Deformation nanomechanics and dislocation quantification at the atomic scale in nanocrystalline magnesium
Deformation nanomechanics and dislocation quantification at the atomic scale in nanocrystalline magnesium
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DOI：
10.1016/j.jma.2020.08.014
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发表时间：
2020-12
影响因子：
17.6
通讯作者：
Md Shahrier Hasan;R. Lee;Wenwu Xu
中科院分区：
文献类型：
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作者：
Md Shahrier Hasan;R. Lee;Wenwu Xu
采用经典的分子动力学模拟方法研究了不同晶粒尺寸的纳米晶镁的单轴拉伸变形行为。样品的平均晶粒尺寸从6.4 nm到45 nm不等，每个样品在建模系统中包含约4300万个原子。变形纳米力学揭示了两种不同的变形机制。对于较大晶粒尺寸的样品，观察到位错为主的变形，而在较小晶粒尺寸的样品，观察到晶界为基础的机制，如晶界滑动，晶界旋转。在10 nm附近发生正常和逆Hall-Petch关系的转变。位错密度定量表明，样品中的位错密度随着晶粒尺寸的减小而急剧降低。平均晶粒尺寸在20 nm以上的纳米晶镁的弹性模量保持与粗晶粒多晶块体的弹性模量相当，随后在该晶粒尺寸以下快速减小。本研究揭示了纳米晶镁的纳米力学特性，为设计和开发具有上级力学性能的镁基纳米结构合金提供了理论依据。
Classical molecular dynamics (MD) simulation method is employed to study the uniaxial tensile deformation of nanocrystalline magnesium (Mg) of varying grain size levels. The mean grain size of the sample is varied from 6.4 nm to 45 nm, with each sample containing about 43 million atoms in the modeling system. The deformation nanomechanics reveals two distinct deformation mechanisms. For larger grain-sized samples, dislocation dominated deformation is observed while, in smaller grain-sized samples, grain boundary-based mechanisms such as grain boundary sliding, grain boundary rotation are observed. The transition of normal and inverse Hall–Petch relation occurs at around 10 nm. Dislocation density quantification shows that the dislocation density in the sample drastically reduces with decreasing grain size. Elastic modulus of nanocrystalline Mg with mean grain size above 20 nm remains comparable to that of the coarse-grained polycrystalline bulk, followed by a rapid reduction below that grain size. The present work reveals the nanomechanics of nanocrystalline Mg, facilitating the design and development of Mg-based nanostructured alloys with superior mechanical properties.