Abstract
The advent of miniaturised testing techniques led to excessive studies on size effects in materials. Concomitantly, these techniques also offer the capability to thoroughly examine deformation mechanisms operative in small volumes, in particular when performed in-situ in electron microscopes. This opens the feasibility of a comprehensive assessment of plasticity by spatially arranging samples specifically with respect to the crystal unit cell of interest. In the present manuscript, we will showcase this less commonly utilised aspect of small-scale testing on the case of the hexagonal metal Mg, where, besides dislocation slip on different slip planes, twinning also exists as a possible deformation mechanism. While it is close to impossible to examine individual deformation mechanisms in macroscale tests, where local multiaxial stress states in polycrystalline structures will always favour multiple mechanisms of plasticity, we demonstrate that miniaturised uniaxial experiments conducted in-situ in the scanning electron microscope are ideally suited for a detailed assessment of specific processes.
Highlights
Small scale experiments have provided numerous insights regarding the mechanical properties of confined volumes
Due to the large difference in the activation energy of each deformation mode in Mg, strongly anisotropic deformation behaviours can be investigated depending on loading axes and conditions. While this allows the examination of the influence of crystal orientation, and the impact of crystal size, strain rate and deformation temperature on the resulting mechanical response, we will limit this consideration to the fundamental modes of deformation, the related extensions towards the mentioned other variables are trivial but beyond the scope of this work
An overview of the directions along Mg[211 respective orientations, loading modes and the Schmid factors corresponding on the one hand to dislocation plasticity on the basal, prismatic or pyramidal plane, and on the other hand to tension or contraction twinning, respectively, are given in 4 the different crystal orientations visualised combination with unit ure 4 the different crystal orientations areare visualised in in combination with thethe unit cellcell and and the expected deformation mechanisms based on the actual the expected deformation mechanisms based on the actual Schmid [30]
Summary
Small scale experiments have provided numerous insights regarding the mechanical properties of confined volumes. With the increasing complexity of the research in question, it becomes more and more demanding to assess the single crystal properties for a fundamental understanding rather than just examining the bulk response of a new experimental alloy This is where the strength of small scale testing should be embraced, as it allows comprehensive testing utilising only minimal amounts of material. Due to the large difference in the activation energy of each deformation mode in Mg, strongly anisotropic deformation behaviours can be investigated depending on loading axes and conditions While this allows the examination of the influence of crystal orientation, and the impact of crystal size, strain rate and deformation temperature on the resulting mechanical response, we will limit this consideration to the fundamental modes of deformation, the related extensions towards the mentioned other variables are trivial but beyond the scope of this work. In the remainder we will detail a possible testing scheme using in-situ testing in the scanning electron microscope (SEM), apply it to the defined fundamental hexagonal crystal orientations, and detail the resultant deformation features and their relation to previous works
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