SLIDING MEMBER

Abstract

A sliding member may include a metallic base, at least one intermediate bonding layer disposed on the metallic base, and a multilayer protective coating disposed on the intermediate bonding layer. The at least one intermediate bonding layer may be composed of at least one metal. The multilayer protective coating may include a plurality of CrAlN layers and a plurality of Cr(Al)N layers arranged in an alternating manner. The multilayer protective coating may include a plurality of periodicity layer groups, each of which may be defined by a CrAlN layer and an adjacent Cr(Al)N layer. The plurality of CrAlN layers may have a higher Al content than the plurality of Cr(Al)N layers. A thickness ratio of the CrAlN layer to the Cr(Al)N layer in each periodicity layer group may be from 1 to 10. The multilayer protective coating may have a total Al content of 15 to 40 atom-%.

Claims

1. A sliding member, comprising: a metallic base; at least one intermediate bonding layer composed of at least one metal and disposed on the metallic base such that the at least one intermediate bonding layer covers at least part of a surface of the metallic base; and a multilayer protective coating disposed on the intermediate bonding layer; wherein the multilayer protective coating includes a plurality of CrAlN layers and a plurality of Cr(Al)N, layers arranged in an alternating manner; wherein the multilayer protective coating further includes a plurality of periodicity layer groups, each periodicity layer group of the plurality of periodicity layer groups defined by a CrAlN layer of the plurality of CrAlN layers and an adjacent Cr(Al)N layer of the plurality of Cr(Al)N layers; wherein the plurality of CrAlN layers have has a higher Al content than the plurality of Cr(Al)N layers; wherein a thickness ratio of the CrAlN layer to the Cr(Al)N layer in each periodicity layer group of the plurality of periodicity layer groups is from 1 to 10; and wherein the multilayer protective coating has a total Al content of 15 to 40 atom-%.

2. The sliding member according to claim 1, wherein the metallic base is composed of at least one of: steel having 10 to 17 mass-% Cr; carbon steel; and cast iron.

3. The sliding member according to claim 2, wherein the metallic base is nitrided.

4. The sliding member according to claim 1, wherein the at least one intermediate bonding layer includes at least one of Cr, Ni, and Co.

5. The sliding member according to claim 1, wherein a total thickness of the at least one intermediate bonding layer and the multilayer protective coating is from 6 ?m to 70 ?m.

6. The sliding member according to claim 1, wherein the thickness ratio of the CrAlN layer to the Cr(Al)N layer in each periodicity layer group of the plurality of periodicity layer groups is from 1.3 to 10.

7. The sliding member according to claim 1, wherein: the plurality of CrAlN layers include 20 to 40 atom-% of Al; and the plurality of Cr(Al)N layers include 10 to 25 atom-% of Al.

8. The sliding member according to claim 1, wherein each periodicity layer group of the plurality of periodicity layer groups has a thickness of less than 20 nm.

9. The sliding member according to claim 8, wherein each periodicity layer group of the plurality of periodicity layer groups has a thickness of 4 to 15 nm.

10. The sliding member according to claim 1, wherein a hardness of the multilayer protective coating is from 1600 to 2600 HV.

11. The sliding member according to claim 1, wherein an internal compressive stress of the multilayer protective coating is from 1000 to 2500 MPa.

12. The sliding member according to claim 1, wherein the multilayer protective coating has a porosity lower than 6%.

13. The sliding member according to claim 1, wherein the multilayer protective coating is a cathodic arc deposited layer.

14. An internal combustion engine, comprising the sliding member according to claim 1.

15. The internal combustion engine according to claim 14, wherein the sliding member is one of a piston ring, a tappet, a valve, and a cam.

16. A compressor, comprising the sliding member according to claim 1.

17. The compressor according to claim 16, wherein the sliding member is one of a piston ring, a tappet, a valve, and a cam.

18. The sliding member according to claim 1, wherein the multilayer protective coating has: a hardness of 1900 to 2000 HV; an internal compressive stress of 1400 to 2000 MPa; and a porosity lower than 3%.

19. The sliding member according to claim 1, wherein: a total thickness of the at least one intermediate bonding layer and the multilayer protective coating is from 10 ?m to 50 ?m; each periodicity layer group of the plurality of periodicity layer groups has a thickness of 5 to 15 nm; and the thickness ratio of the CrAlN layer to the Cr(Al)N layer in each periodicity layer group of the plurality of periodicity layer groups is from 1.7 to 5.

