Lattice Distortions in Concentrated Metallic Alloys

浓缩金属合金中的晶格畸变

• 批准号: 2104764
• 负责人: Todd Hufnagel
• 金额: $ 38.19万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2104764&HistoricalAwards=false
• 关键词: Lattice; Distortions; Concentrated; Metallic; Alloys

Non-technical SummaryMost metallic alloys are based on a single principal element with other elements added in small amounts. Common structural steel, for example, is mostly iron with less than two percent of other elements present. Recently, complex concentrated alloys in which multiple elements are present in large amounts, with no single majority element, have been the subject of much research interest because they show promising properties. The precise reasons why the properties of these complex alloys are different from those of simpler alloys are the subject of intense debate. One idea is that the atomic-scale structure of complex alloys is heavily distorted by the presence of so many different kinds of atoms, each of different size. This project seeks to test this idea by careful experimental measurement and detailed computer simulations of structural distortions in complex alloys. An improved understanding of the atomic-scale structure of these novel alloys could lead to the development of new materials with superior mechanical and functional properties. A related educational aspect of the project is to validate a new tool for assessing how well students learn concepts related to the structure of materials, which will contribute to the development of better teaching methods in materials science and engineering.Technical SummaryMultiple-principal element alloys (MPEAs) have been the subject of intense research over the past fifteen years due in part to their promise in structural and functional applications. Early on it was suggested that the crystal lattices of these alloys should be highly distorted due to the need to accommodate atoms of various sizes. Although the lattice distortion hypothesis is widely invoked to explain some of the novel properties of high entropy alloys, evidence in support of it is sparse and contradictory. This program uses diffuse x-ray and neutron scattering studies of MPEA single crystals together with total scattering experiments on polycrystals to provide unparalleled insight into the nature of lattice distortions, and structural disorder more generally, in complex concentrated alloys. The experiments are supplemented and cross-validated with density functional theory calculations of structure. By comparing disorder in complex (four- and five-component) alloys with compositionally similar but simpler (two- and three-component) alloys the hypothesis that adding components results in a different degree or type of disorder can be tested. In a complementary set of educational activities, a concept inventory for use in undergraduate courses in Structure of Materials is being completed and validated to show that it measures expert thinking by students. When complete, the validated concept inventory will be disseminated to instructors for use in their courses.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

大多数金属合金是由单一的主元素和少量添加的其他元素构成的。例如，普通的结构钢主要是铁，其他元素的含量不到2%。近年来，大量存在多种元素而不存在单一多数元素的复杂浓缩合金因其具有良好的性能而成为研究的热点。这些复杂合金的性能与简单合金不同的确切原因是激烈争论的主题。一种观点认为，复杂合金的原子尺度结构由于存在如此多不同种类的原子而严重扭曲，每种原子的大小都不同。该项目试图通过仔细的实验测量和复杂合金结构扭曲的详细计算机模拟来验证这一想法。提高对这些新型合金的原子尺度结构的理解可以导致具有优越机械和功能性能的新材料的开发。该项目的一个相关教育方面是验证一种新的工具，用于评估学生如何学习与材料结构相关的概念，这将有助于开发更好的材料科学和工程教学方法。多主元素合金（mpea）由于其在结构和功能上的应用前景，在过去的15年中一直是研究的热点。早期有人提出，由于需要容纳不同大小的原子，这些合金的晶格应该是高度扭曲的。虽然晶格畸变假说被广泛用来解释高熵合金的一些新特性，但支持它的证据很少，而且相互矛盾。该程序使用MPEA单晶的漫射x射线和中子散射研究以及多晶的总散射实验，以提供对复杂浓缩合金中晶格扭曲和更普遍的结构紊乱的本质的无与伦比的见解。并用结构密度泛函理论计算对实验进行了补充和交叉验证。通过比较复杂合金（四组分和五组分）和成分相似但较简单的合金（二组分和三组分）的无序性，可以验证添加组分会导致不同程度或类型的无序性的假设。在一组补充教育活动中，正在完成并验证用于本科材料结构课程的概念清单，以表明它可以衡量学生的专家思维。完成后，经过验证的概念清单将分发给教师，供他们在课程中使用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。