R-T-B Sintered Magnet Grain Boundary Phase Engineering
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Solution Overview
Problem
R-T-B-based sintered magnets face a decrease in coercivity (HcJ) at elevated temperatures, leading to irreversible thermal demagnetization, and the use of heavy rare-earth elements like Dy results in unstable supply and price fluctuations, necessitating a method to enhance HcJ without Dy while maintaining high residual magnetic flux density (Br).
Innovation Solution
Optimizing the composition of R-T-B-based sintered magnets by adjusting the content of R, B, and Ga to include an R-Ga phase and an R-Ga-Cu phase in the grain boundary phases, while avoiding the formation of an R-T-Ga phase, to increase the existence ratio of the Nd2Fe14B main phase and enhance both Br and HcJ.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heavy rare-earth elements (Dy) are added to increase HcJ, then coercivity is improved, but residual magnetic flux density decreases and supply stability deteriorates
Solution Approach 1:
The invention changes the chemical composition parameters by precisely controlling B content (0.86-0.90% by mass) and introducing Ga (0.4-0.6% by mass) to form R-Ga phases in grain boundaries, thereby achieving high HcJ without Dy while maintaining high Br
Solution Approach 2:
The invention creates a composite microstructure consisting of Nd2Fe14B main phase grains surrounded by R-Ga and R-Ga-Cu grain boundary phases, where the R-Ga phase forms a protective shell that enhances coercivity without the need for heavy rare-earth elements
2Strength
If B concentration is significantly decreased to form R2T17 phase, then coercivity is improved, but main phase existence ratio decreases leading to reduced residual magnetic flux density
Solution Approach 1:
The invention optimizes B content within a narrow range (0.86-0.90% by mass) to maintain sufficient main phase content while introducing Ga to form R-Ga phases that provide the necessary coercivity enhancement without requiring excessive B depletion
Solution Approach 2:
The R-Ga phase acts as an intermediary structure in the grain boundaries that mediates between the main phase grains, providing the coercivity enhancement normally achieved by heavy rare-earth elements or high B content, while preserving main phase integrity and Br
3Stability of the object's composition
If R-T-Ga phase is formed in grain boundary, then structural stability is improved, but coercivity increases are suppressed due to magnetization of R-T-Ga phase
Solution Approach 1:
The invention creates local quality differentiation by forming R-Ga phases with specific composition ranges (R: 70-95% by mass, Ga: 5-30% by mass, Fe: 0-20% by mass) in the grain boundaries, which have different magnetic properties than the main phase, thereby achieving high coercivity through localized phase engineering
Solution Approach 2:
The invention changes the phase composition parameters by controlling Ga content (0.4-0.6% by mass in overall alloy) and R content (29.0-31.5% by mass) to ensure formation of R-Ga phases with optimal magnetic properties that provide coercivity enhancement without the detrimental magnetization effects of R-T-Ga phases
Data Source
AI summary
To provide an R-T-B based sintered magnet having high Br and high HcJ without using Dy. 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 composition of the R-T-B based sintered magnet comprises: R: 29.0% by mass or more and 31.5% by mass or less, B: 0.86% by mass or more and 0.4% by mass or less, Ga: 0.4% by mass or more and 0.6% by mass or less, Al: 0.5% by mass or less (including 0% by mass), and balance being T and inevitable impurities.