Investigations on mode of action of a short-term electron beam liquid Phase surface treatment on the structure and load behaviour of nitrided Al alloys (AlN EB-Flash-02)

在第一个研究阶段，成功开发了一种新的铝合金表面处理方法，即氮化和随后的电子束重熔（EBR）。EBR过程中的能量输入通过氮化铝层进行，氮化铝层首先由等离子体渗氮产生。在不明显破坏AlN层的情况下，由于熔池的快速凝固，Al基体的硬度增加了三倍。因此，薄而硬的AlN层的承载能力大大提高。该技术的特别创新之处在于可以消除AlN层下的空洞，这些空洞是由Al向外扩散造成的，并产生一个中间层，保证AlN层与衬底的连续连接。此外，表面出现织构，典型的氮化表面缺陷被熔化的金属填充。在第二个研究阶段（本应用），应深入研究、分析和评价非均匀吸收层的能量输入、层间结构和表面织构等前人研究结果所产生的新问题。通过高分辨率的显微组织研究，现有的关于过共晶铝合金氮化机理的知识将得到扩展和细化。在此基础上，将解释由EBR处理产生的中间层结构、扩散过程和相形成。基于这一新的基础研究成果，采用两种定义的能量输入值分析了夹层结构、厚度与硬度和附着力之间的关系。在面向工艺的研究中，层基化合物的摩擦学行为将被系统地检查和影响。通过确定能量输入和/或光束引导参数的变化，分析和研究了层基化合物在EBR后对表面织构和摩擦磨损行为的影响。此外，对于非均匀吸收层的能量吸收机理，特别是氮化铝的高电阻率，还必须加以阐明。因此，不同厚度的AlN层对能量吸收的影响将被研究和描述示例性。能量吸收模型的结果、中间层的结构和硬度以及粘附性能和摩擦学性能作为处理参数的函数，将有助于推导出由AlN层作为功能表面的层基化合物的负载适应设计的广义陈述。

In the first research period a new combined surface treatment for aluminum alloys, consisting of nitriding and subsequent electron beam remelting (EBR), was developed and evaluated successfully. The energy input during EBR takes place through the AlN layer, which is generated by plasma nitriding at first. Without damaging the AlN layer significantly, the hardness of the Al substrate increases by the factor of three because of the rapid solidification of the occurring melting pool. Hence, the load supporting capacity for the thin and hard AlN layer increases considerably.The special innovation of this technology is the possibility to eliminate the cavities beneath the AlN layer, which result from the outwards-diffusion of Al and to generate an interlayer, guaranteeing a continuous connection of the AlN layer to the substrate. Additionally, surface texturing occurs and typical surface defects caused by nitriding fill up with molten metal.In the second research period (this application) the new issues arising from the previous results regarding the energy input of inhomogeneous absorption layers, the structure of the interlayer and the surface texturing should be investigated, analyzed and evaluated profoundly.By means of high-resolution microstructural investigations, the present knowledge about the nitriding mechanism of hypereutectic Al alloys will be extended and specified. On this basis, the structure of the interlayer, which results from the EBR treatment, and diffusion processes as well as phase formation will be explained. Based on the new fundamental research results, the relationship between structure and thickness of the interlayer and its hardness and adhesion will be analyzed using two defined energy input values. In process-oriented investigations, the tribological behavior of the layer-matrix compounds will be examined and affected systematically. By a defined variation of the energy input and/or the beam guiding parameters the effects on the surface texturing after EBR and the friction and wear behavior of the layer-matrix compounds will be analyzed and investigated.Furthermore, the mechanism of energy absorption during EBR for inhomogeneous absorption layers has to be elucidated with particular regard on the high electric resistivity of AlN. Therefore, the influence of different thicknesses of the AlN layer on the energy absorption will be investigated and described exemplary.The results of the energy absorption model, the structure and the hardness of the interlayer as well as the adhesion and tribological properties, being a function of the treatment parameters, will help to deduce generalized statements on a load-adapted design of layer-matrix compounds, which consist of an AlN layer as functional surface on Al alloys.