Study Of Phase Equilibriu And Magnetic Properties Of RE-Co-Cu(RE=Sm,Ce) Alloys

Since the discovery of Sm-Co permanent magnets,many studies have been made on its magnetic properties through synthesis,doping and other methods.Sm-Co permanent magnets containing Cu were studied by many researchers due to the advantages of high intrinsic coercivity,high temperature stability and good corrosion resistance.Sm-Co permanent magnets with the addition of rare earth metal Ce have been attracted extensivelyto comprehensively utilize rare earth metals.In order to clarify the effect of rare earth Ce on its microstructure in Sm-Co permanent magnets,the basic information such as phase composition,phase equilibria and phase stability of（Sm-Ce）-Co based alloys is still needed.In this work,phase equilibria,phase transitions and solidification behaviors of Sm-Co-Cu and Ce-Co-Cu ternary systems and the magnetic properties of Sm-Co-Cu alloys were studied experimentally.（1）The phase equilibria of Sm-Co-Cu ternary system were measured by X-ray diffraction（XRD）and scanning electron microscopy（SEM-EDS）.Ten binary intermetallic compounds,SmCo2,SmCo3,Sm2Co7,Sm5Co19,SmCo5,Sm2Co17,SmCu2,SmCu4,SmCu5 and SmCu6 were confirmed,while no ternary intermetallic compounds were detected in the present experiments.The solubility of the third element in binary intermetallic compounds was determined by EDS and lattice parameters method.According to the experimental results determined in this work and reported in the literature,the phase equilibria of the Sm-Co-Cu ternary system were calculated using the CALPHAD method,and reasonable thermodynamic parameters of Sm-Co-Cu ternary system were obtained finally.The calculated isothermal sections and vertical sections of Sm-Co-Cu ternary system agree well with the experimental results.The Scheil solidification module is used to predict the solidification path of the alloy.The results show that the experimental solidification structure is consistent with the calculated results.（2）The phase equilibria of Ce-Co-Cu ternary system were measured by X-ray diffraction（XRD）and scanning electron microscopy（SEM-EDS）.Ten binary intermetallic compounds,Ce Co₂、Ce Co₃、Ce₂Co₇、Ce₅Co₁₉、Ce Co₅、Ce₂Co₁₇、Ce Cu2、Ce Cu4、Ce Cu5 and Ce Cu6 were confirmed,while no ternary intermetallic compounds were detected in the present experiments.According to the experimental results determined in this work and reported in the literature,the phase equilibria of the Ce-Co-Cu ternary system were calculated using the CALPHAD method,and reasonable thermodynamic parameters of Ce-Co-Cu ternary system were obtained finally.The calculated results agree well with the experimental results.（3）The phase composition,phase structure and magnetic properties of Sm12Co88-x Cux（x=0,2,4,6,8,10）as-cast alloys and melt-spun ribbons were studied experimentally.The thermodynamics calculation was used to analyze the phase formation of Sm12Co88-x Cux alloys.The magnetic properties of Sm12Co88-x Cux melt-spun ribbons were measured by vibrating sample magnetometer（VSM）.Magnetic measurement results show that with the increase of Cu content,the coercivity（Hcj）increases gradually,while the remanence（Br）increases first and then decreases.When the Cu content is x≤2,the crystallinity of SmCo7 phase and internal microstructure of the ribbons can be improved by crystallization treatment,so as to improve the magnetic properties of the ribbons.However,when the Cu content is x>2,the magnetic properties of the aged ribbons are significantly improved.