R-Fe-B Sintered Magnet Grain Boundary Diffusion
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Solution Overview
Problem
Existing R—Fe—B base sintered magnets face challenges in achieving high coercivity while minimizing the content of Dy, Tb, and Ho, which are scarce and have unstable prices, limiting their market expansion, especially for high-temperature applications.
Innovation Solution
A method for preparing R—Fe—B base sintered magnets with a composition of 12-17 at% R, 0.1-3 at% M1, 0.05-0.5 at% M2, 4.8+2×m to 5.9+2×m at% boron, up to 10 at% Co, and the balance Fe, containing an intermetallic compound R2(Fe,(Co))14B as a main phase, and a grain boundary phase of (R′,HR)—Fe(Co)-M1 phase, where R′ is yttrium or rare earth elements excluding Dy, Tb, and Ho, and HR is Dy, Tb, or Ho, with HR rich phases formed via grain boundary diffusion.
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 the content of scarce and expensive elements increases
Solution Approach 1:
The patent applies local quality by concentrating Dy and Tb elements specifically at the grain boundary regions rather than uniformly distributing them throughout the magnet. This is achieved through controlled cooling rates (0.1 to 5°C/min) from 700°C to 500°C during sintering, which causes these rare earth elements to segregate and form an R-Fe(Co)-Si grain boundary phase locally. This localized enrichment provides the necessary coercivity enhancement while minimizing the overall content of expensive Dy and Tb in the bulk material.
Solution Approach 2:
The patent utilizes parameter changes by controlling the cooling rate during sintering (0.1 to 5°C/min from 700°C to 500°C) to alter the phase formation and element distribution. This controlled thermal parameter change enables the formation of a specific grain boundary phase composition that enriches Dy and Tb at grain boundaries, thereby achieving high coercivity with reduced overall rare earth content.
2Reliability
If high coercivity is preset at room temperature to ensure acceptable coercivity at service temperature, then high-temperature performance is improved, but the cost and scarcity issues of Dy and Tb are exacerbated
Solution Approach 1:
The patent addresses high-temperature reliability by locally enriching grain boundary regions with Dy and Tb elements through controlled phase formation. The slow cooling process (0.1 to 5°C/min) creates an R-Fe(Co)-Si grain boundary phase that concentrates these elements at critical grain boundary positions, providing localized magnetic shielding that maintains coercivity at elevated temperatures without requiring high overall concentrations of expensive rare earth elements.
Solution Approach 2:
The patent employs composite material strategy by creating a two-phase structure: a main R2Fe14B phase and a specialized R-Fe(Co)-Si grain boundary phase. This composite structure allows the grain boundary phase to perform the specific function of maintaining coercivity at high temperatures through localized Dy and Tb enrichment, while the bulk material maintains lower overall rare earth content, reducing cost and scarcity concerns.
3Adaptability or versatility
If R-Fe-B magnets are designed for high-temperature service applications, then adaptability to high-temperature environments is improved, but the requirement for high coercivity increases the dependency on scarce elements
Solution Approach 1:
The patent enables high-temperature service adaptability through local quality enhancement at grain boundaries. By controlling the cooling rate (0.1 to 5°C/min) to form an R-Fe(Co)-Si grain boundary phase enriched with Dy and Tb, the patent creates localized regions that provide the necessary magnetic stability at elevated temperatures. This approach allows the magnet to adapt to high-temperature environments without requiring high bulk concentrations of scarce elements.
Solution Approach 2:
The patent uses parameter changes in the sintering and cooling process to achieve high-temperature adaptability. The controlled cooling rate (0.1 to 5°C/min from 700°C to 500°C) is a critical parameter change that drives the formation of the grain boundary phase with appropriate Dy and Tb distribution. This parameter control enables the magnet to achieve the necessary thermal stability and coercivity retention for high-temperature applications with minimized rare earth content.
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 method successfully enhances coercivity of R—Fe—B base sintered magnets with minimal Dy, Tb, and Ho content, achieving high coercivity and remanence, suitable for high-temperature applications, while reducing the reliance on scarce and expensive elements.
Implementation Method 1
compression shaping the alloy fine powder in an applied magnetic field into a compact
Implementation Method 2
sintering the compact at a temperature of 900 to 1,250° C. into a sintered body
Implementation Method 3
cooling the sintered body to a temperature of up to 400° C.
Data Source
AI summary
An R—Fe—B base sintered magnet is prepared through the steps of providing an alloy fine powder having a predetermined composition, compression shaping the alloy fine powder in an applied magnetic field into a compact, sintering the compact at a temperature of 900-1,250° C. into a sintered body, cooling the sintered body to 400° C. or below, high-temperature heat treatment including placing a metal, compound or intermetallic compound containing HR which is Dy, Tb and/or Ho, on the surface of the sintered body, heating at a temperature from more than 950° C. to 1,100° C., for causing grain boundary diffusion of HR into the sintered body, and cooling to 400° C. or below, and low-temperature heat treatment including heating at a temperature of 400-600° C. and cooling to 300° C. or below. The sintered magnet produces a high coercivity despite a low content of Dy, Tb and Ho.