COATING SYSTEM FOR PLASTIC PROCESSING APPLICATIONS

Abstract

A multilayer coating exhibits good corrosion resistance and good abrasion resistance. The multilayer coating includes layers A and layers B deposited forming a sequence of the type . . . A/B/A/B/A . . . , with the layers A being CrN-based layers or CrN layers and the layers B being CrON-based layers or CrON layers. The multilayer coating exhibits a modulated ratio of the thicknesses of the A layers and B layers, in a manner that the multilayer coating comprises at least two different coating portions along the whole multilayer coating thickness, with differently adjusted ratio of the thicknesses of the A layers and B layers.

Claims

1-6. (canceled)

7. A multilayer coating with layers A and layers B deposited forming a sequence of the type . . . A/B/A/B/A . . . , the layers A being CrN-based layers or CrN layers and the layers B being CrON-based layers or CrON layers, wherein the multilayer coating exhibits a modulated ratio of the thicknesses of the A layers and B layers, in a manner that the multilayer coating comprises at least two different coating portions along the whole multilayer coating thickness, with differently adjusted ratio of the thicknesses of the A layers and B layers, wherein: the multilayer coating comprises: an under multilayer coating portion with an average thickness ratio LTR100 of the average thickness of the A layers regarding the average thickness of the B layers, and an upper multilayer coating portion with an average thickness ratio LTR200 of the average thickness of the A layers regarding the average thickness of the B layers, wherein LTR100>LTR200.

8. The multilayer coating according to claim 7, wherein the multilayer coating is deposited in a substrate surface in such a manner that the under multilayer coating portion is deposited closer to the substrate surface than the upper multilayer coating portion.

9. The multilayer coating according to claims 8, wherein: the under multilayer coating portion has average layer thickness ratio between the A layers and B layers, LTR100, greater than 1, i.e. LTR100>1, and the upper multilayer coating portion having average layer thickness ratio between the A layers and B layers, LTR200, LTR200<1.

10. The multilayer coating according to claim 7, wherein the multilayer coating comprises further coating portions or further coating layers.

11. The multilayer coating according to claim 10, wherein the multilayer coating comprises an intermediate multilayer coating portion deposited between the under multilayer coating portion and the upper multilayer coating portion.

12. The multilayer coating according to claim 11, wherein the intermediate multilayer coating portion has an average layer thickness ratio between the A layers and B layers, LTR150, wherein LTR100>LTR150 >LTR200.

Description

[0050] Hence, in an under multilayer coating portion 100, the average layer thickness ratio, LTR100, is given by considering the average layer thickness of the A layers in the under multilayer coating portion 100, i.e. the average layer thickness of the A100 layers, and the average layer thickness of the B layers in the under multilayer coating portion 100, i.e. average layer thickness of the B100 layers:

[00002]$\mathrm{LTR}100=\frac{\mathrm{average}\mathrm{thickness}\mathrm{of}A100}{\mathrm{average}\mathrm{thickness}\mathrm{of}B100}$

[0051] And similarly, in an upper multilayer coating portion 200, the average layer thickness ratio, LTR200, is given by considering the average layer thickness of the A layers in the upper multilayer coating portion 200, i.e. the average layer thickness of the A200 layers, and the average layer thickness of the B layers in the upper multilayer coating portion 200, i.e. average layer thickness of the B200 layers:

[00003]$\mathrm{LTR}200=\frac{\mathrm{average}\mathrm{thickness}\mathrm{of}A200}{\mathrm{average}\mathrm{thickness}\mathrm{of}B200}$

[0052] The inventor observed an important improvement in the combination of corrosion resistance and abrasion resistance, when a multilayer coating with at least two multilayer coating portions was produced, in a manner that the average layer thickness ratio LTR100 in the under multilayer coating portion 100 was greater than the average layer thickness ratio LTR200 in the upper multilayer coating portion 200, i.e. when LTR100>LTR200.

