Plasma methods for nanodiamond coatings

Abstract

The present invention relates to a new coating and a new method for producing said new coating, wherein the new coating comprises at least one polycrystalline diamond coating layer of the type nanodiamond coating layer, whose crystallite grains have a crystallite grain size in nanometer range, i.e. lower or equal to 100 nm, wherein the new coating exhibits enhanced wear resistance and make possible to attain enhanced cutting tools performance in cutting operations.

Description

[0001] Plasma methods for nanodiamond coatings

[0002] The present invention relates to a new coating and a new method for producing said new coating, wherein the new coating comprises at least one polycrystalline diamond coating layer of the type nanodiamond coating layer, whose crystallite grains have a crystallite grain size in nanometer range, i.e. lower or equal to 100 nm, wherein the new coating exhibits enhanced and more predictive wear resistance and make possible to attain enhanced cutting tools performance in cutting operations.

[0003] Furthermore, the present invention relates to a new method for removing (stripping) the new coating from a substrate to which the coating has been applied, allowing in this manner reconditioning of the originally coated substrate and re-use of the recoated substrate.

[0004] The term more predictive wear resistance is used to refer to the continuous almost lineal wear behavior of the inventive coatings as shown for example in Figures 6 and 7.

[0005] Prior Art

[0006] Franz et al. disclose in US 2005 / 0016444 A1 a method for diamond coating of substrates in which the substrate is exposed in a vacuum atmosphere to a reactive gas mixture excited by means of a plasma discharge, the plasma discharge comprising a plasma beam in an evacuated receiver that is formed between a cathode chamber and an anode, and the reactive gas mixture comprising a reactive gas and a working gas, the reactive gas and the working gas introduced into the receiver, and the receiver is evacuated by a pump arrangement , and the hydrogen concentration of the reactive gas mixture being 0-45 vol.%. As explained in US 2005 / 0016444 A1 , coatings deposited by means of CVD methods are described as microcrystalline or nanocrystalline with respect to the average size of the deposited crystallite particles, which may be determined for example by transmission electron microscopy. With microcrystalline coatings, the average crystallite size is greater than 1 pm and varies typically between 1 and 10 pm. With nanocrystalline coatings, the average crystallite size, by contrast, is smaller than 1 pm and especially smaller than 100 nm. Control and adjustability of the average crystallite size are important for optimizing properties of the diamond coatings, such as their hardness, surface roughness and their electrical and optical characteristics. It is suggested to choose the hydrogen concentration in the range 0 to 45 vol.% for attaining that the diamond coating has an average crystalline size of less than 50 nm and preferably between 1 and 30 nm. It is suggested that the plasma beam is generated as a low voltage arc discharge and especially as a high current arc discharge.

[0007] Breidt et al. disclose in US 2006 / 0219158 A1 a method for CVD coating, where in a coating procedure under a carbon-containing gas atmosphere a diamond layer is deposited directly on a substrate made out of cemented carbide or silicon, where during said coating procedure, process parameters are varied such that said parameters are changed multiple times between a first and a second operating state, wherein said first operating state there is a higher carbon over-saturation of said carbon-containing atmosphere close to said substrate, and in said second operating state there is a lower over-saturation of said carbon-containing atmosphere close to said substrate, where the change between the two operating states is effected such that a nanocrystalline diamond layer is deposited on said substrate, where the surface of said layer has a surface roughness Rz which is less than the surface roughness Rz of said substrate surface.

[0008] Disadvantages of the Prior Art

[0009] Diamond coatings solutions provided according to the Prior Art involve still at least following two big disadvantages:

[0010] • the cutting performance attained does not meet the increased demands in the technical field, and / or

[0011] • the production costs are very high at least because the very long coating process times required for the deposition of diamond coatings on cutting tools. Objective of the present invention

[0012] The main objective of the present invention is to overcome at least the above- mentioned disadvantages of the Prior Art.

[0013] Description of the present invention

[0014] The objective of the present invention is attained by providing a new coating according to claim 1 , a new method for producing said new coating according to claim 12 and a substrate, comprising said new coating, wherein the new coating comprises at least one polycrystalline diamond coating layer of the type nanodiamond coating layer, whose crystallite grains have a crystallite grain size in nanometer range, i.e. crystallite grain size lower or equal to 100 nm, wherein the new coating exhibits enhanced wear resistance and makes possible to attain enhanced cutting tool performance in cutting operations. Furthermore, the objective of the present invention is attained by removing a new coating via a method according to claim 21 .

