COATING FOR ENHANCED PERFORMANCE AND LIFETIME IN PLASTIC PROCESSING APPLICATIONS

Abstract

An improved coating used in plastic processing applications including a first layer system that includes at least one corrosion resistant material layer; a second layer system that includes at least one abrasion resistant material layers; and a transition layer provided between the first layer and the second layer. The coating is resistant to both abrasion and corrosion, while maintaining ductility and impact resistance.

Claims

1. A coating deposited on a surface of a substrate, said coating comprising: a first layer comprising at least one corrosion resistant material layer; a second layer comprising at least one abrasion resistant material layers; and a transition layer provided between the first layer and the second layer, wherein the first layer is deposited closer to the substrate than the second layer.

2. The coating according to claim 1, wherein the first layer is part of a first layer system deposited closer to the substrate than the second layer, said first layer system comprising one or more corrosion resistant layers, wherein at least one corrosion resistant layer being an AlCrO layer.

3. The coating according to claim 1, wherein the second layer is part of a second layer system deposited more distant from the substrate than the first layer system, said second layer system comprising one or more abrasion resistant layers, wherein at least one abrasion resistant layer being a CrON layer.

4. The coating according to claim 1, wherein the transition layer is part of a transition layer system, said transition layer system comprising one or more transition layers, wherein at least one transition layer being a CrON layer.

5. The coating according to claim 1, wherein the transition layer system comprises a Cr.sub.2O.sub.3 layer.

6. The coating according to claim 3, wherein the second layer system comprises at least one CrN layer.

7. The coating according to claim 3, wherein the second layer system comprises at least one CrO layer.

8. The coating according to claim 3, wherein the second layer system comprises at least one Cr.sub.2O.sub.3 layer deposited as outermost layer.

9. The coating according to claim 2, wherein the first layer system comprises at least one AlCrN layer deposited between the substrate and the AlCrO layer.

10. The coating according to claim 1, wherein at least one adhesion layer is deposited between the substrate and the first layer or between the substrate and the first layer system.

11. The coating according to claim 10, wherein the at least one adhesion layer is a CrN layer.

12. The coating according to claim 1, wherein the first layer or the first layer system includes one or more layers of the following materials: aluminum chromium oxide (AlCrO), aluminum chromium oxynitride (AlCrON), chromium oxides (CrO.sub.x), and chromium (III) oxide (Cr.sub.2O.sub.3).

13. The coating according to claim 1, wherein the second layer or the second layer system includes one or more layers of the following materials: chromium (Cr), chromium nitride (CrN), chromium oxynitride (CrON), chromium oxides (CrO.sub.x), and chromium (III) oxide (Cr.sub.2O.sub.3).

14. The coating according to claim 1, wherein the second layer or the second layer system has a hardness between 29 GPa and 33 GPa.

15. The coating according to claim 1, wherein the first layer or the first layer system is a multilayer part including at least one of AlCrO, AlCrON, CrO.sub.x, and Cr.sub.2O.sub.3.

16. The coating according to claim 1, wherein the second layer or the second layer system is a multilayer part including at least one of Cr, CrN, CrON, CrO.sub.x, and Cr.sub.2O.sub.3.

17. A substrate having a coating deposited on a surface of a substrate, said coating comprising: a first layer comprising at least one corrosion resistant material layer; a second layer comprising at least one abrasion resistant material layers; and a transition layer provided between the first layer and the second layer, wherein the first layer is deposited closer to the substrate than the second layer, wherein the surface on which the coating is deposited is made of a material including a ferrous metal.

18. A substrate having a coating deposited on a surface of a substrate, said coating comprising: a first layer comprising at least one corrosion resistant material layer; a second layer comprising at least one abrasion resistant material layers; and a transition layer provided between the first layer and the second layer, wherein the first layer is deposited closer to the substrate than the second layer, wherein the surface on which the coating is deposited is made of a material including steel or is made of a material of the type steel.

Description

DETAILED DESCRIPTION

[0031] FIG. 1 illustrates a prior art cross sectional image of glass fiber reinforced plastics.

