Multi-Layer NdFeB Alloy Powder for High-Coercivity Grain Boundaries
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Solution Overview
Problem
Conventional magnetic powder surface diffusion methods for enhancing the coercivity of sintered NdFeB magnets face limitations due to shallow diffusion depth and inability to form a uniform, continuous network of grain boundary phases, leading to weakened demagnetization coupling and limited improvement in coercivity.
Innovation Solution
A novel NdFeB alloy powder with a multi-layered coating comprising a first metal layer of Tb or Dy, a second metal layer of W, Mo, Ti, Zr, or Nb, and a third metal layer of Pr, Nd, La, or Ce, which prevents direct contact between grains and promotes network formation at grain boundaries, thereby enhancing coercivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heavy rare earth elements (Dy, Tb) are added to increase coercivity, then the coercive force of the magnet increases, but the cost of the magnet alloy increases significantly
Solution Approach 1:
The patent segments the heavy rare earth element distribution into two zones: main phase grains (where they provide coercivity enhancement) and grain boundaries (where they form continuous network phases). This segmentation allows optimized utilization of heavy rare earth elements, reducing overall content while maintaining coercivity improvement.
Solution Approach 2:
The patent applies local quality by concentrating heavy rare earth elements at specific locations: within main phase grains for coercivity enhancement and at grain boundaries for forming continuous network phases. This localized distribution optimizes the function of heavy rare earth elements while reducing their total quantity required.
2Strength
If conventional grain boundary diffusion method is used, then demagnetization coupling is strengthened, but the diffusion depth is shallow and thicker products cannot be treated
Solution Approach 1:
The patent applies preliminary action by pre-forming a continuous network phase structure at grain boundaries before final sintering. This pre-structured network phase serves as a diffusion pathway, enabling deeper and more uniform diffusion of heavy rare earth elements throughout the magnet thickness, overcoming the shallow diffusion limitation of conventional methods.
Solution Approach 2:
The patent introduces a continuous network phase as an intermediary structure at grain boundaries that facilitates deep diffusion of heavy rare earth elements. This network phase acts as a mediator between the surface-applied heavy rare earth elements and the interior of the magnet, enabling thorough penetration even in thicker products.
3Shape
If conventional dual alloy method is used, then light rare earth alloys are distributed in thin-layer grid shape, but the main phase grains cannot be completely separated, leading to limited coercivity increase
Solution Approach 1:
The patent changes the parameter of grain boundary phase continuity by forming a continuous network phase structure instead of discontinuous thin-layer grid distribution. This parameter change enables complete separation of main phase grains, achieving optimal demagnetization coupling and significant coercivity improvement.
4Quantity of substance
If magnetic powder surface diffusion method is used, then heavy rare earth film is coated on powder surface, but direct contact between crystal grains leads to solid phase diffusion and grain growth, weakening the network grain boundary phase formation
Solution Approach 1:
The patent applies preliminary action by pre-forming the continuous network phase structure at grain boundaries before heavy rare earth element diffusion occurs. This pre-established network structure acts as a barrier that prevents direct contact between main phase grains, thereby preventing solid phase diffusion and grain growth while maintaining the integrity of the grain boundary network.
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 multi-layered coating effectively increases the coercivity of sintered NdFeB magnets by preventing grain growth and ensuring a robust demagnetization coupling effect, resulting in higher coercivity values compared to magnets produced using traditional methods.
Implementation Method 1
the intermediate second metal layer... acts as a barrier to prevent heavy rare earth element diffusion into the grain boundaries... The high melting point metal elements in the second metal layer do not participate in the flow and diffusion process during sintering, thereby preventing growth of the grains
Implementation Method 2
the heavy rare earth elements of the first metal layer diffuse to the edge of the main phase thereby hardening the main phase grains
Implementation Method 3
Due to the high melting point, the elements of the intermediate second metal layer do not participate in the flow and diffusion process during the sintering process... The light rare earth elements of the third metal layer form a network
Data Source
Figure 1
AI summary
The invention refers to a NdFeB alloy powder for forming high-coercivity sintered NdFeB magnets. The NdFeB alloy powder includes NdFeB alloy core particles with a multi-layered coating, wherein the multi-layered coating comprises: a first metal layer directly disposed on the NdFeB alloy core particles, wherein the first metal layer consists of at least one of Tb and Dy; a second metal layer directly disposed on the first metal layer, wherein the second metal layer consists of at least one of W, Mo, Ti, Zr, and Nb; and a third metal layer directly disposed on the second metal layer, wherein the third metal layer consists of (i) at least one of Pr, Nd, La, and Ce; or (ii) a combination of one of the group consisting of Cu, Al, and Ga and at least one of the group consisting of Pr, Nd, La, and Ce.