Lattice Distortions in Concentrated Metallic Alloys

大多数金属合金都是基于单一的主要元素，并添加少量的其他元素。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，其中多种元素大量存在而没有单一多数元素的复杂浓缩合金已经成为许多研究兴趣的主题，因为它们显示出有前途的性质。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的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测试这一想法。对这些新型合金的原子尺度结构的更好理解可以导致具有上级机械和功能特性的新材料的开发。该项目的一个相关的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。技术摘要多主元素合金（MPEAs）在过去的十五年中一直是激烈研究的主题，部分原因是它们在结构和功能应用中的前景。早期有人提出，这些合金的晶格应该是高度扭曲的，因为需要容纳各种尺寸的原子。尽管晶格畸变假设被广泛用来解释高熵合金的一些新颖性质，但支持它的证据却很少且相互矛盾。 该计划使用MPEA单晶的扩散X射线和中子散射研究以及多晶体的总散射实验，以提供对复杂浓缩合金中晶格畸变和结构无序性质的无与伦比的洞察。实验的补充和交叉验证与密度泛函理论计算的结构。通过比较复杂（四和五组分）合金与组成相似但更简单（两组分和三组分）合金中的无序，可以测试添加组分导致不同程度或类型的无序的假设。 在一套补充的教育活动中，正在完成和验证用于材料结构本科课程的概念清单，以表明它衡量学生的专家思维。完成后，经验证的概念清单将分发给教师，供其在课程中使用。该奖项反映了NSF的法定使命，并被认为值得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来支持。

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.