Synergistic trapping and desorption effects of vacancy and heterogeneous interface on helium in W-TiC alloys by first-principles calculations

The synergistic trapping effect of vacancies and the W/TiC interface on helium, as well as the desorption behaviors of helium at the W/TiC interface with and without vacancies were investigated using first-principles calculations. The stability of interface structures with multiple interfacial orientations was assessed through the work of separation. Building on this, the thermodynamic stability of vacancies near the interface and their trapping effect on helium were examined. The presence of these vacancies significantly hindered the absorption of helium at the interface. Helium initially accumulated at vacancies near the interface, forming small Vac-nHe clusters. As the number of captured helium atoms increased, helium became more prone to capture by the interface, thereby inhibiting the growth of Vac-nHe clusters. The nearest-neighbor and second-nearest-neighbor vacancies near the interface together with the interface formed community and co-solvent structures, respectively. These structures can effectively promote the interface's ability to trap helium within bulk W, compared to the pure interface. The desorption temperatures of helium at the W/TiC interface with and without vacancy range from 1060 K to 1580 K and from 900 K to 1100 K, respectively. The presence of vacancies significantly elevated the desorption temperature of helium at the interface. These research findings contribute to a deeper understanding of the nucleation and growth mechanisms of helium bubbles, as well as the desorption of helium at the W/TiC interface.