Alloying Effects on the Oxygen Diffusion in Nb Alloys: A First-Principles Study

Abstract

Aiming to understand fundamentally the alloying effects on the oxidation behaviors of Nb alloys, we combined the first-principles density functional theory and Kinetic Monte Carlo simulations to calculate systematically the binding energies, energy barriers, and diffusion coefficients of oxygen in Nb-X alloys where X = thirty 3d, 4d, and 5d transition metal (TM) elements plus Al and Si in this work. According to the calculated binding energies and energy barriers, we classify the alloying effects into three categories: (a) local short-range trapping effects (X = V, Ti, Cr, Y, Zr, and Hf); (b) local long-range trapping effects (X = Si and Ru); (c) non-local non-trapping effects (X = Mo, W, and Al). Our results show that the solute elements with the short-range trapping effects at near regions had the most effective reduction effects on the O diffusion coefficients while the long-range trapping effects and the non-local effects are less significant but non-negligible. Specifically, the reduction effects of the partial studied alloying elements decrease in the order of Y> V> Ti> Si> Cr> Zr> Hf> Al> Mo> Ru> W. For all the studied 30 TM elements, the diffusion coefficients were calculated for O at the near regions of the solute atoms and their trends were discussed. These intrinsic alloying effects on the oxygen diffusion in Nb alloys provide the theoretical evidence for the rational composition design of oxidation-resistant Nb alloys.