Laue X-ray microdiffraction experiments were conducted at the microXAS beamline of the Swiss Light Source at the Paul Scherrer Institute in Villigen, Switzerland. In the work presented here, we characterise microcast samples, which are free of ion-milling artefacts and show strong size effects already in 10 μ m diameter samples. Larger pillars (10 μ m diameter) on the other hand were found to deform more conventionally, that is, by slip on the predicted system and with unconstrained rotation of the crystal. The smaller pillars (2 μ m diameter) were found to deform by activation of a geometrically unexpected slip system, which was activated because of the preexisting strain gradient induced by the focused ion beam milling process that was used to prepare the samples, and by crystal rotation. performed in situ compression tests on ion-milled Au micropillars. Since then, Laue microdiffraction has been established as a powerful technique in the study of mechanisms that govern plastic deformation at the micro scale. showed that (i) the continuous streaking of Laue diffraction peaks can be related to internal strain gradients and (ii) discontinuous streaking happens in the presence of dislocation walls forming geometrically necessary boundaries. Laue microdiffraction has been used before on small-scale samples: Barabash et al. We provide here such data, gleaned by means of synchrotron X-ray Laue microdiffraction characterisation of as-cast and deformed aluminium microcrystals. In, these parameters were estimated by means of a few transmission electron microscopy images given the long length of microcrystals that can be produced and tested by the process of, alternative measurements giving access to the dislocation distribution in such samples, before and after deformation, are of clear interest to further understand their nature and deformation mechanisms. The initial dislocation distribution in such microcrystals, and its evolution during deformation, are important parameters and signatures of their plastic deformation. This is seemingly because the small size of the crystals leads to source truncation, that is, typical double-pinned Frank–Read sources becoming single-ended (spiral) sources with higher activation stress, as predicted by statistical models and dislocation dynamics simulations, and evidenced by in another class of microcrystals extracted from solidified specimens. As is reported in, these microcast crystals show a size effect in plasticity. Cast microwires also have a low initial dislocation density, and their high aspect ratio ( ≈50) makes them suitable for tensile testing. As compared to other methods used for the fabrication of microtest specimens, specific characteristics of the microcast wires are that they are generally single-crystalline and free of the artefacts that are introduced by other preparation methods such as ion-milling. It was shown in a recent publication that single-crystalline net-shape Al microwires, with a diameter in the range of 7–100 μ m, can be produced by a new microcasting process. Recent reviews of the extensive work on the subject can be found in. The observed behaviour depends on a number of factors, including both the nature of the material, how it was produced, its geometry and the sample size. Generally, it is found that, as the sample size decreases, the plastic flow stress increases, and deformation proceeds in a more irregular, at times stochastic burst-like, manner. Plastic deformation in small-scale metallic samples often differs from what is observed in bulk, macroscopic samples of the same metal or alloy.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |