Modification of the thermodynamic model for the Mg-Zr system

A previous thermodynamic model for the Mg-Zr system has been modified by using new information derived from first-principles calculations in combination with existing experimental data on phase boundaries, invariant reactions as well as limited thermochernical measurements in the liquid phase. Special quasirandom structures for the hcp and bcc structures are used to simulate random solid solutions at 25, 50 and 75 at.%. The total energies of these structures are calculated through first-principles methods and the enthalpies of mixing are used in combination with the available experimental information as input data in the thermodynamic modelling. In addition to experiments and first-principles calculations, stability conditions are also used to prevent unrealistic metastable and higher-order extrapolations. In general, the calculated phase diagram is found to agree well with experiments. The present model is also compared to previous thermodynamic descriptions and it is shown that some of the inconsistencies of the previous model can be resolved by the combined first-principles/CALPHAD approach. (c) 2005 Elsevier Ltd. All rights reserved.