Diamond / DLC heterogeneous composite coating and preparation method and application thereof

Abstract

The invention discloses a diamond / DLC heterogeneous composite coating and a preparation method and application thereof, and belongs to the technical field of composite coatings, the diamond / DLC heterogeneous composite coating sequentially comprises a base body, a micron diamond base layer with the thickness of 2-10 microns, a nano diamond middle layer with the thickness of 1-5 microns and a DLC surface layer with the thickness of 0.1-1.0 microns from bottom to top; the preparation method comprises the following steps: sequentially depositing the micron diamond base layer and the nano diamond middle layer on the surface of the substrate by adopting a chemical vapor deposition (CVD) method, then forming the DLC surface layer on the nano diamond middle layer by utilizing a physical vapor deposition (PVD) method, and finally preparing the diamond / DLC heterogeneous composite coating. The diamond / DLC heterogeneous composite coating disclosed by the invention has high binding force, low friction coefficient and self-lubricating property, and has a good application prospect in the aspects of expansion type products, cutting tools and the like.

Description

Technical Field

[0001] This invention belongs to the field of composite coating technology, and particularly relates to a diamond / DLC heterogeneous composite coating, its preparation method and application. Background Technology

[0002] Micron-diamond undercoating, due to its extremely high hardness, excellent wear resistance, and good interfacial adhesion with the cemented carbide substrate, has been widely used in critical components under high-wear conditions such as cutting tools and wire drawing dies, becoming an important means to improve tool life and machining efficiency. However, in practical applications, micron-diamond undercoating still has some significant technical defects that limit its further promotion and use. One of the most prominent problems is its relatively high surface roughness, resulting in a high coefficient of friction between the coating and the abrasive material. A high coefficient of friction not only increases frictional resistance during machining and reduces machining efficiency, but also generates large interfacial shear stress between the coating and the substrate, thereby inducing interface cracking, peeling, and other failure behaviors, seriously affecting the service life and stability of coated tools.

[0003] In contrast, while nanodiamond coatings have a significantly lower surface roughness than micron-diamonds, giving them an advantage in friction performance, their hardness is only 40%–60% of that of micron-diamonds, and their interfacial adhesion to the substrate is weak, making it difficult to meet the requirements of high-stress, high-wear conditions. Furthermore, nanodiamond coatings are prone to particle agglomeration and porous structures during preparation, further affecting their overall mechanical properties.

[0004] On the other hand, although DLC (diamond-like carbon) coatings are less hard than nanodiamonds, they have an extremely low coefficient of friction (typically between 0.05 and 0.15) and excellent self-lubricating properties, thus performing well in friction reduction and wear resistance. However, DLC coatings exhibit significant internal stress during deposition, especially at the interface with the substrate, where stress concentration is prone to occur. This leads to problems such as cracking and peeling during use, limiting their application in high-intensity, high-load processing environments.

[0005] In summary, single-structure diamond or DLC coatings all have certain performance limitations in practical applications. While micron-diamond undercoats offer high hardness and good adhesion, they suffer from surface roughness and a high coefficient of friction. Nanodiamond coatings, although relatively smooth, lack sufficient hardness and adhesion. DLC coatings, while possessing excellent friction-reducing properties, suffer from high internal stress and are prone to cracking. Therefore, in the processing of products with high performance requirements, such as bulging tools or molds under complex conditions, single-structure coatings struggle to simultaneously meet the comprehensive demands of high hardness, high adhesion, low coefficient of friction, and good wear resistance. This has prompted researchers to explore more rational composite coating structure designs to achieve complementary and synergistic performance advantages, thereby improving the overall service performance and engineering application value of the coatings. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a diamond / DLC heterogeneous composite coating, its preparation method, and its applications. The diamond / DLC heterogeneous composite coating disclosed in this invention exhibits high adhesion, low coefficient of friction, and self-lubricating properties, showing promising application prospects in bulging products and cutting tools.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A diamond / DLC heterogeneous composite coating, comprising, from bottom to top:

[0009] Matrix

[0010] Micron-sized diamond substrate with a thickness of 2–10 μm.

[0011] The nanodiamond interlayer has a thickness of 1–5 μm.

[0012] The DLC surface layer has a thickness of 0.1–1.0 μm.

