Preparation method of ultra-smooth nanocrystalline tungsten coating on surface of emitter

Abstract

The invention discloses a preparation method of an ultra-smooth nanocrystalline tungsten coating on the surface of an emitter, the tungsten coating is prepared by adopting a magnetron sputtering method, and the specific process is as follows: pretreating an emitter workpiece, then placing the emitter workpiece in a vacuum chamber, pre-vacuumizing, then introducing inert gas, cleaning the surface of the emitter workpiece by utilizing gas ion reverse sputtering, and finally removing the surface of the emitter workpiece. And then adjusting the gas pressure, bombarding and cleaning the surface of the emitter workpiece by using metal ions, and finally sputtering and depositing to form the tungsten coating. The tungsten coating is prepared through the magnetron sputtering technology, the tungsten coating has the characteristics of being compact in structure, good in combination and uniform and smooth in surface, the mechanical property and structural stability of the tungsten coating in the high-temperature service environment can be guaranteed, the deposition technology is simple, the preparation efficiency is high, and the tungsten coating is green and free of pollution, in addition, preparation of the tungsten coating composed of different phases can be achieved, and the application prospect is wide. The application requirements in the fields of electronic industry, nuclear industry and the like are met.

Description

Technical Field

[0001] The invention relates to the technical field of surface protective coatings, and in particular to a method for preparing an ultra-smooth nanocrystalline tungsten coating on an emitter surface. Background Art

[0002] The power supply of a space nuclear reactor is the most important component of the future space nuclear power system. It can directly convert nuclear fission heat into electrical energy through thermionic energy converters, which can effectively guarantee the high-power and long-life energy needs of future space missions. The emitter is the core component of thermionic energy converters, serving as both a nuclear fuel protection cladding and a surface thermal electron emission material. Tungsten has the characteristics of high melting point, high vacuum work function, low thermal neutron absorption cross section, excellent high-temperature mechanical properties and high-temperature structural stability. It is currently the only coating material used on the surface of the emitter of a space nuclear reactor.

[0003] At present, the main preparation technology of emitter tungsten coating is chemical vapor deposition, but chemical vapor deposition tungsten coating has some obvious disadvantages, such as large surface roughness of coating, complicated preparation process, too high deposition temperature, serious environmental pollution, etc. (see reference: Yan Binyou, Song Jiupeng, Huang Zexi, Lin Baozhi, a thick tungsten coating and its preparation method and plasma-facing component, patent application number: CN117660916A). Other tungsten coating preparation technologies such as spraying (see reference: Huang Jianjun, Guo Zongxiao, Wang Xingli, Wang Fan, tungsten composite coating applied to the first wall of nuclear fusion device blanket and its preparation method, patent application number: CN115216720A), molten salt electrodeposition (see reference: Xi Xiaoli, Qin Wenxuan, Ma Liwen, Nie Zuoren, Zhang Qinghua, a method for preparing tungsten coating by in-situ electrodeposition of molten salt, patent authorization number: CN110528033B) also have disadvantages such as poor coating density, large surface roughness, and high oxygen impurity content. In addition, the tungsten coatings prepared by the above-mentioned technologies are often in the form of coarse grains (tens of microns), and their resistance to thermal shock in high-temperature service environments needs to be improved. In comparison, magnetron sputtering technology has a simple process flow, low-temperature deposition does not produce additional thermal effects on the base material, and is environmentally friendly. It can obtain a tungsten coating with a dense structure, good bonding, and a uniform and smooth surface. At the same time, magnetron sputtering can achieve flexible regulation of the microstructure and phase composition of the tungsten coating, meeting its application needs in different fields such as the electronics industry and the nuclear industry. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing an ultra-smooth nanocrystalline tungsten coating on the emitter surface in view of the deficiencies of the above-mentioned prior art. The method adopts a magnetron sputtering method to prepare an emitter tungsten coating, and the tungsten coating has a dense columnar nanocrystalline structure and extremely low surface roughness, which can ensure its mechanical properties and structural stability in a high-temperature service environment, and the process is simple, no subsequent treatment is required, the preparation efficiency is high, and it is green and pollution-free, which solves the problems of complicated preparation procedures, low efficiency, serious environmental pollution, and excessive surface roughness of the coating in the emitter tungsten coating process.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing an ultra-smooth nanocrystalline tungsten coating on the surface of an emitter, characterized in that the tungsten coating is prepared by a magnetron sputtering method, and the specific process is: the emitter workpiece is pre-treated and placed in a vacuum chamber and pre-vacuumed, and then an inert gas is introduced, and the surface of the emitter workpiece is cleaned by gas ion reverse sputtering, and then the gas pressure is adjusted, and the surface of the emitter workpiece is cleaned by metal ion bombardment, and finally the tungsten coating is formed by sputtering deposition; the tungsten coating presents a dense columnar nanocrystalline structure, the surface is uniform and smooth, and it is well bonded to the emitter workpiece substrate.

[0006] The above-mentioned method for preparing an ultra-smooth nanocrystalline tungsten coating on the emitter surface is characterized in that the emitter workpiece pretreatment method is selected from degreasing, rust removal, sandblasting, pickling, and surface grinding and polishing.

[0007] The above-mentioned method for preparing an ultra-smooth nanocrystalline tungsten coating on the emitter surface is characterized in that the vacuum degree after the pre-vacuuming is 1.0×10 -4 Pa~9.9×10 -3 Pa.

[0008] The above-mentioned method for preparing an ultra-smooth nanocrystalline tungsten coating on the emitter surface is characterized in that the inert gas comes from Ar, He, and Ne gases, and the inert gas introduction pressure is 1Pa~10Pa; the process conditions for cleaning the emitter workpiece surface by gas ion sputtering are: negative bias voltage 600V~1000V, cleaning time 5min~30min.

[0009] The above-mentioned method for preparing an ultra-smooth nanocrystalline tungsten coating on the emitter surface is characterized in that the pressure of the regulating gas is 0.1Pa~5Pa.

[0010] The above-mentioned method for preparing an ultra-smooth nanocrystalline tungsten coating on the emitter surface is characterized in that the process conditions for cleaning the emitter workpiece surface by bombarding with metal ions are: sputtering current 0.2A~5A, negative bias voltage 600V~1000V, and cleaning time 30s~10min.

[0011] The above-mentioned method for preparing an ultra-smooth nanocrystalline tungsten coating on the emitter surface is characterized in that the process conditions for sputtering and deposition to form the tungsten coating are: gas pressure 0.1Pa~5Pa, sputtering current 0.2A~5A, negative bias 0V~500V, deposition temperature 25℃~500℃, and deposition time 0.5h~10h.

[0012] The above-mentioned method for preparing an ultra-smooth nanocrystalline tungsten coating on the emitter surface is characterized in that the width of the columnar nanocrystals in the tungsten coating is 50nm to 500nm.

[0013] The above-mentioned method for preparing an ultra-smooth nanocrystalline tungsten coating on the emitter surface is characterized in that the surface roughness of the tungsten coating is Ra≤100nm.

[0014] The above-mentioned method for preparing an ultra-smooth nanocrystalline tungsten coating on the emitter surface is characterized in that the phase composition of the tungsten coating is α-W or / and β-W.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. Compared with conventional emitter tungsten coating preparation methods such as chemical vapor deposition, spraying, etc., the present invention adopts magnetron sputtering method to prepare emitter tungsten coating for the first time. The tungsten coating has a dense columnar nanocrystalline structure and extremely low surface roughness, which can ensure its mechanical properties and structural stability in high-temperature service environment.

[0017] 2. The magnetron sputtering method adopted in the present invention has a simple process, does not require subsequent surface processing, and has a wide range of application for the base material, high preparation efficiency, and is green and pollution-free.

