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 Å 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 1.32×10^-19 m² s^-1 and 3.11×10^-23 m² s^-1 at a typical temperature of 600 K, respectively.