[0013] Optionally, the micron-sized diamond substrate has a thickness of 2-8 μm.

[0014] The nanodiamond interlayer has a thickness of 1-4 μm.

[0015] The DLC surface layer has a thickness of 0.1-0.6 μm.

[0016] Optionally, the micron-sized diamond substrate has a thickness of 5 μm.

[0017] The nanodiamond interlayer is 3μm thick.

[0018] The DLC surface layer has a thickness of 0.3 μm.

[0019] Optionally, the substrate is a cemented carbide substrate.

[0020] Furthermore, the substrate needs to be sandblasted and passivated, followed by ultrasonic cleaning.

[0021] Optionally, the diamond / DLC heterogeneous composite coating has a hardness of 84-92 GPa, a friction coefficient of 0.05-0.08, and a wear rate of (2-3.8)×10⁻⁶. -16 m 3 / Nm.

[0022] The preparation method of the above-mentioned diamond / DLC heterocomposite coating includes the following steps:

[0023] A micron-sized diamond underlayer and a nano-diamond intermediate layer are sequentially deposited on the substrate surface using chemical vapor deposition (CVD). Then, a DLC surface layer is formed on the nano-diamond intermediate layer using physical vapor deposition (PVD), thus finally preparing the diamond / DLC heterocomposite coating.

[0024] Optionally, the deposition conditions for the micron-sized diamond underlayer are as follows:

[0025] The gas source is hydrogen and methane, the carbon source flow rate accounts for 1-5% of the total gas source flow rate, the substrate temperature is 900-1100℃, the deposition time is 2-10h, the gas pressure inside the furnace is 600-2000Pa, the distance between the workpiece and the hot wire is 10-20mm, and the hot wire power is 6-10kW.

[0026] Optionally, the deposition conditions for the nanodiamond intermediate layer are as follows:

[0027] The gas source is hydrogen and methane, the carbon source flow rate accounts for 2-9% of the total gas source flow rate, the deposition temperature is 800-1100℃, the deposition time is 1-5h, the gas pressure in the furnace is 2000-5000Pa, the distance between the workpiece and the hot wire is 10-20mm, the hot wire power is 5-8kW, and the deposition temperature is 800-1100℃ for the substrate with the micron diamond underlayer.

[0028] Optionally, the deposition conditions for the DLC surface layer are:

[0029] The target material is graphite; the deposition temperature is 350–450℃, the nitrogen pressure is 0.5–3.0 Pa; the target current is 100–180 A; the substrate negative bias voltage is -120–-40 V; the deposition time is 10–100 min; and the deposition temperature is 350–450℃ for the substrate with the nanodiamond interlayer deposited.

[0030] Optionally, the method for preparing the diamond / DLC heterogeneous composite coating includes the following steps:

[0031] A 5μm diamond underlayer was deposited on the substrate surface using CVD. The process parameters were as follows: the gas source was hydrogen and methane, the carbon source flow rate was 2% of the total gas source flow rate, the substrate temperature was 950℃, the deposition time was 5h, the gas pressure in the furnace was 1500Pa, the distance between the workpiece and the hot wire was 15mm, and the hot wire power was 8kW.

[0032] A 3μm nanodiamond intermediate layer was deposited on the micron-diamond substrate using CVD. The process parameters were as follows: the gas source was hydrogen and methane, the carbon source flow rate accounted for 6% of the total gas source flow rate, the substrate temperature was 950℃, the deposition time was 3h, the gas pressure in the furnace was 3000Pa, the distance between the workpiece and the hot wire was 15mm, and the hot wire power was 8kW.

[0033] A 0.3 μm DLC surface layer was deposited on the nanodiamond intermediate layer using PVD. The process parameters were: substrate temperature of 400℃, argon pressure of 2.0 Pa, target current of 160 A, substrate negative bias of -80 V, and deposition time of 30 min. The diamond / DLC heterocomposite coating was finally prepared.

[0034] The present invention also provides the application of the above-mentioned diamond / DLC heterogeneous composite coating in the field of metal parts processing.

