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 R_1-xZr_x(FeCo)₁₁Ti alloys, where R is a rare earth and Ti a transition metal, are promising candidates for permanent magnets. Sm_1-xZr_x(Fe_0.8Co_0.2)_12-yTi_y (x = 0 and 0.25; y = 1 and 0.7) master alloys were prepared by arc melting under argon atmosphere. Some of the samples were almost single-phase compounds at 1:12, with a very small amount of a-Fe(Co). Partially replacing Sm with Zr produced alloys with small amounts of Sm(FeCo)₂ Laves-type phases. The as-cast ingots were milled using high-energy ball milling (HEBM) for different times in an argon atmosphere and then annealed at 973 K-1173 K at different interval times (15-90 min). After annealing, the sample milled for 4 h contained a large variation of grain size from 2-4 μm to 20 μm or larger, while, after annealing, the other sampled milled for 8 h exhibited grains size in the range of 2-6 μm; therefore, their coercivity was higher, reaching a maximum value of 5.5 kOe for SmFe₉Co₂Ti annealed at 1123 K 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 are herein discussed.