Research on Martensitic Transformation Behaviors and Properties of Pseudobinary (TiZrHf)(NiCoCu)-based High Entropy Shape Memory Alloys
| Autor: | Yue-Jin Chen, 陳躍今 |
|---|---|
| Rok vydání: | 2018 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 106 The influence of high entropy effect on Ti40Zr10Ni40Co5Cu5, Ti30Zr20Ni30Co10Cu10, Ti25Zr25(NiCoCu)50, TiZrHfNiCoCu, (TiZrHf)50Ni25Co10Cu15 and (Ti16.5Zr16.5Hf16.5)Ni30.5Co5Cu15 alloys is discussed in this study. All of the alloys form the mixing phases of B2 solid solution and Ti2Ni-like precipitate rather than a single solid solution. The martensitic transformation temperature will decrease by adding cobalt and increase by adding zirconium and hafnium. Martensitic transformation can be observed only in (TiZrHf)50Ni25Co10Cu15 and (Ti16.5Zr16.5Hf16.5)Ni30.5Co5Cu15. The forward and the reverse transformation peaks of furnace-cooled (TiZrHf)50Ni25Co10Cu15 alloy are at -24.0 °C and 8.9 °C, and increase to -0.3 °C and 40.6 °C after solid-solution treatment, respectively. The forward and reverse transformation peaks of furnace-cooled (Ti16.5Zr16.5Hf16.5)Ni30.5Co5Cu15 are 156.2 °C and 200.3 °C. Due to the poor compatibility of austenite and martensite, dislocations are introduced in (TiZrHf)50Ni25Co10Cu15 and (Ti16.5Zr16.5Hf16.5)Ni30.5Co5Cu15 alloys during the thermal cycle, and thus their martensitic transformation temperatures decrease as the number of martensitic transformation increases. The shape memory effect of (TiZrHf)50Ni25Co10Cu15 is improved after solution treatment. Its reversible strain reaches 4.78% and irreversible strain is smaller than 0.38% under 650MPa. (Ti16.5Zr16.5Hf16.5)Ni30.5Co5Cu15¬ is a high temperature shape memory alloy and its transformation temperature can be adjusted by aging treatment. After 500 °C aging for 10 hours, the reversible strain and the reversible strain ratio are 0.35% and 74.47%, respectively, better than 0.17% and 54.84% after 600 °C aging for 1 hour. Finally, (TiZrHf)50Ni25Co10Cu15 has better shape memory effect than Ni-rich (Ti16.5Zr16.5Hf16.5)Ni30.5Co5Cu15¬ alloy. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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