Interaction of He with Cu, V, and Ta in bcc Fe: A first-principles study

Abstract

Precipitates often play key roles in improving the mechanical performance of structural materials. Using first-principles density functional theory method, we have calculated the geometry and energetics of small Xn and XnHe (X = Cu, V, and Ta) clusters in bcc Fe matrix to investigate the effect of He on X precipitation on the initial stage in neutron-irradiated Fe alloys. Both substitutional and interstitial He attract solute atoms. The attraction of a substitutional He and a Cu atom is as strong as 0.30 eV (nearest neighbor) or 0.25 eV (next-nearest neighbor), even stronger than the vacancy-Cu pair. Such an attraction facilitates the clustering of Cu atoms. By comparison, the attraction of He to V (0.02 eV) or Ta (0.22 eV) is weaker than that of a vacancy. We find that one He can bind up to four Ta atoms to form a tetrahedron, despite the fact that in the absence of He, Ta atoms prefer to stay away from each other. The effect of He on the solute-solute and solute-matrix interactions can be understood from the facts that He behaves both as a free-volume filler and as a bonding insulator.