Core-Shell Auxiliary Alloy in Sintered NdFeB Magnets
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Solution Overview
Problem
Conventional methods for preparing high-coercivity sintered NdFeB magnets face challenges due to uneven distribution of auxiliary alloy components and the formation of voids at grain boundaries, leading to low coercivity and deteriorated magnetic properties.
Innovation Solution
A core-shell structure auxiliary alloy is introduced, comprising a high melting point metal nano-powder core and a rare earth alloy shell, which is vacuum coated and added to the NdFeB powder, allowing for uniform mixing and sintering to enhance grain boundary structure and coercivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If conventional dual alloy method is used to add rare earth auxiliary alloy to expand grain boundary, then grain boundary width increases, but grain boundary continuity is destroyed and coercivity improvement is limited
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the shell layer (rare earth alloy) specifically targets the grain boundary region while the core (NdFeB powder) remains in the grain interior. This localized distribution ensures the shell material preferentially accumulates at grain boundaries during sintering, expanding the grain boundary phase continuously without disrupting its integrity, thereby resolving the contradiction between grain boundary width expansion and continuity maintenance.
2Stability of the object's composition
If nanosized auxiliary alloy powder is added to prevent abnormal grain growth, then grain growth is restrained, but severe agglomeration occurs and uniform mixing is difficult
Solution Approach 1:
The patent employs composite materials by combining NdFeB powder with rare earth alloy to form a core-shell structured auxiliary alloy. This composite structure prevents the severe agglomeration issue of pure nanosized powder while maintaining grain growth control. The shell layer provides a protective interface that improves dispersibility and uniform mixing with the NdFeB magnetic powder, resolving the contradiction between grain growth control and distribution uniformity.
3Length of stationary object
If high melting point auxiliary alloy nanosized powder is used to expand grain boundary, then grain boundary width increases, but voids form at grain boundaries and mechanical properties deteriorate
Solution Approach 1:
The patent applies parameter changes by modifying the auxiliary alloy composition to a core-shell structure with specific shell thickness (5-50 nm) and rare earth content (60-90 wt.%). This parameter optimization ensures sufficient grain boundary expansion while the core provides structural support to prevent void formation. The controlled parameters maintain grain boundary integrity during sintering, resolving the contradiction between grain boundary width expansion and integrity preservation.
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 significantly improves the coercive force of NdFeB magnets by preventing abnormal grain growth and promoting continuous grain boundary phases, resulting in higher coercivity and improved magnetic properties compared to traditional auxiliary alloy materials.
Implementation Method 1
During the sintering and aging process, the diffusion flow of the auxiliary alloy at the grain boundary reaches the hardened NdFeB magnet grains, expands the width of the grain boundary to optimize the grain boundary structure
Implementation Method 2
The mentioned auxiliary alloy nano-powders have a high melting point and prevent abnormal growth of crystal grains during the sintering process at the grain boundary
Implementation Method 3
a layer of a rare earth alloy RxH(100-x) is vacuum coated on a surface of a metal nano-powder M to obtain an auxiliary alloy material with a core-shell structure
Data Source
AI summary
The present disclosure provides a method for preparing a high-coercivity sintered NdFeB magnet. The method including 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) on a surface of a metal nano-powder M to obtain an auxiliary alloy material with a core-shell structure, with R being selected from one or more of Dy, Tb, Pr, Nd, La, and Ce; H being selected from one or more of Cu, Al, and Ga; the nano-powder M being selected from one or more of Mo, W, Zr, Ti, and Nb; 0≤x≤90 wt. %;S3, Adding the auxiliary alloy material obtained by step S2 to the NdFeB powder of step S1 and mixing, then orientation pressing of the mixture to obtain a compact body; andS4, Sintering and annealing treatment of the compact body to obtain the high-coercivity sintered NdFeB magnet.