Mechanical and chemical effects of solute elements on generalized stacking fault energy of Mg
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Mamoru Mabuchi Department of Energy Science and Technology, Graduate School of Energy Science, Kyoto University, Yoshidahonmachi, Sakyo-ku, Kyoto 606-8501, Japan (Received 18 April 2014; accepted 14 August 2014)
First-principles shear tests were performed on pure Mg, Mg–Li, Mg–Ca, Mg–Al, Mg–Sn, Mg–Ag, and Mg–Zn models to investigate the mechanical and chemical effects of the solute elements on the generalized stacking fault energy (GSFE) of Mg. The mechanical effect increased the unstable stacking fault energy (USFE), independent of the kind of solute element tested. The intensity of the mechanical effect was explained by the average distance between a solute atom and the surrounding Mg atoms, not by a difference in atomic radius between a solute atom and a Mg atom. In contrast, the chemical effect on the USFE was complicated, and the chemical effects of Ag and Zn were lower than expected from their electronegativity. Also, the chemical effect increased the USFE for the Li addition, but it decreased the USFE for the Ca addition although the electronegativity of Li is almost the same as that of Ca. I. INTRODUCTION
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.270
Razumovskiy et al.12 showed that Mg and Zr solute atoms strengthened an Al grain boundary due to the chemical effect. These works suggested that the mechanical effect decreased the fracture energy, while the chemical effect increased the fracture energy. However, Zhong et al.14 showed that in a Fe–H system, the mechanical effect increased the fracture energy, and the chemical effect decreased it. The decreased fracture energy due to the chemical effect is because of the charge transfer from Fe to H atoms.14,15 Thus, there are many understandings of the mechanical and chemical effects on the fracture energy. The GSFE also depends on the expansion (or contraction) and chemical states of the interatomic bonds. To date, the GSFEs have been investigated for many metallic materials. 16–23 Siegel19 investigated the effects of the solute elements on the GSFE of Ni by the first-principles shear tests and showed that the GSFE increased with the addition of Mn and Fe, while it decreased with the addition of Cu, Nb, and W. Thus, the effects of the solute elements on the GSFE are complicated, and systematic investigations are needed to understand these effects. To the authors’ knowledge, there are no studies about the mechanical and chemical effects on the GSFE. Investigations of the GSFE from the viewpoint of the mechanical and chemical effects can give an insight into understanding the effects of the solute elements on the GSFE. Magnesium alloys are promising light structural materials due to their high specific strength and stiffness. However, Mg alloys often show low ductility and poor stretch formability because the slip systems are limited.
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Ó Materials Research Society 2014
The effects of solute elements on the fracture energy and the generalized stacking fault energy (GSFE) are interesting studies not only fo
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