Preparation And Properties Of Sintered Sm(Co_0.717Fe_0.15Cu_0.10Zr_0.033)_7.2 Permanent Magnets With ZrB₂ Addition

New-type 2:17 SmCo permanent magnets are the best choice in high tempweature application area because of its high magnetic properties,good temperature stability, high curie temperature(about 825℃)and low temperature coefficient.But its low strength and toughness leads to poor machinability and costly fabrication, and limit its use in some rigorous area.Up to now, there is quite few studies on strength and toughness of this materials and the mechanism of fracture is not determined. The systematic investigations on the improvement of sintered SmCo permanent magnetic materials have been rarely reported.In this paper,the magnets were prepared by powder metallurgy .Powders of ZrB₂ wereadded during ball milling process.The effect of ZrB₂ addition on the sinter and heat treatment technics, magnetics and mechanics properties were intensively studied. The magnetic properties and fracture toughness were measured, the microstructure and fracture surfaces were observed by SEM.The results showed that the sintering and heating treatment technics, magnetics and mechanics properties were affectted in different degree by the addition of ZrB₂.Some of the ZrB₂ particles distributed uniformly in the alloy,and the others decomposed to combine with Fe,Co to form low-melting point Co-Zr-Fe-B phase,which was helpful to accelerate the pyknosis process of the alloy,beacause of the change from solid-phase sintering to liquid-phase sintering,and lower the optimal sintering and heat treatment temperatures.With the addition of ZrB₂, the room-temperature magnetic properties of the magnets were increased sharply than the magnets without ZrB₂ addition. The optimal sinter and heat treatment processes of the alloy with 0.5%ZrB₂was sintered at 1190℃for 15min, heat treated at 1150℃for 2h. The magnetic properties of this magnet were B_r≈0.906T, H_cb≈618kA/m, H_ci≈1976 kA/m, (BH)_m≈140 kJ/m³,and the temperature coefficientα(27-200℃)≈-0.028%/℃,β(27-200)℃≈-0.031%/℃of magnet with 0.5%ZrB₂ was achieved.At the same time, the fracture toughness were increased obviously with the addition of ZrB₂, however, the fracture mechanism of magnets still was cleavage fracture. The improvement of the fracture toughness could be attributed partly to the increase of grain boundary thickness and bond strength, and the other to the dispersion strengthening of ZrB₂ particlesIn addition, The method of ball milling with refractory powerders was introduce to improve the mechanical propertie of the sintered SmCo permanent magnets, andimprovement of toughness was obtained without hazard to the magnetic properties.