A method for forming high-hardness and ultra-smooth aC by sputtering.

Abstract

The present invention relates to a method for forming a coating on a substrate with the aid of a coating device and a device for supplying non-reactive ions, characterized in that a negative bias is applied to the substrate in order to bring about ion bombardment of the material deposited on the substrate, thereby increasing the density of the deposited material.

Description

[Technical field]

[0001] The present invention relates to wear-resistant, high-hardness carbon coatings and to a method for improving the mechanical properties of wear-resistant, high-hardness carbon coatings compared to the state of the art, without sacrificing high surface quality. More specifically, the present invention relates to a method for growing a-C films, in which a pulsed plasma carbon sputter source is operated together with an adjacent auxiliary plasma source to provide a periodic, but intense, ion bombardment treatment, resulting in coating mechanical properties approaching those associated with high sp3 fraction ta-C films, even at low temperatures. [Background technology]

[0002] High-hardness carbon coatings such as hydrogen-doped amorphous diamond-like carbon (DLC) or hydrogen-free amorphous diamond-like carbon (the former is often called aC:H and the latter aC or ta-C depending on the ratio of sp3 bonds) are nowadays considered as one of the most effective protective solutions to achieve improved wear resistance on the surfaces of substrate tools in demanding cutting and forming operations or precision components operating under severe loading conditions or exposed to severe friction and contact pressures with other sliding partners (i.e. engine parts in the automotive sector or mechanical engineering parts).

[0003] High quality hard carbon coatings are well known to exhibit an excellent combination of properties such as high hardness, high wear resistance in dry operating and poorly lubricated conditions, low coefficient of friction, and chemical inertness, which can be specifically tailored (e.g., by varying the sp3 / sp2 mixing ratio, adjusting the hydrogen content, or selecting additional metallic and non-metallic doping elements) to meet the performance requirements of various operating conditions. Further details on the characteristics and industrial applications of DLC coatings are found, inter alia, in J. Vetter, "Surface & Coatings Technology 257 (2014) 213-240" and A. Grill, "Diamond and Related Materials 8 (1999) 428-434".

[0004] Hydrogen-free amorphous carbon coatings such as aC and ta-C are known to offer higher hardness and therefore higher wear resistance compared to aC:H coatings while maintaining an extremely low coefficient of friction. Due to the high sp3 ratio of 85%, ta-C coatings are classified as ultra-hard coatings with nanoindentation hardness of about 40-60 GPa, which makes them an excellent solution for components exposed to harsh thermal and mechanical conditions over time, such as shafts and seals or piston pins that have to operate in harsh tribological environments.

[0005] High quality ta-C carbon coatings are typically deposited by physical vapor deposition (PVD) under suitable thermodynamic and kinetic growth conditions. The formation of a high sp3 ratio in a-C is generally attributed to subsurface densification caused by the displacement of C atoms (knock-on atoms) to subsurface positions resulting in sp2 to sp3 conversion of the surrounding carbon-carbon bonds. This displacement is due to the transfer of energy and momentum to atoms close to the ion impact site by ionic species bombarding the growing film. This densification process is generally assumed to be achieved under suitable kinetic conditions such that energetic ions are incident on the substrate with energies up to 100 eV above the carbon atom displacement threshold energy of about 25 eV, and most importantly with a high ion flux to neutral flux ratio (Φi / Φn). The latter is a key parameter to achieve the formation of dense and hard ta-C coatings, for which a highly ionized deposition process is required.

[0006] A method known in the art for achieving a highly ionized plasma to produce hard, dense, and wear-resistant ta-C coatings with relatively high productivity is vacuum arc evaporation, which produces a highly ionized carbon plasma that is highly attractive because it offers control of the kinetic energy of the depositing carbon ion flux, for example by using substrate bias.

[0007] US Patent Publication No. 20190040518 discloses a wear-resistant high-hardness carbon layer on a substrate in a vacuum chamber from a graphite cathode by a low-voltage pulsed arc. The wear-resistant high-hardness carbon layer has a wear-resistant layer made of tetrahedral amorphous carbon (ta-C) and a titanium adhesion layer between the substrate and the wear protection layer. The adhesion layer is also applied by a low-voltage pulsed arc.

[0008] However, a drawback of the arc evaporation process is that a large amount of macroparticles, i.e. so-called droplets, are generated and become incorporated into the coating, which leads to coating defects and thus to undesirable inhomogeneities within the layer, which undesirably increase the coating roughness and in some applications reduces the coating performance, which in tribological applications can lead to increased wear of the counter object.

[0009] Possible solutions to improve the surface quality of arc-evaporated ta-C are post-finishing methods such as brushing or polishing. However, these methods require additional manufacturing steps that negatively impact the economics of the coating process.

