Sintered Magnet Grain Boundary Optimization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for preparing R—Fe—B sintered magnets face challenges in achieving high coercive force and remanence while minimizing the use of expensive heavy rare earth elements, leading to increased production costs and inefficient diffusion of these elements within the magnet structure.
Innovation Solution
A sintered body with a composition of Nd2Fe14B crystal phase and a rare earth rich grain boundary phase, optimized with specific atomic percentages of elements like Nd, Ga, Cu, and Co, and a controlled grain size and thickness, is developed to enhance the diffusion efficiency of heavy rare earth elements such as Dy and Tb, reducing the amount needed and improving magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a large amount of heavy rare earth element RH is used in R2Fe14B to improve coercive force, then coercive force Hcj increases, but residual magnetic flux density Br decreases and production cost increases
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where heavy rare earth elements are concentrated at the grain boundaries (shell) rather than uniformly distributed throughout the magnet. This localized concentration at interfaces provides enhanced coercive force where it is most needed for domain wall pinning, while preserving the bulk magnetic properties and minimizing overall heavy rare earth content.
Solution Approach 2:
The patent employs composite materials by combining light rare earth elements (Nd, Pr) in the bulk R2Fe14B phase with heavy rare earth elements (Dy, Tb) at the grain boundaries. This composite approach leverages the high saturation magnetization of light rare earth compounds while utilizing the high magnetocrystalline anisotropy of heavy rare earth compounds at critical interfaces, achieving optimized magnetic performance.
2Force
If a large amount of heavy rare earth element RH is used to improve coercive force, then coercive force Hcj increases, but production cost increases
Solution Approach 1:
By concentrating heavy rare earth elements specifically at grain boundaries rather than uniform distribution, the patent achieves high coercive force with minimal heavy rare earth content. This localized approach dramatically reduces material cost while maintaining performance, as heavy rare earth elements constitute only a small fraction of the total magnet volume.
Solution Approach 2:
The patent applies partial action by introducing heavy rare earth elements only where most needed (at grain boundaries) rather than throughout the entire magnet. This partial infiltration approach provides sufficient coercive force enhancement without the excessive cost associated with bulk substitution of heavy rare earth elements.
3Force
If heavy rare earth element RH is diffused from surface to form core-shell structure, then coercive force Hcj increases and remanence Br is suppressed from decreasing, but diffusion efficiency is insufficient with current methods
Solution Approach 1:
The patent applies parameter changes by optimizing the composition of the rare earth rich grain boundary phase with specific atomic percentages (40-70 at% R, 10-30 at% Ga, 5-20 at% Cu, 5-20 at% Co). These compositional parameters create favorable thermodynamic and kinetic conditions for efficient heavy rare earth diffusion during heat treatment, enabling complete infiltration at reduced temperatures and times.
Solution Approach 2:
The rare earth rich grain boundary phase acts as an intermediary medium that facilitates the diffusion of heavy rare earth elements from the surface into the magnet. This intermediate phase with specific composition creates a diffusion pathway that enhances the infiltration efficiency and enables uniform distribution of heavy rare earth elements throughout the grain boundaries.
4Reliability
If traditional preparation method is used, then magnetic energy product BH and coercive force Hcj are high, but heavy rare earth element content must be large leading to high cost
Solution Approach 1:
The patent resolves this contradiction by maintaining high magnetic energy product through the core-shell structure where heavy rare earth elements are localized at grain boundaries. This local enhancement of coercive force preserves overall magnetic performance while minimizing heavy rare earth content and associated costs compared to traditional bulk substitution methods.
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
The approach results in a sintered permanent magnet with enhanced coercive force and remanence while significantly reducing the amount of heavy rare earth elements required, thereby lowering production costs and improving diffusion efficiency.
Implementation Method 1
The heavy rare earth element RH is diffused into the R—Fe—B sintered body from its surface
Implementation Method 2
subjecting the green body to a first vacuum heat treatment, a second vacuum heat treatment, and a third vacuum heat treatment
Data Source
AI summary
Disclosed is a sintered body composition used in improved diffusion efficiency of heavy rare earth elements RH, and related sintered permanent magnet and preparation methods. The sintered body includes Nd2Fe14B crystal phase as a primary phase, and a rare earth rich phase as a grain boundary phase. The sintered body includes a composition expressed by RaBbGacCudAleMfCogFebalance; wherein R is one or more selected from rare earth elements, and R includes Nd; M is one or more selected from the group consisting of Zr, Ti, and Nb; and wherein “a” satisfies 13%≤a≤15.3%; “b” satisfies 5.4%≤b≤5.8%; “c” satisfies 0.05%≤c≤0.25%; “d” satisfies 0.08%≤d≤0.3%; “e” satisfies 0≤e≤1.2%; “f” satisfies 0.08%≤f≤0.2%; and “g” satisfies 0.8%≤g≤2.5%. Grains in Nd2Fe14B crystal phase have average size L of 4-8 μm, and the relationship between L and t for grain boundary phases average thickness is: σ=t/L, wherein σ is defined as 0.009≤σ≤0.012.