Patent Description:
A large variety of deposition techniques are used to coat substrates. Vapor deposition technology is typically used to form thin film deposition layers in various types of applications, including microelectronic applications and heavy-duty applications. Such deposition technology can be classified in two main categories. A first category of such deposition technology is known as Chemical Vapor Deposition (CVD). CVD generally refers to deposition processes occurring due to a chemical reaction. Common examples of CVD processes include semiconducting Si layer deposition, epitaxy and thermal oxidation.

A second category of deposition is commonly known as Physical Vapor Deposition (PVD). PVD generally refers to the deposition of solid substances occurring as a result of a physical process. The main concept underlying the PVD processes is that the deposited material is physically transferred onto the substrate surface via direct mass transfer. Typically, no chemical reaction takes place during the process and the thickness of the deposited layer is independent of chemical reaction kinetics as opposed to CVD processes.

Sputtering is a known physical vapor deposition technique for depositing compounds on a substrate, wherein atoms, ions or molecules are ejected from a target material (also called the sputter target) by particle bombardment so that the ejected atoms or molecules accumulate on a substrate surface as a thin film.

Another known physical vapor deposition technique is cathodic vapor arc deposition methods. In this method, an electric arc is used to vaporize material from a cathode target. Consequently, the resulting vaporized material condenses on a substrate to form a thin film of coating.

Amorphous carbon is a free, reactive form of carbon which does not have a crystalline form. Various forms of amorphous carbon films exist and these are usually categorised by the hydrogen content of the film and the sp<NUM>:sp<NUM> ratio of the carbon atoms in the film.

In an example of the literature in this field, amorphous carbon films are categorised into <NUM> categories (see table below taken from "Name Index of Carbon Coatings" from Fraunhofer Institut Schich- und Oberflächentechnik):.

Tetrahedral hydrogen-free amorphous carbon (ta-C) is characterised in that it contains little or no hydrogen (less than <NUM>% mol, typically less than <NUM>% mol) and a high content of sp<NUM> hybridised carbon atoms (typically greater than <NUM>% of the carbon atoms being in the sp<NUM> state).

Whilst the term "diamond-like carbon" (DLC) is sometimes used to refer to all forms of amorphous carbon materials, the term as used herein refers to amorphous carbon materials other than ta-C. Common methods of DLC manufacture use hydrocarbons (such as acetylene), hence introducing hydrogen into the films (in contrast to ta-C films in which the raw material is typically hydrogen free high purity graphite).

In other words, DLC typically has an sp<NUM> carbon content of greater than <NUM>% and/or a hydrogen content of <NUM>%mol and above. The DLC may be undoped or doped with metals or non-metals (see table above).

Conventional DLC coatings can have a hardness value of up to about <NUM> HV (Vickers hardness) and thickness of approximately <NUM> or greater. For example, automobile (e.g. engine) components coated with DLC can be obtained from Oerlikon Balzers, HEF USA and IHI Ionbond AG. However, their hardness is limited and the thicknesses of these coatings limit their applications and are prohibitive for some precision devices.

DLC can similarly have acceptable hardness and friction coefficient for cutting tools and other uses. The hardness of DLC coatings currently on the market for tools is again around <NUM> HV Vickers hardness for a thickness of about <NUM> microns. But for some precision devices, this thickness will limit its application. Therefore, there is a need in the market to develop a thinner but equally wear-resistant diamond-like film.

<CIT> describes coating a substrate with a metallic/silicon adhesion layer, a metal carbide/silicon carbide transition layer and a DLC layer. In the examples in this document, chromium is selected as the metal for the adhesion layer.

<CIT> refers to a coated substrate comprising a substrate, an intermediate later and a tetrahedral carbon layer where the Young's modulus of the tetrahedral carbon layer must be greater than that of the intermediate layer.

<CIT> discloses a multi-layer coating comprising a carbide or nitride layer followed by further DLC layers.

