NdFeB Magnet Grain Boundary Phase Design
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Solution Overview
Problem
R-T-B based sintered magnets face a challenge in maintaining high coercivity (HcJ) at elevated temperatures without using heavy rare-earth elements like Dy, which also results in a decrease in residual magnetic flux density (Br) due to reduced B concentration.
Innovation Solution
The development of an R-T-B based sintered magnet with a specific composition and grain boundary phase structure, including a first grain boundary phase with a thickness of 5 nm to 30 nm, optimized atomic percentages of elements like Nd, B, Ga, and Cu, and controlled inclusion of Al, to enhance coercivity and residual magnetic flux density without relying on Dy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If heavy rare-earth elements (Dy) are added to increase coercivity, then coercivity HcJ increases, but residual magnetic flux density Br decreases
Solution Approach 1:
The patent applies local quality by creating a dual-structure grain boundary phase where the first grain boundary phase (between two main phases) has a specific thickness of 5-30 nm with optimized composition, while the second grain boundary phase (between three or more main phases) has different characteristics. This localized structural differentiation enables enhanced coercivity in critical regions without uniformly reducing Br throughout the material.
Solution Approach 2:
The patent employs composite materials by forming a complex grain boundary phase composed of multiple phases with distinct functions. The first grain boundary phase acts as a magnetic isolation layer with controlled thickness, while the second grain boundary phase provides structural support. This composite grain boundary structure achieves high coercivity through phase differentiation without relying on heavy rare-earth elements.
2Force
If B concentration is significantly decreased to form R2T17 phase, then coercivity HcJ increases, but existence ratio of main phase decreases leading to significant reduction in Br
Solution Approach 1:
The patent applies parameter changes by precisely controlling the thickness of the first grain boundary phase within 5-30 nm and optimizing the composition ratios of R, T, and B elements. This parameter optimization allows the formation of beneficial phases like R2T17 while maintaining sufficient main phase content, thereby achieving high coercivity without significant Br reduction.
Solution Approach 2:
The patent implements local quality by creating a differentiated grain boundary structure where the first grain boundary phase (between two main phases) has specific thickness and composition tailored for magnetic isolation, while the overall material maintains adequate B concentration to preserve main phase existence ratio and Br.
3Force
If heavy rare-earth elements are diffused from surface into inside to increase concentration at outer shell, then coercivity HcJ increases, but this method is complex and Dy supply is unstable
Solution Approach 1:
The patent applies preliminary action by incorporating the optimized grain boundary phase structure directly during the initial alloy manufacturing and sintering process, rather than requiring subsequent diffusion treatments. The first and second grain boundary phases are formed in-situ during sintering, eliminating the need for complex post-processing diffusion steps and reducing dependency on Dy supply stability.
Solution Approach 2:
The patent extracts the heavy rare-earth element diffusion process from the manufacturing sequence by achieving high coercivity through the optimized grain boundary phase structure formed during standard sintering. This removes the complex diffusion step and reduces reliance on Dy, simplifying the overall manufacturing process.
Data Source
Figure 1
Figure 2(a)~2(b)
AI summary
To provide an R-T-B based sintered magnet having high Br and high HcJ without using Dy by solving a problem that a significant reduction in Br due to a decrease in B concentration and HcJ are insufficient to satisfy recent requirements. Disclosed is an R-T-B based sintered magnet which includes an Nd2Fe14B type compound as a main phase, and comprises the main phase, a first grain boundary phase located between two main phases, and a second grain boundary phase located between three or more main phases, wherein the first grain boundary phase having a thickness of 5 nm or more and 30 nm or less is present.