Preparation device and method for in-situ deposition of DLC film on inner surface of metal pipe fitting after ion nitridation

Abstract

The invention discloses a preparation device and method for in-situ deposition of a DLC film on the inner surface of a metal pipe fitting after ion nitriding, and belongs to the technical field of material processes. The preparation device comprises a first air inlet pipe, a second air inlet pipe, an infrared thermometer, a vacuum chamber, and a mixed air inlet pipe, a direct-current pulse bias power supply, a sample table and a heating piece which are positioned in the vacuum chamber. The device can realize the integrated treatment of glow discharge ion nitriding and plasma chemical vapor deposition DLC film on the inner surface of the metal pipe fitting, effectively improves the binding force and surface hardness of the DLC film, reduces the equipment and operation threshold of the ion nitriding composite coating deposition technology, has the characteristics of simple equipment, low operation difficulty, high treatment efficiency and the like, and is suitable for industrial production. And large-scale industrial production is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material process, in particular to a preparation device and method for depositing DLC film on inner surface of metal pipe after ion nitriding. BACKGROUND

[0002] Metal pipe and other pipe-shaped workpieces are widely used in the fields of automobile, aerospace, petrochemical, precision mold and medical device. The inner surface of the pipe is prone to adhesive wear, fatigue wear and abrasive wear under the working conditions of high contact stress, boundary lubrication or insufficient lubrication, especially under the working conditions of high speed, high pressure or particle-containing medium, the inner hole surface wear is more serious, which leads to problems such as decrease of size precision, deterioration of surface roughness and shortening of service life.

[0003] In view of this, the present application is proposed. SUMMARY

[0004] The present application aims to provide a preparation device and method for depositing DLC film on inner surface of metal pipe after ion nitriding, so as to solve or improve the above technical problems.

[0005] The present application can be realized as follows:

[0006] In a first aspect, the present application provides a preparation device for depositing DLC film on inner surface of metal pipe after ion nitriding, which comprises a first gas inlet pipe, a second gas inlet pipe, an infrared temperature measuring instrument, a vacuum chamber, a mixed gas inlet pipe in the vacuum chamber, a direct current pulse bias power supply, a sample stage and a heating element.

[0007] The first gas inlet pipe is used for conveying argon, and the second gas inlet pipe is used for conveying at least one of hydrogen, nitrogen and methane; the gas inlet end of the mixed gas inlet pipe is connected with at least one pipe of the first gas inlet pipe and the second gas inlet pipe; the gas outlet end of the mixed gas inlet pipe faces the sample stage in the vacuum chamber, so as to guide the gas in the mixed gas inlet pipe to the metal pipe to be treated on the sample stage;

[0008] The metal pipe to be treated is connected with the negative electrode of the direct current pulse bias power supply, the vacuum chamber is connected with the positive electrode of the direct current pulse bias power supply and grounded; the heating element is used for heating the vacuum chamber, and the infrared temperature measuring instrument is used for real-time monitoring of the inner surface temperature of the metal pipe to be treated.

[0009] In an optional embodiment, the center axis of the metal pipe to be treated is collinear with the center of the gas outlet end of the mixed gas inlet pipe.

[0010] In a second aspect, the present application provides a preparation method of depositing DLC film on the inner surface of a metal pipe after ion nitriding in situ, comprising the following steps: using the preparation device of the preceding embodiments to perform ion nitriding and depositing DLC film in situ on the inner wall of the metal pipe to be treated.

[0011] In an optional embodiment, the ion nitriding comprises: introducing a first working gas into the metal pipe to be treated through the mixed gas inlet pipe, turning on the direct current pulse bias power supply, and performing glow discharge ion nitriding on the inner surface of the metal pipe to be treated; wherein the first working gas comprises 10-50 sccm of high-purity argon, 50-150 sccm of high-purity N2, and 50-100 sccm of high-purity H2; the conditions for glow discharge ion nitriding comprise: a direct current pulse bias of -500 to -600 V, a duty cycle of 20-60%, a time of 60-240 min, and a temperature of 400-600°C measured by an infrared temperature detector.

[0012] In an optional embodiment, the depositing DLC film in situ comprises: introducing a second working gas into the metal pipe after ion nitriding through the mixed gas inlet pipe, turning on the direct current pulse bias power supply, and depositing DLC film on the inner surface of the metal pipe; wherein the second working gas comprises 50-100 sccm of high-purity argon and 5-20 sccm of high-purity CH4; the conditions for depositing DLC film comprise: a direct current pulse bias of -450 to -600 V, a duty cycle of 2-10%, a time of 60-120 min, and a temperature of 150-250°C measured by an infrared temperature detector.

[0013] In an optional embodiment, the method further comprises, before the ion nitriding: pretreating the metal pipe to be treated.

[0014] The pretreating comprises: after ultrasonic cleaning and drying the metal pipe to be treated, fixing the metal pipe to be treated on the sample table, making the central axis of the metal pipe to be treated collinear with the center of the gas outlet end of the mixed gas inlet pipe, vacuumizing the vacuum chamber until the vacuum degree is ≤5×10 -3 Pa, turning on the heating element, and setting the heating temperature to 200-350°C.

[0015] In an optional embodiment, the method further comprises, before the ion nitriding: performing first glow ion etching cleaning on the metal pipe to be treated after the pretreating.

[0016] The first glow discharge ion etching cleaning comprises: introducing 50-150 sccm of high-purity Ar and 10-50 sccm of high-purity H2 into the metal pipe to be treated through the mixed inlet pipe, turning on the direct current pulse bias power supply, and performing glow discharge ion etching cleaning on the inner surface of the metal pipe to be treated; the glow discharge ion etching cleaning conditions comprise: a direct current pulse bias of -500 to -600 V, a duty cycle of 10-30%, and a time of 60-120 min.

[0017] In an optional embodiment, before depositing the DLC film in situ, the metal pipe subjected to ion nitriding is subjected to a second glow discharge ion etching cleaning.

[0018] The second glow discharge ion etching cleaning comprises: turning off the heating element, introducing 50-150 sccm of high-purity Ar and 10-50 sccm of high-purity H2 into the metal pipe through the mixed inlet pipe, a direct current pulse bias of -500 to -600 V, a duty cycle of 10-30%, and a time of 60-120 min.

[0019] In an optional embodiment, before depositing the DLC film in situ, the metal pipe subjected to the second glow discharge ion etching cleaning is further cooled.

[0020] The cooling comprises: turning off the direct current pulse bias power supply, introducing 50-100 sccm of high-purity Ar into the metal pipe through the mixed inlet pipe, and cooling the metal pipe along with the vacuum chamber under a vacuum state until the inner wall temperature of the metal pipe monitored by the infrared temperature detector is ≤100℃.

[0021] In a third aspect, the present application provides a metal workpiece, which comprises a metal pipe, the inner wall of the metal pipe has a nitrided layer, the surface of the nitrided layer has a DLC film, and the nitrided layer and the DLC film are prepared by the preparation device of any one of the foregoing embodiments or by the preparation method of any one of the foregoing embodiments.

[0022] In an optional embodiment, the hardness of the DLC film on the surface of the metal workpiece is not less than 16.5 GPa.

[0023] In an optional embodiment, the elastic modulus of the DLC film on the surface of the metal workpiece is not less than 124 GPa.

[0024] The present application has the following beneficial effects:

[0025] The preparation device for depositing DLC film on the inner surface of metal pipe after ion nitriding in situ provided by the application can prepare the nitriding layer and the DLC film in the same equipment, realizes integrated processing of glow discharge ion nitriding and plasma chemical vapor deposition of the DLC film on the inner surface of the metal pipe, and can effectively improve the bonding strength and surface hardness of the DLC film, and avoids and improves the defects such as interface pollution, poor bonding strength of the DLC film and low processing efficiency caused by the process of first performing in-pipe nitriding on the pipe to be processed by using a special ion nitriding device and then depositing the in-pipe DLC film on the pipe in a film coating equipment. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0027] Figure 1 The structural schematic diagram of the preparation device for depositing DLC film on the inner surface of metal pipe after ion nitriding in situ provided by the application;

[0028] Figure 2 The scanning electron microscope result graph in Example 1;

[0029] Figure 3 The indentation test result graph in Example 1;

[0030] Figure 4 The load-displacement curve graph in Example 1;

[0031] Figure 5 The scanning electron microscope result graph in Comparative Example 1.

[0032] Figure legend: 1-first gas inlet pipe; 2-second gas inlet pipe; 3-mixed gas inlet pipe; 4-vacuum chamber; 5-direct current pulse bias power supply; 6-sample table; 7-metal pipe to be processed; 8-heating element; 9-infrared temperature detector. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the application more clear, the technical solutions in the embodiments of the application will be clearly and completely described below. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not mentioned by the manufacturer can be obtained by market purchase.

[0034] The preparation device and method for depositing DLC film on the inner surface of a metal pipe after ion nitriding will be described in detail below.

[0035] The inventors propose that a hardened diffusion layer can be formed on the surface of a metal through nitriding treatment, effectively improving the surface hardness and load capacity. However, a single nitriding treatment on the surface of a metal will result in a high friction coefficient and limited wear resistance under boundary lubrication conditions. Diamond-like carbon (DLC) film has a low friction coefficient, high hardness, and good wear resistance. However, when DLC film is directly deposited on a metal substrate, the film is prone to cracking or peeling under frictional load due to the large difference in thermal expansion coefficient and insufficient interfacial bonding force. The present application forms a hardened diffusion layer on the surface of the substrate by first performing nitriding treatment on the inner hole surface of the metal, and then deposits DLC film on the surface of the nitriding layer, effectively balancing high hardness and low friction performance. The nitriding layer can significantly improve the load capacity of the substrate and serve as a transition layer between DLC and the metal substrate, improving the bonding force of the DLC film.

[0036] Furthermore, it should be noted that when preparing the nitriding layer and DLC film, if a special ion nitriding device is used to first perform an in-pipe nitriding process on the pipe to be treated, and then the pipe is placed in a film plating equipment for in-pipe DLC film deposition process, there may be defects such as interface contamination, poor DLC film bonding strength, and low processing efficiency due to process fragmentation.

[0037] Therefore, the present application creatively provides a preparation device for depositing DLC film on the inner surface of a metal pipe after ion nitriding, as shown in Figure 1 The preparation device includes a first gas inlet pipe 1, a second gas inlet pipe 2, an infrared temperature measuring instrument 9, a vacuum chamber 4, and a mixed gas inlet pipe 3, a direct current pulse bias power supply 5, a sample stage 6, and a heating element 8 located in the vacuum chamber 4.

[0038] The first gas inlet pipe 1 is used to transport argon, and the second gas inlet pipe 2 is used to transport at least one of hydrogen, nitrogen, and methane. The gas inlet end of the mixed gas inlet pipe 3 is connected to at least one of the first gas inlet pipe 1 and the second gas inlet pipe 2. Specifically, the mixed gas inlet pipe 3 can be connected to only the first gas inlet pipe 1 or simultaneously connected to the first gas inlet pipe 1 and the second gas inlet pipe 2, so that the required gases among Ar, N2, H2, and CH4 are input into the metal pipe.

[0039] The gas outlet end of the mixed gas inlet pipe 3 faces the sample stage 6 in the vacuum chamber 4, so as to guide the gas in the mixed gas inlet pipe 3 to the metal pipe to be treated 7 located on the sample stage 6. The metal pipe to be treated 7 can be fixed on the sample stage 6 by a copper wire, for example.

[0040] The metal pipe 7 to be treated is connected to the negative pole of the direct current pulse bias power supply 5, and the vacuum chamber 4 is connected to the positive pole of the direct current pulse bias power supply 5 and grounded. The bias voltage and duty cycle of the direct current pulse bias power supply 5 can be adjusted to continuously perform ion nitriding and DLC film deposition on the inner surface of the metal pipe.

[0041] The heating element 8 is used to heat the vacuum chamber 4, and the infrared thermometer 9 is used to monitor the temperature of the inner surface of the metal pipe 7 to be treated in real time.

[0042] In some optional embodiments, the central axis of the metal pipe 7 to be treated is collinear with the center of the outlet end of the mixed gas inlet pipe 3, so as to facilitate the preparation of a uniform (including thickness and coating composition) nitriding layer and DLC film.

[0043] Correspondingly, the application also provides a preparation method for in-situ deposition of DLC film on the inner surface of a metal pipe after ion nitriding, which comprises the following steps: using the preparation device of the aforementioned embodiments to perform ion nitriding and in-situ deposition of DLC film on the inner wall of the metal pipe 7 to be treated.

