2020 Fiscal Year Research-status Report
Developing models for CALPHAD-type phase diagrams that directly consider the effect of structural point defects
| Project/Area Number |
19K15273
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| Research Institution | Tohoku University |
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Principal Investigator |
DAVEY THERESA 東北大学, 工学研究科, 特任助教 (10816987)
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| Project Period (FY) |
2019-04-01 – 2022-03-31
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| Keywords | CALPHAD / point defects / phase diagram / zirconium carbide / vacancies / short range ordering |
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| Outline of Annual Research Achievements |
A vacancy-centric excess energy model for zirconium carbide was developed, based on finite temperature first-principles calculations of the formation and interaction energies of the most stable vacancy pair and triplet clusters. This model was used alongside all available information regarding the solid solution zirconium carbides, to create a description of the energy landscape that is consistent with the various short-range-ordering (SRO) effects. Finite temperature DFT calculations of the long-range ordered (LRO) zirconium carbides showed transitions from a LRO to SRO to disordered arrangement of vacancies. The transition temperatures were calculated as a function of composition by combining first-principles calculations with the newly developed excess energy model, and all information was incorporated into a thermodynamic database and phase diagram description.
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.
A first-principles investigation into the origin of the vacancy-ordering was conducted, and some of the mechanisms (including the geometry of the underlying crystal structures and the electronic charge distribution) were elucidated.
Results were presented at (virtual) international conferences, and all the above results are currently being prepared for publication.
Planned collaborations with researchers at Imperial College London and thermodynamic software developers were delayed due to the COVID-19 pandemic, but will continue as soon as possible.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The planned calculations to develop a new excess energy model to describe the structural ordering in zirconium carbide have been conducted as planned, and several other interesting phenomena have been observed at the same time. The calculated order-disorder transitions have been incorporated into the thermodynamic databases as much as is possible with conventional Gibbs energy models. The obtained results are very promising and have attracted interest from experimental researchers in the field following presentations at international conferences. However, while conventional thermodynamic models have the advantage of being compatible with other studies, one aim of this project was to work with thermodynamic software developers to incorporate the information more directly. Unfortunately, due to delays arising from the COVID-19 pandemic, these collaborations have not progressed as much as was hoped. However, there are plans to complete this task within the FY2021-FY2022 year.
Although several presentations were made at virtual international conferences this year, some cancellations reduced the information dissemination over the year. In the next year, presenting and publishing information as much as possible will be prioritised.
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| Strategy for Future Research Activity |
In FY2021, collaborations with thermodynamic software developers will be continued to create a excess energy model that is directly assigned from first-principles calculations of vacancy-related properties.
Calculations will be performed for hafnium carbides to demonstrate the transferability of the developed approach.
Results are planned to be presented at domestic and international conferences virtually, or in-person if possible (MS&T (USA), ICACC (USA), PACRIM (Canada), MRM (Japan), TMS (USA)), and results that are currently in preparation for publication will be finalised this year.
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| Causes of Carryover |
Significant amounts of the budget were planned to be used for travel to international conferences to disseminate information, and to host visitors to allow collaborations. Unfortunately, due to the ongoing COVID-19 pandemic, international travel has not been possible in the last year, therefore these expenses have been delayed until such meetings and in-person collaborations are possible.
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