Effect of Annealing Conditions of High-Energy Ball-Milled Sm(Fe, CO, Ti)12 Alloys Doped with Zr on Microstructure and Magnetic Properties

The tetragonal R1-xZrx (FeCo)11Ti alloys, where R is a rare earth and T is a transition metal, are promising candidates for permanent magnets. Sm1-xZrx(Fe0.8Co0.2)12-yTiy (x=0 and 0.25; y=1 and 0.7) master alloys were prepared by arc-melting under argon atmosphere. The two samples with an atomic amount of Ti equal to 1 are almost single-phase 1:12 compounds with a small amount of a-Fe(Co), while after the replacement of Sm with Zr a third phase of the TbCu7 type appeared in the other two samples. The as-cast ingots were milled using high-energy ball milling (HEBM) for different times in an argon atmosphere then annealed at 973K-1173K at different interval times (15-90 min. After annealing, the sample milled for 4 h contains a large variation of grain size from 2-4 μ to 20 μ or larger. While the others sample milled for 8 h, after annealing exhibits grains size in the range of 2-6 μ, therefore their coercivity is higher, reaching a maximum value of 5.5 kOe for SmFe9Co2Ti annealed at 1123K for 60 min. Coercivity was strongly affected by the annealing temperature and time. The microstructure evolution with emphasis on the particles size during annealing and their correlation with coercivity will be discussed.