Thermodynamic re-assessment of the Co-Al-W system

Published

October 2, 2017

Author(s)

Peisheng Wang, Wei Xiong, Ursula R. Kattner, Carelyn E. Campbell, Eric Lass, Oleg Y. Kontsevoi, Gregory B. Olson

Abstract

The Co-Al-W system and its binary sub-systems Al-Co, Al-W and Co-W were critically reviewed. The thermodynamic description of the Co-Al-W system including all three binaries was developed considering thermodynamic and constitutional data of the systems. Results from density functional theory (DFT) calculations were employed to improve reliability of the descriptions. The Gibbs energy for the thermal vacancy in the Bcc_A2 phase is discussed. GVa = 30 J/(mol∙K)×T is suggested for the Gibbs energy of the pure vacancy end-member. Large positive values were used for the interaction parameters between the elements, Al, Co and W, and this vacancy. The descriptions obtained for the Al-W and Co-W systems describe the thermodynamic and phase equilibrium data well. Earlier description of the Al-Co and Al-W systems result in the formation of inverse miscibility gaps below 5000 K. In the present work, the inverse miscibility gaps were successfully eliminated for temperatures below 6000 K while describing the phase equilibria and thermodynamic data well. The ordered γ’ (Fcc_L12) phase of the Co-Al-W system is described as a metastable phase in the entire temperature range. The calculated Gibbs energy of the γ’ is only slightly above that of the equilibrium state, which indicates that there is good possibility of stabilizing the γ’ phase with the addition of γ’-stabilizing elements, such as Ti, Ta and Hf.

Citation

Calphad-Computer Coupling of Phase Diagrams and Thermochemistry

Volume

59

Pub Type

Journals

Download Paper

https://doi.org/10.1016/j.calphad.2017.09.007

Keywords

CALPHAD, Co alloys, superalloys, thermodynamics, phase diagram

Citation

Wang, P. , Xiong, W. , Kattner, U. , Campbell, C. , Lass, E. , Kontsevoi, O. and Olson, G. (2017), Thermodynamic re-assessment of the Co-Al-W system, Calphad-Computer Coupling of Phase Diagrams and Thermochemistry, [online], https://doi.org/10.1016/j.calphad.2017.09.007 (Accessed April 23, 2024)