Site-distributions of Fe alloying additions to B2-ordered NiAl

The site-distributions of Fe alloying additions to BZ-ordered NiAl alloys have been measured by ALCHEMI (atom location by channeling-enhanced microanalysis). Twelve alloy compositions were examined, of stoichiometries Ni50-xAl50Fex (Ni-deficient), Ni50Al50-xFex (Al-deficient), and Ni50-x/2Al50-x/2Fex (intermediate), with four different alloying levels, x=0.25, 2, 5, and 10. The data indicate that Fe tends to act as a buffer between the two sublattices, preferentially occupying the site of the stoichiometrically deficient host element. However, the Fe alloying addition was found to partition between the two sublattices to some extent in all alloys, so that 'Ni'-site vacancies or Ni anti-site defects are required to maintain the site balance. The observed trends in the site-distributions suggest that the range of compositions reported by Darolia et al. (Darolia R, Lahrman DF, Field RD. Scripta Metall Mater 1992;26:1007). to exhibit enhanced ductility may coincide with an inversion in the site-substitution behavior, where more Ni than Fe occupies the aluminum sublattice. Published by Elsevier Science Ltd.