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New simulation software sheds light on radiation resistance in polycrystalline metals

by News Staff
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A recent study by a research group led by Professor Liu Changsong from the Institute of Solid State Physics at the Hefei Institutes of Physical Science, which is part of the Chinese Academy of Sciences, has developed new software for simulating the evolution of displacement damage in polycrystalline metals across time and space scales. The software, named object kinetic Monte Carlo-lattice kinetic Monte Carlo (OKMC-LKMC) hybridization simulation software, was used to investigate the accumulation and evolution of vacancies at iron (Fe) grain boundaries (GBs). The team’s findings, published in the Journal of Nuclear Materials, showed that polycrystalline/nanocrystalline (PC/NC) Fe has improved radiation resistance.

In the past, GBs were often simplified as two-dimensional planes without specific structures, with energetic and kinetic parameters used to characterize their properties. However, the diverse nature of GBs means that they exhibit distinct local structures and defect properties, which cannot be accurately predicted with a single interaction parameter. The new technology developed by the research team can distinguish the spatial position dependence of defect properties at GBs, and simulate the evolution of defects away from the GB region in a coarse-grained manner, providing a more accurate prediction of defect evolution over a long time scale.

Several V motion trajectories near the GBs drawn from LKMC simulation. The horizontal line indicates the GB position. Credit: Li Xiaolin

A group of researchers conducted a study on the accumulation mechanisms of vacancies (Vs) at iron (Fe) grain boundaries (GBs), with a focus on the interaction processes of Vs with different types of GBs.

Their findings revealed that the accumulation of Vs is dependent on the GB character, and at high temperatures, the atomic processes of V emission and leakage were discovered, in addition to the well-known trapping of V by the GB. The occurrence of these processes was found to be dependent on the GB character, which led to the proposal of a coupling equation of grain size with GB character based on V formation energy at the GB and migration energy barrier within the GB.

The coupling equation proposes that when it is satisfied, the defect emission process that originally occurred in the high energy level region is inhibited by the defect cruise along the GB. However, this brings about uncertainty regarding the relationship between radiation performance and the defect-GB binding strength, especially in the case of a small grain size.

Overall, this research reveals new V-GB interaction processes and the coupling between these processes, which has significant implications for other polycrystalline systems. It can provide insight into the radiation response of polycrystalline materials and serve as a mechanism reference for experimentally optimizing the radiation resistance of materials through GB engineering.

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