Imaging atom probe study of the segregation behaviour of Nb–Ta binary alloys

The segregation behaviour on Nb–Ta alloy specimen tips with nominal 39, 66 and 85 at.% Nb has been studied by imaging atom-probe technique. Theoretical model calculations predict surface enrichment of Nb for this system which behaves very close to an ideal solution. In depth profiling measurements after in situ annealing, Nb enrichment up to 58 at.% on the surface was observed on samples with 39 at.% Nb bulk content. The Nb enrichment is found to be limited to the first two atomic layers. The quantitative result is in good agreement with thermodynamic model calculations. q1999 Elsevier Science B.V. All rights reserved