[0032] FIG. 2 illustrates a prior art coated substrate with corrosion apparition and corrosion failure.

[0033] FIG. 3 illustrates schematically an example of an inventive coating 105 deposited on a surface of a substrate 110 according to one embodiment of the present invention, in which: the second layer system 140 is a multilayer film comprising layers for example of the type Cr, CrN, CrON, CrOx or CrO.sub.3; the first layer system 120 is a multilayer film comprising layers for example of the type AlCrO, AlCrON, Cr.sub.2O.sub.3; the transition layer or transition layers 130 are deposited between the first layer system 120 and the second layer system 140.

[0034] FIG. 4 illustrates abrasive resistance test results showing a comparation of the evolution of the wear depth produced under same conditions by using substrates coated with prior art comparative coatings of the type AlTiN and AlCrN as well as by using a new multilayer coating according to one embodiment of the present invention. In this graphic not any of the coatings has presented coating failure yet.

[0035] FIG. 5 illustrates corrosive resistance test results showing a comparation of the corrosion apparition and in some cases even coating failure produced under same conditions by using substrates coated with prior art comparative coatings of the type AlTiN and AlCrN as well as by using a new multilayer coating according to one embodiment of the present invention.

[0036] Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience.

[0037] Examples incorporating one or more embodiments of the present invention are described and where appropriate illustrated in the drawings. These described and/or illustrated examples are not intended to be limiting. For example, one or more aspects of an embodiment of the present invention may be utilized in other embodiments and even other types of substrates (e.g. tools, components or devices).

[0038] Described herein is an example of a coating architecture with multilayers and material selections that exhibit high abrasive resistance and high corrosive resistance as well as ductility and impact resistance. A corrosion attack typically occurs at an interface between a coating and a substrate. Accordingly, a corrosive resistant layer or a corrosive resistant part of a multilayer coating can be provided at this interface. Turning now to FIG. 3, an example of a corrosive resistance part 100 (e.g. part of a component, tool or device coated with a coating comprising a corrosive resistant part according to the present invention) is illustrated. In this example a corrosive and abrasive resistant coating 105 is applied to a substrate 110. The substrate 110 can be a tool, such as an injection mold, with a ferrous metal surface, such as steel or cast iron. However, the coating 105 can be applied to non-ferrous metal surfaces as well. The coating 105 includes a first layer system 120 comprising at least one corrosive resistant layer, exhibiting in this manner corrosive resistant properties. For example, the first layer system 120 can include one or more layers of aluminum chromium oxide (AlCrO), aluminum chromium oxynitride (AlCrON), chromium oxides (CrO.sub.x), and/or chromium (III) oxide (Cr.sub.2O.sub.3). Such corrosive resistant oxide and oxynitrides layers act as an insulator to mitigate outward diffusions of electrons and also as a barrier for the inward diffusion of corrosive ions from the environment. These layers prevent or slow down the diffusion of corrosive ions.

[0039] A second layer system 140 can be provided on top of the first layer system 120. The second layer system 140 can be deposited as monolayer or multilayer including one or more abrasive resistant layers for exhibiting in this manner abrasive resistant properties. This second layer system 140 protects the substrate 110 against abrasive wear and the at least one corrosive resistant layer forming the first layer system 120 protects the substrate against corrosive wear, in this manner the inventive coating 105 provides to the substrate 110 besides good corrosion resistance properties also resistance against both abrasive wear and mechanical loads during application. More specifically, the second layer system 120 can include one or more of the following layers for forming a multilayer: chromium (Cr), chromium nitride (CrN), chromium oxynitride (CrON), chromium oxides (CrO.sub.x), and/or chromium (III) oxide (Cr.sub.2O.sub.3).

