Interstitial diffusion of O, N and C in alpha-Ti from first-principles: analytical model and kinetic Monte Carlo simulations

The high affinity of O, N, and C with α-Ti has a serious detrimental influence on the high-temperature properties of these alloys, promoting the formation of α-case phase. These elements dissolve in interstitial sites and diffuse very fast in α-Ti (103-108 times higher than the self-diffusivity of Ti) at high temperature accelerating the growth of α phase surface layer. Understanding the diffusion mechanisms of these elements is crucial to the design of high-temperature Ti alloys. This work aims to determine the stable interstitial sites and migration paths of O, N, and C in α-Ti. Diffusion coefficients were evaluated applying an analytical model, Multi-State Diffusion method, and kinetic Monte Carlo simulations informed by first-principles calculations. The results show the reliability of these two methods with respect to the experimental data. In addition to octahedral sites, less traditional interstitial sites are shown to be stable configurations for these elements instead of tetrahedral sites. This requires to update the transition pathway networks through which these elements have been thought to migrate in α-Ti.