different oxides (Nakamura et al, 2023).…”

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

“…to generation of dislocations at the twin boundary (J. Li et al, 2021). In addition, our experiments reveal that a low-energy SB, comprised of arrays of periodic dislocations with the [001] Burgers vector (Heinemann et al, 2005) is not a potent source of dislocations (Figure 3a and A9).…”

Calibration and data analysis routines for nanoindentation with spherical tips

“…The potential to produce a large number of measurements and generate indentation stress-strain curves from a small volume of material makes spherical nanoindentation a desirable technique with a wide range of applications. For example, spherical nanoindentation has been deployed to investigate yield stress and size effects in brittle engineering ceramics and natural minerals [e.g., 12,16,17,27,48,58], the mechanical properties of twin and grain boundaries in metals [e.g., 29,52,56], the effects of ion-induced damage in metals and alloys [e.g., 1,8,42], the relationship between structure and mechanical properties in biomaterials (bone [e.g., 41], human enamel [e.g., 18]), elasto-plastic transitions in bulk metallic glasses [e.g, 3,10], and fracture in thin films [e.g., 33,57]. This versatility of mechanical testing using spherical indentation has motivated studies on the reliability of measurements and prompted efforts to improve data analysis.…”