CAREER: An Efficient First-Principles Method for Calculating Deformation Properties, Diffusivity, and Secondary Creep-Rate Behavior in BCC High-Entropy Alloys

该项目由材料研究部的凝聚态物质与材料理论项目和促进竞争研究的既定项目（EPSCoR）共同资助。该职业奖支持计算研究和教育活动，旨在了解新型工程合金（称为高熵合金（HEAs））的基本失效机制。HEAs是一种相对较新的工程材料，在高温和承重应用中有望取代传统的工程合金，如钢。HEAs是独特的，因为它们通常由五种元素以大约相等的比例组成，而传统的工程合金，如常规钢，具有一种基本合金元素（例如铁），其成分至少占95%。然而，使用基于物理的模拟来确定HEAs的属性是具有挑战性的，因为处理HEAs的多个元素和原子配置需要大量的计算资源。PI和她的团队将研究HEAs的一个重要力学特性，即蠕变破坏，这是材料在施加载荷或应力下的时间依赖性和永久性变形。对这些材料蠕变失效的基本理解，可能会导致用HEAs取代传统的工程合金，从而制造出更快、更省油、更便宜的机器。该奖项还支持一项教育计划，该计划旨在(i)为本科生开发和提供以研究为重点的研讨会，以及（ii）促进教师参与当前的指导计划。PI和她的团队将为一年级和第一学期的学生创建一系列研讨会，这些研讨会将被添加到新墨西哥理工学院的指导计划中。这些研讨会将由教师授课，并将为学生提供在本科研究环境中有用的技术工具箱。参与的学生将获得小额奖学金，作为消耗性实验室用品在教师的研究实验室使用。参与该项目的研究和教育部分的本科生和研究生将被培训为研究技术和计算材料科学方面受过良好教育的劳动力。本职业奖支持计算研究和教育活动，重点是使用基于密度泛函理论的第一性原理计算来预测影响体心立方高熵合金（HEAs）二次蠕变速率特性的因素。HEAs是一类相对较新的工程材料，在高温或结构工程应用中有望取代传统的单主元素工程合金。然而，当原子级计算用于确定HEAs的性质时，HEAs提出了几个挑战，因为(i)这种计算比具有相同原子数量的有序系统的计算更耗时，（ii）当存在缺陷时，它们需要对结构的几个原子构型排列进行平均，以及（iii）预测非稀释随机结构中的扩散率的模型不存在于原子水平的体心立方材料。将完成四个研究目标，以解决将原子级计算应用于HEAs的挑战。首先，将开发一种有效的第一性原理方法，并通过统计推理验证具有点缺陷和面缺陷的结构。推理统计方法允许用户根据更大的全局总体的样本集选择适当的误差条。其次，将Manning的随机合金扩散理论与体心立方主晶格中成对溶质的新频率模型相结合，建立用于计算HEAs中原子跳跃频率和扩散系数的扩散模型。结合推理统计，得到了计算HEA中各元素扩散系数的有效方法。第三，应用推理统计方法计算层错能和弹性常数。探讨了杂质偏析对体心立方HEAs层错能的影响。最后，计算得到的扩散和变形特性将纳入通用的二次蠕变规律。通过通用蠕变定律中的一系列关系，研究变形和扩散特性对蠕变行为的影响。该项目将为未来HEA系统的实验和计算研究提供有价值的数据，同时为材料科学界提供一个框架，可用于其他工程合金的有效性能测定。该奖项还支持一项教育计划，该计划旨在(i)为本科生开发和提供以研究为重点的研讨会，以及（ii）促进教师参与当前的指导计划。PI和她的团队将为一年级和第一学期的学生创建一系列研讨会，这些研讨会将被添加到新墨西哥理工学院的指导计划中。这些研讨会将由教师授课，并将为学生提供在本科研究环境中有用的技术工具箱。参与的学生将获得小额奖学金，作为消耗性实验室用品在教师的研究实验室使用。参与该项目的研究和教育部分的本科生和研究生将被培训为研究技术和计算材料科学方面受过良好教育的劳动力。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。

This project is jointly funded by the Condensed-Matter-and-Materials-Theory program in the Division of Materials Research and by the Established Program to Stimulate Competitive Research (EPSCoR).NONTECHNICAL SUMMARYThis CAREER award supports computational research and educational activities with an aim to understand fundamental failure mechanisms in a new class of engineering alloys called high-entropy alloys (HEAs). HEAs are a relatively new class of engineering materials that show significant promise for replacing traditional engineering alloys, such as steel, in high temperature and load-bearing applications. HEAs are unique because they are typically composed of five elements in approximately equal proportions, whereas traditional engineering alloys, such as conventional steel, have one base alloying element (e.g. iron) which makes up at least 95% of the composition. Determining properties of HEAs using physics-based simulations, however, are challenging because of the large computational resources required to handle the multiple elements and atomic configurations of HEAs. The PI and her team will investigate an important mechanical property of HEAs, known as creep failure, which is the time-dependent and permanent deformation of a material under applied load or stress. A fundamental understanding of creep failure in these materials could potentially lead to the replacement of traditional engineering alloys with HEAs that could create faster, more fuel-efficient, and less costly machines. This award also supports an education plan which is aimed at (i) developing and delivering research-focused workshops to undergraduates, and (ii) facilitating faculty involvement in the current mentoring program. The PI and her team will create a series of workshops for first-year, first-semester students that will be added into the mentoring program at New Mexico Tech. These workshops will be delivered by faculty and will provide students with a toolbox of techniques useful in an undergraduate research setting. Participating students will be offered a small scholarship to use as consumable