Phase Equilibria And Magnetic Properties Of Sm-Co-Ti Alloys

SmCo₅ and Sm₂Co₁₇ series of Sm-Co based high temperature permanent magnet material have been widely used due to their excellent magnetic properties.Recently,SmCo₇based permanent magnet material have been attracted attention.SmCo₇ phase with TbCu₇-type structure is a metastable phase in the Sm-Co binary system,in order to obtain the stable SmCo₇ phase,the transition elements are usually added to Sm-Co alloys.Among the transition elements,Ti element can not only stabilize SmCo₇ phase,and also improve magnetic properties of SmCo₇ based permanent magnets.The phase equilibria information on the Sm-Co-Ti ternary system is an important basis for the design and fabrication of SmCo₇based permanent magnets.Therefore,in this paper,the phase equilibria in Sm-Co-Ti ternary alloys and the phase structure and magnetic properties of related compounds were experimentally determined,and the results are as follows:（1）The phase equilibria in the Sm-Co-Ti ternary alloys at 1073 K and 773 K were determined using diffusion couples and equilibrated alloys by using scanning electron microscopy（SEM）with energy dispersive spectroscopy（EDS）,electronic probe microanalysis（EPMA）and X-ray diffraction（XRD）techniques.The ternary intermetallic compound Sm Ti_xCo_12-x（τ）with Th Mn₁₂-typed structure was confirmed to be stable at 1073K and 773 K.The composition of this compound were determined to range from 9.3 to 17.5at.%Ti at 1073 K and from 9.4 to 15.6 at.%Ti at 773 K,respectively.SmCo₇ metastable phase with TbCu₇-type structure was found to be stable at 773 K in the Sm-Co-Ti ternary system,while it was not found at 1073 K.（2）The ribbons of SmCo_7-xTi_x（x=0,0.15,0.3,0.45,0.6）at various speeds were prepared by arc melting and melt-spinning,meanwhile,the SmCo_6.55Ti_0.45 ribbons annealed at several temperatures between 573 K and 1073 K for 1.5 h.The effects of Ti content,wheel speed and heat treatment on the structure and magnetic properties of SmCo_7-xTi_x ribbons were investigated,respectively.The results showed that the addition of Ti contributed to the formation of the SmCo₇ phase with TbCu₇-type structure,and the melt-spun ribbons at the speed of 40 m/s all formed a single TbCu₇-type structure.When the speed was 30 m/s,the SmCo_6.7Ti_0.3 melt-spun ribbons had good magnetic properties,its coercivity(H_cj)was 4.0k Oe,and the remanence（B_r）was 4.55 k Gs,respectively.The structure of the ribbons did not change significantly when the heat treatment temperature were between 573 K and 873 K,but the ribbons undergoed an obvious phase transition at 973 K to 1073 K,and decomposed into Sm₂Co₁₇ phase and SmCo₅ phase,resulting in a rapid decrease in its coercivity and the magnetic properties deteriorated.