C. Friedrich

Development of chromium nitride coatings substituting titanium nitride

Abstract The deposition of chromium nitrides by reactive magnetron sputtering on machine parts seems to be very promising, because the mechanical properties are similar to those of TiN hard coatings. Especially the corrosion resistance of CrN is an interesting aspect related to the known problems of TiN films. The presented research deals with the deposition of CrN films by using r.f.-magnetron sputtering units. Starting with common deposition parameters for titanium nitride and a variation of the deposition parameters, partial pressure and bias voltage, chromium nitride coatings are deposited on steel substrates. The results show that the reactive sputtering process of CrN is more sensitive to minor changes of the adjustable deposition parameters and the related plasma conditions than that of TiN. The deposition of CrN allows the production of coatings with a wide field of properties but only within small windows of deposition parameters, especially when sputtering Cr2N films. The characterization of the coatings by their basic properties, such as thickness, hardness, adhesion, phase analysis and residual stress, indicates possibilities and limits of CrN coating systems.

Deposition, properties and applications of PVD CrxN coatings

Abstract The deposition, properties and application of PVD Cr x N coatings have been discussed increasingly in recent years. One reason for this are the environmental problems associated with the use of electroplated chromium and the resulting need for a replacement of the production method. Another reason for a discussion of PVD Cr x N is that the field of application of PVD TiN coatings seems to be examined up to the point were coating properties are difficult to improve by processing parameters. Cr x N is one answer to these two demands, showing similar mechanical properties to TiN and a good corrosion resistance. The following paper presents the engineering of functional properties of PVD Cr x N coatings performed at the Darmstadt University of Technology in the last decade. Boundary conditions of deposition by PVD r.f.-magnetron sputtering as well as characteristic physical and mechanical properites are presented, followed by selected tribological applications.

Measurement of the hardness of hard coatings using a force indentation function

Abstract Today the so-called dynamic micro hardness with analysis of the force indentation function is replacing in many cases the conventional Vickers hardness measurement for evaluating the hardness of thin films such as coatings for wear protection with thicknesses in the range of several micrometers. This test procedure requires equipment with a numerically controlled loading unit and a high resolution measurement of the indentation depth. This contribution shows, using various different examples, that the load indentation measurement can solve problems such as the influence of the operator, but the test conditions should be well selected to give comparable and meaningful results. Therefore, this paper analyzes the most important reasons for deviations in practice, and makes suggestions for a standardized test procedure and test documentation.

Comparison of fundamental properties of r.f.-sputtered TiNx and HfNx coatings on steel substrates

Abstract Titanium and hafnium based coatings in this work were sputtered on steel substrates in a r.f. sputtering unit with a diode arrangement. By feeding nitrogen in addition to the inert processing gas argon, TiN x and HfN x coatings were deposited under reactive sputtering conditions. Deposition pressure, nitrogen flow in the chamber and bias voltage on the substrates were systematically varied to get optimized coating systems. The coatings were investigated on their fundamental properties in order to compare titanium and hafnium based films, sputtered under identical process conditions. The results for hardness, deposition rate, internal stress, adhesion, structure, phase analysis and wear show that the properties of HfN x coatings are less influenced by the deposition process than the coatings of TiN x in the field of selected deposition parameters. The behavior of HfN x is comparable to TiN x , owing to a very similar crystal structure of the materials, but the conclusion of this present paper the well known TiN x has to be preferred for tribological applications in mechanical components.

Reliable Light Weight Fastening of Magnesium Components in Automotive Applications

This paper deals with optimized fastening of magnesium components to overcome serious problems in practice. For this, fasteners made of aluminum have significant advantages compared to conventional steel fasteners. The reasons are shown to the reader; calculations and established examples of application from series production confirm the behavior in practice.

Friction characteristics in light weight design focusing bolted joints

Today more and more light weight structures are used for moved components in automotive, aviation and general industry. Often assemblies of these structures are realized by friction-based connections. Therefore precise information about the friction coefficients are necessary, because in light weight design no simple approximation of the loading capacity with significant over-dimensioning is possible. Furthermore, the short-time tribology of mechanical contacts plays an important role during tightening of bolted joints, especially when using light metals and coated surfaces.Still today, the tightening method of torque controlled screw assembly is the most used. For this tightening method the friction coefficients have to be well-known for an efficient design of the bolted joint. Up to now analytical calculations do not consider any local deviation of friction behavior in component systems, only average values are taken. This is the reason why in modern engineering processes extended friction laws are necessary. A suitable formulation should take contact pressure and sliding velocity into account.Based on this, the contribution shows experimental examples for main uncertainties of frictional behavior during tightening with different material combinations (results from assembly test stand).Copyright

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. 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 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. 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, das das Korrosionsverhalten von allen Aufbauparametern abhangt und das 8 μm Chromnitrid denselben Korrosionsschutz liefern kann, wie 48 μm galvanisch abgeschiedenes Chrom.

Fundamental economical aspects of functional coatings for tribological applications

Abstract Today, a wide range of coatings for wear protection on different substrate materials in various technical applications is available. However, until now, only a few categories of hard coated components are established, such as cutting tools, machine parts for plastics processing or textile production and forming tools. The often high costs for hard coatings associated with the deposition depend, amongst others, mainly on the deposition process itself and the conception of the deposition unit. These aspects are important from the coaters point of view. For users of hard coatings for wear protection, it is important for the economy of a coating substrate system how the cost of the coating and the estimated increased lifetime of the coated component correlate in a given tribological system. This mainly determines the potential for coatings on commonly used machine parts in series production together with other resulting costs for the tribological system, modified by the coating. The contribution shows the flow of costs for tribological applications in their product life cycle. This analysis leads to the main cost factors. In addition, because of this, the future requirements for coating processes and coating units as well as the coating technology of mechanical components in general are obvious.

Schrauben aus hochfesten Aluminiumlegierungen : statisches und zyklisches Verhalten sowie Einsatzfelder

Kurzfassung Der im Fahrzeugbau zunehmende Einsatz von Bauteilen aus Leichtmetallen wie Aluminium- und Magnesiumlegierungen kann beim Verspannen mit den zurzeit üblichen Schrauben aus niedrig legierten hochfesten Stählen zu erheblichen Problemen führen. Eine Reihe dieser Probleme kann durch Verwendung von Schrauben aus Aluminiumlegierungen verringert oder gar vermieden werden.

Berechnung der drehwinkelgesteuerten Montage von Schraubenverbindungen

Um Schraubenverbindungen hinsichtlich ihres Vorspannkraftpotentials moglichst gut auszunutzen, werden hochbeanspruchbare Schrauben uber ihre Fliesgrenze hinaus vorgespannt – unter dem Stichwort „drehwinkelgesteuertes Anziehen” bekannt. Bisherige Auslegungsrechnungen beziehen sich allerdings immer noch auf ein elastisches Montieren, so das eine uberelastische Berechnungsvorschrift aus Erfahrung oder Versuchen abgeleitet werden mus. Der Beitrag stellt erstmals ein handhabbares Verfahren zur Berechnung von Fugemoment und Drehwinkel vor und zeigt anhand des Berechnungsalgorithmus die Abhangigkeiten einzelner Parameter. Schlieslich wird die Ubereinstimmung der Berechnungen mit Prufstandsversuchen abgesichert. Als wesentliche Einflusparameter werden Werkstoffeigenschaften der Schraube sowie Geometrie, Plastifizierungslange und Reibung betrachtet.