[0040] The resultant coating can have a high hardness of 31±2 GPa, where the coating can be deposited exhibiting a multilayer structure comprising individual layers with respective individual layer thickness in micro-meter range and/or in nano-meter range. This structure exhibits higher ductility and crack deflection as well as being highly abrasive resistant and tolerant of mechanical loads. As show in FIG. 3 at least one transition layer 130 can be provided between the first layer 120 and the second layer 130 to mitigate delamination of the corrosive and abrasive resistant parts. Since layers have different crystal structures and lattice parameters as well as chemical compositions, a precise transition (comprising one or more transition layers) can be important for example for improving cohesion within the coating 105 by increasing adhesion between the first layer system 120 and the second layer system 140.

[0041] Tests were conducted in order to evaluate abrasive resistance properties of the inventive example coatings (new multilayer inventive coatings) in comparison with prior art comparative coatings against glass fiber reinforced plastics. Turning now to FIG. 4, coated steel substrates were tested against polyamide with 50% glass fiber content in a dry sliding test with 100 N perpendicular load for a distance of 120 km FIG. 4 presents the wear depth of a coating in accordance with the embodiment disclosed in FIG. 3 in comparison with conventional (prior art) abrasive resistant PVD coatings of the type aluminum chromium nitride (AlCrN) and auch of the type titanium aluminum nitride (TiAlN). The superior performance of the inventive coatings in terms of abrasive resistance can be clearly seen.

[0042] In order to evaluate the corrosion resistance of the inventive coatings in accordance with the embodiment disclosed in FIG. 3 in comparison with the same both above-mentioned conventional (prior art) abrasive resistant PVD coatings, a neutral salt spray test (NSST) was conducted. The coatings were applied to a substrate made of 1.2842 cold work steel with 0.4 at. % Cr. The low amount of Cr content allows for a higher galvanic potential between substrate (steel) and Cr containing coatings and therefore a higher degree and rate for corrosion during NSST. As it can be seen in FIG. 5, the conventional AlCrN and AlTiN coatings exhibited severe pitting corrosion at many spots. This pitting corrosion propagated quickly during the next days. By the 6.sup.th day, oxidized iron from the substrate covers almost the whole surface of the coating. In contrast, the inventive coatings according to the example embodiment described in FIG. 3, showed very few minor pitting spots on the 1st day. Moreover, this remained stable throughout the 6th day, on which no further corrosion spot or propagation is observed.

[0043] A number of examples of inventive coatings and materials that can be used as layers in the inventive coatings have been described above. Nevertheless, it will be understood that various modifications may be made. For example, suitable results may be achieved if the described elements are combined in a different manner and/or replaced or supplemented by other elements or their equivalents. Accordingly, other implementations are within the scope of the following claims.

[0044] A preferred embodiment of the present invention refers to a coating comprising: a first layer system, a second layer system and at least one transition layer, where

[0045] the first layer system comprises at least one AlCrN layer and preferably also at least one AlCrO layer as corrosion resistant layers,

[0046] the second layer system comprises at least one CrON layer and preferably also at least one CrN layer and/or one CrO layer, and

[0047] a transition layer system formed of one or more transition layers deposited between the first layer system and the second layer system, where the transition layer system comprises at least one transition layer of Cr.sub.2O.sub.3 and/or at least one transition layer of CrON, where the transition layers can be deposited as gradient layers or as non-gradient layers or as a combination of gradient and non-gradient layers.

[0048] Each one of the embodiments and preferred embodiments of the present invention described above can also include one or more adhesion layers deposited between the substrate and the first layer system for improving adhesion of the first layer system to the substrate, preferably a CrN layer can be used as adhesion layer. This adhesion layer or in case of more than one adhesion layer is deposited, the total thickness of the adhesion layers is preferably not higher than 1 micrometer. However, the layer thickness of the adhesion layer or of the sum of adhesion layers can be also higher than 1 micrometer, but preferably not higher than 1.5 micrometer.

[0049] Each one of the above-mentioned embodiments and preferred embodiments of the present invention can include a Cr.sub.2O.sub.3 layer as top layer of the coating, it means as outermost layer of the second layer system for improving performance, especially regarding abrasive wear resistance. This outermost layer is preferably deposited having a layer thickness of 1 micrometer or more. However, the layer thickness of this outermost layer can be also less than 1 micrometer, but preferably not less than 0.5 micrometer.

