Dual-Main-Phase NdFeB Magnet Diffusion for Higher Coercivity
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Solution Overview
Problem
The high cost and limited diffusion depth of heavy rare earth elements in existing methods for enhancing the coercivity of sintered NdFeB magnets, along with the deterioration of magnetic properties due to mischmetal substitution, necessitate a more effective and cost-efficient approach for preparing high-performance rare earth permanent magnets.
Innovation Solution
A two-step diffusion method using PrHoFe and ZrCu strip-casting alloys to coat hydrogen decrepitation powders, improving coercivity by forming Pr2Fe14B and Ho2Fe14B phases with higher anisotropic fields and preventing grain growth and inter-diffusion, thereby enhancing the magnetic properties of mischmetal-iron-boron magnets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If mischmetal is used to replace expensive Nd and Pr to prepare magnets, then cost is reduced and rare earth resources are comprehensively utilized, but the magnet's performance deteriorates and coercivity is seriously reduced
Solution Approach 1:
The patent applies local quality by creating a dual-main-phase structure where PrHoFe main phase particles are embedded in an (E,Nd)2Fe14B matrix. The PrHoFe phase provides high coercivity locally at the particle level, while the mischmetal phase reduces overall rare earth consumption. This local differentiation allows the magnet to achieve both cost reduction and performance maintenance.
Solution Approach 2:
The patent uses composite materials by combining two different main phases (PrHoFe and (E,Nd)2Fe14B) in a single magnet structure. This composite approach allows the high-performance PrHoFe phase to compensate for the lower performance of the mischmetal phase, achieving overall high performance while reducing rare earth element consumption through the use of mischmetal.
2Reliability
If heavy rare earth elements such as Dy, Tb are used for diffusion to enhance coercivity, then coercivity is improved, but the diffusion depth is limited and cost increases significantly
Solution Approach 1:
The patent applies preliminary action by pre-forming PrHoFe main phase particles with high coercivity before the final magnet fabrication. This preliminary creation of high-coercivity phases eliminates the need for subsequent heavy rare earth diffusion treatments, as the coercivity enhancement is already achieved through the phase composition and structure design.
Solution Approach 2:
The patent replaces expensive heavy rare earth elements (Dy, Tb) with a more cost-effective approach using PrHoFe phase particles. This substitution uses relatively cheaper rare earth elements (Pr, Ho) in a controlled phase structure to achieve the same coercivity enhancement effect, significantly reducing material cost while maintaining performance.
3Manufacturing precision
If jet milling powders are used for diffusion treatment, then surface diffusion effect is improved, but severe oxidation occurs and equipment requirements increase
Solution Approach 1:
The patent applies preliminary action by pre-alloying Pr and Ho elements into Fe-based strip-casting alloys before powder preparation. This preliminary incorporation of rare earth elements into the metal matrix prevents oxidation during subsequent hydrogen decrepitation and processing, as the rare earth elements are already protected within the alloy structure rather than being exposed as separate phases requiring diffusion.
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 results in high-performance, cost-effective magnets with improved coercivity and reduced rare earth element consumption, facilitating industrialization and comprehensive resource utilization.
Implementation Method 1
In the first-step diffusion, PrHoFe strip-casting alloy is used as a diffusion source. A PrHo-rich layer is uniformly coated on the surface of hydrogen decrepitation powders.
Implementation Method 2
In the second-step diffusion, the ZrCu strip-casting alloy is used as a diffusion source. A Zr-rich layer is uniformly coated on the surface of the powders after the first-step diffusion, which prevents the growth of the E main phase grains during the sintering process and the inter-diffusion between the two main phases
Implementation Method 3
hydrogen decrepitation powders
Data Source
AI summary
A two-step diffusion method for preparing high-performance dual-main-phase sintered mischmetal-iron-boron magnet belongs to the preparing technical field of rare earth permanent magnet materials. The compositions of the two main phase alloys are RE-Fe—B (RE is Nd or Pr) and (Nd, MM)-Fe—B (MM is mischmetal), respectively. First, PrHoFe strip-casting alloy is used as a diffusion source. Next, a PrHo-rich layer is uniformly coated on the surface of (Nd, MM)-Fe—B hydrogen decrepitation powders. The higher anisotropic fields of Pr2Fe14B and Ho2Fe14B are used to improve the coercivity. Then, the ZrCu strip-casting alloy is used as a diffusion source. A Zr-rich layer is uniformly coated on the surface of the powders after the first-step diffusion, which prevents the growth of the MM-rich main phase grains during the sintering process and the inter-diffusion between the two main phases, thus obtaining high coercivity.