Defect Structure and Mechanical Behavior of High Entropy Alloys

技术概要：传统上，多组分合金系统在合金化过程中形成金属间相、脆性显微结构或金属玻璃。最近，人们发现，某些合金含有五种或五种以上的成分，它们都具有近似等原子的组成，形成具有独特物理性质的简单结构。这些材料可以表现出高的机械硬度和强度。对这些理想结构的机械性能和稳定程度的基本理解尚未达到。拟议的工作调查的缺陷的性质，以及一系列的fcc固溶体合金，包含两个到七个等原子组成的成分的机械性能。合金样品将通过铸造或球磨方法进行实验。EDS和SEM将用于进行化学分析，TEM和XRD将用于测量稳定的堆垛层错能，DSC将用于研究结构稳定性。机械性能将通过拉伸试验和纳米压痕测量。基于第一性原理密度泛函理论的方法将被用来研究合金系统的物理性质。弹性常数将被计算并用于帮助解释用XRD实验测量的堆垛层错能量。此外，弹性常数也将用于直接评估合金的机械稳定性。通过计算广义层错能曲线，直接计算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，低角度晶界能和任何优先原子偏析晶界将直接从第一原理studyed.Non-Technical摘要：一个基本的理解的性质的缺陷和高熵合金的机械特性，预计将提供一个变革性的评估这些新型合金的潜在能力。这些材料的性能将被系统地探索为具有相同的基本原子结构的合金的组分（即原子类型）的数量的函数。 这项研究将提供关键的洞察如何在同一晶格中的缺陷变化作为一个功能的组件的数量。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。对这些理想结构的机械性能和稳定性的性质和程度的基本理解可以为未来新型合金的设计提供变革能力，并使其能够用于各种应用。该项目的一个同样重要的目标是以M.S.的形式开发智力资源。和博士研究生。PI致力于这一教育工作，特别是对科学代表性不足的群体。

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.