[0050] The thickness of the first layer system is preferably higher than 1 micrometer, more preferably higher than 2 micrometers. However, the layer thickness of the first layer system can be also less than 1 micrometer, but preferably not less than 0.5 micrometer.

[0051] The thickness of the second layer system is preferably higher than 2 micrometers, more preferably higher than 2.5 micrometers. However, the layer thickness of the first layer system can be also less than 2 micrometers, but preferably not less than 1.5 micrometer.

[0052] The thickness of the second layer system is preferably higher than the layer thickness of the first layer thickness.

[0053] Coatings according to the present invention are preferably deposited having a total coating thickness between 1 and 30 micrometers, more preferably between 2.5 micrometers and 20 micrometers. However, this preferred coating thickness range should not be understood as a limitation of the invention. In general, the total coating thickness as well as the thickness of the individual layers or layer systems can be selected depending on the application of the tool or the use of the substrate.

[0054] Coatings according to the present invention are especially suitable for improving performance and increasing lifetime of injection molds used for manufacture of parts made of plastics materials, for example polyester materials.

[0055] In order to show improvements attained with the inventive coatings in more detail, a further example will be described as showcase coating below:

[0056] This showcase coating was deposited on surfaces of injection molding tools (e.g. injection molds or parts of injection molds) to be in contact with the work piece material by using physical vapour deposition (PVD) techniques of the type reactive cathodic arc evaporation. During coating deposition, Cr-targets and/or AlCr-targets were arc evaporated in a coating chamber comprising nitrogen gas and/or oxygen gas as reactive gas. In this particular showcase the AlCr-targets were selected having element composition in atomic percentage of 70 at.-% Al and 30 at.-% Cr. This showcase coating was deposited comprising an adhesion layer of CrN deposited directly of the surface of the injection molding tool to be coated, subsequently a first layer system (also called corrosion layer system in the context of the present invention) comprising one layer of AlCrN and one layer of AlCrO was deposited on the adhesion layer, subsequently a transition layer system (transition layer system=two or more transition layers) comprising one transition layer of Cr.sub.2O.sub.3 and one transition layer of CrON was deposited on the first layer system, subsequently a second layer system (also called abrasive layer system in the context of the present invention) comprising a plurality of layers deposited alternate one of each other as layer sequences, each layer sequence comprising layers of CrN, layers of CrON and layers of CrO and comprising also a Cr.sub.2O.sub.3 layer as outermost layer, was deposited on the transition layer system. For some real application tests, the as they are for example shown in FIG. 6, the showcase coating was deposited having a total coating thickness between 6 and 8 micrometers.

[0057] The inventive coatings can be applied on previously nitrided substrate, e.g. on previously nitride surfaces of injection molding tools.

[0058] The inventive coatings are preferably deposited by any PVD method, for example arc PVD or sputtering PVD by maintaining preferably a substrate temperature between 250° C. and 450° C. However, this preferred substrate temperature during coating should not be understood as a limitation of the invention.

[0059] Preferably the deposition of the nitride layers (e.g. CrN and AlCrN) is carried out by applying a DC substrate bias at the substrate, while the deposition of the oxygen containing layers (e.g. oxide or oxynitride layers such as CrO, Cr.sub.2O.sub.3 and CrON layers) is preferably carried out by applying a bipolar bias.

[0060] Preferably for the deposition of layers comprising nitrogen and/or oxygen which are deposited subsequently one on each other the oxygen, the nitrogen flow and the oxygen flow entering in the coating chamber are correspondingly increased and/or decreased gradually for producing a sequence of layers or simply layers deposited one on each other, for example for depositing first a CrN layer, afterwards a CrON layers and afterwards a CrO layer, then the Cr-targets can be evaporated initially by maintaining a determined nitrogen flow entering in the coating chamber for depositing the CrN layer, subsequently a oxygen flow can introduced and increased gradually in the coating chamber, while the nitrogen flow can be maintained or decreased gradually for the deposition of the CrON layer, and finally the nitrogen flow can be reduced gradually till 0 sccm, while the oxygen flow is maintained or increased or reduced gradually till a determined oxygen flow for the deposition of the CrO layer. A similar process can be carried out in reverse for depositing a reverse sequence of layers, e.g. CrO.fwdarw.CrON.fwdarw.CrN.

