Sintered permanent magnets prepared from hydrogenated (Nd-Fe-b strip-cast alloy + pr3(Co,cu) compound) mixture

Abstract

The application of powder blending procedure shows promise in manufacturing Nd-Fe-B magnets; in this case, hydrides, oxides, intermetallic compounds, etc. are used as one of the mixture components. The application of these additions allows one to increase the hysteretic characteristics of Nd-Fe-B magnets at the expense of realized grain-boundary diffusion and grain-boundary structuring processes since these characteristics of the magnets are highly sensitive to their microstructure, composition of phases, and distribution of alloy components as well. This study is focused on the possibility of using the Pr3Co0.6Cu0.4Hx composition as the addition to the powder mixture for manufacturing Nd-Fe-B magnets and on the processes occurred during hydrogen treatment of the addition. The base alloy having the composition Nd-24.0, Pr-6.5, Dy-0.5, B-1.0, Al0.2, Fe-balance was prepared by strip-casting and subjected to hydrogen decrepitation at 270 °C for 1 h. The Pr3Co0.6Cu0.4 alloy was prepared by arc melting in an argon atmosphere and subjected to homogenizing annealing at 600 °C for 90 h and subsequent hydrogenation under the conditions used for the strip-cast alloy. The phase composition of Pr3Co0.6Cu0.4Hx was studied by X-ray diffraction analysis, DTA, scanning electron microscopy, and electron microprobe analysis. The Pr3Co0.6Cu0.4Hx composition was shown to undergo the hydrogenolysis with the formation of PrHx hydride (or hydrogen solid solution in Pr), Co+Cu fine mixture, and PrCu compound. The behavior of the additions in manufacturing sintered permanent magnets is analyzed from the viewpoint of the grain-boundary structuring effect of the addition. The sintered magnet prepared from the hydrogenated mixture Nd-Fe-B strip-cast alloy + Pr3(Co,Cu) compound exhibits the following hysteretic parameters: Br = 1.35 T, jHc = 1008 kA/m, and (BH)max = 349 kJ/m3.