[0053] In particular, a surprisingly good combination of high corrosion resistance and high abrasion resistance was obtained in a preferred embodiment of the present invention, in which the multilayer coating was produced with at least two multilayer coating portions, an under multilayer coating portion 100 having average layer thickness ratio LTR100>1 and an upper multilayer coating portion 200 having average layer thickness ratio LTR200<1.

[0054] A multilayer coating according to the present invention can also comprise further coating portions or further coating layers.

[0055] According to a further preferred embodiment of the present invention the multilayer coating comprises an intermediate multilayer coating portion 150 deposited between the under multilayer coating portion 100 and the upper multilayer coating portion 200.

[0056] The intermediate multilayer coating portion 150, having an average layer thickness ratio, LTR150, given by considering the average layer thickness of the A layers in the intermediate multilayer coating portion 150, i.e. the average layer thickness of the A150 layers, and the average layer thickness of the B layers in the intermediate multilayer coating portion 150, i.e. average layer thickness of the B150 layers:

[00004]$\mathrm{LTR}150=\frac{\mathrm{average}\mathrm{thickness}\mathrm{of}A150}{\mathrm{average}\mathrm{thickness}\mathrm{of}B150}$

[0057] wherein LTR100>LTR150>LTR200 According to one more further preferred embodiment, the multilayer coating comprises more than three multilayer coating portions, wherein the first multilayer coating portion is the under multilayer coating portion 100 and the last multilayer coating portion is the upper multilayer coating portion 200, wherein each multilayer coating portion has a different average layer thickness ratio LTR and the LTR decreases gradually (continuously or stepwise) from the under multilayer coating portion up to the upper multilayer coating portion.

[0058] Preferably, the layers of CrN within one coating portion have approximately the same coating thickness, and preferably the layers of CrON within one coating portion have approximately the same coating thickness. Variations can occur for instance though due to substrate rotation and relative orientation of the deposition sources in the PVD deposition system.

[0059] Preferably the thickness of one bilayer, i.e. the thickness of the sum of one B layer plus one A layer deposited one on the other is in a range of 30 nm to 500 nm, more preferably in a range of 100 nm to 200 nm, for example the bilayer thickness can be 150 nm.

[0060] The total multilayer coating thickness is preferably between 1 m and 30 m, more preferably between 2 m and 20 m, still more preferably between 5 and 10 m.

[0061] The thickness of one multilayer coating portion, e.g. the thickness of the under multilayer coating portion 100 or the thickness of the upper multilayer coating portion 200 is preferably not lower than 10% of the total multilayer coating thickness.

[0062] Preferably, the coating comprise a cubic fcc-CrN phase. This can for example be characterized by X-ray diffraction.

[0063] The coating has preferably an indentation hardness larger than 20 GPa, in particular in the range 25-35 GPa.

[0064] The coating according to the present invention can also comprise a bottom coating layer, which is deposited between the substrate surface on which the multilayer coating is deposited and the under multilayer coating portion.

[0065] The bottom coating layer can be for example be deposited directly on the substrate surface for improving adhesion of the coating to the substrate surface. In this case, the bottom coating layer can be for example a CrN layer or a Cr layer or can be a layer comprising any of CrN or Cr.

[0066] The coating according to the present invention can also comprise a top coating layer, which is deposited atop the coating, above the upper multilayer coating portion.

[0067] The top coating layer can be for example be deposited as outermost layer directly on the upper multilayer coating portion for improving any further surface properties.

[0068] The top coating layer can be for example a CrON layer for reducing tendency to stick to plastic materials.

[0069] Application of the described coatings can be combined with nitriding pre-treatment. This can be done either in a separate vacuum or atmospheric nitriding process, or in-situ prior to application of the first surface layer.

[0070] The inventive coatings can be deposited by using known PVD techniques.

[0071] The use of a negative bias voltage applied to the substrate during deposition of the multilayer coating portions was found to be advantageous, for example a negative bias voltage between 10 V and 150 V (in absolute value).