laboratory supplies in a faculty member's research laboratory. The undergraduate and graduate students engaged in the research and education components of this project will be trained as an educated workforce in research techniques and computational materials science. TECHNICAL SUMMARYThis CAREER award supports computational research and educational activities focused on the use of first-principles calculations based on density functional theory to predict factors that contribute to secondary creep rate properties of body-centered cubic high-entropy alloys (HEAs). HEAs are a relatively new class of engineering materials that show significant promise for replacing traditional, single-principal element engineering alloys in high temperature or structural engineering applications. However, HEAs pose several challenges when atomistic-level calculations are used to determine their properties, since (i) such calculations are more time consuming than those for ordered systems with an equivalent number of atoms, (ii) they require averaging of several atomic configuration permutations of a structure when a defect is present, and (iii) a model for predicting diffusivity in non-dilute random structures does not exist for body-centered cubic materials at the atomic level. Four research objectives will be completed to solve the challenges of applying atomistic-level calculations to HEAs. First, an efficient first-principles methodology validated with statistical inference will be developed for structures with point and planar defects. The inferential statistics method allows the user to select an appropriate error bar based on the sample set of a larger, global population. Second, a diffusion model for calculating atomic jump frequencies and diffusion coefficients in HEAs will be developed by combining Manning’s theory of diffusivity in random alloys with a novel frequency model for paired solutes in a body-centered cubic host lattice. When combined with inferential statistics, an efficient method for calculating the diffusion coefficients of each element in the HEA will be obtained. Third, stacking fault energy and elastic constants will be calculated by applying the inferential statistics method. The effect of impurity segregation on stacking fault energy in body-centered cubic HEAs will be explored. Finally, the calculated diffusion and deformation properties will be incorporated into a universal secondary creep law. Through a series of relationships in the universal creep law, contributions to creep behavior from deformation and diffusion properties will be investigated. This project will provide valuable data that is necessary to focus future experimental and computational research on HEA systems, while giving the materials science community a framework that can be used for efficient property determination in other engineering alloys.This award also supports an education plan which is aimed at (i) developing and delivering research-focused workshops to undergraduates, and (ii) facilitating faculty involvement in the current mentoring program. The PI and her team will create a series of workshops for first-year, first-semester students that will be added into the mentoring program at New Mexico Tech. These workshops will be delivered by faculty and will provide students with a toolbox of techniques useful in an undergraduate research setting. Participating students will be offered a small scholarship to use as consumable laboratory supplies in a faculty member's research laboratory. The undergraduate and graduate students engaged in the research and education components of this project will be trained as an educated workforce in research techniques and computational materials science.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.