| 研究課題/領域番号 |
19K15273
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| 研究機関 | 東北大学 |
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研究代表者 |
DAVEY THERESA 東北大学, 工学研究科, 助教 (10816987)
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| 研究期間 (年度) |
2019-04-01 – 2021-03-31
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| キーワード | CALPHAD / point defects / phase diagram / zirconium carbide / vacancies / short range ordering |
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| 研究実績の概要 |
In FY2019-2020 the behaviour of structural vacancies in zirconium carbide was investigated from 0K up to the melting point (around 3700K). It was found that at low temperatures, vacancy-ordered phases are stable, and at high temperature there are many disordered vacancies. Calculations were performed that determined which vacancy-ordered phases were stable. Calculations of the vacancy formation energy, and vacancy interaction energies demonstrated the competing energies that determine high temperature stability.
Thermodynamic data relating to vacancy-defective structures was combined into a new hybrid excess Gibbs energy model that improves the thermodynamic modelling of highly defective ZrC. An analysis of this Gibbs energy suggests that the description of the highly defective ZrC is improved compared to the conventional description. Data from first principles calculations relating to the vacancy-ordered phases was incorporated directly into the phase diagram, clarifying the low temperature stability behaviour.
A parallel study on interstitial defects was initiated. Meetings with collaborators from Imperial College London and FactSage and Pycalphad software were scheduled in early 2020, but had to be postponed due to coronavirus. Collaborative work will be performed online or postponed for later in the year when business travel is possible. Results were presented at international conferences in Japan (PACRIM) and the USA (ICACC, TMS) where discussions with experimental researchers provided guidance for future directions of research.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
The calculations relating to structural vacancy-type defects in zirconium carbide have progressed as planned and new prototype excess Gibbs energy models for highly defective phases were developed using newly-calculated and already published data. Due to the coronavirus, planned in-person meetings relating to this project with software collaborators (FactSage and Pycalphad) could not take place, meaning that the developed models cannot yet be used in any commercial software. However, a thorough analysis was done by hand that confirms that the thermodynamic description is improved compared to the conventional description. Work with software companies to enable general use of the developed models will be prioritised in FY2020.
Presenting the results at international conferences yielded potential collaboration from experimental researchers that could allow further validation of the Gibbs energy models. Calculations to incorporate other point defects into the description (eg. Frenkel defects, interstitials) are underway and it is hoped that meetings with collaborators can be held in the coming year, allowing the project to proceed as planned.
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| 今後の研究の推進方策 |
In FY2020, planned collaborations will be undertaken with software developers to implement the developed Gibbs energy models which will allow their general use. Collaborations with researchers at Imperial College London will give assistance to performing the relevant calculations relating to bound defects that will be incorporated into Gibbs energy models. Collaborators will be hosted as required in order to perform research efficiently.
Further first principles calculations to elucidate the order-disorder transition where vacancy-ordered phases in zirconium carbide will be performed and used to parameterise the Gibbs energy models. This will be done using the special quasirandom structures (SQS) technique. Oxygen is often present in experimental samples, and so calculations examining how the presence of dilute oxygen affects the properties of zirconium carbide will also be performed. To confirm that the developed Gibbs energy model is transferrable between highly defective phases, some calculations will be performed for a different material (such as hafnium carbide) to demonstrate its use.
Results are planned to be presented at international conferences (MS&T (USA), MRS (USA), TOFA (Germany)) and drafted for publication in FY2020. If business travel is disrupted by coronavirus for a longer period, conferences further in the future will be used for dissemination of results.
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| 次年度使用額が生じた理由 |
Hosting a visitor from Imperial College London, UK (Dr. Thomas Mellan) was planned in March 2020, but unfortunately due to the coronavirus this visit had to be cancelled. The cost of cancellation was 45,022yen. An additional visit to the University of California in the United States (invited lecture and discussion) was planned for late March 2020 but was cancelled due to coronavirus. Luckily no cancellation costs were incurred. The money allocated for these visits will be used in FY2020 for the planned purpose if possible.
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