[0044] The high-purity argon gas mentioned below refers to argon gas with a purity of not less than 99.999%; the high-purity N2 refers to N2 with a purity of not less than 99.999%; and the high-purity H2 refers to H2 with a purity of not less than 99.999%.

[0045] In some optional embodiments, the ion nitriding comprises: introducing a first working gas into the metal pipe 7 to be treated through the mixing gas inlet pipe 3, turning on the direct current pulse bias power supply 5, and performing glow discharge ion nitriding on the inner surface of the metal pipe 7 to be treated. The first working gas comprises 10-50 sccm (such as 10, 20, 30, 40 or 50 sccm, etc.) of high-purity argon, 50-150 sccm (such as 50, 60, 70, 80, 90, 100, 110, 120, 130, 140 or 150 sccm, etc.) of high-purity N2, and 50-100 sccm (such as 50, 60, 70, 80, 90 or 100 sccm, etc.) of high-purity H2. The glow discharge ion nitriding conditions comprise: a direct current pulse bias of -500 to -600 V (such as -500, -520, -540, -560, -580 or -600 V, etc.), a duty cycle of 20-60% (such as 20, 30, 40, 50 or 60%, etc.), a time of 60-240 min (such as 60, 90, 120, 150, 180, 210 or 240 min, etc.), and a temperature of 400-600°C (such as 400, 450, 500, 550 or 600°C, etc.) measured by the infrared temperature detector 9.

[0046] In an optional embodiment, the in-situ deposition of the DLC film comprises: introducing a second working gas into the ion-nitrided metal pipe through the mixed gas inlet pipe 3, turning on the direct current pulse bias power supply 5, and depositing a DLC film on the inner surface of the metal pipe; wherein the second working gas comprises 50-100 sccm (e.g., 50 sccm, 60 sccm, 70 sccm, 80 sccm, 90 sccm, or 100 sccm, etc.) of high-purity argon and 5-20 sccm (e.g., 5 sccm, 8 sccm, 11 sccm, 14 sccm, 17 sccm, or 20 sccm, etc.) of high-purity CH4; the deposition conditions of the DLC film comprise: a direct current pulse bias of -450 V to -600 V (e.g., -450 V, -480 V, -510 V, -540 V, -570 V, or -600 V), a duty cycle of 2% to 10% (e.g., 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc.), a time of 60-120 min (e.g., 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, or 120 min, etc.), and an infrared temperature measuring instrument 9 measured temperature of 150-250℃ (e.g., 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, or 250℃, etc.).

[0047] In some optional embodiments, before ion nitriding, the method further comprises: pretreating the metal pipe to be treated 7. The pretreatment comprises: after ultrasonic cleaning and drying the metal pipe to be treated 7, fixing the metal pipe to be treated 7 on the sample table 6, making the central axis of the metal pipe to be treated 7 collinear with the center of the gas outlet end of the mixed gas inlet pipe 3, vacuumizing the vacuum chamber 4 until the vacuum degree is ≤5×10 -3 Pa, turning on the heating element 8, and setting the heating temperature to 200-350℃ (e.g., 200℃, 250℃, 300℃, or 350℃, etc.).

[0048] In some alternative embodiments, before the ion nitriding, the pre-processed metal pipe 7 is subjected to a first glow discharge etching cleaning. The first glow discharge etching cleaning comprises: introducing 50-150 sccm (e.g. 50, 60, 70, 80, 90, 100, 110, 120, 130, 140 or 150 sccm) of high-purity Ar and 10-50 sccm (e.g. 10, 20, 30, 40 or 50 sccm) of high-purity H2 into the metal pipe 7 through the mixing gas inlet pipe 3, turning on the direct current pulse bias power supply 5, and performing glow discharge etching cleaning on the inner surface of the metal pipe 7. The glow discharge etching cleaning is performed under the following conditions: a direct current pulse bias of -500 to -600 V (e.g. -500, -520, -540, -560, -580 or -600 V), a duty cycle of 10-30% (e.g. 10, 14, 18, 22, 26 or 30%), and a time of 60-120 min (e.g. 60, 80, 100 or 120 min).

[0049] In some alternative embodiments, before the in-situ deposition of the DLC film, the metal pipe subjected to the ion nitriding is subjected to a second glow discharge etching cleaning. The second glow discharge etching cleaning comprises: turning off the heating element 8, introducing 50-150 sccm (e.g. 50, 60, 70, 80, 90, 100, 110, 120, 130, 140 or 150 sccm) of high-purity Ar and 10-50 sccm (e.g. 10, 20, 30, 40 or 50 sccm) of high-purity H2 into the metal pipe through the mixing gas inlet pipe 3, a direct current pulse bias of -500 to -600 V (e.g. -500, -520, -540, -560, -580 or -600 V), a duty cycle of 10-30% (e.g. 10, 14, 18, 22, 26 or 30%), and a time of 60-120 min (e.g. 60, 70, 80, 90, 100, 110 or 120 min).

[0050] In some alternative embodiments, before depositing the DLC film in situ, the metal pipe after the second glow discharge ion etching cleaning is further cooled. The cooling comprises: turning off the direct current pulse bias power supply 5, introducing 50-100 sccm of high-purity Ar into the metal pipe through the mixed gas inlet pipe 3, and cooling the metal pipe along with the vacuum chamber 4 under vacuum until the inner wall temperature of the metal pipe monitored by the infrared temperature detector 9 is ≤100℃.

[0051] Further, after depositing the DLC film in situ, the metal pipe is discharged. The discharging comprises: turning off the direct current pulse bias power supply 5, stopping the introduction of all gases, and taking out the metal pipe after the inner surface of the metal pipe is cooled to ≤100℃.

[0052] In addition, the application further provides a metal workpiece, which comprises a metal pipe, the inner wall of the metal pipe has a nitrided layer, and the surface of the nitrided layer has a DLC film. The nitrided layer and the DLC film are prepared by the preparation device or by the preparation method described above.

[0053] In alternative embodiments, the hardness of the DLC film on the surface of the metal workpiece is not less than 16.5 GPa.

[0054] In alternative embodiments, the elastic modulus of the DLC film on the surface of the metal workpiece is not less than 124 GPa.

[0055] The features and performances of the application are further described in detail below in combination with examples.

[0056] It should be noted that in the following examples, the metal pipe is taken as a Φ40mm×420mm 304 stainless steel pipe. In order to facilitate characterization and testing, a 20mm×20mm×2mm 304 stainless steel sample is placed on the inner surface of the metal pipe as an experimental sample for relevant characterization and testing.

