J. Senf

Corrosion behaviour of steel with PVD CrxN coatings

The application of PVD coatings for wear protection of tools is well known. Since many years, TiN coated cutting and forming tools are state of the art. In contrast, the application of PVD coatings on machine parts is not standard today. This is caused by the problems of coating deposition on components as well as the fact that wear protection and corrosion protection is demanded for many parts with longer lifetime. TiN produced by means of PVD technique is good for wear protection, but with respect to corrosion there are problems. On the other hand electropolated chromium is a reliable coating to resist corrosion, but wear resistance is limited. n n n nPVD CrxN coatings promise to combine the advantages of hard coatings and electropolated chromium. The present study focuses on the corrosion properties of magnetron sputtered CrxN coatings. Different types of coatings on steel substrates with various amounts of nitrogen were investigated in order to take into account aspects of coating deposition resp. coating material, coating structure and coating morphology. Additionally several graded and multilayer coatings were studied to show influences of coating system design. Electroplated hard chromium was used as reference material for corrosion resistance. To explain the corrosion behaviour, crystallographic phases and structure of coatings were analysed by X-ray diffraction and morphology by SEM. n n n nIt could be shown that the corrosion behaviour depends on all these parameters and that 8 μm chromium nitride provides the same corrosion protection as 48 μm electroplated chromium. n n n nKorrosionsverhalten von CrxN beschichtetem Stahl n n n nAnwendungen von PVD-Beschichtungen im Bereich des Verschleisschutzes, z. B. TiN-Schichten auf Zerspanungs- und Umformwerkzeugen sind Stand der Technik. Im Gegensatz dazu sind Anwendungen von PVD-Schichten auf Bauteilen kaum im Einsatz. Grunde hierfur sind unter anderem Probleme bei der Schichtabscheidung, aber auch die fur Bauteile im Gegensatz zu Werkzeugen typischen kombinierten Anforderungen bzgl. Verschleis- und Korrosionsschutz. TiN (PVD) zeichnet sich durch gute Verschleiseigenschaften, nicht aber durch die Verbesserung von Korrosionseigenschaften aus. Bei galvanisch abgeschiedenen Chromschichten kann man hingegen von gutem bzw. verlasslichem Korrosionsschutz bei hinlanglich ausreichendem Verschleiswiderstand sprechen. n n n nPVD CrxN Schichtsysteme scheinen die Vorteile von Hartstoffschichten und galvanisch abgeschiedenen Chromschichten zu vereinen. Inhalt dieser Arbeit sind die Korrosionseigenschaften von mittels HF-Magnetronsputtern abgeschiedenen CrxN Schichten. Die dazu untersuchten auf Stahlsubstraten abgeschiedenen Schichtsysteme unterscheiden sich in ihrem Schichtaufbau (Gardientenschicht, Mehrlagenschicht) und in ihrer stofflichen Zusammensetzung (Stickstoffgehalt). Es konnte gezeigt werden, das das Korrosionsverhalten von allen Aufbauparametern abhangt und das 8 μm Chromnitrid denselben Korrosionsschutz liefern kann, wie 48 μm galvanisch abgeschiedenes Chrom.

Reliable PVD coatings on components: aspects of deposition and characterization for quality management

Although the characteristics of PVD coatings in research and development papers are very promising, in the field of tribology the industrial application of these types of coating has until now been restricted to special market segments. The deposition of hard coatings is state-of-the-art on tools, whereas PVD-coated machine components are quite rare. This is caused by the profile of properties of the coatings, their various surroundings and the demands for application reliability. This last aspect is the main topic of this contribution. Reliability is especially important for machine components, because tools may fail after a relatively short lifetime as compared to machine parts. Besides this, tools and the corresponding production equipment are designed for fast tool replacement, in contrast to other machines which should work without standstill and with a minimum of maintenance. Characteristics of coated systems must be guaranteed in practice, and theory and laboratory experiments have to show what is possible. On the one hand, reproduction of the deposition process must be guaranteed to fulfil application fields with high demands for reliability, while on the other hand, characterization of coated systems must be standardized with admissible deviations which can be communicated between coaters and users. These aspects are important for decisions concerning the use of coating substrate systems in tribology as well as decisions concerning technical functions. The present investigation details the main reasons for deviations in the results of investigations of PVD coatings.

Verschleiß- und Korrosionsschutz durch Chrom und Chromnitrid (PVD-Abscheidung auf Al und Mg)

Investigations of the wear behaviour of uncoated Magnesium and Aluminium alloys (AZ 91hp, AlSi 7Mg) are showing very high wear rates of these materials. To improve the wear behaviour both materials were coated with 9 μm CrN using PVD (Physical Vapour Deposition) technology. The tribological behaviour of the coated light metals was tested afterwards by using a plate on cylinder tribometer. Looking at the results, wear is reduced enormously. The great number of defects in the coating of the magnesium alloy is showing almost no influence to the wear behaviour. The corrosion behaviour of chromium and chromium nitride coatings was tested on the magnesium alloy. Because of the defects in the coating, caused by defects like pores in the magnesium, only a short term protection of the alloy can be achieved. The corrosion behaviour of multilayer coatings is better than the behaviour of single layer coatings.

Lokale Schichterzeugung beim HF-Magnetronsputtern

The following paper illustrates the state of the art of the RF-magnetron sputter technology for tribological applications. First the parameters to determine the results of deposition are presented and second a possible way of systematical engineering of coatings for tribological applications is discussed. Exemplary spots on different influencing variables are given. The macroscopic boundary conditions of the deposition unit and the objects to coat play a similar important role as the kinematic of threedimensional functional surfaces on the objects. Further more the substrat material (of the object to coat) as well as the load bearing capacity of the coated component in a special tribological application is of special importance. The presented measuring results are extracted from the quoted reference.