Reducing NdFeB magnet cost with cerium and grain boundary diffusion

Cerium is a lower-cost rare earth that can replace part of the NdPr used in the alloy. The difficulty is retaining the required magnetic properties. Composition and microstructure both matter; the Ce addition cannot be selected from the raw-material price difference alone. Toyota's 2018 magnet development announcement is a useful example.

Its approach combined lanthanum and cerium substitution with grain refinement and a structure that concentrated neodymium near grain surfaces. Toyota also reported that simple substitution caused a decline in performance. That was a specific development programme, with application and production work still ahead at the time of the announcement.

For a buyer, the useful question is whether a proposed Ce-containing material meets the agreed minimum properties in the available geometry. Ask for its demagnetization curves at the relevant temperatures. A Ce addition figure alone gives too little information to approve a material change.

In Dy- or Tb-based grain boundary diffusion, a diffusion source is applied to the magnet surface and heat-treated. The heavy rare earth travels inward along grain boundaries and forms enriched regions near the surfaces of the magnetic grains. This can raise coercivity while limiting the remanence penalty associated with distributing more heavy rare earth through the grains. Shin-Etsu's technical explanation describes this mechanism.

This route is worth evaluating when the required coercivity makes conventional heavy rare earth additions expensive. Its economics include the diffusion material and the extra processing. The final comparison must account for both. Thickness also matters because the treatment enters from the surface.

Research on property variation through a diffused magnet shows why a result on one section cannot be assumed for another. Ask the supplier to confirm the process for the proposed dimensions.

Mainrich's factory-verified GBD case took N45H to N45UH using a 0.35% Tb surface coating. Intrinsic coercivity, Hcj, increased from 17.67 to 26.55 kOe, approximately a 50% Hcj increase, with no loss of remanence, Br. The factory-verified case used 75% less Dy than the conventional route.

These results support a discussion about reducing the heavy rare earth requirement. They do not establish the finished price of a different part. Terbium input, diffusion processing, machining and inspection still have to be included in the quotation. The figures also belong to that specific case. They do not establish the same result for every shape or for a Ce-containing alloy. For a new drawing, agree the required magnetic properties and compare samples from the proposed production route.

Ce substitution and diffusion can be combined, but the diffusion response changes with the base material. Yu and colleagues examined this directly in a 2024 study of Ce-containing magnets treated with Tb-Cu diffusion. The coercivity response varied with Ce content.

At higher Ce contents, phases formed at grain boundaries that obstructed Tb diffusion and consumed Tb. That makes the combined route a material-development question. A diffusion result measured on a conventional alloy cannot simply be carried over to a Ce-containing one. If both routes are being considered, ask for evidence on the actual combination: the proposed base alloy, diffusion source, finished thickness and heat treatment.

Keep the existing material as the reference during testing. Compare Br and Hcj, then measure irreversible flux loss after the agreed thermal exposure. For a motor, the final decision also needs the assembly's performance under its operating conditions.

Engineering and procurement need a common comparison. Request a baseline quotation and suitable alternative routes against the same drawing, quantity and acceptance criteria. Where an alternative needs a geometry change, quote that separately and include the effect on the assembly. Include sample qualification, machining yield, coating, inspection and any additional process lead time.

A saving on alloy input can shrink once those items are counted. Conversely, an alternative that needs modest qualification work may be worth investigating early in a programme with substantial annual volume. To start a cost-reduction review, send Mainrich the drawing and operating requirements. Include the following so the team can assess which route is worth sampling: