A method for preparing a high-hardness tetrahedral amorphous carbon film ta-c coating based on reverse positive pulse technology

Abstract

The application discloses a preparation method of a tetrahedral amorphous carbon film ta-C multilayer structure coating based on a reverse positive pulse technology, and comprises the following steps: S1, stopping a cleaned substrate in front of a Cr target, and performing pulse reaction sputtering on a CrN bottom layer by using a power of 15-20 kW; S2, stopping in front of the Cr target, and performing pulse reaction sputtering on a CrC transition layer by using a power of 5-10 kW; S3, stopping in front of a graphite target again, and performing pulse multi-target magnetron sputtering on a ta-C coating by using a power of 5-8 kW; and a 50-550 V reverse voltage of a reverse positive pulse is applied at the tail of each pulse cycle, and the frequency ranges from 200 Hz to 5000 Hz. The ta-C coating prepared by the method has a hardness of more than 30 GPa, a friction coefficient of less than 0.1, the ion energy of the thin film can be increased by 2-4 times when the ta-C carbon thin film is prepared, and the effective ion utilization rate and the thin film deposition rate are increased by 50-60%.

Description

Technical Field

[0001] This invention relates to the field of material surface modification technology, and more specifically, to a method for preparing a high-hardness tetrahedral amorphous carbon film ta-C coating based on reverse positive pulse technology and high-power pulsed magnetron sputtering technology. Background Technology

[0002] In machining, tool performance has a decisive impact on machining efficiency, accuracy, and surface quality. To improve tool cutting performance, a relatively effective method is to apply one or more layers of high-hardness, high-wear-resistant materials to the substrate using various coating technologies. The coating on the tool surface acts as a chemical and thermal barrier, reducing crater wear and significantly improving machining efficiency, accuracy, tool life, and cost.

[0003] The coating is characterized by the combination of the coating film and the tool substrate, which improves the wear resistance of the tool without reducing the toughness of the substrate, thereby reducing the friction factor between the tool and the workpiece and extending the tool's service life.

[0004] Hipims (High Energy Pulsed Magnetron Sputtering) is a newly introduced PVD coating technology in recent years. Currently, in the field of PVD hard nano-coating materials, arc ion plating and DC / DC pulsed magnetron sputtering are the two main technologies.

[0005] As the operating conditions of cutting tools become increasingly demanding, higher requirements are placed not only on the hardness of the tool coating but also on the coating material's excellent self-lubricating properties to effectively improve tool performance. However, coatings prepared by existing technologies have relatively large surface roughness; magnetron sputtering technology has low deposition rates, weak adhesion, and poor diffraction.

[0006] The preparation of tetrahedral amorphous carbon coatings ta-C using Hipims has been a hot topic in coating research in recent years. However, due to the characteristics of carbon materials, the ionization rate is low and the ion energy for film formation is low during the sputtering process, resulting in a low content of SP3 bonds in the tetrahedral amorphous carbon ta-C formed. Summary of the Invention

[0007] The purpose of this invention is to use reverse positive pulse technology to control carbon ions (C2O3) generated in front of a magnetron sputtering target. + Applying a positive pulse voltage accelerates deposition onto the substrate surface, while simultaneously improving the pre-target ionization utilization, increasing the ion energy for film formation, and enhancing the film deposition rate.

[0008] This invention provides a method for preparing a tetrahedral amorphous carbon film ta-C multilayer structure coating based on reverse positive pulse technology, comprising the following steps:

[0009] S1. Sputtering CrN substrate: The cleaned substrate is placed in front of the Cr target and a CrN substrate is obtained by pulsed reactive sputtering with a power of 15-20kW.

[0010] S2. Preparation of CrC transition layer: The substrate of sputtered CrN bottom layer in step S1 is placed in front of Cr target, and CrC transition layer is obtained by pulse reactive sputtering with a power of 5-10kW, thus obtaining the substrate of sputtered CrC transition layer.

[0011] S3. Preparation of ta-C coating: The substrate in step S2 where the sputtered CrC transition layer was placed in front of the graphite target, and the ta-C coating was obtained by pulsed multi-target magnetron sputtering with a power of 5-8 kW.

[0012] Preferably, the cleaning method for the substrate includes: after polishing the substrate, performing ultrasonic cleaning with anhydrous alcohol and acetone sequentially at a power of 15-30 kHz for 10-15 min, followed by vacuuming to 6×10⁻⁶. -3 After Pa, Ar gas with a flow rate of 200 sccm is introduced to maintain a vacuum of 0.4-0.8 Pa, and ion bombardment with a power of 1000-1500 W is carried out for 45 min.