[0057] In the following examples and comparative examples, the purity of high-purity argon is 99.999%, the purity of high-purity N2 is 99.999%, and the purity of high-purity H2 is 99.999%.

[0058] Example 1

[0059] The present embodiment provides a metal workpiece, which comprises a metal pipe, the inner wall of the metal pipe has a nitrided layer, and the surface of the nitrided layer has a DLC film.

[0060] The preparation method of the metal workpiece comprises:

[0061] S1: pretreatment.

[0062] 304 stainless steel tube and 304 stainless steel sample in alkaline metal cleaning solution ultrasonic cleaning 20 min, then in acetone and alcohol ultrasonic cleaning 10 min, after drying, fixed on the sample table 6 in the vacuum chamber 4, the center axis of the steel tube and the center of the outlet of the mixed gas inlet pipe 3 are collinear, and the 304 stainless steel sample is horizontally placed in the 304 stainless steel tube. The vacuum chamber 4 is vacuumized until the vacuum degree is less than or equal to 5*10 -3 Pa, open the heating pipe to set the heating temperature to 350℃, to remove the moisture in the chamber and speed up the pumping speed, open the infrared thermometer 9, and monitor the temperature of the inner wall of the steel tube in real time through the observation window.

[0063] S2: first glow discharge ion etching cleaning.

[0064] Through the first gas inlet pipe 1, the second gas inlet pipe 2 and the mixed gas inlet pipe 3, 100sccm high purity Ar and 25sccm high purity H2 are introduced into the steel tube, and the direct current pulse bias power supply 5 is turned on to perform glow discharge ion etching cleaning on the inner surface of the steel tube. The negative bias of the direct current pulse bias power supply 5 is-600V, the duty cycle is 10%, and the time is 120min.

[0065] S3: ion nitriding.

[0066] Through the first gas inlet pipe 1, the second gas inlet pipe 2 and the mixed gas inlet pipe 3, 20sccm high purity Ar, 50sccm high purity N2 and 100sccm high purity H2 are introduced into the steel tube, and the direct current pulse bias power supply 5 is turned on to perform glow ion nitriding on the inner surface of the steel tube. The negative bias of the direct current pulse bias power supply 5 is-550V, the duty cycle is 50%, and the time is 240min. The infrared thermometer 9 shows that the final stable temperature is 440℃.

[0067] S4: second glow discharge ion etching cleaning.

[0068] Close the heating pipe, introduce 100sccm high purity Ar and 25sccm high purity H2 into the steel tube through the first gas inlet pipe 1, the second gas inlet pipe 2 and the mixed gas inlet pipe 3, and perform glow discharge ion etching cleaning on the inner surface of the nitrided steel tube. The negative bias of the direct current pulse bias power supply 5 is-550V, the duty cycle is 20%, and the time is 90min.

[0069] S5: cooling.

[0070] Close the direct current pulse bias power supply 5, introduce 50sccm high purity Ar into the steel tube through the first gas inlet pipe 1 and the mixed gas inlet pipe 3, and cool until the infrared thermometer 9 monitors that the inner wall temperature of the metal pipe is lower than 100℃.

[0071] S6: in-situ DLC film deposition.

[0072] 100 sccm of high-purity Ar and 10 sccm of high-purity CH4 are introduced into the steel pipe through the first air inlet pipe 1, the second air inlet pipe 2, and the mixing air inlet pipe 3. The DC pulse bias power supply 5 is turned on to perform DLC thin film deposition on the inner surface of the steel pipe. The DC pulse bias power supply 5 has a negative bias of -500V, a duty cycle of 5%, and a time of 120min. The highest temperature measured by the infrared thermometer 9 is 162℃.

[0073] S7: Fresh out of the oven.

[0074] Turn off the DC pulse bias power supply 5, stop the flow of all gas, and remove the metal pipe when the inner surface of the pipe has cooled to ≤100℃.

[0075] In this embodiment, after the 304 stainless steel sample was prepared using the above method, the scanning electron microscope image of its cross-section after etching with aqua regia is shown below. Figure 2 As shown. By Figure 2 It can be seen that, from bottom to top, the layers are a 304 stainless steel substrate, a nitrided layer, and a DLC film. The nitrided layer has a uniform thickness distribution, and there is no obvious white layer at the interface with the DLC film. The DLC film is dense and free of cracks and pinholes. The thickness of the nitrided layer is 6.11 μm, and the thickness of the DLC film is 1.28 μm.

[0076] The surface of the 304 stainless steel sample prepared by the above method in this embodiment was subjected to indentation testing using a Rockwell indenter (load: 150 kgf). The indentation morphology under an optical microscope is shown below. Figure 3 As shown. By Figure 3 It can be seen that a small number of cracks appeared around the indentation, and the bonding strength reached the HF1 level.

[0077] The nanohardness of DLC films was tested using a nanoindentation instrument, and the load-displacement curves are shown below. Figure 4 As shown. By Figure 4 It can be seen that the hardness of the DLC film is 20.319 GPa and the elastic modulus is 150.83 GPa.

[0078] Example 2

[0079] This embodiment provides a metal workpiece, which includes a metal pipe with an inner wall having a nitrided layer and a DLC film on the surface of the nitrided layer.

[0080] The method for preparing this metal workpiece includes:

[0081] S1: Preprocessing.

[0082] 304 stainless steel tube and 304 stainless steel sample in alkaline metal cleaning solution ultrasonic cleaning 20 min, then in acetone and alcohol ultrasonic cleaning 10 min, after drying, fixed on the sample table 6 in the vacuum chamber 4, the center axis of the steel tube and the center of the outlet of the mixed gas inlet pipe 3 are collinear, and the 304 stainless steel sample is horizontally placed in the 304 stainless steel tube. The vacuum chamber 4 is vacuumized until the vacuum degree is less than or equal to 5*10 -3 Pa, open the heating pipe to set the heating temperature to 200℃, to remove the moisture in the chamber and speed up the pumping speed, open the infrared thermometer 9, and monitor the temperature of the inner wall of the steel tube in real time through the observation window.

[0083] S2: First glow discharge ion etching cleaning.

[0084] Through the first gas inlet pipe 1, the second gas inlet pipe 2 and the mixed gas inlet pipe 3, 150sccm high purity Ar and 10sccm high purity H2 are introduced into the steel tube, and the direct current pulse bias power supply 5 is turned on to perform glow discharge ion etching cleaning on the inner surface of the steel tube. The negative bias of the direct current pulse bias power supply 5 is-550V, the duty cycle is 20%, and the time is 90min.

