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

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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.