nonstoichiometry and thermodynamic stability of cementite in Fe-C system
| Project/Area Number |
16K14435
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| Research Category |
Grant-in-Aid for Challenging Exploratory Research
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| Allocation Type | Multi-year Fund |
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| Research Field |
Material processing/Microstructural control engineering
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| Research Institution | Tohoku University |
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Principal Investigator |
OHTANI HIROSHI 東北大学, 多元物質科学研究所, 教授 (70176923)
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| Co-Investigator(Kenkyū-buntansha) |
飯久保 智 九州工業大学, 大学院生命体工学研究科, 准教授 (40414594)
徳永 辰也 九州工業大学, 大学院工学研究院, 准教授 (40457453)
榎木 勝徳 東北大学, 多元物質科学研究所, 助教 (60622595)
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| Project Period (FY) |
2016-04-01 – 2019-03-31
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| Project Status |
Completed (Fiscal Year 2018)
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| Budget Amount *help |
¥3,640,000 (Direct Cost: ¥2,800,000、Indirect Cost: ¥840,000)
Fiscal Year 2018: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2017: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000)
Fiscal Year 2016: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
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| Keywords | セメンタイト / 非化学量論化合物 / 混合エントロピー / 結晶・組織制御 |
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| Outline of Final Research Achievements |
Theoretical calculations based on the cluster expansion and cluster variation method were applied to the cementite phase. A thermodynamic model was constructed for the cementite phase, assuming that the C atoms occupied the octahedral interstitial vacancy sites, and the Gibbs free energy in the compositional range between 0% and 40 mol% C was evaluated. It was found that at higher temperature cementite is stabilized in the off-stoichiometric composition region because of the effect of configuration entropy of the C atoms and the vacancies, whereas in the lower temperature region the free energy is minimized almost at the stoichiometric composition. The same technique was applied to the ferrite and austenite phases, and the free energies in the compositional range including the metastable regions were calculated. Calculation of the Fe-C binary phase diagram is also attempted. The same approach was applied to other phases in the binary system.
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| Academic Significance and Societal Importance of the Research Achievements |
Fe-C二元系状態図は鋼の基本系であることから，これまでにもきわめて多くの研究が報告されている．しかし，この二元系は唯一の複平衡状態図として表現されていることからもわかるように，セメンタイトと黒鉛の相対的な熱力学的安定性や低温時効におけるC原子のクラスタリング，準安定炭化物の形成など，この合金系に関わる多くの未解明の問題が残されている．本研究では，人為的なパラメータを必要としない第一原理的手法によって，この状態図に隠された課題に挑戦したものであり，学術的な重要性だけでなく，鉄鋼材料の熱処理などにおける実用性においても重大な意味を持っている．
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Report
(4 results)
Research Products
(8 results)