[0010] It is known that methods have been proposed to remove these droplets. For example, WO 2014177641 proposes a method for producing smoother wear-resistant layers of hydrogen-free tetrahedral amorphous carbon (ta-C) without the need for mechanical and / or chemical machining by a laser arc method, in which an electric arc discharge is ignited in vacuum by a pulsed laser beam and the ionized components of the plasma can be deflected towards the substrate by a magnetic filter in a separate compartment of the coating chamber. However, the design of these systems is complex and therefore expensive, making it difficult to operate the coating process economically. Moreover, the removal of droplets by such systems is usually accompanied by a significant decrease in the deposition rate, which further affects the economics of the coating process.

[0011] It is also possible to produce dense hydrogen-free ta-C coatings by other deposition methods using alternative sources of energetic species, even if the proportion of carbon ions is minimal, such as ion-assisted sputtering deposition, where a large amount of energetic Ar ions simultaneously bombards thermal C atoms during film growth.

[0012] For example, J. Schwan et al, “Tetrahedral amorphous carbon films prepared by magnetron sputtering and dc ion plating”, in Journal Applied physics 79(1996)1416, by proper adjustment of the unbalanced magnetic field strength of the sputtering source, the use of RF excitation, low gas pressure (less than 10-3 mbar), and a small distance between the target and the substrate (about 3 cm), achieve a very large incident ion flux / carbon flux ratio Φi / Φn of 10, making it possible to produce ta-C coatings with sp3 fraction of about 87%, a level similar to that of vacuum arc evaporation. In this way, the substrate is located close enough to the dense plasma near the target that the high density of Ar ions simultaneously provides a sputtering flux to the graphite target and a strong incident ion flux to the growing film to promote the sp2 to sp3 conversion of the surrounding carbon and knock-on subplantation during deposition to subsurface locations resulting in the growth of a dense ta-C film.

[0013] For reference, traditional industrial sputtering deposition methods such as dc or RF sputtering have extremely low plasma density around the substrate, which typically results in a ratio of ion flux to carbon flux of Φi / Φn<1, ultimately resulting in the formation of low-density (1.8-2.3 g.cm-3) and soft (<20 GPa) a-C coatings.

[0014] However, due to the line-of-sight nature of the vaporized flux emitted from the target surface, it is well known that the film thickness uniformity on substrates with different curvatures is controlled by adjusting the z-position of the substrate along the axis of the cathode during deposition. At short distances such as those used by J. Schwan et al., the size and range of substrates that can be treated by the process is significantly reduced. Therefore, it is recommended to have a method with a higher degree of flexibility and coating uniformity for depositing high-quality ta-C coatings on small and large parts with flat and curved surfaces.

[0015] A well-known alternative method for achieving a highly ionized plasma, density and hardness of the sputtered layer similar to those achieved in arc evaporation without compromising the surface quality is the so-called HiPIMS method (HIP-IMS: high power impulse magnetron sputtering).

[0016] A laboratory process is described by Kouznetsov et al., “A novel pulsed magnetron sputter technique utilizing very high target power densities”, Surface and Coatings Technology 122 (1999), 290-293, and an industrialized process is disclosed by Krassnitzer in WO201243091.

[0017] In HiPIMS, a highly ionized flux of sputtered material is achieved by applying very high peak power, also defined as peak power density (Ppeak, in W.cm-2), to the racetrack area (in cm-2) of the cathode target. As a result of the very high peak power density, a high density plasma is achieved. To stay below the power limits of target / magnetron damage, the high HiPIMS power is applied in a repetitive pulsed manner, thus keeping the average power density (PAv) at conventional magnetron sputtering levels to keep the target temperature below the melting point. HiPIMS pulses are applied with a defined pulse length (tpulse), typically in the range of a few microseconds (~μs) to a few milliseconds (~ms), and with a repetition frequency typically in the range of a few Hertz to a few Kilohertz, resulting in a duty cycle (the percentage of time that a pulse is applied) typically in the range of 0.5-30%. As a result of the high pulse power density, a high plasma density is achieved, which results in a high rate of ionization of the sputtered material. When a negative voltage is applied to the workpiece to be coated, these ions are accelerated towards the workpiece and can be used to produce very dense coatings, as described by Samuelsson et al., “Influence of ionization degree on film properties when using high power impulse magnetron sputtering”, in Journal of Vacuum Science&Technology A 30(2012),031507.

[0018] Despite the high plasma density produced by HiPIMS discharges, HiPIMS carbon is known to have a very low degree of carbon ionization. The difficulty in ionizing carbon is due in part to the very low probability of ionization of the sputtered carbon flux due to low self- and gas sputtering yields, high first ionization energy potential (11.3 eV), and small cross section for electron impact ionization.

[0019] WO2012138279 discloses a sputtering process in which more of the sputtered carbon atoms are ionized compared to standard HiPIMS processes. The process mainly involves sputtering carbon in a HiPIMS using neon (Ne) or a gas mixture containing at least 60% neon as a sputtering gas to increase the electron temperature in order to increase the electron impact ionization rate coefficient and therefore the probability of ionization by electron impact of the sputtered carbon atoms.

