R-T-B Permanent Magnet Grain Boundary Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current R-T-B based permanent magnets face challenges in achieving enhanced magnetic properties, particularly in downsizing, lighter weight, and higher efficiency, which are essential for various applications, while maintaining coercivity and residual magnetic flux density.
Innovation Solution
The development of an R-T-B based permanent magnet with main phase grains of R2T14B crystals and two-grain boundaries, where the average thickness of these boundaries is between 5 nm and 50 nm, and an area ratio of R6T13M compounds is 0.50% or less, along with the inclusion of elements like Ga, Al, Cu, and Si, and the use of a method involving sintering with a metal that forms a metal carbide with a lower standard Gibbs energy of formation than rare earth element carbides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the grain boundary thickness is reduced to improve magnetic properties, then coercivity increases, but the structural stability and corrosion resistance deteriorate
Solution Approach 1:
The patent applies local quality by creating a dual-structure grain boundary system: an inner core region (5-50 nm thick) with specific composition for high coercivity, and an outer shell region with different composition for structural stability and corrosion resistance. This localized differentiation allows each region to perform its specific function optimally without compromising the other.
Solution Approach 2:
The grain boundary is designed as a composite structure with two distinct phases: an inner core containing specific rare earth elements and compounds for magnetic performance, and an outer shell with different elemental composition for mechanical and chemical stability. This composite approach resolves the contradiction by combining materials with complementary properties in a spatially organized manner.
2Weight of moving object
If heavy rare earth element content is reduced to achieve lighter weight, then weight decreases, but magnetic properties deteriorate
Solution Approach 1:
The patent changes the compositional parameters by reducing overall heavy rare earth content while concentrating them specifically in the grain boundary core regions. This parameter optimization allows weight reduction in the bulk material while maintaining magnetic performance through localized heavy rare earth enrichment at critical interfaces.
Solution Approach 2:
Instead of uniformly distributing heavy rare earth elements throughout the material, the patent applies local quality by concentrating them specifically in the grain boundary core regions where they are most effective for enhancing coercivity. This localized placement reduces total heavy rare earth content (lighter weight) while maintaining magnetic properties where needed.
3Force
If subphase volume fraction is reduced to improve magnetic properties, then coercivity and residual magnetic flux density increase, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by incorporating carbon-containing substances and metal powders into the molded body before sintering. This pre-positioning of materials ensures that during the sintering process, carbides form preferentially at grain boundaries in the desired locations and compositions, achieving the complex dual-structure grain boundary configuration through a relatively simple one-step sintering process rather than requiring multiple post-processing steps.
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 results in improved magnetic properties, including increased coercivity and residual magnetic flux density, while reducing the volume fraction of subphases and maintaining production stability, even with reduced heavy rare earth element content.
Implementation Method 1
a standard Gibbs energy of formation for forming a metal carbide from the metal is lower than a standard Gibbs energy of formation for forming a rare earth element carbide from a rare earth element most included in the molded body as R
Implementation Method 2
sintering the molded body adhered with a metal
Data Source
AI summary
An R-T-B-based permanent magnet having improved magnetic properties contains R that represents at least one rare earth element essentially including Nd or Pr, T that represents at least one iron-group element essentially including Fe, B that represents boron, and M that represents at least one element selected from Ga, Al, Cu and Si. The R-T-B-based permanent magnet includes main-phase grains which include R2T14B crystals and two-grain grain boundaries each of which exists between adjacent two of the main-phase grains. The average thickness of the two-grain grain boundaries is 5 to 50 nm inclusive. The area ratio of an R6T13M compound in an arbitrary cross section is 0.50% or less (including 0%).