Sintered Rare-Earth Magnet Microstructure for High Coercivity
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Solution Overview
Problem
Sintered rare-earth magnets with high coercivity (HcJ) and squareness are difficult to produce without using heavy rare-earth elements like Dy, which are expensive and supply-unstable, and existing methods either compromise on squareness or increase production costs.
Innovation Solution
Incorporating TiB2 crystals within main-phase grains, intergranular grain boundaries, and grain boundary triple junctions, and optimizing the temperature and cooling rate of the alloy melt during the manufacturing process to form a sintered rare-earth magnet with R2T14B main-phase grains and R6T13M phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If heavy rare-earth elements (Dy) are added to increase HcJ, then coercivity is improved, but residual flux density decreases
Solution Approach 1:
The patent applies local quality by concentrating heavy rare-earth elements specifically at grain boundary regions rather than uniformly distributing them throughout the magnet. This localized approach allows the grain boundaries to provide pinning sites for domain walls (improving coercivity) while preserving the magnetic properties of the main phase grains (maintaining residual flux density).
Solution Approach 2:
The patent creates a composite microstructure consisting of main-phase grains (R2T14B) and grain boundary phases containing heavy rare-earth elements. This composite structure allows the two phases to perform different functions: the main phase provides high residual flux density while the grain boundary phase provides pinning sites for high coercivity.
2Force
If grain boundary diffusion method is used to concentrate heavy rare-earths in shell region, then coercivity is improved while residual flux density is maintained, but production cost increases due to unstable supply of heavy rare-earth elements
Solution Approach 1:
The patent changes the compositional parameters by form an R2T14B main phase with specific stoichiometry that inherently provides a eutectic microstructure during solidification. This parameter change eliminates the need for post-processing grain boundary diffusion, thereby reducing production costs while maintaining the beneficial grain boundary structure.
3Force
If R2T17 phase is used as starting material with transition metal-rich phase, then coercivity is improved with lower Dy content, but squareness becomes lower
Solution Approach 1:
Instead of starting with an R2T17 phase and adding transition metals, the patent inverts the approach by forming an R2T14B main phase that naturally produces the desired microstructure during solidification. This inversion of the phase formation sequence allows simultaneous achievement of high coercivity and high squareness by controlling the primary solidification structure.
4Force
If titanium hydride powder is separately prepared and mixed to eliminate heavy rare-earth elements, then coercivity and squareness are improved, but number of production steps increases resulting in higher production costs
Solution Approach 1:
The patent merges the functions of multiple separate processes into a single alloy solidification process. Instead of separately preparing titanium hydride powder, mixing it with alloy powder, and then sintering, the patent combines all elements in an alloy composition that forms the desired microstructure during a single casting and solidification process, thereby eliminating multiple production steps.
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 approach results in high-performance sintered rare-earth magnets with enhanced coercivity and squareness, reducing the reliance on heavy rare-earth elements and lowering production costs by simplifying the production process.
Implementation Method 1
when casting an alloy melt of a prescribed composition to form a starting alloy, optimizes the temperature and cooling rate of the melt... raising the alloy melt to a temperature of between 1480°C and 1600°C and subsequently cooling the melt while regulating the average rate of cooling down to 500°C at between 100 and 1200°C/s
Implementation Method 2
the sintered rare-earth magnet include TiB2 crystals within main-phase grains, within intergranular grain boundaries and within grain boundary triple junctions
Implementation Method 3
the heat treatment step includes a sintering step that holds the compact within a temperature range of from 950°C to 1200°C for between 0.5 to 20 hours
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3
AI summary
In a sintered rare-earth magnet containing R2T14B main-phase grains (R being one or more element selected from rare-earth elements and T being one or more element selected from iron group elements), intergranular grain boundaries that form between two mutually adjoining main-phase grains and grain boundary triple junctions surrounded by three or more main-phase grains, the main-phase grains, the intergranular grain boundaries and the grain boundary triple junctions all include TiB2 crystals. The sintered rare-earth magnet is a high-performance magnet of high coercivity and good squareness.