Mg中$\langle c+a \rangle$位错的第一性原理研究
First-principles study of $\langle c+a \rangle$ dislocations in Mg
摘要：
我们利用第一性原理密度泛函理论研究了Mg中的第一滑移系和第二滑移系的广义层错能面。我们证明了垂直于滑移方向的原子运动的额外弛豫允许在广义层错能（GSFE）曲线中找到适当的局部最小值。计算的双晶-II GSFE曲线还表明，完整的锥型II位错将解离成Stohr和Poirier（SP）配置，由两个$\frac{1}{2}\langle c+a \rangle$部分，$\frac{1}{6}[11{\bar2}3] + \frac{1}{6}[11{\bar2}3]$，但双晶-I GSFE曲线，虽然也具有局部最小值，不会解离成相同的SP配置。我们报告观察到这些部分在这里发出的$\{10{\bar1}2 \}$孪生边界。用MEAM势对Mg进行MD模拟，发现全位错Ⅱ型$\langle c+a \rangle $位错分裂为两个相等的部分位错$\frac{1}{6}[11{\bar2}3] + \frac{1}{6}[11{\bar2}3]$，位错间距约为22.6 $Å$。我们发现，完整的MATERIAL-I $\langle c+a \rangle$位错也解离成两个相等值的部分，但到交替的$(30{\bar3}4)$和$(30{\bar3}2)$平面与$\frac{1}{6} [20{\bar2}3]$和$\frac{1}{6} [02{\bar2}3]$ Burgers矢量分离的30.4 $Å$宽堆垛层错。当施加应力时，扩展的双晶-II型位错的刃位错和混合位错可以在其滑移面上移动;然而，具有类似特征的双晶-I型位错不能。
英文摘要：
We use first-principles density functional theory to study the generalized stacking fault energy surfaces for pyramidal-I and pyramidal-II slip systems in Mg. We demonstrate that the additional relaxation of atomic motions normal to the slip direction allows for the appropriate local minimum in the generalized stacking fault energy (GSFE) curve to be found. The fault energy calculations suggest that formation of pyramidal-I dislocations would be slightly more energetically favorable than that for pyramidal-II dislocations. The calculated pyramidal-II GSFE curves also indicate that the full pyramidal II dislocations would dissociate into the Stohr and Poirier (SP) configuration, consisting of two $\frac{1}{2}\langle c+a \rangle$ partials, $\frac{1}{6}[11{\bar2}3] + \frac{1}{6}[11{\bar2}3]$ , but the pyramidal-I GSFE curves, while also possessing a local minimum, would not dissociate into the same SP configuration. We report observation of these partials here emanating from a $\{10{\bar1}2 \}$ twin boundary. Using MD simulations with MEAM potential for Mg, we find that the full pyramidal-II $\langle c+a \rangle $ dislocation splits into two equal value partials $\frac{1}{6}[11{\bar2}3] + \frac{1}{6}[11{\bar2}3]$ separated by ~22.6 $Å$. We reveal that the full pyramidal-I $\langle c+a \rangle$ dislocation dissociates also into two equal value partials but onto alternating $(30{\bar3}4)$ and $(30{\bar3}2)$ planes with $\frac{1}{6} [20{\bar2}3]$ and $\frac{1}{6} [02{\bar2}3]$ Burgers vectors separated by a 30.4 $Å$ wide stacking fault. When a stress is applied, edge and mixed dislocations of the extended pyramidal-II dislocation can move on their glide plane; however, pyramidal-I dislocations of similar character cannot.
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