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Experimental and Thermodynamic Assessment of Phase Equilibria in the Co-Mo system



Katsunari Oikawa, Ursula R. Kattner, J. Sato, T. Omori, M. Jang, K. Anzai, Kiyohito Ishida


Phase equilibria of the solid phases in the Co-Mo system were investigated using two-phase alloys and the diffusion couple technique. In addition, systematic studies of phase transformations were conducted by differential scanning calorimetry, and vibrating sample magnetomermagnetometry. Furthermore, ab initio calculations of D019-Co3Mo and several fcc-based ordered structures, including metastable compounds, were carried out to estimate the formation energy including metastable compounds. Based on these results, a thermodynamic assessment by using the CALPHAD approach method was performed. FA four-sublattice model was applied toused for the fcc-base phase to describe the order-disorder phase transformation. For the  phase, both a three and a four-sublattice models were applied. Sets The set of thermodynamic values describing the Gibbs energy of the Co-Mo system was in good agreement withreproduces the experimental phase diagram well. The four-sublattice model for the  phase reproduces the site fractions as well as the phase boundaries is better than the three-sublattice model to reproduce the site fraction as well as the phase boundaries. Metastable The calculated metastable fcc-based phase diagram calculated including theconsidering chemical and magnetic ordering was is also reasonable., which This is useful toimportant for estimatinge the phase stability of the L12 phase in the Co-base γ/γ' superalloys.
Materials Transactions


phase diagram, first-principles, thermodynamic, order-disorder transition, superalloys


Oikawa, K. , Kattner, U. , Sato, J. , Omori, T. , Jang, M. , Anzai, K. and Ishida, K. (2012), Experimental and Thermodynamic Assessment of Phase Equilibria in the Co-Mo system, Materials Transactions, [online], (Accessed May 18, 2024)


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Created June 19, 2012, Updated October 12, 2021