[0013] Preferably, the conditions for obtaining the CrN underlayer by pulse reactive sputtering in step S1 include: pulse frequency of 1000-2000Hz, pulse width of 100-200µs, maximum peak current of 300A, gas pressure of 0.4-0.8Pa, Ar gas flow rate of 100-250sccm, and N2 gas flow rate of 75-150sccm.

[0014] Preferably, the conditions for obtaining the CrC transition layer by pulse reactive sputtering in step S2 include: pulse frequency of 2500-5000Hz, pulse width of 50-200µs, maximum peak current of 300A, gas pressure of 0.4-0.8Pa, and Ar gas flow rate of 100-250sccm.

[0015] Preferably, the conditions for obtaining the ta-C coating by pulsed multi-target magnetron sputtering in step S3 include: Ar gas flow rate of 50-250 sccm, gas pressure range of 0.4-0.8 Pa; maximum peak current of 300 A; and temperature range of 80-105 °C.

[0016] This invention provides a method for preparing a tetrahedral amorphous carbon film ta-C multilayer structure coating based on reverse positive pulse technology, resulting in a ta-C multilayer structure coating.

[0017] Preferably, the CrN bottom layer has a thickness of 0.5-1.0 μm, the CrC transition layer has a thickness of 0.2-0.5 μm, and the ta-C layer has a thickness of 0.4-1.0 μm.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] This invention employs high-power pulsed magnetron sputtering technology, applying a reverse positive pulse signal at the end of each high-energy negative pulse cycle. By adjusting pulse parameters and precisely controlling Ar flow and temperature, an optimized ta-C coating is obtained. The prepared ta-C coating achieves a hardness of over 30 GPa and a friction coefficient below 0.1, exhibiting good lubrication performance. This invention comprehensively utilizes the advantages of high hardness and low friction coefficient in the preparation of tetrahedral amorphous carbon ta-C using reverse positive pulse technology and high-power pulsed magnetron sputtering, resulting in a coating that combines high hardness and low friction. In the preparation of ta-C carbon thin films, the ion energy of the film can be increased by 2-4 times; the effective ion utilization rate and film deposition rate can be increased by 50-60%. The coating of this invention can overcome the shortcomings of traditional tool coatings, broaden the research scope of tool coatings, and features a simple, low-cost, and high-efficiency process, making it suitable for the efficient machining of materials such as aluminum alloys. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the frequency of the reverse positive pulse of the oscilloscope in this invention;

[0021] Figure 2 These are nanoindentation test images of the ta-C films prepared in Examples 1-3 of this invention;

[0022] Figure 3 This is a nanoindentation test image of the ta-C film prepared in Example 4 of this invention;

[0023] Figure 4 This is a nanoindentation test image of the ta-C film prepared in Example 5 of this invention;

[0024] Figure 5 Here is a SEM image of the surface morphology of the ta-C film prepared in this invention;

[0025] Figure 6 This is a SEM image of the cross-sectional morphology of the ta-C membrane prepared in this invention;

[0026] Figure 7 This is a graph showing the improvement in ion energy of the ta-C membrane prepared by this invention. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments and accompanying drawings, but this does not limit the present invention in any way.

[0028] This invention relates to the following devices:

[0029] JGP-450 magnetron sputtering system, Shenyang Scientific Instruments Research Center Co., Ltd., Chinese Academy of Sciences;

[0030] QPlex magnetron sputtering system, Shanghai Xinhuyuan Coating Technology Co., Ltd.

[0031] NANO Indenter G200 nanoindenter, Agilent Technologies, USA;

[0032] Quanta FEG450 scanning electron microscope, FEI Corporation, USA;

[0033] NANO Indenter G200 nanoindenter, Agilent Technologies, USA.

[0034] The method for preparing high-hardness tetrahedral amorphous carbon film ta-C multilayer structure coatings using high-power pulsed magnetron sputtering (HiPIMS) based on reverse positive pulse technology provided by this invention specifically includes the following steps:

[0035] S1. Ion cleaning of the substrate before use: After polishing the substrate, ultrasonic cleaning is performed sequentially with anhydrous alcohol and acetone, followed by placing it in a vacuum chamber and evacuating to a vacuum level of 6×10⁻⁶. -3 After Pa, Ar gas is introduced at a flow rate of 200 sccm to maintain a vacuum of 0.4-0.8 Pa, and the substrate is bombarded with high-energy ions. The high-energy ion bombardment power is 1000-1500 W, and the time is 45 min; the ultrasonic cleaning using anhydrous alcohol and acetone has an ultrasonic power of 15-30 kHz and a time of 10-15 min.

