Effect of β-stabilizer niobium on diffusional properties of the BCC β-Ti(Al) phase using a pseudo-binary diffusion couple technique

The study examines the influence of Nb on diffusional properties of the body-centered cubic (BCC) solid solution phase, β-Ti(Al) by determining the interdiffusion and intrinsic diffusion coefficients using a pseudo-binary diffusion couple method. The interdiffusion coefficients are higher for the ternary β-Ti(Al, Nb) system than those of the Nb-free binary β-Ti(Al) system at all the temperatures studied and for any fixed Al content in β. An increase in $\tilde{D}$ for the ternary case has been attributed to an increase in the thermodynamic factor in β with the addition of Nb and a decrease in the activation energy for the interdiffusion (Q). Q decreases because of reduction in the vacancy formation energy determined using DFT analysis and lowering of migration energy in the presence of Nb. The Kirkendall marker experiment demonstrated a higher intrinsic diffusion coefficient for Ti than Al, which had been explained considering the Lazarus’ valence model for diffusion.