[0085] S3: Ion nitriding.

[0086] Through the first gas inlet pipe 1, the second gas inlet pipe 2 and the mixed gas inlet pipe 3, 50sccm high purity Ar, 150sccm high purity N2 and 50sccm high purity H2 are introduced into the steel tube, and the direct current pulse bias power supply 5 is turned on to perform glow ion nitriding on the inner surface of the steel tube. The negative bias of the direct current pulse bias power supply 5 is-575V, the duty cycle is 60%, and the time is 60min. The infrared thermometer 9 shows that the final stable temperature is 569℃.

[0087] S4: Second glow discharge ion etching cleaning.

[0088] Close the heating pipe, introduce 150sccm high purity Ar and 10sccm high purity H2 into the steel tube through the first gas inlet pipe 1, the second gas inlet pipe 2 and the mixed gas inlet pipe 3, and perform glow discharge ion etching cleaning on the inner surface of the steel tube after nitriding. The negative bias of the direct current pulse bias power supply 5 is-500V, the duty cycle is 30%, and the time is 100min.

[0089] S5: Cooling.

[0090] Close the direct current pulse bias power supply 5, introduce 75sccm high purity Ar into the steel tube through the first gas inlet pipe 1 and the mixed gas inlet pipe 3, and cool until the infrared thermometer 9 monitors that the inner wall temperature of the metal pipe is lower than 100℃.

[0091] S6: In-situ DLC film deposition.

[0092] The first inlet pipe 1, the second inlet pipe 2 and the mixed inlet pipe 3 are used to introduce 50sccm high-purity Ar and 5sccm high-purity CH4 into the steel pipe, and the direct current pulse bias power supply 5 is turned on to deposit the DLC film on the inner surface of the steel pipe. The negative bias of the direct current pulse bias power supply 5 is -450V, the duty cycle is 10%, the time is 60min, and the highest temperature measured by the infrared temperature detector 9 is 227℃.

[0093] S7: discharging.

[0094] The direct current pulse bias power supply 5 is turned off, and all the gases are stopped. The metal pipe is taken out when the inner surface of the metal pipe is cooled to ≤100℃.

[0095] The cross section of the 304 stainless steel sample after the preparation method is observed by scanning electron microscopy. The results show that the thickness distribution of the nitrided layer on the surface of the stainless steel sample is uniform, there is no obvious white layer at the interface of the DLC film, the DLC film is dense without cracks and pinholes, and the thickness distribution is uniform.

[0096] The surface of the 304 stainless steel sample after the preparation method is tested by indentation (the method is the same as in Example 1). The results show that a small amount of cracks appear around the indentation, and the bonding force reaches the HF1 level.

[0097] The hardness of the DLC film after the preparation method is tested (the method is the same as in Example 1). The results show that the hardness of the DLC film is 16.509GPa, and the elastic modulus is 142.79GPa.

[0098] Example 3

[0099] The metal workpiece provided in the embodiment includes a metal pipe, and the inner wall of the metal pipe has a nitrided layer, and the surface of the nitrided layer has a DLC film.

[0100] The preparation method of the metal workpiece includes:

[0101] S1: pretreatment.

[0102] The 304 stainless steel pipe and the 304 stainless steel sample are ultrasonically cleaned in an alkaline metal cleaning solution for 20min, and then ultrasonically cleaned in acetone and alcohol for 10min respectively. After drying, the steel pipe is fixed on the sample table 6 in the vacuum chamber 4, the center axis of the steel pipe is collinear with the center of the outlet end of the mixed inlet pipe 3, and the 304 stainless steel sample is horizontally placed in the 304 stainless steel pipe. The vacuum chamber 4 is evacuated until the vacuum degree is ≤5×10 -3 Pa, the heating pipe is turned on to set the heating temperature to 300℃ to remove the moisture in the chamber and speed up the evacuation, and the infrared temperature detector 9 is turned on to monitor the temperature of the inner wall of the steel pipe in real time through the observation window.

[0103] S2: first glow discharge ion etching cleaning.

[0104] Through the first gas inlet pipe 1, the second gas inlet pipe 2 and the mixed gas inlet pipe 3, 50sccm of high-purity Ar and 50sccm of high-purity H2 are introduced into the steel pipe, and the direct current pulse bias power supply 5 is turned on to perform glow discharge ion etching cleaning on the inner surface of the steel pipe. The negative bias of the direct current pulse bias power supply 5 is -500V, the duty cycle is 30%, and the time is 60min.

[0105] S3: ion nitriding.

[0106] Through the first gas inlet pipe 1, the second gas inlet pipe 2 and the mixed gas inlet pipe 3, 10sccm of high-purity Ar, 75sccm of high-purity N2 and 75sccm of high-purity H2 are introduced into the steel pipe, and the direct current pulse bias power supply 5 is turned on to perform glow ion nitriding on the inner surface of the steel pipe. The negative bias of the direct current pulse bias power supply 5 is -600V, the duty cycle is 30%, and the time is 120min. The infrared temperature instrument 9 shows that the final stable temperature is 501℃.

[0107] S4: second glow discharge ion etching cleaning.

[0108] The heating pipe is turned off, 50sccm of high-purity Ar and 50sccm of high-purity H2 are introduced into the steel pipe through the first gas inlet pipe 1, the second gas inlet pipe 2 and the mixed gas inlet pipe 3, and the inner surface of the steel pipe after nitriding is subjected to glow discharge ion etching cleaning. The negative bias of the direct current pulse bias power supply 5 is -600V, the duty cycle is 10%, and the time is 120min.

[0109] S5: cooling.

[0110] The direct current pulse bias power supply 5 is turned off, 100sccm of high-purity Ar is introduced into the steel pipe through the first gas inlet pipe 1 and the mixed gas inlet pipe 3 for cooling, and the infrared temperature instrument 9 monitors that the temperature of the inner wall of the metal pipe is lower than 100℃.

[0111] S6: in-situ DLC film deposition.

[0112] Through the first gas inlet pipe 1, the second gas inlet pipe 2 and the mixed gas inlet pipe 3, 80sccm of high-purity Ar and 20sccm of high-purity CH4 are introduced into the steel pipe, and the direct current pulse bias power supply 5 is turned on to perform DLC film deposition on the inner surface of the steel pipe. The negative bias of the direct current pulse bias power supply 5 is -550V, the duty cycle is 6%, and the time is 90min. The infrared temperature instrument 9 measures that the highest temperature is 203℃.