[0020] Despite improvements in carbon ion flux, the authors have only reported the growth of hydrogen-containing aC in this process with a film density of up to 2.57 g.cm-3. K. Bobzin et al., “Synthesis of aC coatings by HPPMS using Ar,Ne and He as process gases”, in Surface & Coating Technology 308 (2016) 80, recently reported the growth of aC coatings with a coating hardness of about 45 GPa in this neon HiPIMS process, but the material characterization evidence is not universally consistent and there are conflicting reports regarding the optimal conditions for achieving a high density of tetrahedral bonds.

[0021] For the most part, studies using neon HiPIMS have not found operating conditions that result in high sp3 ratios and coating hardnesses of around 20-30 GPa. This is a consequence of the sputtering process itself, where the ratio of incident ion flux to carbon flux, Φi / Φn, in the growing film in a HiPIMS carbon discharge is found to be at most around 5-6.

[0022] The strategy of increasing the ion flux to carbon flux ratio by converting the sputtered carbon atoms to carbon ions requires a significant increase in plasma density and electron temperature, which can only be achieved by applying very high peak powers in each pulse.

[0023] EP 2587518 discloses a method for depositing hydrogen-free ta-C coatings on substrates of metal or ceramic material by a HiPIMS sputtering process. In EP 2587518, the authors report that hydrogen-free ta-C coatings with a hardness of 50 GPa can be easily deposited on metal or ceramic surfaces. To achieve such properties, the peak power applied in each pulse is in the range of up to 2 megawatts.

[0024] A common problem in carbon sputtering is the occurrence of micro-arcing, as highlighted by Vitelaru et al, “A strategy for Alleviating Micro Arcing during HiPIMS Deposition of DLC coatings”, in the journal Materials 13(2020)1038. The frequency of arcing depends mainly on the quality of the target material and its surface state during sputtering, but also on the peak power used for sputtering. Since the degree of ionization can be increased by increasing the peak power to the target, a further increase in hardness may be accompanied by an undesirable increase in the density of defects on the surface. EP 2587518 does not provide any data to refute this assumption. It can therefore be assumed that high-hardness ta-C coatings such as those described in EP 2587518 will have a disadvantageously large coating roughness and will require the use of post-treatment methods to improve their performance in practical applications.

[0025] As a result, there is a need for an alternative HIPIMS sputtering process for depositing high hardness carbon coatings formed from at least one hydrogen-free tetrahedral amorphous carbon (ta-C) and having a very smooth surface while at the same time exhibiting high hardness (about 50 GPa) and very good sliding friction properties, preferably a HIPIMS sputtering process that represents the simplest and more flexible industrial process with a high degree of process reliability and uniformity. Summary of the Invention [Problem to be solved by the invention]

[0026] It is therefore an object of the present invention to provide a wear-resistant, hard carbon coating by HiPIMS which, compared to the state of the art, offers excellent mechanical properties without sacrificing high surface quality, while at the same time also offering very good sliding friction properties.

[0027] It is a further object of the present invention to provide an alternative industrially suitable coating method for producing tools or components coated with the aforementioned high performance ultra-smooth ta-C coatings. [Means for solving the problem]

[0028] In experiments to improve mechanical properties by HiPIMS, i.e. to form a higher proportion of sp3 bonds in the aC layer, the inventors of the present invention noticed that on the one hand the particle flux incident on the growing substrate surface, generated by the pulsed power plasma, contains neutral (Φn) and ionic (Φi) species. The neutral flux Φn consists of carbon atoms with a rather low kinetic energy resulting from the energy distribution of the sputtering process, corresponding to a few eV (about 5 eV). Analysis of the ion energy distribution function (IEDF) by in situ mass spectrometer analysis showed that in addition to a continuous flux of neutral C, the growing film contains about 95% Ar +ions and about a few percent C + It is shown that the sample is exposed to an ion flux Φi consisting of ions.

[0029] This incident flux, deposited at low temperatures (Ts<150°C), exhibits high hardness (H=30-40GPa), low friction in the dry state against steel (CoF=0.1-0.2), ultra-smooth surface, ca. 10-4 Ω.cm -1 It produces a-C films with a good combination of low electrical resistivity of 0.1 nm, and film density of 2.6-2.8 g.cm-3. The sp3 fraction was estimated to be about 50-60%. The growth of dense a-C films by HiPIMS is highly dependent on the mass and energy of the incident ion species and, crucially, on the ratio of the flux of the impinging ion species to the atoms being deposited.

[0030] According to the findings by J. Schwan et al “Tetrahedral amorphous carbon films prepared by magnetron sputtering and dc ion plating”, in Journal Applied physics 79(1996)1416, the production of ta-C coatings with sp3 fraction of about 87%, similar to that of vacuum arc evaporation, requires process conditions capable of providing a very high incident ion flux / carbon flux ratio Φi / Φn of 10 or more during the growth of the carbon film. However, the ion flux to neutral flux ratio Φi / Φn for HiPIMS discharges is known to be typically in the range of 2-6.