[0015] The dependent claims describe preferred embodiments of the coating as well as of the method for producing the coating according to the present invention.

[0016] For the deposition of coatings and the production of the coated substrates according to the present invention, a plasma induced vapor deposition process (abbreviated PICVD process) is used. Also for the de-coating process according to the invention a plasma-induced process is used.

[0017] For the experiments described as showcases of the present invention in the present description (in particular for the production of the coated substrates), a coater of the type arc-beam PICVD system as it is described by Zuger in the international patent applications WO 2022 / 171697 A1 and WO 2022 / 171702 A1 may be used. These documents are hereby incorporated by reference.

[0018] It is understood that the use of the above-mentioned coater for the conduction of the above-mentioned experiments should not be considered as a limitation of the present invention but just as a showcase of one possible coater to be used for producing the coatings and the production of the coated substrates according to the present invention.

[0019] According to a preferred embodiment of a method according to the present invention, the plasma induced vapor deposition process may be of the type arc-beam plasma induced vapor deposition process (abbreviated arc-beam PICVD process).

[0020] The present invention relates in particular to a coating 1 deposited on a surface of a substrate 2, said coating 1 comprising at least one polycrystalline diamond coating layer of the type nanodiamond coating layer 100, whose crystallite grains have a crystallite grain size lower or equal than 100 nm, preferably lower than 100 nm, when the crystallite grain size is measured by using scanning electron microscopy (SEM) or transmission electron microscopy (TEM), wherein the nanodiamond coating layer 100 exhibits a peak (also called main peak in the present description because of the relevance of the presence of this peak for some properties of the coating) in Raman spectroscopy in a range between 1330 and 1350, preferably between 1330 cm-1and 1340 cm-1, still more preferably in range from 1333 cm-1to 1348 cm-1or in range from 1334 cm-1to 1344 cm-1. As explained above the term "main peak" does not necessarily refer to the most prominent peak and also not to the prominent peak observed in the Raman spectrum of the nanodiamond coating layer but a peak that is important to be present in the Raman spectrum of the nanodiamond coating layer, it means this peak does not need to be the highest one, therefore it will be also simply referred to as a peak or the peak in the present description. Specifically, this peak (mentioned above) may correspond to the characteristic vibrational mode of the diamond structure, known as the diamond Raman peak. The location and sharpness of this peak can be used to assess the quality and size of the diamond crystallites.

[0021] The Raman peak mentioned above may be analyzed by using a Bruker Raman Spectrophotometer. For the measurements preferably:

[0022] - the wavelength used was 532 nm (3.3 mW power), and

[0023] - the size of the spot was calculated as follows: D = 1 .22 x (I / NA), where NA is the numerical aperture of the lens (in our case: 0.80), thus the size of the spot was therefore 811 nm. Advantageously, the main peak in Raman spectroscopy in a range between 1330 and 1350 cm-1may have a FWHM-value (Full Width Half Maximum) in the range of 6-12 cm-1. Moreover, it can also be advantageous if the nanodiamond coating layer 100 exhibits further prominent peaks in Raman spectroscopy, preferably in the range between 1125 and 1135 cm-1. The term “prominent peak” can be understood here in particular as a peak that has an intensity in the Raman spectrum (under the conditions described above) that is at least half the intensity of the main peak.

[0024] Furthermore, it can also be advantageous if the nanodiamond coating layer 100 exhibits further prominent peaks in Raman spectroscopy, preferably in the range between 1542 and 1552 cm-1. This peak may show the presence of graphite which has been found to be the reason of the faster removal of the coating (faster stripping process) after deposition of the coating.

[0025] The coating 1 according to the present invention is especially advantageous when the nanodiamond coating layer 100 exhibits a layer thickness in a range between 2 pm and 30 pm, preferably in a range between 10 pm and 30 pm.

[0026] The layer thickness can be measured for example by using SEM cross section analysis.

