Investigation of solid state phase transformations in manganese-aluminum alloys

Acar, Özgün
Permanent magnets have a wide range of application areas such as electric motors, loudspeakers, and generators. The permanent magnet industry is highly dependent on rare-earth (RE) elements. Because of the strategical importance of these RE elements, these magnets become less available and more expensive to reach, which bears a need for RE-free permanent magnets with higher magnetic properties than the conventionally available ones. Mn-Al alloys have a great potential of being used in emerging magnetic applications. This study mainly focused on the solid-state phase transformations of Mn-Al magnetic alloys. In the first part, general characterization of Mn-Al alloys was conducted. Several characteristics of the system were examined. It was observed that composition had an important effect on the magnetic behavior of the system. Alloys with manganese content higher than 71.0 wt% contained the stable phases only and they showed paramagnetic behavior. The in-situ heating high-energy X-ray diffraction (HEXRD) was used to understand phase transformations and critical kinetic analyses were conducted. The composition was ineffective on the activation energies and the activation energy of τ phase formation was calculated as ~140 kJ/mol. In the second part, detailed in-situ heating HEXRD experiments were conducted. The dependence of ε to τ phase transformation on εꞌ phase was investigated. The relationship between the ferromagnetic behavior of the system and composition was observed. It was found that the presence of εꞌ phase rather than the ε phase acts as the precursor for the ferromagnetic τ phase. The formation of τ phase is designated by the presence of εꞌ phase.  
Citation Formats
Ö. Acar, “Investigation of solid state phase transformations in manganese-aluminum alloys,” M.S. - Master of Science, Middle East Technical University, 2016.