Surface-Modified Rare Earth Sintered Magnets Corrosion Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Rare earth metal-based sintered magnets face corrosion issues in fluctuating humidity environments, and existing oxidative heat treatment methods to enhance corrosion resistance often deteriorate magnetic characteristics due to excessive hydrogen generation.
Innovation Solution
A heat treatment process under controlled oxygen and water vapor partial pressures, forming a multi-layer surface modification with a main layer containing R, Fe, and oxygen, an amorphous layer, and an outermost hematite-based iron oxide layer, which provides corrosion resistance without compromising magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxidative heat treatment is performed under high water vapor partial pressure (10 hPa or higher) to improve corrosion resistance, then corrosion resistance is enhanced, but hydrogen is generated in large amounts causing embrittlement and deterioration of magnetic characteristics
Solution Approach 1:
The patent applies parameter changes by precisely controlling the water vapor partial pressure to be below 10 hPa during oxidative heat treatment. This parameter adjustment allows the formation of a protective oxide layer on the magnet surface while preventing excessive hydrogen generation that would cause embrittlement, thus resolving the contradiction between corrosion resistance and magnetic property preservation
Solution Approach 2:
The patent uses oxygen as a strong oxidant in the heat treatment atmosphere to accelerate the formation of a dense oxide layer on the magnet surface. This accelerated oxidation process creates effective corrosion protection without requiring high water vapor partial pressure, thereby avoiding hydrogen embrittlement while achieving the desired corrosion resistance
2Reliability
If oxidative heat treatment is performed to improve corrosion resistance in fluctuating humidity environments, then corrosion resistance is enhanced, but magnetic characteristics deteriorate due to oxidative reaction
Solution Approach 1:
The patent employs parameter changes by optimizing the oxygen partial pressure and temperature conditions during heat treatment. These controlled parameter changes enable the formation of a protective surface oxide layer while minimizing internal oxidation that would affect magnetic properties, thus resolving the contradiction between corrosion resistance and magnetic characteristic stability
Solution Approach 2:
The patent applies local quality by creating a differentiated structure where the surface layer is oxidized for corrosion protection while the bulk material maintains its original magnetic properties. The heat treatment parameters are controlled to ensure oxidation occurs primarily at the surface, providing localized corrosion resistance without compromising the overall magnetic characteristics of the magnet
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 achieves sufficient corrosion resistance in fluctuating humidity environments while maintaining the magnetic characteristics of the rare earth metal-based sintered magnets, as demonstrated by the surface-modified layer's composition and thickness.
Implementation Method 1
a heat treatment under an oxidative atmosphere, and this method has attracted attention as an easy technique for improving corrosion resistance
Implementation Method 2
the heat treatment conducted under such a high water vapor partial pressure atmosphere causes oxidative reaction on the surface of the magnet as to generate hydrogen as by-products in large amount
Data Source
Figure 1(a)~2
Figure 3~4
Figure 5~6
AI summary
An objective of the present invention is to provide a rare earth metal-based sintered magnet having imparted thereto sufficient corrosion resistance by an oxidative heat treatment, which is resistant even in an environment of fluctuating humidity, while suppressing the deterioration of the magnetic characteristics ascribed to the oxidative heat treatment, and to provide a method for producing the same. As a means of achieving the objective above, the surface-modified rare earth metal-based sintered magnet of the present invention is characterized in that the surface-modified part comprises a surface-modified layer comprising at least three layers formed in this order from the inner side of the magnet, a main layer containing R, Fe, B, and oxygen, an amorphous layer containing at least R, Fe, and oxygen, and an outermost layer containing iron oxide comprising mainly hematite as the constituent, and the method for producing the same is characterized in that it comprises a step of applying a heat treatment to a bulk magnet body in the temperature range of from 200 °C to 600 °C, under an atmosphere with oxygen partial pressure in a range of from 1×102 Pa to 1×105 Pa and water vapor partial pressure in a range of from 0.1 Pa to 1000 Pa (exclusive of 1000 Pa).