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Influence of hydrogen concentration and defects introduced by neutron irradiation on hydrogen diffusion in tungsten has been investigated by molecular dynamics simulation at elevated temperatures. Hydrogen diffusion is shown to be significantly restrained at high concentrations due to spontaneous formation of platelet-like hydrogen clusters. For neutron irradiation defects, self-interstitials, mono-vacancies and vacancy clusters are considered. By clustering and acting as dislocation loops, self-interstitials show considerable trapping effects on hydrogen, leading to the suppression of hydrogen effective diffusion and the change of diffusion model in which hydrogen mainly diffuses along dislocation lines instead of hopping between tetrahedral interstitial sites. Moreover, an equation connecting hydrogen diffusion parameters and the total length of dislocation loops is empirically established. Different influences of mono-vacancies and vacancy clusters on hydrogen diffusion have been carefully identified. With the same vacancy concentration, hydrogen diffusivity is lower with mono-vacancies than that with vacancy clusters because more isolated trapping sites are provided by mono-vacancies. This work is not only helpful for understanding the synergistic effects of neutron irradiation and plasma interaction, but also potentially applicable for larger scale simulations as input data.

The L21 (NiCo)2TiAl phase plays a key role in the excellent mechanics of 3d high-entropy alloys. In this work, we investigate the phase stability and intrinsic mechanical properties of L21 (NixM1-x)2TiAl (M = Co, Fe, x = 0–1) alloys by using ab initio methods. The phonon dispersion relations suggest that the thermodynamic stability of L21 Ni2TiAl, Co2TiAl and Fe2TiAl as well as Y-type NiTiCoAl, NiTiFeAl and CoTiFeAl intermetallic compounds. The formation enthalpy and the energy contribution from vibrational entropy indicated that (NiCo)2TiAl is easier to form with respect to (NiFe)2TiAl and (CoFe)2TiAl. With the increase of the Co content, both the ductility and Young's modulus of L21 (Ni1-xCox)2TiAl (x = 0–1) alloy decrease, while anisotropy become strong. The Co content has no almost effect on the ductility, Young's modulus and anisotropy of the Y-type (Ni1-yCoy)Ti(NiyCo1-y)Al (y = 0–0.5) solid-solution alloys, whereas the (Ni1-yFey)Ti(NiyFe1-y)Al (y = 0–0.5) solid solutions show different ductility and anisotropy, compared with NiTiFeAl intermetallic compound.