[0031] One strategy to increase the ion flux relative to the neutral flux consists in increasing the peak power density of the HiPIMS pulses while keeping all other process parameters constant. In this way, the plasma density is increased, which tends to improve the degree of ionization of the plasma and ultimately increase the contribution of ions compared to neutrals during film growth. When increasing the peak power density, an interesting improvement in the mechanical properties of the aC coatings was observed.

[0032] Unfortunately, increasing the peak power in the HiPIMS pulse dramatically increases the frequency of arcing at the surface of the graphite target, as shown in Figure 1. These arcing events are partially responsible for the emission of large macroparticles that lead to the accumulation of undesirable surface defects (see Figure 2), increasing coating roughness, and in some cases reducing the coating performance during application. For optimal surface quality, a maximum of 0.5 kW.cm -2 A lower peak power of less than 10 ...

[0033] On the other hand, the present inventors have surprisingly found in their experiments that aC films can be grown at relatively low peak power densities (0.5 kW.cm -2 They found that by operating the HiPIMS source at 1000 nm inlet and 1000 nm in outlet with an adjacent auxiliary plasma source, the mechanical properties of the aC films were dramatically improved to a level approaching that achieved by vacuum arc evaporation, while maintaining a very high level of surface quality similar to that achieved by sputtering.

[0034] The present inventors have surprisingly found that the relatively low peak power density (0.5 kW.cm -2 It has been found that by operating a HiPIMS source of a-C 2000 Å (1000 Å) simultaneously with an adjacent auxiliary plasma source and appropriately adjusting the process parameters of both plasma sources in such a way as to densify the sputtered a-C layer by means of an intense but periodic ion bombardment treatment resulting in coating properties close to ta-C films with a high proportion of sp3 even at low temperatures (the term low temperature is used in the context of the present invention to refer to a surface temperature of the substrate up to 150° C., preferably below 150° C.), it is possible to produce wear-resistant coatings in an industrial coating system consisting of an ultrahard material made of amorphous carbon and at the same time having an extremely high surface quality.

[0035] As noted above, sputtering processes can be classified with respect to duty cycle (fraction of time the pulse is on) and peak power density delivered at the target racetrack. For purposes of the present invention, the term conventional magnetron sputtering processes refers to processes in which the power density of individual pulses is typically 80 W.cm. -2 The HIPIMS process is defined as a process in which the power density of the individual pulses is less than 0.50 kW.cm with a duty cycle in the range of 0.5% to 10%. -2 All discharges operating above the conventional magnetron sputtering power density limit and below the HiPIMS range are referred to as intermediate power impulse magnetron sputtering techniques, abbreviated as InPIMS. The InPIMS technique operates at intermediate power densities of 0.08-0.50 kW.cm with duty cycles above 10%. -2 These definitions are used throughout this specification.

[0036] In order to keep the coating system in a low-temperature coating process suitable for reaching the optimal sp3 bond ratio according to the invention, the vacuum coating chamber is equipped with a special protective shield that allows for increased heat dissipation so that a highly efficient low-temperature coating process can be performed without compromising the deposition rate, for example. The corresponding coating apparatus is described in more detail in WO2019025559. The vacuum coating chamber does not have a radiant heater. However, the vacuum coating chamber can also be equipped with one or more radiant heaters that can be used as a heat source to introduce heat into the chamber to heat the substrate to be coated.

[0037] According to the present invention, the high-hardness carbon layer can comprise at least one ultra-hard hydrogen-free amorphous carbon layer by a method by hybrid InPIMS / auxiliary plasma source, in which at least one target containing C, such as a graphite target, is used as a source of primary ions (Ar+ and some C+) and neutral carbon to deposit the ultra-hardness carbon layer, which is used for sputtering in a coating chamber operating with an InPIMS power source in an inert atmosphere with at least one inert gas, preferably argon, and at least one auxiliary plasma source, such as a plasma ARC (see, for example, WO2014090389), which is conventionally used to pre-clean substrates before the deposition of coatings, is used as a source of additional ion bombardment (see FIG. 3). The term "ultra-hard" in this context means a coating with a hardness of more than 40 GPa.

[0038] The electrical InPIMS power supplied to the graphite target is preferentially delivered in pulses having a length (tpulse) of less than 10 ms, preferably less than 1 ms, and particularly preferably less than 0.1 ms, with a peak power density and duty cycle preferably within the range of the intermediate pulse regime to achieve a sufficiently highly ionized Ar plasma during the InPIMS pulse suitable for promoting the growth of dense and hard a-C, but not so energetic as to induce arcing events at the surface of the graphite target, thus resulting in the deposition of a smooth a-C layer with few surface droplets (see FIG. 1 ).

[0039] The inventors of the present invention have surprisingly found that in order to produce the ultra-hard aC layers of the present invention, it is preferable to achieve growth conditions with a high ion to neutral flux ratio Φi / Φn. According to one embodiment of the present invention, this condition is achieved by simultaneously applying a low peak power InPIMS plasma source and a Plasma ARC, where the rotation of the substrate causes the film to be adjacent to a strong Ar ion source from an auxiliary plasma source. +Before exposure to the ion flux, deposition from each graphite target occurs to a thickness of a few nanometers. + The ions bombard and / or implant into the a-C layer when exposed to an adjacent auxiliary plasma source, resulting in densification to achieve a high sp3 a-C film while the substrate is facing the auxiliary plasma source.

