| 配分額 *注記 |
4,550千円 (直接経費: 3,500千円、間接経費: 1,050千円)
2023年度: 1,170千円 (直接経費: 900千円、間接経費: 270千円)
2022年度: 1,170千円 (直接経費: 900千円、間接経費: 270千円)
2021年度: 2,210千円 (直接経費: 1,700千円、間接経費: 510千円)
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| 研究開始時の研究の概要 |
Zirconium carbide and zirconia ceramics are widely used, but there is limited understanding of the atomic-scale effects of impurities and atomic arrangements. This research will combine insights from several theoretical methods (DFT, CEM, MD) with scale-bridging approaches such as CALPHAD to obtain a self-consistent description of the C-O-Zr phase diagram that may be used for design of tuneable high-temperature ceramics. This will also represent a development in the use of first-principles calculations in CALPHAD modelling by extending previously developed defect-centric models.
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| 研究実績の概要 |
In FY2022, density functional theory (DFT) calculations were performed to further examine the C-O-Zr system, including improving the cluster expansion method calculations calculated previously and generating special quasirandom structures (SQS) to examine disordered phases at different compositions. The lattice parameter was evaluated for these results and mapped as planned across the calculated composition space. Results were presented at international conferences: MS&T2022 (in-person in Pittsburgh, USA) - Invited, ICAMMM (virtually in Chandigarh, India) - Invited keynote, and international seminars: Thermo-Calc (virtually in Stockholm, Sweden) research webinar - Invited, UC Davis (in-person in Davis, USA) research seminar - Invited.
The aim of the proposed work was to explore the C-O-Zr system to understand oxidation behaviour of the ultra-high temperature ceramic (UHTC) ZrC. In very recent years, an exciting new field has emerged of “high-entropy” UHTCs based on the ZrC structure, where Zr is replaced with multi-principal component refractory transition metals such as Zr, Hf, Ti, Ta, Nb. These high-entropy UHTCs have improved oxidation resistance compared to the single metal carbides such as ZrC. Therefore, in addition to exploring the C-O-Zr phase diagram, the properties of some high-entropy UHTCs have also been explored. Results from this work was presented at the ICACC2023 conference (in-person in Daytona Beach, USA), and following this an abstract submitted to ECerS 2023 (to take place in Lyon, France, in July 2023) has been selected as a highlight presentation.
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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
Most of the planned calculations to explore the carbon-oxygen-zirconium-vacancy system have progressed as planned, however as the ongoing COVID-19 pandemic has limited travel, it has been challenging to have the discussion needed to implement new techniques such as molecular dynamics simulations to fully examine the interfaces. However, the plan has been adjusted to account for the availability of calculations at different times. This year, international travel finally resumed and it was possible to present work in-person at conferences and workshops after several years, which has resulted in good dissemination of results and discussion with others in the field.
This year the research pivoted to also include examination of high-entropy UHTCs based on ZrC, which have been found to have improved oxidation resistance and so are relevant to this study to understand the oxidation of ZrC. Calculations are ongoing to examine the high-entropy carbide space considering the effect of vacancies and will eventually look at oxygen defects. The results obtained so far are very promising and have attracted interest from experimental researchers in the field following presentations and discussions at international conferences.
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| 今後の研究の推進方策 |
In the remainder of this project, calculations will be performed to further clarify the oxidation pathway between zirconium carbide and zirconia as a function of composition and temperature, building on the partial results already obtained. The thermal and mechanical properties will be examined further and mapped onto the phase diagram to complement the volume results already obtained. Geometric constraints on the mixing of the carbide and oxide phases and their interfaces will be examined. CALPHAD modelling of the C-O-Zr ternary system and remaining work on the binary subsystems will be started as planned. DFT and MD calculations will be performed as necessary to populate the modified quasichemical model which will be used to describe the liquid phase.
Further calculations will be performed on the high-entropy ceramic topic, examining the effect of doping the high-entropy UHTCs with oxygen and looking further at vacancy ordering in these structures.
Results are planned to be presented at domestic and international conferences (Thermo-Calc expert users webinar (Sweden) - Invited, ECerS 2023 (France) - Highlight presentation, MS&T 2023 (USA) - Invited, PACRIM 2023 (China), ICACC 2024 (USA), セラミッ クス基礎科学討論会 (Japan)). Several publications are in progress to be submitted in the next fiscal year.
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