Dissolution and diffusion properties of carbon in tungsten

We have investigated the structure, solution and diffusion behavior of carbon (C) in tungsten (W) based on first-principles calculations. The single C atom is energetically favorable sitting at the octahedral interstitial site (OIS) with a solution energy of 0.78 eV in W. Double C atoms tend to be paired up at the two neighboring OISs along the (210) direction with a distance of ∼ 3.57 A and a binding energy of + 0.50 eV. This suggests that a positive attractive interaction between C atoms exists, which might lead to a local higher concentration of C in W and form carbide. Kinetically, the C and vacancy diffusion co-efficients as a function of temperature have been determined, and are 1.32 x 10-19 m2 s-1 and 3.11 x 10-23 m2 s-1 at a typical temperature of 600 K, respectively.