[0035] Compared with the prior art, the present invention has the following advantages and technical effects:

[0036] (1) The diamond / DLC heterogeneous composite coating of the present invention comprises, from bottom to top, a CVD micron diamond substrate, a CVD nano diamond intermediate layer, and a DLC surface layer. The coating hardness is improved by utilizing the bonding strength and hardness of the CVD micron diamond substrate; the surface roughness of the micron diamond is reduced by utilizing the CVD nano diamond, thus reducing the coefficient of friction; and the PVD DLC surface layer further reduces the surface roughness and coefficient of friction of the composite coating and provides a self-lubricating effect.

[0037] (2) The diamond / DLC heterocomposite coating prepared by this invention has high hardness and adhesion, excellent wear resistance and low coefficient of friction. The expansion head or expansion tool prepared with the coating has excellent service performance. In addition, the diamond / DLC heterocomposite coating prepared by this invention can also be used in other cemented carbide substrates to improve the hardness and wear resistance of the substrate. Attached Figure Description

[0038] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0039] Figure 1This is a surface morphology image of the nanodiamond intermediate layer after a DLC coating has been deposited on it, as shown in Example 1 of the present invention.

[0040] Figure 2 This is a surface morphology diagram of the coating in Comparative Example 1;

[0041] Figure 3 The image shows the surface morphology of the coating in Comparative Example 2. Detailed Implementation

[0042] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0044] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0045] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0046] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0047] This invention provides a diamond / DLC heterogeneous composite coating, comprising, from bottom to top, a CVD micron diamond underlayer, a CVD nano diamond intermediate layer, and a PVD DLC surface layer.

[0048] Among them, the thickness of the CVD micron diamond substrate is 2 to 10 μm;

[0049] The thickness of the CVD nanodiamond interlayer is 1–5 μm;

[0050] The thickness of the DLC surface layer is 0.1–1.0 μm.

[0051] This invention also proposes a method for preparing the above-mentioned diamond / DLC heterocomposite coating, comprising the following steps:

[0052] On the substrate surface, a micron-sized diamond underlayer and a nano-diamond intermediate layer are prepared sequentially using chemical vapor deposition (CVD), and then a DLC surface layer is prepared using PVD (physical vapor deposition).

[0053] The performance of diamond / DLC heterocomposite coatings depends on the synergistic effect of each layer's function. The "nucleation-reinforcement" of the micron-diamond interface, the "leveling-reinforcement" of the nano-diamond surface, and the "self-lubrication-friction reduction" of the DLC surface layer form a progressive protective system. Changing the preparation sequence will disrupt the functional matching between layers, leading to weakened interfacial bonding, increased friction coefficient and surface roughness, ultimately resulting in a comprehensive deterioration of coating performance. Specifically:

[0054] If a CVD nanodiamond interlayer is first deposited, followed by a CVD microdiamond interlayer and a DLC surface layer, the interfacial adhesion between the nanodiamond and the substrate is poor, resulting in low interfacial bonding. Furthermore, the SP content in the nanodiamond... 2 High graphite content reduces SP content in subsequent micron-sized diamonds. 3 The content of diamond bonds (diamond bonds) leads to a significant reduction in the hardness of micron-sized diamonds;

[0055] If the DLC surface layer is brought into contact with the substrate, and CVD micron diamond is subsequently deposited, the deposition temperature of CVD micron diamond is much higher than that of PVD DLC. This causes the DLC microstructure to graphitize during the subsequent CVD deposition, which in turn affects the nucleation and growth of micron diamond, significantly reducing the hardness and adhesion of the coating. Such structural changes will lead to a significant reduction in the service performance of the coated product.

[0056] In some alternative embodiments, the CVD deposition process parameters for preparing the micron-sized diamond underlayer include:

[0057] The gas source is hydrogen and methane, the carbon source flow rate accounts for 1-5% of the total gas source flow rate, the substrate temperature is 900-1100℃, the deposition time is 2-10h, the gas pressure inside the furnace is 600-2000Pa, the distance between the workpiece and the hot wire is 10-20mm, and the hot wire power is 6-10kW.

[0058] In some alternative embodiments, the CVD deposition process parameters for preparing the nanodiamond interlayer include:

[0059] The gas source is hydrogen and methane, the carbon source flow rate accounts for 2-9% of the total gas source flow rate, the substrate temperature is 800-1100℃, the deposition time is 1-5h, the gas pressure inside the furnace is 2000-5000Pa, the distance between the workpiece and the hot wire is 10-20mm, and the hot wire power is 5-8kW.

