锥体 I<c+a> 螺旋位错的双交叉滑移分析及其对镁合金延展性的影响,Acta Materialia

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锥体 I<c+a> 螺旋位错的双交叉滑移分析及其对镁合金延展性的影响
Acta Materialia ( IF 8.3 ) Pub Date : 2020-01-01 , DOI: 10.1016/j.actamat.2019.10.053
Rasool Ahmad , Zhaoxuan Wu , W.A. Curtin

摘要锥体〈c+a〉螺旋位错的溶质加速交叉滑移最近被认为是提高固溶镁合金延展性的关键机制。在纯镁中，由于高能金字塔 I 和低能金字塔 II < c + a > 螺旋位错之间的能量差异，交叉滑移是无效的。添加少量溶质，尤其是稀土 (RE) 元素，可以减少这种能量差异并加速横向滑移，从而增强延展性。随着溶质浓度的增加，锥体 I 位错可以在能量上变得有利，这会切换主 < c + a > 滑移平面并改变交叉滑移过程。这里，在金字塔 I 位错比金字塔 II 在能量上更有利的情况下，分析了金字塔 I 〈 c + a 〉位错的双交叉滑移的过渡路径和能量学。这是通过对 Mg 的代理 MEAM 潜力的轻推弹性带模拟来实现的，该模拟旨在支持金字塔 I 而非金字塔 II。发现金字塔 I 双交叉滑移的最小能量转移路径始于在金字塔 II 平面上的交叉滑动，然后是在平行于原始金字塔 I 平面的金字塔 I 平面上的交叉滑动。然后将先前的延展性机械模型扩展到更高的溶质浓度，其中金字塔 I 是有利的。该模型预测溶质浓度的上限，超过该上限，镁合金的延展性再次变差。

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Analysis of double cross-slip of pyramidal I 〈c+a〉 screw dislocations and implications for ductility in Mg alloys

Abstract Solute accelerated cross-slip of pyramidal 〈 c + a 〉 screw dislocations has recently been recognized as a crucial mechanism in enhancing the ductility of solid-solution Mg alloys. In pure Mg, cross-slip is ineffective owing to the energy difference between the high energy pyramidal I and low energy pyramidal II 〈 c + a 〉 screw dislocations. A small addition of solutes, especially rare earth (RE) elements, can reduce this energy difference and accelerate cross-slip, thus enabling enhanced ductility. With increasing solute concentrations, the pyramidal I dislocation can become energetically favorable, which switches the primary 〈 c + a 〉 slip plane and alters the cross-slip process. Here, the transition path and energetics for double cross-slip of pyramidal I 〈 c + a 〉 dislocations are analysed in the regime where the pyramidal I dislocation is energetically more favorable than the pyramidal II. This is achieved using nudged elastic band simulations on a proxy MEAM potential for Mg designed to favor the pyramidal I over pyramidal II. The minimum energy transition path for pyramidal I double cross-slip is found to initiate with cross-slip onto a pyramidal II plane followed by cross-slip onto a pyramidal I plane parallel to the original pyramidal I plane. A previous mechanistic model for ductility is then extended to higher solute concentrations where pyramidal I is favorable. The model predicts an upper limit of solute concentrations beyond which ductility again becomes poor in Mg alloys. The model predictions are consistent with limited experiments of Mg-RE alloys at high concentrations and motivate further experimental studies in the high concentration regime.

更新日期：2020-01-01

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