This invention relates to carbon containing coatings and also to a method and apparatus for the deposition of such coatings and to articles which include the coatmgs.

The provision of carbon coatings for articles is well-known and the performance and characteristics of the coatings can vary depending on the particular form of the carbon coating which is applied. For example, it is known that certain carbon coatings have good hardness and wear resistance and that coatings of this type in the past have been used to provide highly wear resistance surfaces which have a diamondlike carbon characteristic. Carbon coatmgs which are particularly useful in this form have a significant amount of material with carbon-carbon sp3 bonding.

It is also known from, for example, the Applicant’s patent GB2331998 to provide a carbon containing coating in which carbon-carbon bonding within the coating is mostly of an sp2 form.

While this form of coating has had many uses, the aim of the present invention is to provide an adaptation of this type of coating in order to enhance the characteristics and use of the same whilst maintaining the advantages such as hardwearing and other mechanical properties of the coating.

In a first aspect of the invention, there is provided a graphite like carbon containing coating, said coating having, at least at and/or adjacent to its external surface, between 0 and 10% chromium or titanium and carbon carbon bonding substantially of the sp2 form and wherein the coating is doped with particles of at least one further material.

In one embodiment said at least one further material is selected from silver and copper.

Typically the said at least one further material is selected so as to provide the coating with an enhanced and/ or additional characteristics. In one embodiment, the coating is doped with silver and/ or copper to the extent that the silver or copper in the coating is between 0.1 and 20% and more typically between 0.5 and 10% of the atomic weight.

In one embodiment, when silver is provided it acts as a solid lubricant and thereby aids the self lubrication characteristic of the coating. In one embodiment, when silver is provided, it acts as an antimicrobial agent.

Typically, the particles are added in a form to the coating such that during use of the coating the particles move towards the surface of the coating to thereby provide low friction characteristics of the coating, lubrication and to act to replenish the antimicrobial properties of the coating.

In one embodiment, the size of the particles is provided to be in the range of 1 to 100 nanometres.

In one embodiment the said particles are added or doped into the coating using a cluster generator apparatus and the size of the particles can be controlled to be in the range of 1 to 20nm.

In one embodiment the said cluster particles are added or doped into the coating using a raster system so as to provide a substantially uniform pattern of doping of the particles.

In one embodiment, the said particles are doped into the coating so as to be substantially uniformly dispersed throughout at least a predefined depth from the external face of the coating. In an alternative embodiment, the particles are added to the coating in a manner such that there is a greater percentage of the particles at/ or adjacent to the external surface of the coating.

Typically, the particular format and configuration of the particles in the coating is dependent upon the particular use and the expected length of use of the coating.

In one embodiment, the coating is applied to an article which is formed of a metal or a metal alloy, or a plastic, ceramic or glass. In one embodiment, the coating includes a base layer formed of chromium, titanium and/ or zirconium, a layer which is mostly sp2 bonded carbon in form and applied thereto or graded therewith is a layer which is sp2 bonded carbon in form with said particles applied therein.

In one embodiment, the top layer includes ramping carbon layers having sp2 and sp3 bonding either combined or in separate layers.

In one embodiment, silver or copper particles are used or a combination of silver and copper particles are used.

In one embodiment, the coating which is applied has lubricant properties, low friction, antimicrobial properties and it is found that the usefulness of the particles extends through the life of the coating in use.

In a further aspect of the mvention there is provided apparatus for forming a coating as herein described on an article, said apparatus includes a holder on which the article is located, a target of material which is sputter deposited to form a coating base layer on a surface of the article, one or more target of a carbon material located with one or more magnetrons, control means to gradually increase the level of carbon which is deposited and decrease the level of metal which is deposited so as to form a blended interface between the base layer and subsequent layer of the coating and then apply one or more substantially uniform carbon coating layer in which the carbon-carbon bondmg within the, or each, carbon layer is mostly of the sp2 form at the external surface of the coating and wherein one or more targets of a further material or materials are located with one or more magnetrons and are selectively operated to deposit particles of said further material or materials and so dope said further material particles into said one or more substantially uniform carbon coating layer.

In one embodiment the apparatus mcludes a cluster beam generator in order to apply the particles of the said further material to dope the said coating.

