Effect of vacancy on the stability of the AlNbTiZr/Zr interface: a first-principles study

The structure and properties of AlNbTiZr/Zr interface change significantly when defects are present within AlNbTiZr coating. However, the effect of defects on interfacial bonding lacks quantitative assessment, and the results of experimentally studies are also difficult to guide the design of interface structures. In this paper, the interfacial structure of AlNbTiZr/Zr with different kind of vacancy defect types and vacancy formation energy (VFE) has been investigated by first-principle calculations, and the interfacial bonding was calculated by quantifying the interfacial energy and adhesion work. It is interesting that VFE of Vac_Zr (Zr vacancy) is higher in the matrix side of the interface than in pure Zr, making it harder to form. This implies the high-entropy coating suppresses vacancy formation, enhancing initial irradiation resistance of Zr cladding. Regardless of the type of vacancy, the interfacial energy of interfaces containing vacancies is higher, and the adhesion work is lower than that of perfect interfaces. Therefore, they are less stable than perfect interfaces, meaning that vacancies weaken the stability of the interface. Moreover, interfaces with Vac_Al (Al vacancy) exhibit the poorest stability. It can be inferred that during experimental research, efforts should be made to minimize the concentration of Al vacancies at the coating interface. According to the charge analysis results, compared to interfaces containing vacancies, there is more pronounced charge rearrangement and accumulation at the perfect interface. Additionally, the PDOS of Al-p with Zr-e_g and Zr-t_2g orbitals shows stronger electronic coupling at the perfect interface, indicating stronger chemical bonding. This further demonstrates that vacancies weaken the bonding strength and stability of the interface. These results have important implications for the field of Zr alloy cladding high-entropy coating, as they provide new insights from the perspective of interfacial stability to discuss the effect of vacancy on the performance of AlNbTiZr/Zr interface.