A controllable delamination method of diamond-like carbon coating on workpiece surface

Abstract

The application discloses a controllable stripping and plating method for a diamond-like carbon coating on a workpiece surface, and is aimed at processing a workpiece with a diamond-like carbon coating on the surface, and comprises the following steps: adopting oxygen plasma to bombard the surface of the workpiece after pretreatment, completely stripping carbon substances on the surface layer of the workpiece, and converting part or all of a transition layer deposited in gas phase into a metal carbon / oxide compound; then immersing the workpiece after the oxygen plasma bombardment in an alkaline immersion liquid A and an alkaline immersion liquid B in sequence, completely stripping the metal carbon / oxide compound remaining on the surface of the workpiece, and performing chemical polishing on exposed metal substances. The application does not damage the water plating metal layer, the stripping and plating quality is easy to control, and is beneficial to industrial production.

Description

Technical Field

[0001] This invention relates to the field of surface coating removal technology, and in particular to a controllable method for removing diamond-like carbon coatings from workpiece surfaces. Background Technology

[0002] Diamond-like carbon (DLC) coating is a sp 2 C and sp 3 The composite structure of two allotropic carbons (C and C) offers a vast range of adjustable physicochemical properties, leading to its increasing applications in numerous fields, such as advanced tooling, sporting goods, biomedical devices, solid lubricants, and optoelectronic sensors. Diamond-like carbon (DLC) coatings possess excellent resistance to acid and alkali corrosion; however, due to current limitations in vapor deposition technology, achieving 100% dense DLC coatings remains challenging. In applications where the substrate material has poor corrosion resistance and extremely high corrosion resistance is required, a composite treatment method is typically employed. This involves first preparing a thick, corrosion-resistant hard chromium layer on the substrate surface using an electrochemical method (hereinafter referred to as "water plating"), and then using various vapor deposition methods (hereinafter referred to as "VD") to prepare the DLC coating on the hard chromium layer. Such a surface typically has the following structure, from the core of the workpiece to the surface: workpiece substrate / Ni layer (water plating) / Cr layer (water plating) / Me layer (VD) / WC+C layer (VD) / DLC layer (VD), where Me is a single-element metal transition layer, and currently many commercial processes use metallic chromium.

[0003] The carbon-based coating on the surface of a workpiece needs to be removed in the following two situations: (1) the coating quality is substandard during the coating preparation process; (2) the coating wears off after a period of use, but the workpiece is to be reused. Therefore, the removal method is required to completely remove all vapor-deposited layers on the surface, including the Me layer (VD) / WC+C layer (VD) / DLC layer (VD), while preserving and not damaging the substrate and water-plated layer, i.e., the workpiece substrate / Ni layer (water-plated) / Cr layer (water-plated), and the workpiece surface is required to have a smooth finish after removal so that it can be directly replated.

[0004] Currently, commonly used plating removal methods include mechanical polishing, plasma etching, chemical immersion, and composite treatment methods involving plasma etching. Among these, mechanical polishing has low precision, easily damages the workpiece substrate, and is not suitable for workpieces with complex shapes. Plasma etching uses oxygen plasma to oxidize the carbon layer (e.g., patent CN115404487A) and hydrogen plasma to convert carbon into hydrocarbon gas (e.g., patent CN110423994A), but it is difficult to quickly remove other non-carbon vapor-phase deposited layers. Chemical immersion mainly uses an etching solution to penetrate the coating to reach the interface and selectively dissolve the Me(VD) layer (e.g., patents CN116219391A, CN105839127A, CN107759109A). When the Me(VD) used is Cr metal, this method will also cause Cr (water plating) to be dissolved, thereby damaging the corrosion resistance of the water plating layer. In general, for the mass production applications of the aforementioned specific workpieces and products, there is currently a lack of a reasonable removal method that can efficiently remove the vapor deposition layer in the coating system while protecting the water-based coating layer. Summary of the Invention

[0005] The purpose of this invention is to provide a highly efficient, fast, and easy-to-operate method for controlling the removal of diamond-like carbon coatings from workpieces, especially metal-based workpieces, to facilitate industrial application.

[0006] The core problem this invention aims to solve is, for a surface coating system with the structure of "workpiece substrate / Ni metal layer (water plating) / Me1 metal layer (water plating) / Me2 metal layer (VD) / WC+C layer (VD) / DLC layer (VD)", how to effectively control the removal boundary when Me1 = Me2 (i.e., the same metal) in both the Me1 metal layer (water plating) and the Me2 metal layer (VD), removing the vapor-deposited layers between Me1 and Me2 without damaging the Me1 metal layer, and removing the vapor-deposited layers, including the Me2 layer, as cleanly and thoroughly as possible, thereby ensuring a consistent coating structure and consistent film-substrate adhesion during recoating. Secondly, a secondary technical problem this invention aims to solve is how to effectively remove each vapor-deposited layer while achieving a chemical polishing effect on the remaining water-plated layer.

[0007] The concept of this invention is to address the core problem by using the diffusion depth of active oxygen in the metal layer of the coating surface as an indicator of the removal depth. That is, substances above the oxygen diffusion depth are removed or oxidized, while substances below the oxygen diffusion layer retain their metallic state. This goal can be effectively achieved by using oxidation and oxygen etching under various atmospheres. Using an oxygen plasma source is the preferred method, as it is fast, clean, and controllable. Various technical solutions exist for obtaining and realizing oxygen plasma; oxygen plasma source devices can be purchased commercially, or existing vacuum coating devices can be easily modified or have their parameters adjusted. This invention provides an example of using high-pressure oxygen glow discharge technology and a hollow cathode ion source to obtain oxygen plasma for the removal of carbonaceous materials and control of the oxidation depth of the Me2 layer. Regarding secondary technical problems: a suitable immersion solution is used to rapidly dissolve and remove oxide layers and residual carbides, and this immersion solution has strong corrosion inhibition and polishing capabilities for the exposed metal layer. For Me2, which is an oxide formed from Cr, Ti, Zr, Si, W, etc., this invention optimizes the formulation and treatment method of a strongly alkaline immersion solution supplemented with corrosion inhibitors and surfactants.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A controllable removal method for diamond-like carbon (DLC) coatings on workpiece surfaces is provided. The method involves the following steps: bombarding the pretreated workpiece surface with oxygen plasma to completely remove carbon material from the workpiece surface and partially or completely converting the vapor-deposited transition layer into a metal-carbon / oxide composite; then immersing the oxygen plasma-bombarded workpiece in alkaline immersion solution A and alkaline immersion solution B to completely remove the residual metal-carbon / oxide composite from the workpiece surface, and chemically polishing the exposed metal material.

[0010] Furthermore, the diamond-like carbon coating on the workpiece surface includes a metal layer formed by water plating and a composite diamond-like carbon layer with a transition layer formed by vapor deposition. The metal layer and the transition layer each contain any one of the elements selected from Cr, Ti, Zr, W, Ni, and Si.

[0011] Furthermore, the surface structure of the workpiece, from the core to the surface, is as follows: workpiece substrate, water-plated Ni layer, water-plated Me1 metal layer, Me2 metal layer formed by vapor deposition, carbide layer formed by vapor deposition, and DLC layer formed by vapor deposition. Me1 and Me2 are any one of the metals selected from Cr, Ti, Zr, W, and Ni. Me1 and Me2 can be the same metal, or they can be different metals.

[0012] As a specific embodiment of the present invention, the specific steps of the controllable removal method for diamond-like carbon coating on the workpiece surface include:

[0013] S1. Pretreatment of workpiece surface: Remove oil stains from the workpiece surface with metal cleaning agent, rinse and dry before use;

[0014] S2. Oxygen plasma stripping of carbonaceous material from the workpiece surface and controlled oxidation of the Me2 metal layer: The pretreated workpiece is fixed on the workpiece holder, the vacuum chamber door is closed, and the workpiece holder is started to rotate; the vacuum chamber is evacuated to a background vacuum below 5x10⁻¹⁰. -3 Pa, oxygen glow discharge or high-density oxygen plasma is obtained in a vacuum chamber; the bias voltage applied to the workpiece is controlled at 200V~600V, the bias current at 3A~150A, and the etching time at 45min~2.5h, completely stripping the carbon material on the surface of the workpiece and partially or completely converting the vapor-deposited transition layer into a metal-carbon / oxide composite; wherein, the carbon material in the coating system is completely oxidized into CO2 or CO gas and discharged outside the vacuum chamber; the metal carbides in the coating system are completely or partially converted into metal oxides; oxygen diffuses into the Me2 metal layer, and the oxide layer depth on the surface of the Me2 metal layer is effectively controlled according to the etching time, which is between 0% and 100% of the original Me2 metal layer thickness.

