HYDROGEN-FREE CARBON-BASED HARD MATERIAL LAYER WITH GRADIENT COATED ON A SUBSTRATE

Abstract

A method for producing a hard coating on a substrate, wherein the hard coating comprises a hydrogen-free amorphous carbon coating, wherein the amorphous carbon coating is deposited onto the substrate using a cathodic arc discharge deposition technique, wherein a bias voltage is applied to the substrate with an absolute value greater than 0 V, preferably greater than 10 V and less than 1000 V, and wherein the absolute value of the bias voltage is increased during the coating process to obtain a first structure and a second structure and a gradient between the first and second structures along the coating thickness, wherein the first and second structures comprise sp2 and sp3 carbon bonds but differ in their relative concentration,wherein at least one coating pause is applied during the coating process in order to reduce the substrate temperature during the coating pause.

Description

HYDROGEN-FREE CARBON-BASED HARD MATERIAL LAYER WITH GRADIENT COATED ON A SUBSTRATE Technical background Hard carbon-based coatings, particularly tetrahedral amorphous carbon (ta-C) coatings, are used in industrial applications due to their remarkable tribological properties. Specifically, hydrogen-free amorphous carbon coatings can have coating hardnesses of 40 GPa or higher and an E-modulus of 300 GPa or higher. Typical coating thicknesses for ta-C coatings range from 0.2 µm to 30 µm, particularly between 0.7 and 2 µm. These coatings are defined according to VDI 2840 (Carbon coatings - Fundamentals, types and properties of coatings) or ISO 20523 (Carbon-based films - Classification and designations). To produce these specific coatings, high-energy physical vapor deposition (PVD) processes are required. One commonly used VVD method is cathodic arc evaporation. This process allows the generation of energies of approximately 100 eV per atom, which is then implanted into the augmented coating. For the formation of ta-C structures, substrate temperatures must be below 165 °C, which is low compared to the high energy of the incident particles. At higher substrate temperatures, unwanted sp2 bonds (graphite bonds) form in addition to the desired sp3 bond (diamond bond), even in relatively high proportions. Underlying problem The main challenge of cathodic arc evaporation is the inevitable formation of macroparticles, which are incorporated as droplets into the coating. These droplets must be removed during post-treatment, especially when the coating is used in tribological systems, such as bearings, particularly bearing piston pins / connecting rod eyes. Post-treatment may include sandblasting or grinding to smooth the surface and prevent wear due to the presence of the droplets. Since ta-C coatings are very hard, these finishing methods are time-consuming and expensive. lqp Lnn / zznz / e / Yi / u There are methods and devices that can be installed on the coating machine to reduce droplet production during the coating process, known as arc filtration. However, implementing these filters drastically reduces the deposition rate, which negatively impacts coating costs. Objective of the invention One objective of the invention is to provide a method for producing a hard coating on a substrate with, preferably, a high deposition rate, wherein the hard coating preferably comprises only a few droplets. Another objective of the invention is to provide a workpiece with a hard coating applied over it. This task of the invention is solved by a method as claimed in claim 1 and by a workpiece according to claim 14. Ta-C coatings have hardnesses exceeding approximately 40 GPa and a high E-modulus exceeding approximately 300 GPa. The substrate material typically has a hardness of approximately 6 GPa and an E-modulus around 200 GPa. As a result, the substrate and the hard coating can behave differently under load. Furthermore, due to the difference in elastic and mechanical properties between the substrate and the hard coating, deformation and subsequently cracking can begin to form, eventually leading to delamination of the coating. This is sometimes referred to as the eggshell effect, which illustrates the effect of a hard shell wrapped around a soft core.An intermediate bonding layer can be deposited before the hard coating layer in order to compensate for the mismatch in elastic and mechanical properties and thus reduce the risk of coating delamination during operation. In tribological configurations, where two moving bodies come into contact, if the body and counterbody have comparable hardness, abrasion effects begin to occur. Both friction counterparts will acquire smoothed surfaces due to their interaction. If only one of the bodies is coated with ta-C, the abrasion effect only occurs on the uncoated body. This can produce very smooth surfaces after material loss due to wear. The production of hydrogen-free carbon-based coatings that have different hardnesses in different places of the coating in the coating thickness can have several technical and economic advantages. A low coating hardness at the interface between the substrate surface and the coating can reduce stresses caused by mismatches in the E-modulus and hardness between the hard coating and the substrate. This is advantageous in preventing coating cracking or even delamination. In some cases, an intermediate bonding layer to compensate for the different properties between the coating and the substrate could even be omitted. Closer to the outer surface of the coating, greater hardness is preferred to ensure wear resistance and the desired tribological properties during operation. However, on the other hand, lower surface hardness would also be advantageous in order to reduce the costs and effort of the post-treatment processes required to smooth the surface and remove droplets. In some other specialized applications of tribological systems, it is desirable not to have a hard top layer, but rather to have one body rubbing against another, which has a coating that can act as an abrasive coating. In that case, the surface of the coated