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. PVD 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. It 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. Korrosionsverhalten von CrxN beschichtetem Stahl Anwendungen von PVD-Beschichtungen im Bereich des Verschleißschutzes, 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. Gründe hierfür sind unter anderem Probleme bei der Schichtabscheidung, aber auch die für Bauteile im Gegensatz zu Werkzeugen typischen kombinierten Anforderungen bzgl. Verschleiß- und Korrosionsschutz. TiN (PVD) zeichnet sich durch gute Verschleißeigenschaften, nicht aber durch die Verbesserung von Korrosionseigenschaften aus. Bei galvanisch abgeschiedenen Chromschichten kann man hingegen von gutem bzw. verlässlichem Korrosionsschutz bei hinlänglich ausreichendem Verschleißwiderstand sprechen. PVD 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, daß das Korrosionsverhalten von allen Aufbauparametern abhängt und daß 8 μm Chromnitrid denselben Korrosionsschutz liefern kann, wie 48 μm galvanisch abgeschiedenes Chrom.

Increasing applications of light weight materials are expected in the future. Pursuing this trend surface engineering of these materials - especially ion- and plasma-assisted methods - will be of increasing interest to enhance their wear and corrosion resistance. In a research co-operation some promising methods were examined on different aluminium and titanium alloys to assess their potential to increase the surface properties. Among these were magnetron sputtering of chromium nitride, ion beam assisted deposition of Cr/CrN and Al/A(2)O(3) layers, ion implantation and ion beam assisted nitriding. Compared to the steel substrates the assessment of the mechanical properties such as the critical load of the scratch test of the coated light weight materials is different. Furthermore, it could be shown that both spherical section and glow discharge optical spectroscopy are useful methods to characterize the near-surface zone influenced by ion implantation.

Hard and corrosion-resistant ceramic coatings like Al2O3 have shown promising protective properties in previous investigations. The aim of this work is to deposit optimized Al → Al2O3 layers on tool steel (Ck45) and a common aluminum alloy (AlMgSi0.5). The major consideration is to examine the influence of a graded metal-ceramic interface on internal stress, adhesion and corrosion properties. For this purpose the width of the Al → Al2O3 interface was varied by controlling the process parameters during deposition. The electrochemical and corrosion behaviour was determined by potentiodynamically controlled current-potential measurements under conditions of uniform corrosion attack and pitting corrosion. Further examinations of the local surface conditions were made by scanning-micro-electrode (SME) microscopy. The adhesion was determined by scratch and pull-off tests and the internal stress was recorded in situ during the deposition process. The results show that optimized Al → Al2O3 graded interfaces increase the hardness and improve the corrosion resistance in comparison with pure Al2O3 coatings. The adhesion is very good in all cases.

The application of thin hard coatings on machining tools, e.g. drilling tools is state of the art. The increase of lifetime of coated tools compared to uncoated tools is well known. [1]. In this context "separation of functions" is an often used phrase, by meaning the separation of functions of the volume and the surface of materials. Going one step forward, from the point of view of tribology or corrosion this means, you have "only" to protect the surface by using a "good" coating without looking at the material underneath. In the past the influence of substrate materials or the optimization of the system (substrate-coating) was not the main aim of PVD development. Looking at substrate and coating as a system is especially necessary, if the differences of the properties of substrate and coating are large (e.g. hard coating - light metals).This paper shows different aspects of the tribological and electrochemical characterization of PVD coated light metals (CrN coating).

Ein beschichtetes Bauteil stellt in seiner einfachsten Form einen Dreierverbund aus Substrat, Interface und Schicht dar, in vielen Fällen kann die Schicht aus mehreren Untersystemen bzw. das Interface aus der modifizierten Substatrandschicht und einem Zwischenbereich zur Schicht bestehen. Eine ideale Beschichtungsmethode sollte es daher erlauben, alle diese Schichten bzw. Schichtbereiche in kontrollierter und aufeinander abgestimmter Form zu erzeugen.

In this contribution the application of a modern technique‐scanning electrochemical microelectrode – for the evaluation of thin films which were deposited (IBAD) is illustrated. New tendencies in the development of thin films with anticorrosive purpose lead to the development of multi‐layer systems acting similar to those commonly, applied in the industry, however, being much thinner. Imperfections and defects are commonly introduced in the coating during the deposition process, and these affect the anticorrosive properties of the film. In order to make a local electrochemical study of these multi‐layer systems we have developed equipment in order to perform electrochemical surface‐scans (potential and current density) on the basis of a microelectrode with a good lateral resolution (approximately 20 μm). Al‐Al2O3 multilayers on steel substrates with differently designed interfaces were investigated to show the variation of uniform and local electrochemical information obtained in dependence on the coating deposition parameters.

