Kinking Nonlinear Elasticity and the Deformation of Magnesium

Abstract

Despite a large body of work devoted to understanding the deformation of polycrystalline magnesium, there are still some outstanding questions, not the least of which are the nature of its microyielding and the nature of its fully reversible, hysteretic, stress-strain curves. In this article, we provide further evidence that Mg is a kinking nonlinear solid by showing excellent agreement between the predictions of our microscale model, in which fully reversible, dislocation-based incipient kink bands (IKBs) are the key microscale element, the experimental results obtained in our study, and, just as important, the results obtained by others. It follows that microyielding and the fully reversible hysteresis loops are most likely to be due to IKB formation, with the propensity for kinking being enhanced for coarse-grained samples up to a grain size of %50 lm, after which further increases in grain size have little effect. From the areas of the reversible loops, the critical resolved shear stresses (CRSSs) associated with the movement of basal plane dislocations are obtained and are shown to scale with the maximum flow stresses at which the loops are obtained. We also make the case that, at least for low strains, strains along the c-axis can be accommodated by invoking the formation of IKBs, mobile dislocation walls, and kink boundaries and should be included in future modeling of the deformation of polycrystalline Mg.

In situ neutron diffraction evidence for fully reversible dislocation motion in highly textured polycrystalline Ti2AlC samples

“…If one assumes, w = b, then s loc % G/30, and c c is of the order of 0.05 rad. If, as assumed here and in our previous work [4][5][6][7], w = 5b, then c c = 0.012 rad.…”

“…As noted above, due to their high c/a ratios (3)(4)(5)(6)(7)(8), neither non-basal dislocations nor twins have ever been implicated in the deformation of the MAX phases under normal loading conditions. Referring to insets (i) and (ii) in Fig.…”

“…Over the past decade we have shown that KNE solids are quite ubiquitous and exist in many types of solids: from graphite to mica, to hexagonal metals, to the MAX phases (see below) [2]. In 2005, we developed a micromechanical model [3] to explain KNE behavior and have since published several papers in which we presented strong circumstantial evidence for the existence of IKBs [4][5][6][7].…”

First-principles study of dislocations in hcp metals through the investigation of the (112¯1) twin boundary

“…A breakthrough toward understanding the early deformation of HM came about recently when we showed that they are kinking nonlinear elastic, KNE, solids. [1][2][3] Macroscopically, KNE solids are characterized by the formation of fully, and spontaneously, reversible closed hysteresis stress-strain loops. The size of these loops, which corresponds to the energy dissipated per unit volume, scales with the maximum applied stress squared and is a strong function of grain size.…”

Micro-Kinking of the Long-Period Stacking/Order (LPSO) Phase in a Hot-Extruded Mg₉₇Zn₁Y₂ Alloy

“…Kinking is generally known as a minor deformation mode in crystalline materials, 15) but it appears to be an essential mode for the LPSO crystals, for which both the non-basal slip and twinning are strongly suppressed. Typical microstructures of the kink-deformation bands in the LPSO phase grains were shown to be represented by straight boundaries, across which the host crystals are sharply bended with rotational angles from 10 to 90 degrees.…”