A workpiece comprises a substrate having a sliding surface provided with a friction-reducing coating. Such coating consists essentially of elemental carbon dispersed in a matrix formed of at least one metallic element in the proportions of 50.1 to 99.1 at % of the elemental carbon and 0.1 to 49.9 at % of the metallic element. The ratio of the metallic element to the elemental carbon differs from the stoichiometric ratio of the carbide.
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1. A workpiece comprising a substrate having a sliding surface provided with a friction-reducing coating;
said coating consisting essentially of elemental carbon dispersed in a matrix formed of at least one metallic element in the proportions of 50.1 to 99.9 at % of the elemental carbon and 0.1 to 49.9 at % of the metallic element, the ratio of the metallic element to the elemental carbon differing from the stoichiometric ratio of a carbide.
13. A workpiece comprising:
a substrate having a surface; and a friction-reducing coating on the surface of the substrate having a coefficient of sliding friction; characterized in that the friction-reducing coating consists essentially of elemental carbon dispersed in a matrix formed by at least one metallic element, the ratio of carbon to the metallic element ranging from 50.1/49.9 to 99.9/0.1, said ratio differing from the stoichiometric ratio of a carbide.
3. A workpiece according to
4. A workpiece according to
5. A workpiece according to
6. A workpiece according to
7. A method of making a workpiece according to
8. A method according to
9. A method according to
10. A method according to
11. A method according to
12. A method according to
14. A workpiece as claimed in
a substrate having a surface; and a friction-reducing coating on the surface of the substrate, said friction-reducing coating having a coefficient of sliding friction; characterized in that the friction-reducing coating consists essentially of elemental carbon dispersed in a matrix formed by at least one metallic element, the ratio of carbon to the metallic element ranging from 50.1/49.9 to 99.9/0.1 said ratio differing from the stoichiometric ratio of a carbide, said coating further containing impurities in amounts which do not materially increase the coefficient of sliding friction of the coating as compared to such a coating without such impurities. 16. A workpiece as claimed in claim 15, characterized in that the
friction-reducing coating is X-ray amorphous. 17. A system comprising: a first workpiece having a surface; a second workpiece having a surface, the surface of the first workpiece bearing against and sliding with respect to the surface of the second workpiece; and a friction-reducing coating on the surface of the first workpiece; characterized in that the friction-reducing coating consists essentially of elemental carbon dispersed in a matrix formed by at least one metallic element, the ratio of carbon to the metallic element ranging from 50.1/49.9 to 99.9/0.1 said ratio differing from the stoichiometric ratio of a carbide. 18. A system as claimed in claim 17, characterized in that the friction-reducing coating is X-ray amorphous. 19. A system as claimed in claim 18, further comprising a friction-reducing coating on the surface of the second workpiece. |
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The invention will now be described with reference to the accompanying drawing, in which the FIGURE is a sectional view of a sliding layer provided on a substrate with an intermediate layer promoting its adhesion to the substrate.
The FIGURE is a sectional view of a substrate 1, for example, of chromium-nickel steel, having an adhesion-promoting intermediate layer 3 of pure iron and a sliding layer 5 of iron and carbon. These layers can be obtained, for example, as follows: layers having a thickness of 0.9 μm and a micro hardness of 15×103 N/mm2 were manufactured by cathode sputtering of a pure iron target in an atmosphere of an inert gas at a pressure of 20 mbar, for example argon, and a hydrocarbon gas at a pressure of 0.2 mbar, for example, acetylene. Flat rings of 100 Cr6 steel served as a substrate. The layers approximately 20 at % iron, 78 at % carbon and the remainder unknown impurities (it is assumed that the latter derives from the atmosphere of the cathode sputtering process), have an excellent adhesion to their substrate, which is due inter alia to the fact that during the first minutes of the coating process the cathode sputtering process was carried out in a pure inert gas atmosphere so that first a pure iron layer was deposited. The further coating then occurred in the above-mentioned atmosphere. The layers thus manufactured have a sliding friction coefficient in a dry atmosphere (<0.1% relative humidity) of μ≈0.06 and in a moist atmosphere (≈80% relative humidity) of μ≈0.15.
Layers which were manufactured by sputtering of an iron target and an iron carbon target, respectively, in an inert gas-hydrocarbon gas atmosphere, have a hardness in the range from 15×103 to 30×103 N/mm2 (Knoop hardness). The sliding friction coefficients against steel as a friction member as a rule are in the range from μ≈0.05 to 0.3 depending on the coating conditions. For example , for a layer which contains <49.9 at % iron as well as >5.01 at % carbon a coefficient of sliding friction which is far less dependent on the relative air humidity can be achieved than is the case for pure carbon layers. For pure carbon the values for the coefficient of sliding friction μ against steel with a relative air humidity of <0.1% are μ≈0.02 and with a relative air humidity of 95% μ≈0.2.
