Core-Shell Auxiliary Alloy for High-Coercivity Sintered NdFeB Magnets
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Solution Overview
Problem
Conventional methods for preparing high-coercivity sintered NdFeB magnets face challenges due to grain boundary phase destruction and uneven distribution of auxiliary alloy components, leading to limited coercivity enhancement and compromised mechanical and corrosion properties.
Innovation Solution
A core-shell structure auxiliary alloy is introduced, comprising a high melting point metal nanopowder core and a rare earth alloy shell, which is vacuum coated and mixed with NdFeB powder, followed by orientation pressing and sintering to enhance grain boundary structure and coercivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If nanosized auxiliary alloy powder is added to expand grain boundaries, then coercivity is improved, but the nanosized powder agglomerates and distributes unevenly, deteriorating mechanical and corrosion properties
Solution Approach 1:
The patent uses a core-shell structured auxiliary alloy composite material where a rare earth alloy core is coated with a metal shell. This composite structure combines the grain boundary expansion effect of rare earth alloys with the dispersibility and processability of metal shells, preventing agglomeration while maintaining coercivity enhancement.
Solution Approach 2:
The patent changes the physical and chemical parameters of the auxiliary alloy by coating the rare earth alloy core with a metal shell. This parameter change transforms the raw rare earth alloy powder into a core-shell structured auxiliary alloy with improved dispersibility, uniform distribution, and controlled reactivity during sintering.
2Stability of the object's composition
If high melting point nanosized auxiliary alloy powder is used to prevent abnormal grain growth, then grain boundary continuity is improved, but voids form at grain boundaries due to expansion, deteriorating mechanical properties
Solution Approach 1:
The core-shell structure combines a rare earth alloy core that expands grain boundaries to maintain continuity with a metal shell that controls the expansion process and prevents void formation. The shell acts as a buffer that moderates the interaction between the rare earth alloy and the NdFeB matrix during sintering.
Solution Approach 2:
The metal shell acts as an intermediary between the rare earth alloy core and the NdFeB matrix. It mediates the grain boundary expansion process, allowing the rare earth alloy to diffuse and expand the grain boundary while preventing excessive expansion that would create voids and compromise mechanical strength.
3Reliability
If rare earth auxiliary alloy is added and sintered to expand grain boundaries, then coercivity is improved, but grain growth occurs and grain boundary phase continuity is destroyed
Solution Approach 1:
The core-shell auxiliary alloy composite enables controlled grain boundary expansion without uncontrolled grain growth. The metal shell regulates the diffusion process, allowing the rare earth alloy to expand the grain boundary phase while maintaining its continuity and preventing main phase grain coalescence.
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 core-shell structure effectively prevents grain growth, broadens grain boundaries, and significantly increases the coercive force of NdFeB magnets, outperforming traditional auxiliary alloys in magnetic properties and mechanical integrity.
Implementation Method 1
The core-shell structure effectively prevents grain growth, broadens grain boundaries
Implementation Method 2
vacuum coating a layer of a rare earth alloy RxH(100-x) on a surface of a metal nanopowder M
Implementation Method 3
sintering and aging treatment to obtain a high-coercivity sintered NdFeB magnet
Data Source
Figure 1
AI summary
The present invention provides a method for preparing a high-coercivity sintered NdFeB magnet. The method includes the steps of: (S1) Providing a NdFeB powder as a main material; (S2) Vacuum coating a layer of a rare earth alloy RxH(100-x) (2) on a surface of a metal nanopowder M (1) to obtain an auxiliary alloy material with a core-shell structure, with R is at least one selected from the group of Dy, Tb, Pr, Nd, La, and Ce; H is at least one selected from the group of Cu, Al, and Ga; M is at least one selected from the group of Mo, W, Zr, Ti, and Nb; and x is 30 wt.% ≤ x ≤ 90 wt.%, preferably 40 wt.% ≤ x ≤ 85 wt.%; and (S3) Adding the auxiliary alloy material obtained by step (S2) to the NdFeB powder of step (S1) and mixing, and after the mixture is uniformly mixed, orientation pressing of the mixture to obtain a compact body; and (S4) Sintering and annealing treatment of the compact body to obtain the high-coercivity sintered NdFeB magnet.