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首页> 外文期刊>Journal of the Mechanics and Physics of Solids >On the role of pre-existing defects in influencing hardness in nanoscale indentations - Insights from atomistic simulations
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On the role of pre-existing defects in influencing hardness in nanoscale indentations - Insights from atomistic simulations

机译：关于预先存在缺陷在纳米级凹陷的硬度中的作用 - 原子模拟中的见解

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Using in-situ nanoindentation experiments it is possible to study the dislocation mechanisms which unfold under an indenter.Large-scale atomistic simulations of the same are possible due to similarities in length scale, provided that defects can be included in the simulation. Yet, nanoindentation simulations have so far been mostly undertaken on defect free samples, while studies with pre-existing defects are few. The latter show that the average hardness is not affected by the presence of pre-existing defects, which justifies the use of ideal crystals in such simulations. However, this observation is counter-intuitive, as indenter-defect interactions should lead to work hardening and manifest themselves in hardness calculations. Our simulations along with a new look at the evolution of dislocations under the indenter, show for the first time, that hardness in atomistic simulations is influenced by pre-existing defects in the sample. Utilizing a face-centred tetragonal TiAl bicrystal with misfit dislocations at the interface, to populate the sample with defects, we correlate the contact-pressure variations to defect-indenter interactions. We show that the measured contact-pressure is affected by the presence and nature of defects under the indenter. Dislocation pile ups lead to intermittent rise in contact pressure, while seamless growth leads to steady convergence. The sensitivity to detect such defect interactions depends upon indenter size while convergence to average hardness is a result of curvature accommodation near the surface. Our findings prove that pre-existing defects have a profound influence on calculated hardness in indentation simulations which also corroborates with experimental observations in the literature.
机译：使用原位纳米狭窄实验，可以研究在压模下展开的位错机制。由于长度尺度的相似性，因此可能具有相同的标识原子模拟，条件是缺陷可以包括在模拟中。然而，到目前为止，纳米indentation模拟主要是在缺陷免费样品上进行的，而具有预先存在的缺陷的研究很少。后者表明，平均硬度不受存在预先存在的缺陷的影响，这证明了这种模拟中的理想晶体的使用。然而，这种观察是反向直观的，因为缩进缺陷相互作用应该导致硬化并在硬度计算中表现出来。我们的模拟以及缩进下的脱位的演变，首次出现，原子模拟中的硬度受到样本预先存在的缺陷的影响。利用在界面处的带有错位脱位的面向中心的四方的Tigrystal，以填充样品，与缺陷相关，我们将接触压力变化与缺陷 - 压痕相互作用相关联。我们表明，测量的接触压力受压痕下缺陷的存在和性质的影响。脱位堆积升高导致接触压力间歇性升高，而无缝增长导致稳定收敛。检测这种缺陷相互作用的灵敏度取决于压紧尺寸，同时收敛到平均硬度是表面附近的曲率的结果。我们的研究结果证明，预先存在的缺陷对压痕模拟中的计算硬度产生了深刻的影响，这也是在文献中的实验观察中得到证实的。

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