Investigation on the Influence of Vacancy and Alloying Element Content on the Performance of Fe/NbN Interface

The alloying elements usually lead to the precipitation of second phases in steel, readily forming at grain boundaries, and the type and distribution of these phases significantly influence the mechanical properties of the matrix. In the present contribution, the austenitic matrix fcc-Fe, the precipitate NbN, and the interface properties between them are investigated by first-principles calculations in detail. The effects of vacancy and alloying element content on the interface performance are examined. The results indicate that the density of states (DOS) of the former is primarily contributed by the Fe d-orbitals, and both exhibit elastic anisotropy. Under a tensile strain of 20%, the maximum tensile strength of fcc-Fe reaches 32.6 GPa. For NbN, the maximum tensile strength comes to 29 GPa at a strain of 10%, after which the stress rapidly decreases with the increasing of strain. In the meantime, the uneven distribution of electron cloud density increases in both. Regarding the interface, the introduction of vacancies enhances atomic interaction and improves interface stability by altering electron cloud distribution. As the Co doping content increases, the covalent interactions between atoms strengthen at the interface, enhancing interface stability. However, excessive V doping may reduce the interface stability. Furthermore, when the vacancies coexist with alloying elements, the stronger covalent characteristics are observed due to shortened bond lengths and positive bond population values. These insights provide a data foundation and theoretical basis for designing high-performance austenitic stainless steels.