Abstract
The Ni-rich portion of the Ni-Al phase diagram is examined in light of dataon coherent equilibrium between the γ (Ni-Al solid solution) andγ' (Ni3Al) phases, as well as on the thermodynamicrequirements of coherent equilibrium. The model of Ardell and Maheshwari wasused to calculate the difference between the incoherent and coherentsolubility limits over the temperature range of 400-800 °C. New dataon the elastic constants of Ni3Al as a function of temperatureand composition, as well as the Gibbs free energy functions of the most recentthermodynamic model of the Ni-Al alloy system, were used in the calculations.With these input parameters the predicted differences between the incoherentand coherent solubility limits are very small, and inconsistent with recentexperimental data on the variation of the coherent solubility with theγ' volume fraction. The inconsistency is a consequence of the largecurvature of the Gibbs free energy function for the γ phase obtainedfrom the thermodynamic model. These findings are discussed in the context ofthe accuracy of thermodynamic modelling of phase diagrams.
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