Methods to suppress partial discharge in vacuum coating of anodized workpieces

Abstract

This invention provides a method for suppressing partial discharge during vacuum coating of anodized workpieces. The method includes cleaning and drying an unsealed anodized workpiece and placing it in a vacuum coating chamber; evacuating to a base vacuum and then introducing an inert gas; applying a negative bias voltage to the workpiece to pre-deposit a conductive layer on the surface of the anodized film; stopping the pre-deposition and continuing vacuuming; and performing vacuum coating. This invention creates a charge discharge channel on the surface of the anodized film by pre-depositing a conductive layer, eliminating local electric field concentration and preventing dielectric breakdown-type partial discharge. During the pre-deposition process, the workpiece heats up, driving away water vapor and residues adsorbed in the micropores of the oxide film. Combined with delayed vacuuming, the gas is removed, cutting off the gas source for gas discharge. This invention synergistically suppresses partial discharge by eliminating charge accumulation and removing gas release, allowing for partial discharge-free coating at 400–500V, effectively preventing dielectric breakdown or macroscopic arcing, and is suitable for vacuum coating treatment of various anodized workpieces.

Description

Technical Field

[0001] This invention relates to the field of vacuum coating technology, and more specifically, to a method for suppressing partial discharge during vacuum coating of anodized workpieces. Background Technology

[0002] Aluminum alloys, with their excellent specific strength, good corrosion resistance, and convenient processing and forming capabilities, have become an indispensable key material in the field of space structures. In large-scale space infrastructure, aluminum alloy components are often used as core components of space station trusses, solar panel support arms, and antenna reflectors, capable of withstanding the extreme temperature differences of space and maintaining long-term dimensional stability. With the increasing demand for spacecraft weight reduction, a large amount of aluminum alloy has begun to be used as friction pairs in space mechanisms. However, aluminum alloys have significant shortcomings as friction pairs in the space field. Their low hardness and poor wear resistance make them prone to adhesive wear and severe scratches; aluminum alloys also lack self-lubricating ability, increasing the risk of spacecraft failure and limiting their direct application in critical transmission components.

[0003] To improve the wear resistance and self-lubricating properties of aluminum alloy surfaces, aluminum alloys used as friction pairs need to undergo surface anodizing to generate a high-hardness ceramic layer, thereby enhancing wear resistance and preventing adhesive wear. Then, vacuum deposition technology is used to embed lubricants such as molybdenum disulfide to address issues like vacuum cold welding and insufficient lubrication. The research results of Li Zhongjian et al., published in *Surface Technology* in 2020, on "The Influence of Different Oxidation Processes on the Wear Resistance of Sputtered MoS2 Films on Aluminum Alloys," show that pre-treating aluminum alloy substrates with three different oxidation processes—sulfuric acid anodizing, micro-arc oxidation, and hard oxidation—followed by sputtering a MoS2 lubricating film, effectively improves the wear resistance of aluminum alloy surfaces. The research results of Xiao Jintao et al., published in *Chinese Journal of Surface Engineering* in 2021, on "Preparation and Performance Analysis of Lubricating and Corrosion-Resistant Composite Coatings on Aluminum Alloy Surfaces," indicate that depositing a reasonable thickness of hard oxide film on an aluminum alloy substrate followed by sputtering a MoS2 lubricating film improves the lubrication and corrosion resistance of the aluminum alloy surface.

[0004] However, while aluminum alloy anodized films possess advantages such as high hardness and corrosion resistance, they are essentially highly insulating porous ceramic layers. During vacuum coating processes, especially when applying a bias voltage (e.g., -400~-500V negative bias voltage) for ion cleaning or deposition, partial discharge is highly likely to occur at the edges and sharp corners of the workpiece. Partial discharge not only disrupts the uniformity of the film layer but can also lead to dielectric breakdown or macroscopic arcing in severe cases, resulting in product scrap. The fundamental causes of partial discharge are mainly twofold: First, the anodic oxide film has extremely high resistivity. In a plasma environment, charge cannot be conducted away and accumulates on the surface. When the accumulated charge exceeds the dielectric breakdown strength of the film layer, breakdown partial discharge occurs. Second, the porous structure of the oxide film easily adsorbs moisture, gas, and residual electrolyte, which are released in a vacuum, causing a local increase in gas pressure and triggering gas discharge partial discharge.

[0005] Traditional methods, such as reducing the bias voltage, sacrifice film adhesion, while simply extending the vacuum time has limited effect on deep degassing of the oxide film. Therefore, there is an urgent need for a process that can effectively suppress partial discharge under higher bias voltages. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for suppressing partial discharge in vacuum coating of anodized workpieces.

[0007] The method for suppressing partial discharge in vacuum coating of anodized workpieces according to the present invention includes the following steps: S1: After cleaning and drying the unsealed anodized film workpiece, place it into the vacuum coating chamber; S2: After the coating chamber is evacuated to the baseline vacuum level, inert gas is introduced; S3: Apply a negative bias voltage to the workpiece to pre-deposit a conductive layer on the surface of the anodic oxide film; S4: Stop pre-deposition and continue vacuuming; S5: Perform formal vacuum coating.

[0008] Preferably, in step S3, the material of the conductive layer is a metal.

[0009] Preferably, the metal includes Cr, Ti, or Al.

[0010] Preferably, in step S3, the deposition time of the conductive layer is 2 to 10 minutes, the negative bias voltage is 40 to 70V, and the thickness of the conductive layer is 5 to 100nm.

[0011] Preferably, in step S4, the vacuuming time is 20 to 60 minutes.

[0012] Preferably, during the continuous vacuuming process in step S4, the vacuum level is maintained at less than 1.0 × 10⁻⁶. - ³Pa.

[0013] Preferably, in step S5, during the formal vacuum coating process, the negative bias voltage applied to the workpiece is 400-500V.

[0014] Preferably, the anodic oxide film is an unsealed sulfuric acid anodic oxide film, a bright anodic oxide film, or a hard anodic oxide film.

[0015] Preferably, in step S5, the formal vacuum coating includes sputtering deposition.

[0016] Preferably, the sputtering deposition is the sputtering deposition of a molybdenum disulfide solid lubricating film.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention pre-deposits a conductive layer on the surface of the anodic oxide film before the formal coating, forming a continuous metal film on the originally highly insulating anodic oxide film surface. This provides an immediate discharge channel for the charge accumulated in the plasma environment, making the workpiece surface an equipotential body, eliminating local electric field concentration, and transforming the unstable "insulator-plasma" interface into a stable "conductor-plasma" interface. This fundamentally eliminates the occurrence of dielectric breakdown-type partial discharge, thus allowing subsequent coating to be carried out at a bias voltage of 400-500V or even higher, significantly improving the film adhesion, and effectively preventing dielectric breakdown or macroscopic arcing.

[0018] 2. This invention utilizes the high-energy particle bombardment during the pre-deposition process to raise the surface temperature of the workpiece and forcibly expel water vapor and residues adsorbed deep in the micropores of the oxide film by stopping the coating process after pre-depositing the conductive layer and continuously evacuating the vacuum for 20-60 minutes. This, combined with sufficient delay in vacuuming, allows the expelled gas to diffuse out of the micropores and be removed, completely cutting off the gas source for gas discharge during the subsequent coating process and eliminating another fundamental cause of partial discharge, gas release.

[0019] 3. This invention, through the synergistic effect of "pre-depositing a conductive layer" and "delayed vacuuming," addresses both the elimination of charge accumulation and the removal of adsorbed gases, comprehensively covering the two major causes of partial discharge in vacuum coating of anodic oxide films. It fundamentally solves the problem of film uniformity damage and product scrap caused by partial discharge during the vacuum coating process of anodic oxide workpieces, resulting in a stable and reliable process effect.

[0020] 4. The pre-deposited conductive layer in this invention not only eliminates partial discharge, but also serves as the base layer for subsequent formal coating, forming a good bonding interface with the formal coating layer. Without adding extra process steps, the adhesion of the overall film system can be improved simultaneously, further enhancing the quality and reliability of the coated product.

