Abstract
The dynamic behaviour of atomic-size disarrangements of atoms—point defects (self-interstitial atoms (SIAs) and vacancies)—often governs the macroscopic properties of crystalline materials. However, the dynamics of SIAs have not been fully uncovered because of their rapid migration. Using a combination of high-voltage transmission electron microscopy and exhaustive kinetic Monte Carlo simulations, we determine the dynamics of the rapidly migrating SIAs from the formation process of the nanoscale SIA clusters in tungsten as a typical body-centred cubic (BCC) structure metal under the constant-rate production of both types of point defects with high-energy electron irradiation, which must reflect the dynamics of individual SIAs. We reveal that the migration dimension of SIAs is not three-dimensional (3D) but one-dimensional (1D). This result overturns the long-standing and well-accepted view of SIAs in BCC metals and supports recent results obtained by ab-initio simulations. The SIA dynamics clarified here will be one of the key factors to accurately predict the lifetimes of nuclear fission and fusion materials.
Highlights
Have shown that the most stable SIA structures were dumbbell for Fe15,16 but crowdion for other body-centred cubic (BCC) metals, including Mo and W17,18
One of the most hopeful experimental methods for directly detecting the dynamics of defects within material is transmission electron microscopy (TEM), which has been successfully applied to TEM-visible nanoscale defects[20,21]
We propose an alternative method for detecting the dynamics of fast-migrating SIAs, in which high-voltage transmission electron microscopy (HVEM) is effectively combined with computer simulations
Summary
Have shown that the most stable SIA structures were dumbbell for Fe15,16 but crowdion for other BCC metals, including Mo and W17,18. In the present study, we adopted W as a typical BCC metal, which will be an important component for radiation-resistant structural materials for future nuclear fusion reactors[19], and we aimed to experimentally determine the migration dimension of SIAs in high-purity W. We propose an alternative method for detecting the dynamics of fast-migrating SIAs, in which high-voltage transmission electron microscopy (HVEM) is effectively combined with computer simulations. In OKMC simulations, individual objects (point defects and point defect clusters) are tracked in a stochastic manner with the given input parameters With this method, even the spatial correlation among individual objects is taken into account; if the input parameters are correct, the results are expected to be correct. We will show that the range of “correct” parameter sets is strikingly narrow and that the correct parameter sets are fixed with small ambiguities
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