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

The site-distributions of Fe alloying additions to BZ-ordered NiAl alloys h ave been measured by ALCHEMI (atom location by channeling-enhanced microana lysis). Twelve alloy compositions were examined, of stoichiometries Ni50-xA l50Fex (Ni-deficient), Ni50Al50-xFex (Al-deficient), and Ni50-x/2Al50-x/2Fe x (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 sublat tices, preferentially occupying the site of the stoichiometrically deficien t host element. However, the Fe alloying addition was found to partition be tween the two sublattices to some extent in all alloys, so that 'Ni'-site v acancies or Ni anti-site defects are required to maintain the site balance. The observed trends in the site-distributions suggest that the range of co mpositions reported by Darolia et al. (Darolia R, Lahrman DF, Field RD. Scr ipta 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.