Abstract
The sintered (Ce, Nd)-Fe-B magnets were produced widely by Double Main Phase (DMP) method in China as the magnetic properties of the DMP magnets are superior to those of single main phase (SMP) magnets with the same nominal composition. In this work, the microstructure and corrosion mechanism of the sintered (Ce0.2Nd0.8)30FebalB (wt.%) magnets prepared by DMP and SMP method were studied in detail. Compared to SMP magnets, the DMP magnets have more positive corrosion potential, lower corrosion current density, larger electron transfer resistance, and lower mass loss of the free corrosion experiment in 0.5mol/l Na2SO4 aqueous solution. All of the results show that the DMP magnets have better corrosion resistance than SMP magnets. The back scattered electron images show that the crystalline grains of the DMP magnets are sphericity with a smooth surface while the SMP ones have plenty of edges and corners. Besides, the distribution of Ce/Nd is much more uneven in both magnetic phase and rare earth (Re)-rich phase of the DMP magnets than those of SMP magnets. After corrosion, DMP magnets show eroded magnetic phase and intact Re-rich phase, which indicate that galvanic corrosion of the Re-rich phase acting as the cathode appears.
Highlights
A new type of (Ce, Nd)-Fe-B magnets has attract more attention due to its much cheaper price than traditional Nd-Fe-B magnets as well as much better magnetic properties than those of the AlNiCo and sintered ferrite magnets.[1,2,3,4,5,6] Since the reserve of Rare earth (Re) Ce is much larger than Nd and the price is just only 1/10 of Nd, the study of (Ce, Nd)-Fe-B is great practical significance
The shape of single main phase (SMP) crystalline grains are polygon with plenty of edges and corners, while the double main phase (DMP) crystalline grains are spherical with a smooth surface
This phenomenon is related to the Ce-rich phase with low melting point which contributes to increasing the densification of the magnets
Summary
Xiaoning Shi,[1] Minggang Zhu,1,a Dong Zhou,[1] Liwei Song,[1] Zhaohui Guo,[1] Jia Li,[2] and Wei Li1 1Central Iron and Steel Research Institute, Division of Functional Materials, Beijing 100081, China 2Institute of Physics, Chinese Academy of Science, Beijing 100190, China (Presented 9 November 2017; received 2 October 2017; accepted 19 November 2017; published online 9 January 2018)
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