Sliding element, in particular a piston ring, having a coating
The present application relates to a sliding element, in particular a piston ring, having at least one sliding surface which has a coating which has, from the inside outwards, a metal-containing bonding layer and a DLC layer, where the DLC layer is an amorphous hydrogen-free diamond-like carbon layer which has a DLC main layer which extends from the bonding layer to an adjoining DLC covering layer and has a carbon content of more than about 98.5 at %, oxygen and/or hydrogen and/or nitrogen in a proportion of in each case less than about 0.5 at % and an sp2/sp3 ratio of the carbon in the range from about 1 to about 3, and a DLC covering layer which extends from the DLC main layer to the surface of the sliding element and has a lower carbon content and/or higher oxygen content and/or higher hydrogen content compared to the main layer and also metals and/or metal oxides and an sp2/sp3 ratio of the carbon in the range from about 1 to about 3.
1. A sliding element, in particular a piston ring, which has at least one sliding surface having a coating comprising, from the inside outwards,
a metal-containing bonding layer and a DLC layer,
wherein the DLC layer is an amorphous, hydrogen-free, diamond-like carbon layer comprising a DLC main layer that extends from the bonding layer to an adjoining DLC covering layer and has a carbon content of more than about 98.5 at %, oxygen and/or hydrogen and/or nitrogen in a proportion of in each case less than about 0.5 at % and an sp2/sp3 ratio of the carbon of between about 1 and about 3, and
wherein the DLC covering layer extends from the DLC main layer to the surface of the sliding element and has a lower carbon content and/or higher oxygen content and/or higher hydrogen content as compared to the main layer and also has metals and/or metal oxides and an sp2/sp3 ratio of the carbon of between about 1 and about 3.
2. The sliding element according to claim 1 , wherein the DLC layer has an sp2/sp3 ratio of the carbon of 1.05 to approximately 2.
3. The sliding element according to claim 1 , wherein the DLC covering layer comprises iron and/or iron oxides.
4. The sliding element according to claim 3 , wherein the iron oxides are FeO and/or Fe 3 O 4 .
5. The sliding element according to claim 1 , wherein the DLC covering layer has an iron content of approximately 30 at % or less.
6. The sliding element according to claim 1 , wherein the DLC covering layer has a carbon content of approximately 25 at % or more.
7. The sliding element according to claim 1 , wherein the DLC covering layer has an oxygen content of approximately 50 at % or less.
8. The sliding element according to claim 1 , wherein a surface of the DLC covering layer has the following C O bond proportions: C—O approximately 20 at % to approximately 30 at %, C═O approximately 8 at % to approximately 15 at %, O—C═O approximately 6 at % to approximately 10 at %.
9. The sliding element of claim 8 , wherein C=0 is 10 at % to 15 at %.
10. The sliding element according to claim 1 , wherein the metals and/or metal oxides disposed at the surface of the coating have a surface portion of approximately 5 to 40%.
11. The sliding element of claim 10 , wherein the surface portion of the metals and/or metal oxides disposed at the surface of the coating is 5 to 25%.
12. The sliding element according to claim 1 , wherein the DLC covering layer has a thickness of up to approximately 2 μm.
13. The sliding element of claim 12 , wherein the thickness is approximately 1 μm.
14. The sliding element according to claim 1 , wherein the DLC main layer has a thickness of approximately 5 μm to approximately 40 μm.
15. The sliding element according to claim 1 , wherein the metal content and/or the oxygen content and/or the hydrogen content increase(s) in the DLC covering layer towards the outside thereof.
16. The sliding element according to claim 1 , wherein the DLC layer has a hardness of approximately 1800 to 3500 HV0.02.
17. The sliding element according to claim 1 , wherein the DLC layer has an elastic modulus of approximately 150 to 320 GPa.
18. The sliding element according to claim 1 , wherein the DLC layer has a mean roughness depth of Rz<approximately 2 μm, and a reduced peak height of Rpk<approximately 0.15 μm.
19. The sliding element of claim 18 , wherein Rz<approximately 1 μm.
20. The sliding element of claim 18 , wherein Rpk<approximately 1 μm.
21. The sliding element according to claim 1 , wherein the bonding layer has a thickness of approximately 0.05 μm to approximately 1.0 μm.
22. The sliding element according to claim 1 , wherein the bonding layer comprises chromium or titanium.
23. The sliding element according to claim 1 , wherein a basic material of the sliding element is cast-iron or steel.