Title page for etd-0720118-151131


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URN etd-0720118-151131
Author Han-Ting Ye
Author's Email Address No Public.
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Department Materials and Optoelectronic Science
Year 2017
Semester 2
Degree Master
Type of Document
Language English
Title Micro/nano-scaled creep mechanism of TiAlV medium/light weight high entropy alloy
Date of Defense 2018-07-22
Page Count 116
Keyword
  • density
  • high entropy alloy
  • creep
  • mechanical properties
  • microstructure
  • Abstract The high entropy alloys (HEAs) is a new emerging class of metallic alloys which are frequently considered as potential structural materials for high-temperature applications. Nowadays, several refractory HEAs compositions based on transition element have demonstrated remarkable compressive strength at elevated temperatures. But their high density over 8.0 g/cm3 would restrict the application range and the development foreground of HEAs mostly.
    In this study, we use novel medium-density TiAlV HEA as material. The theoretical density of TiAlV equiatomic alloy is about 4.44 g/cm3 which is much lower than that of conventional Fe based HEAs. The TiAlV alloy is firstly investigated by characterizing its microstructure and mechanical properties. In addition to the room temperature (RT) properties, the high temperature (HT) performance is studied by using nanoindenter to extract creep behavior. The results were compared with the traditional FeCoNiCrMn and FeCoNiCrMn-Al high density high entropy alloys, as well as with commercial Ti-6Al-4V alloys.
    The experimental results reveal that TiAlV possess high hardness in room temperature. The Vickers hardness of TiAlV is about 543±14 Hv and the nano-scaled hardness is about 7.2±0.1 GPa. On the other hand, the results of creep testing show that at the temperature regime from 400 to 600oC, under a normalized stress level (σ/E) of 1.3x10-2, the stress exponents for TiAlV are found to be 4.7 from 400 to 450οC and 3.5 from 500 to 600oC, or the strain rate sensitivities are about 0.21 and 0.29 separately. The results indicate the dislocation climb power law creep as the dominant creep mechanism. In addition, although the TiAlV high entropy alloy has higher strength and hardness at room temperature, the creep activation energy of TiAlV (208±7 kJ/mol) is lower than those of FeCoNiCrMn (259±10 kJ/mol), FeCoNiCrMn-Al (260±8 kJ/mol) and Ti-6Al-4V (280 kJ/mol) in high temperature creep experiments. In terms of activation volume, TiAlV also has lower activation volume than those of FeCoNiCrMn, FeCoNiCrMn-Al and Ti-6Al-4V.
    Advisory Committee
  • Sheng-Rui Jian - chair
  • Hsuan-Kai Lin - co-chair
  • Chih-Ching Huang - advisor
  • Files
  • etd-0720118-151131.pdf
  • Indicate in-campus at 3 year and off-campus access at 3 year.
    Date of Submission 2018-08-20

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