Otmar Zimmer

The edge area is especially essential for cutting tools, since this is the contact zone between the work piece and the tool. Hard coatings (PVD or CVD coatings) can protect the edge against wear and they are commonly used. The geometries of the cutting edges change during the coating process, with the edge radius increasing. Therefore, the film thickness is limited and the initial radius of the uncoated tool must be smaller than the target radius of the coated edge. A new coating process based on vacuum arc PVD was developed to overcome this limitation. The film growth at the edges can be properly controlled by means of selected coating materials and process conditions. Thus, it is possible to grow edges sharper than the initial edge geometry. Different substrates were coated with different coating systems. Parameters such as the bias voltage, coating pressure, and initial radius were varied within this work. It was found that the application of a bias voltage is crucial for the generation of sharp edges. It was also found that the edge sharpening caused by coatings works best on samples with an initial radius of around 15 µm.

In recent years, high-entropy alloys have attracted increasing scientific interest. Due to their promising combination of properties, such as high hardness and high temperature stability, they are attractive for use as tool coatings for machining applications, to give but one example. Previous studies often focused on layer deposition using magnetron sputtering. Comparatively little research has been carried out to date on coating deposition using direct current cathodic vacuum arc deposition (CAE), with higher achievable rates and almost completely ionized plasmas. The aim of this work is to investigate (HfNbTaTiZr)N-coatings produced by CAE. The nitrogen content was varied and the effects on the coating properties were investigated. Changing the N₂/(N₂ + Ar) ratio between 0.1 and 1.0 and varying the working pressure in the chamber from 2 Pa to 5 Pa resulted in variations of the nitrogen content of the coatings, ranging from 30 at% to 50 at%. Although different microstructures of the coatings were obtained, there was only a minor influence on the hardness and Young’s modulus.

Plasma generation by cathodic arc spots plays a crucial role for coating processes that make use of the Arc-PVD technology. Usually, the arc spot motion over the cathode is steered by a magnetic field of a particular distribution and magnitude to ensure a continuous plasma generation, the avoidance of liquid droplets, and a proper utilization of cathode material by homogeneous erosion. This study presents a semi-empirical model that allows for an examination and characterization of the arc spot motion with regard to direction and speed as a function of an imposed magnetic field. This model considers the different components of random walk, retrograde, and Robson drift motion. Introduced empirical coefficients were determined by corresponding experimental investigations. The calibrated model describes the arc spot motion in good agreement to the recorded spot tracks and can therefore be applied for an evaluation of different magnetic field configurations.