20. A sliding member, comprising: a metallic base; at least one intermediate bonding layer composed of at least one metal and disposed on the metallic base; and a multilayer protective coating disposed on the intermediate bonding layer, the multilayer protective coating including a plurality of CrAlN layers and a plurality of Cr(Al)N layers arranged in an alternating manner; the multilayer protective coating further including a plurality of periodicity layer groups each defined by a CrAlN layer of the plurality of CrAlN layers and an adjacent Cr(Al)N layer of the plurality of Cr(Al)N layers; wherein, in each periodicity layer group of the plurality of periodicity layer groups, a thickness ratio of the CrAlN layer to the Cr(Al)N layer is from 1.5 to 5; wherein the plurality of CrAlN layers each include 27 to 32 atom-% of Al; wherein the plurality of Cr(Al)N layers each include 18 to 20 atom-% of Al; and wherein the multilayer protective coating has a total Al content of 15 to 40 atom-%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] It is schematically shown in

[0050] FIG. 1 shows a cross-sectional view of a sliding member (1) of the present invention, including a metallic base (2), an intermediate bonding layer (3) and a plurality of CrAlN and Cr(Al)N layers (4a, 4b) forming a multilayer protective coating (4),

[0051] FIG. 2 shows a schematic plan view of a cathodic arc deposition device suitable for manufacturing a multilayer protective coating (4) of the present invention,

[0052] FIG. 3 shows a sliding member (1) of the present invention in the form of a piston ring, and

[0053] FIG. 4 shows a bar diagram for comparing the relative wear of prior art protective coatings and the multilayer protective coating according to the present invention.

DETAILED DESCRIPTION

[0054] According to FIG. 1, a cross-sectional view of a sliding member (1) of the present invention comprises a metallic base (2), an intermediate bonding layer (3) present on the metallic base (2), and a plurality of CrAlN and Cr(Al)N layers (4a, 4b) forming a multilayer protective coating (4) on the intermediate bonding layer (3). The plurality of CrAlN and Cr(Al)N layers (4a, 4b) are alternately arranged on the intermediate bonding layer (3), wherein the layer immediately above the intermediate bonding layer (3) is a CrAlN layer (4a). However, starting with a CrAlN layer (4a) is not compulsory, i.e., the first layer on the intermediate bonding layer (3) may also be a Cr(Al)N layer (4b). According to the present invention and as schematically shown in FIG. 1, the thickness of the CrAlN layers (4a) is set to be larger than the thickness of the Cr(Al)N layers (4b), as mentioned above. Furthermore, according to the present invention, the Al concentration in the CrAlN layers (4a) is set to be larger than the Al concentration in the Cr(Al)N layers (4b), as mentioned above. Two alternating layers of CrAlN and Cr(Al)N (4a, 4b) each form a periodicity layer group (4c), as it is exemplarily indicated for the two lowermost CrAlN and Cr(Al)N layers (4a, 4b) in FIG. 1.

[0055] FIG. 2 shows a schematic plan view of a cathodic arc deposition device suitable for manufacturing a multilayer protective coating (4) of the present invention.

[0056] Nitride multilayers, such as CrAlN/Cr(Al)N used in the present invention, are isostructural and mutually miscible. Mixing of the constituents was defined by the PVD (Physical Vapour Deposition) chamber configuration to happen during deposition, leading to compositional gradients. The degree of mixing is a function of the deposition conditions, particularly regarding the cross-contamination between the targets during the process and mainly due to the own target composition (for instance, in the present case, half of the target with a high amount of Al in a range of 50 to 75 at-% Al and the other half of the target with Al in a range of 3 to 10 at-% Al).

[0057] According to FIG. 2, as an example for manufacturing a sliding member of the present invention, CrAlN/Cr(Al)N nanostructured multilayer protective coatings were deposited by Cathodic Arc Physical Vapour Deposition (CAPVD) onto gas nitrided martensitic stainless steel (AISI 440B) coupons (5) in an industrial-size chamber (6). Two cathodes [one package of Cr(Al) (7b) with an Al content of 3 to 10 at-% and one package of CrAl (7a) with an Al content of 50 to 75 at-%) in alternate positions were fed with their own power supply. By varying the rotating speed of the table (8) in the center of the chamber (6), a 30 ?m thick coating was obtained with a thickness of the periodicity layer group (4c) of lower than 15 nm. The rotating speed controlled the time the substrate passes in front of each CrAl or Cr(Al) targets (7a, 7b) in such a way that it lead to the control of the periodicity thickness ensuring a very reduced cross contamination between the targets. The average deposition rate for all the depositions was 5 ?m/h.

[0058] FIG. 3 show a sliding member (1) of the present invention in the form of a piston ring, which may be manufactured by a CAPVD discussed above. The piston ring of FIG. 3 includes a metallic base (2) (only a ring segment of the piston ring is shown), an intermediate bonding layer (3) present on the outer ring surface of the metallic base (2), and a multilayer protective coating (4) present on the intermediate bonding layer (3).

[0059] Finally, FIG. 4 shows a bar diagram for comparing the relative wear of prior art protective coatings and the multilayer protective coating according to the present invention. All the engine tests were performed in an HDD platform with a bore diameter of 128 mm and power of 320 to 370 kW and with a duration of 250 hours up to 1.000 hours. The first bar shows the results of a prior art multilayer coating structure composed by NbN/CrN with a periodicity of 20 nm (proportion 1:1, 10 nm NbN and 10 nm CrN), while the second bar shows a CrAlN monolayer coating (without multilayers) and finally the third bar shows the results of the multilayer CrAlN/Cr(Al)N having a periodicity of 20 nm and also having a proportion of 1:1.

[0060] As shown in the remaining four bars encircled by a rectangle in FIG. 4, variants of CrAlN/Cr(AlN) according to the present invention were tested. As a result, it was found that the total coating wear was reduced significantly.