The Ni bulk diffusion was measured in the B2 ordered Ni-Fe-Al alloys with a constant Al content of about 50at%. The 63Ni radioisotope, in combination with radiotracer serial sectioning, was used at higher temperatures and secondary ion mass spectrometry (64Ni isotope) was used at lower temperatures. Arrhenius-type temperature dependences were established, for all of the compositions, at 1050 to 1500K. The data for the 5 alloys (table 8) could be described by:
Ni-5Fe-49.2at%Al: D (m2/s) = 1.18 x 10-5 exp[-267(kJ/mol)/RT]
Ni-21.2Fe-48.9at%Al: D (m2/s) = 2.55 x 10-4 exp[-309(kJ/mol)/RT]
Ni-27.9Fe-49at%Al: D (m2/s) = 1.39 x 10-3 exp[-310(kJ/mol)/RT]
Ni-32.5Fe-49at%Al: D (m2/s) = 9.87 x 10-4 exp[-306(kJ/mol)/RT]
Ni-5.7Fe-51.7at%Al: D (m2/s) = 6.10 x 10-5 exp[-273(kJ/mol)/RT]
As the Fe content of the Ni50−xFexAl50 ternary alloys increased, the Ni diffusivity generally increased along the quasi-binary section between stoichiometric NiAl and FeAl. The activation enthalpy for Ni diffusion changed strongly non-monotonically in the alloys, between the binary end-members NiAl and FeAl; revealing a marked minimum at the Ni40Fe10Al50 composition and a maximum at around the Ni25Fe25Al50 composition.
Ni Radiotracer Diffusion in B2 Ordered NiFeAl Alloys. S.Divinski, F.Hisker, W.Löser, U.Södervall, C.Herzig: Intermetallics, 2006, 14, 308-14