Wear-resistant, corrosion-resistant and high-toughness coating structure and preparation method thereof

Abstract

The invention discloses a wear-resistant anti-corrosion high-toughness coating structure and a preparation method thereof, and relates to the technical field of coating preparation, and the coating structure comprises a binding force layer formed on the surface of a base material; the tungsten carbide layer is formed on the surface of the binding force layer; the carbon layer is formed on the surface of the tungsten carbide layer; the binding force layer is made of chromium and / or titanium. The coating structure provided by the invention contains the carbon layer, so that the coating structure shows better toughness and impact resistance. Meanwhile, due to the addition of the carbon layer, the lubricity of the coating is improved, the friction coefficient of the surface of the coating is reduced, and the coating can be conveniently applied to the application fields needing wear resistance and toughness at the same time, such as various high-load mechanical parts, sliding surfaces and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of coating preparation, and in particular to a wear-resistant, corrosion-resistant and high-toughness coating structure and a preparation method thereof. Background Art

[0002] In tribology and machining applications (such as steel and alloy processing), the demand for coating materials with specific properties is increasing. Tungsten carbide (WC) coatings prepared by physical vapor deposition (PVD) technology have become a widely used coating material due to their excellent hardness, unique tribological properties and good chemical inertness. Although tungsten carbide coatings have extremely high hardness and wear resistance, they are relatively brittle and easily cracked under high impact or high stress conditions.

[0003] Therefore, how to provide a wear-resistant and corrosion-resistant coating structure with high toughness and good impact resistance and a preparation method thereof has become a difficult problem to be solved urgently by those skilled in the art. Summary of the invention

[0004] The purpose of the present invention is to provide a wear-resistant, corrosion-resistant and high-toughness coating structure and a preparation method thereof, so as to solve the problem that the existing tungsten carbide coating has low toughness and is easy to break under high impact or high stress conditions.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a wear-resistant, corrosion-resistant and high-toughness coating structure, comprising:

[0007] A bonding layer is formed on the surface of the substrate;

[0008] A tungsten carbide layer is formed on the surface of the bonding layer;

[0009] A carbon layer formed on the surface of the tungsten carbide layer;

[0010] The bonding layer is made of chromium and / or titanium.

[0011] Preferably, the thickness of the bonding layer is 500 nm.

[0012] Preferably, the thickness of the tungsten carbide layer is 4 μm.

[0013] Preferably, the thickness of the carbon layer is 500 nm.

[0014] The present invention also provides a method for preparing a wear-resistant, corrosion-resistant and high-toughness coating structure, comprising the following steps:

[0015] Step 1: placing the substrate in a vacuum chamber and evacuating the vacuum chamber;

[0016] Step 2: performing an ion cleaning operation on the surface of the substrate in the vacuum chamber;

[0017] Step 3: performing surface activation treatment on the substrate after ion cleaning;

[0018] Step 4: preparing a bonding layer on the substrate after surface activation treatment;

[0019] Step 5: sputtering a tungsten carbide target on the bonding layer to obtain a tungsten carbide layer;

[0020] Step six: preparing a carbon layer on the tungsten carbide layer.

[0021] Preferably, the substrate in step 1 includes a tool substrate and a non-tool substrate, the tool substrate includes a boring tool, and the non-tool substrate includes stainless steel, a bearing and a silicon wafer; after the vacuum chamber is evacuated, the air pressure in the vacuum chamber is 1×10 -4 Pa.

[0022] Preferably, in the step 2, when the non-tool substrate is subjected to ion cleaning, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, the pressure of the argon gas in the vacuum chamber is maintained at 0.8-1.4 Pa, a negative bias voltage of -500 to -800 V is applied to the substrate 2 to discharge clean the surface of the substrate 2, and the cleaning time is 1 to 2 hrs;

[0023] When the tool substrate is subjected to ion cleaning, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, the pressure of the argon gas in the vacuum chamber is maintained at 0.8-1.4 Pa, and a negative bias voltage of -500 to -800 V is applied to the substrate 2 to discharge clean the surface of the substrate 2, and the cleaning time is 30-60 minutes.

[0024] Preferably, in the step 3, when the non-tool substrate is subjected to surface activation treatment, the pressure of the vacuum chamber is maintained at 0.6-1.4 Pa, the titanium target is sputtered at a power of 8-10 kW, the micro-pulse on time is 4-10 μs, the off time is 50 μs, the negative bias voltage is set to -400 to -500 V, the sample stage speed is 3 rpm, and the total sputtering time is 10 min;

[0025] When the tool substrate is subjected to surface activation treatment, the pressure of the vacuum chamber is maintained at 0.6-1.4 Pa, the target is sputtered at a power of 8-10 kW, the micro-pulse on time is 2-10 ms, the off time is 60 ms, the negative bias voltage is set to -500 to -800 V, the sample stage speed is 2 rpm, and the total sputtering time is 10 min.

