NSF-Europe: Collaborative Modeling and Experiemental Research Program to Understand the Dynamics of Dislocation--Particle Interactions

本研究侧重于原子到微观尺度，特别强调通过原子建模和动态原位和静态非原位透射电子显微镜实验相结合，在铝合金中识别位错-颗粒相互作用的控制机制。分子静力学模拟将用于表征沉淀物的原子结构以及界面和位错核心结构，分子动力学将用于确定时间演化动力学。静态异位电子显微镜将使用预变形材料来表征沉淀物结构和化学以及位错-沉淀物相互作用。一个主要目标是确定滑移位错和不同的沉淀物之间的相互作用的性质，在铝合金作为温度和应变的函数，并使用这些信息来模拟沉淀硬化合金的机械性能。预变形的材料将在不同温度下在电子显微镜中原位进一步变形，以确定反应途径和动力学。相关的模拟和实验结果将提供信息的空间和时间尺度的范围内，是无法访问的其他方法，但占主导地位的观察到的反应。这种结合的方法将确定作为应力，温度，沉淀形式和一致性的函数的位错沉淀相互作用的动力学，包括确定可能的晶体结构的转变后位错interactions.The材料系统的调查将从铝合金绘制，虽然调查结果可能是适用于一系列的系统。最终，位错沉淀物的相互作用规则将被纳入更高的长度尺度模型，以预测材料的机械响应。国外合作者一直在与主要研究人员合作，研究铁素体材料中富铜沉淀物的结构和演变，以及它们在硬化中的作用，方法是结合使用原位和非原位电子显微镜和原子尺度计算机建模。该项目由美国国家科学基金会多学科活动办公室、材料研究部（金属研究）和国际办公室（西欧）共同资助，是美国国家科学基金会和欧洲在材料研究方面的一项合作活动（NSF 02-135）。该项目是与英国牛津大学和利物浦大学合作进行的。

This research focuses on the atomic to the microscopic scale with a particular emphasis on identifying the controlling mechanisms of dislocation - particle interactions through a combination of atomistic modeling and dynamic in-situ and static ex-situ transmission electron microscopy experiments in Al-alloys. Molecular statics simulations will be used to characterize the atomic structure of precipitates and the interface and dislocation core structures, and molecular dynamics will be used to determine time evolution dynamics. The static ex-situ electron microscopy will use predeformed material to characterize the precipitate structure and chemistry, and dislocation-precipitate interactions. A major objective is to determine the nature of the interaction between glide dislocations and different precipitates in Al-alloys as a function of temperature and strain, and to use this information to model mechanical properties in precipitate hardened alloys. Predeformed material will be further deformed in situ in the electron microscope at different temperatures to determine reaction pathways and kinetics. Correlation of the simulation and experimental results will provide information over a range of spatial and temporal scales that are inaccessible to the other approach but dominates the observed response. This combined approach will determine the dynamics of dislocation precipitate interactions as a function of stress, temperature, precipitate form and coherency, including identifying possible crystallographic structural transformations following dislocation interactions.The material systems investigated will be drawn from Al-alloys, although the findings are likely to be applicable to a range of systems. Ultimately, the dislocation-precipitate interaction rules developed will be incorporated in higher length scale models to predict the mechanical response of materials. The foreign collaborators have been working with the principal investigators on the structure and evolution of copper-rich precipitates in ferritic materials, and their role in hardening by using a combination of in-situ and ex-situ electron microscopy, and atomic-scale computer modeling. It is also proposed to create age-appropriate educational modules to relate structure to mechanical properties.This NSF project is co-funded by the Office of Multidisciplinary Activities, the Division of Materials Research (Metals Research) and International Office (Western Europe) as a Cooperative Activity in Materials Research between the NSF and Europe (NSF 02-135). This project is being carried out in collaboration with Oxford and Liverpool Universities in UK.