J.J. Wysłocki

Nanocrystalline (Pr,Dy)-(Fe,Co)-Zr-Ti-B magnets produced directly by rapid solidification

Hard magnetic thick ribbon samples of a series of Pr9-xDyxFe60Co13Zr1+yTi3-yB14 alloys (where x=0;1 and y=0;1) (having average thicknesses tr of~ 140 µm) were produced directly by the melt-spinning technique under an Ar atmosphere. The phase constitution of the samples in the as-cast state was determined by X-ray diffractomety and Mossbauer spectroscopy. Hysteresis loops measurements at room temperature indicated very good hard magnetic properties for the alloys, which the coercivity attaining a maximum values of 1.58 MA/m. This is comparable with the coercivities of commercial NdFeB magnets based on melt spun ribbon and with those for nanocrystalline Nd-Fe-B magnets produces by other processes such as mechanical alloying or HDDR.

High-coercivity sintered Nd14.5Dy1.5Fq68Co5Al1.5Cr2B7.5 permanent magnet

Abstract Effect of 1.5 at. % Al and 2.0 at.% Cr additions on microstructure, magnetic properties, thermal stability and corrosion resistance of (Nd,Dy)-(Fe,Co)-B sintered magnet have been studied. It is shown that simultaneous substitution of these elements for Fe in (Nd,Dy)-(Fe,Co)-B magnet causes significant improvement in coercivity and thermal stability; maximum operating temperature up to 473 K may be possible. The corrosion resistance in acid solution and atmospheric environment is also significantly improved by blocking the selective oxidation of the Nd-rieh phase owing to the formation of (Nd,Dy)-(Co,Al,Fe) and (Nd,Dy))-(Fe,Cr,Co) phases.

Corrosion resistance of the FeAlC permanent magnet alloy

Abstract The correlation between corrosion behaviour rate of hard magnetic FeAlC alloys and their microstructure and phase composition is presented. Potentiokinetic polarization curves of the tested material in acid (pH = 1 and 2) and neutral (pH = 7) sulphate solutions have been measured. For open-circuit condition, kinetic curves of etching of the samples in 0.5 M H2SO4 have been determined. The resistance of the tested magnets against atmospheric corrosion has been evaluated using a salt-spray test. The atmospheric corrosion rate is 1.5–2 times slower than that found for Nd-Fe-B type magnets. The FeAlC alloys show good corrosion resistance in neutral environments and corrode at rates comparable to that of white cast-iron in acid environments.

Mössbauer Spectroscopy in Phase Determination of the Anisotropic Fe–Al–C Permanent Magnet

The phase changes caused by heat treatment were investigated in the anisotropic Fe-Al-C permanent magnet using both Mossbauer spectroscopy and X-ray diffraction. However, only Mossbauer spectroscopy reveals the retained austenite (5%) in the samples after final heat treatment. It is shown that this austenite improves the magnetic properties of the Fe-Al-C magnet, causing magnetic isolation between Fe3AlC and the ferrite phase.

Magnetic properties of sintered Nd17−xPrxFe75B8 magnets

Abstract The effect of partial substitution of Nd by Pr on the intrinsic properties of the Nd 17− x Pr x Fe 78 B 8 magnets (where 0 x

Magnetic properties of sintered Nd-Fe-B type magnets containing calcium, chlorine and carbon

The microstructure and magnetic properties of Nd16-xXxFe70.5Co5AlB7.5 and Nd14-xDy2XxFe71Co5B8 (X=Ca, Cl and C) magnets with various x were examined. In magnets after sintering and heat treatment carbon-rich areas were produced within the non-magnets Nd-rich phase. However chlorine-rich and calcium-rich areas were present in both non-magnetic Nd-rich and B-rich phases. The contribution of C≤0.35 at%, Cl≤0.013 at% and Ca≤0.09 at% had no influence on the magnetic properties (Br and iHc), but higher concentration of these elements caused decrease in these properties. Abnormal grain growth was found in magnets containing Cl.

Rotational hysteresis and magnetization reversal mechanisms in Sm–Fe–N permanent magnets

Abstract The mechanism of magnetization reversal processes in Sm–Fe–N permanent magnets has been investigated on the basis of the analysis of the rotational hysteresis energy, W r , calculated from the magnetic torque curves. Moreover, the anisotropy constants K 1 and K 2 have been determined from the Fourier analysis of the torque curves. The results are compared with the theoretical predictions.