The effect of titanium doping on carbon behavior in tungsten: A first-principles study

We investigated the structural and mechanical properties, the solution and diffusion behavior of carbon atom in the W-Ti lattice from first-principles calculations. The single C atom is energetically most favorable sitting at the octahedral interstitial site (OIS) nearest neighboring to the Ti atom in the W-Ti lattice. The minimum solution energy is about 0.874 eV. It is shown that the effect of titanium doping on the carbon migration behavior is small, while the migration energy barrier is quite high, and the highest energy barrier is up to 1.60 eV. Based on the elastic constants analysis, titanium doping tungsten can compensate the degradation of mechanical strength induced by carbon impurities. On the other hand, it is found that the ductility of pure W metal and W-Ti alloys is improved substantially by carbon impurities from the B/G ratio and the Poisson's ratio ν. The effect of the improved ductility is more obvious in pure W than that in the W-Ti alloys. In addition, substitutional C atom is better than interstitial C atom in terms of enhancing the ductility of pure W.