Development of rare-earth free permanent magnets

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Tezin Türü: Doktora

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Metalurji ve Malzeme Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2017

Tezin Dili: İngilizce

Öğrenci: AYŞE MERVE GENÇ ÜNALAN

Asıl Danışman (Eş Danışmanlı Tezler İçin): Yunus Eren Kalay

Eş Danışman: Mahmut Vedat Akdeniz

Özet:

Magnetic materials play a critical role in devices for the conversion, transmission and energy storage. There is a growing demand for NdFeB permanent magnets with high coercivity and magnetic flux. These magnets have been the focus of research for almost 30 years. While magnets are increasingly dependent upon rare-earths, there has been an effort to minimize or substitute their use. In this study, two permanent magnet alloys without any rare-earth elements have been investigated in details. AlNiCo magnets are good candidates to be produced with novel methods and investigated with the latest analysis techniques. Magnetic materials exhibit unique properties at nanoscales and the behavior of AlNiCo magnets in nanoscale is uncertain. Ball milling and hydrogen plasma experiments have been carried out for nanopowder synthesis. Nanoparticles of AlNiCo 5-7 alloy produced by plasma technique showed higher coercivity relative to ball-milled powders. Core/shell structure contributes to the increase in coercivity due to effective exchange coupling and the shell serves as a protective layer against room temperature oxidation. Magnetism of MnAl alloys derives from a ferromagnetic metastable τ-phase. In order to improve the magnetic properties, ε-to-τ transformation should be well established. Microstructural, thermal and crystallographic analysis are carried out with synchrotron analysis. It is observed that there is a compositional limit to ferromagnetic τ-phase formation. ε→τ transformation is found to be dependent on ordering of the ε-phase and can only proceed with ε'-phase. As Mn content increases compositional ordering do not take place and stable phases form. In the third part of the study, 3D printing is presented as a novel manufacturing method for permanent magnets in composite structure. A filament of magnetic MnAl powders embedded in a polymer binding material is produced through extrusion. Operating parameters are optimized and several prototypes are printed. It is observed that magnetic properties of bonded magnets are affected by the weight ratio and magnetic properties of the magnetic filler.