Effect of DyF₃ on the corrosion behavior of hot‐pressed Nd–Fe–B permanent magnets

Abstract

The grain boundary diffusion process (GBDP) with DyF3 is a promising method to obtain excellent magnetic properties in Nd–Fe–B permanent magnets. Compared to conventionally prepared (Dy,Nd)–Fe–B magnets the overall content of the precious heavy rare earth Dy is reduced. Thus, the GBDP with DyF3 is highly attractive to cut down costs and save resources. However, it is not well known how the addition of DyF3 affects the corrosion resistance of Nd–Fe–B permanent magnets. In this work, the anodic polarization behavior of hot‐pressed Nd–Fe–B magnets with and without DyF3 additions was investigated in electrolytes of different pH values. The results were compared with measurements on a commercially sintered Nd–Fe–B permanent magnet. In the polarization studies the only observed significant impact of DyF3 additions is an increased passive current density in alkaline media. The pitting susceptibility in NaOH solutions containing chloride ions is not affected by DyF3. Also in contrast to expectations, first free corrosion studies indicated no significant impact of the DyF3 additions on the dissolution rate.

Microwave-Assisted Hydrothermal Synthesis and Annealing of DyF3Nanoparticles

“…The other trifluoride compound of great interest is DyF 3 . Recent research showed that DyF 3 powders could significantly improve the properties of Nd-Fe-B magnets [22][23][24][25]. In addition, DyF 3 is an important component of oxyfluoride glasses [26].…”

Coercivity Increase of the Recycled HDDR Nd-Fe-B Powders Doped with DyF3 and Processed via Spark Plasma Sintering & the Effect of Thermal Treatments

“…Several researchers have utilized rare earth fluorides (RE-F 3 ) as dopant or surface diffusion agents, to increase the coercivity in sintered magnets; with the coercivities reaching up to 2790 kA/m (35 kOe) [21,22,23,24,25,26,27,28,29,30,31,32] and in rapidly consolidated melt-spun ribbons, where coercivities reached up to 1990 kA/m [33,34]. On the contrary, no such research has been made on the HDDR Nd-Fe-B powders, which is a relatively cheap hydrogen reprocessing alternative for the EOL magnetic products [6].…”

Nd-Fe-B Magnets: The Gradient Change of Microstructures and the Diffusion Principle after Grain Boundary Diffusion Process

“…Chen et al [10] showed that the diffusion of the low-melting alloy, DyF 3 , along the parallel c-axis was better than that in the vertical direction, which was conducive to improving magnetic properties and reducing HRE consumption. Sueptitz et al [11] found that the diffusion of DyF 3 was conducive to the passivation of magnets under acidic conditions, showing better corrosion resistance. Komuro et al [12] obtained an improvement in coercivity and lowered the loss of remanence through the Dy-F diffusion coating.…”