Nanocomposite solid lubricant coating

Abstract

A solid lubricant magnetron sputtering physical vapor deposition (MS PVD) coating can be used e.g. in automotive, aircraft and space industries for increasing lifetime of moving parts such as bearings, chains, pistons and joints that experience sliding or rolling friction. A nanocomposite solid lubricant coating contains a carbon matrix with copper grains and at least one of Ti, Zr, Hf, and V, in bulk proportions, at. %: TABLE-US-00001 carbon 5-35; copper 50-90; additional metal 5-15.
The carbon matrix with copper grains is reinforced with interlayers of the additional metal. The thickness of each layer of the carbon matrix with copper grains is in the range between 30 and 150 nanometers and the thickness of each interlayer of the additional metal is in the range between 5 and 20 nanometers. The hardness of said coating is in the range between 200 and 1000 HV.

Claims

1. A nanocomposite solid lubricant coating containing a carbon matrix with copper grains characterized in that it contains an additional metal selected from the group consisting of Ti, Zr, Hf, V, in bulk proportions, at. %: TABLE-US-00010 carbon 5-35; copper 50-90; additional metal 5-15; the carbon matrix with copper grains is reinforced with interlayers of the additional metal; the thickness of each layer of the carbon matrix with copper grains is in the range between 30 and 150 nanometers and the thickness of each interlayer of the additional metal is in the range between 5 and 20 nanometers; the hardness of said coating is in the range between 200 and 1000 HV.

2. The coating as in claim 1, wherein the copper grain size is in the range between 20 and 100 nanometers, and said copper grains are wrapped in nanolayers of the carbon matrix with thickness in the range between 1 and 10 nanometers.

3. The coating as in claim 1, wherein the thickness of said coating is in the range between 2.5 and 150 micrometers.

4. The coating as in claim 1, wherein the thickness of said coating is in the range between 5 and 15 micrometers.

5. A method of magnetron sputtering physical vapor deposition of the nanocomposite solid lubricant coating as in claim 1, wherein at least one copper-carbon mosaic target and at least one additional metal target are used consecutively with the power density of the copper-carbon mosaic target in the range between 40 W/cm.sup.2 and 250 W/cm.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is illustrated by figures, which show:

(2) FIG. 1greatly schematized sketch of the layers of the nanocomposite solid lubricant coating.

(3) FIG. 2Transmission electron microscopy (TEM) image of the layer of the carbon matrix with copper grains.

DETAILED DESCRIPTION

(4) The invention will now be described by way of examples.

Example 1

(5) Gearwheels were placed in a vacuum chamber with two-fold rotation with four copper-carbon mosaic targets (with 14% carbon surface area) and two zirconium targets. The gearwheels were coated by MS PVD method at argon (99.999%) pressure of 2.8 mTorr for 40 minutes at a substrate-target distance of 40-60 mm with an 11 micrometers thick nanocomposite solid lubricant coating. The bias voltage of 100V was used during the deposition process. The power density of the copper-carbon mosaic target was 115 W/cm.sup.2 and the power density of zirconium target was 60 W/cm.sup.2. The bulk proportions of the elements were in the coating, at. % (excluding oxygen trapped from the environment on the surface of the coating after deposition):

(6) TABLE-US-00003 carbon 14; copper 80; additional metal (zirconium) 6.

(7) The nanocomposite solid lubricant coating consisted of the alternating layers of zirconium and carbon matrix with copper grains. The investigation of the cross sectional Scanning electron microscopy (SEM) image of the coating showed that the thickness of each zirconium layer was in the range between 5 and 10 nm and the thickness of each copper-carbon layerin the range between 80 and 90 nm. The gearwheels were coated with the nanocomposite solid lubricant coating, which showed HF2 adhesion, the hardness of 700 HV, the wear rate lower than 10.sup.16 m.sup.3/N.Math.m, the friction coefficient of 0.21 in dry conditions and 0.07 in an oil environment.

(8) The layers of the nanocomposite solid lubricant coating are schematically shown on the sketch (FIG. 1), where carbon matrix 1 with copper grains 2 is reinforced with interlayers 3 of the additional metal.

Example 2

(9) 100Cr6 shims were coated by MS PVD method at argon (99.999%) pressure of 3.0 mTorr for 70 minutes at a substrate-target distance of 30-40 mm using two copper-carbon mosaic targets (with 26% carbon surface area) and one titanium target. The resulting nanocomposite solid lubricant coating was 10 micrometers thick with the copper grain size varying from 40 to 80 nm. The bias voltage of 100V was used during the deposition process. The power density of the copper-carbon mosaic target was 100 W/cm.sup.2 and the power density of the titanium target was 60 W/cm.sup.2. The deposited nanocomposite solid lubricant coating contained in bulk proportions, at. % (excluding oxygen trapped from the environment on the surface of the coating after deposition):

(10) TABLE-US-00004 carbon 23; copper 67; additional metal (titanium) 10.

(11) The 100Cr6 shims were coated with the nanocomposite solid lubricant coating, which had the wear rate lower than 10.sup.16 m.sup.3/N.Math.m, the dry friction coefficient of 0.2 and the friction coefficient of 0.08 in an oil environment. FIG. 2 shows the TEM image of a layer of a carbon matrix with copper grains 2, where copper grains 2 are wrapped in the carbon matrix (not visible at this scale) nanolayers.

