In order to increase the power density of tribologically stressed drive train components, different approaches are being pursued in material and production technology. In addition to the development of efficient base materials, especially the optimization of surface finishing processes and the application of coating systems are promising. By combining mechanically highly stressable substrate materials and tribologically effective, extremely thin coatings, the components show modified wear and friction properties, which often lead to an increase of tooth flank load carrying capacity. A major advantage of this approach is that the highly accurate component geometry is only slightly changed by the coating. The influence of PVD/PECVD hard coatings on the load carrying capacity of cylindrical gears made of alloy steel is the subject of scientific research since the nineties. Several reports show that diamond-like carbon (DLC) coating systems reduce the occurrence of specific forms of gear damages, such as pitting or scuffing, and optimize the frictional behavior of gears. Despite the good results, PVD/PECVD coating technology could not be established in gear transmission technology yet. The use of a PVD/PECVD coating leads to higher component costs and longer manufacturing time. Furthermore, the surface finishing process before coating can influence the resulting tooth flank load capacity, and in some studies, a reduction of tooth root strength by the application of a coating can be observed. An extensive research concerning the influence of specific surface finishing processes on the tooth flank load capacity of uncoated and coated gears have not been focused in existing works. Furthermore, the existing works focus on the coating of both gears in contact and not on the coating of just one gear combined with optimized surface finishing processes. Therefore, the aim of this work is the investigation and determination of the influence of surface finishing processes on the impact of PVD/PECVD coatings concerning the pitting load capacity of gears. By means of running tests, the influence of different surface finishing processes on the pitting resistance is examined for the uncoated and coated tooth flank contact. The coated tooth flank contact will be further separated in the cases with just one or two coated gears in contact. By coating only one gear, a possible reduction of coating costs with simultaneous increase of the pitting resistance is targeted. As a DLC coating, a modified tungsten carbide coating (a-C:H:W (WC/C)) will be applied. Due to an optimized coating process, consistent coating adhesion without loss of hardness of the substrate material will be achieved. The result of this optimization will additionally be proven by the investigation of tooth root strength by means of pulsator testing.
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