Defect Structure and Mechanical Behavior of High Entropy Alloys

技术概述：惯例规定，在合金化过程中，多组分合金体系要么形成金属间相，要么形成脆性显微组织，要么形成金属玻璃。近年来，人们发现某些合金具有五种或五种以上的成分，它们都具有近似等原子组成，结构简单，具有独特的物理性能。这些材料可能具有很高的机械硬度和强度。对这些理想结构的力学性能和稳定程度的基本理解尚未达到。提出的工作研究缺陷的性质以及一系列fcc固溶体合金的机械性能，这些合金含有2到7个等原子组成的组分。合金样品将通过铸造或球磨方法进行实验制备。使用EDS和SEM进行化学分析，使用TEM和XRD测量稳定层错能，使用DSC研究结构稳定性。机械性能将通过拉伸测试和纳米压痕来测量。基于第一性原理密度泛函理论的方法将用于研究合金体系的物理性质。弹性常数将被计算并用于帮助解释用XRD实验测量的层错能。此外，弹性常数也将用于直接评价合金的机械稳定性。通过广义层错能曲线的计算，直接计算出稳定和不稳定层错能。这些量将用于预测和解释塑性力学响应。最后，从第一性原理出发，直接研究低角度晶界能和任何偏向晶界的原子偏析。非技术总结：对缺陷的本质和高熵合金的机械特性的基本理解有望为这些新型合金的潜在能力提供变革性的评估。对于具有相同底层原子结构的合金，这些材料的性质将作为组分（即原子类型）数量的函数进行系统探索。这项研究将提供关键的见解，如何在相同的晶格缺陷的变化作为一个函数的组件数量。这种衍生的理解可以为如何更好地设计具有简单金属晶体结构的多组分合金提供基础。由此产生的对这些理想结构的机械性能、性质和稳定性程度的基本理解，可以为未来新型合金的设计提供变革性的能力，并使其在各种应用中得到应用。该项目的另一个同样重要的目标是以硕士和博士研究生的形式开发智力资源。pi致力于这项教育工作，特别是对科学领域代表性不足的群体。

TECHNICAL SUMMARY: Convention has dictated that multi-component alloy systems either form intermetallic phases, brittle microstructures, or metallic glasses during alloying. Recently it has been found that some alloys with five components or more, all with approximately equiatomic compositions, form simple structures with unique physical properties. These materials may exhibit high mechanical hardness and strength. A fundamental understanding of the mechanical properties and the degree of the stability of these desirable structures has not been reached. The proposed work investigates the nature of defects as well as the mechanical properties of a series of fcc solid solution alloys that contain two to seven components of equiatomic composition. Alloy samples will be created experimentally by either casting or ball milling methods. EDS and SEM will be used to perform chemical analysis, TEM and XRD will be used to measure stable stacking fault energies, and DSC will be used to study structural stability. Mechanical properties will be measured through both tensile tests and nanoindentation. First-principles density functional theory based methods will be used to investigate the physical properties of the alloy system. Elastic constants will be calculated and used to help interpret the stacking fault energies measured experimentally with XRD. Additionally, the elastic constants will also be used to directly evaluate the mechanical stability of the alloy. Stable and unstable stacking fault energies will be directly calculated through calculation of generalized stacking fault energy curves. These quantities will be used to predict and interpret the plastic mechanical response. Finally, low-angle grain boundary energies and any preferential atomic segregation to grain boundaries will be directly studied from first principles.NON-TECHNICAL SUMMARY: A fundamental understanding of the nature of defects and the mechanical characteristics of high entropy alloys is expected to provide a transformative assessment of the potential capabilities of these novel alloys. The properties of these materials will be systematically explored as a function of number of components (i.e. atom types) for alloys with the same underlying atomic structure. This study will provide critical insight into how defects in the same lattice change as a function of number of components. This derived understanding could then provide a foundation for how to better design multi-component alloys with simple metallic crystal structures. The resulting fundamental understanding of the mechanical properties and the nature and degree of the stability of these desirable structures could provide transformative capabilities in the design of future novel alloys and enable their use in a variety of applications. An equally important goal of this project is the development of intellectual resources in the form of M.S. and Ph.D. research students. The PIs are committed to this education effort, especially for groups underrepresented in science.