Fundamental research on deposition of amorphous coatings on surfaces of inner geometries and evaluation of phase stability under tribological loading

与晶体材料相比，非晶态合金具有独特的性能。只有在合金允许过冷度高且能够实现快速冷却的情况下，才能制造这种材料。所需的高冷却速率可以通过涂层技术“热喷涂”实现，允许沉积非晶涂层。通过基于粉末的APS和HVOF以及通过基于线的WAS在外表面上的涂层的适用性被深入地研究。因此，已知间距是影响非晶相的量的关键参数之一。对于WAS涂层，s = 100和200 mm之间的间距是常见的。在这个项目的背景下，它将研究是否可以在内部几何形状表现出小直径的非晶铁基涂层沉积。因此，需要实现s<40 mm的非常小的间隔距离。由于短的间隔距离和芯线的使用，形成合金的时间也很短。在本项目中，将研究短的隔离距离对合金形成以及非晶相的影响。因此，将考虑其他工艺参数的影响。除金相分析外，还将测定结晶能。这些结果将与工艺参数、颗粒飞行特性和金相结果相关联。随后，将在结晶温度下在真空炉中对合适的样品进行热处理。由于不均匀性，特别是化学成分方面的不均匀性，结晶将局部发生。这些领域将被确定和分析，以澄清非晶涂层的结晶机制。然后，将通过模型试验对选定的涂层的摩擦学行为进行表征。因此，将研究在什么条件下可能发生结晶。此外，还将表征表现出部分非晶和完全结晶微观结构的温度处理样品。已知结晶涂层的磨损痕迹的特征，可以对未热处理的样品上的结晶过程进行假设。为了证实这些结果，将通过XRD和TEM进行分析。

In comparison to crystalline materials, amorphous alloys exhibit unique properties.This type of materials can only be manufactured if the alloy allows high undercooling and if rapid cooling rates can be realised. Required high cooling rates can be achieved by the coating technology "Thermal Spraying", allowing the deposition of amorphous coatings. The applicability of coatings on outer surfaces by means of powder based APS and HVOF as well as by means of wire based WAS is investigated intensively. Thereby the stand-off distance is known to be one of the key parameters influencing the amount of amorphous phases. For WAS coatings, stand-off distances between s = 100 and 200 mm are common. In the context of this project, it will be investigated whether amorphous Fe-based coatings can be deposited on inner geometries exhibiting small diameters. Thereby very small stand-off distance of s<40 mm needs to be realized. Due to the short stand-off distance and the utilization of a cored wire, the time for the formation of the alloy is short as well. Within this project the influence of the short stand-off distance on the formation of the alloy as well as the amorphous phases will be investigated. Thereby the effect of further process parameters will be considered. Besides metallographic analysis, the crystallization energy will be determined. These results will be correlated with the process parameters, particle in-flight properties and results from metallography. Subsequently, suitable samples will be heat treated in a vacuum furnace at crystallization temperature. Due to the heterogeneity especially with regard to the chemical composition, crystallization will occur locally. These areas will be identified and analysed in order to clarify the crystallization mechanisms of amorphous coatings. Afterwards, selected coatings will be characterized with regard to the tribological behaviour by means of a model test. Thereby, it will be investigated under which conditions crystallization might occur. In addition, temperature treated samples exhibiting a partially amorphous and a fully crystalline microstructure will be characterized as well. Knowing the characteristics of the wear track of crystallized coatings, assumptions with regard to the crystallisation process on the samples, which are not heat treated, can be made. In order to confirm these results analysis by means of XRD and TEM will be conducted.