Rare Earth Sintered Magnet Grain-Boundary Diffusion for Thermal Stability
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Solution Overview
Problem
The challenge is to improve the temperature coefficient of residual magnetic flux density and coercivity in Nd—Fe—B sintered magnets while minimizing the decrease in magnetic characteristics with temperature, particularly due to the limitations of using Dy or Tb, which are scarce and unevenly distributed, and the increased cost and corrosion issues with high Ni and Co content.
Innovation Solution
A method involving the preparation of rare earth alloy and heavy rare earth compound or metal alloy powders, aligned and compacted in a magnetic field, with a heavy rare earth element diffused to the grain boundary, followed by sintering and heat treatment to enhance coercivity and temperature stability of the magnets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Dy or Tb is used to increase coercivity, then coercivity is improved, but resource availability deteriorates and cost increases
Solution Approach 1:
The patent applies local quality by concentrating heavy rare earth elements specifically at the grain boundaries of the magnet rather than uniformly distributing them throughout. This localized approach at the grain boundary regions provides the necessary coercivity enhancement while using minimal amounts of scarce Dy or Tb resources, thereby resolving the contradiction between improving coercivity and maintaining resource availability.
Solution Approach 2:
The patent changes the distribution parameter of heavy rare earth elements from uniform distribution to localized concentration at grain boundaries. By controlling the spatial distribution parameter rather than the total concentration, the invention achieves high coercivity with reduced material usage, addressing both the coercivity improvement and resource conservation objectives.
2Strength
If Dy or Tb is uniformly distributed throughout the magnet, then coercivity is improved, but residual magnetic flux density decreases
Solution Approach 1:
The patent implements local quality by restricting heavy rare earth element distribution to grain boundary regions only, leaving the main phase particles largely unaffected. This localized enrichment provides coercivity enhancement at the boundaries while preserving the magnetic flux density within the bulk material, thereby resolving the contradiction between improving coercivity and maintaining residual magnetic flux density.
Solution Approach 2:
The patent segments the magnet structure into grain boundary regions and main phase particles, applying different compositional characteristics to each segment. The grain boundaries are enriched with heavy rare earth elements for coercivity, while the main phase particles maintain their original composition for high magnetic flux density, thus resolving the contradiction through spatial segmentation.
3Reliability
If Ni and Co are used to improve corrosion resistance, then corrosion resistance is improved, but cost increases and magnetic characteristics deteriorate
Solution Approach 1:
The patent applies local quality by providing corrosion protection through grain boundary engineering rather than bulk material substitution. The grain boundaries, which are typically the initiation sites for corrosion, are selectively modified with heavy rare earth elements to enhance corrosion resistance locally, avoiding the need for widespread Ni or Co addition that would degrade magnetic properties and increase cost.
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
This method effectively increases coercivity and reduces the temperature-dependent decrease in residual magnetic flux density, maintaining high magnetic performance without the need for scarce elements like Dy or Tb, while also improving corrosion resistance.
Implementation Method 1
the Dy or Tb adhered to the sintered NdFeB magnet is sent to the inside of a sintered compact through the grain boundary of the sintered compact and diffuses from the grain boundary into each particle of a main phase
Implementation Method 2
aligning and compacting the mixed powder in a magnetic field
Implementation Method 3
heating it at 700 ̃1000° C.
Implementation Method 4
sintering the alloy powder with the diffused heavy rare earth element
Data Source
AI summary
There is provided a method for manufacturing a rare earth sintered magnet having a stable magnetic performance, by uniformly distributing a heavy rear earth element to the surface of the magnet and the grain boundary inside of the magnet by using a mixture of a heavy rare earth compound or a heavy rare earth metal alloy and a rare earth magnet powder, to lower a decrease rate of the magnetic characteristics based on the temperature of the rare earth sintered magnet.