Influence of orientation on twin nucleation and growth at low strains in a magnesium alloy

Barnett, MR, Ghaderi, A, Quinta Da Fonseca, J and Robson, JD 2014, Influence of orientation on twin nucleation and growth at low strains in a magnesium alloy, Acta Materialia, vol. 80, pp. 380-391, doi: 10.1016/j.actamat.2014.07.013.

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Title Influence of orientation on twin nucleation and growth at low strains in a magnesium alloy
Author(s) Barnett, MRORCID iD for Barnett, MR
Ghaderi, AORCID iD for Ghaderi, A
Quinta Da Fonseca, J
Robson, JD
Journal name Acta Materialia
Volume number 80
Start page 380
End page 391
Publisher Elsevier
Place of publication Amsterdam, The Netherlands
Publication date 2014
ISSN 1359-6454
Keyword(s) Crystal plasticity
Twin nucleation and growth
Science & Technology
Materials Science, Multidisciplinary
Metallurgy & Metallurgical Engineering
Materials Science
Summary The resolved shear stress is believed to play an important role in twin formation. The present study tests this idea for an extruded magnesium alloy by examining "tension" twinning in different grain orientations. Electron backscatter diffraction analysis is employed for alloy AZ31 tested in compression along the extrusion axis to strains between 0.008 and 0.015. For heavily twinned grains, it is seen that twinning occurs on 2.3 twin systems per grain on average. The active systems are also most commonly those with, or very near to, the highest Schmid factor. The most active system in multiply twinned grains accounts on average for ∼0.6 of the twinning events. In addition, it is found that the twin habit plane falls within 6° of the K1 plane. Orientations with the highest Schmid factors (0.45-0.5) for twinning display twin aspect ratios greater by ∼40% and twin number densities greater by ∼10 times than orientations with maximum Schmid factors for twinning of 0.15-0.2. Thus the Schmid factor for twinning is seen to affect nucleation more than thickening in the present material. Viscoplastic crystal plasticity simulations are employed to obtain approximations for the resolved shear stress. Both the twin aspect ratio and number density correlate quite well with this term. The effect of the former can be assumed to be linear and that of the latter follows a power law with exponent ∼13. Increased aspect ratios and number densities are seen at low Schmid factors and this may relate to stress fluctuations, caused most probably in the present material by the stress fields at the tips of blocked twins. Overall, it is evident that the dominance of twinning on high Schmid factor systems is preserved at the low strains examined in the present work, despite the stress fluctuations known to be present. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Language eng
DOI 10.1016/j.actamat.2014.07.013
Field of Research 091207 Metals and Alloy Materials
Socio Economic Objective 861199 Basic Metal Products (incl. Smelting
HERDC Research category C1 Refereed article in a scholarly journal
ERA Research output type C Journal article
Copyright notice ©2014, Elsevier
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