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gamma-prime Phase Stability and Phase Equilibrium in Ternary Co-W-Al at 900 °C



Eric Lass, Maureen E. Williams, Carelyn E. Campbell, Kil-Won Moon, Ursula R. Kattner


Phase equilibria at 900 °C in the Co-rich Co-W-Al ternary system is investigated through isothermal annealing of six alloy compositions for times up to 8000 h. The volume fraction of the L12-gamma-prime phase co-existing with disordered FCC-gamma, B2 and D019 phases is found to steadily decrease with increasing annealing time indicating that it is unstable at 900 °C. Additional heat treatments at 850 °C and 1000 °C further suggest it is a nonequilibrium phase at all temperatures in the ternary system. The L12-gamma-prime phase dissolves slowly with significant amounts remaining in some alloys after 8000 h at 900 °C. However, the present work clearly indicates the microstructure is moving toward a three-phase equilibrium between gamma, D019, and B2. The collected compositional and phase equilibria information provide much needed data for improving the available thermodynamic assessments of the ternary Co-W-Al alloy system.
Journal of Phase Equilibria and Diffusion


Co-based, superalloy, thermodynamics, phase equilibrium, phase diagram


Lass, E. , Williams, M. , Campbell, C. , Moon, K. and Kattner, U. (2014), gamma-prime Phase Stability and Phase Equilibrium in Ternary Co-W-Al at 900 °C, Journal of Phase Equilibria and Diffusion (Accessed February 27, 2024)
Created October 15, 2014, Updated February 19, 2017