We investigate the interaction between <111> self-interstitial atoms(SIAs) and 1/2<111> self-interstitial dislocation loops in tungsten(W) via atomistic simulations. We explore the variation of the anisotropic distribution of binding energies with the shapes and sizes of the 1/2[111] loop and the nonequivalent configurations of <111> SIAs. For an arbitrarily shaped loop, SIA can be more easily trapped in the concave region of the loop than the convex region, which forms a loop whose curvature is closer to that of a circular loop. The direction of SIAs can largely affect the interaction behaviors with the loop. The capture distance of an SIA by the edge of a circular-shaped 1/2[111] loop is clearly elongated along the direction of the SIA;however, it weakly depends on the size of the loop. Then, we analyze the slanted ring-like capture volume of <111> SIAs formed by the circular loop based on their generated anisotropic stress fields. Furthermore, the binding energies obtained from the elastic theory and atomistic simulations are compared. The results provide a reasonable interpretation of the growth mechanism of the loop and the anisotropic interaction that induces irregular-shaped capture volume, affording an insight into the numerical and Object Kinetic Monte Carlo simulations to evaluate the long-term and large-scale microstructural evolution and mechanical properties of W.
Hao WangKe XuDong WangNing GaoYu-Hao LiShuo JinXiaoLin ShuLinYun LiangGuang-Hong Lu
The behaviors of helium clusters and self-interstitial tungsten atoms at different temperatures are investigated with the molecular dynamics method. The self-interstitial tungsten atoms prefer to form crowdions which can tightly bind the helium cluster at low temperature. The crowdion can change its position around the helium cluster by rotating and slipping at medium temperatures, which leads to formation of combined crowdions or dislocation loop locating at one side of a helium cluster. The combined crowdions or dislocation loop even separates from the helium cluster at high temperature. It is found that a big helium cluster is more stable and its interaction with crowdions or dislocation loop is stronger.
Materials served in nuclear energy systems usually expose to high irradiation doses of particles.Projectile particles lead to creations of a large numbers of vacancies(Vs)and self-interstitial atoms(SIAs)in materials.The SIAs may gather to form dislocation loops and stacking-fault tetrahedrons,and the Vs usually gather to form voids.These defects contribute to material swelling,hardening,amorphization and embrittlement,and may accelerate material failure under irradiation[1].As recombination center of Vs and SIAs,grain boundaries(GBs)are able to enhance the radiation resistance of materials[2].However,experimental investigation show that point defects sink strengths might depend on GB structures.The vacancy sink efficiency of the twin boundaryΣ3(110)[111]is significantly lower than that of other GBs[3−5].
Materials served in nuclear energy systems usually expose to high irradiation doses of particles.Projectile particles lead to creations of a large numbers of vacancies(Vs)and self-interstitial atoms(SIAs)in materials.The SIAs may gather to form dislocation loops and stacking-fault tetrahedrons,and the Vs usually gather to form voids.These defects contribute to material swelling,hardening,amorphization and embrittlement,and may accelerate material failure under irradiation[1].Extensive experimental results demonstrated that nano-crystalline materials generally showed good radiation resistance than common poly-crystalline materials because there existed a high fraction of grain boundaries(GBs)in nano-crystalline materials[2].
Based on the density functional theory, we calculated the structures of the two main possible self-interstitial atoms（SIAs） as well as the migration energy of tungsten（W） atoms. It was found that the difference of the 110 and 111 formation energies is 0.05–0.3 e V. Further analysis indicated that the stability of SIAs is closely related to the concentration of the defect. When the concentration of the point defect is high, 110 SIAs are more likely to exist, 111 SIAs are the opposite. In addition, the vacancy migration probability and self-recovery zones for these SIAs were researched by making a detailed comparison. The calculation provided a new viewpoint about the stability of point defects for selfinterstitial configurations and would benefit the understanding of the control mechanism of defect behavior for this novel fusion material.
Employing a first-principles method based on the density function theory, we systematically investigate the structures, stability and diffusion of self-interstitial atoms （SIAs） in tungsten （W）. The （111 〉 dumbbell is shown to be the most stable SIA defect configuration with the formation energy of -9.43 eV. The on-site rotation modes can be described by a quite soft floating mechanism and a down-hill ＂drift＂ diffusion process from （110） dumbbell to 〈111〉 dumbbell and from （001） dumbbell to 〈110〉 dumbbell, respectively. Among different SIA configurations jumping to near neighboring site, the 〈111 〉 dumbbell is more preferable to migrate directly to first-nearest-neighboring site with a much lower energy barrier of 0.004 eV. These resuits provide a useful reference for W as a candidate plasma facing material in fusion Tokamak.