[0061] The inventive coatings are suitable for coating any kind of substrate material. In the case of applications in the field of plastic forming processes (e.g. injection molding and extrusion) the substrates materials are dominantly different kinds of steels.

[0062] During deposition of oxygen containing layers, in particular during deposition of oxide layers the inventors recommend using oxygen flows adjusted for the coating device that is being used and the coating conditions, e.g. kind of target material and quantity of targets being evaporated. It is recommended to find an oxygen flow range in which the mechanical properties as well as the density of the coating morphology are appropriate for the intended application. A “too high oxygen content in the coating chamber can lead to poor mechanical properties as well as an under-dense morphology of the oxygen-containing layer being deposited.

[0063] During deposition of some inventive coatings comprising for example a layer sequence of the type CrN.fwdarw.CrNO.fwdarw.CrO the oxygen flow was ramped up and the nitrogen flow was ramped down. For example, the oxygen flow was ramped up from 200 sccm to 600 sccm for the deposition of the CrNO and CrO layers and the nitrogen flow was ramped down from 1100 sccm to 100 sccm for the deposition of the CrN and CrNO layers. For deposition of reverse sequences, e.g. CrO.fwdarw.CrNO.fwdarw.CrN the oxygen and nitrogen flows were likewise ramped up and ramped down but in a reverse manner.

[0064] FIG. 6 shows the results obtained by injection molding (application tests under real conditions) of four injection molds (identified as as Mold 1, Mold 2, Mold 3 and Mold 4 in FIG. 6) coated with an inventive coating deposited in the same manner that the showcase coating described above and one injection mold coated with a prior art coating of the type AlTiN. These results allow quantifying the improvement obtained by the present invention comparing the number of injection molding shots (produced parts, in this case produced electrical switches) realized with molds coated with AlTiN and molds coated according to the present invention.

[0065] As it is indicated in the graphic shown in FIG. 6, with the mold coated with the prior art AlTiN coating only 40′000 to 50′000 shots could be attained before the coated mold turned no more operational (average lifetime was approximately 50′000 shots). With the molds coated with coatings according to the present invention the improvement was considerably high, even in one case more than 400% and these molds coated with inventive coatings were still operational. The work piece material used in these tests was unsaturated polyester with 30% glass fiber, the produced parts were electrical switches.

[0066] A coating deposited on a substrate, the coating comprising a first layer or a first layer system comprising at least one corrosion resistant material layer; a second layer or a second layer system comprising at least one abrasion resistant material layer; and a transition layer provided between the first layer and the second layer, wherein the first layer or first layer system is deposited closer to the substrate than the second layer or second layer system has been disclosed in the present invention.

[0067] This coating has the advantage in comparison with coatings having only an abrasion resistance part, e.g. a multilayer structure of the type . . . CrN/CrON/CrN/CrON . . . that the mentioned abrasion resistant part only provides a good abrasion resistance but a poor corrosion resistance.

[0068] Including a corrosion resistant part closer to the substrate, e.g. at least one AlCrO layer improves corrosion resistance because the AlCrO layer acts as barrier for corrosion. Including furthermore an AlCrN layer between the AlCrO layer and the substrate, it is possible to have the corrosion barrier effect but improving adhesion of the coating to the substrate. Likewise, including an adhesion layer e.g. of the type CrN it is possible to attain a much better adhesion of the corrosion resistant part to the substrate.

[0069] The transition layers improve cohesion of the coating by improving adhesion between the corrosion resistant part and the abrasion resistant part of the coating.

[0070] The use of a Cr.sub.2O.sub.3 outermost layer increase performance of the coating, especially by applications including processing of plastic materials, e.g. injection molding, because AlCrO reduce tendency to stick to plastic materials during processing of the work piece (because of effect of less chemical affinity to plastic materials).

