Research On The Structure And Magnetic Properties Of Melt-spun PrCo₅ Ribbons

PrCo₅ compound,with strong magnetocrystalline anisotropic field HA, high saturation magnetization Ms and high Curie temperature Tc, has had the basic condition of being a permanent magnet. While it has not been applied practically, mainly due to the poor coercivity that results from the coarse microstructure. The Pr resources are rich and the price is very low, so the development of PrCo₅ permanent magnet is of great significance.The technology of rapid quenching (melt-spun) have extremely high cooling rate and the speed can be adjusted, so it is easy to obtain tiny and uniform microstructure.This technology has been widely applied in the production of bond NdFeB permanent magnets for its convenience and low energy consumption. Recently obvious crystalline texture had discovered in rapid quenched RCo₅ alloy, which made it possible to produce magnetically anisotropic bond RCo₅ magnet by rapid quenching.In this work, PrCo₅ ribbon is prepared by melt-spinning and the change rule of crystalline texture is investigated systemically and the Fe, C was added in an attempt to improve the coercivity. The main works are shown as follows:1. Ingots with composition of PrCo₅.4, PrCo₅.0 and PrCo4.6 were manufactured by arc-melting under the argon protection. According to the X-RAD spectrum, PrCo₅.4 is essentially single 1:5 phase, but there is a small quantity of other phases in the PrCo₅.0 and PrCo4.6 powder.Ribbon samples are obtained by melt-spinning the ingots with a wheel of speed of 5m/s, 15m/s, 25m/s and 35m/s. X-RAD spectrum indicates that there are obvious crystalline textures in all ribbons. In ribbon with low tangential velocity, the C-axis (easy axes) is parallel to the ribbon plane. With the increase of the wheel speed, C-axes are rotate to the perpendicular direction gradually. Magnetic measurement confirms this conclusion also. Coercivities measured along easy axes are smaller than that alone the hard axes, indicating that the coercivity mechanism belongs to domain wall pinning. At even high wheel speed, both X-RAD and magnetic measurement showed that the ribbons tend to be isotropic, and the velocity tending to be isotropic are large for the ribbons with more rare-earth.2. Substituted Fe for partial Co, PrCo_4.9Fe0.5, PrCo_4.4Fe1.0 and PrCo_3.9Fe1.5 ribbons were prepared with v =5 m/s, 15m/s, 25m/s and 35m/s. The crystalline and magnetic anisotropy are still exist and the change rules are similar to that of ribbons without Fe substitution, namely the C-axes is parallel to the ribbon plane at low wheel speed and perpendicular to the plane at high wheel speed. At even high speed the crystalline texture and magnetic anisotropy are getting vanished gradually. Due the substitution of Fe, the coercivity drop and the magnetion increase pronouncedly.3. In order to refine the microstructure and improved the permanent magnetic properties, C is doped in PrCo₅ ribbons. Ribbon's compositions are PrCo₅.4C0.2, PrCo₅.4C_0.4 and PrCo₅.4C0.6. There are still magnetism anisotropy after the C doping, but only exists in the sample with low quenching velocity and already weakened. We extrapolated that the C doping has suppressed the sample's anisotropy. Coercivities rise obviously for all samples, and there appear an optimal wheel speed at which the coercive reach its maximum value. Coercivity of PrCo₅.4C_0.4 ribbon with v=25m/s is 6151Oe, which is the maximum in all ribbons. As result of the increase of coercive, magnetic energy rapidly enhanced and reach 6.44MGOe for PrCo₅.4C_0.4 with v=35m/s. The reduced remanence of PrCo₅.4C_0.4 quenched at four velocities was all larger than 0.5 and reach 0.78 when the wheel speed reaches 35m/s, meaning that the crystal grains were very small and the exchange coupling between the crystal grains is very strong. Based on the results, we consider that the enhancement of coercive force is the result of the crystal grain refinement, for coercivity and crystal grain size are correlative closely. The C content has an optimal value of 0.4, at which the largest coercivity and the magnetic energy product have been obtained. The hysteresis loop of PrCo₅.4C0.2 and PrCo₅.4C0.6 quenched at some velocities appeared a waspwaist phenomenon, which is due to the existence of two magnetic phases with different coercivity. 4. Addition of both Co and C was expected to increase the magnetic energy product further. So PrCo_4.9Fe0.5C0.2,PrCo_4.9Fe0.5C_0.4 and PrCo_4.9Fe0.5C0.6are prepared. Generally, substituting of Fe for Co results in the decrease of coercivity and increase of residual magnetism. While doping of C has the contrary effect. As the combined effect, the biggest magnetic energy increased and the maximum of 7.22MGOe is obtained in PrCo_4.9Fe0.5C_0.4 with v = 35m/s. The change rule of coercive force versus Fe content is the same as that without Fe substitution. The optical C content is still 0.4.