[论文解读] Effect of slip transmission at grain boundaries in Al bicrystals

S. Haouala, Reza Alizadeh+3 more|arXiv (Cornell University)|Sep 7, 2019

Microstructure and mechanical properties参考文献 58被引用 7

一句话总结

本研究开发了一种与应变速率相关的基于位错的晶体塑性模型，用于研究铝双晶中晶界（GB）处的滑移传输行为，通过修改Kocks-Mecking定律，引入完全不透明、部分透明和完全透明三种GB类型。主要发现为：滑移传输显著改变了变形机制：部分透明GB可减少位错塞积和应力集中，而完全透明GB虽可消除应力集中，但与实验观测结果不一致，表明大多数GB由于滑移系统取向匹配度有限及潜在加工硬化效应，实际行为近乎不透明。

ABSTRACT

The effect of slip transfer on the deformation mechanisms of Al bicrystals was explored using a rate-dependent dislocation-based crystal plasticity model. Three different types of grain boundaries (GBs) were included in the model by modifying the rate of dislocation accumulation near the GB in the Kocks-Mecking law, leading to fully-opaque (dislocation blocking), fully-transparent and partially-transparent GBs. In the latter, slip transmission is only allowed in pairs of SS in neighbour grains that are suitably oriented for slip transfer according to the Luster-Morris parameter. Modifications of the GB character led to important changes in the deformation mechanisms at the GB. In general, bicrystals with fully-opaque boundaries showed an increase in the dislocation density near the GB, which was associated with an increase in the Von Mises stress. In contrast, the dislocation pile-ups and the stress concentration were less pronounced in the case of partially-transparent boundaries as the slip in one grain can progress into the next grain with some degree of continuity. No stress concentrations were found at these boundaries for fully-transparent boundaries, and there was continuity of strain across the boundary, which is not typical of most experimentally observed GBs. Simulations of ideal bicrystals oriented for favorable slip transfer on the most highly favored slip system in grains with high Schmid factors for slip transfer depends on the number of active SS in operation in the neighborhood and that most boundaries will lead to nearly opaque conditions while some boundaries will be transparent. Finally, the model was applied to a particular experimentally observed GB in which slip transfer was clearly operating indicating that the model predicted a nearly transparent GB.

研究动机与目标

• 理解晶界（GB）特征如何影响铝双晶中滑移传输与变形机制。
• 开发一种晶体塑性模型，通过修改Kocks-Mecking定律中的位错累积速率，显式考虑晶界对位错传输的阻力。
• 评估GB透明度（完全不透明、部分透明、完全透明）对位错塞积、应力集中和应变连续性的影响。
• 评估该模型是否能够预测真实GB中实验观测到的滑移传输行为。
• 确定多个活性滑移系统及Luster-Morris参数在促进或抑制GB处滑移传输中的作用。

提出的方法

• 采用应变速率相关的基于位错的晶体塑性有限元模型，通过调整边界附近位错累积速率，对Kocks-Mecking定律进行修改，以表征不同类型的GB。
• 模拟了三种GB类型：完全不透明（完全阻断）、完全透明（无阻力）和部分透明（仅当Luster-Morris参数超过临界值时才允许滑移传输）。
• 利用Luster-Morris参数判断相邻晶粒中滑移系统之间的几何相容性，仅当两个系统均处于有利取向时才允许滑移传输。
• 在理想化的双晶上进行模拟，采用无约束和有约束的周期性边界条件，选取的取向可实现单滑移和双滑移激活。
• 通过将模型应用于某一实验中已观测到的GB（滑移传输已被证实），将预测的滑移系统活性与实验观测结果进行比较，实现模型验证。
• 通过硬化相互作用矩阵引入潜在加工硬化，以捕捉非激活滑移系统引起的加工硬化效应。

实验结果

研究问题

• RQ1 GB的透明度在多大程度上影响铝双晶中界面处的位错塞积与应力集中？
• RQ2 相邻晶粒中活性滑移系统的数量在多大程度上影响GB的有效透明度？
• RQ3 Luster-Morris参数是否能够在晶体塑性模型中可靠预测GB处的滑移传输？
• RQ4 无约束与有约束周期性边界条件对变形响应受GB特征影响的敏感性有何不同？
• RQ5 与完全不透明或完全透明假设相比，部分透明GB模型是否更准确地捕捉了实验中观测到的应变连续性与应力集中降低现象？

主要发现

• 具有完全不透明GB的双晶在边界附近表现出显著的位错塞积，并伴随Von Mises应力显著升高，表明存在强烈的应力集中。
• 部分透明GB通过在Luster-Morris参数超过临界阈值时允许滑移传输，有效减少了位错塞积和应力集中。
• 完全透明GB消除了应力集中，并确保了边界处应变的连续性，但该行为与铝中实际GB的实验观测结果不一致。
• 当多个具有相近Schmid因子的活性滑移系统共存时，会产生强烈的潜在加工硬化，即使某一滑移系统对齐良好，边界仍表现出近乎不透明的行为。
• 在对某一实际实验观测GB的模拟中，模型预测的滑移系统活性介于完全不透明与完全透明情况之间，且与实验观测到的高活性系统一致，表明模型具有实际相关性。
• 结果表明，由于潜在加工硬化与几何相容性有限的共同作用，即使某些滑移系统取向有利，大多数GB在实际中仍表现为有效不透明。