Experimental Determination Of Phase Equilibrium And Magnetic Properties Of Rare Earth Sm-Co-Zr Alloys

Sm-Co-based permanent magnets with good magnetic properties at high temperature have been widely used in traction motors,aerospace and military industrial applications.At present,researchers have improved the magnetic properties of Sm-Co permanent magnets by adding Cu,Fe,Zr,and Ti to them.The addition of Zr elements into the Sm-Co alloy will form cellular structure,which not only has the effect of refining the grain,but also can homogenize the organization of Sm-Co alloy,thus improving the comprehensive magnetic properties of Sm-Co permanent magnets.In this work,phase equilibria of the Sm-Co-Zr ternary system at 1073 K and 773 K were determined.Study of the effect of Zr addition to Sm-Co alloys on phase organization and phase structure.And Study on the relationship between microstructure,properties and composition,wheel speed,heat treatment temperature of Sm-Co-Zr alloy melt-spun ribbun.The results of the study are as follows:（1）The phase equilibria of the Sm-Co-Zr ternary system at 1073 K and 773 K were investigated based on the combination of diffusion couple method and equilibrium alloy method.Alloy samples were prepared by arc melting,and diffusion couple samples were prepared by fixture method,instantaneous melting method and spark plasma sintering method.The scanning electron microscopy with energy dispersive spectrometry（SEM-EDS）,X-ray diffraction（XRD）and electron probe microanalysis（EPMA）were used to analyze the phase composition,phase composition and phase structure in the diffusion couple and alloy samples.No stable ternary intermetallic compounds in Sm-Co-Zr alloys were found at 1073 K and 773 K.The solubilities of Zr in intermetallic compounds Sm Co₂,Sm Co₃,Sm₂Co₇,Sm₅Co₁₉,Sm Co₅ and Sm₂Co₁₇ at 1073 K were determined to be 7.3 at.%,18.6 at.%,9.9 at.%,5.1 at.%,1.4 at.%and 4.9 at.%,respectively,while those of Zr in these intermetallic compounds at 773 K was measured to be 4.3 at.%,17.4 at.%,9.5 at.%,1.9 at.%,0.9 at.%and 5.6 at.%.Meanwhile,the solubility of Sm in Co₂₃Zr₆ was measured to be 6.5 at.%and 5.1 at.%at 1073 K and 773 K,respectively,while the solubility of Sm in other intermetallic compounds is very limited（less than 2at.%）.（2）Sm(Co_1-xZrx)₇（x=0.02-0.08）melt-spun ribbons were prepared by arc melting and melt-spun methods.The microstructure of the melt-spun ribbons and magnetic properties were investigated using scanning electron microscopy（SEM）,X-ray diffraction（XRD）,and vibrating sample magnetometer（VSM）.The experimental results show that the coercivity of Sm(Co_1-xZr_x)₇（x=0.02～0.08）melt-spun ribbons gradually becomes larger with the increase of x content,and the maximum coercivity（Hcj）of 7.34 k Oe is obtained at x=0.08（wheel speed of 45 m/s）.when the Sm(Co_1-xZr_x)₇（x=0.08）melt-spun ribbons of wheel speed is 45 m/s and heat treatment at 623 K for 2 hrs,the melt-spun ribbons has the best comprehensive magnetic properties（coercivity（Hcj）of 7.67 k Oe,remanence（Br）of2.81 k Gs,and maximum magnetic energy product（BH）max of 7.64 MGOe）.