Relative grain boundary energies from triple junction geometry: Limitations to assuming the Herring condition in nanocrystalline thin films
Relative grain boundary energies from triple junction geometry: Limitations to assuming the Herring condition in nanocrystalline thin films
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三结几何形状的相对晶界能量：假设纳米晶薄膜中赫林条件的局限性
DOI：
10.1016/j.actamat.2022.118476
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发表时间：
2023
期刊：
影响因子：
9.4
通讯作者：
Barmak, Katayun
中科院分区：
文献类型：
--
作者：
Patrick, Matthew J.;Rohrer, Gregory S.;Chirayutthanasak, Ooraphan;Ratanaphan, Sutatch;Homer, Eric R.;Hart, Gus L． W.;Epshteyn, Yekaterina;Barmak, Katayun
利用电子后向散射衍射（EBSD）和连续切片技术对体微晶样品的晶界特征分布（GBCD）进行了常规测量，并在满足Herring力平衡条件的前提下，利用该数据重建基于三线三维几何形状的相对晶界能量分布（GBED）。这些gbed与分子动力学（MD）预测的相关；此外，发现GBCD和GBED呈负相关。对于纳米晶体薄膜，采用进动增强电子衍射（PED）进行取向映射是有效的，但尚未提取出GBED。在这里，建立的相对能量提取技术适用于四种溅射沉积样品的PED数据：40 nm厚的钨膜和100 nm的铝膜，在400°C退火30和150 min后沉积。这些薄膜具有柱状晶粒结构，因此不需要连续切片来确定边界倾角。除了能量各向异性最强和居群边界最高的边界，即铝Σ3边界外，从这些数据中提取的相对GBED与使用MD计算的能量无关，也与实验确定的钨或铝薄膜的GBCD无关。未能重现预测的能量趋势意味着传统的鲱鱼方程不能应用于确定相对GBEDs，因此在这些膜的三结处的几何形状不能很好地描述这个条件；在空间受限的多晶材料中，额外的几何因素必须有助于确定三重结的几何形状和边界网络结构。
Grain boundary character distributions (GBCD) are routinely measured from bulk microcrystalline samples by electron backscatter diffraction (EBSD) and serial sectioning, and this data can be used to reconstruct relative grain boundary energy distributions (GBED) based on the 3D geometry of triple lines, assuming that the Herring condition of force balance is satisfied. These GBEDs correlate to those predicted from molecular dynamics (MD); furthermore, the GBCD and GBED are found to be inversely correlated. For nanocrystalline thin films, orientation mapping via precession enhanced electron diffraction (PED) has proven effective in measuring the GBCD, but the GBED has not been extracted. Here, the established relative energy extraction technique is adapted to PED data from four sputter deposited samples: a 40 nm-thick tungsten film and a 100 nm aluminum film as-deposited, after 30 and after 150 min annealing at 400 °C. These films have columnar grain structures, so serial sectioning is not required to determine boundary inclination. Excepting the most energetically anisotropic and highest population boundaries, i.e. aluminum Σ3 boundaries, the relative GBED extracted from these data do not correlate with energies calculated using MD nor do they inversely correlate with the experimentally determined GBCD for either the tungsten or aluminum films. Failure to reproduce predicted energetic trends implies that the conventional Herring equation cannot be applied to determine relative GBEDs and thus geometries at triple junctions in these films are not well described by this condition; additional geometric factors must contribute to determining triple junction geometry and boundary network structure in spatially constrained, polycrystalline materials.