Magnetic hardening of the Pr 2Co 14B-based rapidly quenched alloys

Abstract

Pr 2Co 14B-based permanent magnets have been prepared by heat treatment of melt-spun ribbons. The ribbons were produced using the melt-spinning technique at linear speeds of the wheel higher than 35 m/s. The as-spun ribbons were found to be ‘X-ray amorphous’ with a near-zero intrinsic coercivity and saturation magnetization of 80–100 emu/g depending on the composition. Upon annealing at temperatures above 560°C, the intrinsic coercivity increases sharply reaching values higher than 15 kOe. At the same time the saturation magnetization decreases sharply. At high heat treatment temperatures (800–1000°C) the intrinsic coercivity drops slightly and the saturation magnetization increases largely. Thermomagnetic analysis (TMA) of the amorphous as-spun ribbons revealed that their Curie and crystallization temperatures are approximately 520 and 560°C, respectively. During crystallization from the amorphous state, the first phase to precipitate is Pr 2Co 14B followed by the PrCo 4B phase. At high temperatures a third phase appears which, depending on the alloy composition, can be the PrCo 5 or the PrCo 12B 6. The development of the magnetic properties following heat treatment at different temperatures can be interpreted in terms of the phases generated at each temperature. The tendency towards the formation of these phases can be interpreted in terms of the Pr-Co-B phase diagram. No PrCo 2 phase has been observed in the alloys. The maximum energy product of the isotropic Pr 2Co 14B-based permanent magnets is about 5 MGOe. The properties of Nd 2Co 14B-based rapidly quenched permanent magnets can be discussed in a way similar to the Pr 2Co 14B magnets. Their intrinsic coercivity and maximum energy product are about 10 kOe and 5.5 MgOe, respectively.