Effects of Nb Content on the Microstructure and Magnetic Properties of the Sm.Zr.(Fe.Co.).- Ti.Nb (x=0 0.4, at.%) Alloys

ThMn12-type SmFe12-based magnet is suggested to be a promising permanent magnet because of its intrinsic magnetic properties and thermal stability. However, their potential applications are currently limited, as the existence of a soft magnetic alpha-Fe phase in the alloy deteriorates the hard magnetic properties. Hence, in this work, Nb element was introduced into the SmFe12 alloy to inhibit the precipitation of alpha-(Fe, Co) phase, and the effects of Nb addition on the microstructure and magnetic properties of melt-spun, hot-pressed (HP), and hot-deformed (HD) Sm1.2Zr0.2(Fe0.8Co0.2)11.5-x Ti0.5Nbx (x = 0-0.4, at.%) alloys were systematically investigated. Experimental results indicate that the additional Nb element could increase the glass-forming ability and thus inhibit the formation of the alpha-(Fe, Co) phase in the melt-spun ribbon. However, a zero-field shoulder appears in the demagnetization curves of the heat-treated ribbons due to the appearance of alpha-(Fe, Co) phase, which could be suppressed by the HP process. As a result, the coercivity of Nb = 0.2 HP magnet reaches 3.8 kOe, and the magnetic energy product (BH)max reaches 58.40 kJ/m3. Furthermore, a weak (001) texture of the 1:12 phase is obtained for the one-step HD magnet from the amorphous ribbons, which results in a remanence Jr of 0.11 T higher in the direction parallel to the c-axis compared to the direction perpendicular to the c-axis. The present result suggests a route to fabricate high-performance bulk SmFe12-based permanent magnets.