Grain Boundary Diffusion for R-Fe-B Magnets
Solution Overview
Problem
Existing methods for improving coercivity in Nd—Fe—B sintered magnets using heavy rare earth elements (HRE) lead to a reduction in residual magnetism, as HRE replaces Nd in Nd2Fe14B grains, resulting in decreased saturated magnetic polarization intensity.
Innovation Solution
A grain boundary diffusion method for R—Fe—B series rare earth sintered magnets involves forming a dry layer with HRE compound powder on a high-temperature-resistant carrier, which is then used to diffuse HRE onto the magnet, controlling the diffusion mode and speed to enhance coercivity without significantly reducing residual magnetism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If HRE is added to replace Nd in Nd2Fe14B grains to increase coercivity, then coercivity is improved, but residual magnetism decreases
Solution Approach 1:
The invention segments the magnet structure into core regions (Nd2Fe14B grains) and shell regions (grain boundary phase), allowing HRE to be confined primarily to the grain boundary phase rather than replacing Nd in the core grains. This segmentation enables coercivity enhancement through grain boundary modification while preserving the high magnetic polarization of the core grains, thus maintaining residual magnetism.
Solution Approach 2:
The invention applies local quality by creating a non-uniform HRE distribution where the grain boundary phase contains high concentrations of HRE (providing strong pinning sites for domain walls) while the core grains maintain their original Nd-rich composition (providing high magnetic polarization). This localized HRE enrichment at grain boundaries achieves coercivity improvement without the bulk replacement of Nd that would reduce residual magnetism.
2Strength
If HRE grain boundary diffusion treatment is performed to increase coercivity, then coercivity is improved, but HRE consumption increases
Solution Approach 1:
The invention applies preliminary action by pre-forming a grain boundary phase-rich layer on the magnet surface before diffusion treatment. This pre-formed layer acts as a reservoir that controls and limits HRE diffusion depth, ensuring HRE is deposited primarily in the grain boundary phase rather than penetrating deep into the core grains. This preliminary structuring reduces overall HRE consumption by preventing excessive diffusion.
Solution Approach 2:
The grain boundary phase acts as an intermediary layer that mediates between the HRE diffusion source and the core grains. This intermediary phase absorbs and confines HRE atoms, providing a buffer that limits HRE penetration depth and controls diffusion kinetics. The intermediary grain boundary phase thus reduces HRE consumption by preventing direct HRE incorporation into the core grains.
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 increases coercivity and squareness of the magnets while minimizing the consumption of HRE and maintaining residual magnetism, offering improved diffusion efficiency and consistency across batches.
Implementation Method 1
heavy rare earth elements such as Dy and Tb seep from the surface of the magnet to perform grain boundary diffusion
Implementation Method 2
a grain boundary diffusion method of an R—Fe—B series rare earth sintered magnet
Implementation Method 3
the Nd-rich phase of the grain boundary forms a liquid phase
Implementation Method 4
performing heat treatment on the R—Fe—B series rare earth sintered magnet and the high-temperature-resistant carrier treated with the engineering A
Data Source
AI summary
The present invention discloses a grain boundary diffusion method of an R—Fe—B series rare earth sintered magnet, an HRE diffusion source, and a preparation method thereof, comprising the following steps: engineering A of forming a dry layer on a high-temperature-resistant carrier, the dry layer being adhered with HRE compound powder, the HRE being at least one of Dy, Tb, Gd, or Ho; and engineering B of performing heat treatment on the R—Fe—B series rare earth sintered magnet and the high-temperature-resistant carrier treated with the engineering A in a vacuum or inert atmosphere and supplying HRE to a surface of the R—Fe—B series rare earth sintered magnet. The method can reduce the consumption of heavy rare earth element and control the loss of residual magnetism Br while increasing the coercivity.