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PVD hard coatings of the system CrAlON for cutting tools

Subject Area Metal-Cutting and Abrasive Manufacturing Engineering
Term since 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 516751164
 
During the machining of Q & T steels, PVD coated cemented carbide tools are exposed to thermal and mechanical loads that can cause different damage mechanisms, such as abrasive and adhesive wear, and can plastically deform the coated cutting edge. Nitride PVD hard coatings for wear protection of cutting tools have been state of the art for several decades. Oxynitride PVD hard coatings have been little researched. The oxynitride coating system CrAlON exhibits altered deformation and fracture behavior compared to the nitride CrAlN. This is probably due to a preferential incorporation of the oxygen atoms in the region of the grain boundaries, as observed in own preliminary work. In addition, the incorporation of oxygen influences the chip formation and friction behavior. How the incorporation of oxygen influences the damage mechanisms during machining has not yet been sufficiently investigated. The overall objective of the research project is to gain knowledge about the influence of oxygen incorporation in CrAlON hard coatings for cutting tools on their deformation and damage behavior. This will be done with regard to possible element enrichments of oxygen in the area of the grain boundaries, which change the fracture and deformation behavior of the coatings. In addition, knowledge will be gained about the extent to which the oxygen content of the coatings influences the friction and chip formation behavior. Overall, this will contribute to building a better understanding of the abrasive and adhesive wear mechanism of CrAlON coated tools during the turning of Q & T steels. In order to achieve the desired objectives, the samples are investigated by means of correlative methods. The pre-characterized coatings by scanning electron microscopy will be examined by high-resolution transmission electron microscopy. This will be done using CrAlON coated cemented carbide samples that have previously been statically or dynamically deformed or used in machining. The residual stress state of the coatings will also be considered. For the analysis of the friction and chip formation behavior, a special planning test rig will be used, which realistically reproduces the boundary conditions of machining. The damage behavior of the coated cemented carbide tools will also be analyzed after use in hard turning of the steel 42CrMo4+QT. Oxidation appears as a damage mechanism in particular at increased cutting speeds. In a possible third research year, an analysis of the influence of the oxygen content on the oxidation behavior of the coatings is planned.
DFG Programme Research Grants
 
 

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