2020 Fiscal Year Final Research Report
The mechanism of martensitic transformation induced by tempering of Ti-X-7Al alloy.
| Project/Area Number |
17K06773
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Research Field |
Physical properties of metals/Metal-base materials
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| Research Institution | Okayama University |
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Principal Investigator |
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| Project Period (FY) |
2017-04-01 – 2021-03-31
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| Keywords | マルテンサイト / スピノーダル分解 / 逆変態 / 形状変化 / 焼戻し / 熱応力 |
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| Outline of Final Research Achievements |
The transformation mechanism of the orthorhombic α" phase induced by tempering of the Ti-X-7Al alloy was investigated. Quenching from the β single phase region forms a slight α"-M (martensite) with the residual β phase. Rapid tempering to about 500 ° C using a salt bath or convergent light heating results in the formation of coarse α"-M over the entire surface during heating. After holding for 3 minutes or more, α"-M disappears and changes to fine α" iso due to atomic diffusion. Furthermore, α"-M reverses to the β phase when heated to about 200 ° C. Complex transformation behavior suggests that the free energy of the α phase is spinodal decomposition. It is suggested that the complicated transformation behavior is caused by the thermal stress associated with rapid heat treatment and the spinodal decomposition type free energy of α phase.
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| Free Research Field |
材料工学
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| Academic Significance and Societal Importance of the Research Achievements |
マルテンサイト変態は材料の強化だけでなく，形状記憶や超弾性などの機能発現に重要な役割を果たす．本研究では鉄鋼材料でよく理解されている常識的なマルテンサイト変態とは大きく異なる変態挙動がTi-X-7Al合金で発現することを明らかにした．特に焼戻しでマルテンサイトが形成することや，それより低温でβ逆変態する現象，焼入れで試料内部にマルテンサイトが生成することなどは，マルテンサイトの利用の幅を広げるものと確信している．また形状記憶とは逆向きの形状変化の発現や，焼戻しによる急速な硬化現象などは実用的な利用が見込まれる．
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