[0113] S7: furnace discharge.

[0114] The cross section of the 304 stainless steel sample after the preparation method in the embodiment was observed by scanning electron microscope, and the results showed that the thickness distribution of the nitrided layer on the surface of the stainless steel sample was uniform, there was no obvious white layer at the interface of the DLC film, the DLC film was dense without cracks and pinholes, and the thickness distribution was uniform.

[0115] The surface of the 304 stainless steel sample after the preparation method in the embodiment was subjected to indentation test (the method was the same as in Embodiment 1), and the results showed that a small amount of cracks appeared around the indentation, and the bonding force reached the HF1 level.

[0116] The DLC film of the 304 stainless steel sample after the preparation method in the embodiment was subjected to hardness test (the method was the same as in Embodiment 1), and the results showed that the hardness of the DLC film was 18.299 GPa, and the elastic modulus was 124.67 GPa.

[0117] Embodiment 4

[0118] The embodiment provides a metal workpiece, which comprises a metal pipe, and the inner wall of the metal pipe has a nitrided layer, and the surface of the nitrided layer has a DLC film.

[0119] The preparation method of the metal workpiece comprises:

[0120] S1: pretreatment.

[0121] The 304 stainless steel pipe and the 304 stainless steel sample were ultrasonically cleaned in an alkaline metal cleaning solution for 20 min, and then ultrasonically cleaned in acetone and alcohol for 10 min respectively. After drying, the steel pipe was fixed on the sample table 6 in the vacuum chamber 4, so that the center axis of the steel pipe was collinear with the center of the outlet end of the mixed gas inlet pipe 3, and the 304 stainless steel sample was horizontally placed in the 304 stainless steel pipe. The vacuum chamber 4 was evacuated until the vacuum degree was ≤5×10 -3 Pa, the heating pipe was started to set the heating temperature to 250℃, so as to remove the moisture in the chamber and speed up the evacuation, the infrared temperature measuring instrument 9 was turned on, and the inner wall temperature of the steel pipe was monitored in real time through the observation window.

[0122] S2: first glow discharge ion etching cleaning.

[0123] 120sccm of high-purity Ar and 30sccm of high-purity H2 were introduced into the steel pipe through the first gas inlet pipe 1, the second gas inlet pipe 2 and the mixed gas inlet pipe 3, and the inner surface of the steel pipe was subjected to glow discharge ion etching cleaning by starting the direct current pulse bias power supply 5, the negative bias of the direct current pulse bias power supply 5 was-550V, the duty cycle was 15%, and the time was 100 min.

[0124] S3: ion nitriding.

[0125] The first inlet pipe 1, the second inlet pipe 2 and the mixed inlet pipe 3 are used to introduce 30sccm high-purity Ar, 100sccm high-purity N2 and 50sccm high-purity H2 into the steel pipe, and the direct current pulse bias power supply 5 is turned on to perform glow discharge ion nitriding on the inner surface of the steel pipe, the negative bias of the direct current pulse bias power supply 5 is -600V, the duty cycle is 20%, the time is 180min, and the infrared temperature detector 9 shows that the final stable temperature is 484℃.

[0126] S4: second glow discharge ion etching cleaning.

[0127] The heating pipe is turned off, the first inlet pipe 1, the second inlet pipe 2 and the mixed inlet pipe 3 are used to introduce 120sccm high-purity Ar and 30sccm high-purity H2 into the steel pipe, and the glow discharge ion etching cleaning is performed on the inner surface of the steel pipe after nitriding, the negative bias of the direct current pulse bias power supply 5 is -575V, the duty cycle is 15%, and the time is 60min.

[0128] S5: cooling.

[0129] The direct current pulse bias power supply 5 is turned off, 80sccm high-purity Ar is introduced into the steel pipe through the first inlet pipe 1 and the mixed inlet pipe 3, and the inner wall temperature of the metal pipe is monitored by the infrared temperature detector 9 until the inner wall temperature of the metal pipe is lower than 100℃.

[0130] S6: in-situ DLC film deposition.

[0131] The first inlet pipe 1, the second inlet pipe 2 and the mixed inlet pipe 3 are used to introduce 75sccm high-purity Ar and 15sccm high-purity CH4 into the steel pipe, and the direct current pulse bias power supply 5 is turned on to perform DLC film deposition on the inner surface of the steel pipe, the negative bias of the direct current pulse bias power supply 5 is -600V, the duty cycle is 2%, the time is 80min, and the infrared temperature detector 9 shows that the maximum temperature is 197℃.

[0132] S7: discharging.

[0133] The direct current pulse bias power supply 5 is turned off, all the gases are stopped, and the inner surface of the metal pipe is cooled to ≤100℃ and then taken out.

[0134] The cross section of the 304 stainless steel sample in the embodiment after the preparation method is observed by a scanning electron microscope, and the results show that the thickness distribution of the nitrided layer on the surface of the stainless steel sample is uniform, there is no obvious white layer at the interface of the DLC film, the DLC film is dense without cracks and pinholes, and the thickness distribution is uniform.

[0135] The surface of the 304 stainless steel sample in the embodiment after the preparation method is tested by indentation (the method is the same as that in Embodiment 1), and the results show that a small amount of cracks appear around the indentation, and the bonding force reaches the HF1 level.

[0136] The hardness of the DLC film on the 304 stainless steel sample after the preparation method described above was tested (the method was the same as in Embodiment 1), and the results showed that the hardness of the DLC film was 18.566 GPa, and the elastic modulus was 151.62 GPa.

[0137] Comparative Example 1

[0138] The preparation method provided in the present comparative example is basically the same as that in Embodiment 1, except that after the ion nitriding of steps S1, S2, and S3, the vacuum chamber 4 is opened, and then steps S1, S4, S5, S6, and S7 are performed to complete the deposition of the DLC film.

[0139] The cross section of the 304 stainless steel sample after the preparation method described above in the present comparative example was observed by scanning electron microscopy, and the results are shown in FIG. 6. Figure 5 Figure 5 It can be seen that the thickness distribution of the nitriding layer on the surface of the stainless steel sample is uneven, and the overall shape is jagged, the thickness distribution of the DLC film is uneven, and there is a clear white layer at the interface between the nitriding layer and the DLC film.