[0060] In some alternative embodiments, the PVD deposition process parameters for preparing the DLC surface layer include:

[0061] The target material is graphite; the substrate temperature is 350–450℃; the nitrogen pressure is 0.5–3.0 Pa; the target current is 100–180 A; the substrate negative bias voltage is -120–-40 V; and the deposition time is 10–100 min.

[0062] In some alternative embodiments, the substrate needs to be ultrasonically cleaned.

[0063] In some alternative embodiments, the equipment used in physical vapor deposition and chemical vapor deposition are commonly used equipment in the art. For example, physical vapor deposition is performed using an arc ion plating device.

[0064] All raw materials used in this invention were purchased commercially. The cemented carbide workpieces used in the following embodiments are YG6 cemented carbide.

[0065] The technical solution of the present invention is further illustrated by the following examples.

[0066] Example 1

[0067] A method for preparing a diamond / DLC heterogeneous composite coating includes the following steps:

[0068] (1) The cemented carbide workpiece is used as the substrate for sandblasting passivation, and then ultrasonic cleaning is performed.

[0069] (2) On the surface of the cemented carbide workpiece, a micron-sized diamond underlayer is deposited on the substrate surface using the CVD method. The specific process parameters are as follows: the gas source is hydrogen and methane, the carbon source flow rate (i.e., methane flow rate) accounts for 2% of the total gas source flow rate, the substrate temperature is 950℃, the deposition time is 5h, the gas pressure in the furnace is 1500Pa, the distance between the workpiece and the hot wire is 15mm, and the power of the hot wire is 8kW. Through the above process, a micron-sized diamond underlayer with a thickness of 5μm is prepared.

[0070] (3) After step (2) is completed, a nanodiamond intermediate layer is deposited using the CVD method. The specific process parameters are as follows: the gas source is hydrogen and methane, the carbon source flow rate accounts for 6% of the total gas source flow rate, the substrate temperature is 950℃, the deposition time is 3h, the gas pressure in the furnace is 3000Pa, the distance between the workpiece and the hot wire is 15mm, the hot wire power is 8kW, and the thickness of the nanodiamond intermediate layer is 3μm.

[0071] (4) Using a graphite target, a DLC surface layer was deposited on the surface of the nanodiamond intermediate layer. The deposition process parameters were: substrate temperature of 400℃, argon pressure of 2.0Pa, target current of 160A, substrate negative bias of -80V, deposition time of 30min, and DLC surface layer thickness of 0.3μm. Finally, a diamond / DLC composite coating was prepared.

[0072] Examples 2-6

[0073] (1) Consistent with Example 1;

[0074] (2) On the surface of the cemented carbide workpiece, a micron-sized diamond underlayer is deposited using the CVD method. The distance between the workpiece and the hot wire is 14 mm, the power of the hot wire is 8 kW, and other process parameters are shown in Table 1.

[0075] Table 1. Relevant deposition process parameters for CVD micron-diamond underlayer preparation in Examples 2-6.

[0076]

[0077] (3) A nano-diamond intermediate layer is deposited on the prepared micron diamond substrate. The workpiece is 14 mm away from the hot wire, and the hot wire power is 8 kW. The deposition process parameters are shown in Table 2.

[0078] Table 2. Relevant deposition process parameters for preparing CVD nanodiamond intermediate layers in Examples 2-6

[0079]

[0080] (4) A DLC surface layer was deposited on the surface of the CVD nanodiamond intermediate layer, and the process parameters are shown in Table 3.

[0081] Table 3. Relevant deposition process parameters for preparing DLC ​​surface layers in Examples 2-6

[0082]

[0083] Comparative Example 1

[0084] Commercially available CVD micron-diamond substrate with a thickness of 8.5μm.

[0085] Comparative Example 2

[0086] Commercially available CVD nanodiamond coatings have a thickness of 8.6 μm.

[0087] Comparative Example 3

[0088] Commercially available DLC coatings have a thickness of 3.2 μm.

[0089] Comparative Example 4

[0090] Same as Example 1, except that step (2) is omitted, while the parameters of other steps remain the same.

[0091] Comparative Example 5

[0092] Same as Example 1, except that step (3) is omitted, while the parameters of other steps remain the same.

[0093] Comparative Example 6

[0094] Same as Example 1, except that step (4) is omitted, while the parameters of other steps remain the same.