Example 3

(12) 100Cr6 shims were coated by MS PVD method at argon (99.999%) pressure of 2.8 mTorr for 40 minutes at a substrate-target distance of 40-60 mm with a 6.5 micrometers thick nanocomposite solid lubricant coating. The bias voltage of 100V was used during the deposition process. 2 copper-carbon mosaic targets (with 18% carbon surface area) and one molybdenum target were used. The power density of the copper-carbon mosaic target was 115 W/cm.sup.2 and the power density of the molybdenum target was 50 W/cm.sup.2. The bulk proportions of the elements were in the coating, at. % (excluding oxygen trapped from the environment on the surface of the coating after deposition):

(13) TABLE-US-00005 carbon 17; copper 78; additional metal (molybdenum) 5.

(14) The 100Cr6 shims were coated with the nanocomposite solid lubricant coating, which showed the very high dry friction coefficient of 0.7 and the wear rate higher than 10.sup.11 m.sup.3/N.Math.m. Therefore, molybdenum was found unsuitable for the role of the additional metal.

Example 4

(15) 100Cr6 shims were coated by MS PVD method at argon (99.999%) pressure of 3.0 mTorr for 70 minutes at a substrate-target distance of 30-40 mm using two copper-carbon mosaic targets (with 18% carbon surface area) and one titanium target. The resulting nanocomposite solid lubricant coating was 14 micrometers thick. The bias voltage of 100V was used during the deposition process. The power density of the copper-carbon mosaic target up to 140 W/cm.sup.2 was used. Such high power density led to the finer structure of the deposited nanocompositethe copper grain size was in the range between 20 and 40 nm and the carbon matrix nanolayers had thickness in the range between 1 and 3 nm. The deposited nanocomposite solid lubricant coating contained in bulk proportions, at. % (excluding oxygen trapped from the environment on the surface of the coating after deposition):

(16) TABLE-US-00006 carbon 18; copper 76; additional metal (titanium) 6.

(17) The investigation of the cross sectional SEM image of the coating showed that the thickness of each titanium layer was in the range between 5 and 8 nm and the thickness of each copper-carbon layerin the range between 100 and 130 nm. The 100Cr6 shims were coated with the nanocomposite solid lubricant that had the dry friction coefficient of 0.16 and the friction coefficient of 0.05 in an oil environment.

(18) The present invention proposes MS PVD copper-carbon nanocomposite coatings, which have increased hardness, decreased wear rate and are adapted for application in mechanical engineering as solid lubricant coatings.

Example 5

(19) Pins of engine chains were placed in a vacuum chamber with two-fold rotation with two copper-carbon mosaic targets (with 26% carbon surface area) and two titanium targets. A nanocomposite solid lubricant coating was deposited on the bushes of the engine chains by MS PVD method at argon (99.999%) pressure of 2.8 mTorr for 15 minutes with a substrate-target distance of 60-80 mm. The power density of the copper-carbon mosaic target was 100 W/cm.sup.2 and the power density of the titanium target was 70 W/cm.sup.2. The deposited nanocomposite solid lubricant coating had the thickness of 3 micrometers and contained in bulk proportions, at. % (excluding oxygen trapped from the environment on the surface of the coating after deposition):

(20) TABLE-US-00007 carbon 17; copper 57; additional metal (titanium) 26.

(21) The pins of the engine chains were coated with the nanocomposite solid lubricant coating with the hardness of 800 HV and the friction coefficient of 0.5 in dry environment. Because of the high friction coefficient, the increase in the lifetime of the chains was negligible and the coatings with the titanium concentration higher than 15 at. % were considered as unsuitable for tribological applications.

Example 6

(22) Bushes of engine chains were placed in a vacuum chamber with two-fold rotation with two copper-carbon mosaic targets (with 26% carbon surface area) and one titanium target. A nanocomposite solid lubricant coating was deposited on the bushes of the engine chains by MS PVD method at argon (99.999%) pressure of 2.8 mTorr for 40 minutes with a substrate-target distance of 60-80 mm. The power density of the copper-carbon mosaic target was 100 W/cm.sup.2 and the power density of the titanium target was 60 W/cm.sup.2. The deposited nanocomposite solid lubricant coating had the thickness of 5 micrometers and contained in bulk proportions, at. % (excluding oxygen trapped from the environment on the surface of the coating after deposition):

(23) TABLE-US-00008 carbon 23; copper 67; additional metal (titanium) 10.

(24) The bushes of the engine chains were coated with the nanocomposite solid lubricant coating, which showed the hardness of 460 HV, the wear rate lower than 10.sup.17 m.sup.3/N.Math.m, the friction coefficient of 0.09 in an oil environment and it increased the lifetime of the chain by 2.5 times (relative to an uncoated chain).

Example 7

(25) Inner and outer rings of bearings were coated in a vacuum chamber with 3 copper-carbon mosaic targets (with 18% carbon surface area) and one titanium target. A nanocomposite solid lubricant coating was deposited on the bearing rings by MS PVD method with the power density of the copper-carbon mosaic target 120 W/cm.sup.2 and the power density of the titanium target 60 W/cm.sup.2 at argon (99.999%) pressure of 3 mTorr for 65 minutes. The deposited nanocomposite solid lubricant coating had the thickness of 15 micrometers and contained in bulk proportions, at. % (excluding oxygen trapped from the environment on the surface of the coating after deposition):

(26) TABLE-US-00009 carbon 17; copper 77; additional metal (titanium) 6.

(27) The inner and outer rings of the bearings were coated with the nanocomposite solid lubricant coating, which showed the hardness of 310 HV, the wear rate lower than 10.sup.16 m.sup.3/N.Math.m, the dry friction coefficient of 0.17 and the friction coefficient of 0.06 in an oil environment

(28) The present invention proposes MS PVD copper-carbon nanocomposite coatings, which have increased hardness, decreased wear rate and are adapted for application in mechanical engineering as solid lubricant coatings.