<CIT> discloses a substrate comprising alumina, coated with a first material comprising titanium and a second material comprising carbon wherein at least <NUM>% of the carbon is tetrahedrally bonded.

<NPL> describes a multilayer coated substrate comprising a Ti substrate, a TiC layer, followed by a ta-C layer, wherein the ta-C layer is formed using a metal plasma immersion ion implantation and deposition technique.

<NPL> discloses the preparation of multilayered nonhydrogenated diamond like amorphous carbon films using filtered cathodic vacuum arc deposition under various deposition biasing conditions.

Whilst greater hardness values can be obtained using ta-C instead of DLC, these layers are often brittle and easily delaminate from the substrate. Thinner but harder coatings which still have good adhesion can not currently be made. There is a need for thinner but equally or more wear-resistant carbon coatings.

An object of the invention is to provide an alternative to existing carbon-containing coatings, preferably to provide improved coatings.

The inventor of the present application has found that by selecting appropriate intermediate layers for adhering ta-C to a substrate, coatings of increased hardness can be obtained which are also wear resistant and do not easily delaminate. Such coatings can have increased hardness and reduced thickness compared to conventional coatings which make use of DLC.

Accordingly, the invention provides a substrate coated with a multi-layer coating, comprising in order from the outside towards the substrate:.

Also provided is a method of making a coated substrate, comprising depositing onto the substrate a coating comprising in order:.

wherein (<NUM>) the Young's modulus or (<NUM>) the hardness or (<NUM>) both the Young's modulus and the hardness independently stay the same or increase from layer to layer from the first intermediate layer to the first functional layer; and wherein the hardness is measured using the Vickers hardness test (ASTM E384-<NUM>) and the Young's Modulus is measured by nanoindentation.

Gradual increase in Young's modulus and hardness in the transition from the layer adjacent the substrate to the uppermost functional layer provides a hard coating securely adhered to the substrate. The transition is generally across at least <NUM> layers and may be across a greater number; in examples, at least <NUM> or <NUM> layers make up specific coatings of the invention.

Thus, the invention enables coating of a substrate with a thin, hard coating that shows good hardness and wear resistance, as illustrated by the testing of embodiments of the invention described in more detail below.

As discussed above, the term "tetrahedral amorphous carbon" (ta-C or TAC) as used herein refers to amorphous carbon having a low hydrogen content and a low sp<NUM> carbon content.

Ta-C is a dense amorphous material described as composed of disordered sp<NUM>, interlinked by strong bonds, similar to those that exist in disordered diamond (see <NPL>). Due to its structural similarity with diamond, ta-C also is a very hard material with hardness values often greater than <NUM> GPa.

For example, the ta-C may have a hydrogen content less than <NUM>%, typically <NUM>% or less, preferably <NUM>% or less (for example <NUM>% or less). The percentage content of hydrogen provided here refers to the molar percentage (rather than the percentage of hydrogen by mass). The ta-C may have an sp<NUM> carbon content less than <NUM>%, typically <NUM>% or less, preferably <NUM>% or less. Preferably, the ta-C may have a hydrogen content of <NUM>% or less and an sp<NUM> carbon content of <NUM>% or less. The ta-C is preferably not doped with other materials (either metals or non-metals).

By contrast, the term "diamond-like carbon" (DLC) as used herein refers to amorphous carbon other than ta-C. Accordingly, DLC has a greater hydrogen content and a greater sp<NUM> carbon content than ta-C. For example, the DLC may have a hydrogen content of <NUM>% or greater, typically <NUM>% or greater, for example <NUM>% or greater. The percentage content of hydrogen provided here again refers to the molar percentage (rather than the percentage of hydrogen by mass). The DLC may have an sp<NUM> carbon content of <NUM>% or greater, typically <NUM>% or greater. Typically, the DLC may have a hydrogen content of greater than <NUM>% and an sp<NUM> carbon content of greater than <NUM>%. The DLC may be undoped or doped with metals and/or non-metals.

