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Graduate Defense: Shane Palmer

December 9 @ 8:00 am - 9:00 am MST

Thesis Information

Title: Transformation Pathways of Lanthanide-free Mn-Al-Ga-X alloys where X= Co, Fe, and Ni

Program: Master of Science in Materials Science and Engineering

Advisor: Dr. Peter Müllner, Materials Science and Engineering

Committee Members: Dr. Brian Jaques, Materials Science and Engineering, and Dr. Alexander King, Materials Science and Engineering

Abstract

Ubiquitous rare-earth, (i.e. lanthanide) permanent magnets (PMs) composed of Nd-Fe-B are the strongest PMs on the market. However, limited mineral sources, complex elemental separation, and supply chain volatility have shifted the lanthanides to critical material status. A performance gap respective to the energy product of PMs is described in the literature, where less expensive, more readily available materials could be applied in efforts to reduce the market dependency on lanthanide PMs. Frequently, lanthanide PMs are incorporated into magnetic applications for which the lanthanide PM’s energy products are excessively high. Mn-Al based permanent magnets offer a potential substitute for PM applications which do not require the high energy product of a lanthanide PM. Atomically, Mn is antiferromagnetic and Al is paramagnetic. However, Mn-Al alloys form a metastable ferromagnetic tetragonal crystal structure designated by L10 (Pearson symbol tP2) ordering after proper thermal and kinetic treatments. This is called τ-phase. Previous work has shown that adding Ga to the Mn-Al alloy stabilizes the τ-phase. The resulting phase transformations, magnetic saturation, and the energy product which arise from Co, Fe, and Ni additions to Mn-Al-Ga are investigated. The magnetic saturation would be improved if 3d transition metals with strong magnetic moments (e.g. Co, Fe, or Ni) alloyed with Mn-Al replaced excess Mn and magnetically coupled. Additionally, by restricting magnetic domain wall motion the energy product of Mn-Al-Ga based PM alloys would increase. A new transformation pathway was demonstrated to form τ-phase and the energy product of Ni-added, Mn-Al-Ga alloys increased by factor of 3.