Relative stability of bcc structures in ternary alloys with Ti50Al25Mo25 composition

In reviewing the literature that concerns the CsCl-type intermetallic compo und Ti2AlMo (B2), the question arises if this compound is preferably formed with respect to the high-temperature bcc completely disordered structure ( A2). Our present work takes an ab initio approach to this subject. The firs t-principles linear-muffin-tin-orbital method was used to calculate the tot al energy of a series of bcc structures in the ternary system Ti-Al-Mo. Sec ond, a cluster expansion in the tetrahedron approximation was calculated fo r each formation energy. Finally, a Connolly-Williams-like inversion scheme was used to obtain the formation energy of both the A2 phase and the parti ally ordered structure B2. From the calculations, the B2 formation energy c ame out to be aprox 10 mRy/atom lower than the A2 energy, suggesting a rela tive greater stability. The relative stability of other possible structures with the same global composition Ti50Al25Mo25 is discussed.