Study On The Process, Microstructure And Magnetic Properties Of Sm₂Fe₁₇N_x Magnets With HDDR

The preparation of Sm₂Fe₁₇N_x magnets with HDDR is a very complex process and it's magnetic properties are affected by many factors, so it is the purpose of this paper to investigate the microstructure of each process and their influence to the magnetic properties which optimizes the preparation of Sm₂Fe₁₇N_x magnets. And the paper provides the direct of the development and the existing problems. It is shown that the volatility of Sm can be reduced by adding Sm later and controlling the melting-efficiency and the melting-time strictly. The growing of the α-Fe can be controlled by increasing the cooling velocity of the as-cast. To optimize the cooling velocity of the as-cast alloy by investigating the microstructure of Sm-Fe alloy with different cooling velocity, the volatilize of Sm can not avoid when melting, it will not obtain the single phase Sm₂Fe₁₇ alloy if the compensate of Sm is too much or too short. And the optimal compensate of Sm can be determined by investigate the changing of the Sm-Fe alloy's microstructure of before and after the annealing with different Sm compensate. At these bases the optimal annealing temperature and time are obtained by analyze the microstructure and the phase composition of the Sm-Fe alloy with different annealing-time. The mechanism and the phase composition's evolution of the HDDR can be summarized from analyzing the phase composition and the microstructure of the Sm-Fe alloy in the different stages of the HDDR process. And the physical models of the changing of the microstructure in the HDDR process are established by analyzing the principle detailed. The size of the grain of the powder is not changed after the HDDR process but the size of the crystalline grain will be fined. The micro-crack emerging from the HDDR process can provide passages for the nitrogenation process, and the activity of the Sm2Fe17 powder can be improved greatly. The proper nitrogenation processes are determined by the simple investigating of the process and the mechanism of the nitrogenation. The proper process is obtained by investigating the effect of the milling-time and the hydrogenation process and the recombination process to the Sm2Fe17Nx magnets'magnetic properties. The conclusion is that: The proper milling-time is 20min. The proper hydrogenation process is adding hydrogen in lower temperature, then rising to 750 ℃slowly, and keeping an hour at 750 ℃. The proper recombination process is keeping in 800℃for 2 hours. The properties of the Sm2Fe17Nx magnets we obtained followed by the optimized processes: Br=0.5154T, Hcj=1300kA/m, (BH)m=40kJ/m3. At the same time, the reasons that existing in each processes which can decline the properties of the Sm2Fe17Nx magnets are all analyzed in this paper; it is point that the α-Fe is the main factor to decline the properties.