Coating for metal components, method for coating a metal component, piston for internal combustion engines and motor vehicle

Abstract

An abrasion-resistant and friction-reduced coating for metal components is provided. The coating includes an inner layer, an intermediate layer and an outer layer. The inner layer is intended to be applied to the metal component and has at least one layer selected from: a metal layer, a metal-carbide layer, a metal-nitride layer, a metalcarbide- nitride layer and a metal-containing hydrocarbon layer. The intermediate layer includes at least one layer of amorphous carbon and the outer layer includes a WC:H layer or a a-C:H* layer. A maximum layer thickness of the coating is at most 5 m. The coating is suitable in particular as a piston coating for use in internal combustion engines.

Claims

1. A motor vehicle, comprising at least one piston of an internal combustion engine, the piston having a coating comprising: an inner layer which is applied to the piston; an intermediate layer; and a covering layer, wherein the inner layer comprises at least one layer selected from among: a metal layer, a metal carbide layer, a metal nitride layer, a metal carbonitride layer and a metal-containing hydrocarbon layer, the intermediate layer comprises an a-C:H layer and an a-C:H* layer, wherein the a-C:H* layer has a higher proportion of graphite-like parts than in the a-C:H layer, the covering layer comprises a W C:H layer or an a-C:H* layer, a maximum layer thickness of the coating is not more than 5 m.

2. The motor vehicle according to claim 1, wherein in the coating, one of: the inner layer has a Cr layer, a Cr/WC layer and a WC:H layer and the Cr layer is provided for application to the piston, or the inner layer has a CrN layer, a Cr/WC layer and a WC:H layer and the CrN layer is provided for application to the piston, or the inner layer has a Cr layer, a CrN layer and a Cr/WC layer and the Cr layer is provided for application to the piston.

3. The motor vehicle according to claim 2, wherein the intermediate layer comprises an a-C:H layer.

4. The motor vehicle according to claim 1, wherein in the intermediate layer, the a-C:H layer faces the inner layer and the a-C:H* layer faces the covering layer.

5. The motor vehicle according to claim 1, wherein the inner layer is formed by a Cr layer or CrN layer, a Cr/WC layer and a WC:H layer in this order, where the Cr layer or the CrN layer is provided for application to the piston, the intermediate layer is an a-C:H layer, and the covering layer is a WC:H layer or an a-C:H* layer.

6. The motor vehicle according to claim 1, wherein the inner layer is formed by a Cr layer, a Cr/WC layer and a WC/WC:H layer in this order, where the Cr layer is provided for application to the piston, the intermediate layer comprises an a C:H layer facing the inner layer and an a-C:H* layer facing the covering layer, and the covering layer is a WC:H layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a coating for metal components according to a first embodiment.

(2) FIG. 2 illustrates a coating for metal components according to a second embodiment.

(3) FIG. 3 illustrates a coating for metal components according to a third embodiment.

(4) FIG. 4 illustrates a coating for metal components according to a fourth embodiment and

(5) FIG. 5 illustrates a sectional view of part of a piston according to an advantageous further development.

DETAILED DESCRIPTION OF THE DRAWINGS

(6) The present invention will be explained in detail with the aid of working examples. In the figures, only the parts of the coating of the invention or of the piston of the invention which are of interest here are depicted; all other elements have been left out in the interests of clarity. Furthermore, identical reference numerals denote identical elements.

(7) In detail, FIG. 1 shows a layer structure of a coating 10 for metal components according to a first advantageous embodiment of the invention. The coating 10 has three individual layers which are arranged on top of one another so that the superposed layer in each case covers the layer located underneath. The first layer is an inner layer 1. The inner layer 1 is provided for establishing direct contact with a metal component and thus serves to bond the coating 10 to the metal component. The inner layer 1 includes at least one layer which is selected from among a metal layer, a metal carbide layer, a metal nitride layer, a metal carbonitride layer and a metal-containing hydrocarbon layer. Owing to the metal content, the inner layer 10 adheres well to metal surfaces. The coating 10 further includes an intermediate layer 2 which is arranged on top of the inner layer 1. The intermediate layer 2 includes at least one layer of amorphous carbon, preferably of a-C:H or a combination of an a-C:H layer facing the inner layer and a superposed a-C:H* layer. A covering layer 3 is arranged on top of the intermediate layer 2. The covering layer 3 includes or is formed by a WC:H layer or an a-C:H* layer. The intermediate layer 2 and, in particular, the covering layer 3 are responsible for the very good sliding properties of the coating 10. As a result of friction, the covering layer 3 is capable of forming solid lubricants, namely tungsten sulfide in the case of a covering layer composed of WC:H and graphite in the case of a covering layer composed of a-C:H*. In the case of an a-C:H* covering layer, the proportion of sp.sup.2 parts in the a-C:H* layer is greater than the proportion of sp.sup.2 parts in an a-C:H intermediate layer. A maximum layer thickness d of the coating 10 is not more than 5 m.

