A thermodynamic re-assessment of Al-V toward an assessment of the ternary Al-Ti-V system

Titanium alloys are highly sought after due to their excellent mechanical properties. One of the most commonly used Ti alloys is Ti-6Al-4V, which contains 6% Al and 4% V by weight. Despite the popularity of this alloy, no thermodynamic description of the ternary Al-Ti-V system has been published in the open literature. In this work an assessment procedure of the ternary Al-Ti-V system was initiated based on the binary descriptions by Witusiewitcz et al. (J. Alloys Compds. 465 (2008) 64-77 [1]) for (Al-Ti), Gong et al. (Int. J. Mater. Res. 95 (2004) 978-986 [2]) for (Al-V) and Saunders (COST 507, 2 (1998) 297-298 [3]) for (Ti-V). When combining the three binary systems and looking at the extrapolated ternary isothermal sections, it was found that there was a very large miscibility gap in the bcc phase. The origin of this miscibility gap was mainly the Al-V system and therefore it was decided to reassess this system. The Al-V system was reassessed according to available experimental data along with the enthalpies of formation of all compounds as well as the enthalpies of mixing for all terminal phases obtained by first-principles calculations based on the density functional theory. For the Al₈V₅ phase there are two different sets of data for the enthalpies of formation. These two sets are investigated in this work and it is found that the set not used by Gong et al. in their assessment of the Al-V binary system gives better extrapolations. The final description produced improved extrapolated ternary isothermal sections.