A "mechano-chemical" synergic interfacial strengthening technique to improve the adhesion of DLC coatings

Abstract

This invention relates to the field of "mechanical-chemical" synergistic interface strengthening technology for improving the adhesion of DLC coatings. It is a method that forms a "mechanical-chemical" synergistic interface strengthening through surface texturing of the substrate and multi-layer structure design of the DLC coating, which effectively improves the film-substrate adhesion. The concentration of the deposited Cr / WC transition layer exhibits a gradient change, which can achieve a gradient increase in coating hardness and buffer film stress. By adopting a combination of multi-layer structure and doping, the internal stress of the coating is effectively released, thereby improving the film-substrate adhesion and achieving a gradient increase in hardness, reducing the probability of brittle coating detachment.

Description

Technical Field

[0001] This invention belongs to the field of surface coating technology, specifically relating to a method for preparing a highly adhesive diamond-like carbon (DLC) coating through laser surface texturing pretreatment and gradient transition layer synergistic design. Background Technology

[0002] DLC coatings are widely used in machinery, aerospace, and medical devices due to their high hardness, low coefficient of friction, and excellent wear resistance. However, the adhesion between the DLC coating and the substrate has always been a key factor limiting its application. Traditional DLC coating preparation methods often fail to form a strong bond on the substrate surface, leading to easy coating peeling during use and severely affecting the service life and performance of the DLC coating. Therefore, developing a new technology that can effectively improve the adhesion of DLC coatings is particularly important.

[0003] Currently, various methods have been attempted to address the insufficient adhesion of DLC coatings, such as adding transition layers and optimizing deposition parameters. However, while these methods improve adhesion, they often introduce new problems, such as increased internal stress within the coating and more complex fabrication processes. Therefore, there is an urgent need for a new technology that can significantly improve the adhesion of DLC coatings while maintaining their excellent performance.

[0004] This invention aims to solve this problem by achieving efficient deposition of DLC coatings with high adhesion and low residual stress under low-temperature conditions through the synergistic design of substrate surface texturing, gradient transition layers, and multilayer structures of doped DLC. This invention overcomes the performance bottlenecks of traditional technologies through innovative process integration and microstructure control. Summary of the Invention

[0005] This invention proposes a "mechanical-chemical" synergistic interface strengthening technology to improve the adhesion of DLC coatings. First, a submicron or micron-scale trench array is fabricated on the substrate surface using a femtosecond laser, utilizing a physical interlocking effect to enhance adhesion. Then, a Cr transition layer is deposited. At the interface, Cr diffuses between elements in the substrate and the substrate, forming an alloy layer, thereby improving the adhesion between the substrate and the film. Next, a Cr / WC transition layer is deposited, where the Cr and WC contents exhibit a gradient change, with the Cr content gradually decreasing to zero and the WC content gradually increasing to 100%. This gradient transition layer achieves a hardness gradient increase, buffering film stress. Subsequently, a W-doped DLC film is deposited. The incorporated tungsten readily forms WC or W2C microcrystalline phases with carbon bonds, exhibiting low diffusivity and high thermal stability. These microcrystalline phases are uniformly distributed within the amorphous carbon matrix, thus forming a microcrystalline / amorphous composite structure in the coating, effectively releasing the internal stress of the film. Simultaneously, the formation of the WC or W2C microcrystalline phase reduces the coordination number of carbon atoms in the amorphous carbon matrix network. The reduction in the number of coordinated carbon atoms and the decrease in carbon atom density increase the content of sp2 hybrid bonds in the amorphous carbon-based network, which is beneficial for the release of film stress and improves film adhesion. Finally, a hydrogen-containing DLC ​​layer is deposited to improve the overall macroscopic hardness of the film.

[0006] The process and steps are as follows:

[0007] ① Matrix surface texturing

[0008] A femtosecond laser (wavelength 1030nm, pulse width 300fs, power 20W) is used to process submicron or micron-scale trench arrays on the substrate surface, such as grid arrays (width 0.5-10μm, depth 0.5-10μm, spacing 10-100μm), micropit arrays (diameter 0.5-10μm, depth 0.5-10μm, spacing 10-100μm), and stripe structures (width 0.5-10μm, depth 0.5-10μm, spacing 10-100μm), to form a mechanical anchoring structure.

