Nd5Fe17 Phase Rare-Earth Magnet Grain Control
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Solution Overview
Problem
Rare-earth sintered magnets with a Sm5Fe17 intermetallic compound as a main phase face challenges in maintaining high magnetic properties due to decomposition at high temperatures and low residual magnetization, leading to decreased coercivity and sintered density.
Innovation Solution
Control the average grain size and grain size distribution of Nd5Fe17 type crystal structure main phase crystal grains, ensuring a compositional ratio of 20-40 at% R and 50-99 at% Sm, with a sintering process that maintains particle size distribution and orientation in a magnetic field to prevent decomposition and enhance magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If heat treatment temperature is increased to improve sintering and magnetic properties, then residual magnetization can be increased, but the Sm5Fe17 phase decomposes and coercivity significantly decreases
Solution Approach 1:
The invention changes the compositional parameters by precisely controlling the Sm content (20-40 at%) and Fe content (50-99 at%) within specific ranges. This parameter optimization allows the material to maintain phase stability at sintering temperatures while achieving high residual magnetization, resolving the contradiction between improving magnetic properties and maintaining phase stability
Solution Approach 2:
The invention creates a composite microstructure consisting of the Sm5Fe17 main phase with controlled grain size distribution (80% of grains within 0.7Dv≤Di≤2.0Dv range) and specific grain boundary characteristics. This composite approach at the microstructural level enables simultaneous achievement of high residual magnetization and phase stability during sintering
2Quantity of substance
If sintering is performed to increase residual magnetization, then magnetic properties improve, but sintered density decreases due to phase decomposition
Solution Approach 1:
The invention performs preliminary grain size control during the powder preparation stage, ensuring that 80% of main phase grains fall within the specific size range (0.7Dv≤Di≤2.0Dv) before sintering. This preliminary action prevents excessive grain growth and phase decomposition during sintering, thereby maintaining both high residual magnetization and high sintered density
3Quantity of substance
If grain size is reduced to improve orientation and residual magnetization, then degree of orientation improves, but phase decomposition occurs at high temperature
Solution Approach 1:
The invention optimizes the grain size distribution parameters by controlling the average grain size Dv and ensuring that 80% of grains satisfy 0.7Dv≤Di≤2.0Dv. This specific parameter range provides sufficient grain size for good orientation and high residual magnetic flux density, while being small enough to prevent phase decomposition at sintering temperatures
Solution Approach 2:
The invention creates local quality differences through the grain size distribution control, where the majority of grains (80%) are within the optimal size range for both orientation and thermal stability. This localized optimization at the grain level allows the material to simultaneously achieve high residual magnetization and phase stability
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
Achieves high residual magnetic flux density and coercivity by maintaining the stability of the Nd5Fe17 phase, improving the magnetic properties and sintered density of the rare-earth sintered magnet.
Implementation Method 1
a rare-earth sintered magnet having main phase crystal grains having Nd5Fe17 type crystal structure
Implementation Method 2
a sintering process that maintains particle size distribution and orientation in a magnetic field to prevent decomposition and enhance magnetic properties
Implementation Method 3
orientation in a magnetic field to prevent decomposition and enhance magnetic properties
Data Source
AI summary
A rare-earth sintered magnet contains main phase crystal grains having an Nd5Fe17-type crystal structure, includes R and T (where R represents one or more rare-earth elements that essentially include Sm and T represents Fe or one or more transition metal elements that essentially include Fe and Co), and wherein the compositional ratio of R is 20-40 at % and the remaining portion is substantially T; the remaining portion other than R is substantially only T or only T and C; and when the main phase crystal grains' average grain size in one cross-sectional surface of the rare-earth sintered magnet is defined as Dv, while grain size of individual main phase crystal grains is defined as Di, Dv is at least 1.0 μm, and the main phase crystal grains' area ratio that satisfy 0.7Dv≤Di≤2.0Dv is at least 80% with respect to the area of a cross-sectional surface of the rare-earth sintered magnet.