[0018] 3. The preparation method of the present invention can achieve the regulation of the phase composition of the tungsten coating by precisely controlling deposition parameters such as gas pressure and bias voltage to meet different application requirements, and is suitable for the electronics industry, nuclear industry and other fields.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a surface scanning electron microscope image of the tungsten coating prepared in Example 1 of the present invention.

[0021] Figure 2 This is a cross-sectional scanning electron microscope image of the tungsten coating prepared in Example 1 of the present invention.

[0022] Figure 3 This is the XRD spectrum of the tungsten coating prepared in Example 1 of the present invention.

[0023] Figure 4This is a cross-sectional scanning electron microscope image of the tungsten coating prepared in Example 1 of the present invention.

[0024] Figure 5 This is a surface AFM image of the tungsten coating prepared in Example 1 of the present invention.

[0025] Figure 6 This is a surface AFM image of the tungsten coating prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0026] Example 1

[0027] This embodiment includes the following steps:

[0028] Step 1: Use 240-2000 grit sandpaper to grind the emitter workpiece surface in sequence, then polish it with 2.5 μm diamond grinding paste, then put it into ethanol solution for ultrasonic cleaning for 10 minutes, blow dry it and hang it on the rotating rack facing the tungsten target in the vacuum chamber of the magnetron sputtering equipment;

[0029] Step 2: Close the vacuum chamber door and pre-evacuate to a vacuum degree of 8×10 -3 Pa, heated to 180℃~220℃, turned on the gas flowmeter to introduce Ar gas into the vacuum chamber to maintain the vacuum degree at about 2Pa, turned on the pulse bias and set the negative bias voltage to 600V to perform Ar ion back sputtering cleaning on the surface of the emitter workpiece substrate for 5min;

[0030] Step 3: Adjust the gas pressure to 1 Pa, turn on the medium frequency magnetron sputtering power supply and set the sputtering current to 0.5 A, and use tungsten ion bombardment to clean the emitter workpiece substrate surface for 1 min under a negative bias voltage of 600 V;

[0031] Step 4: Maintain the vacuum chamber temperature, gas pressure, and sputtering current unchanged, adjust the negative bias voltage to 200 V, and continue sputtering deposition to form a tungsten coating for 5.5 hours.

[0032] Figure 1 and Figure 2 The surface and cross-sectional scanning electron microscopy images of the tungsten coating prepared in this embodiment are shown in FIG. Figure 1 and Figure 2 It can be seen that the surface of the tungsten coating is smooth and uniform, the cross-sectional structure of the tungsten coating is dense, it is well bonded to the emitter workpiece substrate, and there are no cracks or holes on the interface and inside the coating. The thickness of the tungsten coating is about 4.3μm.

[0033] Figure 3 The XRD pattern of the tungsten coating prepared in this example is as follows: Figure 3 It can be seen that the tungsten coating is composed of an α-W phase with a body-centered cubic structure.

[0034] Figure 4This is a cross-sectional SEM image of the tungsten coating prepared in this embodiment. Figure 4 It can be seen that the tungsten coating presents a dense columnar nanocrystal structure, and the width of the columnar nanocrystal is less than 200 nm.

[0035] Figure 5 This is the surface AFM image of the tungsten coating prepared in this example. Figure 5 It can be seen that the surface of the tungsten coating is smooth and uniform with a roughness of Ra=8.37nm.