body becomes smoother as the two bodies come into mechanical contact, while at the same time keeping the two bodies as close as possible without compromising their wear resistance. The objective of the invention is to produce different hardness levels and variations in the properties of the hydrogen-free carbon-based coating described above, gradually increasing the coating thickness by applying and varying different coating parameters during a single process run. This can be achieved primarily by varying the bias voltage on the substrate (which typically has negative values), preferably by varying the deposition rate through the arc current itself, and by controlling the coating temperature (i.e., the surface temperature) established through energy transfer from the coating material to the substrate. lqp Lnn / zznz / e / Yi / u In particular, by increasing the absolute value of the applied polarization voltage and / or increasing the substrate temperature during the coating process, the hydrogen-free carbon-based coating can change from an amorphous carbon having predominantly sp2 bonds with lower hardness near the substrate, to a tetrahedral amorphous carbon (ta-C) coating having predominantly sp3 bonds with higher hardness, preferably anywhere in the center of the coating and, preferably, by decreasing the absolute value of the applied polarization voltage and / or, preferably, decreasing the substrate temperature, the coating having predominantly sp3 bonds can be changed back to a coating having predominantly sp2 bonds with lower hardness on the outer surface of the coating.The resulting coating will have lower hardness closer to the substrate and on the outer surface of the coating and higher hardness anywhere between these two regions. In a typical coating process without controlling the aforementioned coating parameters (polarization voltage, substrate temperature), the substrate temperature (i.e., the surface temperature) continuously increases due to the high energy of the process, which can have various repercussions on the coating properties. For example, when the substrate temperature exceeds a specific temperature, sp2 bonding is favored, and the coating loses its ta-C structure. This means that in the same coating process, it is no longer possible to produce a coating on the outer surface that has predominantly sp2 bonding and a ta-C structure once this specific temperature is reached at any point during the coating process.Therefore, it is necessary to control both the bias voltage and the substrate temperature during the coating process to obtain the desired coating transitions. Using the cathodic arc evaporation technique, sp2 bonds become predominantly present in the coating at temperatures above approximately 165 °C. In the inventive process, the substrate temperature and coating structure can be controlled by applying a negative bias voltage to the substrate, the absolute value of which can be increased at a predetermined rate, and by applying at least one coating pause during the process for at least one minute, preferably several minutes, to allow the substrate to cool during the pause. When the substrate has reached a predetermined lower temperature, the coating process can be resumed.There can be as many coating pauses as necessary to maintain the substrate temperature, i.e., a low surface temperature, and to remain within the regime that produces, for example, predominantly sp3 bonds in the carbon-based coating. This temperature and process control allows for the establishment of a specific region along the coating thickness where either ta-C structures with sp3 bonds or amorphous carbon structures with sp2 bonds can be obtained. In a preferred embodiment, the increase in the absolute value of the bias voltage can be established by a rate defined by the ratio (AU / As), which is the ratio of the absolute voltage difference to the unit of time. Alternatively, since the deposition rate of the carbon-based coating depends on the coating parameters, the ratio could refer to the total coating thickness and be defined by a rate (AU / Ad), which is the ratio of the absolute voltage difference to the coating thickness difference. For example, an absolute increase in the bias voltage on the substrate from 0 to 200 V for a coating thickness of 1000 nm could be defined by an AU / Ad ratio of 0.2 V / nm.In the preferred embodiment, the absolute rise in bias voltage during the coating process of the carbon-based coating is greater than 0 V but less than 1000 V, preferably greater than 10 V but less than 1000 V, typically from 10 V to 200 V. The ratio of the rise in bias voltage to the coating thickness can be set between 0.02 V / nm and 0.5 V / nm; this would correspond to an absolute linear rise in bias voltage of 100 V at a coating thickness of 5000 nm, and of 1000 V at a coating thickness of 2000 nm. In a special embodiment, instead of linearly increasing the absolute bias voltage during the coating process, a preferred approach would be to establish the ratio of the absolute bias voltage increase to different values ​​during the coating process. In this way, for example, the region along the coating thickness where favorable ta-C occurs could be expanded. This effect could be combined with coating pauses applied during the coating process to maintain or reduce the temperature within a specific range where ta-C occurs with sp3 bonding. Another improvement to the hard coating system could be achieved by using a pretreatment of the substrate surface before the deposition of the carbon-based coating, such as metal ion pickling (DIM) or the addition of a very thin bonding layer, such as a Cr-based layer, which can be produced using the residual Cr from the previous metal ion pickling process. Another advantage of the invention, as described above, is the possibility of further processing the surface of the carbon-based coating, which would have a lower hardness than the coating core. Surface smoothing and droplet removal processes may include sandblasting, grinding, and in particular, strip finishing. These are described in detail