Effect of hydrogen–helium interaction on their segregation and desorption at the W/HfC interfaces by first-principles calculations

Understanding the effect of the interaction between hydrogen (H) and helium (He) in tungsten (W)-based plasma-facing materials is essential for predicting materials performance in the context of fusion environments. In this work, the effect of H-He interaction on their segregation, accumulation and desorption behaviors at typical W/HfC interfaces were systematically investigated by first-principles calculations. Both H and He atoms tend to segregate at the W/HfC interfaces, where H atoms are discretely distributed and He atoms aggregate in a closely packed arrangement between W(110) planes. At the interface with a vacancy, the pre-existing He atoms can mitigate the accumulation of H atoms and promote their diffusion, which accounts for the reduction of H retention in W-carbide composites as observed in experiments. However, the pre-captured H has a minimal impact on the trapping of He. Furthermore, the maximum desorption temperatures of H and He from the interface are evaluated, ranging from 400 to 550 K and 700 to 1600 K, respectively. The pre-existing He atoms at the interfacial W vacancy also lower the desorption temperature of H. This work provides deep insight at the atomic scale towards a better understanding of the effect of H-He interaction on their retention and desorption in plasma facing-materials in the fusion environment.