Since its discovery by Sagawa in 1984, the Nd-Fe-B magnet has been one of the most sought- permanent magnetic material. The coercivity of Nd-Fe-B magnet deteriorates at high temperatures and therefore, enhancing the coercivity is a key research topic in the area of Nd-Fe-B. Dy and Tb are added to Nd-Fe-B to enhance the coercivity but unfavoured due to the scarcity, and high cost of Dy and Tb. Nb doping in melt-spun Nd-Fe-B can increase the coercivity to 1.4 T at RT, but is still low for high temperature applications [1]. Grain boundary diffusion process (GBDP) with low-melting eutectics is the effective approach for enhancing the coercivity of Nd-Fe-B by magnetically isolating the Nd2Fe14B grains [2]. However, the diffusion treatment can lead to grain growth, partially negating the benefits of GBDP. As Nb doping in Nd-Fe-B has been observed to restrict grain growth, GBDP in Nd-Fe-Nb-B can be advantageous for coercivity enhancement. The present work on the one hand focuses on understanding the role of Nb in grain boundary engineering while on the other intends to design suitable low-melting grain boundary eutectics for coercivity enhancement in these magnets.
References:
[1] Z. Chen, Y.Q. Wu, M.J. Kramer, B.R. Smith, B.M. Ma, M.Q. Huang, A study on the role of Nb in melt-spun nanocrystalline Nd-Fe-B magnets, J. Magn. Magn. Mater. 268 (2004) 105–113. https://doi.org/10.1016/S0304-8853(03)00481-5.
[2] S. Sawatzki, C. Kubel, S. Ener, O. Gutfleisch, Grain boundary diffusion in nanocrystalline Nd-Fe-B permanent magnets with low-melting eutectics, Acta Mater. 115 (2016) 354–363. https://doi.org/10.1016/j.actamat.2016.05.048.