[0040] Although the inventors of the present invention do not wish to be bound by any particular theory, they believe that Ar + The periodic ion treatment with Ar ions is believed to be highly effective in further densifying the growing a-C film by InPIMS due to the fact that the region of intense mixing near the surface is much larger compared to the thickness of the a-C layer deposited during successive exposure to the InPIMS source. + The ions penetrate deep into the near-surface region and induce sp2 to sp3 conversion of the surrounding carbon, resulting in coating properties closer to the high sp3 fraction ta-C films traditionally observed from vacuum arc deposition.

[0041] The inventors of the present invention have surprisingly found that, in order to deposit the above-mentioned ultra-hard aC coatings, suitable adjustments of the rotational speed of the carousel carrying the substrate to be coated and the power applied to the target can be made such that the thickness of the aC layer deposited with each pass in front of the graphite target is proportional to the Ar in the aC. + It has been found that deposition must be performed in such a way that it is below the penetration depth of the ions. Proper adjustment of the deposition rate versus the spin speed must be performed prior to deposition.

[0042] This process can be carried out, for example, at an Ar pressure of about 0.3-0.5 Pa. The negative bias voltage may be continuous or synchronized with the InPIMS pulse or auxiliary plasma source applied to the graphite target, and the bias voltage value is between -50V and -150V, more preferably between -50V and -100V, such that the kinetic energy of the incident ions is favorable for promoting sp2 to sp3 conversion.

[0043] The arc current generated by the Plasma ARC is preferentially continuous or pulsed, with an average current value preferably greater than 10A, most preferably greater than 30A, and even more preferably greater than 50A.

[0044] In the deposition process, the temperature of the substrate can be kept below 150° C., most preferably below 120° C., and even more preferably below 100° C., to avoid carbon graphitization during film growth. The process can be carried out without external heating.

[0045] The hardness of the non-hydrogen-containing amorphous material is preferably higher than 40 GPa. The preferred range of hardness of the amorphous carbon layer is between 20 GPa and 60 GPa.

[0046] The elastic modulus of the hydrogen-free amorphous layer is preferably greater than 300 GPa. The elastic modulus of the amorphous carbon layer is preferably in the range of 200 to 450 GPa.

[0047] The proportion of sp3 bonds in the hydrogen-free amorphous carbon is preferably higher than 50%, more preferably higher than 70%, for example, between 50% and 85%.

[0048] Preferably, the at least one hydrogen-free amorphous carbon is R z It exhibits an extremely smooth surface, characterized by a grain size of <0.5 μm.

[0049] Preferably, the argon concentration in said at least one hydrogen-free amorphous carbon layer is less than 10 atomic %, such as for example less than 5 atomic %.

[0050] Preferably, the electrical resistivity of the at least hydrogen-free amorphous carbon layer is 10-3 Ω cm -1 Less than 10-4 Ω.cm -1 is less than.

[0051] Preferably, the hydrogen-free amorphous carbon layer has an anthracite grey value L* between 50 and 55 (according to the CIE 1976 L*a*b* colour space based on D65 standard illuminant). Preferably, the at least hydrogen-free amorphous carbon layer has an abrasive wear rate (in the ball crater microabrasion test according to DIN EN ISO 1071-6) lower than 2.0.10-16 m3 / Nm.

[0052] Preferably, the total thickness of said at least one hydrogen-free amorphous carbon layer is greater than 0.1 μm, preferably greater than 0.5 μm, most preferably greater than 1.0 μm. For certain applications, such as for example fuel cell bipolar plates, it makes sense to choose a thickness between 0.01 μm and 0.1 μm, including the limits of this range.

[0053] Although argon ion bombardment and / or implantation has been described above, embodiments of the present invention may also be applied to the implantation of other elements having a mass greater than carbon, including noble gas elements such as Ne, Ar, Kr, Xe, etc.

[0054] Although a supplemental plasma source, Plasma ARC, which is traditionally used to pre-clean a substrate prior to coating deposition, has been described above, embodiments of the present invention may also include ion sources such as HiPIMS sources, vacuum cathodic arcs, ion beams, and other sources known in the art.

[0055] It is very convenient to produce carbon coatings with the method of the present invention described. However, the inventors of the present invention understand that the present invention can also be used to produce other high-quality ultra-hard coatings, such as nitride-based (e.g., AlTiN, AlCrN, TiN, SiN, BN) and / or carbide-based (e.g., SiC, HfC, WC, MoC, BC) and oxide-based (e.g., Al2O3, Y2O3, AlCrO, Cr2O3, AlTiO) coatings. Oxynitrides and multi-component materials (also called high entropy alloys) can also be advantageously utilized with this novel method.

