Investigating the Possibility of Fabricating Pr2Fe14B/α-Fe Composite Materials by Oxidation of the Pr–Fe–B Alloy in a Fluidized-Bed Jet Mill

Abstract

The results of studying the possibility of fabricating the Pr2Fe14B/α-Fe composite materials by oxidation of the Pr–Fe–B alloy in a fluidized-bed jet mill are presented. It is shown that the use of the standard powder metallurgy technology supplemented by oxidation of the Pr–Fe–B alloy in a fluidized-bed jet mill for rare-earth magnetically hard materials (MHMs) makes it possible to fabricate Pr2Fe14B/α-Fe composites with high magnetic characteristics. It is established that, when fabricating finely dispersed powders according to the proposed technology in the argon medium containing 0.2 vol % oxygen, residual magnetic induction (Br) occurs with an insignificant drop in the coercive force (jHc). This effect causes a 5% increase in the maximal energy product (BH)max. The almost complete oxidation of the highly praseodymium phase PrxFe occurs with a further increase in the oxygen concentration, which leads to an abrupt drop in the coercive force and, consequently, a decrease in (BH)max. The particles of the α-Fe phase formed due to the oxidation of the magnetic material are formed at the boundaries between the grains of the Pr2Fe14B phase. Herewith, the highest magnetic characteristics are implemented if the α-Fe particles are separated from the grains of the main magnetic phase by thin interlayers of nonmagnetic phases, which makes it possible to hold a high level of jHc for sintered MHM samples. Herewith, the optimal thickness of the α-Fe layers is 0.2–0.3 μm. The α-Fe layers formed with an oxygen content of 0.3 vol % turned out considerably thicker (from 0.8 to 1.1 μm), which leads to an almost 10% decrease in the coercive force of the samples and 3–7% decrease in other magnetic parameters (Br, (BH)max). Thus, when controlling the oxygen content in the working medium of the jet mill, we can vary the thickness of the interlayer of the forming α-Fe phase in the Pr2Fe14B/α-Fe composite material and control its magnetic parameters.