below. Belt finishing is a process where the workpiece, for example, a piston pin, is mounted on a rotating spindle. Another piece of equipment, called a finishing machine, is then pressed against the workpiece by a belt that advances slowly with a defined air pressure. The tape on the belt, with a Shore hardness of approximately A65° or approximately A85°, preferably between approximately A65° and A85°, rotates with the belt and rubs against the workpiece. The choice of tape material (grit type, grit size, weave style) is essential for the finishing result. In particular, diamond microfinishing tape material is used, with grit sizes between approximately 9 µm and approximately 30 µm, depending on the desired finish and surface finishing time.Preferably, for the best finishing result, a diamond belt grit size of approximately 9 µm is used in conjunction with a belt of approximately A 65° Shore hardness. In addition to feeding, the finishing machine can also oscillate left and right along the axis of the rotating workpiece to create a so-called cross-finish. A coolant lubricant is often used to reduce belt overheating during the grinding process, but it is not always necessary. Typical roughness values ​​for the unfiltered polarization ramp layer (Lnn / zznz / e / Yi / u) before (coating finish) and after finishing can typically be reduced from Rz=1.5 to 0.5 µm. The target values ​​for roughness and the optimum values ​​shown in parentheses have turned out to be Spk <0.4 pm (0.3 pm), Rpk < 0.5 pm (0.3 pm), Rpkx < 0.2 pm (0.1 pm), RfpH5n(F)<0.6 pm (<0.3 pm), GKV < 6 pm (3 pm).Figure 5 shows more detailed values. Surface roughness measurement is crucial, particularly for coatings produced by cathodic arc discharge, where the presence of droplets on the coating must also be considered in the roughness measurement. Optical methods, such as those developed by Confovis, combined with specially designed algorithms, can be used to count the droplets on the surface and characterize the effectiveness of the finishing method. The process steps to illustrate the production of a tetrahedral carbon (ta-C) layer using cathodic arc evaporation on steel substrates are as follows: Preheating The substrate is heated to approximately 150 °C in a vacuum chamber using integrated radiant heaters. The substrate is rotated in different degrees of freedom—single, double, or triple rotation—for optimal heat distribution across the surface. Pickling In a second stage, the substrates are pickled with argon ions. Pickling is carried out using advanced luminescent energy discharge (LEDD) technology. In the coating chamber, titanium targets designed for this purpose operate behind a shutter (shutter at chamber potential) using an arc with a target current of 100 A. The resulting titanium ions (Ti+) are captured by the shutter. At a positive potential, the electrons produced by the ionization of the titanium are conducted through tubular anodes. During this phase, the argon flow is pressure-controlled and fed into the coating chamber, which is at approximately 1 x 10⁻² mbar. The ionized argon (Ar+) is directed toward the substrate by a negative bias voltage of -200 V. Surface pickling is then performed by ion bombardment. DIM Chromium (chromium metal ion pickling) lqp Lnn / zznz / e / Yi / u Under a high vacuum of 1.3 x 10⁻³ mbar and an argon flux of approximately 178 sccm, chromium targets are ignited with a trigger wire and then operated with a target current of 80 A. The result is an arc, which can be moved on the target by applying magnetic fields to the target surface. By applying a negative bias voltage of -800 V to the substrate, chromium ions (Cr⁺) are strongly accelerated from the target to the substrate. Oxides can be removed from the surface due to the high impact of these ions, and simultaneously, the ions can penetrate the substrate material, producing chromium ion implantation. Additionally, a very thin chromium layer of 20–100 nm can be produced from the remaining chromium present on the surface. Chromium metal ion etching (CrI) ensures a smooth transition at the interface between the substrate and the coating material.Additionally, the chromium implantation acts as an anchor to the substrate, ensuring good layer adhesion. Since DIM Cr is a high-energy stage of the process, the substrate can become quite hot. Therefore, it is necessary to implement pauses to keep the substrate temperature below the tempering temperature of the substrate material. Cooling period Before applying the carbon-based coating, the substrate is cooled to approximately 100°C to ensure good adhesion between the thin chromium layer and the carbon layer. During the cooling phase, the substrate rotates in a vacuum chamber. The cooling time may vary depending on the substrate's mass and volume. Carbon transition layer (C intercalated layer) Carbon doping is carried out at a process pressure between 1 x 10⁻³ and 2 x 10⁻³ mbar, preferably approximately 1.7 x 10⁻³ mbar, and an argon flow rate between 50 and 80 sccm, preferably approximately 64 sccm. Argon is introduced by gas sprayers directly in front of the carbon targets. The carbon targets are ignited with a trigger wire and operated at a target current of between 40 and 55 A, preferably approximately 45 A. The resulting carbon ions (C⁺) are then accelerated onto the substrate by a bias voltage of -500 to -300 V, preferably -500 V. This leads to carbon implantation onto the thin chromium layer lqp Lnn / zznz / e / YiAi. The absolute value of the negative bias voltage can then be reduced from -500 V to -150 V. Carbon-based coating process (ta-C coating) Carbon-based coatings, particularly ta-C coatings, are produced at a process pressure between 1 x 10³ and 2 x 10³ mbar, preferably around 1.3 x 10⁻³ mbar, and an argon flow rate between 80 and 100 sccm, preferably around 90 sccm. In this case, the carbon targets operate at a lower target current of 25 to 35 A. The absolute value of the negative bias voltage increases at a predetermined rate (ramp) throughout the coating process, from 0 to -200 V. The target current of the carbon targets remains