[0027] According to a preferred embodiment of the present invention the coating 1 may comprise at least one further polycrystalline diamond coating layer deposited between the substrate 2 and the nanodiamond coating layer 100, wherein said at least one further polycrystalline diamond coating layer is of the type microdiamond coating layer (10), whose crystallite grains have a crystallite grain size higher than 100 nm and lower than 10 pm, when the crystallite grain size is measured by using scanning electron microscopy SEM or transmission electron microscopy TEM.

[0028] The coating 1 according to the above-mentioned embodiment of the present invention is especially advantageous when the microdiamond coating layer 10 exhibits a layer thickness in a range between 1 pm and 4 pm.

[0029] The layer thickness of the microdiamond coating layer can be measured in the same manner as above mentioned for the nanodiamond coating layer. It is especially advantageous when the ratio between the layer thickness of the nanodiamond coating layer 100 and the microdiamond coating layer 10 is greater than 1.

[0030] Advantageously, the nanodiamond coating layer 100 may be the outermost layer of the coating 1 . The present invention relates also to substrates coated with a coating 1 according to any of the embodiments and variants of the present invention as described in the present description of the invention.

[0031] The substrate preferably may be a tool, in particular a cutting tool or a forming tool, or the substrate may be a component.

[0032] Especially high improvements of the tool performance were attained in cutting operations as for example shown in Figure 3. The cutting tests conditions are shown in Figure 4.

[0033] Substrates coated according to the present invention are preferably made of cemented carbides or cermet materials.

[0034] In the case that the substrate is a cutting tool, especially good results may be attained with cutting tools of the type cutting inserts, drilling tools or milling tools.

[0035] The present invention relates likewise to a method for producing the inventive coating as well as the inventive substrates coated with the inventive coating as mentioned above.

[0036] The inventive method comprises at least one step, in which the inventive nanodiamond coating layer 100 is produced by using a plasma induced chemical vapor deposition process, i.e. PICVD process, preferably of the type arc beam PICVD process, and the method comprises following steps:

[0037] - Introducing one or more substrates to be coated in the interior of a vacuum coating chamber of an PICVD coating system,

[0038] - Fixing the substrates in a holding system in the interior of the vacuum coating chamber, preferably a holding system allowing rotation of the substrates around the plasma source, preferably allowing one-fold, two-fold and / or three-fold rotation, - Entering into the vacuum coating chamber one or more gas flows comprising at least one carbon-containing gas, at least one inert gas, and at least one of hydrogen gas and oxygen gas for having a reactive gas mixture in the interior of the vacuum coating chamber,

[0039] - Activating a plasma source in the interior of the vacuum coating chamber for inducting a chemical deposition process, in which reactants coming from the reactive gas mixture are used, for producing the nanodiamond coating layer 100,

[0040] - Varying the flow of oxygen gas entering into the interior of the vacuum coating chamber between at least two different values, wherein:

[0041] • one of the at least two values is a low value, Chjow-fiow, and the another value is a high value, O2_high-fiow, wherein 0 seem < C>2_ Jow-flow — 50 seem, and the ratio 0 — O2_iow-fiow I O2_high-fiow — 0.5, and

[0042] • the oxygen flow is varied during the deposition of the nanodiamond coating layer 100 iteratively at least 20 times to obtain a nanodiamond coating layer 100 of a layer thickness of > 1 pm, wherein the total pressure during deposition of the nanodiamond layer 100 is maintained constant at a value in a range from 0.5 Pa up to 2Pa.

[0043] The inventive method is preferably carried out in such a manner that during the deposition of the nanodiamond coating layer 100, when the high value of oxygen flow, O2_high-fiow, is used, the ratio between the hydrogen gas flow, H2-fiow [seem], and the oxygen gas flow, O2-fiow [seem], in the reactive gas mixture, is maintained in a range from 20 up to 170, i.e. 20 < H2-fiow [sccm] / O2-fiow [seem] < 170, when O2-fiow = O2_high-fiow.

[0044] Especially outstanding results may be obtained when during the deposition of the nanodiamond coating layer 100, only the oxygen flow is varied while all other gas flows entering into the vacuum coating chamber is maintained constant.

[0045] Particular good results may be obtained by using a low value of oxygen flow of 0 seem, i.e. O2_iow-fiow—0 seem.

[0046] The method according to the present invention preferably comprises a step in which at least one microdiamond coating layer 10 is deposited between the substrate 2 and the at least one nanodiamond coating layer 100, this layer is preferably deposited by using a PICVD process, wherein during deposition of the at least one microdiamond coating layer 10, preferably no oxygen flow is used.