[0015] S3. Remove the carbon oxide layer and ablation residue from the composite metal on the workpiece surface, and simultaneously perform chemical polishing on the exposed metal: First, immerse the workpiece after oxygen plasma bombardment etching in alkaline immersion solution A at room temperature for 5-10 minutes to dissolve the carbides, and then ultrasonically rinse for 2 minutes; then immerse the workpiece in alkaline immersion solution B for 1-5 minutes to dissolve the oxides, then ultrasonically rinse for 2 minutes, and finally dry it with dry nitrogen gas.

[0016] Furthermore, the alkaline soaking solution A is composed of 95%–98% Murakami reagent and 2%–5% additives; wherein, the Murakami reagent is K3Fe(CN)6:KOH:H2O = 1:1:10, and the additive is sodium dodecyl sulfate.

[0017] Furthermore, the alkaline soaking solution B consists of 15%–30% strong alkali, 3%–5% sodium carbonate, 1%–2% sodium dodecyl sulfate, 1%–2% ammonium bifluoride, 1%–2% disodium EDTA, and the balance being deionized water; wherein the strong alkali is either potassium hydroxide or sodium hydroxide.

[0018] Compared with the prior art, the present invention provides a controllable method for removing diamond-like carbon coatings from workpiece surfaces, which has the following advantages:

[0019] (1) The present invention uses oxygen plasma to controllably convert the vapor-deposited Me2 metal layer into a metal oxide layer, thereby forming a clear interface with the Me1 layer. This facilitates the subsequent selection of a reasonable method to selectively remove the oxide layer or carbon oxide layer, thus achieving the preservation and protection of the water-plated layer. At the same time, it leverages the ability of oxygen plasma to efficiently remove carbon substances.

[0020] (2) The present invention adopts a method similar to the currently widely used chemical immersion etching method for removing carbides and oxides, which avoids corrosion damage to the surface metal layer and the substrate. After removal, the workpiece surface is smooth and can be directly replated. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below through detailed embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1

[0023] This embodiment addresses the removal process for Cr / WC / DLC coatings deposited via vapor deposition on A45 steel specimens after water-plating a Cr layer.

[0024] Specifically, an A45 steel specimen measuring 100mm x 30mm x 2mm was water-deposited with a 20-micron thick Ni layer and a 10-micron thick chromium layer (Me1 metal layer). Then, a Cr (Me2 metal layer, 1 micron thickness) / WC (0.3 micron thickness) / hydrogen-containing DLC ​​coating (1.5 micron thickness) was prepared on top using a Hauzer 850 vacuum deposition system. All vapor-deposited coatings were removed, leaving the water-deposited layer.

[0025] The specific steps of this controllable plating removal method are as follows:

[0026] S1. Place the test piece in an aqueous solution containing 5wt% of commercially available "Qiqiang" metal degreasing cleaner, boil for about 5 minutes, then rinse the test piece with deionized water and dry it.

[0027] S2. Hang the sample on a special fixture and place it on the workpiece rack in the PVD-660 vacuum coating equipment equipped with a hollow cathode ion source; close the vacuum chamber door and start the workpiece rack rotation; the vacuum chamber is evacuated to a background vacuum level below 5x10. -3Pa; Argon and oxygen are introduced, Ar:O2 = 10:1, to make the vacuum chamber pressure reach 10Pa. A bias voltage of 600V is applied to the workpiece holder to generate gas glow discharge. The bias current is 3A. After etching the test piece for 45 minutes, the bias voltage is turned off. The test piece is taken out from the vacuum chamber. The carbon material on the surface of the test piece has been completely removed, and the test piece is multicolored.

[0028] S3. Place the sample in a tank containing alkaline soaking solution A and soak it at room temperature for 5 minutes. Remove it and ultrasonically clean it in a deionized water ultrasonic bath for 2 minutes. Then soak it in a tank containing alkaline soaking solution B for 1 minute and ultrasonically clean it in a deionized water ultrasonic bath for 2 minutes. Finally, dry the surface of the sample with dry nitrogen gas; the sample should have a bright metallic color. Alkaline soaking solution A consists of 95% Murakami reagent and 5% auxiliaries. The Murakami reagent is K3Fe(CN)6:KOH:H2O = 1:1:10, and the auxiliaries are sodium dodecyl sulfate. Alkaline soaking solution B, by mass, consists of 15% sodium hydroxide, 3% sodium carbonate, 1% sodium dodecyl sulfate, 2% ammonium bifluoride, 2% disodium EDTA, and the remainder is deionized water.