[0026] Preferably, in the step 4, when the bonding layer is prepared for the non-tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, so that the pressure of the argon gas in the vacuum chamber is maintained at 0.6-1.4 Pa, the titanium target is sputtered at a power of 6-10 kW, the micro-pulse on time is 4-10 μs, the off time is 50 μs, the negative bias voltage is set at -100--300 V, the temperature in the vacuum chamber is 200° C., the sample stage speed is 1-3 rpm, and the total sputtering time of the titanium target is 5 min;

[0027] When preparing the bonding layer for the tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120sccm, so that the pressure of the argon gas in the vacuum chamber is maintained at 0.8-1.5Pa, and the titanium target is sputtered at a power of 8-10kW. The micro-pulse opening time is 2-8μs, the closing time is 30μs, the negative bias voltage is set at -100-300V, the sample stage rotation speed is 1-3rpm, and the total sputtering time of the titanium target is 10min.

[0028] Preferably, in the step 5, when the tungsten carbide layer is prepared on the non-tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, so that the argon gas pressure in the vacuum chamber is maintained at 0.5-1 Pa, the tungsten carbide target is sputtered at a power of 6-10 kW, the micro-pulse on time is 10-20 μs, the off time is 50 μs, the negative bias voltage is set to -100-300 V, the temperature in the vacuum chamber is 200 ° C, the sample stage speed is 1-3 rpm, and the total sputtering time of the tungsten carbide target is 30 min;

[0029] When preparing the tungsten carbide layer on the tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, so that the argon gas pressure in the vacuum chamber is maintained at 0.8-1.5 Pa, the tungsten carbide target is sputtered at a power of 8-10 kW, the micro-pulse opening time is 2-8 ms, the closing time is 30 ms, the negative bias voltage is set to -300-500 V, the sample stage speed is 1-3 rpm, and the total sputtering time of the tungsten carbide target is 30 min;

[0030] In the step six, when the carbon layer is prepared on the non-tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, so that the pressure of the argon gas in the vacuum chamber is maintained at 0.6-1.4 Pa, the carbon target is sputtered at a power of 6-10 kW, the micro-pulse opening time is 10-20 μs, the closing time is 50 μs, the negative bias voltage is set to -100-300 V, the temperature in the vacuum chamber is 200° C., the sample stage speed is 1-3 rpm, and the total sputtering time of the carbon target is 5 min;

[0031] When preparing a carbon layer for the tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120sccm so that the pressure of the argon gas in the vacuum chamber is maintained at 0.8-1.5Pa, and the carbon target is sputtered at a power of 8-10kW, with a micro-pulse on time of 2-8μs, an off time of 30μs, a negative bias voltage of -100-300V, a sample stage speed of 1-3rpm, and a total sputtering time of the carbon target of 10min.

[0032] Compared with the prior art, the beneficial technical effects of the present invention are:

[0033] The present invention provides a wear-resistant, corrosion-resistant and highly tough coating structure, comprising a bonding layer formed on the surface of a substrate; a tungsten carbide layer formed on the surface of the bonding layer; a carbon layer formed on the surface of the tungsten carbide layer; the bonding layer is composed of chromium and / or titanium. The coating structure of the present invention exhibits better toughness and impact resistance due to the carbon layer. At the same time, the addition of the carbon layer improves the lubricity of the coating and reduces the friction coefficient of the coating surface, making it easier for the coating of the present invention to be used in application fields that require both wear resistance and toughness, such as various high-load mechanical parts, sliding surfaces, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described below in conjunction with the accompanying drawings.

[0035] Figure 1 This is a schematic diagram of the structure of the wear-resistant, corrosion-resistant and high-toughness coating of the present invention;

[0036] Figure 2 The hardness test data of the present invention on the non-tool substrate covered with the coating structure;

[0037] Figure 3 The friction test data of the present invention on a non-tool substrate covered with a coating structure;

[0038] Figure 4 The hardness test data of the tool substrate covered with the coating structure of the present invention.