[0036] S2. Sputtering CrN Substrate: The substrate is placed in a high-power pulsed magnetron sputtering system, positioned before the Cr target, and a CrN substrate is obtained through high-power pulsed reactive sputtering, resulting in a substrate with a sputtered CrN substrate. The high-power pulsed sputtering power is 15-20kW, the pulse frequency is 1000-2000Hz, the pulse width is 100-200µs, the maximum peak current is 300A, the gas pressure is 0.4-0.8Pa, the Ar gas flow rate is 100-250sccm, and the N2 gas flow rate is 75-150sccm.

[0037] S3. Preparation of the CrC transition layer: The substrate with the sputtered CrN bottom layer from step S2 is placed in a high-power pulsed magnetron sputtering system, positioned before the Cr target, and then subjected to high-power pulsed reactive sputtering again to obtain the CrC transition layer, thus obtaining the substrate with the sputtered CrC transition layer. The high-power pulsed sputtering power is 5-10 kW, the pulse frequency is 2500-5000 Hz, the pulse width is 50-200 μs, the maximum peak current is 300 A, the gas pressure is 0.4-0.8 Pa, and the Ar gas flow rate is 100-250 sccm.

[0038] S4. Preparation of the ta-C coating: The substrate from step S3, onto which the sputtered CrC transition layer was deposited, is placed in a high-power pulsed magnetron sputtering system, positioned in front of a graphite target. During high-power pulsed multi-target magnetron sputtering, the Ar gas flow rate is 50–250 sccm, and the total gas pressure ranges from 0.4 to 0.8 Pa. The pulse power is 5–8 kW, the maximum peak current is 300 A, and a reverse voltage range of 50–550 V and a frequency range of 200–5000 Hz are applied at the end of each pulse cycle; the pulse width is 50–200 μs; and the temperature is precisely controlled within the range of 80–105 °C during ta-C layer preparation. Multi-target sputtering involves preparing a transition layer using a Cr target before sputtering ta-C, followed by ta-C preparation using a graphite target. This method increases the adhesion between the ta-C coating and the substrate.

[0039] High-power pulsed magnetron sputtering technology, which applies a reverse positive pulse at the end of each pulse cycle, has a reverse voltage range of 50-550V and a frequency range of 200-5000Hz.

[0040] Pulse width 50-200μs; total coating thickness 1.0-2.5μm, hardness 30-37Gpa; CrN underlayer 0.5-1.0μm.

[0041] The thicknesses of the CrC transition layer are 0.2-0.5 μm and the thicknesses of the ta-C layer are 0.4-1.0 μm.

[0042] Example 1

[0043] The metal substrate was polished, then ultrasonically cleaned sequentially with anhydrous alcohol and acetone (both ultrasonic cleaning powers were 30 kHz, and the time was 5 min each). It was then placed in a vacuum chamber and evacuated to a vacuum level of 6 × 10⁻⁶. -3 After Pa, Ar gas is introduced to maintain a vacuum of 0.5 Pa, and the substrate is bombarded with high-energy ions (power of 1500 W, time of 25 min). Figure 1 This is a schematic diagram of the frequency of the reverse positive pulse of the oscilloscope of the present invention, which shows that the reverse voltage is applied normally.

[0044] Using a Cr target, multi-target magnetron sputtering is performed on the surface of a metal substrate to form a CrN / CrC hardness transition layer. The high-power pulsed magnetron sputtering parameters are as follows: a CrN underlayer and a CrC transition layer are sputtered onto the cleaned substrate. The substrate is then placed in the high-power pulsed magnetron sputtering system, positioned before the Cr target, and a CrN underlayer with a thickness of 0.5 μm is obtained through high-power pulsed reactive sputtering. The process is as follows: high-power pulsed sputtering power of 15 kW, pulse frequency of 1000 Hz, pulse width of 200 μs, maximum peak current of 300 A, gas pressure of 0.5 Pa, Ar gas flow rate of 250 sccm, and N2 gas flow rate of 150 sccm. A CrC transition layer with a thickness of 0.5 μm was prepared. The substrate was placed in a high-power pulsed magnetron sputtering system, positioned before the Cr target. The process involved a high-power pulsed sputtering power of 5 kW, a pulse frequency of 2500 Hz, a pulse width of 100 μs, a maximum peak current of 300 A, a gas pressure of 0.4-0.5 Pa, and an Ar gas flow rate of 150-250 sccm.

