B含量对Fe90-xPt10Bx液态急冷合金组织结构和磁性能的影响

Effects of B content on structure evolution and magnetic properties of melt-spun Fe90-xPt10Bx alloys

摘要:

本工作研究了低Pt含量的Fe_90-xPt₁₀B_x (x=15~40,原子分数,%)系液态急冷合金热处理前后的组织结构和磁性能。结果表明,x由15增加至25~30可提高合金的非晶形成能力,急冷合金由非晶+fcc-FePt复相组织转变为单一非晶态结构；当x进一步增加至35和40时,合金分别由fcc-FePt+Fe₂B+FeB和L1₀-FePt+FeB纳米复相组织构成。经适当热处理后,x=15~20的合金具有fcc-FePt+Fe₂B复相组织而呈软磁性；x=25~40的合金形成了由有序面心四方结构的永磁L1₀-FePt相和软磁Fe₂B/FeB组成的纳米复相组织,显示出永磁特性,其中x=30的合金经823 K热处理900 s后具有最佳的永磁性能,矫顽力、剩磁和最大磁能积分别为173.2 kA/m,1.20 T和88.3 kJ/m^₃,其优异的永磁性能源于分布均匀、平均晶粒尺寸约为15 nm的永磁L1₀-FePt相和软磁Fe₂B相间的交换耦合作用。

Abstract:

The structure evolution and magnetic properties of melt-spun Fe_90-xPt₁₀B_x (x = 20–40) alloys before and after annealing have been investigated. The increase of x from 15 to 25–30 changes the melt-spun structure 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 L1₀-FePt + FeB phases, respectively. After appropriate annealing, dual phases of fcc-FePt + Fe₂B are formed for the alloys with x = 15–20, which have soft magnetic properties, while the nanocomposite structure consisting of L1₀-FePt together with Fe₂B and /or FeB phases are obtained for the alloys with x = 25–40, which exhibit the characteristics of the nanocomposite magnets. The best hard 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 hard magnetic performance is due to the formation of a more fine and homogeneous L10-FePt /Fe₂B nanocomposite structure with an average grain size of about 15 nm.