Influence of nitriding parameters on the tribological properties and the adhesion of Ti- and Cr-based multilayer designs

The growing competitive pressure in the industry makes the reduction of process costs increasingly important. One possibility to decrease the costs is to increase the lifetime of the tools by applying wear resistant and friction reduced PVD coatings. Especially in the field of hot forming, tools are exposed to high mechanical and thermal loads. The special requirements of these tools can be met by multilayer systems such as Ti/TiAlN or Cr/CrAlN, which provide properties such as a high hardness, sufficient heat resistance, and smooth surfaces. However, varying hardnesses and different thermoelastic properties between the multilayer systems and the substrate can lead to the delamination and spallation of the layers. Using an upstream plasma nitriding process, it is possible to produce a hardness gradient between the basis material and the coatings, thus ensuring a sufficient supporting effect for the coating. In this study for the first time a plasma nitriding process was integrated into the PVD coating device (Cemecon CC800/9 sinox ML) to realize a duplex coating process. The nitriding parameters were successively varied and the influence of the parameters on the material performance in the nitriding zone was examined. The morphology and structure of the nitriding zone were examined using scanning electron microscopy (SEM), energy dispersive scattering and X-ray diffractometry (XRD). ards, the adhesion of the applied PVD layers was investigated in dependency on the nitriding parameters. The PVD layers were deposited on tool steel substrates AISI H11 (1.2343) by means of magnetron sputtering. The mechanical and tribological properties as well as the adhesion of these coating systems were studied using a scratch tester, a nanoindenter, and a ball-on-disc test.