Grain boundary diffusion / high-coercivity NdFeB

Put heavy rare earthwhere coercivity is decided.

GBD diffuses dysprosium or terbium along grain boundaries instead of mixing it through the magnet body. The route is reviewed for high-temperature motor programs that need more coercivity with controlled heavy rare-earth input.

Discuss a GBD grade View capability matrix

N45H to N45UHVerified GBD case

H / SH / UH / EHCoercivity review

Blocks / arcs / ringsDeveloped geometries

In-houseMOFCOM handling

Finished sintered neodymium magnets in several cylindrical sizes and coatings — **Sintered NdFeB / product reference**Finished magnets shown as product evidence, with GBD route confirmed against each drawing and grade target.

Material route and documentation confirmed against the drawing · Engineering response within 1 business day

01 / THE BUYER DECISION

Coercivity at the boundary, not through the bulk.

Conventional alloying distributes Dy or Tb through the blank. GBD concentrates it along the grain boundary network, where resistance to demagnetization is established.

GBD decision ledgerConventional route / GBD route

Decision point	Conventional alloying	GBD route
Where Dy or Tb goes	Mixed through the entire magnet blank.	Diffused along the grain boundaries.
Material use	Heavy rare earth is added through the bulk to reach the coercivity target.	The reported N45H comparison used a 0.35% Tb surface coating. Material-composition and magnetic-test records need separate review; this measurement is not a total heavy-rare-earth or cost saving.
Magnetic strength	Bulk heavy rare earth can dilute the main magnetic phase and reduce Br.	The reported specimen comparison raised Hcj from 17.67 to 26.55 kOe; Br changed from 13.62 to 13.61 kGs.
Supply exposure	More Dy or Tb mass per part increases price and supply exposure.	Compare the actual composition and diffusion inputs; the reported N45H magnetic result does not establish total heavy-rare-earth savings.

GBD is a grade and geometry decision, not a blanket upgrade.

Mainrich reviews the thermal envelope, demagnetization margin, coating, magnet dimensions, volume, and export destination before recommending the route.

02 / VERIFIED PERFORMANCE

One measured case, four procurement facts.

The specimen measurements below are from the supplier workbook. Measurement uncertainty is not stated. They do not establish a motor-performance improvement, total heavy-rare-earth reduction or finished-part cost saving.

Reported specimen comparison / 0.35% Tb surface coating

Reported N45H to N45UH specimen comparison.

Hcj +50%Verified coercivity increase

17.67 to 26.55 kOeMeasured Hcj result

13.62 to 13.61 kGsMeasured Br before and after

45.42 to 45.40 MGOeMeasured BHmax before and after

Thermal marginGBD is evaluated when H, SH, UH, or EH coercivity is needed and bulk heavy rare-earth loading can be reduced.

Motor geometriesConfirm the intended geometry and treated surfaces. The diffusion path is measured from treated surfaces, rather than from the longest face dimension.

Buyer documentationQuotes separate grade, diffusion route, coating, export licensing, and QC evidence.

03 / PROCESS WALK

Surface preparation to verified batch.

The process changes the grain boundary while leaving the Nd2Fe14B grain interior largely untouched. Each release still depends on geometry, heat treatment, finish, and magnetic verification.

Set the base magnet

Confirm grade, geometry, tolerance, coating, and operating temperature before diffusion.

Prepare the surface

Clean and prepare the magnet so the Dy or Tb compound can be applied consistently.

Apply the surface layer

Use a controlled surface layer instead of alloying heavy rare earth through the full magnet body.

Diffuse under heat

Vacuum heat treatment moves Dy or Tb inward along the grain boundary network.

Finish and verify

Complete coating, BH curve confirmation, dimensional checks, and batch records.

04 / PRODUCTION FIT

Use it where heat and demagnetization margin justify it.

GBD is most relevant to compact motors and qualification-heavy programs already calling for H, SH, UH, or EH coercivity. Final grade selection follows the motor's actual thermal and magnetic load.

Application review ledgerStarting points

Application	Starting grade	Review driver
Humanoid joints	Grade confirmed per drawing	Review magnet temperature and demagnetization margin
EV traction	N42SH / N45UH	High duty cycle and demagnetization margin
Servo motors	N42H / N45SH	Stable torque under repeated acceleration
Wind generators	N42SH / N45SH	Long service life and supply resilience

Material review

Confirm the starting material and required magnetic properties.

Geometry review

Review treated surfaces, diffusion distance and finishing allowance.

Sample validation

Agree the applicable curves and inspection criteria.

Production review

Confirm documentation, material composition and shipment requirements.

RFQ NOTES

Before the grade review.

A drawing and real operating temperature make the comparison more useful than a grade name alone.

Does every high-temperature magnet need GBD?

No. GBD is reviewed when a design needs high-coercivity material and the grade, geometry, volume, and heavy rare-earth exposure justify the route.

Does GBD remove MOFCOM licensing requirements?

GBD is a manufacturing process, not an export classification. The actual composition, finished item and transaction must be reviewed against the applicable controls.

What should be sent for a GBD review?

Send the drawing, target grade, operating temperature, coating requirement, destination, prototype quantity, and annual volume.

Put the thermal envelope on the table

Compare the GBD and conventional routes.

Send the drawing, grade target, operating temperature, coating, quantity, and destination. An engineer responds within 1 business day. Pricing follows within 2 business days.

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Permanent Magnets

Motors & Assemblies