The ordering mechanism, and the properties of defects in B2-type aluminides, were studied. It was shown that the size effect was unable to explain the defect structure or ordering. This was evident in the case of PdAl, which was found to exhibit all of the physical characteristics of a strongly ordered alloy even though the difference in atomic radii between the constituent Pd and Al atoms was very small. It was found that there was a large heat of formation, a high antiphase boundary energy that was associated with partial ½<111> slip, and a number of triple defects in the case of PdAl. Similar analyses were presented for NiAl and FeAl, and the results revealed that the electronic structure at the transition metal sites had a decisive effect upon the energies and types of defects.

C.L.Fu: Physical Review B, 1995, 52[5], 3151-8