First-principles Study Of V-5Cr-5Ti Alloy

V-5Cr-5Ti alloy, with excellent mechanical properties, oxidation resistance,high temperature performance, neutron irradiation resistance and good machinability, etc., has become identified as a leading candidate material for first-wall and blanket components of the fusion reactor. To date, the relation between microstructure and properties, the effect of impurity atoms on V-5Cr-5Ti alloy are lack of understanding and researching. So, This thesis is based on the density-functional theory, the mechanical and thermodynamic properties of V-5Cr-5Ti alloy are studied by using the first-principles calculation method at the atomic level, and the behavioral of impurity atoms(C, N, O) on pure vanadium and V-5Cr-5Ti alloy are researched. The study can complement the basic research data of V-5Cr-5Ti alloy, provide fundamental basis for the optimization design of of the alloy, to promote the application of the alloy in the fusion reactor has great theoretical and practical significance.The study shows that the ductility of V-5Cr-5Ti alloy is slightly less than that of pure vanadium, but its strength is higher than that of pure vanadium, due to the effect of solid solution strengthening by addition of alloying elements Cr and Ti. In addition, ductility and strength of V-5Cr-5Ti alloy are reduced in different degree because of the addition of oxygen atom. In the aspect of thermodynamic, when the temperature is 298.15 K, the Debye temperature,constant volume heat capacity, entropy and expansion coefficient of the V-5Cr-5Ti calculated are 416.34 K, 29.89J/(mol·K), 31.97J/(mol·K) and 7.48 ×10-6K-1, respectively. And the curves of the heat capacity for V-5Cr-5Ti alloy are investigated from 0 to 1500 K.C, N and O atoms are the most stable in the octahedral interstitial site of the pure vanadium, and their diffusion barrier are 0.89 e V and 1.26 e V and 0.98 e V,respectively. And the diffusion coefficient of C, N and O atoms are8.11×10-7exp(-0.89 e V/k BT) m2/s, 8.94×10-7exp(-1.26 e V/k BT) m2/s and 7.33×10-7exp(-0.98 e V/k BT)m2/s in pure vanadium, respectively. This work shows that C, N and O atoms tend to occupy closer from the Ti atoms octahedral interstitial site by comparing the binding energy of C, N and O atoms in V-5Cr-5Ti alloy. Theconclusion indicate that C, N and O elements are more easily combine with Ti element in V-5Cr-5Ti alloy, and formed that carbide-nitride-oxide is rich in titanium(denoted by Ti(CON)).