Multiscale Modeling of Irradiation Induced Hardening in Iron Alloys
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Multiscale Modeling of Irradiation Induced Hardening in Iron Alloys Ioannis N. Mastorakos1, Hussein M. Zbib1,2, Dongsheng Li2, Mohamed A. Khaleel2, Xin Sun2 1 School of Mechanical Engineering and Materials Science, Washington State University, Pullman, Washington, U.S.A. 2 Pacific Northwest National Laboratory, Rischland, Washington, U.S.A. ABSTRACT Structural materials in the new Generation IV reactors will operate in harsh radiation conditions coupled with high levels of hydrogen and helium production and will experience severe degradation of mechanical properties. Therefore, understanding of the physical mechanisms responsible for the microstructural evolution and corresponding mechanical property changes is critical. As the involved phenomena are very complex and span in several length scales, a multiscale approach is necessary in order to fully understand the degradation of materials in irradiated environments. In previous work, we used molecular dynamics simulations to develop critical rules for the mobility of dislocations in various iron alloys and their interaction with several types of defects that include, among others, helium bubbles and grain boundaries. In this work, Dislocation Dynamics simulations of iron alloys are used to study the mechanical behavior and the degradation under irradiation of large systems with high dislocation and defect densities. INTRODUCTION The development of new generation fission and fusion nuclear reactors depends on the availability of materials to operate safely in severe environments for an extended service lifetime. Structural materials in nuclear reactors will function in harsh radiation conditions coupled with defect clusters of high density, and thus will experience severe degradation of mechanical properties. Over the past two decades, significant advances have been made in understanding the effects of irradiation on materials microstructure and mechanical properties by focusing theory, experiments and modeling on the basic underlying physical mechanisms. However, the prediction of the material behavior based on this knowledge is still an open problem. Furthermore, more advances in our understanding of radiation effects in materials are needed especially in order to provide the underpinning science to support materials development for the next generation of nuclear reactors. In particular, materials that perform well in extreme environments need to be developed based on an understanding of the atomic-level structural changes and their effects on the performance of materials over an extended amount of time. At the smaller scales (nanometer and picoseconds), irradiation dose and temperature cause the coalescence of vacancies and interstitials into voids and dislocation loops. These defects and clusters diffuse over macroscopic length and time scales, altering significantly the chemistry and microstructure of the material. On the other hand, experiments are also limited in their ability to observe dynamic processes that occur at the nanosecond and nanometer scales. Howe
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