constant. Applying a ramped bias voltage has the advantage that a lower-hardness ta-C layer can be produced initially. By increasing the bias voltage, a harder layer is subsequently created in the range of 40 to 50 GPa.At bias voltages of approximately -160 V and a substrate temperature close to 160 °C, the proportion of sp2 bonds increases while the proportion of sp3 bonds decreases. This results in a graphite-like top layer, which has a significantly lower hardness than the core cladding, approximately 15 to 30 GPa. The lower hardness of this top layer has the important advantage that it can be finished more easily. Advantages, effects, and further details of the invention are given in the description and accompanying drawings. It is understood that the features mentioned above and those explained below may be used not only in the combination indicated in each case, but also in other combinations or in a single position without departing from the scope of the present invention. The invention is shown schematically in the drawings on the basis of the embodiments and is further described with reference to the drawings. Figure 1 shows a carbon-based coating build-up from left to right, illustrating different coating structures along its thickness. The substrate temperature is shown in red, and the bias voltage in blue. The different coating structures are visible in the three regions labeled A, B, and C. lqp Lnn / zznz / e / Yi / u Figure 2 shows the same cross-section as Figure 1 without the legend and with greater contrast to show the difference between the cladding structures along the cladding thickness. Figure 3 shows a coating as described in the present invention. (1) is the substrate, (2) Cr layer, (3) intermediate C layer, (4) ta-C at low bias voltage (0 - 20 V), (5) ta-C at an intermediate bias voltage (20 - 160 V) and (6) the top ta-C layer at bias voltages (160 - 200 V). Figure 4 shows the relevant process data, such as cathode arc current, absolute bias voltage, gas flow, and substrate temperature, where the values ​​in the legend represent the full scale to 100. The X-axis represents time in minutes. Figure 5 shows a table with the different roughness values ​​before and after the surface finishing of the coating using a) classical methods and b) optical method. Figure 1 shows the carbon-based coating buildup from left to right, illustrating the different coating structures along the coating thickness. The substrate temperature is shown in red, and the bias voltage in blue. The coating can be divided into three intervals: A, B, and C. Region A, closest to the substrate, corresponds to a thin structure with a coating thickness between 200 and 1000 nm, preferably around 700 nm, where the absolute bias voltage increases from 10 V to 100 V and the substrate temperature increases from approximately 140 to 180 °C. The coating gap between regions A and B induces a decrease in substrate temperature of approximately 20 °C, and subsequently, when the bias current is increased from 100 V to 150 V, the temperature rises from approximately 160 °C to 190 °C.The coating in region B is glassy and denser (ta-C) with a coating thickness ranging from 200 to 500 nm, preferably approximately 400 nm. Region C exhibits a more porous and rough coating, where the absolute bias voltage increases from 150 V to 200 V, and the substrate temperature increases from 190°C to 220°C. In this region of the coating, sp2 bonds are predominant, the coating has reduced hardness, and the coating thickness is in the range of 200 to 500 nm, preferably approximately 400 nm. Figure 2 shows the same cross-section as Figure 1 without the legend and with greater contrast to show the difference between the cladding structures along the cladding thickness. Figure 3 shows a coating as described by the present invention with absolute bias voltage values ​​as illustration. (1) is the substrate, (2) Cr layer, (3) intermediate C layer, (4) ta-C at low bias voltage (0 - 20 V), (5) ta-C at an intermediate bias voltage (20 - 160 V) and (6) the top ta-C layer at bias voltages (160 - 200 V). Figure 4 shows some relevant process data, such as cathode arc current, absolute bias voltage, gas flow, and substrate temperature, where the values ​​in the legend represent the full scale up to 100. The X-axis represents time in minutes. The cladding process in this example is represented by the dark blue line, which is the cathode arc current input and lasts approximately 200 minutes. After about 100 minutes, the process is interrupted for a cladding pause of approximately 20 minutes, and then the cladding process continues until the desired cladding thickness is reached. During the entire 200-minute cladding time, including the cladding pause, the absolute bias voltage, represented by the green line, increases from 10 V to 200 V.During the pause, there is no coating process, and the bias voltage remains constant but has no effect on the substrate. The positive effect of the coating pause can be observed in the substrate temperature, which drops from 175 °C to 140 °C. This results in a temperature favorable for creating more sp3 bonds over a longer period, consequently increasing the region of the coating where the ta-C structure is present. The various data and ramps, such as the rate of rise of the absolute bias voltage, coating time, coating pause time, and number of coating pauses, are shown for illustrative purposes only.For example, a different rate of rise of the absolute bias voltage could be chosen between each interruption of the coatings, or the coating could be interrupted more than once, or the coating pause could last less or more than 20 minutes but not less than 1 minute. lqp Lnn / zznz / e / Yi / u Figure 5 shows typical roughness values ​​for the unfiltered polarization ramp layer before (coating finish) and after finishing. These values ​​can typically be reduced from Rz=1.5 to 0.5 pm. Target roughness values ​​and optimum values ​​shown in parentheses have been found to be Spk 5 <0.4 pm (0.3 pm), Rpk < 0.5 pm (0.3 pm), Rpkx < 0.2 pm (0.1 pm), RfpH5n(F)<0.6 pm (<0.3 pm), GKV < 6 pm (3 pm).