The invention advantageously provides deposited ta-C coatings that are not thick but are hard and have high wear resistance.

As per the invention, a substrate coated with a multi-layer coating comprises in order from the outside towards the substrate:.

In certain embodiments the coating may suitably comprise one or more further intermediate layers between the first intermediate layer and the substrate.

In certain embodiments the coating suitably may comprise one or more further functional layers comprising ta-C between the second functional layer and the first intermediate layer.

Preferred embodiments are namely as per the invention, a substrate coated with a multi-layer coating comprises in order from the outside towards the substrate:.

Further preferred embodiments are namely a substrate coated with a multi-layer coating, comprises in order from the outside towards the substrate:.

The functional layers comprise ta-C, and preferably consist of ta-C. There may be several such functional layers, with Young's modulus and/or hardness remaining the same or increasing from layer to layer, peaking or culminating with the properties of an uppermost functional layer, usually the one exposed on the outside of the coated substrate. Testing e.g. of coating hardness of the coated substrate (as reported e.g. below in examples) takes place on this end product, though the Young's modulus and hardness of individual layers can also be tested or otherwise determined, e.g. theoretically or by testing an unfinished product, prior to application / deposition of further or final layer(s). The total thickness of the functional layers comprising ta-C is typically <NUM> or less, preferably <NUM> or less, for example <NUM> or less.

The second intermediate layer is described as 'intermediate' in that it is one of the layers, intermediate between a ta-C layer and the substrate. In the coated substrate, the second intermediate layer comprises or consists of tungsten carbide, as used in examples herein. The total thickness of the second intermediate layer is typically <NUM> or less, preferably <NUM> or less, for example <NUM> or less.

The first intermediate layer comprises chromium tungstide, so that tungsten is contained within both first and second intermediate layers, as a carbide in the second intermediate layer and as a non-carbide compound in the first intermediate layer. There is as a result continuity between these layers, which generally means Young's modulus and hardness can be matched more easily and there is good adherence between the layers. The total thickness of the first intermediate layer is typically <NUM> or less, preferably <NUM> or less, for example <NUM> or less.

The further intermediate layer is a layer that is applied to the substrate, e.g. as an adhesion or seed layer. Good adhesion to the substrate is desirable and it is found that layers with good substrate adhesion are often not those that are hardest or with highest Young's modulus, as seed layer properties are more suitably closer to those of the substrate. The invention addresses this by providing the further layers to gradually increase the two properties and confer overall improved such properties to the finished coating while retaining good adhesion.

The coated substrate comprises a further intermediate layer between the substrate and the first intermediate layer, the further intermediate layer comprising chromium. Continuity as described above between layers is desirable, and so chromium is contained within both the first and further intermediate layers. The total thickness of the further intermediate layer is typically <NUM> or less, preferably <NUM> or less, for example <NUM> or less.

When the substrate is metallic (e.g. steel), it is preferable that the intermediate layer adjacent the substrate is also metallic or comprises a metallic element in order to provide metal-metal bonding between the metallic substrate and the intermediate layer to promote adhesion.

In the invention the Young's modulus stays the same or increases from layer to layer between the second intermediate layer and the first functional layer. In addition, the Young's modulus preferably increases over any set of three adjacent layers in the coating, and more preferably increases from the adhesion or seed layer to the final, uppermost functional layer. Suitably, the average increase in the Young's modulus is <NUM> GPa per layer or more, or <NUM> GPa per layer or more, or <NUM> GPa per layer, or more. In examples below, the average increase was approximately <NUM>, <NUM>, <NUM>, <NUM> and <NUM> GPa respectively per layer (e.g. <NUM> GPa increase over <NUM> layers is an average of 15GPa as there are three additional layers on top of the first layer).

