Effects of B Content on Structure Evolution and Magnetic Properties of Melt-Spun Fe90-xPt10Bx(x=15∼40) Alloys

The structure evolution and magnetic properties of melt-spun Fe90-xPt10Bx(x=15 similar to 40) alloys before and after annealing were investigated. The results show that the increase of x from 15 to 25 similar to 30 can improve the amorphous forming ability of the alloy, and the melt-spun structure transforms from a composite composed of amorphous and fcc-FePt phases to a single amorphous phase. Further increasing x to 35 and 40 results in the formation of fcc-FePt+Fe2B+FeB and L1(0)-FePt+FeB phases, respectively. After appropriate annealing, dual phases of fcc-FePt+Fe2B are formed for the alloys with x=15 similar to 20, which have soft magnetic properties, while the nanocomposite structure consisting of L1(0)-FePt together with Fe2B and/or FeB phases is obtained for the alloys with x=25 similar to 40, which exhibit the characteristics of the nanocomposite magnets. The best permanent magnetic properties are obtained for the alloy with x=30 annealed at 823 K for 900 s, of which the coercivity, remanence and maximum energy product are 173.2 kA/m, 1.20 T, and 88.3 kJ/m(3), respectively. The good permanent magnetic performance is due to the formation of a more fine and homogeneous L1(0)-FePt/Fe2B nanocomposite structure with an average grain size of about 15 nm.