Ce Substitution Level in NdFeB Magnets
Ce substitution level in Nd-Fe-B magnets has been significantly increased via the binary main phase (BMP) approach, i.e. sintering the mixture of Ce-free and Ce-containing RE 2 Fe 14 B (RE, rare earth) powders. REFe 2 phase that forms in the high Ce-containing Nd-Ce-Fe-B magnets has been considered to be harmful to magnetic performance due to its soft magnetism. In this work, we found that REFe 2 phase with lower melting point than the 2:14:1 phase plays positive role on optimizing the microstructure and retaining magnetic performance of the Nd-Ce-Fe-B BMP magnets. The wettability of 2:14:1 phase can be improved by sintering above the melting point of REFe 2 phase, which promotes densification of the magnet and the formation of continuous and smooth grain boundary (GB) phases. This contributes to the weakened short-range exchange coupling between adjacent grains, hence ensures superior magnetic performance of BMP magnets to the single main phase (SMP) ones with the same average composition.
The influence of zirconium addition and process parameters on the magnetic properties of Pr-Fe-B sintered magnets
Sintered magnets based on the compositions Pr 16Fe 76B 8 and Pr 16Fe 75.5B 8Zr 0.5 were produced using the hydrogen decrepitation process. Sintered magnets prepared under specific processing conditions from the zirconium-free alloy exhibited excellent remanence (1.22 T), intrinsic coercivity (1.22 T) and energy product (278 kJm -3). The squareness factor of magnets prepared from the Pr 16Fe 75.5B 8Zr 0.5 alloy was improved considerably (0.96). This investigation also shows the remarkable influence of zirconium addition on the intrinsic coercivity of these permanent magnets.
Effects of powder flowability on the alignment degree and magnetic properties for NdFeB sintermagnets
The magnetic powders for sintered NdFeB magnets have been prepared by using the strip casting (SC), hydrogen decrepitation (HD) and jet milling (JM) techniques. The effects of powder flowability and addition of a lubricant on the alignment degree and the hard magnetic properties of sintered magnets have been studied. The results show that the main factor affecting powder flowability is the aggregation of magnetic particles for powders in a loose state, but it is the friction between the powder particles for powders that are in a compact state. The addition of a lubricant with suitable dose can slightly prevent the congregating of powders, obviously decrease the friction between the powder particles, improve the powder flowability, and increase the alignment degree, remanence and energy product density of sintered magnets. Mixing a suitable dose of lubricant and adopting rubber isostatic pressing (RIP) with a pulse magnetic field, we have succeeded in producing the sintered NdFeB magnet with high hard magnetic properties of Br=14.57KG, jHc =14.43KOe, ( BH) max=51.3MGOe.
Effects of Hot Pressing and Deforming on the Microstructure and Properties of NdFeB Magnets
In this paper, the NdFeB magnets were prepared by hot pressing and deforming, the influence of pressing temperature, pressing strain, deforming temperature, deforming rate and amount on the density, hardness and magnetic properties of magnets were analyzed with the microstructure analysis. The results show that the density of the magnets and the hardness increase with the increase of the hot pressing temperature and pressure, but the hardness decreases when the pressing temperature reaches 800 ℃ .After thermal deformation, the gap of the magnets reduced, the density is increased, the hardness becomes larger, and the grains are oriented in the direction of deformation, which leads to higher magnetic properties. However, when the deformation rate is too low, or the deformation temperature is too high, there is an abnormal phenomenon of grain growth, leading to the decrease of coercivity and harness of the material.