In a further aspect of the invention there is provided a method for forming a coating as herein described said method including the steps of depositing a base layer of the coating is deposited onto a surface of an article from at least one target of a metal material, then depositing carbon from the targets of one or more magnetrons to form a subsequent layer on the base layer and gradually increasing the level of carbon which is deposited and decreasing the level of said metal material which is deposited so as to form a blended interface between the layers and applying one or more layers of a substantially uniform carbon coating in which the carbon-carbon bonding within the, or each, carbon layer is mostly of the sp2 form at the external surface of the coating and wherein doping particles of one or more further materials are deposited within the one or more substantially uniform carbon layer by depositing said one or more further materials from or more magnetron targets.

Specific embodiments of the invention are now described with reference to the accompanying drawings wherein:

Figure 1 illustrates a coating applied to an article and the coating is shown in accordance with the one embodiment of the invention;

Figure 2 illustrates the coating and article of Figure 1 which has been in use for a period of time;

Figures 3a and b illustrate coating apparatus in accordance with one embodiment of the invention which can be used to form the said coating;

Figure 4 shows a TEM image of a portion at or adjacent to the external surface of a coating in accordance with one embodiment of the invention;

Figure 5 illustrates graphically the silver particle size distribution of a coating in accordance with the invention; and

Figures 6a and b illustrate the friction coefficient of a coating formed in accordance with one embodiment of the invention by co-sputtering of carbon and silver and as measured using a pin-on-disc wear test apparatus.

In accordance with the invention, there is provided a method and apparatus for forming a coating on an article which uses, in one embodiment, targets of materials which are sputter deposited from the respective targets using apparatus of a type described with regard to Figures 3a and b. Although one form of apparatus is shown in Figures 3a and b, it should be appreciated that other types of apparatus could also be used to create the coating.

In accordance with Figures 3a and b, the apparatus 2 comprises a chamber 4 in which there is created a vacuum and, in said chamber 4, there is provided a carrier 5 which is located so as to be rotatable about an axis 6. On the external surface of the carrier, there are provided a plurality of articles 7 at spaced intervals around the carrier 5 and each of the articles has an exposed surface 8 onto which the coating is to be applied. Also provided, at respective openings into the chamber, are magnetrons 9 which are provided at spaced locations around the side walls 10 of the chamber and which include a metal, metal alloy or carbon material target 11. The magnetrons can be selectively operated so that, when operated, particles of material of the particular target fitted to that magnetron, are deposited into the chamber 4 and, as the carrier 5 of the articles 7 rotates, the sputtered particles apply to the surfaces 8 of the articles so as to build-up the coating.

It will therefore be appreciated that during the formation of the coating 12, one or more of the magnetrons can be selectively turned on or off so as to deposit the particular material as required at that instant of time to form a coating which, for example, can have a series of layers of different materials.

In accordance with one embodiment, a metal containing target or targets are provided and the magnetrons are operated to deposit particles of the metal therefrom to create a coating underlayer on the surface of the article. It is found that the underlayer is effective in enhancing the bonding of the subsequent coating layer to the article.

In one embodiment, the underlayer can be deposited to a thickness of between 50- 1000 nm.

While, in one embodiment, there may be a distinct interface between the underlayer and the subsequent layer applied thereto, in another embodiment, the underlayer and subsequent layer can be blended by the gradual introduction of further material from other targets of magnetrons such as, for example, by the deposition of carbon particles from one or more carbon targets. This co-deposition can be created so as to gradually increase the level of carbon which is deposited and decrease the level of metal which is deposited so as to form a blended interface. Typically, there is then a uniform carbon coating applied in which the carbon-carbon bonding within the, or each, carbon layer is mostly of the sp2 form.

In accordance with the invention, in addition to the sputtering of the carbon material to form the further and external layer of the coating, particles of another material are also deposited so as to be part of the said coating and in accordance with one embodiment, the further material which is deposited are particles of silver.