[0045] In the ta-C coating preparation process, the workpiece is positioned in front of a graphite target. During high-power pulsed multi-target magnetron sputtering, the Ar gas flow rate is 50-150 sccm, and the total gas pressure ranges from 0.4-0.5 Pa. The pulse power is 5.5 kW, the maximum peak current is 300 A, and a reverse voltage range of 250 V and a frequency range of 5000 Hz are applied at the end of each pulse cycle; the pulse width is 50 μs. The ta-C thickness is 0.75 μm.

[0046] The coating was tested and found to have a hardness of 30.9 GPa and a coefficient of friction of 0.07.

[0047] Example 2

[0048] Similar to Example 1, the difference lies in the polishing treatment of the metal substrate, followed by ultrasonic cleaning with anhydrous alcohol and acetone in sequence (the ultrasonic power for both anhydrous alcohol and acetone ultrasonic cleaning is 30 kHz, and the time is 5 min for both). Then, it is placed in a vacuum chamber and evacuated to a vacuum level of 6 × 10⁻⁶. -3 After Pa, Ar gas is introduced to maintain a vacuum of 0.5 Pa, and the substrate is bombarded with high-energy ions (power of 1000 W, time of 35 min).

[0049] Alternating Cr targets were used to deposit a CrN / CrC hardness transition layer. The substrate was then placed in a high-power pulsed magnetron sputtering system, positioned before the Cr target, and a CrN underlayer with a thickness of 0.5 μm was obtained through high-power pulsed reactive sputtering. The process involved a high-power pulsed sputtering power of 20 kW, a pulse frequency of 1000 Hz, a pulse width of 150 μs, a maximum peak current of 300 A, a gas pressure of 0.5 Pa, an Ar gas flow rate of 250 sccm, and a N2 gas flow rate of 150 sccm. The final thickness was 0.71 μm.

[0050] Testing revealed that the coating has a hardness of 31.2 GPa and a coefficient of friction of 0.07. Changes in the underlying CrN process parameters had little impact on the overall coating performance.

[0051] Example 3

[0052] Similar to Example 1, the difference lies in the preparation of a CrC transition layer with a thickness of 1.0 μm. The substrate is placed in a high-power pulsed magnetron sputtering system, positioned before the Cr target. The process involves a high-power pulsed sputtering power of 10 kW, a pulse frequency of 4000 Hz, a pulse width of 100 μs, a maximum peak current of 300 A, a gas pressure of 0.4-0.5 Pa, an Ar gas flow rate of 150-250 sccm, and a C2H2 gas flow rate of 50-100 sccm. The ta-C thickness is 0.81 μm.

[0053] Figure 2 These are nanoindentation test images of the ta-C films prepared in Examples 1-3 of this invention. The coating hardness was measured to be 33.1 GPa, and the coefficient of friction was 0.07. Adjusting the pulse parameters of the CrC transition layer, which acts as a hardness transition layer, affects the overall coating hardness.

[0054] Example 4

[0055] Similar to Example 1, the difference lies in the ta-C coating preparation step. The workpiece is held in front of the graphite target. The Ar gas flow rate during high-power pulsed multi-target magnetron sputtering is 50-150 sccm, and the total gas pressure ranges from 0.4-0.5 Pa. The pulse power is 5.5 kW, the maximum peak current is 300 A, and a reverse voltage range of 350 V and a frequency range of 5000 Hz are applied at the end of each pulse cycle; the pulse width is 50 μs. The ta-C thickness is 0.75 μm.

[0056] Figure 3 This is a nanoindentation test image of the ta-C film prepared in Example 4 of this invention. The coating hardness was measured to be 32.9 GPa, and the coefficient of friction was 0.06. The hardness of the ta-C coating was improved by adjusting the voltage parameter of the reverse positive pulse in the process parameters.

