| 研究実績の概要 |
A thermodynamic database was created using the CALPHAD approach, incorporating insights on short and long range ordering in the carbon-zirconium system obtained during previous years. For the zirconium carbide solution phase, a vacancy-centric excess energy model was developed to include the effects of short-range ordering. This model is based on finite temperature first-principles calculations of the formation and interaction energies of the most stable vacancy pair and triplet clusters. Long-range ordered superstructural zirconium carbide phases were described based on phonon calculations of the lowest energy structures on the convex hull determined by cluster expansion methods (CEM). Order-disorder transition temperatures were determined directly from the first principles calculations. All calculated information relating to the fully disordered, short-range ordered, and long-range ordered zirconium carbide phases was incorporated into a phase diagram description, also considering all available experimental insights in the literature. The effects of oxygen defects on vacancy ordering was investigated, determining that the presence of dissolved oxygen reduces the tendency to vacancy ordering at 0K, with more significant effect at finite temperature.
Results were published in RSC Advances (two papers) and the International Journal of Ceramic Engineering and Science (invited review) with one further manuscript in preparation for publication. Results were presented at virtual international conferences (MH21, MS&T, MRM, PACRIM, ICACC, TMS) and domestic meetings.
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