A systematic ALCHEMI study of Fe-doped NiAl alloys

Abstract

ALCHEMI site-occupation studies of alloying additions to ordered aluminide intermetallic alloys have been performed with varying degrees of success, depending on the ionization delocalization correction procedure applied to the data. Most published studies have been applied to just one or two alloys in order to ascertain qualitatively the site-preference of the alloying element. However, quantitative siteoccupancies can be extracted from carefully performed ALCHEMI experiments as long as the data are properly treated for ionization delocalization and anti-site occupancies. Systematic studies can therefore yield the dependence of site-occupancies in alloys on independent thermodynamic variables. The purpose of the present study is to examine the variation in the site-occupancy of Fe in B2-ordered NiAl as a function of solute concentration and alloy stoichiometry.Twelve different alloys were prepared for this study with stoichiometrics Ni50-xAl50Fex (Ni-deficient), Ni50-x/2Al50-x/2Fex (intermediate), and Ni50-xAl50Fex (Al-deficient), with x = 0.25, 2, 5, and 10. All alloys were homogenized at 1300°C for 5 h, step-cooled to room temperature, then annealed at 800°C for 72 h and water quenched.