[0056] The invention will now be described in detail, by way of example only, with reference to process descriptions and drawings. [Brief description of the drawings]

[0057] [Figure 1] The effect of the peak power density delivered to the racetrack region in each HiPIMS pulse on the arcing rate at the surface of the target. [Diagram 2] Effect of the peak power density delivered to the racetrack region in each HiPIMS pulse on the surface quality of the as-deposited aC coating. [Diagram 3] Comparison of coating hardness of carbon coatings deposited by the method of the present invention and without the method of the present invention at various positions (on the substrate carousel) along the height of the coating chamber. [Figure 4] 1 is a cross-sectional SEM micrograph of a hydrogen-free, ultra-hard aC carbon coating of the present invention. [Diagram 5] Optimization of process conditions: (a) projected ion range versus ion kinetic energy; and b) effect of rotation speed on the thickness of the a-C layer deposited per pass. [Figure 6] Wear rates of some selected carbon-based coatings based on the ball crater microwear test (according to DIN EN ISO 1071-6). [Figure 7] Planar optical micrographs of selected hydrogen-free carbon coatings: (a) aC (38 GPa), (b) ultra-hard aC coating of the present invention (52 GPa), and (c) Cathodic Arc ta-C (60 GPa). [Figure 8] Profilometer profiles of some selected hydrogen-free carbon coatings: (a) ultra-hard aC coating of the present invention (52 GPa) and (b) Cathodic Arc ta-C (60 GPa). [Figure 9] Friction coefficient versus sliding distance for some selected carbon-based coatings: (a) ultra-hard aC coating of the present invention (52 GPa) and (b) Cathodic Arc ta-C (60 GPa). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] Example 1 To produce the carbon coating system according to the invention, a steel workpiece having a hardness of 62 HRC was placed in an Oerlikon Balzers INGENIA s3p vacuum processing chamber equipped with three targets of chromium and three targets of graphite, and the vacuum chamber was heated for approximately 10 -5 The pressure was evacuated to 1000 mbar.

[0059] To demonstrate the effectiveness of the periodic ion densification treatment during the growth of aC in accordance with the present invention, two samples, one with and one without periodic ion densification treatment, were deposited with identical parameters for all remaining process steps, including the deposition of the metal adhesion promotion layer and the metal carbide transition layer.

[0060] As the first part of the process, a plasma heating process was carried out for 30 minutes to bring the substrate to be coated to a higher temperature of about 170°C and remove volatile materials from the substrate surface and the walls of the vacuum chamber by vacuum pumping. In this pretreatment step, an Ar hydrogen plasma is ignited by a Plasma ARC between the ionization chamber and the auxiliary anode.

[0061] A 20 minute Ar ion plasma etching process is initiated by activating the low voltage arc ionization method.

[0062] Ar ions are drawn from the Plasma ARC to the substrate to be cleaned by a negative bias voltage of 120 V, the main purpose of which is to remove impurities such as native oxides or also organic impurities by ballistic removal (i.e., native oxides and impurities are knocked away by the powerful Ar+ ion bombardment) and to ensure good layer adhesion of the adhesive metal layer that is applied after ion cleaning.

[0063] For the next process step, the following process parameters were used: 700 W.cm with a coating temperature of less than 180°C for 30 minutes. -2 Using an individual pulse power density of 1000 Å, a total Ar pressure of 0.3 Pa and a constant bias voltage of -50 V, a 300 nm thick adhesion-promoting Cr layer is deposited by the HIPIMS method according to the present invention directly on the surface of the substrate to be coated.

[0064] A 200 nm thick graded CrC transition layer was then immediately deposited by co-sputtering with the following process parameters: three graphite targets at 80 W.cm for gradually increasing C content; -2 Starting from 161W.cm -2 Operated at average powers Pav up to 20 W.cm for chromium targets. -2 The constant average power P avThe power density and duty cycle of the individual pulses delivered to the graphite target were within the range of the intermediate pulse method according to the invention. For the chromium target, the power density of the individual pulses was adjusted to 600 W.cm to provide adequate metal ion bombardment during film growth. -2 was selected.

[0065] Finally, three graphite targets were coated at 60 W.cm for a total deposition time of 196 min, at a coating temperature of 120 °C. -2 The average power P Av and 0.3kW.cm -2 With an individual pulse power density of 0.05ms, pulse A 0.7 μm thick wear-resistant hydrogen-free aC layer was deposited according to the invention operating at 4000 sq. m at a total pressure of 0.3 Pa and a constant bias voltage of −100 V. Related samples deposited under InPIMS plasma source only conditions are listed as “InPIMS a-C”.

[0066] The second aC layer was deposited by the hybrid InPIMS / Plasma ARC method according to the present invention, where in addition to the InPIMS graphite source, an adjacent Plasma ARC was simultaneously applied with the following parameters: a continuous arc current of 30 A and a continuous ion source voltage of 50 V. The related sample deposited under the hybrid InPIMS / Plasma ARC method is labeled "ultra-hard aC of the present invention."

