Interstitial and substitutional diffusion of metallic solutes in Ti3Al

Solute diffusion of Ni, Fe and Nb in the intermetallic compound Ti3Al was s tudied. The diffusion measurements of Ni and Fe were performed with radiotr acers applying the standard precision grinding technique for sectioning, wh ile the concentration profiles of Nb in Ti3Al were analysed through in-dept h profiling by secondary ion mass spectrometry (SIMS). Ni and Fe exhibit fa st diffusion behaviour of about 4 and 2 orders of magnitude, respectively, larger than titanium self-diffusion. The temperature dependencies of the di ffusion coefficients yield the Arrhenius parameters D-0(Ni) = 1.76 x 10(-5) m(2)/s, Q(Ni) = 195 kJ/mol and D-0(Fe) = 1.96 x 10(-3) m(2)/s, Q(Fe) =277. 2 kJ/mol, respectively. The high mobility of these solutes with comparative ly small atomic radii suggests in the D0(19)-structure of Ti3Al some type o f interstitial diffusion that is discussed in the context of results of ana logous diffusion investigations in alpha-Ti. Nb-diffusion coefficients in T i3Al were found to be lower by about one order of magnitude than self-diffu sion. The Arrhenius relation is characterized by D-0(Nb) = 3.15 X 10(-4) m( 2)/s and Q(Nb) = 338.7 kJ/mol. It is concluded that Nb-diffusion occurs sub stitutionally via thermal vacancies in the Ti-sublattice. (C) 1999 Elsevier Science Ltd. All rights reserved.