Tests of MacPherson-Srolovitz Grain Growth in Metallic Polycrystals

金属多晶中麦克弗森-斯罗洛维茨晶粒生长试验

• 批准号: 0805100
• 负责人: Robert Suter
• 金额: $ 35万
• 依托单位: Carnegie-Mellon University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-06-15 至 2012-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0805100&HistoricalAwards=false
• 关键词: Tests; MacPherson; Srolovitz; Grain; Growth

TECHNICAL: Cellular structures, ranging from soap bubbles or other froths to crystalline grains in polycrystals, tend to coarsen over time. Coarsening refers to the fact that some cells grow while others shrink and disappear. Understanding this process in any cellular structure contributes to controlling it and tailoring it for particular needs and applications. In two dimensions, the famous 1950s von Neumann-Mullins calculation expresses the rate of change of the area of a cell in terms of the number of its triple points (points where the cell has two neighbors). Until 2007, when MacPherson and Srolovitz published a d-dimensional generalization, there was no analogous formula in three dimensions. The MacPherson and Srolovitz calculation gives the rate of change of a cell volume in terms of simple geometrical quantities: the grain size (the mean width) and the total length of triple lines bounding the grain. However, applying this calculation to grain growth in polycrystals is somewhat suspect since it assumes that all boundaries have the same properties. Unfortunately, this is not true for crystal-to-crystal interfaces where properties depend on five mesoscopic parameters. So the question is, does the theoretical result help us understand growth in real materials? Can it be taken as a starting point from which to develop more complex models? These are basic scientific questions with direct implications for real world materials. Making materials with desirable properties requires control over grain size and grain boundary type distributions. Gaining predictive control over these properties requires a detailed, verified model. Contemporaneous with theoretical developments is the development of x-ray diffraction microscopy (XDM), a non-destructive, high energy, synchrotron x-ray technique that measures the location, shape, and orientation of large numbers of crystalline grains inside bulk polycrystals. Being non-destructive means that an ensemble of grains can be mapped, the sample annealed to allow growth, and the same volume of material re-mapped to determine changes. Within micron scale resolution limits, the measurements yield the types of each grain boundary and the geometry of grains. XDM measurements will begin with a high purity aluminum polycrystal that should approximate assumptions of the MacPherson-Srolovitz theory and continue with more complicated (impure and more anisotropic) materials. The objective is to determine whether the theory is applicable and whether it is useful as a starting point even when the assumptions are not well met. NON-TECHNICAL: The ability to perform non-destructive 3D microstructure measurements will have a broad impact in the materials sciences. Grain growth measurements will demonstrate the capabilities of microstructure mapping at the Advanced Photon Source (APS) and will help attract a community of users to the dedicated facility that has been developed over the past five years. The facility will include hardware and the software and computational power necessary to generate microscope output. Results and other measurements using the facility will help to constrain and/or validate theories and computer simulations of materials response to a variety of processing treatments including thermal, mechanical, and chemical. The technique can be used to study any crystal-based materials. Graduate and undergraduate students in Physics and Materials Science and Engineering will work in an interdisciplinary environment that cuts across fundamental materials issues, x-ray science, and applications technology. They will work within a large, active microstructure-community at CMU and at APS.

技术：细胞结构，从肥皂泡或其他泡沫到多晶体中的晶粒，往往会随着时间的推移而变粗。粗化指的是一些细胞生长而另一些细胞萎缩和消失。了解任何细胞结构中的这一过程有助于控制它，并根据特定的需求和应用对其进行调整。在二维空间中，20世纪50年代著名的冯·诺伊曼-穆林斯计算用一个细胞的三重点（该细胞有两个邻居的点）的数量来表示细胞面积的变化率。直到2007年，当MacPherson和Srolovitz发表了d维推广时，在三维中没有类似的公式。MacPherson和Srolovitz的计算给出了一个简单的几何量的细胞体积的变化率：晶粒尺寸（平均宽度）和总长度的三线界定的颗粒。然而，将这种计算应用于多晶体中的晶粒生长有些可疑，因为它假设所有的边界具有相同的性质。不幸的是，这是不正确的晶体-晶体界面的性能取决于五个介观参数。所以问题是，理论结果是否有助于我们理解真实的材料中的生长？它是否可以作为开发更复杂模型的起点？这些都是对真实的世界材料有直接影响的基本科学问题。制造具有所需性能的材料需要控制晶粒尺寸和晶界类型分布。获得对这些属性的预测控制需要一个详细的，经过验证的模型。与理论发展同步的是X射线衍射显微镜（XDM）的发展，这是一种非破坏性的高能同步X射线技术，可以测量大块多晶体内大量晶粒的位置、形状和取向。非破坏性意味着可以映射晶粒的集合，样品退火以允许生长，并且相同体积的材料重新映射以确定变化。在微米级分辨率范围内，测量产生每个晶界的类型和晶粒的几何形状。XDM测量将开始与高纯度铝多晶，应该近似MacPherson-Srolovitz理论的假设，并继续与更复杂（不纯和更各向异性）的材料。其目的是确定理论是否适用，以及即使在假设没有得到很好满足的情况下，它作为起点是否有用。非技术性：执行非破坏性3D微观结构测量的能力将对材料科学产生广泛影响。晶粒生长测量将展示高级光子源（APS）的微观结构测绘能力，并将有助于吸引用户社区到过去五年开发的专用设施。该设施将包括硬件和软件以及生成显微镜输出所需的计算能力。使用该设施的结果和其他测量将有助于约束和/或验证材料对各种加工处理（包括热处理、机械处理和化学处理）的响应的理论和计算机模拟。该技术可用于研究任何基于晶体的材料。物理学和材料科学与工程的研究生和本科生将在跨学科的环境中工作，该环境跨越基本材料问题，x射线科学和应用技术。他们将在CMU和APS的一个大型，活跃的微结构社区内工作。