First-principles Study on Formation Behavior of Point Defects in TiVTaZr High-entropy Alloy

In the modern energy system, nuclear energy is an important component. High-entropy alloys (HEAs) received extensive attention due to their core effects and the characteristics of their constituent elements, which show stronger radiation resistance than traditional alloys and excellent ductility and strength at elevated temperatures. In this paper, the point defect properties of the TiVTaZr HEA were investigated using first-principles calculations to provide a theoretical basis for further research into the mechanical and irradiation resistance properties of the alloy. First-principles calculations are based on density functional theory (DFT) which is a quantum theory for studying the electronic structure of multi-electron systems and can perform more accurate energy calculations on a given atomic sequence. The results show that Vacancy formation energy (VFE) increases with the increment of the number of V atoms in the 1st nearest neighbour (1NN) shell of the vacancy. Due to the large atomic radius of Zr atoms, the local lattice distortion is more serious in the Zr-rich environment, so the formation energy of vacancy and interstitial decreases with the increase of the number of Zr atoms in the 1NN shell. The average formation energy of vacancy and interstitial is (1.27±0.59) eV and (1.38±0.78) eV respectively, which are lower than those in TiVTa alloy ((1.68±0.34) eV and (1.76±0.37) eV), it means that the vacancy and interstitial are easier to form in the TiVTaZr alloy. In addition, dumbbell is more inclined to the 111 direction, and 111 oriented VV and TiV dumbbell are the most stable configurations in TiVTaZr alloys. The lattice distortion and electronic structure were studied too. The results show that TiVTaZr alloy has a larger local lattice distortion due to the addition of Zr atoms, which will result in a more irregular energy landscape, so that the vacancy and interstitial become easier to form because of the decrease of their formation energy. Through the study of the electronic structure, it is found that the TiVTaZr alloy has a shorter pseudo-gap and a greater degree of charge transfer than the TiVTa alloy. In summary, through the first-principles calculations, it is found that compared with TiVTa alloy, TiVTaZr alloy has greater local lattice distortion due to the addition of Zr element, which will make the formation energy of vacancy and interstitial decrease and thus easier to produce. At the same time, the addition of Zr element also shortens the pseudo-gap and increases the degree of charge transfer, which indicates that the increase of metal bonds will lead to the promotion of the bonding strength of the alloy and the improvement of the mechanical properties of the alloy. These results provide a basis for the defect evolution and component design of bcc HEAs.