Author: Nie, Zhengwen
Title: Microstructures and mechanical properties of AIxCrCuFeNi₂high entropy alloys
Degree: M.Sc.
Year: 2014
Subject: Alloys -- Microstructure.
Alloys -- Mechanical properties.
Hong Kong Polytechnic University -- Dissertations
Department: Faculty of Engineering
Pages: xvi, 111 leaves : ill. (some col.) ; 30 cm.
Language: English
Abstract: In recent years, high entropy alloys (HEAs) have attracted more researchers' attentions into this metallurgy field due to their unique properties, such as high wear resistance, high temperature softening resistance, and great oxidation resistance, due to the unique phase constitution and microstructure compared with those of conventional alloys. High entropy alloys usually contain no less than five principal elements, in equal or near equal atomic percent, resulting in the high mixing entropy effect which tends to stabilize simple solid-solution phases during solidification. It should be noted that only carefully chosen alloys can form solid solutions in specific conditions due to the probable formation of intermetallics or amorphous phases. Recently a newly developed AlxCrCuFeNI₂ alloys have shown distinctive microstructures resulting in unique macroscopic properties. So the mechanical performance is tested here, and the corresponding fractured surface will be analyzed based on the typical features shown. Even more, the trends of change of different properties show some relativity in a way. And it is save to say the macroscopic features are decided by their phase constitution and microstructure. Meanwhile, the fracture analysis can also verify these results. Besides, the trend of change for mechanical properties can uncover the effect of the doping element Aluminum.
Until now some theoretical rules have been proposed to predict the phase formation and transformation before preparation. For instance, when mixing enthalpy ΔHmix is between - 15 and 5 KJ/mol and δ is less than 5%, the solid-solution phase will be stabilized rather than intermetallics or amorphous phases. For transformation, higher VEC tends to form fcc phase, while lower VEC tends to form bcc phase. To verify these rules, the relevant parameters can be calculated and experimental results are compared with theoretical prediction. After comparison, the high fitness of the specific assumption implies these two rules work very well at least for this AlxCrCuFeNI₂ series. In conclusion, combining theory and practice can make us understand the internal mechanism better to develop more HEA alloys with great unique properties we need.
Rights: All rights reserved
Access: restricted access

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