[0047] The inventors found that a big advantage may be obtained by using PICVD processes for the deposition of the nanodiamond coating layer 100 and / or for the microdiamond coating layer 10.

[0048] Especially outstanding results may be obtained by using PICVD processes of the type arc beam PICVD techniques. Therefore, the inventors suggest that preferably the coating 1 may be fully produced by using PICVD processes, preferably of the type arcbeam PICVD.

[0049] Another aspect of the present invention is a method for removing a coating 1 , preferably a coating 1 mentioned above from a substrate 2, preferably from a substrate mentioned above, wherein the coating 1 is removed by using a plasma induced decoating process, and the method comprises the following steps:

[0050] - Introducing one or more coated substrates 2 into the interior of a vacuum coating chamber of plasma generating system,

[0051] - Fixing the substrates 2 in a holding system in the interior of the vacuum coating chamber, preferably a holding system allowing rotation of the substrates around the plasma source, preferably allowing one-fold, two-fold and / or three-fold rotation (to rotate the substrates is not essential and therefore completely optional),

[0052] - Entering into the vacuum coating chamber one or more gas flows comprising at least one of nitrogen gas and hydrogen gas and oxygen gas,

[0053] - Activating a plasma source in the interior of the vacuum coating chamber for inducting a de-coating process, in which the coating 1 is removed from the substrate 2,

[0054] Advantageously, the pressure may be maintained during the de-coating process between 0.2 mbar and 1.0 mbar, preferably between 0.4 and 0.6 mbar, i.e. between 20 Pa and 100 Pa, preferably between 40 Pa and 60 Pa. Moreover, favorably the plasma may be produced using a gas flow comprising nitrogen as the main component, preferably only comprising nitrogen.

[0055] According to a preferred aspect, the gas flow may comprise apart from nitrogen, hydrogen and / or oxygen, wherein the nitrogen gas ratio may vary from 10% to 100%.

[0056] Furthermore, advantageously the plasma power used for de-coating may be in a range from 800 W to 5000 W, preferably in a range from 1500 W to 3000 W.

[0057] It can also be an advantage, if the de-coating rate is in a range from 2-7 mp per hour, preferably in a range from 4-6 mp per hour, wherein in particular the de-coating rate may be varied depending on the position of a substrate 2 in the vacuum coating chamber of the plasma generating system.

[0058] According to a further aspect of the invention, after producing a coating 1 on a substrate 2 via the method described above, the coating 1 may be removed from the substrate 2 via a de-coating process described above.

[0059] According to another aspect of the invention, after removal of the coating 1 from the substrate 2 via a de-coating process described above a new coating 1 may be deposited on the substrate 2 via a coating method described above.

[0060] Specific aspects and advantages provided by the present invention

[0061] • A nanodiamond coating layer (also called nanocrystalline diamond film) with hardness close to natural diamond (10000 HV10) was achieved by using PICVD (plasma induced chemical vapor deposition) according to the present invention.

[0062] • The critical Raman peak observed in the inventive nanodiamond coating layer was between 1330 and 1350, particularly good results were observed when the critical Raman peak was in range from 1333 cm-1to 1348 cm or in a range between 1330 cm-1and 1340 cm-1, or in range from 1334 cm-1to 1344 cm-1represents single crystalline diamond with particularly high wear resistance (see one example in Figure 2).

[0063] • Deposition rate of the nanodiamond coating layer was significantly higher than it attained in prior art methods, for example the deposition rate of 0.3 pm / h attained by using HFCVD (hot filament CVD) was increased up to a deposition rate in a range from 0.5 pm / h to 1 pm / h, frequently it is about 0.75 pm / h by using PICVD, in particular arc-beam PICVD, according to the present invention.

[0064] • No post treatment is needed for improving outermost surface roughness of the coating for cutting applications.

[0065] • The best results were obtained by using a DC-Plasma technology of the type arc beam PICVD developed by Oerlikon and used in the arc-beam PICVD coaters from Oerlikon Balzers.

[0066] • Cutting tests results (see for example Figure 3) show higher performance, at least an increment of 70 to 80%, in comparison with the performance attained by using coatings comprising nanodiamond coating layers produced by using HFCVD processes (hot filament chemical vapor deposition processes). These cutting results were obtained by using a drilling test for CFRP (carbon fiber- reinforced plastic) material set up as described in Figure 4.