(8) FIG. 2 likewise shows a layer structure of a coating 20 for metal components. The coating 20 differs from that in FIG. 1 in that the inner layer 1 itself has a multilayer structure. The inner layer 1 is formed by a Cr layer 1a, a Cr/WC layer lb and a WC:H layer 1c. The Cr layer 1a is the layer of the inner layer 1 which is intended to be applied to a metal component and bonded to the metal component. The abrasion resistance, mechanical stability and the layer structure stability of the coating 20 can be improved by the multilayer structure of the inner layer 1. A layer thickness d of the coating 20 is likewise not more than 5 m. As an alternative to the Cr layer la, a CrN layer can also be used.

(9) FIG. 3 shows a further layer structure according to the invention of a coating 30 for metal components. The coating 30 differs from that in FIG. 2 in that the inner layer 1 has a multilayer structure formed by a Cr layer 1a, a CrN layer 1d and a Cr/WC layer 1b. The Cr layer la is again the layer of the inner layer 1 which is intended to be applied to a metal component and bonded to the metal component. The abrasion resistance, mechanical stability and the layer structure stability of the coating 30 can also be improved by this multilayer structure of the inner layer 1. A layer thickness d of the coating 30 is likewise not more than 5 m.

(10) FIG. 4 shows a layer structure of a coating 40 for metal components according to a fourth embodiment. The coating 40 again includes a three-layer structure of the inner layer 1, which includes a Cr layer 1a, a Cr/WC layer 1b and a WC/WC:H layer 1e. Unlike the coatings in FIGS. 1 to 3, the intermediate layer 2 is a two-layer structure which includes an a-C:H layer 2a facing the inner layer 1 and an a-C:H* layer 2b facing the WC:H covering layer 3. A coating 40 having very good tribological properties and good adhesion can also be obtained by use of this layer structure. A layer thickness d of the coating 30 is not more than 5 m.

(11) FIG. 5 shows a sectional view through a piston 100 according to an advantageous embodiment of the invention. The piston 100 is a metal component pursuant to the invention and can have a cylindrical geometry. The piston 100 comprises a piston volume 4. The side surfaces 5 bounding the piston volume 4 are the surfaces which are in frictional contact with a piston slideway during operation of the piston 100, for example in an internal combustion engine, and are also referred to as sliding surfaces or as the piston skirt. The side surfaces 5 have a coating 10 which is here formed by way of example of three individual layers and can thus be considered to be the coating 10 of FIG. 1. However, it is also possible for the purposes of the invention for the inner layer 1 to comprise a plurality of individual layers, for example like the inner layer 1 in FIGS. 2 to 4 or for the intermediate layer 2 and/or the covering layer 3 to be made up of a plurality of layers.

(12) In the section of the piston 100 shown in FIG. 5, an inner layer 1 serves to establish the bond between the side surface 5 of the piston 100 and the coating 10. An intermediate layer 2 and a covering layer 3 are arranged on the inner layer 1. The covering layer 3 is located on the surface of the piston 100 and allows friction-minimized sliding of the piston 100 in its piston slideway during the intended use of the piston 100. The individual layers can be applied to the side surfaces 5 of the piston 100, preferably by use of physical or chemical vapor deposition, in particular by PVD or PECVD. The piston 100 is highly wear resistant, abrasion resistant and has very good tribological properties which allow a long operational range with reduced fuel consumption and thus low CO.sub.2 emission and hydrocarbon emission.

(13) The above description of the present invention is merely for illustrative purposes and not for the purpose of restricting the invention. In the context of the invention, various changes and modifications are possible without going outside the scope of the invention and its equivalents.

LIST OF REFERENCE NUMERALS

(14) 1 inner layer 1a Cr layer 1b Cr/WC layer 1c WC:H layer 1d CrN layer 1e WC/WC:H layer 2 intermediate layer 2a a-C:H layer 2b a-C:H* layer 3 covering layer 4 piston volume 5 side surface of the piston 10 coating 20 coating 30 coating 40 coating 100 piston

(15) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.