[0057] Example 5

[0058] Similar to Example 1, the difference lies in the ta-C coating preparation step. The workpiece is held in front of the graphite target. The Ar gas flow rate during high-power pulsed multi-target magnetron sputtering is 50–150 sccm, and the total gas pressure ranges from 0.4 to 0.5 Pa. The pulse power is 5.5 kW, the maximum peak current is 300 A, and a reverse voltage range of 550 V and a frequency range of 5000 Hz are applied at the end of each pulse cycle; the pulse width is 50 μs. The ta-C thickness is 0.77 μm.

[0059] The coating was tested and found to have a hardness of 34.3 GPa and a coefficient of friction of 0.06.

[0060] Figure 4 This is a nanoindentation test image of the ta-C film prepared in Example 5 of the present invention. Obtaining the optimal hardness value through indentation testing is beneficial for experimental research. Figure 5 This is a SEM image of the surface morphology of the ta-C film prepared by the present invention; it shows that the surface is relatively smooth and has good uniformity. Figure 6 This is a SEM image of the cross-sectional morphology of the ta-C membrane prepared by this invention; the membrane thickness can be observed, and the thickness is uniform, indicating good compactness. Figure 7 This diagram shows the improvement in ion energy of the ta-C membrane prepared by this invention. It can provide the specific energy value of the bias voltage, which is beneficial for changing the coating parameters.

[0061] By adjusting the voltage parameter of the reverse positive pulse in the process parameters, the hardness of the ta-C coating was further improved. The coefficient of friction was slightly improved.

[0062] For anyone skilled in the art, many possible variations and modifications can be made to the technical solutions of this invention, or equivalent embodiments can be modified based on the disclosed technical content, without departing from the scope of the technical solutions of this invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this invention without departing from the content of the technical solutions of this invention should still fall within the protection scope of the technical solutions of this invention.

Claims

1. A method for preparing a tetrahedral amorphous carbon film ta-C multilayer structure coating based on reverse positive pulse technology, characterized in that, Includes the following steps: S1. Sputtering CrN substrate: The cleaned substrate is placed in front of the Cr target and a CrN substrate is obtained by pulsed reactive sputtering with a power of 15-20 kW. S2. Preparation of CrC transition layer: The substrate of sputtered CrN bottom layer in step S1 is placed in front of Cr target, and CrC transition layer is obtained by pulse reactive sputtering with a power of 5-10kW, thus obtaining the substrate of sputtered CrC transition layer. S3. Preparation of ta-C coating: The substrate in step S2 where the sputtered CrC transition layer was placed in front of the graphite target, and the ta-C coating was obtained by pulsed multi-target magnetron sputtering with a power of 5-8kW. In step S3, a reverse voltage of 250-550 V and a frequency of 5000 Hz are applied at the end of the pulse period; The conditions for obtaining the CrN underlayer by pulse reactive sputtering in step S1 include: pulse frequency 1000-2000 Hz, pulse width 100-200 μs, maximum peak current 300 A, gas pressure 0.4-0.8 Pa, Ar gas flow rate 100-250 sccm, and N2 gas flow rate 75-150 sccm. The conditions for obtaining the CrC transition layer by pulse reactive sputtering in step S2 include: pulse frequency 2500-5000 Hz, pulse width 50-200 μs, maximum peak current 300 A, gas pressure 0.4-0.8 Pa, and Ar gas flow rate 100-250 sccm. The conditions for obtaining the ta-C coating by pulsed multi-target magnetron sputtering in step S3 include: pulse frequency of 5000 Hz; Ar gas flow rate of 50-250 sccm and gas pressure range of 0.4-0.8 Pa; maximum peak current of 300 A; and temperature range of 80-105℃.

2. The method for preparing a tetrahedral amorphous carbon film ta-C multilayer structure coating based on reverse positive pulse technology according to claim 1, characterized in that, The cleaning method for the substrate includes: after polishing the substrate, ultrasonic cleaning is performed sequentially using anhydrous alcohol and acetone, followed by vacuuming to 6×10⁻⁶. -3 After Pa, Ar gas with a flow rate of 200 sccm is introduced to maintain a vacuum of 0.4-0.8 Pa, and ion bombardment with a power of 1000-1500 W is carried out for 45 min.

3. A ta-C multilayer coating prepared by the method of preparing a tetrahedral amorphous carbon film ta-C multilayer structure coating based on reverse positive pulse technology as described in claim 1 or 2.

4. The ta-C multilayer structure coating according to claim 3, characterized in that, The thickness of the CrN bottom layer is 0.5-1.0 μm, the thickness of the CrC transition layer is 0.2-0.5 μm, and the thickness of the ta-C layer is 0.4-1.0 μm.

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