[0067] A preferred method for producing the coatings and coated substrates according to the present invention has in particular following features:

[0068] • The nanodiamond coating layer is produced by using a reactive mixture of a carbon-containing gas (e.g. methane, CH4), oxygen gas, an inert gas (e.g. argon gas) and hydrogen gas, where the reactive gas mixture is chosen as described in the present description and in the claims, in such that the nanodiamond coating has an average crystallite size of less than 100 nm.

[0069] • The H2 concentration in the reactive gas mixture is preferably in a range from 2000 seem up to 5000 seem, chosen such that the nanodiamond coating layer has an average crystallite size between 1 nm and 100 nm.

[0070] • The O2 concentration in the reactive gas mixture is preferably in a range from 0 seem and 100 seem, more preferably in a range from 30 seem up to 100 seem, at least regarding the O2_high-fiow (see meaning of O2_high-fiow above). The value of oxygen flow, as explained below varies preferably between 0 seem and 100 seem or between 30 seem and 100 seem, being chosen in this manner such that, the diamond coating (in this context the nanodiamond coating layer) has an average crystallite size between 1 nm and 100 nm. • The carbon-containing gas, preferably CH4 is introduced in the coating chamber preferably in such a manner that its concentration in the reactive gas mixture is in a range between and including the values 50 seem and 150 seem , chosen in this manner such that the diamond coating (in this context the nanodiamond coating layer) has an average crystallite size between 1 nm and100 nm.

[0071] • The inert gas is preferably argon gas, and its concentration in the reactive gas mixture is attained by selecting an inert gas flow in a range between and including the values 1500 seem and 3000 seem, thereby chosen the inert gas flow such that the diamond coating (the nanodiamond coating layer in the present context) has an average crystallite size between 1 nm and 100 nm.

[0072] • The H2 flow is selected so that its concentration in the reactive gas mixture is chosen such that the substrate temperature established without external additional heating or cooling is between 450° C and 900° C.

[0073] • The working gas comprises at least one noble gas (inert gas as already mentioned above, preferably argon).

[0074] • The PICVD technology used is preferably arc-beam, PICVD technology, wherein the plasma source is a plasma beam (or arc beam) formed as a low voltage arc discharge, preferably as high current arc discharge.

[0075] • The arc current in the arc beam is preferably between 300 A and 600 A.

[0076] • The overall pressure (also called total pressure of full pressure) in the coating chamber (also called vacuum coating chamber) is preferably between and including the values 0.5 Pa and 2 Pa.

[0077] • The flow of the reactive gas mixture flow or the sum of the gas flows resulting in the reactive gas mixture flow runs essentially parallel to the axis of the plasma beam (parallel to the vertical axis along which the plasma beam or arc beam extends) and is preferably between and including the values 5000 seem and 10000 seem.

[0078] One of the main advantages of these new inventive diamond coatings produced according to the present invention is that they allow the removal (stripping) of the coatings from the substrates on which they were deposited in a very fast manner when using the de-coating process (also referred to as stripping process in the present description) according to the present invention. Concretely, the inventive coatings allow stripping at a faster rate compared to state of the art due to its structure (see Raman Spectra of a coating according to the present invention in Fig. 2). The 1336 cm-1peak corresponds to single crystal diamond or a multicrystalline diamond peak. The 1336 cm-1peak according to the inventive coating is broader with a typical FWHM-value (Full Width Half Maximum) of 6-12 cm-1versus a typical FWHM-value of 4-6 cm-1of coatings according to the state of the art due to the smaller crystal size and the higher defect density of the nanocrystalline structures (see Raman Spectrum of a coating according to the state of the art in Fig. 5 vs. the Raman Spectrum of a coating according to the invention in Fig. 2). The peak around 1224 cm-1represents disordered diamond and it is present in both state of art and inventive coating (in the inventive coating at lower wavenumbers). The additional 1131 cm-1peak in the inventive coating represents nanocrystalline diamond. Furthermore, the presence of 1547 cm-1peak in the inventive coating suggests presence of (a significant amount of > 10 %, preferably 10-20 %) graphite which has been found to be the reason of the faster removal of the coating (faster stripping process) observed for the inventive coatings produced via the inventive plasma chemical vapor deposition method compared to coatings produced according to the state of art. It is also assumed that the amount of graphite is the reason of the continuous linear wear of the inventive coatings observed in cutting test evaluations which is more beneficial than the non- continuous linear wear observed in same cutting test evaluations of coatings of the state of the art (see Figures 6 and 7).