[0140] The surface of the 304 stainless steel sample after the preparation method described above in the present comparative example was tested by indentation (the method was the same as in Embodiment 1), and the results showed that the film layer around the indentation appeared different degrees of block shedding, and the adhesion was HF4 grade.

[0141] The hardness of the DLC film on the 304 stainless steel sample after the preparation method described above in the present comparative example was tested (the method was the same as in Embodiment 1), and the results showed that the hardness of the DLC film was 16.067 GPa, and the elastic modulus was 118.24 GPa.

[0142] Comparative Example 2

[0143] The preparation method provided in the present comparative example is basically the same as that in Embodiment 1, except that the present comparative example does not perform step S3 ion nitriding treatment.

[0144] The cross section of the 304 stainless steel sample after the preparation method described above in the present comparative example was observed by scanning electron microscopy, and the results showed that the thickness distribution of the DLC film was uniform.

[0145] The surface of the 304 stainless steel sample after the preparation method described above in the present comparative example was tested by indentation (the method was the same as in Embodiment 1), and the results showed that the film layer around the indentation appeared large-scale peeling, and the adhesion was HF5 grade.

[0146] Comparative Example 3

[0147] The preparation method provided in the present comparative example is basically the same as that in Embodiment 1, except that the present comparative example does not perform step S4 second glow discharge ion etching cleaning after step S3 ion nitriding treatment.​

[0148] The cross section of the 304 stainless steel sample in the present comparative example after the preparation method described above was observed by scanning electron microscopy, and the results showed that the thickness distribution of the nitrided layer was relatively uniform, and there was a white layer at the interface between the nitrided layer and the DLC film. Different degrees of point and block peeling phenomenon appeared on the surface of the DLC film.

[0149] The surface of the 304 stainless steel sample in the present comparative example after the preparation method described above was tested by indentation (the method was the same as in Example 1), and the results showed that the film layer around the indentation appeared block peeling, and the adhesion was HF4 grade.

[0150] Comparative Example 4

[0151] The preparation method provided in the present comparative example was basically the same as that in Example 1, except that the present comparative example did not perform step S5 inner wall cooling.

[0152] The cross section of the 304 stainless steel sample in the present comparative example after the preparation method described above was observed by scanning electron microscopy, and the results showed that the thickness distribution of the nitrided layer was relatively uniform, and the DLC film was unevenly distributed. Large area peeling phenomenon occurred from the center to the periphery of the DLC film.

[0153] The surface of the 304 stainless steel sample in the present comparative example after the preparation method described above was tested by indentation (the method was the same as in Example 1), and the results showed that the film layer around the indentation appeared large area peeling, and the adhesion was HF5 grade.

[0154] Comparative Example 5

[0155] The preparation method provided in the present comparative example was basically the same as that in Example 1, except that the negative bias voltage during the ion nitriding process in the present comparative example was -700 V. During the ion nitriding process, the infrared temperature instrument 9 showed that the temperature of the inner wall of the pipeline reached a maximum of 780°C.

[0156] The surface of the 304 stainless steel sample in the present comparative example after the preparation method described above was deposited with a layer of carbon powder, and after wiping, no DLC film was deposited.

[0157] The cross section of the 304 stainless steel sample in the present comparative example after the preparation method described above was observed by scanning electron microscopy, and the results showed that the thickness distribution of the nitrided layer was uneven, and a white layer was observed on the surface of the nitrided layer. No DLC film layer was observed.

[0158] Comparative Example 6

[0159] The preparation method provided in the present comparative example was basically the same as that in Example 1, except that the time for the second glow discharge ion etching cleaning in step S4 in the present comparative example was 40 min.

[0160] The cross section of the 304 stainless steel sample in the present comparative example after the preparation method is observed by scanning electron microscope, and the result shows that the thickness distribution of the nitriding layer is relatively uniform, and a white layer appears at the interface between the nitriding layer and the DLC film. The DLC film appears block peeling in different degrees from the middle to the periphery.

[0161] The surface of the 304 stainless steel sample in the present comparative example after the preparation method is tested by indentation (the method is the same as that in Example 1), and the result shows that a small amount of block peeling appears around the indentation, and the bonding force is HF3 grade.

[0162] Comparative Example 7

[0163] The preparation method provided in the present comparative example is basically the same as that in Example 1, and the only difference is that the negative bias of the DLC film in step S6 of the present comparative example is-700 V. During the in-situ deposition of the DLC film, the infrared temperature instrument 9 shows that the temperature of the inner wall of the pipeline reaches 289 ℃ at most.

[0164] The surface of the 304 stainless steel sample in the present comparative example after the preparation method is deposited with a layer of carbon powder, and no DLC film is deposited after wiping.

[0165] The cross section of the 304 stainless steel sample in the present comparative example after the preparation method is observed by scanning electron microscope, and the result shows that the thickness distribution of the nitriding layer is uniform, and there is no obvious white layer on the surface of the nitriding layer, and no DLC film is observed.

[0166] Comparative Example 8

[0167] The preparation method provided in the present comparative example is basically the same as that in Example 1, and the only difference is that the negative bias of the DLC film in step S6 of the present comparative example is-400 V.

[0168] During the deposition of the DLC film, the glow intensity in the pipeline is obviously lower than that in Example 1, and the DLC film on the edge region of the sample surface is colored.

[0169] The cross section of the 304 stainless steel sample in the present comparative example after the preparation method is observed by scanning electron microscope, and the result shows that the thickness distribution of the nitriding layer is uniform, and there is no obvious white layer at the interface between the nitriding layer and the DLC film, and the thickness distribution of the DLC film is uneven.

[0170] The surface of the 304 stainless steel sample in the present comparative example after the preparation method is tested by indentation (the method is the same as that in Example 1), and the result shows that block peeling appears around the indentation, and the bonding force is HF4 grade.

[0171] Based on the above, the scheme provided in the present application at least has the following advantages:

[0172] (1) The preparation method for depositing DLC film on the inner surface of metal pipe after ion nitriding in situ provided by the application greatly improves the efficiency of strengthening treatment of the inner surface of the pipe, and effectively prevents the pollution of the nitriding layer interface during the transfer process, compared with the technology of first performing independent nitriding process on the pipe to be treated by using a special device, and then placing the pipe with the inner wall nitrided into a film plating equipment to perform DLC deposition process.

