R-Fe-B Sintered Magnet Core/Shell Structure for High Coercivity
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Solution Overview
Problem
Current R—Fe—B sintered magnets face challenges in maintaining high coercivity at elevated temperatures, particularly due to the instability and geopolitical risks associated with Dy and Tb resources, necessitating the development of new compositions and processes that minimize these elements while achieving high coercivity.
Innovation Solution
A method involving shaping alloy powder into a green compact, sintering, and then applying a powder of HR-containing compounds to the surface, followed by vacuum heating to allow HR elements like Tb, Dy, or Ho to permeate and diffuse, forming a core/shell structure with an HR-rich layer and an amorphous or nano-crystalline (R,HR)—Fe(Co)-M1 phase at the grain boundary, which enhances coercivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Dy or Tb are substituted for Nd in Nd2Fe14B compound to increase coercivity, then coercivity is improved, but resource stability and cost control deteriorate due to limited mining areas and price fluctuations
Solution Approach 1:
The patent applies local quality by concentrating Dy/Tb elements specifically at grain boundaries through controlled diffusion, rather than uniform distribution. This localized placement achieves maximum coercivity enhancement at the grain boundary regions where it is most needed, while minimizing overall Dy/Tb content in the magnet composition, thereby reducing resource dependency and cost.
Solution Approach 2:
The patent changes the distribution parameter of Dy/Tb elements from uniform distribution to gradient distribution with concentration maximum at grain boundaries. By controlling diffusion temperature and time parameters, the patent optimizes the spatial distribution of rare earth elements to achieve high coercivity with minimal total Dy/Tb content, resolving the contradiction between performance and resource stability.
2Reliability
If Dy or Tb content is minimized to improve resource stability, then resource stability is improved, but coercivity deteriorates
Solution Approach 1:
The patent makes the grain boundary region have different composition quality than the main phase by enriching Dy/Tb at grain boundaries while keeping bulk composition low in these elements. This localized enrichment achieves effective coercivity enhancement with minimal overall Dy/Tb content, simultaneously improving resource stability and maintaining high coercivity.
Solution Approach 2:
The patent creates a composite structure with distinct phases: a main phase with low Dy/Tb content and grain boundary phases enriched with Dy/Tb elements. This composite approach allows the magnet to achieve high coercivity through the Dy/Tb-rich grain boundary regions while the overall low Dy/Tb bulk composition ensures resource stability and cost effectiveness.
3Strength
If cooling rate is increased to form R-Fe(Co)-Si phase at grain boundary to improve coercivity, then coercivity is improved, but manufacturing complexity increases due to precise cooling rate control requirements
Solution Approach 1:
The patent optimizes the cooling rate parameter within a specific range (0.1 to 5°C/min) to achieve the desired phase transformation at grain boundaries. By identifying and controlling this critical parameter range, the patent simplifies the manufacturing process while achieving high coercivity through formation of R-Fe(Co)-Si phase at grain boundaries without requiring overly complex process control systems.
4Adaptability or versatility
If Nd magnets are designed for high temperature applications to expand application range, then application versatility is improved, but coercivity at working temperature deteriorates due to significant decrease at elevated temperature
Solution Approach 1:
The patent applies preliminary action by pre-enriching Dy/Tb elements at grain boundaries during the manufacturing process, before the magnet is subjected to high temperature operating conditions. This advance preparation creates a protective grain boundary structure that maintains coercivity during subsequent high temperature operation, enabling the magnet to function reliably in elevated temperature applications.
Solution Approach 2:
The patent provides beforehand cushioning against high temperature degradation by creating Dy/Tb-rich grain boundary regions that act as protective barriers. These pre-formed grain boundary phases cushion the main phase from thermal effects that would otherwise cause significant coercivity decrease at elevated temperatures, thereby maintaining performance in high temperature applications.
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 approach results in R—Fe—B sintered magnets with coercivity of at least 10 kOe, even with minimal Dy, Tb, and Ho content, achieving improved magnetic properties and stability.
Implementation Method 1
heating the powder-coated magnet in vacuum at 700 to 1,100° C. for HR to permeate through the grain boundaries and to diffuse among the sintered magnet
Implementation Method 2
cooling the sintered compact to room temperature
Implementation Method 3
aging treatment including exposing at a temperature in the range of 400 to 600° C. which temperature is lower than the peritectic temperature of (R,HR)—Fe(Co)-M1 phase so as to form the (R,HR)—Fe(Co)-M1 phase at a grain boundary
Data Source
AI summary
The invention provides an R—Fe—B sintered magnet consisting essentially of 12-17 at % of R, 0.1-3 at % of M1, 0.05-0.5 at % of M2, 4.8+2*m to 5.9+2*m at % of B, and the balance of Fe, containing R2(Fe,(Co))14B intermetallic compound as a main phase, and having a core/shell structure that the main phase is covered with a HR-rich layer and a (R,HR)—Fe(Co)-M1 phase wherein HR is Tb, Dy or Ho. The sintered magnet exhibits a coercivity ≧10 kOe despite a low content of Dy, Tb, and Ho.