Claims

1. A method for producing a hard coating on a substrate, wherein the hard coating comprises a hydrogen-free amorphous carbon coating, wherein the amorphous carbon coating is deposited onto the substrate using a cathodic arc discharge deposition technique, wherein a bias voltage is applied to the substrate with an absolute value greater than 0 V, preferably greater than 10 V and less than 1000 V, and wherein the absolute value of the bias voltage is increased during the coating process to obtain a first structure and a second structure and a gradient between the first and second structures along the coating thickness, wherein the first and second structures comprise sp2 and sp3 carbon bonds but differ in their relative concentration,wherein at least one coating pause is applied during the coating process in order to reduce the substrate temperature during the coating pause.

2. The method according to claim 1, characterized in that the coating pause lasts at least one minute, preferably approximately 20 minutes.

3. The method according to claim 1 or 2, characterized in that the increase in the absolute value of the polarization voltage is established by a rate defined by the ratio AU / As, which is the ratio of the absolute voltage difference to the unit of time.

4. The method according to claim 1 or 2, characterized in that the increase in the absolute value of the polarization voltage is established by a rate defined by the ratio of AU / Ad, which is the ratio between the absolute voltage difference and the difference in coating thickness.

5. The method according to claim 4, characterized in that the ratio is between approximately 0.02 V / nm and approximately 0.5 V / nm. lqp Lnn / zznz / e / Yi / u 6. The method according to any one of claims 1 to 5, characterized in that the absolute bias voltage increases linearly.

7. The method according to any one of claims 1 to 5, characterized in that the absolute bias voltage increases in a stepwise manner during the coating process.

8. The method according to any one of claims 1 to 7, characterized in that before the hard coating is applied to the substrate, the substrate is preheated to approximately 150 °C in the vacuum chamber, preferably using an integrated radiation heater.

9. The method according to any one of claims 1 to 8, characterized in that before the hard coating is applied to the substrate, and preferably after preheating the substrate according to claim 8, the substrate is pretreated, in particular by metal ion pickling (MIP) and / or by the addition of a very thin bonding layer, such as preferably a Cr-based layer.

