As a consequence of the increased use of dry machining strategies such as high-speed cutting (HSC), high-performance cutting (HPC) and hard turning, modern tool coatings are constantly challenged by severe environments, combining oxidative, abrasive and adhesive wear.

In order to evaluate the role of coating chemical composition in related high-temperature situations, this study compares friction, wear and oxidation behaviour of different conventional and nanocomposite PVD coatings, deposited using the rotating arc cathodes technology.

At room temperature, dry-sliding experiments were carried out in dry air on coated HSS plates against metalloid (WC-Co) and ceramic (Si₃N₄) counterparts. For both pin materials, a distinct decrease of the coating wear coefficient was found upon addition of carbon, silicon or chromium to the Ti_1-xAl_xN base system. In contrast, the coefficient of friction remained essentially unchanged except for the case of carbon. SEM investigations showed that the wear was dominated by an abrasive mechanism, with only few cases of ball material transfer to the friction track. Neither fracture nor delamination of the coatings were observed.

High-temperature pin-on-disk tests of coatings on cemented carbide plates against alumina balls revealed early failure of carbon-containing coatings due to their low oxidation resistance. Most nitride and oxynitride coatings were able to withstand the conditions with only minimum oxide scale formation, yet the beneficial effect of Cr addition on the wear resistance was found to be less pronounced. The wear volume at 600°C correlated well with dry milling tests in steel, however not strongly with room-temperature nanomechanical properties of the coatings. Therefore, the hot hardness and -modulus of selected coatings were measured in situ, using a special indenter setup.

Recent advances in the technological sectors of aerospace, automotive, biomedical and pharmaceutical applications as well as in energy and environment control stimulate research on high performance functional coatings. In many cases, the ever increasing requirements involve an “ideal” combination of the mechanical, tribological, corrosion, thermal and other characteristics that can only be satisfied by using specifically tailored film architectures including nanocomposite, nanolaminate, multilayer and graded layer systems.

In this presentation, we will outline approaches that allow one to design and fabricate high-performance protective coatings based on understanding the film growth mechanisms, on the lessons learned in the area of optical coatings such as optical interference filters, and on the use simulation techniques. We will briefly describe our recent studies of the ion-surface interactions in plasma environments (bias- and pulse-controlled PECVD and PVD techniques) using a methodology combining in situ real-time spectroscopic ellipsometry and different complementary microstructural and chemical analysis methods, while specifically addressing selected nanostructured systems such as Ti-Si-N, Ti-Si-C-N and Cr-Si-N coatings.

We will show examples in which the modeling approach helped us to enhance our understanding of the growth-structure-property relationships, and that allowed us to predict functional behavior of different coating combinations; this includes: (i) Dynamic Monte-Carlo simulation of the ion bombardment effects on subplantation and interfacial mixing; (ii) Molecular dynamic simulations of the nanocomposite structures capable of predicting the experimentally observed superhardness; and (iii) Finite element design of film architectures for the prediction of enhanced resistance to solid particle erosion. Finally, we will discuss new opportunities and surface engineering strategies leading to attractive technological solutions in the areas of protective coatings for aerospace, biomedical and optical applications.