Fabrication and microstructural analysis of didymium–iron–boron magnet alloys with cerium additions; pp. 166–171Full article in PDF format | doi: 10.3176/proc.2016.2.02
A common industrially accepted method for producing magnetic alloys with fine, α-iron-free microstructure is strip casting. Small amounts of alloys can be rapidly solidified with the method called splat quenching. In both cases the quenching rate can reach 106 K/s. This work reports the results of using a method for producing small amounts of NdFeB magnetic alloys with Ce additions. The aim of the study was to determine the influence of the cooling rate on the microstructure of the cast. Implementing centrifugal casting in vacuum resulted in NdFeB alloys with the following optimal parameters: sample thickness 0.3 mm, cooling rate 105 K/s, rare earth-rich phase content about 4%, thickness of dendrites 1.1 μm, arm spacing of dendrites 0.35 μm, and oxygen content not more than 650 ppm. Theoretically, it is possible to increase the alloy thickness up to 2 mm. Decreasing the cooling speed to the critical level 4 x 103 K/s completely prevented the formation of the undesired features in the microstructure of the cast.
1. Hilzinger, R. and Rodewald, W. Magnetic Materials: Fundamentals, Products, Properties, Applications. Publicis Verlag, 2013.
2. Coey, J. M. D. Rare-Earth Iron Permanent Magnets. Oxford University Press Inc., New York, 1996.
3. Kaneko, Y., Kuniyoshi, F., and Ishigaki, N. Proven technologies on high-performance Nd–Fe–B sintered magnets. J. Alloy. Comp., 2006, 408–412, 1344–1349.
4. Wang, X., Minggang, Z., Wei, L., Liyun, Z., Dongliang, Z., Xiao, D., and An, D. The microstructure and magnetic properties of melt-spun CeFeB ribbons with varying Ce content. Electron. Mater. Lett., 2015, 11(1), 109–112.
5. Scott, D. W., Ma, B. M., Liang, Y. L., and Bounds, C. O. Microstructural control of NdFeB cast ingots for achieving 50 MGOe sintered magnets. J. Appl. Phys., 1996, 79, 4830–4832.
6. Harada, T., Ando, T., O’Handley, R. C., and Grant, N. J. Microstructures and magnetic properties of anisotropic Nd–Fe–B magnets produced by splat-quenching. J. Appl. Phys., 1991, 70, 6468–6470.
7. Nagashio, K., Mingjun, L., and Kazuhiko, K. Containerless solidification and net shaping by splat quenching of undercooled Nd2Fe14B melts. Mater. T. JIM, 2003, 44(5), 853–860.
8. Yan, C., Guo, S., Chen, R., Lee, D., and Yan, A. Effect of Ce on the magnetic properties and microstructure of sintered didymium–Fe–B magnets. IEEE T. Magn., 2014, 50(10), article No. 2102605.
9. Vlachopoulos, J. and Strutt, D. Basic heat transfer and some applications in polymer processing. Plastics Technician’s Toolbox, 2002, 2, 21–33.
10. Yu, L. Q., Yan, M., Wu, J. M., Luo, W., Cui, X. G., and Ying, H. G. On the cooling rate of strip cast ingots for sintered NdFeB magnets. Physica B, 2007, 393, 1–5.
11. Yan, G. H., Chen, R. J., Ding, Y., Guo, S., Lee, D., and Yan, A. R. The preparation of sintered NdFeB magnet with high-coercivity and high temperature-stability. J. Phys. Conf. Ser., 2011, 266, 012052.
12. Vial, F., Joly, F., Nevalainen, E., Sagawa, M., Hiraga, K., and Park, K. T. Improvement of coercivity of sintered NdFeB permanent magnets by heat treatment. J. Magn. Magn. Mater., 2002, 242–245, 1329–1334.
13. Yan, C., Guo, S., Chen, R., Lee, D., and Yan, A. Enhanced magnetic properties of sintered Ce–Fe–B-based magnets by optimizing the microstructure of strip-casting alloys. IEEE T. Magn., 2014, 50(11), article No. 2104604.14. Gao, J., Volkmann, T., Roth, S., Löser, W., and Herlach, D. M. Phase formation in undercooled NdFeB alloy droplets. J. Magn. Magn. Mater., 2001, 234, 313–319.
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