[0095] Comparative Example 7

[0096] Same as Example 1, except that the preparation order of steps (2) and (3) is changed, while the parameters of other steps remain the same.

[0097] Comparative Example 8

[0098] Same as Example 1, except that the preparation order of steps (2) and (4) is changed, while the parameters of other steps remain the same.

[0099] Comparative Example 9

[0100] Same as Example 1, except that the preparation order of steps (3) and (4) is changed, while the parameters of other steps remain the same.

[0101] Performance testing

[0102] The coating hardness and adhesion of Examples 1-6 and Comparative Examples 1-9 were tested using a nanoindenter and a Rockwell hardness tester.

[0103] Friction and wear tests were conducted to measure the coefficient of friction and wear rate of the coating.

[0104] A stainless steel expansion head is used to expand a 304 stainless steel pipe with a diameter of 5.5mm and a wall thickness of 1.0mm. When the shrinkage of the pipe length with a diameter of 1m is greater than 1cm, the expansion head is considered to have failed. The length of the expanded pipe is then counted to determine the service life of the coated expansion head.

[0105] The surface morphology of Example 1, Comparative Example 1 and Comparative Example 2 are as follows: Figure 1-3 As shown, the diamond / DLC composite coating has a smoother surface and an adhesion strength of HF1 (the highest level of adhesion). In comparison, micron-sized diamonds have high adhesion strength (HF1) but a rough surface; while nano-diamonds have a relatively smooth surface but poor adhesion strength (HF2).

[0106] The performance test results of the coatings in Examples 1 to 6 are shown in Table 4, and the performance test results of the coatings in Examples 1 and Comparative Examples 1 to 9 are shown in Table 5.

[0107] Table 4 shows the performance test results of the coatings in Examples 1-6.

[0108] sample Hardness / GPa Bonding force (N) Friction coefficient <![CDATA[Wear rate / (×10 -16 m 3 / Nm)]]> Expansion head life / m Example 1 91.8 HF1 0.05 2.4 6896.3 Example 2 89.5 HF1 0.05 2.8 6589.3 Example 3 89.6 HF1 0.05 3.1 6299.4 Example 4 88.7 HF2 0.06 3.3 6085.6 Example 5 86.2 HF1 0.06 3.5 5940.2 Example 6 84.1 HF1 0.08 3.8 5821.4

[0109] Table 5 Performance test results of the coatings in Example 1 and Comparative Examples 1-9

[0110] sample Hardness / GPa Bonding force (N) Friction coefficient Wear rate / Expansion head life / m Example 1 91.8 HF1 0.05 2.4 6896.3 Comparative Example 1 92.6 HF1 0.39 5.5 5021.3 Comparative Example 2 44.6 HF2 0.25 5.1 4820.5 Comparative Example 3 28.6 HF1 0.05 4.9 1020.5 Comparative Example 4 31.6 HF2 0.12 6.6 4020.5 Comparative Example 5 43.6 HF1 0.31 5.3 4020.5 Comparative Example 6 89.6 HF1 0.28 4.9 1020.5 Comparative Example 7 40.6 HF2 0.11 5.4 4021.6 Comparative Example 8 20.6 HF5 Diamond partial peeling Unable to measure Unable to measure Comparative Example 9 91.2 HF1 0.43 5.9 3945.6

[0111] As shown in Tables 4 and 5, the diamond / DLC heterogeneous composite coatings in Examples 1-6 of this invention exhibit high hardness, bonding strength, low coefficient of friction, and low wear rate. The coated heads prepared according to this invention demonstrate excellent service life when machining 304 stainless steel. In contrast, while commercial micron-sized diamonds have high hardness and layer-substrate bonding strength, they also have high coefficient of friction, high wear rate, and low service life. Commercial nano-diamonds have poor hardness, bonding strength, and wear resistance, resulting in a reduced service life for the coated products. Commercial DLC coatings also exhibit poor hardness and service life. When a step in the heterogeneous composite coating process is omitted or replaced, it becomes difficult to achieve a synergistic improvement in hardness, bonding strength, coefficient of friction, and wear resistance, significantly reducing the service life of the coated products.

