METHOD FOR PRODUCING RFeB-BASED MAGNET, AND ALLOY FOR GRAIN BOUNDARY DIFFUSION PROCESS USED IN THE METHOD
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Solution Overview
Problem
RFeB-based magnets experience a decrease in coercivity and squareness ratio at high temperatures, which is a limitation for their use in applications like car drive motors where temperatures can rise to 130°C, and existing methods to improve these properties also lead to a reduction in remanence when excessive heavy rare earth elements are used.
Innovation Solution
A method involving the use of an RHdCu alloy with a Cu content of 20 mass% to 40 mass% for grain boundary diffusion in RFeB-based magnets, where RHd is either Dy, Tb, or Ho, to enhance coercivity and squareness ratio at high temperatures while maintaining remanence stability, by diffusing the heavy rare earth element through the grain boundary of the base material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heavy rare earth elements are added to improve coercivity, then coercivity increases, but remanence decreases when large amounts are present inside the crystal grain
Solution Approach 1:
The patent applies local quality by concentrating heavy rare earth elements specifically at the grain boundary region rather than distributing them uniformly throughout the crystal grain. The adhesion substance containing heavy rare earth elements is applied to the surface, and during heating treatment, these elements diffuse preferentially along grain boundaries to reach the vicinity of crystal grain surfaces. This localized distribution achieves high coercivity improvement while preventing remanence loss that would occur with bulk addition of heavy rare earth elements.
2Strength
If heavy rare earth elements are diffused into the sintered body to improve coercivity, then coercivity increases, but the elements tend to enter deep into the crystal grain causing remanence reduction
Solution Approach 1:
The patent uses grain boundaries as intermediary pathways for heavy rare earth element diffusion. By applying the adhesion substance containing heavy rare earth elements to the surface and heating to 700-1000°C, the elements diffuse preferentially along grain boundary regions. The grain boundaries act as diffusion channels that guide the heavy rare earth elements to the vicinity of crystal grain surfaces without allowing deep penetration into the crystal grain interior, thus achieving coercivity improvement while maintaining remanence stability.
3Strength
If conventional grain boundary diffusion method is used with low Cu content alloy, then heavy rare earth element diffusion is achieved, but coercivity and squareness ratio decrease at high temperatures
Solution Approach 1:
The patent applies parameter changes by optimizing the Cu content in the adhesion substance to a specific range of 20-40 mass%. This compositional parameter adjustment has a dual effect: Cu prevents excessive heavy rare earth element penetration into crystal grains while also improving high-temperature magnetic properties. The optimized Cu content within this range achieves both room temperature coercivity improvement through grain boundary diffusion and maintains coercivity and squareness ratio at elevated temperatures up to 130°C.
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 effectively increases coercivity and squareness ratio at 130°C, while minimizing the temperature coefficient of remanence and coercivity, providing stable magnetic characteristics over temperature changes, with optimal Cu content between 20 mass% and 40 mass% for improved performance.
Implementation Method 1
the heavy rare earth element in the adhesion substance is diffused into the sintered body through a grain boundary of a crystal grain of the sintered body serving as the base material
Implementation Method 2
heating to a temperature within a predetermined temperature range (typically 700° C. to 1000° C.)
Data Source
AI summary
The present invention relates to a method for producing an RFeB-based magnet, the method including: a base material preparation step of preparing a base material made of a sintered body of an RFeB-based alloy or a hot-deformed body of the RFeB-based alloy; an adhesion substance preparation step of preparing an adhesion substance containing an RHdCu alloy that includes Cu and a heavy rare earth element RHd to be diffused and that has a content of Cu of 20 mass % or more and 40 mass % or less; an adhesion step of adhering the adhesion substance to a surface of the base material; and a heating step of heating the base material to which the adhesion substance has been adhered to a predetermined temperature at which the heavy rare earth element RHd to be diffused is diffused into the base material through a grain boundary of the base material.