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Open AccessArticle

Phase Transitions in Mechanically Milled Mn-Al-C Permanent Magnets

Department of Mechanical and Materials Engineering and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE 68588, USA
Author to whom correspondence should be addressed.
Metals 2014, 4(2), 130-140;
Received: 30 January 2014 / Revised: 3 April 2014 / Accepted: 4 April 2014 / Published: 17 April 2014
(This article belongs to the Special Issue Manganese-based Permanent Magnets)
Mn-Al powders were prepared by rapid solidification followed by high-energy mechanical milling. The rapid solidification resulted in single-phase ε. The milling was performed in both the ε phase and the τ phase, with the τ-phase formation accomplished through a heat treatment at 500 °C for 10 min. For the ε-milled samples, the conversion of the ε to the τ phase was accomplished after milling via the same heat treatment. Mechanical milling induced a significant increase in coercivity in both cases, reaching 4.5 kOe and 4.1 kOe, respectively, followed by a decrease upon further milling. The increase in coercivity was the result of grain refinement induced by the high-energy mechanical milling. Additionally, in both cases a loss in magnetization was observed. Milling in the ε phase showed a smaller decrease in the magnetization due to a higher content of the τ phase. The loss in magnetization was attributed to a stress-induced transition to the equilibrium phases, as no site disorder or oxidation was observed. Surfactant-assisted milling in oleic acid also improved coercivity, but in this case values reached >4 kOe and remained stable at least through 32 h of milling. View Full-Text
Keywords: permanent magnets; mechanical milling permanent magnets; mechanical milling
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Lucis, M.J.; Prost, T.E.; Jiang, X.; Wang, M.; Shield, J.E. Phase Transitions in Mechanically Milled Mn-Al-C Permanent Magnets. Metals 2014, 4, 130-140.

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