[0039] Explanation of reference numerals: 1. bonding layer; 2. substrate; 3. tungsten carbide layer; 4. carbon layer. DETAILED DESCRIPTION

[0040] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] like Figure 1 As shown, the present invention provides a wear-resistant, corrosion-resistant and high-toughness coating structure, comprising:

[0042] A bonding layer 1 is formed on the surface of a substrate 2;

[0043] A tungsten carbide layer 3 is formed on the surface of the bonding layer 1;

[0044] A carbon layer 4 is formed on the surface of the tungsten carbide layer 3;

[0045] The bonding layer 1 is made of chromium and / or titanium.

[0046] Specifically, the thickness of the bonding layer 1 is 500 nm.

[0047] Specifically, the thickness of the tungsten carbide layer 3 is 4 μm.

[0048] Specifically, the thickness of the carbon layer 4 is 500 nm.

[0049] The present invention also provides a method for preparing a wear-resistant, corrosion-resistant and high-toughness coating structure, comprising the following steps:

[0050] Step 1: placing the substrate 2 in a vacuum chamber and evacuating the vacuum chamber;

[0051] Step 2: performing ion cleaning operation on the surface of the substrate 2 in the vacuum chamber;

[0052] Step 3: performing surface activation treatment on the substrate 2 after ion cleaning;

[0053] Step 4: preparing a bonding layer 1 on the substrate 2 after surface activation treatment;

[0054] Step 5: sputtering a tungsten carbide target on the bonding layer 1 to obtain a tungsten carbide layer 3;

[0055] Step six: preparing a carbon layer 4 on the tungsten carbide layer 3 .

[0056] The purpose of step 2 is to use plasma to deeply clean the surface of the workpiece, remove organic pollutants, oil stains, oxides, etc. on the surface, so as to improve the quality of subsequent coating. The purpose of treating the target surface in step 3 is to improve its activity, thereby optimizing the sputtering efficiency and film quality process.

[0057] Specifically, the substrate 2 in step 1 includes a tool substrate and a non-tool substrate, the tool substrate includes a boring tool, and the non-tool substrate includes stainless steel, a bearing, and a silicon wafer; after the vacuum chamber is evacuated, the air pressure in the vacuum chamber is 1×10 -4 Pa.

[0058] Specifically, in the step 2, when the non-tool substrate is subjected to ion cleaning, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, the pressure of the argon gas in the vacuum chamber is maintained at 0.8-1.4 Pa, and a negative bias voltage of -500 to -800 V is applied to the substrate 2 to discharge clean the surface of the substrate 2, and the cleaning time is 1 to 2 hrs;

[0059] When the tool substrate is subjected to ion cleaning, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, the pressure of the argon gas in the vacuum chamber is maintained at 0.8-1.4 Pa, and a negative bias voltage of -500 to -800 V is applied to the substrate 2 to discharge clean the surface of the substrate 2, and the cleaning time is 30-60 minutes.

[0060] Specifically, in the step 3, when the non-tool substrate is subjected to surface activation treatment, the pressure of the vacuum chamber is maintained at 0.6-1.4 Pa, the titanium target is sputtered at a power of 8-10 kW, the micro-pulse on time is 4-10 μs, the off time is 50 μs, the negative bias voltage is set to -400 to -500 V, the sample stage speed is 3 rpm, and the total sputtering time is 10 min;

[0061] When the tool substrate is subjected to surface activation treatment, the air pressure of the vacuum chamber is maintained at 0.6-1.4 Pa, the titanium target is sputtered at a power of 8-10 kW, the micro-pulse on time is 2-10 ms, the off time is 60 ms, the negative bias voltage is set to -500 to -800 V, the sample stage speed is 2 rpm, and the total sputtering time is 10 min.

[0062] Specifically, in the step 4, when the bonding layer 1 is prepared for the non-tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, so that the pressure of the argon gas in the vacuum chamber is maintained at 0.6-1.4 Pa, the titanium target is sputtered at a power of 6-10 kW, the micro-pulse on time is 4-10 μs, the off time is 50 μs, the negative bias voltage is set at -100--300 V, the temperature in the vacuum chamber is 200° C., the sample stage speed is 1-3 rpm, and the total sputtering time of the titanium target is 5 min;

[0063] When preparing the bonding layer 1 for the tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120sccm, so that the pressure of the argon gas in the vacuum chamber is maintained at 0.8-1.5Pa, and the titanium target is sputtered at a power of 8-10kW, the micro-pulse opening time is 2-8μs, the closing time is 30μs, the negative bias voltage is set at -100-300V, the sample stage rotation speed is 1-3rpm, and the total sputtering time of the titanium target is 10min.