In one embodiment, the particles are applied so as to be uniformly spaced throughout the carbon material layer such that as the external surface of the carbon layer is worn, further more deeply embedded, silver particles will be exposed at the surface and therefore allow the benefits of the silver to be obtained continuously until the said carbon layer is completely worn. Thus, it is important that in accordance with the invention, the silver particles are present throughout the depth of the carbon material layer or at least a proportion of the same extending inwardly from the external surface, so as to ensure that the advantageous properties of the provision of the silver, are obtained throughout the said layer and thereby ensure that the advantageous properties which are achieved by the provision of the silver and which are available at the time of the coating being applied, continue to be available through continued use of the coating and hence provide the coating with a definitive lifespan. In one embodiment the particles are deposited by cluster generator apparatus 13 provided in the chamber, either in place of one of the magnetrons 9 or between adjacent magnetrons.

A coating formed in accordance with the invention is exemplified by Figures 1 and 2 which show a cross-section through the article 7 with the coating applied thereto and the coating has an external surface 14 which is formed of carbon material 15 and which has interspersed therein, silver particles 16 m a substantially uniform manner. It is also shown how the silver particles are present in a substantially uniform manner through the depth of the said coating layer 17 as well as across the area of the same, as illustrated in Figure 4 and in which the silver particles 16 are the clear dots with the darker coloured carbon coating on the TEM image, and so, as the coating layer 17’ is worn over time, the advantages of the presence of silver particles can still be obtained. This is illustrated in Figure 2 in which there is shown a partially worn coating layer 17’ formed in accordance with the invention in which silver particles 16 are still present at the external surface 14’.

The provision of the silver or other material particles 16 can be selected so as to provide a particular beneficial effect but, most typically it is expected to be in the region of 0.5-10% of the atomic weight of the coating. By providing the silver particles in this range, so the advantages of the properties of the carbon material in the sp2 form can be maintained in terms of wear resistance and lubrication whilst providing further advantages in terms of the same being antimicrobial and thereby making the coatings particularly useful for industries such as space, medical and for biomedical applications. Furthermore, the provision of the silver particles further aids the self-lubricating effect of the coating.

In one embodiment, the silver particles 16 are applied using the cluster generator source 13, the cluster generator source is operated with parameters which are controlled in order to allow the size of the silver particles or clusters to be held within a predetermined range such as, for example, 1-20 nm.

Furthermore, the cluster generating apparatus may be operated so as to move in a raster pattern and thereby allow the clusters of the silver particles 16 to be substantially uniform across and in the said coating and in particular, the same may be provided to a layer 17 of a depth of 50 nm from the external layer. Again, the depth of the provision of the silver particles, can be selected with regard to the particular expected lifetime of the coating and the specific requirements for the particles to be provided. The TEM image of Figure 4 illustrates a portion of the external surface of a coating in accordance with one embodiment of the invention in which the silver particles 16 have been deposited using the cluster generator apparatus:

In one embodiment, the coating applied to the article 7 of a metal or metal alloy, comprises, a base layer or underlayer 18 which is applied to article surface 8 which is formed of chromium, titanium and/ or zirconium and then at least one layer 1, but in other embodiments further layers, or a layer with graduated material content which forms the external face 14 of the coating 12 and which is formed of carbon which is/or becomes the sp2 carbon form towards the external surface and which includes silver or copper particles applied within the same.

There is therefore provided a coating in accordance with the invention which has improved lubrication properties, low friction antimicrobial properties and is suitable for use in tribological components, medical instruments and biomedical purposes.

Figure 5 illustrates graphically the particle size distribution, in this embodiment, silver particles, of a coating formed in accordance with the invention and as determined using a Grazing-Incidence Small-Angle X-ray Scattering (GISAXS) analysis, for a coating in which carbon and silver have been deposited from magnetron targets and illustrates a high size distribution value of particles with a radius in the range of 7-10.

Figures 6a and b illustrate graphically the friction coefficient of a coating formed in accordance with the invention by the deposition by co-sputtering of carbon and silver particles. The friction coefficient was measured using a pin-on-disc wear tester apparatus as illustrated by the image in Figure 6b. Figure 6a is a graph of Friction in the vertical axis against time and the graphical line 20 illustrates that the Specific wear rate of the coating is substantially constant over time and which illustrates that the coating has self lubricating qualities in that the particles are being exposed as the coating is worn so that the required level of particles are exposed at the external surface of the coating for a relatively long period of time until the base layer is reached. The test conditions involved the Friction of the external surface of the coating being measured under a 40 N load against a WC/Co ball and the friction coefficient value was 3.9 x 10-17 m3/Nm.