[0029] Cross-sectional scanning electron microscopy analysis of the treated specimen revealed a Ni layer thickness of 20.1 μm and a Cr layer thickness of 9.8 μm. This indicates that the vapor deposition layer was completely removed and the water-based plating layer was not eroded.

[0030] Example 2

[0031] This embodiment addresses the removal process for Ti / TiC / DLC coatings deposited via vapor deposition on 304 stainless steel specimens after water-plating a Cr layer.

[0032] Specifically, a 100mm x 30mm x 2mm 304 stainless steel specimen was water-deposited with a 20-micrometer-thick Ni layer and a 10-micrometer-thick chromium layer (Me1 metal layer). Then, a Ti (Me2 metal layer, 2-micrometer thickness) / TiC (0.5-micrometer thickness) / hydrogen-containing DLC ​​coating (1.5-micrometer thickness) was prepared on it using a Hauzer 850 vacuum deposition system. After obtaining an approximately 2-micrometer-thick diamond coating on the specimen surface, all vapor-deposited coatings were removed, leaving the water-deposited layer and the Ti layer.

[0033] The specific steps of this controllable plating removal method are as follows:

[0034] S1. Place the test piece in an aqueous solution containing 5wt% of commercially available "Qiqiang" metal degreasing cleaner, boil for about 5 minutes, then rinse the test piece with deionized water and dry it.

[0035] S2. Hang the sample on a special fixture and place it on the workpiece rack in the PVD-660 vacuum coating equipment equipped with a hollow cathode ion source; close the vacuum chamber door and start the workpiece rack rotation; the vacuum chamber is evacuated to a background vacuum level below 5x10. -3 Pa; Argon gas is introduced to make the vacuum chamber pressure 0.2 Pa, the hollow cathode ion source is turned on and the beam current is maintained at 100 A; Oxygen is introduced to maintain the vacuum chamber pressure at 5 Pa; A DC bias voltage of 200 V is applied to the workpiece holder, and the generated oxygen plasma etches the test piece for 1 hour. The bias voltage and ion source are then turned off; The test piece is taken out from the vacuum chamber. The carbon material on the surface of the test piece has been completely removed, and the test piece is gray-black.

[0036] S3. Place the sample in a tank containing alkaline soaking solution A and soak at room temperature for 7 minutes. Remove the sample and ultrasonically clean it in a deionized water ultrasonic bath for 2 minutes. Then soak it in a tank containing alkaline soaking solution B for 2 minutes and ultrasonically clean it in a deionized water ultrasonic bath for 2 minutes. Finally, dry the surface of the sample with dry nitrogen gas; the sample should have a bright metallic color. Alkaline soaking solution A consists of 97% Murakami reagent and 3% auxiliaries. The Murakami reagent is K3Fe(CN)6:KOH:H2O = 1:1:10, and the auxiliaries are sodium dodecyl sulfate. Alkaline soaking solution B, by mass, consists of 30% potassium hydroxide, 5% sodium carbonate, 2% sodium dodecyl sulfate, 1% ammonium bifluoride, 1% disodium EDTA, and the remainder deionized water.

[0037] Cross-sectional scanning electron microscopy analysis of the treated specimens revealed a Ni layer thickness of 19.3 μm, a Cr layer thickness of 10.2 μm, and a Ti layer thickness of 0.18 μm. This indicates that the vapor deposition layer was completely stripped, without eroding the water-based plating layer, and that the remaining thickness of the Me2 layer was well controlled.

[0038] Example 3

[0039] This embodiment addresses the removal process for a Cr / W / DLC coating deposited via vapor deposition on a brass specimen after water-plating a Ni layer.

[0040] Specifically, a 100mm x 30mm x 2mm brass sample was water-deposited with a 30-micron thick Ni layer and a Me1 metal layer. Then, a Cr (Me2 metal layer, 2 microns thick) / W (1 micron thick) / WC (0.8 microns thick) / hydrogen-containing DLC ​​coating (5 microns thick) was prepared on it using a Hauzer 850 vacuum deposition system. All vapor-deposited coatings were removed, leaving the water-deposited layer and the Cr layer.

[0041] The specific steps of this controllable plating removal method are as follows:

[0042] S1. Place the test piece in an aqueous solution containing 5wt% of commercially available "Qiqiang" metal degreasing cleaner, boil for about 5 minutes, then rinse the test piece with deionized water and dry it.

