Effect of a micro-scale dislocation pileup on the atomic-scale multi-variant phase transformation and twinning
Effect of a micro-scale dislocation pileup on the atomic-scale multi-variant phase transformation and twinning
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DOI：
10.1016/j.commatsci.2023.112508
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发表时间：
2022-08
影响因子：
3.3
通讯作者：
Yipeng Peng;Rigelesaiyin Ji;T. Phan;L. Capolungo;V. Levitas;Liming Xiong
中科院分区：
文献类型：
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作者：
Yipeng Peng;Rigelesaiyin Ji;T. Phan;L. Capolungo;V. Levitas;Liming Xiong
在这篇文章中，我们使用并行原子-连续(CAC)模拟来评估原子结构界面上微尺度位错堆积引起的内应力对原子尺度相变(PTS)、反向PTS和孪晶的贡献。这项工作的主要创新之处在于将界面的原子化描述和远离界面的滞后位错的粗粒度描述统一在一个框架内。我们的主要发现是：(A)界面通过形成台阶/台阶来动态响应堆积，台阶/台阶的高度与到达界面的位错数目成正比；(B)堆积引起的内部应力集中分布不是仅遵循经典的EShelby模型或超位错模型，而是两者的组合；(C)当预先剪切的样品被压缩时，在堆积尖端之前发生直接的正方形到六边形的PT，并最终成长为楔形。六方相的两种变体彼此形成孪晶；(D)随着载荷的进一步增加，新形成的六方相的一部分重新转变为正方形相。由该反向PT产生的方积相相对于初始方相形成孪生相。所有相界(PBS)和孪晶界(TBS)都是静止的，对应于零热力学EShelby驱动力；以及(E)微尺度位错堆积引起的内部剪应力和原子尺度界面的结构变化使启动PT所需的应力比不含位错的样品降低了5.5倍。这项工作首次表征了由微尺度位错滑移和原子结构界面之间的反应导致的PTS/孪生行为。这些知识将促进我们对多相材料在许多复杂物理过程中的行为的理解，如高压扭转下多相高熵合金或超硬陶瓷的合成，地球物理中的深地幔地震等，这些过程都涉及位错滑移、PTS、孪生及其相互作用，从原子到微尺度甚至更远。
In this paper, we perform concurrent atomistic–continuum (CAC) simulations to assess the contribution of the internal stress induced by the microscale dislocation pileup at an atomically structured interface to the atomic-scale phase transformations (PTs), reverse PTs, and twinning. The main novelty of this work is to unify the atomistic description of the interface and the coarse-grained (CG) description of the lagging dislocations away from the interface within one single framework. Our major findings are:(a)the interface dynamically responds to a pileup by forming steps/ledges, the height of which is proportional to the number of dislocations arriving at the interface;(b)the pileup-induced internal stress concentration profile follows neither the classical Eshelby model nor the super-dislocation model alone, but a combination of them;(c)when the pre-sheared sample is compressed, a direct square-to-hexagonal PT occurs ahead of the pileup tip and eventually grows into a wedge shape. The two variants of the hexagonal phases form a twin with respect to each other;(d)upon a further increase of the loading, part of the newly formed hexagonal phase transforms back to the square phase. The square product phase resulting from this reverse PT forms a twin with respect to the initial square phase. All phase boundaries (PBs) and twin boundaries (TBs) are stationary and correspond to zero thermodynamic Eshelby driving forces; and(e)the microscale dislocation pileup-induced internal shear stress and the structural change at the atomic-scale interface reduces the stress required for initiating a PT by a factor of 5.5, comparing with that in the sample containing no dislocations. This work is the first characterization of the behavior of PTs/twinning resulting from the reaction between a microscale dislocation slip and an atomically structured interface. The gained knowledge will advance our understanding of how the multi-phase material behaves in many complex physical processes, such as the synthesis of multi-phase high-entropy alloys or superhard ceramics under high-pressure torsion, deep mantle earthquakes in geophysics, and so on, which all involve dislocation slip, PTs, twinning, and their interactions across from the atomistic to the microscale and beyond.