Beanspruchungsverhalten von PVD‐CrN Beschichtungen auf Leichtmetallwerkstoffen

Abstract

Das Au lbri ngen du nner Harts toffkchic h ten i s t be i tri bolog isc h stark beanspruchten Werkzcugen, wie L. R. bei Dreh-tmd Umfornwerkzeugen, Stand der Technik. StandLeiterhdhungen der beschichteten Werkreugc in1 Vcrgleich 711 unbeschichteten Referen-Len sind vielfach hestiitigt [ I ) . In diese ni Z tisani me nhan g i 5 t in v ielen Fii I len .,Funk t i oils t rcnn ti ng ", d. h. eine Trennung der Aufgiiben von Werkstof'fvolumcn und Werkstoffoberllachc. cin Lentrales Schlagwort. Dabei wii-d davon ausgegangen, daf.3 tribologische und korrosive Beanspruchungen nur auf Oberfliichen wirken und darum nur d i e s mit einer geeigneten Schichl /.u schiitzen sind. Die Wahl der Stibstrntwerkstoffe oder eine Optiinierung des Schicht-Substrat-Vcrbundes stand oft nicht im Mittelpunkt der PVD -Schichtentwicklung. Betrachtungen zum Schicht-Substrat-Verbund sind jedoch unumgiinglich, wenn die Eigenschaften vtfn Schicht und Substrat stark von einander abweichen (z. B. Hnrtstolf'e auf ,.weichen" Leichtmetallen im Gegensatz zu Hartstoften auf hochfestcn Stahlsubstraten). Der Beitrag greift wescntliche Aspekte zur inechanisch-tribologischen und elektrochemischen Bewertung hartstoffbeschichteter Leichtmetalle am Beispiel PVD-CrN aul'.The application of' thin hard coatings on machining tools, e.g. drilling tools i s state of the art. The increase of lifetime of coated tools compared to uncoated tools i s well known. 111. In this context ,,separation of functions" i s 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 ;I ,,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 (c.6. hard coatinglight metals). This paper shows different aspects of the tribological and electrochemical characterimtion oT PVD coated light metals (CrN coating).

Wear and Corrosion Protection of Aluminum and Magnesium Alloys Using Chromium and Chromium Nitride PVD Coatings

“…Already 60±180 s after starting the measurements, the free corrosion potential of coated samples was the same as of uncoated samples. Looking at the results of coated aluminum alloys [3] , these results are astonishing. The reasons for this can be found in the defects in the coating on magnesium.…”

“…Figure 6 illustrates that the three curves are above this value. Looking at the results presented in this paper and in [3,8] . two main con- clusions can be made.…”

“…Looking at the linear thermal expansion coefficients of Cr and CrN (~2.3´10 ±6 K ±1 ), this can lead to high stress in the interface between the coating and substrate. As mentioned, aluminum, and also magnesium, reacts very fast with oxygen, so an oxide film will grow [3] . The oxide film on aluminum is very stable.…”

“…As mentioned earlier, no influence of the substrate on the crystal lattice is detectable. [3,8] The results of the wear and corrosion tests are shown in Figures 2 and 3. Figure 2 shows the wear behavior of the uncoated and coated aluminum and magnesium samples.…”

“…Aluminum and magnesium alloys pass these criteria, but fail with respect to the criteria of corrosion and wear resistance. Investigations published in Senf et al [3] show the enormous potential of PVD CrN coatings on steel (100Cr6) and lightweight materials such as titanium (TiAl6V4) and aluminum (AlMgSi0.5; AlSi7Mg). In this paper results of wear and corrosion investigations of chromium and chromium nitride-coated aluminum and magnesium alloys (AlSi7Mg, AZ91hp) are presented and discussed.…”