[0067] Surprisingly, the current measured at the substrate during deposition of the aC layer under the hybrid InPIMS / Plasma ARC method was almost four times larger than during deposition of aC with only the InPIMS source. By neglecting the contribution of electrons in the total current measured at the substrate, the larger current corresponds to process conditions with stronger ion bombardment occurring during the growth of the aC film for the hybrid method. Furthermore, it is clear that a larger incident ion flux / carbon flux ratio is achieved during the growth of the "inventive ultra-hard aC" since the deposition rate, and therefore the incident carbon neutral flux, is similar during the growth of both the "conventional InPIMS aC" and the "inventive ultra-hard aC".

[0068] An evaluation of the coating hardness along the height of the coating chamber (HIT®) ​​was performed on both aC samples using a Fischerscope Instruments nanoindenter with a load of 10 mN. The results are shown in Figure 3. Under these conditions, a load of 0.3 kW.cm -2 Conventional hydrogen-free aC deposited at an intermediate HiPIMS peak pulse power of 1000 nm showed an average coating hardness of 32±2 GPa with excellent distribution of film mechanical properties along the height of the coating chamber. Surprisingly, the average coating hardness (HIT) of the ultra-hard aC coating of the present invention is much higher, in the range of 48±2 GPa, supporting improved densification of the aC during film growth.

[0069] A cross-sectional scanning electron microscope image of the ultra-hard aC coating of the present invention, shown in FIG. 4, confirms the extremely dense and compact microstructure of the hard carbon coating of the present invention.

[0070] While the inventors of the present invention do not wish to be bound by any particular theory, they believe that periodic irradiation with supplemental Ar ions from an auxiliary plasma source reduces the ion concentration of 100 eV Ar +This is believed to be extremely effective in densifying the growing film due to the fact that the region of strong intermixing near the surface of about 0.7-0.8 nm, determined by the collision cascade range of the ions (see Fig. 5(a)), is much larger than the thickness of the a-C layer deposited during the sequential exposure to the graphite target. For example, as shown in Fig. 5(b), considering 100% maximum rotation speed of the substrate holder used to deposit the a-C film, 0.3 kW.cm -2 The thickness of the a-C layer deposited in one pass under the graphite target delivered by a peak power of 1000 Å was approximately 0.1 nm, based on deposition rate calibration. Therefore, under such conditions, the thickness of the a-C layer deposited in one pass under the graphite target delivered by a peak power of 1000 Å was approximately 0.1 nm, based on deposition rate calibration. + The ions penetrate deep into the near-surface region and produce multiple recoils ensuring improved densification of the film and possibly sp2 to sp3 conversion of the surrounding carbon to subsurface locations.

[0071] To further confirm the improvement of mechanical properties of the ultra-hard aC coating of the present invention, the ball crater microwear method was applied to evaluate the wear resistance of several selected carbon coatings, namely "InPIMS aC", "ultra-hard aC of the present invention" deposited by a hybrid InPIMS / Plasma Arc method, and a 1.0 μm thick 60 GPa hydrogen-free hard carbon coating deposited by cathodic vacuum arc evaporation. The calculated wear coefficients for each of these three carbon coatings are shown in FIG. 6. A clear trend is observed, with the higher hardness values ​​resulting in the lowest abrasive wear coefficients. Moreover, a -67% decrease in the wear coefficient of the ultra-hard aC coating of the present invention compared to the InPIMS aC layer can be seen, again confirming the importance of periodic but powerful ion irradiation for the densification of aC films.

[0072] Furthermore, the surface quality of the ultrahard aC coating of the present invention was compared with the other carbon coatings presented above. Photo-optical planar images of these three carbon coatings are shown in FIG. 7. As can be seen in FIG. 7(c), the ta-C coating deposited by cathodic arc evaporation shows a large amount of macroparticles. Surprisingly, both aC coatings deposited by InPIMS show excellent surface quality with virtually no surface defects, supporting the origin of the macroparticles as originating from arcing events occurring on the surface of the graphite target.

[0073] As shown in FIG. 8, the comparison of surface roughness between cathodic arc evaporated ta-C and the ultra-hard aC of the present invention also confirms the extremely high quality in terms of smoothness (i.e. small roughness Ra and / or Rz and / or Rpk) of the aC grown by the hybrid InPIMS / low voltage arc method.

[0074] The friction of the ultra-hard aC coating of the invention was tested using a pin-on-disk test (pin-on-disk tribometer, CSM Instruments). The test was carried out in air under dry conditions at a temperature of 22°C and a relative humidity of 43%. The sample was worn against an uncoated 100Cr6 steel ball with a diameter of 3 mm. The steel ball acted as a static friction partner under which the coated sample was rotated (radius 5 mm, speed 0.3 m / s). A load of 30 N was applied to the ball, which corresponds to an instantaneous contact pressure of 2.2 GPa on the surface of the hard carbon layer. The measurements of the coating of the invention were compared with a 1.0 μm thick hydrogen-free hard carbon coating of 60 GPa deposited by cathodic arc evaporation. The representative friction coefficients of these two coatings after 33 minutes of dry sliding are plotted in FIG. 9.

