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Effect of selected parameters of the melt-spinning process on the thickness and magnetic properties of Nd-Fe-Al ribbons

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The Nd-Fe-Al alloys, first described by Inoue [1] in 1996, are inferior to Nd-Fe-B magnets as far as the magnetic properties are concerned, but their great advantage is that they do not need additional annealing (performed after melt-spinning) to achieve their possibly good magnetic properties. These properties depend on the cooling rate of the melted material, and the best values achieve at the quenching rates at which the ribbons have a thickness of the order of tenths of millimeter. Magnets of this size could be used directly, without further treatment, in electromechanical micro-devices or in the MEMS technique [2]. In the application range so defined, the melt-spinning processed Nd-Fe-Al alloys can compete with Nd-Fe-B alloys, since the basic technology of Nd-Fe-B magnets does not permit producing easily components with a thickness of the order of tenths of millimeter. The thickness and properties of the Ne-Fe-Al ribbons can be modified by controlling the melt-spinning process parameters, such as the rotational speed of the wheel, the shape and size of the crucible opening, the temperature of the melted material, and the pressure of the ejecting gas [3]. It has been demonstrated thus far that rapid cooling (at a wheel rotational speed of 20÷30 m/s) promotes an increase of the share of an amorphous phase and gives ribbons with poor magnetic properties. When cooled at lower rates, the material contains a greater proportion of crystalline phases and has substantially better magnetic properties [3, 4]. The microstructure of the Nd-Fe-Al alloys has been described in many publications [5, 6], but there is no consistency in the interpretation of the results. At present, we can say that the Nd-Fe-Al alloys with the best properties contain very small amounts of the amorphous phase and that their structure is multi-phase and built on a nanometric level [7]. The aim of the present study was to examine the possibility of producing [...]

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