[0079] Figure 7 shows the wear behavior of a tool coated, de-coated and re-coated a first time and again afterwards again de-coated and re-coated a second time according to the present invention. In both cases, i.e. during the first re-coating as well as during the second recoating a total coating thickness of 15 pm was produced, therefore in both cases the wear tests were initiated with same kind of coatings having 15 pm thickness in each case.

[0080] This wear behavior is observed in tools coated with coatings according to the present invention as shown in Figures 6 and 7 not only after a first time coating but also after decoating and recoating more than one time according to the present invention. As already mentioned above, this wear behavior is described in the present description with the term more predictive wear resistance and this term is used to refer to the continuous almost lineal wear behavior of the inventive coatings as shown for example in Figures 6 and 7.

[0081] The inventive de-coating process according to the invention is carried out with a plasma method using a plasma generating machine where the pressure is maintained between 0.2 mbar - 1.0 mbar preferably around 0.5 mbar, i.e. the pressure is maintained between 20 Pa - 100 Pa, preferably around 50 Pa. The plasma is produced by using nitrogen, hydrogen and / or oxygen gas. Concretely, one or more gases can be used for the production of the plasma to remove the diamond coating from the substrate according to the present invention. The gases should be selected from nitrogen, hydrogen and oxygen.

[0082] According to a preferred embodiment of the decoating method according to the present invention, the plasma is produced using a gas flow comprising nitrogen as the main component, it means if the gas flow comprises nitrogen and hydrogen, or nitrogen and oxygen, or nitrogen, hydrogen and oxygen, the nitrogen flow in seem is at least 50% of the total gas flow in seem.

[0083] According to a more preferred embodiment of the decoating method according to the present invention the plasma is produced using a gas flow that only comprises nitrogen.

[0084] According to a further preferred embodiment of the decoating method according to the present invention the plasma is produced using a gas flow that comprises nitrogen and hydrogen.

[0085] Preferably, the nitrogen gas if the gas flow comprises apart from nitrogen hydrogen and / or oxygen, is present at a nitrogen gas ratio varying from 10% to 100%, i.e. the ratio of nitrogen gas flow in seem in relation to the sum of all gas flows in seem in the process is preferably from 10% to 100%.

[0086] The plasma power used for de-coating can be in a range from 800 W to 5000 W depending on the surface area being de-coated in the plasma generating chamber. The decoating rate is variable and can range from 1 to 5 pm per hour for inventive coatings depending of the parameters selected, for example which gases are being used as well as the plasma power. In other words, the present invention relates to a new coating and a new method for producing said new coating as well as to a method for removing the coating, wherein the new coating comprises at least one polycrystalline diamond coating layer of the type nanodiamond coating layer, whose crystallite grains have a crystallite grain size in nanometer range, i.e. lower or equal to 100 nm, wherein the new coating exhibits enhanced wear resistance leading to enhanced cutting tools performance in cutting operations and also leading to a more efficient and faster removal of the coating after the use of the tools, facilitating reconditioning of the tools, which involves recoating of the already used cutting tools for successful re-use.

Claims

Claims1. A coating (1 ) deposited on a surface of a substrate (2), said coating (1 ) comprising at least one polycrystalline diamond coating layer of the type nanodiamond coating layer (100), whose crystallite grains have a crystallite grain size lower or equal than 100 nm, when the crystallite grain size is measured by using scanning electron microscopy SEM or transmission electron microscopy TEM. characterized in that:- the nanodiamond coating layer (100) exhibits a peak in Raman spectroscopy in a range between 1330 cm-1and 1350 cm-1.

2. The coating (1 ) according to claim 1 , characterized in that:- the nanodiamond coating layer (100) exhibits peaks in Raman spectroscopy in a range between 1125 cm-1and 1140 cm-1, 1220 cm-1and 1250 cm-1, 1330 cm-1and 1350 cm-1, and with a peak between 1542 cm-1and 1552 cm-1, which facilitates decoating processes, making possible reconditioning of substrates coated with the coating (1 ).

