Experimental investigation and thermodynamic assessment of phase equilibria in the Al-Co-Ta ternary system.

Phase equilibria of the Al-Co-Ta ternary system over the whole composition range at 1200 °C and 1300 °C were experimentally determined from the equilibrated alloys using electron probe microanalysis, scanning electron microscopy, and X-ray diffraction. The measured results indicate that, at 1200 °C, the addition of Al can stabilize the λ 1 -Co 2 Ta phase (Laves C14-type), which is absent in binary system, and forms a broad phase region parallel to the Al-Co axis in the Al-Co-Ta ternary isothermal sections. The ternary compound of the Heusler phase AlCo 2 Ta (L2 1 -type) was confirmed at both investigated isothermal sections with the composition range about 49.7–55.7 at% Co and 14.7–23.6 at% Ta. In addition, a large solubility of Al was identified in the μ-Co 6 Ta 7 phase. Based on the experimental results, the published data of the Al-Co and Al-Ta binary systems, and the reassessed Co-Ta parameters from the current work, a thermodynamic assessment of the Al-Co-Ta system was undertaken using the CALPHAD technique. A set of reliable thermodynamic parameters for the Al-Co-Ta system was obtained with a satisfactory agreement with the experimental data. The calculated liquidus projection and invariant reaction scheme in the Al-Co-Ta ternary system were presented. The present work can provide essential experimental and thermodynamic data for the establishment of the Co-based alloy database. • The isothermal sections of the Al-Co-Ta ternary system at 1200 °C and 1300 °C were experimentally determined. • The addition of Al stabilizes the λ 1 -Co 2 Ta phase (Laves C14-type) at 1200 °C. • A large solubility of Al was identified in the μ-Co 6 Ta 7 phase. • The composition range of ternary compound AlCo 2 Ta (L2 1 -type) was defined at 1200 °C and 1300 °C isothermal sections. • The Co-Ta binary and the Al-Co-Ta ternary systems were thermodynamically assessed using CALPHAD technology. [ABSTRACT FROM AUTHOR]