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Determination of positions and curved transition pathways of screw dislocations in BCC crystals from atomic displacements

机译：从原子位移确定BCC晶体中螺丝位错的位置和弯曲过渡路径

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摘要

The theoretical description of the thermally activated dislocation glide in pure crystals depends crucially on the shape of the Peierls barrier that the dislocation has to overcome when moving through the lattice. While the height of this barrier can be obtained using saddle-point search algorithms such as the Nudged Elastic Band (NEB) method, its exact shape depends on the details of the approximation of the transition pathway of the system. The purpose of this paper is to formulate a procedure that allows to identify the dislocation positions along the path directly from the displacements of atoms in its core. We investigate the performance of this model by calculating curved paths of the 1/2 [111] screw dislocation in tungsten modeled by a Bond Order Potential using a series of images obtained by employing a modified NEB method at zero applied stress and for positiveegative shear stresses perpendicular to the slip direction. The Peierls barriers resulting from the curved paths are shown to be substantially different from those obtained when assuming straight dislocation path. For both straight and curved dislocation pathways we calculate the temperature dependencies of the flow stress and compare these predictions with direct experimental measurements. We show that a significantly better agreement with experiments is obtained if the curved dislocation pathway is taken into account.
机译：纯晶体中热活化位错滑移的理论描述主要取决于Peierls势垒的形状，该位错穿过晶格时必须克服。虽然可以使用鞍点搜索算法（例如微动弹性带（NEB）方法）获得此障碍的高度，但其确切形状取决于系统过渡路径的近似细节。本文的目的是制定一种程序，该程序可以直接从原子核的位移确定沿路径的位错位置。我们通过计算一系列的图像，通过使用修正的NEB方法在零施加应力和正负电压下获得的一系列图像，计算通过键序势建模的钨中1/2 [111]螺钉位错在钨中的弯曲路径，从而研究该模型的性能。垂直于滑动方向的剪切应力。弯曲路径产生的Peierls势垒与假定直线位错路径时获得的Peierls势垒显着不同。对于直位错位和弯曲位错位，我们都计算了流动应力的温度依赖性，并将这些预测与直接的实验测量结果进行了比较。我们表明，如果考虑到弯曲位错途径，则可以获得与实验明显更好的一致性。

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