Nanoscale Self-Organization of Metallic Alloys under Ion Irradiation

该奖项由伊利诺伊大学厄巴纳-香槟分校材料研究部颁发，旨在提高对系统弛豫如何偏离平衡导致自组织和首选长度尺度选择的基本理解。该项目将基于驱动系统的一般理论框架，该框架是由该奖项的pi Averback和Bellon教授随着时间的推移而开发的。传统上，工程材料的加工使用时间和温度作为控制变量。在许多先进的加工方案中，或在使用中，材料也受到持续的外部强迫，例如，由离子束加工的薄膜或经历摩擦磨损的材料。这些动态驱动的材料不再局限于遵循由平衡热力学控制的动力学路径。现在有大量的工作表明，在平衡条件下亚稳态，甚至不稳定的相，可以在动力强迫下稳定下来。一个重要的新发展是预测，在适当的条件下，驱动材料的组成和化学顺序可以在纳米尺度上自组织。分析模型和原子计算机模拟表明，由外部强迫引入的特定长度尺度是这些自组织反应的起源。一些初步实验支持辐照和塑性变形均可触发组分图案的结论，但缺乏能够验证这些新模型的关键实验。本研究的中心思想是进行这样的实验，批判性地和系统地测试模型预测。重点是高能离子束辐照的材料，因为对辐照过程中涉及的物理过程的深入了解使得进行具有良好控制的实验成为可能。通过改变照射条件，由外部强迫引入的长度尺度系统地发生变化，从而允许对模式预测进行定量测试。在这项实验工作的同时，原子计算机模拟也得到了发展，以包括间隙原子和表面所起的作用。事实上，当间隙原子选择性地与一种化学物质偶联时，在其与空位重新结合或在汇上消除之前的间隙扩散距离成为合金演化的相关长度尺度。表面不仅提供了一个定义良好的水槽，而且还增加了平衡和非平衡隔离的有趣的新维度。这项研究对促进科学认识具有广泛的影响。在驱动系统的框架内，可以描述各种各样的材料现象，包括疲劳、严重的塑性变形、摩擦磨损和合金化。随着合金辐照作为模型系统的普遍有效性的建立，这些其他行为也得到了更好的理解。此外，该研究为研究生提供了教育机会，他们将接受先进材料表征仪器的培训。目前的工作将整合到教学活动中，让本科生了解纳米结构材料的潜力和挑战。研究小组计划在当地高中引进“材料面包车”，进行材料科学演示，提高学生对技术社会中材料的日常使用的认识。

This award from the Division of Materials Research to University of Illinois at Urbana-Champaign is to improve fundamental understanding how relaxation in systems that are driven away from equilibrium leads to self-organization and the selection of preferred length scales. This project will be based on a general theoretical framework for driven systems that has been developed over time by Professors Averback and Bellon, the PIs of this award. Engineering materials are traditionally processed using time and temperature as control variables. In many advanced processing schemes, or in service, materials are also subjected to a sustained external forcing, for example, thin films processed by ion beams or materials undergoing frictional wear. These dynamically driven materials are no longer constrained to follow kinetic paths controlled by equilibrium thermodynamics. There is now a large base of work showing that phases that would be metastable, or even unstable under equilibrium conditions, can be stabilized under dynamical forcing. An important new development has been the prediction that, under appropriate conditions, the composition and the chemical order in driven materials can self-organize at the nanoscale. Analytical models and atomistic computer simulations suggest that specific length scales introduced by the external forcing are at the origin of these self-organization reactions. Some preliminary experiments support the conclusion that compositional patterning can be triggered by both irradiation and plastic deformation, but the critical experiments that could provide validation of these new models are lacking. The central idea of this research is to perform such experiments, critically and systematically testing the model predictions. The focus is on materials irradiated by energetic ion beams, as the advanced understanding of the physical processes involved during irradiation makes it possible to perform experiments with excellent control. By varying the irradiation conditions the length scales introduced by the external forcing are systematically varied, thus allowing for quantitative tests of the model predictions. In parallel to this experimental work, atomistic computer simulations are developed to include the role played by interstitial atoms and surfaces. Indeed, when interstitial atoms couple selectively to one chemical species, the interstitial diffusion distance before its recombination with a vacancy or its elimination on a sink becomes a relevant length scale for the evolution of the alloy. Surfaces not only provide a well-defined sink, but also add the interesting new dimensions of equilibrium and non-equilibrium segregation. This research has broad impacts for advancing scientific understanding. There is a wide range of materials phenomena that can be described within the framework of driven systems, including fatigue, severe plastic deformation, frictional wear, and dealloying. As the general validity is established for the irradiation of alloys as a model system, these other behaviors become better understood as well. In addition, the research offers educational opportunities for graduate students who will be trained on advanced instruments for materials characterization. The present work will be integrated into teaching activities, exposing undergraduate students to the potentials and the challenges offered by nanostructured materials. The investigators plan to introduce a "Materials Van" for local high schools that would offer materials science demonstrations to increase the awareness of students to the daily use of materials in our technological society.