In this study, the effect of increasing aluminum content and magnetic steering field strength on the structure and wear behavior of arc PVD AlTiN coatings is discussed. Deposition was done by means of an industrial-scale PVD unit for tool coating. The aluminium content in the AlTi source material was increased from 67 to 73 at.%. We applied two settings of the magnetic field that steers the arc across the cathode surface thereby evaporating the AlTi alloy differently. The resulting coating thickness ranged from 3.5 to about 7 µm. Cemented tungsten carbide was used as substrate material. Coating properties like hardness, adhesion, and crystal phases were analyzed by indentation and X-ray diffraction, respectively. The wear behaviour of the different AlTiN hard coatings were investigated in two ways. In a first idealized test, cyclic impacting was done applying a constant force. The resulting wear pattern was quantified by an Alicona multi-focus microscope. A second wear test was done by metal cutting under realistic conditions. Fly milling of ductile cast iron (EN-GJS-700) was performed with regular interruptions in order to measure the increasing wear mark. As expected, aluminium contents above 67 at.% (in the metal fraction of the coating) lead to a decreased wear resistance as the soft hexagonal phase exceeds values of a few vol.%. However, it was found that the formation of the hexagonal phase can be effectively influenced and delayed by increasing the magnetic steering field at the cathode. The wear behavior observed in cyclic impact testing corresponds well to results obtained with the more complex loading situation encountered in milling.

In the last 16 years the CVD-diamond deposition onto steel substrates has been an important aim of research projects because of the enormous potential for various technical applications. The combination of the unique surface properties of diamond (highest hardness, low friction and high corrosion resistance) with steel as the most common substrate material would generate a new solution for machine parts with extreme loads by friction and wear. However, the diamond deposition on steel comes along with several problems. Iron is a catalyst for graphite formation on the surface during diamond deposition process. Iron carbide formation takes place due to the carbon deposition on the steel substrate. This metastable carbide decomposes to iron and graphite again and so a thick graphite layer grows on the steel substrate. Diamond growth on this graphite layer is possible, but due to the low adhesion to the steel substrate useless for technical applications. [1] These problems could be solved by the use of an interlayer which has to fulfil several requirements. At first the interlayer must be a diffusion barrier against the diffusion of carbon from the gas phase into the substrate and against the diffusion of iron from the substrate to the surface. [2] Furthermore the interlayer must work as a bonding agent between the diamond layer and the steel substrate. [3,4] Hence, the coefficient for thermal expansion should be located between the values of diamond and the steel substrate.In the past different interlayer coatings and surface modifications were already applied to avoid graphite formation and accomplish adherent diamond films. [3][4][5][6][7][8][9][10][11][12][13][14] High temperature diffusion chromizing interlayers have shown adequate properties for diamond deposition on steel substrates. An excellent bonding of the interlayer to the steel sample is assured by the chromizing temperature of 1150°C. [3,4] Also the problem of the great mismatch in thermal expansion between diamond (1.05-4.5·10 -6 K -1 ) and steel (11.7·10 -6 K -1 ) has been solved by high temperature diamond deposition in austenite field, [4,14] using the volume expansion during the c-a-transformation.In this work the influence of diamond deposition temperature in a Hot-Filament Chemical Vapour Deposition (HFCVD) process onto the adhesion of the diamond layer is presented. The experiments had been carried out with 41Cr4 steel, which is standard steel for bearing parts. As an interlayer we used a high temperature diffusion chromium carbide interlayer (Cr 23 C 6 ) as mentioned by Bareiß et al. [4] With this interlayer it's possible to fulfil all requirements to deposit CVD-diamond coatings on steel substrate. Diamond deposition at high temperatures (above 850°C) causes a phase transformation in the interlayer. Thus transformation from Cr 23 C 6 to the carbon rich Cr 3 C 2 phase effects an excellent chemical activation of the carbide surface at the initial stage of deposition.In Fig. 1 a specimen with an inhomogeneous chromium carbide layer (Cr 23 C 6 an...

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