Interstitial and substitutional diffusion of metallic solutes in Ti 3Al

Abstract

Solute diffusion of Ni, Fe and Nb in the intermetallic compound Ti 3Al was studied. The diffusion measurements of Ni and Fe were performed with radiotracers applying the standard precision grinding technique for sectioning, while the concentration profiles of Nb in Ti 3Al were analysed through in-depth profiling by secondary ion mass spectrometry (SIMS). Ni and Fe exhibit fast diffusion behaviour of about 4 and 2 orders of magnitude, respectively, larger than titanium self-diffusion. The temperature dependencies of the diffusion coefficients yield the Arrhenius parameters D 0 Ni=1.76 × 10 −5 m 2/s, Q Ni=195 kJ/mol and D 0 Fe=1.96 × 10 −3 m 2/s, Q Fe=277.2 kJ/mol, respectively. The high mobility of these solutes with comparatively small atomic radii suggests in the D0 19-structure of Ti 3Al some type of interstitial diffusion that is discussed in the context of results of analogous diffusion investigations in α-Ti. Nb-diffusion coefficients in Ti 3Al were found to be lower by about one order of magnitude than self-diffusion. The Arrhenius relation is characterized by D 0 Nb=3.15 × 10 −4 m 2/s and Q Nb=338.7 kJ/mol. It is concluded that Nb-diffusion occurs substitutionally via thermal vacancies in the Ti-sublattice.