Niobium and titanium diffusion in the high niobium-containing Ti–54Al–10Nb alloy

Abstract

Titanium and niobium diffusion in the ternary Ti–54Al–10Nb alloy (the composition are in at.%) is investigated in an extended temperature interval by the radiotracer technique. The mechanical sectioning was performed by grinding or sputtering in order to measure the tracer diffusivities at higher and lower temperatures, respectively. Almost linear Arrhenius dependencies are established for Nb (Ti) diffusion with the pre-exponential factor and the activation enthalpy of 1.9×10 −5 (4.0×10 −4) m 2 s −1 and 280 (304) kJ mol −1, respectively. Niobium is a slower diffuser in comparison to Ti in the ternary as well as in the binary (α 2-Ti 3Al and γ-TiAl) titanium aluminides. The heavy alloying of γ-TiAl with 10 at.% niobium, however, enhances significantly both the Ti and the Nb diffusivities. This effect is attributed to an elastic distortion of the L1 0 structure of TiAl induced by the oversized Nb atoms, which may decrease the activation barriers for atomic diffusion.