Probing fractal abnormal grain growth at the nanoscale: a percolation scenario with microstructurally based selection rules

探测纳米尺度的分形异常晶粒生长：具有基于微观结构的选择规则的渗透场景

• 批准号: 262772036
• 负责人: Professor Dr. Rainer Birringer
• 金额: --
• 依托单位: Department of Physics
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/262772036?language=en
• 关键词: Probing; fractal; abnormal; grain; growth

Thanks to their large grain boundary area per unit volume, nanocrystalline materials find themselves quite far removed from thermodynamic equilibrium, as the excess energy stored in grain boundaries provides a huge driving force for coarsening of the nanoscale microstructure. The resulting grain growth typically proceeds in an abnormal manner, with a small fraction of grains growing to extremely large sizes at the expense of the nanometer-sized grains still present in the surrounding matrix. Such behavior is also observed in conventional, coarser-grained polycrystalline metals and ceramics, although it is not their usual mode of coarsening. Surprisingly, neither at the microscale nor at the nanoscale do we have an adequate grasp of the circumstances enabling abnormally growing grains to establish and maintain a remarkable growth advantage over their neighbors. This mystery is compounded at the nanoscale, where recent studies discovered that abnormally growing grains in nanocrystalline model systems (Pd and Pd-Au alloys) develop highly irregular, almost tumor-like shapes! The corresponding grain perimeters are found to be fractal in nature, much like those of structures formed upon the forced migration of domain walls through a randomly distributed field of pinning sites. Moreover, these abnormally growing grains exhibit fractal dimensionalities that closely match those of domains generated by known percolation processes.Inspired by this observation, we hypothesize that abnormal grain growth can be understood at the nanoscale as a manifestation of a percolation phenomenon occurring on a "network" defined by the initial arrangement of nanocrystalline matrix grains. This concept will be scrutinized by a combination of state-of-the-art electron microscopy and large-scale phase field simulation of microstructural evolution. The great advantage of the percolation scenario is its amenability to, on the one hand, exploratory testing of various "selection rules" for accelerated boundary migration (evaluating their impact on the development of fractality) and, on the other hand, providing a framework for narrowing down the experimental search for microscopic factors (such as grain boundary misorientations or concentration gradients) of possible relevance to the physical mechanism(s) governing fractal abnormal grain growth. Ultimately, the experimental findings will be translated into a minimal set of selection rules and inserted into a modified phase field model allowing for simultaneous abnormal and curvature-driven grain growth. The simulation results will be validated with respect to statistically averaged and local measures for growth kinetics and grain morphologies.

由于其每单位体积的晶粒边界面积较大，纳米晶体材料发现自己与热力学平衡相当远，因为晶界中存储的多余能量为纳米级微结构的块化提供了巨大的驱动力。所得谷物的生长通常以异常方式进行，而一小部分谷物生长到极大的尺寸，而牺牲了周围基质中仍然存在的纳米粒晶粒。在常规的，更粗糙的多晶金属和陶瓷中也观察到了这种行为，尽管这不是他们通常的粗化模式。出人意料的是，在微观尺度和纳米级，我们都没有对这种情况有足够的掌握，从而使异常生长的晶粒以建立和保持与邻居相对于邻居的显着增长优势。这个谜团在纳米级复杂化，最近的研究发现，纳米晶模型系统（PD和PD-AU合金）中异常生长的晶粒形成了高度不规则的，几乎类似肿瘤的形状！发现相应的晶圆周在本质上是分形的，就像在域壁通过固定位点的随机分布场的强制迁移迁移而形成的结构的分形一样。此外，这些异常生长的谷物表现出分形维度，这些维度与已知渗透过程所产生的域的域非常匹配。由于这种观察结果，我们假设在纳米级可以理解谷物的异常生长是在纳米级的表现中，是在“网络”上被定义的Nanoc nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan nan of nan and nan of inan of nan of nan of nan cart的表现。该概念将通过最先进的电子显微镜和显微结构进化的大规模相位场模拟的结合来审查。渗透情景的最大优势在于它的能力，一方面是对各种“选择规则”进行探索性测试，以加速边界迁移（评估它们对分形的影响），另一方面，另一方面，为范围缩小了对微观差异或浓度的相关性范围的实验性搜索范围（例如，可能范围）的框架，以缩小范围的范围（例如，素质边界误差或浓缩效果）的范围（可能是可能的范围）。谷物生长异常。最终，实验发现将被转化为最小的选择规则集，并插入改进的相位场模型，从而允许同时异常和曲率驱动的晶粒生长。模拟结果将在统计平均和局部生长动力学和谷物形态的局部测量方面得到验证。

项目成果

Influence of rapid annealing on the evolution of fractal abnormal grains in nanocrystalline Pd–10 at% Au

影响%20of%20rapid%20annealing%20on%20the%20evolution%20of%20fractal%20abnormal%20grains%20in%20nano crystal%20Pdâ10%20at%%20Au

• DOI: 10.1088/1757-899x/580/1/012055
• 发表时间: 2019
• 期刊: IOP Conference Series: Materials Science and Engineering
• 作者: Raphael A. Zeller;Harms J. Fey;Christian Braun;Rainer Birringer;Carl E. Krill III
• 通讯作者: Carl E. Krill III

Orientation mapping linked to fractal analysis: A method for studying abnormal grain growth in nanocrystalline PdAu

与分形分析相关的取向映射：一种研究纳米晶 PdAu 中异常晶粒生长的方法

• DOI: 10.1063/5.0029832
• 发表时间: 2020
• 期刊: Journal of Applied Physics
• 影响因子: 3.2
• 作者: Christian Braun;Raphael A. Zeller;Hanadi Menzel;Jörg Schmauch;Carl E. Krill III;Rainer Birringer
• 通讯作者: Rainer Birringer