Comparison of structures and properties of arc-melted and induction-melted high entropy alloys
Yao, Zhiqi (2016)
2016
Master's Degree Programme in Materials Science
Teknisten tieteiden tiedekunta - Faculty of Engineering Sciences
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Hyväksymispäivämäärä
2016-12-07
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201611244787
https://urn.fi/URN:NBN:fi:tty-201611244787
Tiivistelmä
High entropy alloys contains five to thirteen different kinds of metallic elements which have different mechanical properties compared to the conventional alloys. Generally, high entropy alloys are manufactured firstly by melting the requested metals by arc-melting or induction-melting and then casting in different atmospheres. It is interesting to know whether the HEAs manufactured in different methods show similar structures and properties.
In this master’s thesis, the arc-melted Al0.5CrFeCoNiCu is chosen as the reference sample. Meanwhile, induction-melted Al0.5CrFeCoNiCuMo0.25 and Al0.5CrFeCoNiCu which casted in air and vacuum condition are studied also for finding out whether Al0.5CrFeCoNiCu HEAs with desired properties can be manufactured by this way. The microstructures of HEA samples were observed with optical microscope and scanning electron microscope while the crystalline structure was studied by X-ray diffraction. Afterwards, the compression test was carried out to obtain mechanical properties of HEAs.
By SEM, it could be seen that HEA samples had similar composition distribution. However, dark spots which contains sulfur inclusion could be found in induction-melted samples. The induction-melted Al0.5CrFeCoNiCu HEAs had a bcc+fcc structure and showed more brittle. By contrast, the induction-melted Al0.5CrFeCoNiCuMo0.25 HEAs had a fcc crystalline structures and showed good ductility. In summary, the induction-melted Al0.5CrFeCoNiCu HEAs samples showed relatively poor mechanical properties compared to reference samples. In order to alter this condition, since the mechanical properties are related to the cooling rate and impurities, it is recommended to control the cooling rate and reduce the amount of impurities.
In this master’s thesis, the arc-melted Al0.5CrFeCoNiCu is chosen as the reference sample. Meanwhile, induction-melted Al0.5CrFeCoNiCuMo0.25 and Al0.5CrFeCoNiCu which casted in air and vacuum condition are studied also for finding out whether Al0.5CrFeCoNiCu HEAs with desired properties can be manufactured by this way. The microstructures of HEA samples were observed with optical microscope and scanning electron microscope while the crystalline structure was studied by X-ray diffraction. Afterwards, the compression test was carried out to obtain mechanical properties of HEAs.
By SEM, it could be seen that HEA samples had similar composition distribution. However, dark spots which contains sulfur inclusion could be found in induction-melted samples. The induction-melted Al0.5CrFeCoNiCu HEAs had a bcc+fcc structure and showed more brittle. By contrast, the induction-melted Al0.5CrFeCoNiCuMo0.25 HEAs had a fcc crystalline structures and showed good ductility. In summary, the induction-melted Al0.5CrFeCoNiCu HEAs samples showed relatively poor mechanical properties compared to reference samples. In order to alter this condition, since the mechanical properties are related to the cooling rate and impurities, it is recommended to control the cooling rate and reduce the amount of impurities.