[0075] Surprisingly, the steady-state coefficient of friction of the inventive layer is at a low level with a COF of about 0.2, demonstrating the very good friction behavior of the inventive hard carbon coating, whereas the coefficient of friction of the arc-evaporated ta-C coating is at a higher level, possibly due to the higher surface roughness as evidenced by the surface profilometry measurements mentioned above.

[0076] Quite surprisingly, examination of the worn surfaces after testing showed that the layer of the invention generally showed significantly less layer wear and slightly less wear of the counter part compared to the much rougher arc-evaporated ta-C coating (249 μm vs. 669 μm width of the worn part of the coating and 270 μm vs. 984 μm diameter of the worn area of ​​the ball for the layer of the invention and the arc-evaporated ta-C, respectively), demonstrating the appropriate combination of increased wear resistance, lower friction, and improved surface quality of the hard carbon coating of the invention compared to the state-of-the-art ultra-hard carbon coating. One possible explanation for this surprisingly low wear of the uncoated counter ball can be attributed to the smoothness and low defect density provided by this ultra-hard aC layer of the invention deposited by the hybrid InPIMS / Plasma ARC method.

[0077] A method for forming a coating on a substrate is disclosed, the process comprising: mounting the substrate on a carrier means within a vacuum chamber; Providing a coating means comprising at least a first device in the form of a deposition device arranged adjacent to a carrier means and configured to deposit a selected material on a substrate; providing a second device configured to provide positive non-reactive ions; while operating the coating means to form a selected coating on the substrate, cyclically moving at least one of the carrier means and the coating means relative to one another along a path selected to provide substantially equal deposition rates for the spaced apart similarly configured substrates; A negative bias is applied to the substrate to provide ion bombardment of selected materials deposited on the substrate, thereby densifying the deposited materials.

[0078] The coating means may be a means for performing physical vapor deposition (PVD), and operating the coating means is performing physical vapor deposition.

[0079] The PVD means may comprise a magnetron sputtering means, and operating the coating means comprises performing magnetron sputtering.

[0080] Magnetron sputtering may be carried out in a pulsed manner, with a maximum power density in the pulse being at least 0.08 kW.cm -2 It is.

[0081] Preferably, the maximum power density is at most 0.5 kW.cm -2 is selected to be. The duty cycle of at least some of the pulses, preferably the average duty cycle of the pulses, and most preferably the duty cycle of all of the pulses, may be selected to be greater than 10%.

[0082] The method may include a step of pre-cleaning the substrate prior to deposition of the coating, and a second apparatus for supplying positive ions is used to perform such pre-cleaning, preferably the second apparatus comprises a plasma source.

[0083] The ions provided by the second device are preferably ions having a mass greater than carbon.

[0084] The ions preferably comprise argon ions and / or elements selected from the members of the group formed by the noble gas elements such as (Ne, Ar, Kr, Xe) and / or mixtures thereof.

Claims

1. - mounting the substrate on a carrier means in a vacuum chamber; - providing a coating means arranged adjacent to said carrier means and comprising at least a first device in the form of a deposition device configured to deposit a selected material on said substrate; Providing a second device configured to provide positive non-reactive ions; - cyclically moving at least one of the carrier means and the coating means relative to one another along a path selected to provide substantially equal deposition rates for spaced apart similarly configured substrates while operating the coating means to form a selected coating on the substrate; 1. A method for forming a coating on a substrate, comprising: A method according to any one of claims 1 to 5, wherein a negative bias is applied to the substrate to provide ion bombardment to the selected material deposited on the substrate, thereby densifying the deposited material.

2. 2. The method of claim 1, wherein the coating means is a means for performing physical vapor deposition (PVD), and operating the coating means is performing physical vapor deposition.

3. 3. The method of claim 2, wherein the PVD means comprises magnetron sputtering means, and operating the coating means comprises performing magnetron sputtering.

4. Magnetron sputtering is carried out in a pulsed manner, with a maximum power density in the pulse being at least 0.08 kW.cm －２ 4. The method according to claim 3, wherein:

5. The maximum power density is up to 0.5 kW.cm －２ 5. The method according to claim 4, wherein:

6. 6. The method of claim 5, wherein the duty cycle of at least some of the pulses, preferably the average duty cycle of the pulses, most preferably the duty cycle of all pulses, can be selected to be greater than 10%.

7. The method includes the step of pre-cleaning the substrate prior to deposition of a coating. Including, 7. The method according to any one of claims 1 to 6, characterized in that a second device for supplying positive ions is used to perform the pre-cleaning, preferably said second device comprising a plasma source.

8. 8. The method of claim 7, wherein the ions provided by the second device are ions having a mass greater than carbon.

9. 9. The method of claim 8, wherein the ions comprise argon ions and / or elements selected from the members of the group formed by the noble gas elements such as (Ne, Ar, Kr, Xe) and / or mixtures thereof.

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