Phase formation, crystallization kinetics and properties of (Fe,Co)-based bulk metallic nanocomposites

多组分Fe基或（Fe，Co）基大块金属玻璃（BMG）有趣的软磁性能对其合成和物理性能的研究产生了巨大的刺激。对非晶铁磁薄带的一些研究表明，在某些情况下，退火可以提高软磁性能。尽管非晶薄带具有独特的性能，但其应用仍然有限。更合适的是块状软磁玻璃合金，因为它们可以直接铸造成比快速淬火带更厚尺寸的最终形状。良好的磁性能并不是应用的唯一要求。磁性、机械和/或腐蚀抗性之间的合适组合可以使这种材料对于应用非常有吸引力。BMG具有比晶体材料高得多的硬度、屈服强度、疲劳和耐磨性。由于玻璃态结构固有的脆性，它们缺乏可变形性，但可以通过纳米化来改善。最近的研究表明，少量添加促进软磁纳米相纳米化的元素也可以提高延展性（变形性）。在那里，磁软化的机制应该是类似于在纳米晶Finemet型带的情况下观察到的，但它还没有得到充分的研究和理解。Finemet带在纳米化后变得易碎，而BMG可以变得可变形。 不同的机械性能在于纳米复合材料的不同尺度：带状物具有非常有限的厚度（通常小于50微米），而BMG是真实的3D样品。亚稳纳米相更可能出现在富含类金属的组合物中。然而，磁软化机制和机械行为的细节至今尚未完全了解。此外，在BMG的情况下，通过受控失透的磁性软化从未大规模进行。在某些情况下，亚稳相BMG开发似乎是不同的，从那些生长在带，他们形成只有当一个特定的短程有序存在于散装非晶前体。这个项目的目的是找出这些亚稳相是如何稳定的，以及为了创造它们，需要达到什么样的特定短程有序。主要目标是同时优化玻璃形成能力（GFA）和纳米晶化，以改善块体合金的软磁和机械性能。与此同时，新型块体软磁纳米复合材料可以扩大应用领域：它们适合用作小型化运动传感器、磁芯、磁阀、磁离合器等

The interesting soft magnetic properties of multicomponent Fe- or (Fe,Co)-based bulk metallic glasses (BMGs) have been a great stimulus for research regarding their synthesis and physical properties. Several studies on amorphous ferromagnetic ribbons demonstrated that in some cases the soft magnetic properties can be enhanced by annealing. Despite their unique properties, the amorphous ribbons still have limited application. Much more suitable are bulk soft magnetic glassy alloys because they can be cast directly in the final shape with thicker dimensions than the rapidly quenched ribbons. The good magnetic properties are not the only requirements for applications. A suitable combination between magnetic, mechanical and/or corrosion resistance may make such kind of materials very attractive for applications. The BMGs have a much higher hardness, yield strength, fatigue and wear resistance than the crystalline materials. They lack the deformability, due to the intrinsic brittleness of the glassy structure, but it can be improved by nanocrystallization. Very recent studies show that small additions of elements which promote the nanocrystallization of soft magnetic nanophases may enhance also the ductility (deformability). There the mechanism of magnetic softening is supposed to be similar to what is observed in the case of nanocrystalline Finemet-type ribbons, but it is not yet fully investigated and understood. The Finemet ribbons become brittle upon nanocrystallization, while the BMGs may become deformable. The different mechanical behaviour resides in the different scale of the nanocomposites: the ribbons have a very limited thickness (usually less than 50 µm), while the BMGs are real 3D samples. The metastable nanophases are more likely to appear in metalloid-rich compositions. However, the details of the magnetic softening mechanism(s) and mechanical behaviour are not fully understood so far. Also, magnetic softening by controlled devitrification was never done on a large scale in the case of BMGs. In some cases, the metastable phases developed in BMGs seem to be different from those grown in ribbons and they form only if a particular short-range order exists in the bulk amorphous precursors. The purpose of this project is to find out how these metastable phases can be stabilized and what kind of particular short-range order is necessary to be achieved in order to create them. The main goal is a simultaneous optimization of glass forming ability (GFA) and nanocrystallization for improving the soft magnetic and mechanical behaviour of bulk alloys. In parallel, new bulk soft magnetic nanocomposites can enlarge the application field: they are suitable for use as miniaturized motion sensors, magnetic cores, magnetic valves, magnetic clutches etc