Werkstofftechnologische Untersuchungen zum Funktionsverhalten neuartiger Mischkeramik-Schneidstoffe bei hohen Temperaturen
Zusammenfassung der Projektergebnisse
It was observed that a TiC layer develops on the surface of Al2O3-TiC mixed ceramic upon hot pressing under Ar at 1600°C. Aim of this project was to understand the mechanism and the process parameters which lead to the formation of this layer. It was also intended to modify the bulk of this ceramic to get a tougher and stronger cutting tool. How this modification affects the cutting performance was also a question which had to be answered. Turning of steel using these tools generates high temperatures at the tool, especially at the rake face. Hence thermomechanical characterisation of the coated and just sintered tool was also aimed. The development of a wear mechanism model based on these results was targeted. Hipping of the samples resulted in inconsistent layer formation. Hence, we had to develop a completely new approach for the layer formation. This was achieved by thermal treatment in CO containing atmosphere which lead to consistent formation of a TiC layer at the surface. However, the process window was found to be very narrow and only few micron thick layers could be achieved. The adhesion of such in-situ formed TiC layers was much higher than conventional PVD coatings on ceramic substrates. Cutting performance of these modified inserts has been done and it was found that even 1pm thick coating enhances the performance of these inserts compared to commercially available inserts and also compared to just sintered inserts. Wear mechanism involved during cutting was studied and it was found that plastic deformation of the TiC layer slows down the wear rate at the flank surface. Abrasion and Ti-Fe interdiffusion were the main controlling factors in the crater region. Modification of the original composition by WC and Mo did not result in a new material with promising better mechanical properties. As the development process for the coated mixed ceramic tools has been changed completely from the proposed process, new series of experiments were carried out. As a consequence, lack of time was the main reason for not performing the thermomechanical and wear studies in the extent as originally planned. Further studies are necessary to confirm the proposed mechanism for layer formation. In-depth wear mechanism studies along with thermomechanical characterisation have to be done for developing a detailed wear model.
