Sintered Magnet Eutectic Infiltration for Higher Coercive Force
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Solution Overview
Problem
Existing methods for producing sintered magnets, such as NdFeB, require lengthy pulverizing processes and surface coating, which can lead to reduced coercive force and residual magnetization due to crystal grain growth during sintering.
Innovation Solution
A method involving the production of an R—Fe—B based magnet powder by reduction-diffusion, followed by sintering and infiltration with a eutectic alloy containing Pr, Al, Cu, and Ga, which is then heat-treated to improve coercive force without using heavy rare earth elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional pulverizing and sintering methods are used to produce NdFeB magnets, then magnet powder can be obtained, but crystal grain growth occurs during sintering which reduces coercive force and residual magnetization
Solution Approach 1:
The patent applies preliminary action by performing surface coating with rare earth element-containing powder before sintering. This pre-coating prepares the grain boundaries in advance to resist crystal grain growth during high-temperature sintering, thereby maintaining coercive force without requiring lower sintering temperatures.
Solution Approach 2:
The patent changes the chemical composition parameter by adding rare earth elements (Dy, Tb, Ho, Er, Tm, or Y) to the surface coating layer. This compositional change creates a protective layer at grain boundaries that suppresses crystal grain growth during sintering, allowing the use of optimized sintering temperature and time parameters to maintain magnetic properties.
2Manufacturing precision
If heavy rare earth elements are used in grain boundary diffusion process to increase coercive force, then magnetic performance improves, but production cost increases significantly
Solution Approach 1:
The patent applies local quality by concentrating rare earth elements specifically at the grain boundaries through surface coating, rather than uniformly distributing them throughout the bulk material. This localized approach achieves effective coercive force enhancement at the critical grain boundary regions while minimizing the total quantity of expensive heavy rare earth elements required.
Solution Approach 2:
The patent provides an alternative to expensive heavy rare earth elements by using lighter rare earth elements (Dy, Tb, Ho, Er, Tm, or Y) in the surface coating. While these elements are still rare earth metals, they represent a cost-reduced option compared to traditional heavy rare earth element formulations, achieving similar coercive force enhancement at lower material cost.
3Manufacturing precision
If sintering is performed at high temperature to densify the magnet, then density improves, but crystal grain growth increases which reduces magnetic performance
Solution Approach 1:
The patent creates a differentiated structure where the grain boundary regions have different composition (enriched with rare earth elements) compared to the bulk material. This local compositional quality difference suppresses crystal grain growth at boundaries while allowing high-temperature sintering to achieve dense bulk material, thus simultaneously improving density and controlling grain size.
Solution Approach 2:
The patent creates a composite structure consisting of the bulk R-Fe-B magnetic phase and a rare earth element-enriched surface coating layer. This composite material structure allows the bulk to be densely sintered at high temperature while the coating layer acts as a barrier to crystal grain growth, achieving both high density and controlled grain size.
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 effectively increases the coercive force of sintered magnets by up to 70% compared to as-sintered magnets, while minimizing the use of expensive heavy rare earth elements and avoiding the limitations of conventional pulverizing and surface treatment processes.
Implementation Method 1
heat-treating the sintered magnet to which the eutectic alloy is applied
Implementation Method 2
a rare earth oxide such as Nd2O3 is mixed with Fe, B, and Cu powder in a desired composition ratio, to which a reducing agent such as Ca or CaH2 is then added and heat-treated to synthesize a NdFeB based bulk magnet
Data Source
AI summary
A method of producing a sintered magnet is disclosed herein. In some embodiments, a method of producing a sintered magnet comprises, sintering a R—Fe—B based magnetic powder to produce a sintered magnet; wherein the R is Nd, Pr, Dy, Ce or Tb, and infiltrating a eutectic alloy into the sintered magnet, wherein the eutectic alloy contains Pr, Al, Cu and Ga, and wherein infiltration the eutectic alloy includes applying the eutectic alloy to the sintered magnet and heat-treating the sintered magnet to which the eutectic alloy is applied.