An iron-carbon layer of a different composition, namely 84 at % carbon and 16 at % iron, was manufactured under the same conditions and with a relative air humidity of 50% had sliding friction coefficients μ≈0.14 both against steel and also against a layer of the same composition as a friction member (compare Table 4).
In principle the compositions of the layers with respect to the quantities of carbon and metallic element(s) can be controlled by the target composition and by the amount of the hydrocarbon gas, respectively, in the sputtering atmosphere, for example in the sense that, when the concentration of the carbon in the layer is to be higher, the amount of the hydrocarbon gas in the sputtering atmosphere is increased accordingly. The exact ratios can be determined by simple experiments.
Table 1 illustrates how the coefficient of sliding friction μ for iron-carbon layers containing 3.7 at % iron, 95.5 at % carbon and 0.8 at % residual gas with a friction member in the form of a layer of the same composition as well as with steel as a friction member is influenced by different relative air humidities.
| TABLE 1 |
| ______________________________________ |
| Relative air |
| Sliding layer humidity (%) μ1 |
| μ2 |
| ______________________________________ |
| 3.7 at % Fe 90 0.15 0.13 |
| + 50 0.14 0.12 |
| 95.5 at % C 10 0.13 0.11 |
| + 1 0.07 0.07 |
| 0.8 at % residual gas |
| <0.4 0.04 0.04 |
| ______________________________________ |
| μ1 = coefficient of friction with a friction member in the form o |
| a layer of the same composition as the sliding layer. |
| μ2 = coefficient of friction against steel as a friction member. |
Further compositions in the range from 65.2 to 95.5 at % carbon and 32.9 to 2.3 at % iron with the remainder, consisting of gases incorporated in the resulting layer in the cathode sputtering process were tested for their friction behaviour (compare table 2). The layers were manufactured under the same parameters as indicated for the above-described iron-carbon layer. Coefficients of sliding friction μ from ≈0.10 to ≈0.17 in an atmosphere with 50% relative air humidity with steel as a friction member and values for μ from ≈0.13 to ≈0.22 against a layer of the same composition as a friction member were measured. The layer compositions and the associated coefficients of sliding friction are set forth in Table 2.
| TABLE 2 |
| ______________________________________ |
| Residual gases |
| Fe (at %) C (at %) (at %) μ1 |
| μ2 |
| ______________________________________ |
| 2.3 93 4.7 0.16 0.16 |
| 3.7 95.5 0.8 0.14 0.12 |
| 14.8 78.1 7.1 0.14 0.17 |
| 20.3 78.7 1.0 0.13 0.15 |
| 32.9 65.2 1.9 0.22 0.10 |
| ______________________________________ |
| μ1 = coefficient of friction with 50% relative air humidity and a |
| friction member in the form of a layer of the same composition as the |
| sliding layer. |
| μ2 = coefficient of friction with 50% relative air humidity and |
| steel as a friction member. |
As in the example of the iron-carbon layer, layers having a thickness of 0.9 μm were manufactured by cathode sputtering of a pure tantalum target in an atmosphere of an inert gas at a pressure of 20 mbar, for example, argon, and a hydrocarbon gas at a pressure of 0.2 to 10 mbar, for example, acetylene. As a substrate there were used steel rings or silicon monocrystalline disks.
The layers with 95 at % carbon and 5 at % tantalum in an atmosphere of a relative air humidity of 50% have a coefficient of sliding friction against steel of μ≈0.08 and against a layer of the same composition as a friction member of μ≈0.03 (compare Table 4).
Layers having a thickness of 0.9 μm were manufactured by cathode sputtering of a pure ruthenium target in an atmosphere of an inert gas at a pressure of 20 mbar, for example argon, and a hydrocarbon gas at a pressure of 0.2 to 1.0 mbar, for example, acetylene. As substrates there were used steel rings or silicon monocrystalline disks.
A layer which comprises 18 at % ruthenium at 82 at % carbon has a sliding friction coefficient in an atmosphere with 50% relative air humidity of μ≈0.05 with steel as a friction member and of μ≈0.03 with a layer of the same composition as a friction partner (compare Table 4).
