2020, Volume 6, Issue 2
Engineering >> 2020, Volume 6, Issue 2 doi: 10.1016/j.eng.2019.03.013
Efficient Nanostructuring of Isotropic Gas-Atomized MnAl Powder by Rapid Milling (30 s)
Division of Permanent Magnets and Applications, IMDEA Nanoscience, Campus Universidad Autónoma de Madrid, Madrid 28049, Spain
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Abstract
An unprecedentedly short milling time of 30 s was applied to gas-atomized MnAl powder in order to develop permanent magnet properties and, in particular, coercivity. It is shown that such a short processing time followed by annealing results in efficient nanostructuring and controlled phase transformation. The defects resulting from the microstrain induced during milling, together with the creation of the β-phase during post-annealing, act as pinning centers resulting in an enhanced coercivity. This study shows the importance of finding a balance between the formation of the ferromagnetic τ-MnAl phase and the β-phase in order to establish a compromise between magnetization and coercivity. A coercivity as high as 4.2 kOe (1 Oe = 79.6 A·m-1 ) was obtained after milling (30 s) and annealing, which is comparable to values previously reported in the literature for milling times exceeding 20 h. This reduction of the postannealing temperature by 75 ℃ for the as-milled powder and a 2.5-fold increase in coercivity, while maintaining practically unchanged the remanence of the annealed gas-atomized material, opens a new path for the synthesis of isotropic MnAl-based powder.
Keywords
Permanent magnets (PMs) ; Nanostructuring ; Phase transformation ; MnAl ; Gas atomization ; Ball milling
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