An aim of the invention is to provide hard coatings, for many applications and including for tools, engine components etc. Coated substrates of the invention preferably have a coating with a hardness of at least <NUM> HV, more preferably <NUM> HV or more, <NUM> HV or more, <NUM> HV or more, or <NUM> HV or more. Coatings with a wide range of measured hardness values within these ranges have been made (see examples below), including coatings with hardness of approximately <NUM> HV. For different end applications, according sometimes to user choice, different hardness may be appropriate. While hardness of <NUM> HV is achievable, it can also be that slightly thicker but less hard coatings are preferred for some uses (for example, uses where wear resistance is more important than hardness). To achieve the end hardness, hardness increases through the coating as described. Generally, the ta-C layer in the functional layer adjacent the first intermediate layer, which ta-C layer may also be referred to as being closest to the substrate, is a softer ta-C layer, enabling hardness to transition from seed / intermediate layers through this initial ta-C layer to the uppermost, outer ta-C layer. This closest ta-C layer may have a hardness of <NUM> HV or more. This provides a base for further hardness increase through to the top functional layer. Increase in hardness is suitably achieved by variation in the ta-C deposition parameters, e.g. when using FCVA by adjustment of substrate bias. The ta-C layer (functional layer) adjacent the first intermediate layer also have a hardness of <NUM> HV or more, preferably <NUM> HV or more, preferably <NUM> HV or more, or <NUM> HV or more.

In embodiments of the invention the hardness stays the same or increases from layer to layer from the second intermediate layer to the first functional layer. In addition, the hardness preferably increases over any set of three adjacent layers in the coating, and increases from the adhesion or seed layer to the final, uppermost functional layer. Suitably, the average increase in hardness is at least <NUM> HV per layer, usually at least <NUM> HV per layer, e.g. at least <NUM> HV per layer or at least <NUM> HV per layer. In embodiments with an overall hardness increase across the ta-C layers in excess of <NUM> HV hardness may increase at least <NUM> HV per layer. The average increase varies according to the total number of layers and the end hardness of the top layer. In examples to date the average hardness increases were <NUM>, <NUM>, <NUM>, <NUM> and <NUM> HV per layer.

In preferred embodiments of the invention, some of which are illustrated in the examples, both the Young's modulus and the hardness stays the same or increases from layer to layer from the second intermediate layer to the first functional layer. More preferably, both the Young's modulus and the hardness increase from the second intermediate layer to the first functional layer.

Specific coated substrates according to the invention, comprise, in order from the outside towards the substrate:.

Coatings of the invention can be made with useful thickness, and can be the same thickness as or thinner than known DLC based coatings but with improved hardness. The total coating thickness is <=<NUM> microns and can be <=<NUM> microns or <=<NUM> microns. Some preferred hard coatings have high hardness and thickness of <NUM> microns or less. Within the coating each layer is, independently, generally <NUM> microns or less thick, preferably <NUM> microns or less thick, more typically <NUM> micron or less thick, suitably <NUM> microns or less, or <NUM> microns or less or <NUM> microns or less and may be thinner for coatings of the invention with reduced overall thickness. Within the coating each layer is, also independently, at least <NUM> microns or more thick, and is suitably <NUM> microns or more thick, or <NUM> microns or more thick or <NUM> microns or more thick and may be thicker according to overall coating thickness. Layer thicknesses are usually fairly similar between each of the intermediate / seed layers and are separately fairly similar between the respective ta-C -containing layers with increasing Young's modulus and/or hardness.

Also provided by the invention are methods for coating substrates. Accordingly, the invention provides a method of making a coated substrate, comprising depositing onto the substrate a coating comprising in order from the outside towards the substrate:.

As will be appreciated, methods of the invention comprise depositing intermediate layers, the further intermediate layer comprising chromium, the first intermediate layer comprising chromium tungstide, the second intermediate layer tungsten carbide, and then the functional ta-C-containing layers. The methods deposit coatings with optional and preferred features as described elsewhere herein in relation to coatings of the invention.

