Vapor Control Member for Uniform Heavy Rare-Earth Diffusion in Sintered Magnets
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Solution Overview
Problem
Existing methods for increasing the coercivity of sintered R—Fe—B based rare-earth magnets face challenges such as limited effectiveness in thick magnets, uneven distribution of heavy rare-earth elements, resource inefficiency, and equipment costs, particularly in techniques involving surface deposition and heat treatment.
Innovation Solution
A method involving a vapor control member with specific structural features to diffuse a small amount of heavy rare-earth elements uniformly throughout the magnet body, using a bulk body of Dy, Ho, or Tb, and heating to 700° C. to 1000° C. to ensure efficient penetration without surface deposition, thereby enhancing coercivity and maintaining remanence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a molten alloy including heavy rare-earth element RH is used to replace light rare-earth element RL in R2Fe14B phase, then coercivity is improved, but remanence Br decreases
Solution Approach 1:
The patent applies local quality by concentrating heavy rare-earth element RH specifically at the grain boundary region rather than uniformly distributing it throughout the entire magnet. This localized approach allows the grain boundary phase to have different compositional characteristics (enriched with RH) compared to the main phase, thereby improving coercivity through enhanced magnetocrystalline anisotropy at grain boundaries while preserving the light rare-earth element composition in the main phase to maintain high remanence.
Solution Approach 2:
The patent utilizes the grain boundary phase as a porous or interstitial region between crystal grains, where heavy rare-earth element RH is preferentially distributed. This approach leverages the grain boundary region as a separate functional zone that can be independently composited, allowing RH to exert its coercivity-enhancing effect without displacing RL from the main R2Fe14B phase where it contributes to remanence.
2Force
If alloy or compound powder including heavy rare-earth element RH is added to main phase material and compacted, then heavy rare-earth element RH distributes in grain boundary vicinity improving magnetocrystalline anisotropy, but it is difficult to obtain expected crystal structure
Solution Approach 1:
The patent employs parameter changes by carefully controlling the concentration of heavy rare-earth element RH in the grain boundary phase and optimizing sintering temperature and time parameters. By adjusting these parameters, the patent achieves sufficient RH distribution at grain boundaries to improve magnetocrystalline anisotropy while maintaining the stability and integrity of the R2Fe14B main phase crystal structure, avoiding structural degradation that would occur with excessive RH content or improper processing conditions.
3Force
If heavy rare-earth element RH is deposited on surface and thermally treated, then coercivity is recovered or increased, but equipment cost increases
Solution Approach 1:
The patent applies self-service by enabling the heavy rare-earth element RH to diffuse into the magnet body through its own vapor pressure during a single thermal treatment process, without requiring complex external deposition equipment. The thermal treatment simultaneously achieves both the deposition of RH from bulk material and its diffusion into the grain boundary regions, eliminating the need for separate vacuum deposition systems and reducing overall equipment complexity and cost.
4Force
If heavy rare-earth element RH is used to increase coercivity, then coercivity improves, but resource efficiency decreases
Solution Approach 1:
The patent maximizes resource efficiency by applying local quality - concentrating heavy rare-earth element RH exclusively in the grain boundary phase rather than distributing it uniformly throughout the entire magnet. This localized enrichment allows coercivity improvement with minimal total RH content, as the heavy rare-earth elements exert their maximum effect at the critical grain boundary regions where domain wall pinning occurs, thereby reducing overall consumption of scarce heavy rare-earth resources.
Solution Approach 2:
The patent utilizes the grain boundary phase as a porous or interstitial region to host heavy rare-earth element RH, separating the functional requirements of coercivity enhancement (at grain boundaries) from remanence maintenance (in main phase). This approach allows efficient use of RH by placing it only where needed for coercivity improvement, minimizing waste of this scarce resource while achieving the desired magnetic performance.
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 allows for uniform diffusion of heavy rare-earth elements, increasing coercivity while minimizing remanence loss and reducing manufacturing costs through efficient resource use and equipment durability.
Implementation Method 1
heating the inside of the processing chamber to a temperature of 700° C. to 1000° C., thereby diffusing the heavy rare-earth element RH inside the sintered R—Fe—B based rare-earth magnet body while supplying the heavy rare-earth element RH from the bulk body to the surface of the sintered R—Fe—B based rare-earth magnet body via the vapor control member
Data Source
AI summary
A sintered R—Fe—B based rare-earth magnet body 1 including, as a main phase, crystal grains of an R2Fe14B type compound that includes a light rare-earth element RL, which is Nd and/or Pr, as a major rare-earth element R is provided. A bulk body 2 including a heavy rare-earth element RH, which is at least one of Dy, Ho and Tb is also provided. The sintered magnet body 1 and the bulk body 2 are arranged in a processing chamber 4 with a vapor control member 3 interposed between the sintered magnet body 1 and the bulk body 2. And the inside of the processing chamber 4 is heated to a temperature of 700° C. to 1000° C., thereby diffusing the heavy rare-earth element RH inside the sintered magnet body 1 while supplying the heavy rare-earth element RH from the bulk body 2 to the surface of the sintered magnet body 1 via the vapor control member 3.