W-foil: DuctilityIdentification of the mechanism of plastic deformation

钨(W)是所有金属中熔点最高的金属（TS = 3422°C），因此通常被认为是能量转换系统中高温应用的主要候选者。然而，W有两个主要缺点：(i)超过600°C的灾难性氧化行为；（ii）低断裂韧性，KIC，或高脆-韧转变温度（BDTT），由Charpy测量。特别是对于最后一个问题，找到了一个有趣的解决方案。该解决方案包括通过合成由W箔制成的W层压板（W多层）来实现W的延展性。钨箔具有很高的断裂韧性，在室温下具有均匀的延展性。通过组装和连接，我们成功地将箔片的韧性扩展到整体。许多出版物指出W可以通过冷加工进行延展性加工。然而，这只是通过现象学方法来描述的，并且没有对潜在机制的理解。特别是对W箔或一般bcc UFG材料的塑性变形机理还不完全了解。在本建议的框架内，将评估(i)大量的移动边缘位错，（ii）晶粒细化，以及（iii）自由表面上的位错湮灭对厚度为0.1 mm的W箔非凡延展性的影响。这样，塑性变形的机制将以直接（拉伸试验，TEM）和间接方式（SRS，激活体积）确定，所获得的结果将相互关联。

Tungsten (W) is he metal with the highest melting point of all metals ((TS = 3422°C) and is therefore often considered as primary candidate for high temperature applications in energy conversion systems. However W has two major drawbacks: (i) a catastrophic oxidation behavior beyond 600°C as well as (ii) a low fracture toughness, KIC, or a high brittle-to-ductile transition temperature (BDTT) measured by Charpy. Especially for the last problem an interesting solution was found. This solution consists of the ductilisation of W through the synthesis of a W laminate (W multilayer) made of W foils. W foils have a high fracture toughness and are even ductile at room temperature. By assembling and joining we succeeded in expanding the toughness of the foil to the bulk.Many publications point out that W can be ductilised by cold working. However this is only described by a phenomenological approach and there is no understanding of the underlining mechanism. Especially the mechanism of the plastic deformation of W foil or in general of bcc UFG materials is not understood in its whole.Within the framework of this proposal the influence of (i) the high amount of mobile edge dislocations, (ii) the grain refinement, as well as (iii) the dislocation annihilation on the free surface on the extraordinary ductility of W foil, thickness 0.1 mm, will be assessed. Doing this the mechanism of the plastic deformation will be determined in a direct (tensile tests, TEM) as well as in an indirect manner (SRS, activation volume) and the results obtained will be correlated.