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)

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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.