OMEGA-PHASE FORMATION IN V-AL AND TI-AL-V ALLOYS

omega-phase formation in V-50 at.% Al alloy and Ti-Al-V alloys has bee n studied using electron diffraction. It is shown that both electron a nd size factors are important in affecting the magnitude of the deviat ion of diffuse omega maxima from the commensurate omega maxima positio ns. It is suggested that the addition of the electron-deficient elemen t Al to the later transition metal V will destabilize the high-tempera ture beta-phase and favour omega formation. It is expected by analogy that the omega transformation may occur in other later transition-meta l based alloy systems such as Nb-Al, Mo-Al, Cr-Al and Mn-Al. Structura l models have been proposed to interpret the heavy streaking effects i n beta + omega and B2 + omega structures.