Lattice Distortions in Concentrated Metallic Alloys

非技术概要大多数金属合金都是以单一的主要元素为基础，并加入少量的其他元素。例如，常见的结构钢主要是铁，其他元素的含量不到2%。近年来，多元素大量存在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人们研究的热点。这些复杂合金的性质与简单合金性质不同的确切原因是激烈辩论的主题。一种想法是，复杂合金的原子级结构因存在如此多不同种类的原子而严重扭曲，每个原子的大小都不同。这个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。对这些新型合金原子级结构的更好理解将有助于开发具有优异机械和功能性能的新材料。该项目的一个相关教育方面是验证一种新的工具，用于评估学生学习与材料结构相关的概念的能力，这将有助于材料科学和工程中更好的教学方法的发展。技术摘要在过去的15年里，多元主元合金(MPEA)一直是密集研究的主题，部分原因是它们在结构和功能应用方面的前景。早期有人建议，由于需要容纳不同大小的原子，这些合金的晶格应该高度扭曲。虽然晶格扭曲假说被广泛引用来解释高熵合金的一些新性质，但支持这一假说的证据很少，而且相互矛盾。该计划使用MPEA单晶的弥散X射线和中子散射研究，以及对多晶的总散射实验，以提供无与伦比的洞察复杂浓缩合金中晶格扭曲的本质，以及更广泛的结构无序。用结构的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(四组分和五组分)合金和成分相似但更简单的(两组分和三组分)合金中的无序，可以检验添加组分会导致不同程度或类型的无序的假设。在一套相辅相成的教育活动中，材料结构本科课程中使用的概念清单正在完成并得到验证，以表明它衡量了学生的专家思维。完成后，验证后的概念清单将分发给教师在他们的课程中使用。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.