In contrast to other light materials such as aluminium or titanium, the potential of magnesium to form stable, corrosion-resistant films is limited to alkaline solutions. In neutral, acidic or saline solutions the protective hydroxide or carbonate film breaks through immediately and heavy corrosion takes place. The aim of this work was to deposit protective magnesium oxide layers, by ion beam-assisted deposition (IBAD), which do not grow under natural circumstances. These coatings are different from coatings obtained by anodic oxidation, because of their partial crystallinity, good adhesion and very smooth, non-porous character. The MgO coatings were prepared with IBAD on Mg (hp), AZ91 magnesium alloy and AlMgSi0.5 substrates by the evaporation of high-purity MgO under bombardment with Ar+ ions with energies up to 15 keV. The Ar+ to MgO arrival ratio was chosen in order to obtain dense coatings. The coating thickness was 1 μm. The electrochemical and corrosion behaviour were determined by potentiodynamic controlled current–potential measurements under pitting corrosion conditions and a standard salt-spray test. The crystallinity was determined by X-ray diffraction measurements and the surface quality by atomic force microscopy. The results prove that by IBAD, magnesium oxide coatings with or without the addition of other elements (Sn, Nd) of high hardness and low porosity and with good corrosion protection properties can be formed. The degree of crystallinity and the texture have a strong influence on the quality of the coatings and depend on the ion energy.

The quality of thin surface coatings for wear and corrosion protection is significantly influenced by pores and film defects (voids, micro cracks, coated impurities), which can be formed in the processing stage. These defects are the initiation sites, and are responsible for mechanical and chemical failure of the film. There are processes of oxidation and corrosion of the substrate especially at the site of pores. To meet the requirements of protection the processing stage has to be optimized by minimizing flaws and pores. Suitable testing methods are necessary for early diagnosis and recognition of chemical and mechanical degradation of the film or dissolution of the substrate, respectively. The investigations, presented in this paper, were carried out with TIN layers and TiO2-->TiN multilayers on steel (Ck45) produced by ion beam assisted deposition. The thickness of the film was between 1 and 1.5 mu m In order to obtain a high local resolution of the corrosion phenomena occurring on the surface, electrochemical equipment with a good lateral resolution through a microelectrode of 10 mu m was developed. The contribution shows the evaluations of the films and defects in aqueous solution. The scanning electrochemical results are represented as topographical three-dimensional images of the electrochemical surface reactivity. (C) 1998 Elsevier Science S.A.

To improve the adhesion and corrosion resistance in ceramic and steel systems, zirconium oxide films were deposited on austenitic type 316L stainless-steel substrates by using the ion beam assisted deposition (IBAD) method, in which ZrO2 evaporation and energetic Ar and/or O2 ion bombardment at 250 eV were carried out simultaneously. To study the influence of the film thickness on the performance of coatings, thin (0.2–0.4 μm) and thick (2–3 μm) films were prepared. The film structure was investigated by X-ray diffractometry. The adhesion was evaluated by a tensile pull-off tester, showing that IBAD treatments could provide a remarkable potential to enhance the adhesion. The corrosion behavior was determined by potentio-dynamic polarization measurements. It was found that excellent corrosion-protection ability of zirconium oxide coatings on stainless steel was achieved after IBAD treatments. The mechanism for explaining the results has been discussed in terms of the surface observation and X-ray photoelectron spectroscopy studies.

Insulating ceramic films, which have the property of being hard and corrosion resistant, are good candidates for corrosion protection coatings. Al2O3 has the additional advantage that it is transparent. Therefore it is used as protective coating in many fields, such as microelectronics and laser optics. Ion beam assisted deposition (IBAD) provides a good means for depositing stoichiometric Al2O3 coatings, which have a very good adhesion, on any bind of vacuum compatible materials.Earlier studies already showed that IBAD Al2O3 coatings act as corrosion protection coatings against pitting of aluminium. The present paper deals with its protection ability against uniform corrosion of mild steel.The Al2O3 coatings were prepared with ion beam assisted deposition using three different deposition modes: (1) evaporation of Al in an oxygen atmosphere under bombardment with Ar ions; (2) evaporation of Al in an oxygen atmosphere under bombardment with O ions; (3) evaporation of Al2O3 under bombardment with Ar ions. In all cases appropriate combinations of the process parameters, namely the ion energy, the ion to atom arrival ratio IIA, and the backfilling gas pressure, were chosen in order to deposit stoichiometric Al2O3.The electrochemical and corrosion behaviour were determined by current/potential measurements under conditions for uniform corrosion attack.The results showed that the Al2O3 coatings considerably increase the resistance of steel against uniform corrosion. In the examined range the modes of deposition do not significantly influence the corrosion protection effect. However, there is a distinct influence of the ion energy and the IIA ratio on the protective power. It can be concluded, that, up to a certain level, an increase of the power input per condensing atom during the growth of the Al2O3 films leads to an increased protection ability.