Author: Chen, Long
Title: Microstructure and mechanical properties of CrCuFeNi₂Tix high entropy alloys
Advisors: Shi, San Qiang (ME)
Degree: M.Sc.
Year: 2015
Subject: Alloys
Alloys -- Mechanical properties.
Hong Kong Polytechnic University -- Dissertations
Department: Department of Mechanical Engineering
Pages: xv, 89 leaves : illustrations ; 30 cm
Language: English
Abstract: High entropy alloys (HEAs) have drawn much attraction from researchers in material field. In this thesis, reported studies and developments of HEAs are reviewed. Different from the traditional alloys which depend on one principal element, HEAs usually contain at least five principal elements. Based on their different compositions, HEAs show various unique properties, such as high hardness, good ductility, high heat resistance and high corrosion resistance, which are detailed discussed in the thesis. Varies of phases can form in difference HEAs, including BCC and FCC solid solution, intermetallic compounds and amorphous phase. It is very important to predict the phase formation of HEAs. In this thesis, some related rules are introduced, applied and proved. Based on the existing work, the mainly effects for HEAs are discussed from different perspectives, including thermodynamics, kinetics, and microstructures. The CrCuFeNi₂Tix HEAs (x=0.1-0.7) are prepared and studied. The XRD patterns of CrCuFeNi₂Tix HEAs prove the effectivities of ΔHmix, ΔSmix, δ, ΔX and VEC rules. Just like predicted by these rules, the pure FCC structure changes to FCC+BCC+Ni₃Ti gradually while the proportion of Titanium in HEAs increases. In this case, interesting variation trend of mechanical properties of CrCuFeNi2Tix HEAs is revealed. They show low stiffness and good flexibility. When x value is small, the HEAs show very good ductility, and when x value is large, the HEAs show very high hardness. The microstructures of CrCuFeNi₂Tix HEAs are observed after tensile test and hardness test. Due to the different values of x, both ductile fracture and brittle fracture would occur, while slip bands always can be found as an important characteristic of crystal plastic deformation.
Rights: All rights reserved
Access: restricted access

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