[0064] Specifically, in the step 5, when the tungsten carbide layer 3 is prepared on the non-tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, so that the argon gas pressure in the vacuum chamber is maintained at 0.5-1 Pa, the tungsten carbide target is sputtered at a power of 6-10 kW, the micro-pulse on time is 10-20 μs, the off time is 50 μs, the negative bias voltage is set to -100-300 V, the temperature in the vacuum chamber is 200 ° C, the sample stage speed is 1-3 rpm, and the total sputtering time of the tungsten carbide target is 30 min;

[0065] When preparing the tungsten carbide layer 3 for the tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, so that the argon gas pressure in the vacuum chamber is maintained at 0.8-1.5 Pa, and the tungsten carbide target is sputtered at a power of 8-10 kW, the micro-pulse opening time is 2-8 ms, the closing time is 30 ms, the negative bias voltage is set to -300-500 V, the sample stage speed is 1-3 rpm, and the total sputtering time of the tungsten carbide target is 30 min;

[0066] In the step 6, when the carbon layer 4 is prepared on the non-tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, so that the pressure of the argon gas in the vacuum chamber is maintained at 0.6-1.4 Pa, the carbon target is sputtered at a power of 6-10 kW, the micro-pulse opening time is 10-20 μs, the closing time is 50 μs, the negative bias voltage is set to -100-300 V, the temperature in the vacuum chamber is 200° C., the sample stage speed is 1-3 rpm, and the total sputtering time of the carbon target is 5 min;

[0067] When preparing the carbon layer 4 on the tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120sccm, so that the pressure of the argon gas in the vacuum chamber is maintained at 0.8-1.5Pa, and the carbon target is sputtered at a power of 8-10kW, the micro-pulse opening time is 2-8μs, the closing time is 30μs, the negative bias voltage is set to -100~-300V, the sample stage rotation speed is 1~3rpm, and the total sputtering time of the carbon target is 10min.

[0068] It has been found through testing that the fracture toughness of the non-tool substrate covered with the coating provided by the present invention is greater than 3 MPa·m 1 / 2 . And from Figure 2 It can be seen from the figure that the surface hardness of the coating of the present invention reaches 40 GPa. Figure 3 It shows that under the conditions of a load of 3N and a frequency of 1Hz, the coating exhibits a stable ultra-low friction coefficient, and its friction coefficient value is maintained at around 0.07.

[0069] It is found through testing that the hardness value of the tool substrate covered with the coating provided by the present invention is HV4200. Figure 4It is shown that the surface hardness of the tool substrate covered with the coating provided by the present invention is as high as 60 GPa.

[0070] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0071] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A wear-resistant, corrosion-resistant and high-toughness coating structure, characterized in that: include: A bonding layer (1) is formed on the surface of a substrate (2); A tungsten carbide layer (3) formed on the surface of the bonding layer (1); A carbon layer (4) formed on the surface of the tungsten carbide layer (3); The bonding layer (1) is made of chromium and / or titanium.

2. The wear-resistant, corrosion-resistant and high-toughness coating structure according to claim 1 is characterized in that: The thickness of the bonding layer (1) is 500 nm.

3. The wear-resistant, corrosion-resistant and high-toughness coating structure according to claim 2 is characterized in that: The thickness of the tungsten carbide layer (3) is 4 μm.

4. The wear-resistant, corrosion-resistant and high-toughness coating structure according to claim 3 is characterized in that: The thickness of the carbon layer (4) is 500 nm.

5. A method for preparing a wear-resistant, corrosion-resistant and high-toughness coating structure, characterized in that: The following steps are involved: Step 1: placing the substrate (2) in a vacuum chamber and evacuating the vacuum chamber; Step 2: performing an ion cleaning operation on the surface of the substrate (2) in the vacuum chamber; Step 3: performing surface activation treatment on the substrate (2) after ion cleaning; Step 4: preparing a bonding layer (1) on the substrate (2) after surface activation treatment; Step 5: sputtering a tungsten carbide target on the bonding layer (1) to obtain a tungsten carbide layer (3); Step six: preparing a carbon layer (4) on the tungsten carbide layer (3).

6. The method for preparing the wear-resistant, corrosion-resistant and high-toughness coating structure according to claim 5, characterized in that: The substrate (2) in step 1 includes a tool substrate and a non-tool substrate, wherein the tool substrate includes a boring tool, and the non-tool substrate includes stainless steel, a bearing, and a silicon wafer; after the vacuum chamber is evacuated, the air pressure in the vacuum chamber is 1×10 - 4 Pa.

