Sintered Permanent Magnet with Internal HRE Diffusion Reservoirs

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Solution Overview

Problem

Sintered R-T-B magnets, such as Nd—Fe—B, face limitations in size and geometry due to coercivity loss at high temperatures and excessive rare earth element (REE) consumption when trying to maintain high magnetic performance and remanence, with existing grain boundary diffusion processes only allowing for small magnet sizes.

Innovation Solution

Creating a heavy rare earth element (HRE) reservoir zone within the bulk of the magnet by embedding HRE-containing magnetic powder during the pre-sintering process, allowing for inter-grain diffusion during annealing, which increases coercivity without excessive REE consumption and enables larger magnet sizes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If HRE is added to increase coercivity, then coercivity increases, but remanence decreases

Engineering Contradiction:

ImprovecoercivityVSAvoidremanence

Core Design Contradiction:

StrengthVSQuantity of substance

Solution Approach 1:

The patent applies local quality by concentrating HRE elements specifically at the grain boundaries through diffusion, rather than uniformly distributing them throughout the magnet. This localized enrichment at interfaces provides the necessary coercivity enhancement while preserving the bulk R-T-B phase composition that maintains high remanence.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The grain boundary phase acts as an intermediary medium that facilitates HRE diffusion and distribution. The HRE elements diffuse through this intermediate phase to reach the grain boundaries, mediating between the HRE source and the R-T-B grains to achieve coercivity enhancement without direct contamination of the main magnetic phase.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Quantity of substance

If GBD process is used to reduce HRE consumption, then HRE usage decreases, but magnet size is limited to small dimensions

Engineering Contradiction:

ImproveHRE consumptionVSAvoidmagnet thickness

Core Design Contradiction:

Quantity of substanceVSLength of stationary object

Solution Approach 1:

The patent transitions from surface-based HRE application to volumetric HRE distribution by embedding diffusion sources throughout the magnet bulk. This dimensional change from 2D surface diffusion to 3D volumetric diffusion enables HRE to reach grain boundaries throughout the entire magnet volume, overcoming the thickness limitation of conventional surface GBD processes.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The patent performs preliminary action by pre-embedding HRE-containing powder or diffusion sources within the magnet body before the diffusion process. This advance placement of HRE reservoirs throughout the bulk ensures that HRE is already positioned to diffuse to grain boundaries during subsequent heat treatment, eliminating the need for post-sintering surface application and enabling larger magnet dimensions.

Inventive Principle:

Principle #10Preliminary action

3Strength

If HRE diffusion sources are arranged outside the magnet, then HRE can diffuse to grain boundaries, but the process only works for small magnet sizes

Engineering Contradiction:

ImprovecoercivityVSAvoidmagnet volume

Core Design Contradiction:

StrengthVSVolume of stationary object

Solution Approach 1:

The patent applies the nested doll principle by placing HRE-containing diffusion sources inside the magnet body, nesting them within the R-T-B matrix. This internal embedding of HRE reservoirs throughout the magnet volume allows HRE to diffuse outward to grain boundaries from multiple internal sources, enabling effective coercivity enhancement in large-volume magnets that cannot be treated by external surface diffusion alone.

Inventive Principle:

Principle #7Nested doll (Nesting)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach maintains high magnetic performance with increased coercivity and acceptable remanence while minimizing HRE usage, allowing for the production of magnets with larger thicknesses and varied geometries, overcoming the size limitations of traditional grain boundary diffusion processes.

Implementation Method 1

perform an annealing step with inter-grain diffusion of the HRE from the HRE reservoir zone to the grain boundary phase

Methodology Applied

Scientific EffectInter-grain diffusion: Diffusion

Implementation Method 2

sintering and annealing the body

Methodology Applied

Scientific EffectSintering: Sintering

Data Source

PatentUS11830645B2Permanent magnet with inter-grain heavy-rare-earth element, and method of producing same

Publication Date: 2023.11.28 ABB (SCHWEIZ) AG

AI summary

A manufacturing method of a sintered magnet is described. The method includes forming a pre-sintering body from a first magnetic powder and a second magnetic powder (containing a heavy rare earth element, HRE) so that at least part of the second magnetic powder is provided at at least one inner portion of the pre-sintering body and surrounded format least two opposite sides by the first magnetic powder; sintering the pre-sintering body; and annealing the sintered pre-sintering body at an annealing temperature lower than the sintering temperature, thereby causing inter-grain diffusion of HRE from the HRE reservoir zone to the grain boundary phase. After the annealing, the grain boundary phase contains the HRE in a higher concentration than the main phase.