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

多组分Fe-或（Fe,Co）基大块金属玻璃（bmg）的软磁特性对其合成和物理性能的研究具有重要的刺激作用。一些对非晶铁磁带的研究表明，在某些情况下，退火可以增强软磁性能。尽管非晶带具有独特的性能，但其应用仍然有限。更合适的是大块软磁玻璃合金，因为它们可以直接铸造成最终形状，尺寸比快速淬火的带状更厚。良好的磁性不是应用的唯一要求。磁性，机械和/或耐腐蚀性之间的适当组合可能使这种材料在应用中非常有吸引力。与结晶材料相比，bmg具有更高的硬度、屈服强度、抗疲劳性和耐磨性。由于玻璃结构固有的脆性，它们缺乏可变形性，但可以通过纳米晶化来改善。最近的研究表明，少量添加的元素可以促进软磁纳米相的纳米化，也可以提高延展性（变形能力）。磁软化的机制被认为与纳米晶精细带的情况类似，但尚未得到充分的研究和理解。细晶带在纳米晶化后变脆，而bmg可能会变形。不同的力学行为存在于纳米复合材料的不同尺度：带状材料的厚度非常有限（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金属成分中。然而，到目前为止，磁性软化机理和力学行为的细节尚未完全了解。此外，在bmg的情况下，通过控制脱硝的磁软化从未大规模进行过。在某些情况下，在bmg中形成的亚稳相似乎与在带状中生长的亚稳相不同，它们只有在大块非晶前体中存在特定的短程顺序时才会形成。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的短程秩序。主要目标是同时优化玻璃形成能力（GFA）和纳米化，以改善大块合金的软磁和力学行为。同时，新型块状软磁纳米复合材料可以扩大其应用领域：适用于小型化运动传感器、磁芯、电磁阀、电磁离合器等

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