7. The method for preparing the wear-resistant, corrosion-resistant and high-toughness coating structure according to claim 6, characterized in that: In the step 2, when the non-tool substrate is subjected to ion cleaning, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, the pressure of the argon gas in the vacuum chamber is maintained at 0.8-1.4 Pa, and a negative bias voltage of -500 to -800 V is applied to the substrate (2) to discharge clean the surface of the substrate (2), and the cleaning time is 1 to 2 hrs; When the tool substrate is subjected to ion cleaning, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, the pressure of the argon gas in the vacuum chamber is maintained at 0.8-1.4 Pa, and a negative bias voltage of -500 to -800 V is applied to the substrate (2) to discharge clean the surface of the substrate (2), and the cleaning time is 30-60 minutes.

8. The method for preparing the wear-resistant, corrosion-resistant and high-toughness coating structure according to claim 6, characterized in that: In the step 3, when the non-tool substrate is subjected to surface activation treatment, the pressure of the vacuum chamber is maintained at 0.6-1.4 Pa, the titanium target is sputtered at a power of 8-10 kW, the micro-pulse on time is 4-10 μs, the off time is 50 μs, the negative bias voltage is set to -400 to -500 V, the sample stage speed is 3 rpm, and the total sputtering time is 10 min; When the tool substrate is subjected to surface activation treatment, the air pressure of the vacuum chamber is maintained at 0.6-1.4 Pa, the titanium target is sputtered at a power of 8-10 kW, the micro-pulse on time is 2-10 ms, the off time is 60 ms, the negative bias voltage is set to -500 to -800 V, the sample stage speed is 2 rpm, and the total sputtering time is 10 min.

9. The method for preparing the wear-resistant, corrosion-resistant and high-toughness coating structure according to claim 6, characterized in that: In the step 4, when the bonding layer (1) is prepared for the non-tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, so that the pressure of the argon gas in the vacuum chamber is maintained at 0.6-1.4 Pa, the titanium target is sputtered at a power of 6-10 kW, the micro-pulse on time is 4-10 μs, the off time is 50 μs, the negative bias voltage is set at -100--300 V, the temperature in the vacuum chamber is 200° C., the sample stage rotation speed is 1-3 rpm, and the total sputtering time of the titanium target is 5 min; When preparing the bonding layer (1) for the tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm so that the pressure of the argon gas in the vacuum chamber is maintained at 0.8-1.5 Pa, and the titanium target is sputtered at a power of 8-10 kW, the micro-pulse on time is 2-8 μs, the off time is 30 μs, the negative bias voltage is set at -100--300 V, the sample stage rotation speed is 1-3 rpm, and the total sputtering time of the titanium target is 10 min.

10. The method for preparing the wear-resistant, corrosion-resistant and high-toughness coating structure according to claim 6, characterized in that: In the step 5, when preparing the tungsten carbide layer (3) on the non-tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, so that the argon gas pressure in the vacuum chamber is maintained at 0.5-1 Pa, the tungsten carbide target is sputtered at a power of 6-10 kW, the micro-pulse on time is 10-20 μs, the off time is 50 μs, the negative bias voltage is set to -100--300 V, the temperature in the vacuum chamber is 200° C., the sample stage speed is 1-3 rpm, and the total sputtering time of the tungsten carbide target is 30 min; When preparing the tungsten carbide layer (3) on the tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, so that the argon gas pressure in the vacuum chamber is maintained at 0.8-1.5 Pa, the tungsten carbide target is sputtered at a power of 8-10 kW, the micro-pulse on time is 2-8 ms, the off time is 30 ms, the negative bias voltage is set to -300-500 V, the sample stage speed is 1-3 rpm, and the total sputtering time of the tungsten carbide target is 30 minutes; In the step 6, when the carbon layer (4) is prepared on the non-tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm, so that the pressure of the argon gas in the vacuum chamber is maintained at 0.6-1.4 Pa, the carbon target is sputtered at a power of 6-10 kW, the micro-pulse on time is 10-20 μs, the off time is 50 μs, the negative bias voltage is set to -100--300 V, the temperature in the vacuum chamber is 200° C., the sample stage speed is 1-3 rpm, and the total sputtering time of the carbon target is 5 min; When preparing the carbon layer (4) on the tool substrate, argon gas is introduced into the vacuum chamber at a flow rate of 80-120 sccm so that the pressure of the argon gas in the vacuum chamber is maintained at 0.8-1.5 Pa, and the carbon target is sputtered at a power of 8-10 kW, with a micro-pulse on time of 2-8 μs, an off time of 30 μs, a negative bias voltage of -100-300 V, a sample stage rotation speed of 1-3 rpm, and a total sputtering time of the carbon target of 10 min.

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