Experimental study and thermodynamic modelling of the ternary Al–Ta–Ti system

Structure and properties of titanium-aluminum alloys doped with niobium and tantalum

“…The light-colored layers mostly represent the structure of decomposition as well. Only do alloys with 12 at.% Nb or Ta contain superfine bright grains, which can be considered depending on their composition and the phase ratio [10,11] as the stabilized β phase. The X-ray diffraction patterns of alloy samples containing 12 at.% Nb or Ta ascertain the assumption that the β phase is stabilized⎯they contain one or two strong reflections of the cubic phase (β-Ti, Nb, Al) or (β-Ti, Ta, Al).…”

“…Considering the low content of the cubic phase, the diffraction patterns cannot allow a unique conclusion on its structure, CsCl (B2) or W (A2) crystal structural type. That is, it is not known for certain whether the β(A2) → β 0 (B2) ordering, which might have occurred according to the phase diagrams, has actually taken place [10,11]. The lattice parameters of the identified phases depend little on the composition of alloys: a = 400−403 pm and c = 407−409 pm for the γ phase; a = = 575−577 pm and c = 462−463.5 pm for the α 2 phase; and about 322−323 pm for the cubic phase (β/β 0 ).…”

“…Their phase constituents are most favorable for the Al−Nb−Ti and Al−Ta−Ti isothermal sections at 1050°C [10,11] (Fig. 5), when phase transformations in alloys "freeze" during cooling on the arc furnace hearth.…”

“…The published results have been analyzed in critical reviews [39,40] and assessed recently using thermodynamic modeling (CALPHAD) [10]. The Al−Ta−Ti system has not been studied so well, but overview papers have been published [41−44] and thermodynamic assessment has been reported in [11]. Note that the papers [10] and [11] represent key experimental studies covering the region of two-phase α 2 + γ alloys of the ternary systems in questions to support their thermodynamic descriptions.…”

“…To examine the mechanical properties, we used the same alloys as in [10,11], with 0, 4, 8, and 12 at.% Nb or Ta at 45 or 47 at.% Al, Ti-8Nb-46Al and Ti-8Ta-46Al (at.%) alloys, and Al−Nb−Ta−Ti ternary alloys with 8 at.% Nb +Ta at 45 and 47 at.% Al.…”