[0036] Example 2

[0037] This embodiment includes the following steps:

[0038] Step 1: Use 240-2000 grit sandpaper to grind the emitter workpiece surface in sequence, then polish it with 2.5 μm diamond grinding paste, then put it into ethanol solution for ultrasonic cleaning for 10 minutes, blow dry it and hang it on the rotating rack facing the tungsten target in the vacuum chamber of the magnetron sputtering equipment;

[0039] Step 2: Close the vacuum chamber door and pre-evacuate to a vacuum degree of 6×10 -3 Pa, heated to 180℃~220℃, turned on the gas flowmeter to introduce Ar gas into the vacuum chamber to maintain the vacuum degree at about 2Pa, turned on the pulse bias and set the negative bias voltage to 800V to perform Ar ion back sputtering cleaning on the surface of the emitter workpiece substrate for 5min;

[0040] Step 3: Adjust the gas pressure to 1 Pa, turn on the medium frequency magnetron sputtering power supply and set the sputtering current to 0.5 A, and use tungsten ion bombardment to clean the emitter workpiece substrate surface for 1 min under a negative bias voltage of 600 V;

[0041] Step 4: Maintain the vacuum chamber temperature, gas pressure, and sputtering current unchanged, adjust the negative bias voltage to 100 V, and continue sputtering deposition to form a tungsten coating for 5.5 hours.

[0042] Figure 6 This is the surface AFM image of the tungsten coating prepared in this example. Figure 6 It can be seen that the surface of the tungsten coating is smooth and uniform with a roughness of Ra=8.13 nm.

[0043] After testing, the tungsten coating prepared in this embodiment presents a dense columnar nanocrystal structure, and the width of the columnar nanocrystal is less than 300nm, the surface is flat, uniform and smooth, and it is well bonded to the emitter workpiece substrate; the phase composition of the tungsten coating is α-W phase.

[0044] Example 3

[0045] This embodiment includes the following steps:

[0046] Step 1: Use 240-2000 grit sandpaper to grind the emitter workpiece surface in sequence, then polish it with 2.5 μm diamond grinding paste, then put it into ethanol solution for ultrasonic cleaning for 10 minutes, blow dry it and hang it on the rotating rack facing the tungsten target in the vacuum chamber of the magnetron sputtering equipment;

[0047] Step 2: Close the vacuum chamber door and pre-evacuate to a vacuum degree of 1.0×10 -4 Pa, turn on the gas flow meter to introduce Ar gas into the vacuum chamber to maintain the vacuum degree at about 1Pa, turn on the pulse bias and set the negative bias voltage to 1000V to perform Ar ion back sputtering cleaning on the surface of the emitter workpiece substrate for 5 minutes;

[0048] Step 3: Adjust the gas pressure to 0.1 Pa, turn on the medium frequency magnetron sputtering power supply and set the sputtering current to 0.2 A, and use tungsten ion bombardment to clean the emitter workpiece substrate surface for 30 seconds under a negative bias voltage of 1000 V;

[0049] Step 4: Maintain the vacuum chamber temperature, gas pressure, and sputtering current unchanged, adjust the negative bias voltage to 500 V, and continue sputtering deposition to form a tungsten coating for 0.5 h.

[0050] After testing, the tungsten coating prepared in this embodiment presents a dense columnar nanocrystalline structure, and the width of the columnar nanocrystal is less than 100nm, the surface is uniform and smooth, the surface roughness Ra=13.8nm, and it is well bonded to the emitter workpiece substrate; the phase composition of the tungsten coating is α-W phase.

[0051] Example 4

[0052] This embodiment includes the following steps:

[0053] Step 1: Use 240-2000 grit sandpaper to grind the emitter workpiece surface in sequence, then polish it with 2.5 μm diamond grinding paste, then put it into ethanol solution for ultrasonic cleaning for 10 minutes, blow dry it and hang it on the rotating rack facing the tungsten target in the vacuum chamber of the magnetron sputtering equipment;

[0054] Step 2: Close the vacuum chamber door and pre-evacuate to a vacuum degree of 9.9×10 -3 Pa, heated to 480℃~500℃, turned on the gas flowmeter to introduce He gas into the vacuum chamber to maintain the vacuum degree at about 10Pa, turned on the pulse bias and set the negative bias voltage to 600V to perform He ion reverse sputtering cleaning on the surface of the emitter workpiece substrate for 30min;

[0055] Step 3: Adjust the gas pressure to 5 Pa, turn on the medium frequency magnetron sputtering power supply and set the sputtering current to 5 A, and use tungsten ion bombardment to clean the emitter workpiece substrate surface for 10 minutes under a negative bias voltage of 600 V;

[0056] Step 4: Maintain the vacuum chamber temperature, gas pressure, and sputtering current unchanged, adjust the negative bias voltage to 0 V, and continue sputtering deposition to form a tungsten coating for 10 hours.

