GBD Magnets Explained: How Grain Boundary Diffusion Cuts Costs Without Cutting Performance

High-performance motors - especially in robotics, EVs, and aerospace - need magnets that maintain their strength at elevated temperatures. Traditionally, this means adding Heavy Rare Earth Elements (HREEs) like Dysprosium (Dy) and Terbium (Tb) throughout the entire magnet. These elements increase coercivity (resistance to demagnetization at temperature) but they're expensive and supply-constrained. Dysprosium prices have fluctuated between $200–$500/kg over the past five years. For a magnet that's 2–8% Dysprosium by weight (depending on grade), this adds significant cost per unit.

Grain Boundary Diffusion takes a fundamentally different approach. Instead of mixing HREEs throughout the entire magnet (which is wasteful - only the grain boundaries need protection), GBD applies a thin layer of Dy or Tb compound to the magnet surface and then diffuses it inward through heat treatment. The heavy rare earths migrate along the grain boundaries - exactly where demagnetization initiates - while leaving the grain interiors unaffected. This achieves the same high coercivity with 50–70% less HREE usage.

• •Standard approach: 2–8% Dy/Tb (depending on grade) distributed uniformly throughout the magnet
• •GBD approach: Thin surface application, diffused to grain boundaries only
• •HREE reduction: 50–70% less Dysprosium/Terbium needed
• •Result: Same Hcj (coercivity) at lower cost - or higher Hcj at the same cost

GBD doesn't just reduce cost - it can actually improve magnetic performance. When HREEs are distributed uniformly, they dilute the main magnetic phase (Nd2Fe14B), slightly reducing remanence (Br). With GBD, the grain interiors remain pure Nd2Fe14B, preserving maximum Br while the grain boundaries get the coercivity boost. This means GBD magnets can achieve higher energy product (BH Max) at the same temperature rating compared to conventionally produced magnets.

GBD technology is most impactful for applications that need high-temperature grades (H, SH, UH, EH). If your application uses standard N-grade magnets (80°C max), GBD isn't relevant. But if your motors run hot - which most robotics and EV motors do - GBD is a game-changer.

• •Humanoid robot joints: Motors run under sustained load, internal temps reach 100–130°C
• •EV traction motors: Continuous duty at 150°C+ requires SH or UH grades
• •Servo motors: High-speed cycling creates thermal spikes that demand temperature margin
• •Drone motors: Weight-sensitive applications where every gram of HREE matters
• •Industrial motors: Long duty cycles with elevated ambient temperatures

When requesting quotes, specify the performance you need (grade, Hcj minimum, Br minimum, max operating temperature) and ask whether GBD processing is available. A good supplier will recommend GBD when it offers a cost advantage and will provide comparative pricing for both GBD and conventional processing.

• •Specify: Grade (e.g., N48SH), minimum Hcj (e.g., ≥20 kOe), minimum Br (e.g., ≥13.8 kGs)
• •Ask: 'Is GBD processing available for this grade and geometry?'
• •Compare: Request pricing for both GBD and conventional options
• •Verify: Ask for BH curve data from GBD production batches - not just spec sheets

Mainrich operates in-house GBD processing for the full range of high-temperature NdFeB grades. Our GBD line supports magnets from small coreless motor rings to large radial multi-pole robotics magnets. We provide GBD-processed magnets with full documentation including BH curves at temperature, Hcj verification, and comparative data against conventional processing.