Amorphization induced by 60° shuffle dislocation pileup against different grain boundaries in silicon bicrystal under shear
Amorphization induced by 60° shuffle dislocation pileup against different grain boundaries in silicon bicrystal under shear
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DOI：
10.1016/j.actamat.2019.08.023
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发表时间：
2019-10-15
期刊：
影响因子：
9.4
通讯作者：
Xiong, Liming
中科院分区：
文献类型：
--
作者：
Chen, Hao;Levitas, Valery I.;Xiong, Liming
采用分子动力学（MD）方法模拟了金刚石-立方（dc）硅（Si）双晶在剪切作用下，在不同晶界（GBs）处的60位错堆尖前非晶带形核和生长的过程.当局部分解的剪切应力达到对于相同的非晶化平面在完美单晶中非晶化所需的近似相同的值（8.6- 9.3GPa）时，非晶化开始。由于位错堆积尖端的局部应力随着位错堆积数量的增加而增加，因此形成非晶剪切带的临界外加剪应力Tap随着晶界处位错的积累而显著降低。特别地，当堆积中的位错数量从3增加到8时，对于Sigma 9和Sigma 19 GB，临界剪切应力分别从4.7 GPa下降到1.6 GPa，对于2 Sigma GB，临界剪切应力分别从4.6 GPa下降到2.1 GPa。在晶界处形成台阶和无序晶胚后，不同晶界附近形成非晶剪切带的原子机制不同。对于高角度GB，例如σ 3，非晶带沿着沿着（112）平面传播通过晶相。对于Sigma 9 GB，位错分离并形成堆垛层错，然后在沿（110）面沿着形成非晶带之前。对于Sigma 19 GB，沿（111）平面沿着的单层堆垛层错转变成有趣的中间相：原子键沿（111）平面沿着排列的双层带（即，相对于带外的原子键旋转30度）。该中间相在进一步的剪切作用下沿（111）面沿着转变为非晶带。所获得的结果代表了一个原子级的确认位错堆积在各种应变诱导相变（PT）的成核位点的有效性，并表现出一定的局限性。(C)2019 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
Molecular dynamics (MD) simulations of the amorphous band nucleation and growth ahead of the tip of a shuffle 60 dislocation pileup at different grain boundaries (GBs) in diamond-cubic (dc) silicon (Si) bicrystal under shear are performed. Amorphization initiates when the local resolved shear stress reaches approximately the same value required for amorphization in a perfect single crystal (8.6-9.3 GPa) for the same amorphization plane. Since the local stresses at the tip of a dislocation pileup increase when the number of the dislocations in a pileup is increased, the critical applied shear stress T-ap for the formation of an amorphous shear band significantly decreases with the dislocation accumulation at the GBs. In particular, when the number of the dislocations in a pileup increases from 3 to 8, the critical shear stress drops from 4.7 GPa to 1.6 GPa for both the Sigma 9 and Sigma 19 GBs and from 4.6 GPa to 2.1 GPa for the 2 Sigma GB, respectively. After the formation of steps and disordered embryos at the GBs, the atomistic mechanisms responsible for the subsequent amorphous shear band formations near different GBs are found to distinct from each other. For a high-angle GB, such as Sigma 3, an amorphous band propagates through the crystalline phase along the (112) plane. For the Sigma 9 GB, dislocations disassociate and the stacking faults form, which then precede the formation of an amorphous band along the (110) plane. For the Sigma 19 GB, the one-layer stacking fault along the (111) plane transforms into an interesting intermediate phase: a two-layer band with the atomic bonds being aligned along the (111) plane (i.e., rotated by 30 degrees with respect to the atomic bonds outside the band). This intermediate phase transforms to the amorphous band along the (111) plane under a further shearing. The obtained results represent an atomic-level confirmation of the effectiveness of dislocation pileup at the nucleation site for various strain-induced phase transformations (PTs), and exhibit some limitations. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.