SITE OCCUPANCY OF ALLOYING ELEMENTS IN TI3AL COMPOUNDS

A method is proposed to predict the site occupation behavior of alloyi ng elements in Ti3Al. The electronic structures of 20 alloying element s (M) occupying both Ti and Al sites are calculated using the discrete variational-X alpha cluster method. A diagram is drawn using E-b,E-Ti and E-b,E-Al, the binding energy of clusters when M taking Ti or Al s ites. The elements are divided into three groups by two straight lines . The M located outside the two lines occupy either Ti or Al sites reg ardless of the composition. The substitution behavior of M in between are affected by the composition. The driving force for an element to o rder on one sublattice is related to its position in the diagram. The effects of composition, multi-element alloying and ordering process ar e discussed. The agreement with other results is generally good. The s ite competition phenomena and a new phase transition with stepped orde ring process are predicted. (C) 1997 Elsevier Science S.A.