The first goal of this work involved the study of the effect of variables the HDDR processing, such as: the added pressure of H2 in the system, the time of heat treatment and recombination of Pr12Fe65.9Co16B6Nb0.1 alloy with the aim of improving the magnetic properties like the magnetic properties of the Pr14Fe63.9Co16B6Nb0.1 alloy (Br= 865mT and iHc= 790mT). The second aim of the work involved the characterization of HDDR powders that were analyzed by X-ray diffraction for identification and quantification of crystalline phases. These materials were analyzed by scanning electron microscopy (SEM).
An evaluation of the effect of alloying elements on the microstructure and magnetic properties of Pr15FebalCo8B7Nb0.05Mx (M = Cu, P, Gd and Ga; 0 ≤ x ≤ 0.25) sintered magnets has been carried out. A mixture of alloys and the high-energy milling technique have been used to prepare the magnets. The alloying elements have influenced the remanence, intrinsic coercivity and particularly the squareness factor (SF). Phosphorus addition improved (BH)max (254 kJm-3 ) and SF around 10% (0.89). The same improvement addition on intrinsic coercivity was observed with Gallium (1100mT) compared to the standard composition Pr15FebalCo8B7Nb0.05 (1000mT) magnet. Comparisons between the squareness factors obtained using the J×μ0H curve profile (SF), the estimated (sf) using microstructural parameters and Sf using a (BH)max and Br correlation have also been carried out.
Fine magnetic powder has been produced using the hydrogenation
disproportionation desorption and recombination (HDDR) process. The first goal of this work
involved an investigation of a range of disproportionation/desorption temperatures between
800 and 900°C with the purpose of optimizing the HDDR treatment for a Pr14Fe80B6 alloy.
The cast alloy was annealed at 1100°C for 20 hours for homogenization. The optimum
disproportionation temperature for achieving high anisotropy was 820°C. The influence of the
reaction temperature on the microstructure and magnetic properties of Pr14Fe80B6 HDDR
powders and magnets has been shown. A second stage of this study involved the
characterization, for each temperature, of the HDDR processed powder using X-ray
diffraction analysis. Samples of the HDDR material have been studied by synchrotron
radiation powder diffraction using the Rietveld method for cell refinement, phase
quantification and crystallite sizes determination. Scanning electron microscopy (SEM) has
also been employed to reveal the morphology of the HDDR powder.
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