Thermodynamic assessment of the C-Zr system

Theresa Davey1, T.A. Mellan1, S.G. Fries2, M.W. Finnis1,3

1. Department of Materials, Imperial College London, UK
2. ICAMS, Ruhr-Universität Bochum, Germany
3. Thomas Young Centre, Department of Physics, Imperial College London, UK

CALPHAD XLVI, Saint-Malo, France

Contributed oral presentation

The carbon-zirconium system was assessed in 1995 by A. Fernández Guillermet [1] and has shown remarkable longevity in that it is an example of an assessment done with very little experimental data and some theoretical knowledge, that has survived in wide usage until now without any openly published modifications. However, the use of first principles calculations of thermodynamic quantities has recently become important in understanding the behaviour of phases such as those in this system, which allow the potential for new insights.

An analysis of the defect formation energy in the thermodynamic assessment was conducted recently [2], showing that it is easy to add more physical information to an existing assessment without reducing the extent to which the phase diagram reproduces the experimental data.

Following an extensive literature review, we have collected recent experimental data that suggests changes to the invariant eutectic point and liquidus phase boundary in the zirconium-rich region where previously no experimental data was available.

Taking into consideration this experimental data, a new assessment of the carbon-zirconium system is presented that also evaluates the thermodynamic quantities calculated purely by first principles methods [3] and considers the temperature-dependent formation energy of vacancies on the carbon sublattice.

[1] A. Fernández Guillermet, Journal of Alloys and Compounds, 217, 69–89, 1995.
[2] T. Davey et al., CALPHAD XLV, Awaji Island, Japan, 2016.
[3] A.I. Duff et al., Physical Review B, 91, 214311, 2015.