[0009] ②Deposited Cr transition layer

[0010] The metal sample is placed in a high-energy ion source-assisted PECVD apparatus, evacuated to below 5 × 10⁻⁵ mBar, and the furnace temperature is raised to 100-200℃. Ar ions are used to etch the workpiece surface for 20-60 min. Then, Ar gas is introduced until the pressure is 0.2-0.7 Pa, and the Cr and WC cathode power is set to 10 kW. The target surface is cleaned for 10 min. Argon gas is continuously introduced and maintained at a pressure of 0.2-0.7 Pa. Using a Cr target, the power is 8-12 kW for 20-40 min, the bias voltage is set to 0 V, and the current of the closed-field electromagnetic coil on the back side of the target is set to 3-7 A to deposit a 0.1-0.5 μm thick Cr transition layer.

[0011] ③ Cr / WC transition layer with varying depositional gradient

[0012] The Cr target power was gradually reduced from 8-12kW to 1kW, while the WC target power was gradually increased from 1kW to 8-12kW. The ramp-up time was 60min, the bias voltage was set to 0V, the current of the closed field electromagnetic coil on the back of the target was set to 3-7A, and the thickness of the gradient-varying Cr / WC transition layer was 0.1-0.5μm.

[0013] ④ Deposition of W-doped DLC film

[0014] Turn off the Cr target, turn on only the WC target, keep Ar flowing in, and then introduce 150-250 sccm of C2H2 gas. Set the bias voltage to 40-60V, and the deposition time to 40-80min to deposit a W-doped DLC film with a thickness of 0.2-2μm.

[0015] ⑤ Deposition of hydrogen-containing DLC ​​film

[0016] Turn off the WC target and Ar gas, introduce C2H2 gas until the pressure is 0.5-1 Pa, turn on the bias power supply, adjust it to unipolar pulse mode, pulse frequency 60 kHz, duty cycle 0.75, output voltage 500-700 V, and the thickness of the hydrogen-containing DLC ​​film deposition is 1.5-2.5 μm. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the textured surface of the substrate.

[0018] Figure 2 A schematic diagram of the coating structure.

[0019] Figure 3 The image shows the Raman spectrum of the DLC coating. A distinct D peak and G peak can be observed at 1352 cm⁻¹ and 1566 cm⁻¹, respectively. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0021] Example 1

[0022] ① Matrix surface texturing

[0023] A micron-scale grid array with a width of 1μm, a depth of 1μm, and a spacing of 50μm was fabricated on the surface of a cemented carbide substrate using a femtosecond laser (wavelength 1030nm, pulse width 300fs, power 20W) to form a mechanical anchoring structure.

[0024] ②Deposited Cr transition layer

[0025] The cemented carbide substrate was placed in a high-energy ion source-assisted PECVD apparatus, evacuated to below 5 × 10⁻⁵ mBar, and the furnace temperature was raised to 100 °C. The workpiece surface was etched with Ar ions for 60 min. Then, Ar gas was introduced until the pressure reached 0.6 Pa, and the cathode power for Cr and WC was set to 10 kW. The target surface was cleaned for 10 min. Argon gas was continuously introduced and maintained at a pressure of 0.6 Pa. Using a Cr target, the power was 12 kW for 20 min, the bias voltage was set to 0 V, and the current of the closed-field electromagnetic coil on the back side of the target was set to 4 A to deposit a 0.4 μm thick Cr transition layer.

[0026] ③ Cr / WC transition layer with varying depositional gradient

[0027] The Cr target power was gradually reduced from 12kW to 1kW, while the WC target power was gradually increased from 1kW to 12kW. The ramp-up time was 60min, the bias voltage was set to 0V, the current of the closed-field electromagnetic coil on the back of the target was set to 4A, and the thickness of the gradient-varying Cr / WC transition layer was 0.3μm.

[0028] ④ Deposition of W-doped DLC film

[0029] Turn off the Cr target, turn on only the WC target, keep Ar flowing in, then introduce 250 sccm of C2H2 gas, set the bias voltage to 40V, and deposit for 40 min to deposit a 1 μm thick W-doped DLC film.

