SITE OCCUPATION OF IRON IN INTERMETALLIC NIAL

The site occupation of iron in two NiAl alloys of differing stoichiometries has been characterized with the atom-probe field-ion microscope (APFIM). A nickel-rich NiAl alloy containing 0.3 at% Fe and an aluminum-rich NiAl alloy containing 2.2 at% Fe were used to characterize the behavior of iron in solid solution in NiAl alloys. A nickel-rich alloy was selected so that the iron should have a slight preference for the aluminum sites, whereas an aluminum-rich alloy should favor the substitution of iron for the nickel. The site occupation was determined by measuring the compositions of the (100) plane, which alternately consist of pure nickel and pure aluminum layers, in stoichiometric NiAl. In both alloys the iron was observed to substitute preferentially for aluminum, independent of the nickel-to-aluminum ratio.