Open Access Conference Proceedings

Optimization of conditions of heat treatment of Nd-Fe-B-based permanent magnets, prepared using the strip casting method, was carried out with the aim to enhance their coercivity HCJ and maximal energy product (BH)max, and to improve the shape of the demagnetization curve. The initial alloy with the chemical composition (for high-coercivity magnets) of Fe – 67.05; Nd - 19.50; B – 1; Dy – 6.00; Pr – 6.00; Cu – 0.15; Al – 0.30 (wt.%) in form of strips was submitted to hydrogen decrepitation and vibration milling. The obtained powder with the granulometry of 3-5 μm was mixed with 2.5 wt.% NdH2 in order to improve the liquid phase sintering process and to increase the coercivity as a result of formation of continuous grain boundary. Structural characteristics and phase composition were investigated using scanning electron microscopy equipped with EDX microprobe, light optical microscopy equipped with digital camera and XRPD. The microhardness of the principal Nd(R)2Fe14B phase was measured. Magnetic properties were evaluated using automatic hysteresisgraph and vibrating-sample magnetometer. The maximal values of the coercive force HCJ of 1470 kA·m-1 were achieved by the heat treatment at 500 °C. An increase of this temperature to 550 °C led to a sharp drop in magnetic properties and microhardness. The magneto-optical Kerr microscopy was used to visualize the magnetic domain patterns on the surface of magnetic materials. The observed star-like domain structure indicates a good magnetic texture for permanent magnets. These data are of great importance for choosing the optimum heat treatment of Nd-Fe-B-based magnets.

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