Structure and properties of suction-cast Pr-(Fe, Co)-(Zr, Nb)-B rod magnets

Abstract

GFA of the alloy [5‒7]. Furthermore, doping with Zr and Nb causes the microstructure refinement of the RE-Fe-B magnets and, thus, can enhance the magnetic properties of the annealed specimens [8‒10]. As was reported in [7], the appropriate setting of the composition for the Fe67Co9.4Nd3.1Dy0.5B20 alloy led to an improvement of the GFA that allowed processing of the fully glassy rods with diameters up to 0.5 mm. A further change of composition and addition of Zr facilitated casting 1-mm diameter amorphous rods and up to 3-mm outer diameter tubes for the Fe61Co13.5Zr1Pr3.5Dy1B20 alloy [11]. However, a small amount of RE elements in the chemical composition caused the formation of a relatively low fraction of the RE2Fe14B phase. For this reason, such magnets reveal rather moderate magnetic parameters [12]. We have shown in our previous studies on rapidly solidified plates of various thicknesses produced for Pr9Fe50 + xCo13Zr1Nb4B23 – x (x = 0, 2, 5, 8) alloys that boron content greatly influences the GFA. In the case of the Pr9Fe50Co13Zr1Nb4B23 alloy, the 0.5-mm thick plates were fully amorphous while 1-mm plates were slightly crystalline and only one very low-intensity diffraction peak was detected [6, 13]. However, for alloys of lower B content, the suction cast plates were all crystalline in as-cast state. Furthermore, the critical cooling rate attainable for specific production equipment depends on the sample geometry [14]. The changes in the microstructure and magnetic properties with the sample shape were shown for the Pr9Fe52Co13Zr1Nb4B21 alloy [15]. The aim of the present work was to study the influence of the Fe to B ratio on the GFA as well as on the phase constitution, microstructure, and magnetic properties of the 1-mm diameter rods of Pr9Fe50 + xCo13Zr1Nb4B23 – x (x = 0, 5, 8) alloys in the as-cast state and those subjected to annealing. Preliminary analysis of magnetic parameters has shown that optimal magnetic