[0112] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A diamond / DLC heterogeneous composite coating, characterized in that, From bottom to top, they include: Matrix Micron-sized diamond substrate with a thickness of 2–10 μm. The nanodiamond interlayer has a thickness of 1–5 μm. The DLC surface layer has a thickness of 0.1–1.0 μm.

2. The diamond / DLC heterogeneous composite coating according to claim 1, characterized in that, The micron-sized diamond substrate has a thickness of 2-8 μm. The nanodiamond interlayer has a thickness of 1-4 μm. The DLC surface layer has a thickness of 0.1-0.6 μm.

3. The diamond / DLC heterogeneous composite coating according to claim 2, characterized in that, The micron-sized diamond substrate has a thickness of 5μm. The nanodiamond interlayer is 3μm thick. The DLC surface layer has a thickness of 0.3 μm.

4. A diamond / DLC heterogeneous composite coating according to any one of claims 1-3, characterized in that, The diamond / DLC heterogeneous composite coating has a hardness of 84-92 GPa, a friction coefficient of 0.05-0.08, and a wear rate of (2-3.8)×10⁻⁶. - 16 m 3 / Nm.

5. A method for preparing a diamond / DLC heterogeneous composite coating, characterized in that, Includes the following steps: A micron-sized diamond underlayer and a nano-diamond intermediate layer are sequentially deposited on the substrate surface using chemical vapor deposition. Then, a DLC surface layer is deposited on the nano-diamond intermediate layer using physical vapor deposition, thus finally preparing the diamond / DLC heterogeneous composite coating as described in any one of claims 1-4.

6. The method for preparing a diamond / DLC heterogeneous composite coating according to claim 5, characterized in that, The deposition conditions for the micron-sized diamond underlayer are as follows: The gas source is hydrogen and methane, the carbon source flow rate accounts for 1-5% of the total gas source flow rate, the substrate temperature is 900-1100℃, the deposition time is 2-10h, the gas pressure inside the furnace is 600-2000Pa, the distance between the workpiece and the hot wire is 10-20mm, and the hot wire power is 6-10kW.

7. The method for preparing a diamond / DLC heterogeneous composite coating according to claim 5, characterized in that, The deposition conditions for the nanodiamond intermediate layer are as follows: The gas source is hydrogen and methane, the carbon source flow rate accounts for 2-9% of the total gas source flow rate, the deposition temperature is 800-1100℃, the deposition time is 1-5h, the gas pressure inside the furnace is 2000-5000Pa, the distance between the workpiece and the hot wire is 10-20mm, and the hot wire power is 5-8kW.

8. The method for preparing a diamond / DLC heterogeneous composite coating according to claim 5, characterized in that, The deposition conditions for the DLC surface layer are as follows: The target material is graphite; the deposition temperature is 350–450℃; the nitrogen pressure is 0.5–3.0 Pa; the target current is 100–180 A; the negative bias voltage is -120–-40 V; and the deposition time is 10–100 min.

9. The method for preparing a diamond / DLC heterogeneous composite coating according to claim 5, characterized in that, Specifically, the following steps are included: A 5μm diamond underlayer was deposited on the substrate surface using chemical vapor deposition. The process parameters were as follows: the gas source was hydrogen and methane, the carbon source flow rate was 2% of the total gas source flow rate, the substrate temperature was 950℃, the deposition time was 5h, the gas pressure inside the furnace was 1500Pa, the distance between the workpiece and the hot wire was 15mm, and the hot wire power was 8kW. A 3μm nanodiamond intermediate layer was deposited on the micron-sized diamond substrate using chemical vapor deposition. The process parameters were as follows: the gas source was hydrogen and methane, the carbon source flow rate accounted for 6% of the total gas source flow rate, the substrate temperature was 950℃, the deposition time was 3h, the gas pressure inside the furnace was 3000Pa, the distance between the workpiece and the hot wire was 15mm, and the hot wire power was 8kW. A 0.3 μm DLC surface layer was deposited on the nanodiamond intermediate layer using physical vapor deposition. The process parameters were: substrate temperature of 400℃, argon pressure of 2.0 Pa, target current of 160 A, substrate negative bias of -80 V, and deposition time of 30 min. The diamond / DLC heterocomposite coating was finally prepared.

10. The application of the diamond / DLC heterogeneous composite coating as described in any one of claims 1-4 in the field of metal parts processing.

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