NdFeB Magnet Powder Coating for Grain Boundary Diffusion
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Solution Overview
Problem
Sintered NdFeB permanent magnets face challenges such as insufficient grain shape, surface defects, and difficulty in achieving effective diffusion of heavy rare earth elements like Dy or Tb, leading to suboptimal coercivity and stability issues due to high costs and complex processing requirements.
Innovation Solution
The development of an R-T-B based permanent magnet material with a grain boundary phase enriched with M-R and/or M-T-R compounds, where R is neodymium or praseodymium, T is iron or a mixture of iron with other metal elements, and B is boron, with a M compound coating the alloy powders to enhance grain boundary properties and facilitate heavy rare earth element diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heavy rare earth metal elements (Dy, Tb) are added to increase coercivity, then coercivity is improved, but cost increases and diffusion difficulty increases due to grain boundary defects
Solution Approach 1:
The patent changes the chemical composition parameters by introducing M elements (Al, Ga, In, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Hf, Ta, W) to form M-R and M-T-R compounds at grain boundaries. This compositional modification alters the diffusion characteristics, enabling heavy rare earth elements to diffuse more effectively through grain boundaries while maintaining coercivity improvement.
Solution Approach 2:
The M-R and M-T-R compounds act as intermediary phases at grain boundaries that facilitate the diffusion of heavy rare earth elements. These intermediary compounds create favorable diffusion pathways, reducing the resistance that heavy rare earth elements encounter when attempting to penetrate through defective grain boundary regions.
2Strength
If heavy rare earth elements are added to achieve enrichment in grain boundary phase, then coercivity is improved, but cost increases due to scarce heavy metal elements
Solution Approach 1:
By modifying the grain boundary composition with M elements to form M-R and M-T-R compounds, the patent changes the chemical environment at grain boundaries. This creates more favorable conditions for heavy rare earth element diffusion and enrichment, allowing effective coercivity improvement with reduced amounts of scarce heavy rare earth elements.
Solution Approach 2:
The M-R and M-T-R compounds serve as intermediary phases that enhance the uptake and distribution of heavy rare earth elements at grain boundaries. These intermediaries improve the efficiency of heavy rare earth element utilization, achieving the desired enrichment effect with smaller quantities of expensive heavy rare earth materials.
3Speed
If Dy or Tb permeates into main phase grains, then diffusion occurs, but reverse core-shell structure is formed which is not favorable for diffusion
Solution Approach 1:
The patent creates local compositional differences by concentrating M elements at grain boundaries to form M-R and M-T-R compounds. This local modification creates favorable diffusion conditions specifically at grain boundaries while preventing unfavorable reverse core-shell structure formation in the main phase grains, thus maintaining microstructure stability.
Solution Approach 2:
The M-R and M-T-R compounds at grain boundaries act as intermediary phases that control and regulate the diffusion process. They provide structured pathways that guide heavy rare earth element diffusion along grain boundaries, preventing uncontrolled permeation into main phase grains that would lead to reverse core-shell structure formation.
4Strength
If neodymium-rich phases are uniformly distributed around hard magnetic main phase to obtain clean grain boundaries, then coercivity is improved, but process complexity and cost increase
Solution Approach 1:
The patent changes the grain boundary composition by introducing M elements that form M-R and M-T-R compounds, achieving clean and smooth grain boundaries with improved coercivity. This compositional approach is simpler than the uniform neodymium-rich phase distribution method, requiring less complex sintering process control.
Solution Approach 2:
The patent creates a composite grain boundary structure consisting of M-R and M-T-R compounds. This composite approach provides the benefits of clean grain boundaries and improved coercivity through a relatively simple process, avoiding the complexity of uniformly distributing neodymium-rich phases around main phase particles.
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 improves the coercivity and stability of the R-T-B based permanent magnet material by forming a uniform coating layer, enhancing wettability, and facilitating the permeation of heavy rare earth elements, thereby overcoming the limitations of existing sintered NdFeB magnets.
Implementation Method 1
enhancing wettability
Implementation Method 2
facilitating the permeation of heavy rare earth elements
Data Source
Figure 1~2
Figure 3~4
AI summary
The present disclosure relates to an R-T-B based permanent magnet material, a preparation method therefor and use thereof. According to the present disclosure, the M compound is adhered to or coats the R-T-B based alloy powders to form a uniform coating layer on the surface of the neodymium-iron-boron powders, so that the rounding transformation of the R-T-B based alloy powders can be achieved, and further the wettability of the R-T-B based alloy powders is improved under the condition of significantly reducing the amount of heavy rare earth metals in the substrate. In addition, the grain boundary phases of M-R and/or M-T-R are present in the grain boundary of the R-T-B based permanent magnet material, the physicochemical properties of the grain boundary phases can be significantly improved, the distribution of the grain boundary phases is improved, and the grain boundary is strengthened, so that a reverse core-shell structure can be avoided, and the permeation of heavy rare earth elements is facilitated, so that the Hcj of the R-T-B based permanent magnet material is improved.