Choice of substrate material is broad, and many substrates made of a wide range of materials can be coated. The substrate is usually metallic and generally is or comprises a metal or an alloy. Steels are suitable substrates, e.g. steel, stainless steel, HSS, tool steel and alloy steel. Ti or its alloys, Al or its alloys, ceramics such as Al<NUM>O<NUM>, ZrO<NUM>, Si<NUM>N<NUM>, SiC, and plastics such as PEEK, POM, LCP, ABS, PC. Articles are generally made of the substrate and then have a coating of the invention applied / deposited.

Conventional CVD and PVD methods, specifically CVA and FCVA processes are known and used for a wide range of substrates and the methods of the invention are similarly suitable for coating a wide range of substrates. Solids, both conducting and non-conducting, are generally suitable and seed layers and adhesion layers can be used to improve coating adhesion and strength, and to render surfaces amenable to being coated. Substrates made of metal, alloy, ceramics and mixtures thereof can be coated. Metal and composite substrates can be coated, especially steel and varieties of steel as well as and parts, tools, components etc made thereof. Specific examples of preferred substrates include tools, cutting tools, tooling, industrial machines and components therefor. It is further and separately preferred that the substrate is an engine component, such as a piston ring, a piston pin, a cam shaft, a tappet, a lift valve, an injection nozzle or another component.

Coatings of the invention are multilayered and the respective layers may independently be deposited using a range of known and conventional deposition techniques, including CVD, PVD, magnetron sputtering and multi-arc ion plating. Sputtering is one suitable method, especially for the intermediate layers (including a seed layer). PVD is suitably used for the functional layers, e.g. sputtering; in examples CVA is used. The CVA process is typically a filtered cathodic vacuum arc (FCVA) process, e.g. as described below. Apparatus and methods for FCVA coatings are known and can be used as part of the methods of the invention. The FCVA coating apparatus typically comprises a vacuum chamber, an anode, a cathode assembly for generating plasma from a target and a power supply for biasing the substrate to a given voltage. The nature of the FCVA is conventional and not a part of the invention.

Young's modulus is a conventionally used and understood mechanical property that measures the stiffness of a solid material. It defines the relationship between stress (force per unit area) and strain (proportional deformation) in a material in the linear elasticity regime of a uniaxial deformation. It is measured using standard methods and apparatus, by nanoindentation (see e.g.<NPL> and <NPL>).

Hardness is measured using the Vickers hardness test (developed in <NUM> by Robert L. Smith and George E. Sandland at Vickers Ltd; see also ASTM E384-<NUM> for standard test), which can be used for all metals and has one of the widest scales among hardness tests. The unit of hardness given by the test is known as the Vickers Pyramid Number (HV) and can be converted into units of pascals (GPa). The hardness number is determined by the load over the surface area of the indentation used in the testing. As examples. Martensite a hard form of steel has HV of around <NUM> and diamond can have a HV of around <NUM>,<NUM> HV (around <NUM> GPa). Hardness of diamond can vary according to precise crystal structure and orientation but hardness of from about <NUM> to in excess of <NUM> GPa is common.

In describing the invention a hardness and/or Young's modulus value is given, as a value or a range of values or as a typical range of values. The value is in some cases as measured directly on the finished, coated substrate; this is apparent from the context. Hardness and/or Young's modulus of an individual layer within a multi-layer coating generally indicates the value when that layer is deposited using the given deposition conditions as a single layer on a steel substrate. If coating adhesion to the substrate is poor then the hardness and/or Young's modulus will generally indicate the hardness and/or Young's modulus of that layer deposited onto a seed layer (typically chromium) deposited onto the substrate. The values given accurately reflect the hardness and/or Young's modulus within the individual layers of the multi-layer coating.