10. The method according to any one of claims 1 to 9, characterized in that the substrate has a temperature of approximately 100°C before the hard coating is applied to the substrate, in particular before the hard coating is applied to the substrate, the substrate is cooled to approximately 100°C after preheating according to claim 8 to ensure good adhesion.

11. The method according to any one of claims 1 to 10, characterized in that a carbon transition layer (C interlayer) is coated at a process pressure between 1x10⁻³ and 2x10⁻³ mbar, preferably about 1.7x10⁻³ mbar and an argon flow between 50 and 80 sccm, preferably about 64 sccm, carbon doping is carried out, wherein argon is introduced by gas sprayers, preferably directly, in front of the carbon targets, wherein the carbon targets are ignited with a trigger wire and operated at a target current between 40 and 55 A, preferably about 45 A, wherein the resulting carbon ions (C⁺) are then accelerated onto the substrate by a bias voltage between -500 and -300 V, preferably -500 V, which leads to the implantation of carbon in the thin chromium layer,where the absolute value of the negative bias voltage is then reduced from -300V to -150V, preferably from -500V to -150V.

12. The method according to any one of claims 1 to 11, characterized in that the hard coating (ta-C coating) is applied at a process pressure between 1 x 10'3 and 2 x 10'3 mbar, preferably about 1.3 x 10'3 mbar and an argon flow between 80 and 100 sccm, preferably about 90 sccm, wherein the carbon targets operate at a lower target current of about 25 to about 35 A, wherein the absolute value of the negative bias voltage increases at a rate (ramp), preferably determined, throughout the coating time from about 0 to about -200 V, wherein the target current of the carbon targets is kept constant, wherein applying a ramp of the bias voltage at the beginning of the coating produces the ta-C layer with lower hardness, wherein increasing the bias voltage subsequently creates a harder layer in the range between 40 and 50 GPa.preferably of approximately 50 GPa, where at bias voltages of approximately -160 V and a substrate temperature close to 160°C, the proportion of sp2 bonds increases while the proportion of sp3 bonds decreases, resulting in a graphite-like top layer, which has a significantly lower hardness than the core coating of approximately 15 to 30 GPa.

13. The method according to any one of claims 1 to 12, characterized in that the surface of the carbon-based coating is subsequently processed by sandblasting, grinding, and / or strip finishing. lqp Lnn / zznz / e / Yi / u 14. A workpiece comprising a substrate and a hard coating applied to the substrate, wherein the hard coating comprises a hydrogen-free amorphous carbon coating, wherein the amorphous carbon coating is deposited onto the substrate preferably using a method according to one of the preceding claims, wherein the hard coating has a first structure and a second structure and a gradient between the first and second structures along the coating thickness, wherein the first and second structures comprise sp2 and sp3 carbon bonds but differ in their relative concentration.

15. Workpiece according to claim 14, characterized in that the surface roughness of the workpiece is between Hz = 0.5 pm and 1.5 pm, in particular the target values ​​for roughness are Spk <0.4 pm, preferably Spk = 0.3 pm, and / or in particular Rpk < 0.5 pm, preferably Rpk = 0.3 pm, and / or in particular Rpkx < 0.2 pm, preferably Rpkx = 0.1 pm, and / or in particular RfpH5n(F) < 0.6 pm, preferably RfpH5n = 0.3 pm, and / or in particular GKV < 6 pm, preferably GKV = 3 pm.

16. A workpiece according to any one of claims 14 or 15, characterized in that the hard coating can be divided into three intervals A, B, and C, wherein region A is close to the substrate and corresponds to a fine structure having a coating thickness between 200 and 1000 nm, preferably about 700 nm, above region A, region B is coated and is glassy and denser than region A, region B having a thickness between 200 and 500 nm, preferably about 400 nm, above region B, region C is coated exhibiting a more porous and rough coating compared to region B, wherein in region C, sp2 bonds of the coating are predominant and the coating of region C has reduced hardness compared to region B, wherein the thickness of region C is between 200 and 500 nm, preferably about 400 nm, preferably in addition to about 370 nm.

17. Workpiece according to any one of claims 14 to 16, characterized in that on the top of the substrate, wherein on the top of the substrate a layer of Cr is coated, and on top of the Cr layer lqp Lnn / zznz / e / YiAi an intermediate layer of C is coated, and on top of the intermediate layer of C the hard coating is coated.