Bulk-hardened magnets based on Y2Co17

Abstract

Bulk magnetic hardening of cast Y2Co17-based alloys was systematically studied for different compositions and heat treatments. Additions of Cu and Zr, Hf, or Ti to the Y–Co were found to be essential for developing coercivity. The performance of Y–Co–Cu–Zr magnets can be significantly improved by partial Pr and Fe substitutions for Y and Co, respectively. Anisotropic (Y0.8Pr0.2)11.5Zr2.75Co56.75Fe14Cu15 powders with intrinsic coercivity of 7.8 kOe and energy product of 14.4 MG Oe were obtained after annealing at 900 °C for 15 min and cooling to 200 °C at the rate of 4 °C/min. We also explored the effects of some other rare earths (La, Nd, Gd) and transition metals (Mn, Ni) on the magnetic properties of the Y–Co–Cu–Zr magnets. The phases present and the microstructure were analyzed with x-ray diffraction, thermomagnetic analysis, and transmission electron microscopy. The cellular/lamellar microstructure of the bulk-hardened alloys is similar to that of Sm–Co–Cu–Zr magnets. Among the most noticeable distinctions in the Y–Co–Cu–Zr alloys are a smaller average size of 2:17 cells and a variety of Zr-rich phases, like Zr2Co11 and Zr6Co23. Although the Y2Co17 phase is known to have an “easy-plane” anisotropy, the x-ray diffraction experiments with magnetically oriented powders suggest that in the bulk-hardened Y–Co–Cu–Zr and Y–Co–Cu–Fe–Zr magnets the 2:17 phase has uniaxial anisotropy.