[0021] 5. The process method provided by the present invention does not require modification of existing vacuum coating equipment. It only requires adding two steps, pre-deposition and delayed vacuuming, to the original process flow and can be achieved through program control. It is simple to operate, low in cost, and suitable for mass industrial production of vacuum coating treatment for various anodized workpieces. Detailed Implementation

[0022] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0023] This invention discloses a method for suppressing partial discharge in vacuum coating of anodized workpieces. The core concept is as follows: Before the formal coating process, a conductive metal layer is pre-deposited on the surface of the anodized film. This creates a charge discharge channel on the highly insulating surface of the anodized film, eliminating localized electric field concentration. Subsequently, the pre-deposition is stopped, and a vacuum is continuously pumped. The high-energy particle bombardment during the pre-deposition process heats the workpiece, driving away adsorbed water vapor and residues in the micropores. Combined with delayed vacuuming, this allows for sufficient gas diffusion and removal. These two steps work synergistically, simultaneously addressing both charge accumulation and gas release, comprehensively covering the two major causes of partial discharge in vacuum coating of anodized films. This allows for partial discharge-free coating at bias voltages of 400V or even higher.

[0024] Specifically, the present invention includes the following steps: S1: After cleaning and drying, the unsealed anodized film workpiece is placed in the vacuum coating chamber. The cleaning can be done using ultrasonic cleaning with organic solvents, such as ultrasonic cleaning with acetone and alcohol in sequence, and finally hot air drying to remove oil and impurities from the workpiece surface.

[0025] S2: After evacuating the coating chamber to its base vacuum level, an inert gas is introduced. The inert gas is preferably argon, which is used to maintain a stable working pressure during subsequent pre-deposition and formal coating processes.

[0026] S3: Apply a negative bias voltage to the workpiece to pre-deposit a conductive layer on the surface of the anodic oxide film. The conductive layer is made of metal, preferably Cr, Ti, or Al. During pre-deposition, the negative bias voltage is 40–70V, the deposition time is 2–10 minutes, and the conductive layer thickness is 5–100nm. During the pre-deposition process, metal particles are deposited on the surface of the anodic oxide film under the action of the negative bias voltage, forming a continuous metal film that provides a discharge channel for the charge; at the same time, the bombardment of high-energy particles raises the surface temperature of the workpiece, forcibly driving away water vapor and residues adsorbed deep in the micropores of the oxide film.

[0027] S4: Stop pre-deposition and continue vacuuming. The vacuuming time is 20–60 minutes, maintaining a vacuum level less than 1.0 × 10⁻³ Pa during the process. This step ensures that the forcibly expelled gas has sufficient time to diffuse out of the micropores and be removed, completely eliminating the gas source for subsequent film deposition that could lead to gas discharge.

[0028] S5: Perform formal vacuum coating. During formal vacuum coating, a negative bias voltage of 400–500V is applied to the workpiece. The formal vacuum coating includes sputtering deposition, preferably sputtering deposition of a molybdenum disulfide solid lubricant film.

[0029] In the above method, the anodic oxide film is an unsealed sulfuric acid anodic oxide film, a bright anodic oxide film, or a hard anodic oxide film.

[0030] The basis for selecting the process parameters of this invention is further explained as follows: This invention limits the pre-deposition time to 2–10 minutes to precisely control the thickness of the formed conductive layer within the range of 5–100 nm. Experimental results show that when the conductive layer thickness is less than 5 nm, the partial discharge suppression effect is not significant because the charge discharge channel is not fully constructed. When the conductive layer thickness is greater than 100 nm, although a good partial discharge suppression effect can still be maintained, the excessively thick conductive layer will affect the deposition of the subsequent functional lubricating film, resulting in an overall thicker workpiece surface, which may exceed design tolerances and affect subsequent assembly and use. Therefore, a deposition time of less than 2 minutes will result in an excessively thin conductive layer with an insignificant partial discharge suppression effect; while a deposition time of more than 10 minutes, although the partial discharge suppression effect is significant, it will lead to adverse effects such as workpiece dimensional deviations, making it unsuitable from a comprehensive performance perspective. The deposition time of 2–10 minutes selected in this invention can effectively suppress partial discharge while ensuring the dimensional accuracy of the subsequent film layer, and this range has been experimentally proven to be reasonable and reliable.