[0030] ⑤ Deposition of hydrogen-containing DLC ​​film

[0031] Turn off the WC target and Ar gas, introduce C2H2 gas until the pressure reaches 0.5 Pa, turn on the bias power supply, adjust it to unipolar pulse mode, pulse frequency 60 kHz, duty cycle 0.75, output voltage 700 V, and the thickness of the hydrogen-containing DLC ​​film deposited is 2.5 μm.

[0032] Example 2

[0033] ① Matrix surface texturing

[0034] A femtosecond laser (wavelength 1030nm, pulse width 300fs, power 20W) was used to process a micron-scale array of pits on the surface of a titanium alloy substrate. The pits had a diameter of 1μm, a depth of 1μm, and a spacing of 50μm, forming a mechanical anchoring structure.

[0035] ②Deposited Cr transition layer

[0036] The titanium alloy substrate was placed in a high-energy ion source-assisted PECVD apparatus, evacuated to below 5 × 10⁻⁵ mBar, and the furnace temperature was raised to 200 °C. The workpiece surface was etched with Ar ions for 20 min. Then, Ar gas was introduced until the pressure reached 0.3 Pa, and the cathode power for Cr and WC was set to 10 kW. The target surface was cleaned for 10 min. Argon gas was continuously introduced and maintained at a pressure of 0.3 Pa. Using a Cr target, the power was 8 kW for 40 min, the bias voltage was set to 0 V, and the current of the closed-field electromagnetic coil on the back side of the target was set to 6 A to deposit a 0.2 μm thick Cr transition layer.

[0037] ③ Cr / WC transition layer with varying depositional gradient

[0038] The Cr target power was gradually reduced from 8kW to 1kW, while the WC target power was gradually increased from 1kW to 8kW. The ramp-up time was 60min, the bias voltage was set to 0V, the current of the closed-field electromagnetic coil on the back of the target was set to 6A, and the thickness of the gradient-varying Cr / WC transition layer was 0.5μm.

[0039] ④ Deposition of W-doped DLC film

[0040] Turn off the Cr target, turn on only the WC target, keep Ar flowing in, and then introduce 150 sccm of C2H2 gas. Set the bias voltage to 60V, and the deposition time to 70 min to deposit a 0.5 μm thick W-doped DLC film.

[0041] ⑤ Deposition of hydrogen-containing DLC ​​film

[0042] Turn off the WC target and Ar gas, introduce C2H2 gas until the pressure reaches 0.8 Pa, turn on the bias power supply, adjust it to unipolar pulse mode, pulse frequency 60 kHz, duty cycle 0.75, output voltage 500 V, and the thickness of the hydrogen-containing DLC ​​film deposited is 1.5 μm.

Claims

1. A "mechanical-chemical" synergistic interface strengthening technology for improving the adhesion of DLC coatings, characterized in that: The texturing of the substrate surface and the multi-layer structure design of the DLC coating form a "mechanical-chemical" synergistic interface reinforcement, which effectively improves the film-substrate adhesion.

2. The "mechanical-chemical" synergistic interface strengthening technology for improving the adhesion of DLC coatings according to claim 1, characterized in that: A Cr transition layer is deposited, and at the interface, elements diffuse between Cr and the substrate to form an alloy layer, thereby improving the adhesion between the substrate and the film.

3. The "mechanical-chemical" synergistic interface strengthening technology for improving the adhesion of DLC coatings according to claim 2, characterized in that: A Cr / WC transition layer is deposited, in which the contents of Cr and WC exhibit a gradient change, with the Cr content gradually decreasing to zero and the WC content gradually increasing to 100%. This gradient transition layer can achieve a gradient increase in hardness and buffer the stress of the film layer.

4. The "mechanical-chemical" synergistic interface strengthening technology for improving the adhesion of DLC coatings according to claim 3, characterized in that: A W-doped DLC film is deposited. The tungsten doped element readily forms a WC or W2C microcrystalline phase with low diffusivity and high thermal stability with carbon bonds. This microcrystalline phase is uniformly distributed in the amorphous carbon matrix, thereby forming a microcrystalline / amorphous composite structure in the coating, which can effectively release the internal stress of the film.

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