Study On The Preparation And Microstructure And Magnetic Properties Of Sm₂(Fe,M)₁₇N_x (M=Zr) Magnetic Powers

The preparation of Sm-F-N alloy is a very complex process and it's magnetic properties are affected by many factors, so it is the purpose for this paper to investigate concrete method which optimizes the preparation of Sm2Fe17Nx alloys, makes the cost lower and magnetic properties higher. It has important significance to realize the commercialization of Sm2Fe17Nx permanent magnet materials. Sm2Fe17 and Sm2(Fe,Zr)17 with different contents are prepared by a vacuum arc furnace and tranditional power metallurgical method. The analysis and measurement of the microstucture and magnetic properties are carried out using scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction technique, thermo-gravimetric analyzer and vibrating sample magnetometer etc. A processing used to obtain the Sm2Fe17 phase without a-Fe in the as-cast state is described. The method consists of adding 1.0% of zirconium to the melt.The effect of the melting-current and melting-time on the microstructure of the as-cast Sm-Fe alloy is investigated and the phase composition of the as-cast Sm-Fe alloy with different Sm content is analyzed. The parameters of the melting process and the proportion between different chemical elements are decided, which are based on the above-mentioned investigation and analysis. By analyzing the microstructure and phase composition of Sm-Fe alloy annealed and nitrided for different time using scanning electron microscopy and X-ray diffraction technique, the optimum values for the annealing time and the nitriding time is determined.The phase composition and microstructure of Sm-Fe-Zr alloy with different amount of Zr are analyzed and the effect of Zr content on the microstructure of as-cast Sm-Fe-Zr alloy is studied. The results indicate that microstructure of as-cast Sm-Fe-Zr alloy is improved obviously with 1.0at% Zr added, and that the long-time high temperature homogenization is unnecessary for the alloys with this microstructure. By this way, the purpose of the research to decrease the cost of preparation and optimize process is achieved. The principle of the effect of Zr additions on the microstructure and phase composition of as-cast alloys is discussed detailedly by establishing appropriate model, which makes progress in theoretical study.Comparison of the data from diffusion experiments conducted on thin plates and powers ofthe Sm-Fe alloy and Sm-Fe-Zr alloy in nitrogenation reveal the behavior of N atoms in Sm-Fe alloy and Sm-Fe-Zr alloy. To calculate the diffusion parameters in theory, the Fick second law is used. The calculational results provide valid evidence for determining the nitriding time. The reason for which causes the difference between the real results and the theoretical calculation is analyzed. The change of lattice constants and the cell volume expansion are calculated, which make an important contribution to the increase of the magnetocrystalline anisotropy.By investigating the magnetic properties of Sm-Fe and Sm-Fe-Zr magnetic powers with different composition, different nitriding time and different milling time, the relationship between the magnetic properties and different composition and parameters of process is achieved. Some important factors to affect the magnetic properties of Sm-Fe and Sm-Fe-Zr magnetic powers are discussed. The conclusion is that the main reason for making the magnetic properties lower is because the radius of the particles of magnetic powers is too large and the distribution is irregular, which can't result in obtaining the single-domain particles .