[0031] This invention sets the vacuuming time after pre-deposition to 20–60 minutes, with the core objective of ensuring that the vacuum chamber reaches and maintains a vacuum level of less than 1.0 × 10⁻⁶. -3 High vacuum conditions of Pa are required. During the pre-deposition process, working gases such as argon need to be introduced, at which point the vacuum chamber pressure will rise to approximately 1 × 10⁻⁶ Pa. -1 After pre-deposition, with the pumping rate remaining constant, the residual argon gas in the vacuum chamber and the slowly released moisture from the equipment's inner wall lining and workpieces will cause the pressure drop process to take a certain amount of time. Based on actual verification, when the furnace load is small, maintaining a stable vacuum level of less than 1.0 × 10⁻⁶ Pa is effective. -3 It takes approximately 20 minutes to reach the same vacuum level (Pa); when the furnace load is large and the water vapor release is increased, it takes approximately 60 minutes. If the delayed vacuuming time is less than 20 minutes, the vacuum level cannot be reliably reached below 1.0 × 10⁻⁶.-3 Pa, if the water vapor and residual gas expelled from the micropores of the workpiece are not sufficiently removed, the gas source required for gas discharge cannot be effectively cut off, thus the partial discharge suppression effect will be insignificant. If the vacuuming time exceeds 60 minutes, since the vacuum level has already met the requirements and tends to be balanced, further extending it will not further improve the removal of residual gas and the suppression of partial discharge, but will unnecessarily prolong the production cycle and reduce efficiency. Therefore, this invention, based on the consideration of both excellent partial discharge suppression effect and reasonable process efficiency, preferably sets the delayed vacuuming time after pre-deposition to 20-60 minutes. This range has been proven in practice to achieve stable coating without partial discharge under 400-500V conditions.

[0032] In summary, this invention achieves stable film deposition without partial discharge under high bias voltage of 400-500V by combining the synergistic effect of "pre-deposited conductive layer" and "delayed vacuuming" with reasonable matching of various process parameters. It effectively prevents dielectric breakdown or macroscopic arcing, and the film has good adhesion, making it suitable for vacuum coating treatment of various anodized workpieces.

[0033] The present invention will be further described in detail below through specific embodiments.

[0034] Example 1 The workpiece is made of 7A04 aluminum alloy.

[0035] Workpiece cleaning: For workpieces with unsealed hard anodized surfaces, the anodized film thickness is approximately 15μm. The workpieces are ultrasonically cleaned with acetone and alcohol for 20 minutes each, and finally dried with hot air.

[0036] Pre-deposit conductive layer: Load the workpiece into the vacuum coating machine and evacuate the base vacuum to 5.0 × 10⁻⁶. -4 Argon gas was introduced and maintained at a pressure of 0.01–0.05 Pa for 1 minute. The bias power supply was then turned on, setting the negative bias to 60 V. The Ti target was then turned on with a current of 0.5 A to pre-deposit a pure Ti conductive layer on the anodic oxide film surface for 2 minutes, resulting in a Ti layer thickness of 5 nm. After turning off the Ti target and bias power, evacuation continued for 60 minutes, maintaining a vacuum level less than 1.0 × 10⁻⁶ Pa. -3 Pa.

[0037] Sputtering deposition of molybdenum disulfide solid lubricant film: Vacuum deposition equipment is used, with a back-bottom vacuum of less than 5 × 10⁻⁶. - 4 Pa, Ar gas flow rate 30 sccm. Workpiece surface cleaned with Ar plasma for 20 min, bias voltage 400 V. Pre-deposited metallic Ti: Ti target current 3 A, substrate bias voltage 60 V, time 20 min. Co-sputtering molybdenum disulfide: MoS2 target current varied from 0.5 to 2 A, Ti target current varied from 0.8 to 5 A, substrate bias voltage 60 V, time 180 min.

[0038] Example 2 The workpiece is made of 2A14 aluminum alloy.

[0039] Workpiece cleaning: For workpieces with anodized surfaces that are not sealed, the anodized film thickness is approximately 8 μm. The workpieces are ultrasonically cleaned with acetone and alcohol for 20 minutes each, and finally dried with hot air.

