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Metals 2014, 4(2), 130-140;

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.
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)
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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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