Evaluation of Critical Resolved Shear Stresses for Various Plastic Deformation Mechanisms To Understand Mechanical Prope
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Evaluation of Critical Resolved Shear Stresses for Various Plastic Deformation Mechanisms To Understand Mechanical Properties of Magnesium-Yttrium Alloys T. Mineta1 and S. Miura2 1Graduate
student, Graduate School of Engineering, Hokkaido University, Sapporo
060-8628 2
Faculty of Engineering, Hokkaido University, Sapporo 060-8628
ABSTRACT In order to understand enhanced mechanical properties of magnesium-yttrium (Mg-Y) alloys, applied stresses which were required to operate independent plastic deformation mechanisms on various stress axes were evaluated. Moreover, for this analysis, mechanical tests including newly-established testing method “pure-shear test” were conducted to evaluate Critical Resolved Shear Stresses (CRSSes) for various plastic deformation mechanisms of Mg-Y solid solution alloy single crystals with various Y concentration. Relatively higher solid solution strengthening of dominant plastic deformation mechanisms such as basal slip and extension twin at room temperature, results in increase in the activation of non-basal slip system. By a simple analysis based on von-Mises criterion with experimental CRSS values, it is revealed that enhanced mechanical properties of Mg-Y alloys might be attributed to the decrease of difference in the activity of plastic deformation mechanisms by Y addition. INTRODUCTION Mg alloys attract attentions as materials with a specifically high strength, nonetheless, they show poor ductility at room temperature. The difference in the activity of plastic deformation mechanisms is considered to be one of the reasons for poor ductility. Among plastic deformation mechanisms of Mg alloys, basal slip and extension twin operate more easily at room temperature than non-basal slips of which CRSSes presumably reach to several ten times of that for basal slip[1-8]. Large CRSSes for non-basal slip systems result in the low activation. Therefore, To understand the deformability of Mg alloys in terms of the activity of plastic deformation mechanisms, CRSS values are important. Mg-Y alloys show high solid solution strengthening for basal slip[9-12], but their good mechanical properties are not fully understood. Therefore, we intend to investigate the effect of Y on CRSS using single crystals. In this study, we introduce a new mechanical testing method which allows one to evaluate CRSS for various plastic deformation mechanisms because the high value of CRSS is the reason for the difficulty of evaluation without the operation of low CRSS deformation mechanisms such as basal slip and twinning. It is attempted to understand the mechanical properties such as enhanced ductility and
strength of Mg-Y alloys using evaluated CRSSes. EXPERIMENTAL We used “Pure-shear test” which can evaluate CRSS for a certain plastic deformation mechanisms of Mg alloys[13]. Fig. 1 shows schematics of pure-shear testing jig. Here “shear factor” is defined as a coefficient which converts applied stress to RSS (Resolved Shear Stress) for a certain plastic deformation mechanism.
Fig. 1. Schematics of pure-shear
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