| A type of nanocomposite permanent magnets mainly composed of nanosized hard L10-FePt and soft Fe2B magnetic phases can be obtained from Fe-Pt-B alloys, which show good hard magnetic properties because of the exchange-coupling between the magnetically hard and soft phases. However, the cost of the present alloys is still unacceptable for application due to the high price of platinum. Therefore, it is necessary to further reduce Pt content without detriment to the magnetic properties of the magnets. In this work, the melt-spun and crystalline structures as well as the magnetic properties of Pt-lean Fe-Pt-B alloys with high B concentrations were investigated. In addition, the effects of Co addition on the melt-spun structures and magnetic properties of the alloys were also investigated. The main reasults are shown as follows:1. For the melt-spun Fe90-xPt10Bx alloy ribbons, when x=15-20, the alloys formed fcc-FePt+amorphous phases; As x=25-30, a single amorphous phase was formed; When x = 35, the alloy formed fcc-FePt+Fe2B+FeB phases. After annealing, only soft fcc-FePt+ Fe2B+α-Fe magnetic phases were precipitated in the alloys with x=15-20; As for x= 25-30, the alloys finally crystallized into magnetically hard L10-FePt and soft Fe2B phases.2. For the melt-spun Fe70-xPtxB30 alloy ribbons, a single amorphous phase was formed in the alloys with x= 5-10; When x= 15, the alloy formed fcc-FePt+amorphous phase; As for x= 20, the alloy directly formed fcc-FePt+L10-FePt+Fe2B phases. After annealing, all the Fe-Pt-B alloys formed magnetically hard L10-FePt and soft Fe2B phases.3. In the Fe90-xPt10Bx alloy system, after annealing at appropriate temperatures, the alloys with x= 25-35 obtained hard magnetic properties. The coercivity (iHc), remanence (Br), reduced remanence (Mr/Ms) and maximum energy product (BH)max of the alloys were in the range of 100.1-173.2 kA/m,1.01-1.38 T,0.80-0.84 and 43.0-88.3 kJ/m3, respectively; With the increase of B content, the iHc, Mr/Ms and (BH)max rise gradually. After annealing at 823 K for 900 s, the best nanocomposite permanent magnet obtained from the amorphous Fe6oPtioB3o alloy exhibited the largest iHc of 173.2 kA/m and the highest (BH)max of 88.3 kJ/m3. The good hard magnetic propertises of this alloy originate from the exchange-coupling between the nanosized hard L10-FePt and soft Fe2B magnetic phases.4. After the optimized annealing treatment, in the Fe70-xPtxB30 alloy system, the alloys with x= 10-20 obtained hard magnetic properties. With the growth of Pt content, the iHc improves gradually. The iHc, BT, Mr/Ms and (BH)max of the permanent magnetic alloys were in the range of 173.2-523.1 kA/m,0.81-1.20 T,0.76-0.84 and 64.0-88.3 kJ/m3, respectively.5. The addition of Co element to the Fe55Pt10B30 alloy resulted in the formation of amorphous alloy ribbons. For the Fe55-xCoxPt15B30 alloys after annealing treatment, when x= 0-15, L10-(Fe, Co)Pt+(Fe, Co)2B phases emerged in the alloys; The alloys with x=30-45 crystallized into Llo-(Fe, Co)Pt+(Fe, Co)2B+(Fe, Co)B phases; As for x= 55, only magnetically soft fcc-CoPt and CoB phases were.formed. The as-annealed alloys with x= 0-45 displayed hard magnetic properties. The iHc, Br, Mr/Ms and (BH)max of the alloys were in the range of 190.1-391.1 kA/m,0.50-1.01 T,0.75-0.84 and 29.0-94.4 kJ/m3, respectively. The Fe40Co15Pt15B30 alloy annealed at 823 K for 900 s showed the best hard magnetic properties. The iHc, Br, Mr/Ms and (BH)max of this alloy were 275.9 kA/m,0.97 T,0.84 and 94.4 kJ/m3, respectively. |
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