Experimental investigations of microstructures and phase equilibria in the Co-V-Ta ternary system

The microstructures and the phase equilibria of the equilibrated Co-V-Ta ternary alloys have been investigated. Moreover, four isothermal sections of the Co-V-Ta ternary system at 1300, 1200, 1100 and 900 °C are experimentally established. The corresponding results are summarized as follows: (1) the C14 phase with a large solubility of Co is observed both at 1300 and 1200 °C, while it forms a ternary single phase region at 1100 and 900 °C; (2) the C36 phase, containing a large solubility of V, is identified at 1300, 1200 and 1100 °C, while it exists as a ternary single phase region at 900 °C; (3) Co is in favor of stabilizing the C14 phase against lowerature, while V plays an analogous influence on the C36 phase; (4) the solubility of Ta in σ-Co₂V₃ phase decreases by a small amount as the temperature decreases from 1300 to 900 °C. In addition, the experimental information obtained in the present work is not only essential for the thermodynamic assessment of the Co-V-Ta ternary system, but also important for the development of the Co-base alloys.