Sintered R-T-B Magnet Grain Boundary Diffusion for Coercivity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Sintered R-T-B based magnets experience a decrease in coercivity (HcJ) at high temperatures, leading to irreversible thermal demagnetization, and existing methods to improve HcJ often result in a decrease in remanence (Br) or require excessive heavy rare-earth elements.
Innovation Solution
A method involving a diffusion step where an RL-RH-M based alloy is adhered to the surface of a sintered R-T-B based magnet and heated between 700°C and 1100°C, with specific composition ranges for RL, RH, and M, to enhance the anisotropy field and reduce magnetic element concentration in the grain boundary phase, thereby increasing both Br and HcJ while minimizing heavy rare-earth element usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light rare-earth element in an R2T14B-based compound phase is replaced with a heavy rare-earth element to improve HcJ, then coercivity is improved, but remanence decreases due to decreasing saturation magnetization
Solution Approach 1:
The patent applies local quality by concentrating heavy rare-earth elements specifically in the grain boundary phase rather than uniformly distributing them throughout the main phase. This localized approach allows the heavy rare-earth elements to improve coercivity at grain boundaries without significantly reducing the saturation magnetization of the main R2T14B phase, thereby maintaining high remanence while achieving improved coercivity.
Solution Approach 2:
The patent creates a composite structure consisting of an R2T14B-based main phase and a grain boundary phase containing heavy rare-earth elements. This composite material approach allows the system to combine the high saturation magnetization properties of the light rare-earth-based main phase with the high coercivity properties of the heavy rare-earth-containing grain boundary phase, resolving the contradiction between remanence and coercivity.
2Reliability
If heavy rare-earth elements are used to improve HcJ, then coercivity increases, but the amount of heavy rare-earth elements required becomes excessive
Solution Approach 1:
By localizing heavy rare-earth elements to the grain boundary phase, the patent achieves effective coercivity improvement with minimal heavy rare-earth content. The grain boundary phase acts as a targeted region where small amounts of heavy rare-earth elements can exert maximum effect on coercivity without requiring excessive overall usage.
Solution Approach 2:
The grain boundary phase naturally serves as the functional region for coercivity enhancement, utilizing the inherent structure of the sintered magnet. The heavy rare-earth elements in the grain boundary phase self-organize to provide coercivity improvement, reducing the need for additional heavy rare-earth additions to the main phase.
3Reliability
If heavy rare-earth elements are supplied onto the surface and diffused into the interior to thicken only the outer crust, then HcJ is improved with suppressed decrease in Br, but the diffusion process requires precise control of adhering amount and heating conditions
Solution Approach 1:
The patent employs parameter changes by controlling the composition ratios of heavy rare-earth elements to light rare-earth elements within specific ranges (1:9 to 8:2 by mass). This parameter control during the diffusion process ensures optimal coercivity improvement while minimizing remanence loss, and the specified heating temperature range (700-1100°C) optimizes diffusion kinetics for precise grain boundary phase formation.
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 method achieves high remanence and coercivity in sintered R-T-B based magnets, suitable for high-temperature applications like electric vehicle motors, while reducing the amount of heavy rare-earth elements used.
Implementation Method 1
a diffusion step of allowing at least a portion of the RL-RH-M based alloy to adhere to at least a portion of a surface of the sintered R-T-B based magnet work, and conducting a heating at a temperature which is not lower than 700° C. and not higher than 1100° C.
Implementation Method 2
conducting a heating at a temperature which is not lower than 700° C. and not higher than 1100° C. in a vacuum or an inert gas ambient
Data Source
AI summary
A method for producing a sintered R-T-B based magnet includes: a step of providing a sintered R-T-B based magnet work; a step of providing an RL-RH-M based alloy; and a diffusion step. In the diffusion step, an adhering amount of the RL-RH-M based alloy to the magnet work is 4 to 15 mass %, and an adhering amount of RH is 0.1 to 0.6 mass %; in the magnet work, the R content accounts for 27 to 35 mass %, the Fe content in the entire T accounting for 80 mass % or more; and, in the RL-RH-M based alloy, the RL content accounts for 60 to 97 mass %; the RH content accounting for 1 to 8 mass %; and the M content accounts for 2 to 39 mass %.