Retention of hydrogen in W-Ti-C, W-Ta-C and W-Zr-C alloys:ab initiostudy

Abstract

In previous experiments, compounds TiC, TaC, and ZrC are often added in W to improve the mechanical and thermal properties. However, it is still not clear how atomic Ti, Ta and Zr coexisted with C will affect H behaviors in W. In this work, systematical \emph{ab initio} calculations are carried out to study the interactions among alloying atoms (Ti, Ta and Zr), H, and C. The results illustrate that substitutional alloying atoms Ti, Ta, and Zr can trap H atom, and increase the retention of H in W. The effect of Ti on raising H retention is the strongest, followed by that of Zr and Ta. All Ti-C, Ta-C, and Zr-C can exist in W, and Zr-C is the most stable while the stability of Ta-C is relatively low. The stability of Ti-C is between Zr-C and Ta-C. The binding strength of Zr-C-H is the largest, followed by that of Ti-C-H and Ta-C-H in W, suggesting H retention in W-Zr-C may be the largest while H retention in W-Ta-C may be relatively low. The movement of H is much easier than that of C in W. The presence of alloying atoms Ti, Ta, and Zr in W affects the movement of H and C: the diffusion of H away from the alloying atoms is more difficult than that moving close to the alloying atoms, while the movement of C atoms approaching the alloying atoms is relatively difficult.