EQUILIBRIUM-POINT DEFECTS IN INTERMETALLICS WITH THE B2 STRUCTURE - NIAL AND FEAL

Equilibrium point defects and their relation to the contrasting mechan ical behavior of NiAl and FeAl are investigated. For NiAl, the defect structure is dominated by two types of defects-monovacancies on the Ni sites and substitutional antisite defects on the Al sites. The defect structure of FeAl differs from that of NiAl in the occurrence of anti site defects at the transition-metal sites for Al-rich alloys and the tendency for vacancy clustering. The strong ordering (and brittleness) of NiAl is attributed mainly to the difference in atomic size between constituent atoms.