3. The coating (1 ) according to claim 2, characterized in that said main peak in Raman spectroscopy is in a range between 1330 cm-1and 1350 cm-1.

4. The coating (1 ) according to at least one of the claims 2 to 3, characterized in that the main peak in Raman spectroscopy has a FWHM-value in the range of 6-12 cm-1.

5. The coating (1 ) according to at least one of the claims 2 to 4, characterized in that the nanodiamond coating layer 100 exhibits further prominent peaks in Raman spectroscopy, preferably in the range between 1125 and 1135 cm-1.

6. The coating (1 ) according to at least one of the claims 2 to 5, characterized in that the nanodiamond coating layer 100 exhibits further prominent peaks in Raman spectroscopy, preferably in the range between 1542 and 1552 cm-1.

7. The coating (1 ) according to at least one of the claims 2 to 6, characterized in that the nanodiamond coating layer (100) exhibits a layer thickness in a range between 2 pm and 30 pm, preferably in a range between 10 pm and 30 pm when the layer thickness is measured by SEM cross section.

8. The coating (1 ) according to at least one of the claims 2 to 7, characterized in that said coating (1 ) comprises at least one further polycrystalline diamond coating layer deposited between the substrate (2) and the nanodiamond coating layer (100), wherein said at least one further polycrystalline diamond coating layer is of the type microdiamond coating layer (10), whose crystallite grains have a crystallite grain size higher than 100 nm and lower than 10 pm, when the crystallite grain size is measured by using scanning electron microscopy SEM or transmission electron microscopy TEM.

9. The coating (1 ) according to claim 8, characterized in that the microdiamond coating layer (10) exhibits a layer thickness in a range between 1 pm and 4 pm, when the layer thickness is measured by SEM cross section.

10. The coating (1 ) according to claim 8 or 9, characterized in that the ratio between the layer thickness of the nanodiamond coating layer (100) and the microdiamond coating layer (10) is greater than 1 .11 . The coating (1 ) according to at least one of the claims 2 to 10, characterized in that the nanodiamond coating layer (100) is the outermost layer of the coating (1 ).

12. Coated substrate (2) coated with a coating (1 ) according to any of the previous claims 2 to 11 , characterized in that the substrate (2) is:• a tool, preferably a cutting tool or a forming tool, or• a component.

13. Coated substrate (2) according to claim 12, characterized in that the surface of the substrate (2) on which the coating (1 ) is deposited is made of cemented carbides or cermet materials.

14. Coated substrate (2) according to claims 12 or 13, characterized in that the substrate (2) is a cutting tool of the type cutting insert, drilling tool or milling tool.

15. Coated substrate (2) according to any of the previous claims 12 to 14, characterized in that the coated substrate (2) is a re-coated substrate that was previously coated, afterwards used, afterwards de-coated, afterwards reconditioned by using a process comprising at least a re-grinding step and a re-coating step, wherein the re-coating step results in a new coated substrate (2).

16. A method for producing a coating (1 ), preferably a coating (1 ) according to any of the previous claims 1 to 11 , or for producing a coated substrate (2) according to any of the previous claims 12 to 15, characterized in that, the at least one nanodiamond coating layer (100) is produced by using a plasma induced chemical vapor deposition process, i.e. PICVD process, preferably of the type arc beam PICVD process, and the method comprises following steps:- Introducing one or more substrates (2) to be coated in the interior of a vacuum coating chamber of an PICVD coating system,- Fixing the substrates (2) in a holding system in the interior of the vacuum coating chamber, preferably a holding system allowing rotation of the substrates around the plasma source, preferably allowing one-fold, two-fold and / or three-fold rotation,- Entering into the vacuum coating chamber one or more gas flows comprising at least one carbon-containing gas, at least one inert gas, and at least one of hydrogen gas and oxygen gas for having a reactive gas mixture in the interior of the vacuum coating chamber,- Activating a plasma source in the interior of the vacuum coating chamber for inducting a chemical deposition process, in which reactants coming from the reactive gas mixture are used, for producing the nanodiamond coating layer (100),- Varying the flow of oxygen gas entering into the interior of the vacuum coating chamber between at least two different values, wherein:• one of the at least two values is a low value, Chjow-fiow, and the another value is a high value, O2_high-fiow, wherein 0 seem < C>2_ Jow-flow — 50 seem, and the ratio 0 — O2_iow-fiow / O2_high-fiow — 0.5, and• the oxygen flow is varied during the deposition of the nanodiamond coating layer (100) iteratively at least 20 times to obtain a nanodiamond coating layer (100) of a layer thickness of > 1 pm, wherein the total pressure during deposition of the nanodiamond layer (100) is maintained constant at a value in a range from 0.5 Pa up to 2Pa.

