Sliding element, in particular piston ring, and combination of a sliding element with a mating running element

Abstract

A sliding element, such as a piston ring, for use in diesel or highly supercharged spark-ignition engines with iron-based mating running elements is provided. The sliding element includes a base material made of cast iron or steel and a coating. The coating includes a CrN layer, an Me(C.sub.xN.sub.y) layer, and a DLC layer extending from the inside to the outer side respectively. The DLC layer consists of a metal-containing substructure layer and a metal-free DLC top layer. The Me(C.sub.xN.sub.y) layer is crystalline and Me is tungsten (W), chromium (Cr), or Silicon (Si). The hardness of the metal-free DLC top layer is harder than the metal-containing substructure layer.

Claims

1. A sliding element having a base material made of cast iron or steel and comprising a coating having a CrN layer, an Me(C.sub.xN.sub.y) layer and a DLC layer extending from the inside to the outer side respectively, wherein the DLC layer consists of a metal-containing substructure layer and a metal-free DLC top layer, the Me(C.sub.xN.sub.y) layer is crystalline and Me is tungsten (W), chromium (Cr), or Silicon (Si), the hardness of the metal-free DLC top layer being harder than the metal-containing substructure layer, wherein hardness of the metal-free DLC top layer is 1700-2900 HV 0.002, and the hardness of the CrN layer is 1100-1900 HV 0.002.

2. The sliding element according to claim 1 wherein the metal-containing substructure layer contains hydrogen.

3. The sliding element according to claim 1, wherein the metal-containing substructure layer contains nanocrystalline metal carbide precipitations.

4. The sliding element according to claim 1, wherein the CrN layer has a thickness of 1-30 m.

5. The sliding element according to claim 1, wherein the outer side of the DLC layer has a roughness of Rz<5 m.

6. The sliding element according to claim 1, wherein the CrN layer is metal-vapour deposited.

7. The sliding element according to claim 1, wherein the hardness of the metal containing substructure layer is 800-1600 HV 0.002.

8. The sliding element according to claim 1, wherein the metal-free DLC top layer contains hydrogen.

9. The sliding element according to claim 3, wherein the precipitates are selected form the group consisting of at least one of WC, CRC, SiC, GeC or TiC.

10. The sliding element according to claim 1, wherein the Me(C.sub.xN.sub.y) layer has a maximum thickness of 2 m.

11. The sliding element according to claim 1, wherein the coating has a thickness of 5-40 m.

12. The sliding element according to claim 1 wherein the outer side of the DLC layer has a roughness of Rpk<0.8 m.

13. The sliding element according to claim 1, wherein the metal-containing substructure layer is produced by PA-CVD process.

14. The sliding element according to claim 1, wherein the metal-free DLC top layer is produced by PA-CVD process.

15. The sliding element according to claim 1, wherein the sliding element comprises a piston ring.

16. The sliding element according to claim 15, wherein the sliding element comprises an iron-based mating cylinder liner.

17. The sliding element according to claim 1, wherein the sliding element comprises a piston ring or iron-based mating cylinder liner; the coating has a thickness of 5-40 m; the CrN layer is metal-vapour deposited and has a thickness of greater than 1 m and up to 30 m; the Me(C.sub.xN.sub.y) layer has a maximum thickness of 2 m; the metal-containing substructure layer contains hydrogen and nanocrystalline metal carbide precipitations and has a hardness of 800-1600 HV 0.002; the metal-free DLC top layer contains hydrogen; and the outer side of the DLC layer has a roughness of Rz<5 m and Rpk<0.8 m.

18. The sliding element according to claim 17, wherein the precipitations are selected form the group consisting of at least one of WC, CRC, SiC, GeC or TiC.

19. The sliding element according to claim 1, wherein the Me of the Me(C.sub.xN.sub.y) layer is tungsten (W) or Silicon (Si).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following describes a preferred exemplary embodiment with reference to the drawings, which show:

(2) FIG. 1 a layer structure according to the invention

(3) FIG. 2 the relative wear on a piston ring and a cylinder liner and

(4) FIG. 3 the relative coefficient of friction of different layer systems.

DETAILED DESCRIPTION

(5) As FIG. 1 shows, a CrN layer 12 is applied to the basic material 10 of the sliding element. The adhesive layer 14 shown in FIG. 1 does not necessarily have to be provided. In particular, this is preferably omitted. By means of a Me(C.sub.xN.sub.y) intermediate layer 16, a DLC layer 18 is provided on the outer side with a metal-free DLC layer on the outer side.

(6) Tests with comparative examples were performed with a structure of this kind, without the adhesive layer 14. The table shows the layer systems.

(7) TABLE-US-00001 Layer structure Running Substrate Inter- surface Total layer Adhesive mediate Top thickness layer Substructure layer layer [m] DLC Cr DLC 3.5 series CNDLC01 CrN - 01 Me(CN)x DLC 8.8 CNDLC02 Cr CrON - 02 Cr DLC 14.5 CNDLC03 Cr CrN - 03 Cr DLC 14.6 CNDLC04 Cr CrON - 04 Cr DLC 14.3

(8) Here, the system DLC series is a standard DLC layer system without CrN. These layer systems were applied to a piston ring, and the tribological behavior investigated in combination with a honed cast iron cylinder liner in lubricated condition. FIG. 2 shows the relative wear values for the piston ring (at the top) and for the cylinder liner. The percentage values shown indicate the percentage of the original DLC layer remaining after the end of the test. If this value is more than 100 percent, in addition to the DLC layer, the CrN or CrON layer is also at least partially worn. The highest wear value is used as the reference value for the relative wear of the cylinder liner and hence defined as 100 percent.

(9) As FIG. 2 shows, the coating according to the invention with a Me(C.sub.xN.sub.y) intermediate layer has the lowest relative wear. In the case of wear to the cylinder liner, only the known DLC coating results in a lower value. However, the wear of the cylinder liner is also in an acceptable range for the example according to the invention.

(10) Investigations were also performed into the coefficients of friction and the results are shown in FIG. 3. Here the example according to the invention has the lowest relative coefficient of friction. Hence, this requirement is also fulfilled in addition to the requirement for comparatively low wear and hence a long service life.