[0040] Pre-deposit conductive layer: Load the workpiece into the vacuum coating machine and evacuate the base vacuum to 5.0 × 10⁻⁶. -4 Argon gas was introduced and maintained at a pressure of 0.01–0.05 Pa for 1 minute. The bias power supply was then turned on, setting the negative bias to 60 V. The Al target was then turned on with a current of 1 A to pre-deposit a pure Al conductive layer on the anodic oxide film surface for 5 minutes, resulting in an Al layer thickness of 50 nm. After turning off the Al target and bias power, evacuation continued for 30 minutes, maintaining a vacuum level less than 1.0 × 10⁻⁶ Pa. -3 Pa.

[0041] Sputtering deposition of molybdenum disulfide solid lubricant film: Vacuum deposition equipment is used, with a back-bottom vacuum of less than 5 × 10⁻⁶. - 4 Pa, Ar gas flow rate 30 sccm. Workpiece surface cleaned with Ar plasma for 20 min, bias voltage 450 V. Pre-deposited metallic Ti: Ti target current 3 A, substrate bias voltage 60 V, time 20 min. Co-sputtering molybdenum disulfide: MoS2 target current varied from 0.5 to 2 A, Ti target current varied from 0.8 to 5 A, substrate bias voltage 60 V, time 180 min.

[0042] Example 3 The workpiece is made of 2195 aluminum alloy.

[0043] Workpiece cleaning: The workpiece has a bright, unsealed anodized surface with an anodized film thickness of approximately 7 μm. It is ultrasonically cleaned with acetone and alcohol for 20 minutes each, and finally dried with hot air.

[0044] Pre-deposit conductive layer: Load the workpiece into the vacuum coating machine and evacuate the base vacuum to 5.0 × 10⁻⁶. -4 Argon gas was introduced and maintained at a pressure of 0.01–0.05 Pa for 1 minute. The bias power supply was then turned on, with the negative bias set to 60 V. The Cr target was activated at a current of 2 A to pre-deposit a pure Cr conductive layer on the anodic oxide film surface over 10 minutes, resulting in a Cr layer thickness of 100 nm. After turning off the Cr target and bias power, evacuation continued for 20 minutes, maintaining a vacuum level less than 1.0 × 10⁻⁶ Pa. -3 Pa.

[0045] Sputtering deposition of molybdenum disulfide solid lubricant film: Vacuum deposition equipment is used, with a back-bottom vacuum of less than 5 × 10⁻⁶. -4 Pa, Ar gas flow rate 30 sccm. Workpiece surface cleaned with Ar plasma for 20 min, bias voltage 500 V. Pre-deposited metallic Ti: Ti target current 3 A, substrate bias voltage 60 V, time 20 min. Co-sputtering molybdenum disulfide: MoS2 target current varied from 0.5 to 2 A, Ti target current varied from 0.8 to 5 A, substrate bias voltage 60 V, time 180 min.

[0046] No partial discharge phenomenon was observed in the anodized workpieces treated in the above embodiments during the formal coating process. The film uniformity was good, and no dielectric breakdown or macroscopic arcing occurred.

[0047] To further verify the necessity of the synergistic effect of the two steps of "pre-depositing conductive layer" and "delayed vacuuming" in this invention, the following comparative experiment was conducted.

[0048] Comparative Example 1 (pre-deposited conductive layer omitted) The workpiece is the same as in Example 1. Step S3 (pre-deposition of conductive layer) is omitted, that is, after cleaning, the workpiece directly enters step S4 (delayed vacuuming) before the formal coating, and the remaining process conditions are the same as in Example 1.

[0049] Test results: When the pre-deposited conductive layer is omitted and the film is directly deposited, the surface of the anodic oxide film lacks a charge discharge channel, and the local electric field concentration cannot be effectively eliminated. During the film deposition process, dielectric breakdown-type partial discharge occurs, which leads to the breakdown of the anodic oxide film. The macroscopic arcing phenomenon is obvious, and the power supply triggers the protection shutdown.

[0050] Comparative Example 2 (delayed vacuuming omitted) The workpiece is the same as in Example 2. Step S4 (delayed vacuuming) is omitted, that is, the formal coating is performed immediately after the pre-deposition of the conductive layer, and the remaining process conditions are the same as in Example 2.

