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，一种新的组合表面处理铝合金，氮化和随后的电子束重熔（EBR），成功地开发和评估。EBR过程中的能量输入通过AlN层发生，AlN层首先由等离子体氮化产生。在不显著破坏AlN层的情况下，由于发生的熔池的快速凝固，Al衬底的硬度增加了三倍。因此，薄而硬的AlN层的承载能力显著提高。该技术的特殊创新在于消除了AlN层下的空洞，这是由于Al的向外扩散和产生夹层造成的，确保AlN层与衬底的连续连接。此外，表面织构化发生，并且由渗氮引起的典型表面缺陷被熔融金属填充。（本申请）对于以往研究结果中出现的关于非均匀吸收层的能量输入、中间层的结构和表面织构化的新问题，应进行深入的研究、分析和评价，通过高分辨率的微观结构研究，扩展和具体化了目前对过共晶铝合金氮化机理的认识。在此基础上，将解释EBR处理所产生的中间层结构、扩散过程以及相的形成。基于最新的基础研究成果，采用两个定义的能量输入值，分析了中间层的结构和厚度与其硬度和附着力之间的关系。在面向过程的研究中，将系统地检查和影响层基质化合物的摩擦学行为。通过改变能量输入和/或光束引导参数，分析和研究了EBR后对表面织构和层-基体化合物的摩擦磨损行为的影响，并阐明了非均匀吸收层在EBR过程中的能量吸收机制，特别是考虑到AlN的高电阻率。因此，不同厚度的AlN层对能量吸收的影响将被研究和描述为示例。能量吸收模型的结果，中间层的结构和硬度以及附着力和摩擦学性能，作为处理参数的函数，将有助于推导出关于层-基体化合物的负载适应设计的一般性陈述，其由作为Al合金上的功能表面的AlN层组成。

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.