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Vacancy-type defects created by helium implantation in tungsten and their impact on the nano-hardness characteristics were investigated by correlating the results from the positron annihilation spectroscopy and the nano-indentation technique. Helium implantation was performed at room temperature (RT) and at an elevated temperate of 600 °C. Also, the effect of post-annealing of the RT implanted sample was studied. The S parameter characterizing the open volume in the material was found to increase after helium irradiation and is significantly enhanced for the samples thermally treated at 600 °C either by irradiation at high temperature or by post-annealing. Two types of helium-vacancy defects were detected after helium irradiation; small defects with high helium-to-vacancy ratio (low S parameter) for RT irradiation and large defects with low helium-to-vacancy ratio (high S parameter) for thermally treated tungsten. The hardness of the heat treated tungsten coincides with the S parameter, and hence is controlled by the large helium-vacancy defects. The hardness of tungsten irradiated at RT without thermal treatment is dominated by manufacturing related defects such as dislocation loops and impurity clusters and additionally by trapped He atoms from irradiation effects, which enhance hardness. He-stabilized dislocation loops mainly cause the very high hardness values in RT irradiated samples without post-annealing. [ABSTRACT FROM AUTHOR]

We have investigated the effects of Re on the behaviors of H in W as well as their interaction with point defects using a first-principles method in combination with thermodynamic models. It is clearly found that the influence of Re on H is directly related to the distribution of Re in W. For the state of Re dispersed distribution, both a single Re and its complexes with point defects have very slight effect on H dissolution and retention in W. However, the influence of Re clusters (for the state of Re aggregation) on H is extraordinary stronger than that of a single Re. The retention of H in W can be significantly decreased by Re clusters, and their influences will be enhanced with the increasing of the number of Re atoms. This can be attributed to the electronic interaction between H and Re/W, in which the repulsion of Re–H is stronger than that of W–H. We have further examined the retention of H at different temperature in W based on the Polanyi–Wigner equation. It is found that a Re4-vacancy complex can only accommodate 4 H atoms at room temperature, ~33% lower than the maximum number of H atoms in a mono-vacancy. These results give a reasonable interpretation for the experimentally observed D retention significantly decreasing in damaged W–Re alloy in comparison with that in damaged pure W. Consequently, our calculations provide a good reference for evaluating the influence of Re on the performance of W-PFM. [ABSTRACT FROM AUTHOR]