The difference between conventional neodymium iron boron magnets and cerium containing magnets
What are the differences between cerium magnets and sintered neodymium iron boron permanent magnets produced by conventional processes? Is there a difference in magnetic properties? Will it be more brittle and prone to breakage? This is the most concerning issue for many magnet users, and in today's article, we will provide a detailed explanation for everyone.
Cerium Ce element has a variable valence characteristic and a small ionic radius. When the Ce content is high, it is easy to form CeFe2 phase, making it difficult for the magnet to achieve high coercivity. Due to the low saturation magnetization and anisotropic field of CeFeB, diffusion processing is usually required after adding Ce to the magnet to further improve its performance.
When the amount of Ce element added is relatively small, the impact on diffusion performance can be basically ignored. When the amount of Ce magnet added is relatively large, especially after more than 12%, the microstructure of the magnet deteriorates more severely. Not only does it significantly reduce the improvement of diffusion performance, but it also leads to the deterioration of magnet squareness due to the non-uniformity of microstructure.
From a usage perspective, when the Ce content of the substrate is low, under the same Br and Hcj conditions, there is no significant difference in the magnetic moment and high-temperature demagnetization effect between Ce containing and cerium free magnets, and their usage characteristics are basically the same. When the cerium content of the substrate is greater than 8%, especially 12%, special attention should be paid to the phenomenon of incomplete saturation magnetization and high-temperature demagnetization caused by the dual factors of low Hcj and low squareness, in order to avoid the phenomenon of residual magnetization but insufficient magnetic moment and coercivity but insufficient thermal demagnetization.
There are also certain differences in temperature resistance between the conventional process preparation and diffusion process preparation of cerium magnets.
Compared to conventional magnets, the mechanical properties of Ce doped magnets will also deteriorate with changes in Ce content during processing and use.
The deterioration of the mechanical properties of Ce doped magnets is mainly due to the formation of CeFe2 phase after excessive Ce addition, which greatly destroys the infiltration and coupling effect of grain boundaries relative to the main phase grains, resulting in a significant decrease in mechanical properties. Relevant experimental data shows that when the Ce addition is greater than 10%, the mechanical properties of Ce magnets even decrease by 20-50%. The mechanical performance indicators include hardness, compressive strength, flexural strength, tensile strength, impact toughness, Young's modulus, etc. The decrease in mechanical properties makes neodymium iron boron magnets, which are already brittle, more prone to corner dropping or even cracking during processing, magnetization, and assembly.
In summary, when using ultra-high Ce magnets, we must pay great attention to the poor diffusion effect caused by high Ce, uneven microstructure of the product, local weak magnetic areas, easy demagnetization at high temperatures, and reduced mechanical properties. Currently, with the continuous advancement of process technology, more and more enterprises are paying attention to and overcoming the technical difficulties of CeFe2, and these high Ce accompanying problems are gradually being weakened.