Development of nanocrystalline soft magnetic alloy with high saturation magnetic induction produced in air

采用空气熔体纺丝法制备了具有高饱和磁感应强度和良好软磁性能的纳米晶Fe-Nb-B基软磁合金。Fe_<84>Nb_7B_9合金是Fe-Nb-B三元合金的典型成分，在空气中生成的Fe_<84>Nb_7B_9合金被极度氧化，表现出脆性。结果表明，含6 （% Nb）以下的三元合金获得了具有金属光泽的韧性带。此外，含6%或更低Nb的合金的B_s高于1.6 T。然而，由于合金具有由非晶相和粗α-Fe晶粒组成的混合淬火组织，合金表现出较差的软磁性能。这些颗粒在结晶后仍保留在纳米结构中，使材料的软磁性能恶化。研究了在Fe-Nb-B合金中添加不同元素对其淬火组织和纳米晶态软磁性能的影响。合金中在% P处同时更换1个B，在% Cu处同时更换0.1个Fe，使α-Fe在淬火状态下晶粒尺寸减小到纳米级，晶化后形成具有良好软磁性能的均匀纳米结构。基于随机各向异性模型的分析表明，要实现良好的软磁性能，需要具有小体积分数的晶间非晶相和高居里温度的均匀纳米结构。Fe_<84.9>Nb_6B_8P_1Cu_<0.1>合金在1 kHz时具有41,000的高磁导率，在1.4 T和50 Hz时具有0.11 W/kg的极低铁心损耗，并且比Fe_<84>Nb_7B_9合金的B_S高约1.61 T。

The nanocrystalline soft magnetic Fe-Nb-B based alloys, which can be produced by melt-spinning in air, with high saturation magnetic induction (B_s) as well as good soft magnetic properties have been developed. The Fe_<84>Nb_7B_9 alloy, which is the typical composition of the ternary Fe-Nb-B alloys, produced in air was extremely oxidized and showed brittleness. The ductile ribbons with the metallic luster were obtained for the ternary alloys with 6 at% Nb or less. Furthermore, higher B_s than 1.6 T has been obtained for the alloys with 6 at% Nb or less. However, the alloys exhibit inferior soft magnetic properties because the alloys have a mixed as-quenched structure composed of an amorphous phase and coarse α-Fe grains. These grains remain in the nanostructure after the crystallization and deteriorate the soft magnetic properties.The effect of the addition of some elements to Fe-Nb-B alloys on the as-quenched structure and the soft magnetic properties in the nanocrystallized state has been investigated. The simultaneous replacement of B by 1 at% P and Fe by 0.1 at% Cu in the alloy decreases the α-Fe grain size to the nano-scale in an as-quenched state and leads to a homogeneous nanostructure with good soft magnetic properties after crystallization. Analysis based on the random anisotropy model shows that a homogeneous nanostructure with small volume fraction of an inter-granular amorphous phase which has high Curie temperature is necessary for realizing the good soft magnetic properties. The Fe_<84.9>Nb_6B_8P_1Cu_<0.1> alloy exhibits high permeability of 41,000 at 1 kHz, very low core loss of 0.11 W/kg at 1.4 T and 50 Hz as well as higher B_S of about 1.61 T than that of the Fe_<84>Nb_7B_9 alloy.