Investigation on the effect of carbon on clustering of defects in tungsten by first principles calculations

Carbon (C) impurity would be inevitably introduced in the process of industrial-scale tungsten production. In this work, by using the first-principles density functional theory, the C atom behaviors in tungsten lattice and the effect of C atom on defects clustering have been studied systematically. Calculation results show that C atom prefers to occupy the octahedral interstitial site of the tungsten lattice, the migration barrier energy of C atom is 1.46 eV along the optimal pathway. Both vacancy cluster and C atom can form stable complex structure according to the attractive interaction, and C atom promotes the nucleation of the vacancy cluster. The growth mechanism shows that vacancy clusters are more likely to grow by combining a cluster rather than a single vacancy, where C atom plays a positive role of promoting vacancy clusters nucleation. In addition, C atom can cause tungsten lattice distortion and lead to the formation of the potential well, which prompts SIA rapidly diffuse toward it and forms a SIA-C complex structure. The calculation results of the nucleation rate indicate that C atom can enlarge the effective radius of the 2SIA cluster, and enhance the nucleation rate of 3SIA cluster. Therefore, we conjecture that the C atom can inhibit the recovery of the Frenkel pair and weaken the self-repair of the tungsten materials under irradiation. These results are meaningful for further understanding the mechanism of the effect of C impurity for the defects evolution of irradiation defects of W-based material.