Characterizing Local Chemical Order in Multi-Principal Element Alloys by Femtosecond Time-Resolved Ultrafast Electron Diffraction

通过飞秒时间分辨超快电子衍射表征多主元素合金中的局部化学顺序

• 批准号: 2327777
• 负责人: Mingwei Chen
• 金额: $ 50万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-09-01 至 2026-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2327777&HistoricalAwards=false
• 关键词: Characterizing; Local; Chemical; Order; Multi

NON-TECHNICAL SUMMARYAlloying is an important approach to improve the mechanical performance of metallic materials. The recent discovery of multi-principal element alloys in which equiatomic constituent elements act as both principal and alloying elements opens a new field to search and develop new metallic materials with unprecedented properties for applications under extreme conditions of cryogenic temperatures, shock loading, harsh chemical environments, and ultrahigh temperatures. The distinctive properties of multi-principal element alloys originate from complex chemical interactions amongst constituent elements. It is essential to understand local static arrangements and dynamics (usually termed as phonons) of constituent atoms in the complex alloys for designing and modeling the new class of materials. As the scattering signals of the local static structure and phonons overlap in diffraction spectra, it is challenging to characterize the structure and dynamics of the complex alloys using traditional X-ray and electron diffraction methods. This project is developing a new approach to characterize multi-principal element alloys using femto-second time-resolved MeV electron diffraction. Electron diffraction at ultrafast time regimes can effectively decouple the static and dynamic atomic scattering and unveil the atomic insights of structure and dynamics of multi-principal element alloys. This project is making substantial progress towards understanding the structure-property relations of complex alloys and is helping enable the development of new metallic materials for a wide range of industry applications to strengthen the U.S. competitiveness in advanced and high-performance materials.TECHNICAL SUMMARYIn multi-principal element alloys (MPEAs) local chemical order plays a crucial role in determining structural properties and phase stability, but it is challenging to characterize experimentally due to the entanglement between static diffuse scattering from local chemical order and dynamic diffuse scattering from coherent and incoherent phonons. This project will employ MeV ultrafast electron diffraction (MeV UED) to investigate local chemical order in single-crystal MPEAs. By utilizing the femto-second time resolution and the high reciprocal spatial resolution of MeV UED, the entanglement between the static and dynamic diffuse scatterings is being decoupled. The degree of local chemical order is being measured via the total scattering analysis of femto-second MeV electron diffraction. The quantitative characterization method also enables investigation of the evolution of local chemical order with annealing. The temperature dependence of local chemical order is being determined for modeling the underlying physical mechanism of chemical instability in MPEAs and for optimizing the properties of MPEAs. Moreover, the MeV UED measurements of the dynamic diffuse scattering from the single-crystal MPEAs with different degrees of chemical order are unveiling the correlation between local chemical order and phonon dispersions for developing deep understanding of the relationship between local chemical order and the mechanical, thermal, and electronic properties of MPEAs.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.

合金化是提高金属材料机械性能的重要途径。最近发现的多主元素合金，其中等原子组成元素既作为主元素又作为合金元素，为研究和开发具有前所未有的性能的新金属材料开辟了一个新的领域，用于在低温、冲击载荷、苛刻的化学环境和高温等极端条件下的应用。多主元素合金的独特性能源于组成元素之间复杂的化学相互作用。了解复杂合金中组成原子的局部静态排列和动力学（通常称为声子）对于设计和建模这类新材料至关重要。由于局域静态结构和声子的散射信号在衍射谱中重叠，用传统的X射线和电子衍射方法表征复杂合金的结构和动力学具有挑战性。该项目正在开发一种新的方法，使用飞秒时间分辨MeV电子衍射来表征多主元素合金。超快时间区的电子衍射可以有效地解耦静态和动态原子散射，揭示多主元素合金的结构和动力学的原子见解。该项目在理解复杂合金的结构-性能关系方面取得了实质性进展，并有助于开发新的金属材料，用于广泛的工业应用，以加强美国在先进和高性能材料方面的竞争力。技术概述在多主元素合金（MPEAs）中，局部化学顺序在确定结构性能和相稳定性方面起着至关重要的作用，但是由于来自局部化学秩序的静态漫散射与来自相干和非相干声子的动态漫散射之间的纠缠，实验表征是具有挑战性的。本计画将利用MeV超快电子绕射（MeV UED）来研究单晶MPEAs中的局部化学序。利用MeV超电子衍射的飞秒时间分辨率和高倒易空间分辨率，实现了静态和动态漫散射纠缠的解耦。局部化学秩序的程度正在测量通过飞秒MeV电子衍射的总散射分析。定量表征方法也使调查的演变与退火的局部化学秩序。当地的化学秩序的温度依赖性正在确定建模MPEAs的化学不稳定性的基本物理机制和优化性能的MPEAs。此外，MeV UED测量了不同化学有序度的单晶MPEAs的动态漫散射，揭示了局域化学有序度与声子色散之间的相关性，以深入理解局域化学有序度与机械，热，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智力价值进行评估来支持和更广泛的影响审查标准。