Layers having a thickness of 0.9 μm and a micro hardness of 21×103 N/mm2 were manufactured by cathode sputtering of a pure tungsten target in an atmosphere of an inert gas at a pressure of 20 mbar, for example, argon and a hydrocarbon gas at a pessure of 0.2 to 1.0 mbar, for example, acetylene. As substrates there were used steel rings or silicon monocrystalline discs.
A layer containing 9 at % tungsten and 91 at % carbon has a sliding friction coefficient in an atmosphere with 50% relative air humidity of μ≈0.14 with steel as a friction member and of μ≈0.06 with a layer of the same composition as a friction member (compare Table 4).
Further compositions in the range of 66.2 to 96.5 at % carbon and 30.6 to 1.6 at % tungsten with the remainder consisting of gases incorporated in the resulting layer during the cathode sputtering process were tested for their friction behaviour (compare Table 3). The layers were manufactured under the same parameters as described above for the iron-carbon layers, tantalum-carbon layers and ruthenium-carbon layers. Coefficients of sliding friction μ from ≈0.10 to 26 0.17 in an atmosphere with 50% relative air humidity with steel as a friction member were measured. The layer compositions and the associated coefficients of sliding friction are set forth in Table 3.
Table 3 also includes a layer composition having 59.3 at % tungsten, 36.7 at % carbon and 4.0 at % residual gas from the cathode sputtering atmosphere; said layer composition is beyond the claimed range of compositions. It had a poor adhesion to the substrate, a high detrition in friction tests and coefficient of sliding friction μ≈0.4 with steel as a friction member in an atmosphere with 50% relative air humidity.
The tungsten-carbon layers set forth in Table 3 illustrate that the coefficient of sliding friction of the sliding layers decreases with increasing carbon portion.
| TABLE 3 |
| ______________________________________ |
| W Residual gases |
| (at %) |
| C (at %) (at %) μ2 |
| Remarks |
| ______________________________________ |
| 1.6 94.5 3.9 0.17 |
| 2.8 96.5 0.7 0.10 |
| 4.9 95 0.1 0.13 |
| 5.3 92.9 1.8 0.16 |
| 8.9 90.3 0.8 0.14 |
| 30.6 66.2 3.2 0.14 hardness |
| 30 × 103 N/mm2 |
| 59.3 36.7 4.0 ∼0.4 |
| very high |
| detrition |
| ______________________________________ |
| μ2 = coefficient of friction with 50% relative air humidity and |
| steel as a friction member. |
Layers having a thickness of 0.9 μm were manufactured by cathode sputtering of a pure silicon target in an atmosphere of an inert gas at a pressure of 20 mbar, for example, argon, and a hydrocarbon gas at a pressure of 0.2 to 1.0 mbar, for example, acetylene. Steel rings or silicon monocrystalline discs also served as substrates.
The layers comprising 20 to 5 at % silicon and 80 to 95 at % carbon have a sliding friction coefficient against steel in an atmosphere with 50% relative air humidity of μ≈0.07 (Compare Table 4).
| TABLE 4 |
| ______________________________________ |
| Sliding layer |
| Carbon Metallic element |
| (composition) |
| (at %) (at %) μ1 |
| μ2 |
| ______________________________________ |
| Si--C 80-95 20-5 -- 0.07 |
| Ta--C 95 5 0.03 0.08 |
| W--C 91 9 0.06 0.14 |
| Ru--C 82 18 0.03 0.05 |
| Fe--C 84 16 0.14 0.14 |
| ______________________________________ |
| μ1 = coefficient of friction at 50% relative air humidity and a |
| friction member in the form of a layer of the same composition as the |
| sliding layer. |
| μ2 = coefficient of friction at 50% relative air humidity and |
| steel as a friction member. |
Table 5 below indicates how the coefficient of sliding friction μ for a tungsten-carbon layer containing 1.6 at % tungsten 94.5 at % carbon and 3.9 at % residual gas with a friction member in the form of a layer of the same composition as well as with steel as a friction member is influenced by different relative air humidities.
| TABLE 5 |
| ______________________________________ |
| Sliding layer Relative air |
| (composition) humidity (%) μ1 |
| μ2 |
| ______________________________________ |
| 1.6 at % W 90 0.10 0.16 |
| + 50 0.08 0.12 |
| 94.5 at % C 10 0.06 0.07 |
| + 1 0.02 0.05 |
| 3.9 at % residual gas |
| <0.4 0.01 0.02 |
| ______________________________________ |
| μ1 = coefficient of friction with a friction member in the form o |
| the same composition as the sliding layer. |
| μ2 = coefficient of friction against steel as a friction member. |
Dimigen, Heinz, Hubsch, Hubertus
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