铁基非晶/纳米晶复合结构软磁合金条带弯折塑性的研究

Fe-based amorphous/nanocrystalline composite alloys have been widely used in modern industry because of their superior soft magnetic properties such as higher saturation magnetization and good magnetic softness. However, the extremely brittle nature for the nanocrystalline Fe-based soft magnetic alloys has generally been recognized to be the most serious disadvantage which limited their engineering application. Very recently, we have reported the Fe-based nanocrystalline alloy ribbons with good bending ductility. It is recognized that the "micro-crack" generated by hardness indenter causes the decrease of Vickers' hardness than that of the as-spun amorphous alloy. This project aims to clarify the behaviors and mechanism of indentation and bending deformation on ductile Fe-based nanocrystalline alloy ribbons. Further, we will investigate the mechanism of the brittle/ductile nature through the level of atoms cluster i. e. to study the formation and evolution of micro-structure organization and its effect on bending ductility trough the interaction of micro-structure particles and amorphous matrix. On this basis, to propose some principles and laws on design ductile amorphous / nanocrystalline composite alloy ribbons, in order to lay the theoretical and technical foundation for the further development on the new type of Fe-based ductile nanocrystalline soft magnetic alloy system so as to meet the requirement to overcome the brittle nature.

铁基软磁非晶/纳米晶复合结构合金由于其优异的软磁性能和更高的饱和磁感应强度得到深入研究和广泛应用。但其合金条带不可避免地呈现弯折脆性，一直以来在极大程度上限制了该类材料应用的推广。最近，我们报道了具备弯折塑性的铁基软磁纳米晶合金条带，并发现其压入形变产生“微裂纹”导致合金硬度较退火前的非晶态有所下降。本研究在我们前期成果的基础上，进一步阐述塑性铁基纳米晶合金条压入和弯折变形的行为、规律与机制。进一步地，深入到原子团簇尺度层面研究铁基纳米晶合金条带呈现弯折塑性或脆性的机制。研究铁基非晶合金结晶过程中微结构的演化行为、规律与可控操作，以及微结构演化对合金条带弯折塑/脆性的影响作用与机制。在此基础上，提出一些设计塑性非晶/纳米晶复合结构条带合金成分与制备工艺的原则和规律，为今后进一步开发新型塑性铁基软磁纳米晶合金系奠定理论和技术基础，以满足人们长期以来希望克服铁基纳米晶合金条带弯折脆性的要求。

本研究获得了同时具备优异软磁性能和弯折塑性的FeCo基非晶及非晶/纳米晶复合结构合金条带。其饱和磁感应强度接近1.9 T，矫顽力低于5 A/m。研究表明，较高的饱和磁感应强度源于合金较高的居里温度。Co元素的添加可有效提高居里温度，我们可通过成分的设计优化提高合金的饱和磁感应强度。通过磁场退火我们有效降低了合金的矫顽力。研究表明退火同时施加平行于条带长度方向的磁场可以使磁畴结构重排优化，降低合金的矫顽力。. Fe-Co-B三元合金系退火后的初级析出相与B含量有关。当B的原子百分比含量小于17%时，初级析出相为bcc-Fe(Co)相，而B含量等于17%时初级析出相是bcc-Fe(Co)+Fe-B的共晶成分。析出相仅有bcc-Fe(Co)相和适当的纳米晶演化程度是合金条带保持弯折塑性必须的条件。对于呈弯折塑性的Fe-Co-B复合结构合金条带，维氏硬度随纳米晶体积分数的增大先减小至最小值后迅速增大，同时伴随着合金条带由弯折塑性到脆性的转变。形变过程中外力作用的能量部分被非晶基体吸收，引发微裂纹的生成是纳米晶合金条带硬度降低和具有弯折塑性的原因。. 本研究为开发具备弯折塑性和优异软磁性能的软磁合金条带提供了理论依据。该类合金条带是极具工业应用前景和商业化价值的高性能软磁材料。其应用有利于实现器件小型化，并且带来优异的磁性能和稳定的机械性能，使得提高设备的稳定性、工作效率和使用寿命成为可期的目标。