R-T-B Permanent Magnet Grain Boundary Composition for Crack Resistance
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Solution Overview
Problem
The grain boundary phase in R-T-B rare earth permanent magnets has low strength and poor crack propagation resistance, leading to intergranular fracture under stress, which compromises the mechanical performance of the magnet.
Innovation Solution
A high-strength R-T-B rare earth permanent magnet is prepared by incorporating elements with different atomic radii (large, medium, and small) in the grain boundary phase, achieving an amorphous state through a specific composition and processing method, including second stage aging and controlled cooling rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high content of low melting point elements are added and grain boundary phase is transformed into FCC structure through tempering, then coercivity of the magnet is improved, but grain boundary phase strength decreases and crack propagation resistance deteriorates
Solution Approach 1:
The invention changes the structural parameter of the grain boundary phase from crystalline (FCC) to amorphous state. This parameter change allows the grain boundary phase to simultaneously achieve high strength and good crack propagation resistance while maintaining the coercivity enhancement effect provided by low melting point elements.
Solution Approach 2:
The invention creates a composite microstructure where the grain boundary phase consists of amorphous matrix with dispersed low melting point elements. This composite structure combines the high strength and crack resistance of amorphous material with the coercivity enhancement of low melting point elements like Nd and Pr.
2Ease of manufacture
If traditional crystalline grain boundary phase is used, then processing is simpler, but mechanical strength and crack propagation resistance are insufficient
Solution Approach 1:
The invention utilizes phase transition from crystalline to amorphous state of the grain boundary phase. By controlling the cooling rate and composition during solidification, the grain boundary phase transforms into amorphous structure, which provides superior mechanical properties while maintaining manufacturability through established casting and heat treatment processes.
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 amorphous grain boundary phase significantly enhances the magnet's mechanical performance, with bending strength exceeding 560 MPa, a 20% improvement over existing technologies, by improving crack resistance and intergranular fracture resistance.
Implementation Method 1
The formation of an amorphous material requires the suppression of atomic ordering arrangement. Therefore a certain degree of undercooling is required in the solidification process.
Implementation Method 2
the compact is vacuum-sintered and subjected to first stage aging and second stage aging to prepare the R-T-B rare earth permanent magnet having an amorphous boundary phase
Data Source
AI summary
A high-strength R-T-B rare earth permanent magnet having an amorphous grain boundary phase includes: 29.0 wt. %-34.0 wt. % of large-atomic-radius elements with the atomic radius r satisfying r≥0.16 nm, said large-atomic-radius elements comprising 0.1 wt. %-0.8 wt. % of Mf, and Mf being any one or two of Zr and Mg; 1.05 wt. %-1.65 wt. % of small-atomic-radius elements with r≤0.12 nm, said small-atomic-radius elements comprising 0.8 wt. %-1.1 wt. % of boron element, and the total content C1 of the small-atomic-radius elements satisfying 0.25 wt. %≤[C1]−[B]≤0.55 wt. %; and the balance being medium-atomic-radius elements with 0.12 nm<r<0.16 nm and impurities, said medium-atomic-radius elements at least comprising 60.0 wt. % of TM, the TM being at least one of Fe and Co, and the content of other medium-atomic-radius elements except said TM being ≥0.2 wt. %. In the present invention, the proportion of the amorphous grain boundary phase in the grain boundary phase of the magnet is increased to 20 vol. % or more, thereby improving the capability of resisting crack propagation of the grain boundary phase of the magnet, and manufacturing a high-strength R-T-B rare earth permanent magnet.