Effect of titanium on the precipitation behaviors of transmutation elements in tungsten-titanium alloys from first-principles calculations

Tungsten (W) and W-based alloys will produce a series of transmutation elements (TEs) such as osmium (Os), rhenium (Re), tantalum (Ta) and hafnium (Hf) under high-energy fusion neutron irradiation, which will lead to radiation-induced precipitation. As an alloying element, the effect of titanium (Ti) on the precipitation behaviors of transmutation products is investigated based on first-principles calculations. The stability of Ti occupation and the aggregation properties of TEs in a W lattice are systematically studied. The binding energies obtained between Ti and TEs show that Ti can stably co-exist with Os/Re but becomes repulsive in the presence of Ta/Hf atoms. Furthermore, Ti concentration is an important factor for the nucleation of nTi-mTE clusters. Inducing Ti at a low concentration in a W lattice can enhance the aggregation of Os atoms and the repulsion of Ta or Hf atoms while causing a change from dispersion to aggregation for Re atoms in a W system. Accordingly, Re and Os elements can be clustered with Ti as a nucleation center in W-Ti alloys. However, the nucleation process of Re and Os can be hindered when the amount of Ti is gradually increased. Therefore, the level of Ti elements is a critical regulation factor in radiation-induced precipitation in W-Ti alloys. It is possible to suppress the clustering behaviors of Re and Os to improve the radiation resistance of W materials by adding an appropriate amount of Ti atoms.