The invention advantageously provides high hardness and wear-resistant ta-C-based coatings. Compared to known DLC coatings in the market, thickness can be reduced for comparable and even increased hardness, significant hardness and/or wear-resistance can be achieved, thickness for acceptable coatings can be reduced e.g. below <NUM> microns and thinner, and/or hardness can be is increased e.g. to about <NUM> HV and above or about <NUM> HV and above to maintain wear resistance.

The invention is now illustrated with reference to the accompanying drawings in which:.

Four prior art coatings, all commercially available, were used (named Comparative Coatings <NUM> to <NUM>) as comparative examples, with structures as set out below:.

A coated piston (<NUM>) was obtained from a commercial supplier, with properties (see <FIG>):.

A coated plunger (<NUM>) was obtained from a commercial supplier, with properties (see <FIG>):.

A coated tappet (<NUM>) was obtained from a commercial supplier, with properties (see <FIG>):.

A second coated tappet (<NUM>) was obtained from a commercial supplier, with properties (see <FIG>):.

Two coatings of the invention were prepared as described below:.

In more detail, onto SUS304 HSS substrates a seed layer of Cr was sputtered, followed by subsequent layers in order of CrW, then WC with the thicknesses in the tables above. Onto these intermediate layers was then deposited multi-layer functional ta-C coatings (<NUM> for A and <NUM> for B) using FCVA apparatus. Depositions parameters and Young's modulus and hardness of the layers were as follows:-.

The hardness of the coatings of the invention and comparative coatings were determined using a nanoindenter (CSM NHT2) with a maximum load of 8mN, a load/unload rate of 16mN/min and a pause of <NUM> seconds. From the loading/unloading curve which shows force against indentation, the Vickers hardness value (HV) of each of the coatings was determined. These values are provided below:.

As can be seen, the coatings of the invention had superior hardness values compared to the comparative prior art coatings.

As an indication of the wear-resistance of the coatings, a Taber abrasion test was conducted on each of the coatings, with the following conditions:.

The number of cycles that each coating was subjected to and the status of the coating (acceptable or unacceptable) at the end of the indicated number of cycles is provided below.

The quality of comparative coatings <NUM> and <NUM> was unacceptable after less than <NUM>,<NUM> cycles. Whilst the coating status for comparative coating <NUM> was recorded as acceptable, this coating was only subjected to <NUM>,<NUM> cycles. By contrast, the coatings of the invention (A and B) and comparative coating <NUM> were all deemed acceptable, even after <NUM>,<NUM> cycles.

As a further test of the wear-resistance of the coatings, each of the coatings were subjected to a wear test using a ball crater machine, as described below.

Raman Spectroscopy can be used to provide an indication of the ratio of sp<NUM> to sp<NUM> carbon atoms in amorphous carbon coatings. The measured Raman Spectroscopy curve can be compared with a simulated curve for a sample having <NUM>% sp<NUM> carbon content. The ID/IG ratio is therefore indicative of any differences between the observed spectrum and the expected spectrum for a coating with <NUM>% sp<NUM> carbons - a higher ID/IG ratio being indicative of a greater sp<NUM> carbon content.

The zero ID/IG ratio for the coatings of the invention correlate to a match between the observed curve and the simulated curve for a coating having <NUM>% sp<NUM> carbon content. Therefore, no sp<NUM> carbons were detected using this method in the coatings of the invention. By contrast, in the Comparative Coatings, higher ID/IG ratios show the higher sp<NUM> content of the coatings, characteristic of DLC coatings.

A scratch test was performed on each of the coatings to determine their resistance to scratches applied along the coating surface under force. The scratch test was conducted using a moving diamond indenter/stylus with the following parameters:.

The critical loads (i.e. the load at which severe coating deformations were first observed) for each coating are provided in the table below:.

As can be seen from the table, the greatest critical load was observed for Coating A. Whilst the critical load for Coating B was comparable to comparative coatings <NUM> and <NUM>, it is noted that the thickness of Coating B is much less than for the comparative coatings. Hence, on the basis of these findings, it is expected that the coatings of the invention are improved resistance to scratches compared to conventional coatings of a similar thickness.

