Self-diffusion in Υ-TiAl: an experimental study and atomistic calculations

摘要

This paper presents the results of combinedexperiemental and theoretical studies of Ti self-diffusion in theintermetallic compound Υ-TiAl. Ti self-diffusion coefficientswere measured over a temperature range of 1184-1691 K usingthe radiotracer 44Ti and the serial sectioning method. Thediffusion coefficients show a non-Arrhenius behaviour withsignificant upward deviations at high temperatures(above~1470K). The pre-exponential factor and the activationenergy of self-diffusion determined in rthe low temperaturerange (<1470 K) are (DTi)0≈1.5×10-6m2/s and QTi≈250kJ/mol,respectively. By combining the obtained Ti selfdiffusioncoefficients with interdiffusion coefficients measured previouslyby Sprengel et al. (W.Sprengel, N. Opkawa, H. Nakajima,intermetallics 4 (1996), 185) and using the Darken-Manningequation, Al self-diffusion coefficients in TiAl were evaluated.Within the scatter of the data points, Al self-diffusion followsthe Arrhenius law with (DAl)0≈2.1×10-2m2/sand QAl≈360kJ/mol. The energies of point defect formation andmigration in TiAl were calculated by molecular statics withembedded-atom potentials. Several diffusion mechanisms inTiAl were considered, including migration of Ti and Al alongtheir own sublattices by single vacancy jumps, 3-jump vacancycycles and the anti-structural bridge mechanism. The activationenergies of Ti and Al self-diffusion by different mechanismswere evaluted as functions of the alloy composition. Thecaculations predict that, in the compositions studiedexperimentally, Ti diffusion at low temperatures is dominated bythe vacancy mechanism ,while at higher temperatures the anti-structural bridg mechanism can essentially contribute to theoverall diffusivity. Al diffusion occurs by the vacancymechanism with some contribution of 3-jump cycles and anti-structural bridges. The se predictions are in good agreementwith the experimental results of this work