预退火时间对Fe_(80.8)B_(10)P_8Cu_(1.2)非晶合金微结构及磁性能的影响

研究了预退火时间对Fe_(80.8)B_(10)P_8Cu_(1.2)非晶合金微结构及磁性能的影响.穆斯堡尔谱研究表明:在660 K的预退火温度下,随着预退火时间的增加,Fe原子不断富集,非晶基体中的类Fe_3B化学短程有序结构向类Fe B结构转变,并且非晶基体中Fe第一近邻壳层中Cu原子的逐渐脱离以及Fe-P配位键数量的明显减少可间接表征CuP团簇的形成过程.同时,本研究通过调节预退火时间来调控非晶基体中CuP团簇和Fe团簇的数量,促进后续退火晶化过程中α-Fe纳米晶相的析出,并细化纳米晶尺寸,从而获得综合磁性能更加优异的非晶/纳米晶软磁合金.

Effects of relaxation time on local structural and magnetic properties of Fe80.8B10P8Cu1.2 amorphous alloy

Over past decades, Fe-based amorphous and nanocrystalline alloys have aroused a popular research interest because of their ability to achieve high saturation magnetic flux density and low coercivity, but the mechanisms for modifying annealing-induced magnetic properties on an atomic scale in amorphous matrix due to structural relaxation has not been enough understood. In this work, we study the effects of pre-annealing time on local structural and magnetic properties of Fe_80.8B₁₀P₈Cu_1.2 amorphous alloy to explore the mechanisms for structural relaxation, particularly the evolution of chemical short range order. The alloy ribbons, both melt spun and annealed, are characterized by differential scanning calorimetry, X-ray diffractometry, Mössbauer spectroscopy and magnetometry. The magnetic hyperfine field distribution of Mössbauer spectrum is decomposed into four components adopting Gaussian distributions which represent FeB-, Fe₃P-, Fe₃B- and α-Fe-like atomic arrangements, respectively. The fluctuation of magnetic hyperfine field distribution indicates that accompanied with the aggregation of Fe atoms, the amorphous structures in some atomic regions tend to transform from Fe₃B- to FeB-like chemical short-range order with the pre-annealing time increasing, but the amorphous matrix begins to crystallize when the pre-annealing time reaches 25 min. Before crystallization, the spin-exchange interaction between magnetic atoms is strengthened due to the increase of the number of Fe clusters and the structure compaction. Thus, saturation magnetic flux density increases gradually, then shows a drastic rise when there appear α-Fe grains in the amorphous matrix. Coercivity first declines to a minimum after 5 min pre-annealing and then increases drastically. This is attributed to the fact that excess free volume and residual stresses in the melt spun sample are released out during previous pre-annealing, which can weaken magnetic anisotropy significantly, while the subsequent pre-annealing destroys the homogeneity of amorphous matrix, resulting in the increase of magnetic anisotropy. In addition, the separation of Cu atoms from the first near-neighbor shell of Fe atoms and the obvious decrease in the Fe-P coordination number suggest the formation of CuP clusters, which can provide heterogeneous nucleation sites for α-Fe and contribute to the grain refinement. Therefore, through controlling the pre-annealing time, we successfully tune the content values of CuP and Fe clusters in the amorphous matrix to promote the precipitation of α-Fe and refine grains during crystallization. For Fe_80.8B₁₀P₈Cu_1.2 nanocrystalline alloy, an enhancement of soft magnetic properties is achieved by a pre-annealing at 660 K for 5-10 min followed by a subsequent annealing at 750 K for 5 min.