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The interaction of H or He atoms with a core of edge and screw dislocations (SDs), with Burgers vector a 0 /2 1 1 1 , is studied by means of ab initio calculations. The results show that the edge dislocations are stronger traps for H and He compared to the SDs, while the H/He affinity to both types of dislocation is significantly weaker than to a single vacancy. The lowest energy atomic configurations are rationalized on the basis of the charge density distribution and elasticity theory considerations. The results obtained contribute to the rationalization of the thermal desorption spectroscopy analysis by attributing certain peaks of the release of plasma components to the detrapping from dislocations. Complementary molecular statics (MS) calculations are performed to validate the accuracy of the recently developed W-H-He embedded atom method (EAM) and bond-order potentials. It is revealed that the EAM potential can reproduce correctly the magnitude of the interaction of H with both dislocations as compared to the ab initio results. All the potentials underestimate significantly the He-dislocation interaction and cannot describe correctly the lowest energy positions for H and He around the dislocation core. The reason for the discrepancy between ab initio and the MS results is rationalized by the analysis of the fully relaxed atomic configurations.

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Recent efforts dedicated to the assessment of mechanical properties of tungsten wires, as means for fiber-reinforced composites, have shown that potassium (K) doping in the as-drawn state does not modify the mechanical properties of the wire. High temperature annealing (Ta up to 2300°C) leads to the severe embrittlement of the wire associated with the loss of fracture strength. In this work, we assess the transition behavior of pure and K-doped W wires exposed to the annealing in the temperature range of 1000-2300°C to identify and recommend temperatures suitable for operation and fabrication of the fiber-reinforced composites. The results of mechanical tests performed in the temperature range of RT-500°C are reported and substantiated by the electron microscopy analysis. Room temperature tests demonstrate that pure W wires become fully brittle after annealing above 1300°C, whereas K-doped wires loses ductility above 2100°C. With raising the test temperature to 300-500°C, it is found that the strength of pure W wire reduces by a factor of two at Ta=1000°C (as compared to non-annealed wire), and goes down to 100 MPa at Ta=1900°C. The K-doping suppresses the reduction of the fracture strength at least up to Ta=1900°C, thus offering a temperature gap of ~600°C for the use as reinforcement.

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