Elevated corrosion resistance and improved magnetic properties of sintered Nd-Fe-B magnets via the infiltration of DyCr film

• Published in: Journal of alloys and compounds 2023-04, Vol.940, p.168827, Article 168827
• Main Authors: Feng, Q., Huang, Y.L., Li, H.F., Yu, J.Y., Wang, C.Y., Wu, Z.J., Yao, Y.F., Hou, Y.H., Li, W., Ma, L., Yu, H.B.
• Format: Article
• Language: English
• Subjects: Corrosion resistance; DyCr film; Grain boundary diffusion; Magnetic properties; Sintered Nd-Fe-B magnet
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2023.168827

The low coercivity at high temperature and poor corrosion resistance limit the application field of Nd-Fe-B magnets. In this work, a DyCr film was prepared on the surface of Nd-Fe-B magnet through magnetron sputtering, and then subjected to grain boundary diffusion (GBD) to improve magnetic properties and enhance corrosion resistance. The results show that the residual Cr-rich film exists on the surface of NdFeB magnets, acting as a protective coating to enhance the corrosion resistance, which is evidenced by the weight loss experiment and scanning electron microscopy (SEM) image. Moreover, Cr element in the grain boundary phase increase the electrochemical potential from − 0.985 to − 0.733 V, which is also beneficial in improving corrosion resistance. Transmission electron microscope (TEM) analysis confirmed that the crystal structure of intergranular phase remained unchanged after diffusion, i.e. BCC-RE2O3 (RE=Rare Earth) phase. The coercivity was improved significantly, obtaining an increment of 19.4% comparing to that of initial magnet, which is attributed to the formed Dy-rich shell with high magnetocrystalline anisotropy field and the improved distribution of grain boundary phase. This suggests that it is feasible to fabricate high coercivity magnets and strong corrosion resistance only through grain boundary diffusion, which is expected to further shorten the processing flow of Nd-Fe-B magnets. [Display omitted] •Corrosion resistance and magnetic properties are improved concurrently.•A Cr-rich film can act as a protective coating to enhance corrosion resistance.•The GBD does not change the crystal structure of intergranular phase.•Elemental metallurgical behavior and intergranular phase evolution are studied.