In order to determine the wear resistance of the coatings under repeated, high force oscillating movements, a Tribo test was conducted using the Bruker TriboLab System.

The Tribo test is a reciprocal "pin-on-disk" sliding test and mimics oscillating wear that may occur within an automobile engine. The Tribo test was carried out using the following parameters:.

The maximum loads that each of the coatings were subjected to and the resultant wear track dimensions (width and depth) are provided below.

Coating A had the lowest wear track (in terms of both width and depth) at the highest load (1600N). Whilst the wear track for Coating B was less than for Coating A, good wear resistance is still exhibited at a load of 1600N. Comparative coatings had significant wear tracks at maximum loads of less than 1600N.

The resistance of the coatings were tested against small lengths of pipe in place of drill bits, using a mini bench drill.

For the wear test, the pipe was an SUS304 stainless steel pipe with an outer diameter of <NUM> and an inner diameter of <NUM>. Any delamination of the coating was recorded.

For the scuff test, the pipe was an aluminium pipe with an outer diameter of <NUM> and an inner diameter of <NUM>. Any delamination of the coating or insertion of the aluminium into the coating was recorded.

The drill was set to rotate the pipe at a speed of <NUM> rpm. The loads and drilling times were varied and oil was added evening <NUM> minutes during testing.

The observations are detailed in the table below.

As can be seen in the Example above, coatings of the invention can have increased hardness, critical load, wear resistance and scuff resistance compared to the comparative coatings.

A further coating of the invention was prepared as described below:.

Coating C was tested and found to show high hardness and passed our internal sandpaper test, with no delamination, both before and after exposure to <NUM> for <NUM> hours.

A further comparative coating that is not part of the invention was prepared as described below:.

Comparative Coating <NUM> was tested and passed our internal hatch test both before and after exposure to <NUM> for <NUM> hours. Comparative Coating <NUM> was also subjected to a Taber test with a Taber Abraser set to <NUM>, <NUM> rpm and <NUM>. The coating passed this test with no scratches both before and after exposure to <NUM> for <NUM> hours.

The invention thus provides hard coatings on substrates and methods for preparing the same.

A further coating that is not part of the invention was prepared as described below:.

Coating D was tested and passed our internal hatch test both before and after exposure to <NUM> for <NUM> hours. Coating D was also subjected to a Taber test with a Taber Abraser set to <NUM>, 60rpm and <NUM>. The coating passed this test with no scratches both before and after exposure to <NUM> for <NUM> hours.

Claim 1:
A substrate (<NUM>, <NUM>) coated with a multi-layer coating, comprising in order from the outside towards the substrate (<NUM>, <NUM>):
a first functional ta-C-containing layer (<NUM>, <NUM>) of hardness <NUM> HV or greater,
a second functional ta-C-containing layer (<NUM>, <NUM>) of hardness <NUM> HV or greater,
a second intermediate layer (<NUM>, <NUM>) comprising tungsten carbide,
a first intermediate layer comprising chromium tungstide (<NUM>, <NUM>), and
a further intermediate layer comprising chromium (<NUM>, <NUM>) and adjacent the substrate (<NUM>, <NUM>),
wherein each layer has a thickness of at least <NUM> microns and the total coating has a thickness of <NUM> microns or less;
wherein the ta-C has a hydrogen content less than <NUM>% and an sp<NUM> content less than <NUM>%;
wherein the first functional layer has a hardness at least <NUM> HV greater than the second functional layer;
wherein (<NUM>) the Young's modulus or (<NUM>) the hardness or (<NUM>) both the Young's modulus and the hardness independently stay the same or increase from layer to layer from the first intermediate layer (<NUM>, <NUM>) to the first functional layer (<NUM>, <NUM>); and wherein the hardness is measured using the Vickers hardness test (ASTM E384-<NUM>) and the Young's Modulus is measured by nanoindentation.