[0043] S2. Hang the sample on a special fixture and place it on the workpiece rack in the PVD-660 vacuum coating equipment equipped with a hollow cathode ion source; close the vacuum chamber door and start the workpiece rack rotation; the vacuum chamber is evacuated to a background vacuum level below 5x10. -3 Pa; Argon gas is introduced to make the vacuum chamber pressure 0.2 Pa, the hollow cathode ion source is turned on and the beam current is maintained at 150 A; Oxygen is introduced to maintain the vacuum chamber pressure at 5 Pa; A DC bias voltage of 200 V is applied to the workpiece holder, and the generated oxygen plasma etches the test piece for 2.5 hours. The bias voltage and ion source are then turned off; The test piece is taken out of the vacuum chamber. The carbon material on the surface of the test piece has been completely removed, and the test piece is gray-black.

[0044] S3. Place the sample in a tank containing alkaline soaking solution A and soak at room temperature for 10 minutes. Remove the sample and ultrasonically clean it in a deionized water ultrasonic bath for 2 minutes. Then soak it in a tank containing alkaline soaking solution B for 5 minutes and ultrasonically clean it in a deionized water ultrasonic bath for 2 minutes. Finally, dry the surface of the sample with dry nitrogen gas; the sample should have a bright metallic color. Alkaline soaking solution A consists of 98% Murakami reagent and 2% auxiliaries. The Murakami reagent is K3Fe(CN)6:KOH:H2O = 1:1:10, and the auxiliaries are sodium dodecyl sulfate. Alkaline soaking solution B, by mass, consists of 30% potassium hydroxide, 5% sodium carbonate, 2% sodium dodecyl sulfate, 1.5% ammonium bifluoride, 1.5% disodium EDTA, and the remainder deionized water.

[0045] Cross-sectional scanning electron microscopy analysis of the treated specimens revealed a Ni layer thickness of 29.3 μm and a Cr layer thickness of 0.2 μm. This indicates that not only was the water-coated layer retained, but the thickness of the Me2 layer was also well controlled.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0047] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for controlled removal of diamond-like carbon coatings on a workpiece surface, characterized in that, For the processing of workpieces with diamond-like carbon coatings on the surface, the surface structure of the workpiece from the core to the surface layer is as follows: workpiece substrate, water-plated Ni layer, water-plated Me1 metal layer, Me2 metal layer formed by vapor deposition, carbide layer formed by vapor deposition, and DLC layer formed by vapor deposition, wherein Me1 and Me2 are any one of the metals Cr, Ti, Zr, W and Ni. The steps of the controllable plating removal method include: S1. Pretreatment of workpiece surface: Remove oil stains from the workpiece surface with metal cleaning agent, rinse and dry before use; S2. Oxygen plasma stripping of carbonaceous material from the workpiece surface and controlled oxidation of the Me2 metal layer: The pretreated workpiece is fixed on the workpiece holder, the vacuum chamber door is closed, and the workpiece holder is started to rotate; the vacuum chamber is evacuated to a background vacuum below 5x10⁻¹⁰. -3 Pa, oxygen glow or high-density oxygen plasma is obtained in a vacuum chamber; the bias voltage applied to the workpiece is controlled to be 200V~600V, the bias current is 3A~150A, and the etching time is 45min~2.5h, completely stripping the carbon material on the surface of the workpiece and converting part or all of the vapor-deposited Me2 metal layer into a metal carbon / oxide composite. S3. Remove the carbon oxide layer and ablation residue from the composite metal on the workpiece surface, and simultaneously perform chemical polishing on the exposed metal: First, immerse the workpiece after oxygen plasma bombardment etching in alkaline immersion solution A at room temperature for 5-10 minutes, and then ultrasonically rinse for 2 minutes; then immerse the workpiece in alkaline immersion solution B for 1-5 minutes, then ultrasonically rinse for 2 minutes, and finally dry it with dry nitrogen gas. The alkaline soaking solution A consists of 95%~98% Murakami reagent and 2%~5% additives. The Murakami reagent is K3Fe(CN)6:KOH:H2O = 1:1:10, and the additive is sodium dodecyl sulfate. The alkaline soaking solution B consists of 15%~30% strong alkali, 3%~5% sodium carbonate, 1%~2% sodium dodecyl sulfate, 1%~2% ammonium bifluoride, 1%~2% disodium EDTA, and the balance being deionized water. The strong alkali is either potassium hydroxide or sodium hydroxide.