[0072] Inventive examples and comparative examples:

[0073] The present description including Figures and examples are not provided with the intention to limit the invention but only to help to understand the invention. Therefore, the examples given in the present description should not be understood as a limitation of the invention.

[0074] For the deposition of the inventive coatings as well as for the deposition of the comparative coatings described in the examples below, an Oerlikon Balzers INNOVENTA mega PVD deposition system was used.

[0075] The examples of inventive coatings as presented below were deposited through arc deposition from Cr-targets. The multilayer architecture was obtained through alternating pure N2 atmosphere for deposition of CrN, and an atmosphere of a mixture between N2 and O2. Several sequences of pure N2 atmosphere, followed by mixed N2/O2 atmosphere were repeated to obtain coatings with a sequence of several bilayer periods consisting of CrN and CrON individual layers.

[0076] The thickness ratio between CrN and CrON layers was modulated (i.e. controlled) by adjusting the time duration of the deposition sequence in pure N2 atmosphere and the time in mixed N2/O2 atmosphere.

[0077] In the FIGS. 5 and 6 are shown the results regarding corrosion resistance test and abrasion resistance test conducted in substrates coated with a comparative example according to Example 1 and two comparative examples according to Example 2 and Example 3.

Comparative Examples 1:

[0078] A multilayer coating comprising CrN layers and CrON layers with average layer thickness ratio LTR=1, i.e. with average layer thickness of the individual CrN layers in the same magnitude (same average thickness layer value) as the individual CrON layers was deposited and tested. For some of the tests, in particular for the tests shown in FIGS. 5 and 6 a bottom layer of CrN was deposited between the substrate surface and the multilayer coating.

Inventive Examples 2:

[0079] Different inventive multilayer coatings comprising A layers of the type CrN layers and B layers of the type CrON layers, the multilayer coatings formed by two different multilayer coating portions, an under multilayer coating portion having LTR between 2 and 1.3 and an upper multilayer coating portion with LTR between 0.8 and 0.3 were deposited and tested. For some of the tests, in particular for the tests shown in FIGS. 5 and 6 a bottom layer of CrN was deposited between the substrate surface and the multilayer coating. For the tests shown in FIGS. 5 and 6, LTR in the under multilayer coating portion was between 1.55 and 1.75, and LTR in the upper multilayer coating portion was between 0.4 and 0.7.

Inventive Examples 3:

[0080] The only difference between Example 2 and 3 was that the multilayer coatings were deposited with an additional multilayer coating portion, more exactly an intermediate multilayer coating portion with LTR between 1.2 and 0.9. For the tests shown in FIGS. 5 and 6, LTR in the intermediate multilayer coating portion was about 1.

Description of the tests:

[0081] Abrasive wear resistance of the coatings was investigated using sliding reciprocal wear (SRV) measurements. A ball made of Al2O3was used in reciprocal sliding motion, with 10 Hz under constant applied force (50 N) and for 60 min. The depth of the resulting wear track was measured and is presented in FIG. 5. A low wear track depth correspond to high abrasive wear resistance. As can be seen in FIG. 5, the inventive coatings (see Examples 2 and 3 in FIG. 5) display higher abrasive wear resistance than the comparative coating (see Example 1 in FIG. 5) produced according to the prior-art.

[0082] In order to evaluate the corrosion resistance of the coatings, the inventive coatings and the comparative coatings produced according to the prior-art were tested using a neutral salt spray test (NSST). The coatings were applied to a substrate made of 1.2842 cold work steel with 0.4 at % Cr. As exemplified in FIG. 6, the comparative coating (see Example 1 in FIG. 6) shows pitting corrosion on a main part of the surface after 72-96 hours. With the inventive coating (see Example 2 in FIG. 6), good corrosion resistance was attained.

[0083] These two tests confirm that the inventive coatings combine good corrosion resistance and high abrasive wear resistance.