Composition-dependent tracer diffusion coefficients in the B2 Ni–Al–Ti alloy via a combination of radiotracer and diffusion couple techniques

Abstract

Tracer (44Ti) and inter-diffusion experiments were performed on identical pseudo-binary diffusion couples of the B2 Ni–Al–Ti system at 1411 K. The molar volume of B2 Ni–Al–Ti alloys was critically assessed via CALPHAD approach. The concentration dependencies of pseudo-binary interdiffusion and 44Ti tracer diffusion coefficients are determined for both, constant and variable molar volumes. The results show that while interdiffusivities are sensitive to uncertainties in molar volume, the tracer diffusion coefficients are not. With a decrease of the molar fraction of Al in the pseudo-binary B2 Ni–Al–Ti alloy, the tracer diffusion coefficient of Ti is first decreased and then increased with a minimum around the composition corresponding to 48 at.% of Al and 3.5 at.% of Ti.