[0057] After testing, the tungsten coating prepared in this embodiment presents a dense columnar nanocrystalline structure, and the width of the columnar nanocrystal is less than 500nm, the surface is flat, uniform and smooth, the surface roughness is Ra=15.5nm, and it is well bonded with the emitter workpiece substrate; the phase composition of the tungsten coating is β-W phase.

[0058] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing an ultra-smooth nanocrystalline tungsten coating on an emitter surface, characterized in that: The tungsten coating is prepared by magnetron sputtering, and the specific process is: the emitter workpiece is pre-treated and placed in a vacuum chamber and pre-evacuated, then an inert gas is introduced, and the surface of the emitter workpiece is cleaned by gas ion reverse sputtering, then the gas pressure is adjusted, and the surface of the emitter workpiece is cleaned by metal ion bombardment, and finally the tungsten coating is formed by sputtering deposition; the tungsten coating presents a dense columnar nanocrystalline structure, the surface is uniform and smooth, and it is well bonded to the emitter workpiece substrate.

2. The method for preparing an ultra-smooth nanocrystalline tungsten coating on an emitter surface according to claim 1, characterized in that: The emitter workpiece pretreatment method is selected from degreasing, rust removal, sandblasting, pickling, surface grinding and polishing.

3. The method for preparing an ultra-smooth nanocrystalline tungsten coating on an emitter surface according to claim 1, characterized in that: The vacuum degree after pre-vacuuming is 1.0×10 -4 Pa~9.9×10 -3 Pa.

4. The method for preparing an ultra-smooth nanocrystalline tungsten coating on an emitter surface according to claim 1, characterized in that: The inert gas comes from Ar, He, and Ne gas, and the inert gas has an inlet pressure of 1Pa to 10Pa. The process conditions for cleaning the emitter workpiece surface by gas ion reverse sputtering are: negative bias voltage 600V to 1000V, and cleaning time 5min to 30min.

5. The method for preparing an ultra-smooth nanocrystalline tungsten coating on an emitter surface according to claim 1, characterized in that: The regulating gas pressure is 0.1Pa-5Pa.

6. The method for preparing an ultra-smooth nanocrystalline tungsten coating on an emitter surface according to claim 1, characterized in that: The process conditions for cleaning the emitter workpiece surface by metal ion bombardment are: sputtering current 0.2A-5A, negative bias voltage 600V-1000V, and cleaning time 30s-10min.

7. The method for preparing an ultra-smooth nanocrystalline tungsten coating on an emitter surface according to claim 1, characterized in that: The process conditions for forming the tungsten coating by sputtering deposition are: gas pressure 0.1Pa-5Pa, sputtering current 0.2A-5A, negative bias 0V-500V, deposition temperature 25°C-500°C, and deposition time 0.5h-10h.

8. The method for preparing an ultra-smooth nanocrystalline tungsten coating on an emitter surface according to claim 1, characterized in that: The width of the columnar nanocrystals in the tungsten coating is 50nm to 500nm.

9. The method for preparing an ultra-smooth nanocrystalline tungsten coating on an emitter surface according to claim 1, characterized in that: The surface roughness of the tungsten coating is Ra≤100nm.

10. The method for preparing an ultra-smooth nanocrystalline tungsten coating on an emitter surface according to claim 1, characterized in that: The phase composition of the tungsten coating is α-W or / and β-W.

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