17. The method according to claim 16, characterized in that, during the deposition of the nanodiamond coating layer (100), when the high value of oxygen flow, 02_high- fiow, is used, the ratio between the hydrogen gas flow, H2-fiow [seem], and the oxygen gas flow, 02-fiow [seem], in the reactive gas mixture, is maintained in a range from 20 up to 170, i.e. 20 < H2-fiow [sccm] / O2-fiow [seem] < 170, when 02-fiow = O2_high-fiow.

18. The method according at least one of the previous claims 16 or 17, characterized in that, during the deposition of the nanodiamond coating layer (100), only the oxygen flow is varied while all other gas flows entering in the vacuum coating chamber are maintained constant.

19. The method according to at least one of the previous claims 16 to 18, characterized in that, between the substrate (2) and the at least one nanodiamond coating layer (100), at least one microdiamond coating layer (10) is deposited by using a PICVD process, wherein during deposition of the at least one microdiamond coating layer (10), no oxygen flow is used.

20. The method according to at least one of the previous claims 16 to 19, characterized in that, the PICVD process used for deposition of the nanodiamond coating layer (100), and preferably also for the deposition of the microdiamond coating layer (10), is of the type arc beam PICVD techniques, and preferably the coating (1 ) is fully produced by using PICVD processes, preferably of the type arc-beam PICVD.21 . A method for removing a coating (1 ), preferably a coating (1 ) according to any of the previous claims 1 to 12 from a substrate (2), preferably from a substrate (2) according to claims 13 to 15, characterized in that, the coating (1 ) is removed by using a plasma induced de-coating process, and the method comprises the following steps:- Introducing one or more coated substrates (2) into the interior of a vacuum coating chamber of plasma generating system,- Fixing the substrates (2) in a holding system in the interior of the vacuum coating chamber, preferably a holding system allowing rotation of the substrates around the plasma source, preferably allowing one-fold, two-fold and / or three-fold rotation,- Entering into the vacuum coating chamber one or more gas flows comprising at least one of nitrogen gas and hydrogen gas and oxygen gas,- Activating a plasma source in the interior of the vacuum coating chamber for inducting a de-coating process, in which the coating (1 ) is removed from the substrate (2),22. The method according to claim 21 , characterized in that, the pressure is maintained during the de-coating process between 0.2 mbar and 1 .0 mbar, preferably between 0.4 and 0.6 mbar, i.e. between 20 Pa and 100 Pa, preferably between 40 Pa and 60 Pa.

23. The method according to claim 21 or 22, characterized in that, the plasma is produced using a gas flow comprising nitrogen as the main component, preferably only comprising nitrogen.

24. The method according to at least one of the previous claims 21 to 23, characterized in that, the gas flow comprises apart from nitrogen, hydrogen and / or oxygen, wherein the nitrogen gas ratio varying from 10% to 100%.

25. The method according to at least one of the previous claims 21 to 24, characterized in that, the plasma power used for de-coating is in a range from 800 W to 5000 W, preferably in a range from 1500 W to 3000 W.

26. The method according to at least one of the previous claims 21 to 25, characterized in that, the de-coating rate is in a range from 2-7 mp per hour, preferably in a range from 4-6 mp per hour, wherein in particular the de-coating rate is varied depending on the position of a substrate (2) in the vacuum coating chamber of plasma generating system.

27. The method according to at least one of the previous claims 16 to 26, characterized in that, after producing a coating (1 ) on a substrate (2) via the method according to one of claims 16 to 20, the coating (1 ) is removed from the substrate (2) via a process according to one of claims 21 to 26.

28. The method according to claim 27, characterized in that, after removal of the coating (1 ) from the substrate (2) a new coating (1 ) is deposited on the substrate (2) via a method according to one of claims 16 to 21 .

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