[0173] (2) The preparation method for depositing DLC film on the inner surface of metal pipe after ion nitriding in situ provided by the application based on a simple film plating equipment is not restricted by the limited space inside the pipe, and solves the defect that the DLC film is difficult to be uniformly deposited on the inner surface of the pipe by the conventional PVD method, compared with the integrated technology of depositing DLC film by ion nitriding combined with PVD method such as magnetic sputtering or arc ion plating.

[0174] (3) Based on the simple film plating equipment, the inner surface of the metal pipe is ion nitrided and DLC film is deposited in the same vacuum chamber 4 by inputting different precursor gases, adjusting the bias voltage and duty cycle of the direct current pulse bias power supply 5, which greatly simplifies the equipment and operation complexity required by the ion nitriding and DLC film deposition process in situ, and effectively reduces the cost and threshold of the integrated processing technology of ion nitriding and DLC film deposition.

[0175] The above only describes the preferred embodiments of the application and is not used to limit the application. For those skilled in the art, the application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. An apparatus for preparing an in-situ deposited DLC thin film after ion nitriding of the inner surface of a metal pipe fitting, characterized in that, The preparation apparatus includes a first air inlet pipe, a second air inlet pipe, an infrared thermometer, a vacuum chamber, a mixing air inlet pipe located in the vacuum chamber, a DC pulse bias power supply, a sample stage, and a heating element; The first inlet pipe is used to deliver argon gas, and the second inlet pipe is used to deliver at least one of hydrogen, nitrogen, and methane; the inlet end of the mixing inlet pipe is connected to at least one of the first inlet pipe and the second inlet pipe; the outlet end of the mixing inlet pipe faces the sample stage inside the vacuum chamber, so as to pass the gas in the mixing inlet pipe to the metal tube to be processed located on the sample stage; The metal tube to be processed is connected to the negative terminal of the DC pulse bias power supply, and the vacuum chamber is connected to the positive terminal of the DC pulse bias power supply and grounded; the heating element is used to heat the vacuum chamber, and the infrared thermometer is used to monitor the inner surface temperature of the metal tube to be processed in real time.

2. The preparation apparatus according to claim 1, characterized in that, The central axis of the metal pipe to be processed is collinear with the center of the outlet end of the mixing inlet pipe.

3. A method for preparing an in-situ deposited DLC thin film after ion nitriding of the inner surface of a metal pipe fitting, characterized in that, The process includes the following steps: using the preparation apparatus described in claim 1 or 2, performing ion nitriding on the inner wall of the metal pipe to be treated and in-situ deposition of a DLC thin film.

4. The preparation method according to claim 3, characterized in that, Ion nitriding includes: introducing a first working gas into the metal tube to be treated through the mixed gas inlet pipe, turning on the DC pulse bias power supply, and performing glow discharge ion nitriding on the inner surface of the metal tube to be treated; wherein, the first working gas includes 10 sccm to 50 sccm of high-purity argon, 50 sccm to 150 sccm of high-purity N2, and 50 sccm to 100 sccm of high-purity H2; the conditions for glow discharge ion nitriding include: a DC pulse bias of -500V to -600V, a duty cycle of 20% to 60%, a time of 60 min to 240 min, and a temperature measured by the infrared thermometer of 400℃ to 600℃.

5. The preparation method according to claim 3, characterized in that, The in-situ deposition of DLC thin film includes: introducing a second working gas into the ion-nitrided metal tube through the mixing inlet pipe, turning on the DC pulse bias power supply, and depositing a DLC thin film on the inner surface of the metal tube; wherein, the second working gas includes 50 sccm to 100 sccm of high-purity argon and 5 sccm to 20 sccm of high-purity CH4; the conditions for DLC thin film deposition include: DC pulse bias of -450V to -600V, duty cycle of 2% to 10%, time of 60 min to 120 min, and temperature measured by the infrared thermometer of 150℃ to 250℃.

6. The preparation method according to claim 3, characterized in that, Prior to ion nitriding, the process also includes: pretreatment of the metal fittings to be treated; Pretreatment includes: ultrasonically cleaning and drying the metal tube to be treated, fixing it on the sample stage, ensuring that the central axis of the metal tube to be treated is collinear with the center of the outlet end of the mixing inlet pipe, and evacuating the vacuum chamber until the vacuum degree is ≤5×10. -3 Pa, turn on the heating element, and set the heating temperature to 200℃~350℃.

7. The preparation method according to claim 6, characterized in that, Prior to ion nitriding, the process also includes a first glow discharge ion etching cleaning of the pretreated metal fittings. The first glow discharge ion etching cleaning includes: introducing 50 sccm to 150 sccm of high-purity Ar and 10 sccm to 50 sccm of high-purity H2 into the metal tube to be treated through the mixed air inlet pipe, turning on the DC pulse bias power supply, and performing glow discharge ion etching cleaning on the inner surface of the metal tube to be treated; the conditions for glow discharge ion etching cleaning include: DC pulse bias of -500V to -600V, duty cycle of 10% to 30%, and time of 60 min to 120 min.

8. The preparation method according to claim 7, characterized in that, Before in-situ deposition of DLC thin film, the metal tube after ion nitriding is subjected to a second glow discharge ion etching cleaning. The second glow discharge ion etching cleaning includes: turning off the heating element, introducing 50 sccm to 150 sccm of high-purity Ar and 10 sccm to 50 sccm of high-purity H2 into the metal tube through the mixing inlet pipe, with a DC pulse bias voltage of -500V to -600V, a duty cycle of 10% to 30%, and a time of 60 min to 120 min.

9. The preparation method according to claim 8, characterized in that, Before in-situ deposition of DLC thin films, the process also includes cooling the metal tubes after the second glow discharge ion etching cleaning. Cooling includes: turning off the DC pulse bias power supply, introducing 50 sccm to 100 sccm of high-purity Ar into the metal tube through the mixing inlet pipe, and cooling the metal tube in a vacuum state along with the vacuum chamber until the inner wall temperature of the metal tube monitored by the infrared thermometer is ≤100℃.

10. A metal workpiece, characterized in that, The metal workpiece includes a metal pipe, the inner wall of which has a nitrided layer, and the surface of which has a DLC film. Both the nitrided layer and the DLC film are prepared using the preparation apparatus according to any one of claims 1 to 2, or both the nitrided layer and the DLC film are prepared using the preparation method according to any one of claims 3 to 9. Preferably, the hardness of the DLC film on the surface of the metal workpiece is not less than 16.5 GPa; Preferably, the elastic modulus of the DLC film on the surface of the metal workpiece is not less than 124 GPa.

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