[0051] Experimental results: When the delayed vacuuming step is omitted and the coating is applied directly, the argon gas remaining in the vacuum chamber after pre-deposition, as well as the water vapor released from the inner wall lining of the equipment and the micropores of the workpiece, are not fully removed. The gas source for gas discharge cannot be cut off, and gas discharge occurs during the coating process, which interferes with the normal deposition of the film. The coating has poor adhesion to the substrate and local peeling occurs.

[0052] Comparative Example 3 (vacuuming time after pre-deposition is less than 5 minutes) The workpiece was the same as in Example 3. After pre-depositing the conductive layer, the formal coating was carried out after vacuuming for less than 5 minutes, and the remaining process conditions were the same as in Example 3.

[0053] Experimental results: When the vacuuming time was less than 5 minutes, the vacuum level was far from reaching less than 1.0 × 10⁻⁶. -3The high vacuum conditions required for Pa's formal production meant that the water vapor and residual gas driven out of the workpiece's micropores could not be fully removed, and the function of cutting off the gas discharge source was basically impossible to achieve. As a result, obvious partial discharge phenomena still occurred during the coating process, and the partial discharge suppression effect was not significant.

[0054] The comparison of the results of the above comparative examples and embodiments shows that omitting either the "pre-deposited conductive layer" or the "delayed vacuuming" step alone cannot effectively suppress partial discharge. Only when the two work together can a stable coating without partial discharge be achieved under a bias voltage of 400-500V.

[0055] It should be noted that, due to the instantaneous nature of partial discharge during the experiments of this invention, once macroscopic arcing or dielectric breakdown occurs, the vacuum coating machine power supply will immediately trigger its self-protection program and automatically shut down. The entire discharge process is extremely brief. Under the conditions of the three embodiments of this invention, the coating process was completed continuously and smoothly without any macroscopic arcing or power supply shutdown. In contrast, in the comparative examples without the synergistic measures of this invention, significant partial discharge occurred during the coating process, causing the power supply to shut down for protection within a short period. This clearly demonstrates that the technical solution of this invention can effectively suppress or even eliminate partial discharge phenomena.

[0056] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for suppressing partial discharge in vacuum coating of anodized workpieces, characterized in that, Includes the following steps: S1: After cleaning and drying the unsealed anodized film workpiece, place it into the vacuum coating chamber; S2: After the coating chamber is evacuated to the baseline vacuum level, inert gas is introduced; S3: Apply a negative bias voltage to the workpiece to pre-deposit a metal conductive layer on the surface of the anodic oxide film; S4: Stop pre-deposition and continue vacuuming; S5: Perform formal vacuum coating.

2. The method for suppressing partial discharge in vacuum coating of anodized workpieces according to claim 1, characterized in that, The material of the metal conductive layer includes Cr, Ti, or Al.

3. The method for suppressing partial discharge in vacuum coating of anodized workpieces according to claim 1, characterized in that, In step S3, the deposition time of the conductive layer is 2 to 10 minutes, the negative bias voltage is 40 to 70V, and the thickness of the conductive layer is 5 to 100nm.

4. The method for suppressing partial discharge in vacuum coating of anodized workpieces according to claim 1, characterized in that, In step S4, the vacuuming time is 20 to 60 minutes.

5. The method for suppressing partial discharge in vacuum coating of anodized workpieces according to claim 1, characterized in that, During the continuous evacuation in step S4, the vacuum level is less than 1.0 × 10⁻⁶. - ³Pa.

6. The method for suppressing partial discharge in vacuum coating of anodized workpieces according to claim 1, characterized in that, In step S5, during the formal vacuum coating process, the negative bias voltage applied to the workpiece is 400-500V.

7. The method for suppressing partial discharge in vacuum coating of anodized workpieces according to claim 1, characterized in that, The anodic oxide film is an unsealed sulfuric acid anodic oxide film, a bright anodic oxide film, or a hard anodic oxide film.

8. The method for suppressing partial discharge in vacuum coating of anodized workpieces according to claim 1, characterized in that, In step S5, the formal vacuum coating includes sputtering deposition.

9. The method for suppressing partial discharge in vacuum coating of anodized workpieces according to claim 8, characterized in that, The sputtering deposition is the sputtering deposition of a molybdenum disulfide solid lubricating film.