[0071] The first layer or a first layer system includes preferably one or more layers of the following materials: aluminum chromium oxide (AlCrO), aluminum chromium oxynitride (AlCrON), chromium oxides (CrO.sub.x), and chromium (III) oxide (Cr.sub.2O.sub.3).

[0072] The second layer or second layer system includes preferably one or more layers of the following materials: chromium (Cr), chromium nitride (CrN), chromium oxynitride (CrON), chromium oxides (CrO.sub.x), and chromium (III) oxide (Cr.sub.2O.sub.3).

[0073] Preferably the second layer or the second layer system has a hardness between 29 GPa and 33 GPa measured by using known nano-indentation techniques.

[0074] The first layer or first layer system can be in one embodiment a multilayer part including at least one of AlCrO, AlCrON, CrO.sub.x, and Cr.sub.2O.sub.3.

[0075] The second layer or second layer system can be in one embodiment a multilayer part including at least one of Cr, CrN, CrON, CrO.sub.x, and Cr.sub.2O.sub.3.

[0076] The first layer or first layer system is intended to insulate the substrate from outward diffusions of electrons and inward diffusions of corrosive ions from an environment.

[0077] The transition layer or transition layer system is intended to mitigate delamination between the first layer and the second layer.

[0078] The chemical composition of the first layer or first layer system is different from the chemical composition of the second layer or second layer system.

[0079] In one embodiment the crystal structures and lattice parameters of the first layer or first layer system can be different from the crystal structures and lattice parameters of the second layer or second layer system.

[0080] The present invention relates also to a method of coating a substrate, comprising:

[0081] providing a substrate;

[0082] applying a multilayer corrosive resistant part to the substrate;

[0083] applying at least one transition layer to the multilayer corrosive resistant part; and

[0084] applying a multilayer abrasive resistant part to the at least one transition layer.

[0085] The substrate coated with a coating according to the present invention can include a ferrous metal surface on which the coating is deposited.

[0086] In one further embodiment the multilayer corrosive resistant part comprises at least one of the following materials: AlCrO, AlCrON, CrO.sub.x, and Cr.sub.2O.sub.3 and/or the multilayer abrasive resistant part comprises at least one of the following materials: Cr, CrN, CrON, CrO.sub.x, and Cr.sub.2O.sub.3.

[0087] In particular a coating according to the present invention can be used in plastic processing applications. The coating is resistant to both abrasion and corrosion, while maintaining ductility and impact resistance.

[0088] According to a preferred embodiment of a coating according to the present invention, the inventive coating is deposited on a surface of a substrate and is characterized by comprising: [0089] a first layer comprising at least one corrosion resistant material layer; [0090] a second layer comprising at least one abrasion resistant material layers; and [0091] a transition layer provided between the first layer and the second layer, [0092] wherein the first layer is deposited closer to the substrate than the second layer, wherein [0093] the first layer is part of a first layer system deposited closer to the substrate than the second layer, said first layer system comprising one or more corrosion resistant layers, wherein one corrosion resistant layer is preferably an AlCrO layer.

[0094] Preferably the second layer is part of a second layer system deposited more distant from the substrate than the first layer system, said second layer system comprising one or more abrasion resistant layers, one abrasion resistant layer being a CrON layer.

[0095] Preferably the transition layer is part of a transition layer system, said transition layer system comprising one or more transition layers, one transition layer being a CrON layer.

[0096] Preferably the transition layer system comprises a Cr.sub.2O.sub.3 layer. Preferably the second layer system comprises at least one CrN layer and/or at least one CrO layer.

[0097] Preferably the second layer system comprises at least one Cr.sub.2O.sub.3 layer deposited as outermost layer.

[0098] Preferably, when the first layer system comprises at least one AlCrO layer, at least one AlCrN layer is deposited between the substrate and the AlCrO layer.

[0099] Preferably at least one adhesion layer is deposited between the substrate and the first layer or between the substrate and the first layer system.

[0100] Preferably the at least one adhesion layer is a CrN layer.