Coating structure for valve stem of nuclear power plant and valve stem and method for manufacturing the same

Abstract

The application discloses a coating structure of a valve rod of a nuclear power plant, a valve rod and a preparation method thereof, and the coating structure comprises a transition layer and a hydrogen-free diamond layer which are sequentially arranged from inside to outside, the microstructure of the transition layer is nanotwin, and the coating structure is uniformly covered on the surface of the valve rod. The preparation method comprises the following steps: after the valve rod is cleaned, the valve rod is subjected to plasma surface activation, the transition layer and the hydrogen-free diamond layer are sequentially deposited, and the valve rod is obtained. The coating structure of the valve rod of the nuclear power plant, the valve rod and the preparation method thereof effectively improve the hardness of the surface of the valve rod, reduce the friction loss of the valve rod, make the valve rod have good wear resistance and a reduced friction coefficient, improve the work efficiency, and further improve the service life of the valve rod, can meet the technical performance requirements of the valve rod on impact toughness, corrosion resistance and wear resistance in a high-temperature and high-pressure water environment, and effectively reduce the production cost.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power plant control valve manufacturing technology, specifically relating to a coating structure for a nuclear power plant valve stem, a valve stem including the coating structure, and a method for preparing the valve stem. Background Technology

[0002] Nuclear power plants have numerous piping valves that play a crucial role in the entire nuclear power operation system. These valves operate in high-temperature, high-pressure, water-rich, and abrasive environments. During frequent start-ups and shutdowns, the valve stem of a regulating valve is not only a moving and load-bearing component but also a sealing element, subjected to the impact and corrosion of the medium and friction with the packing. Therefore, the valve stem needs to possess excellent strength, impact toughness, corrosion resistance, and wear resistance at operating temperatures. Although existing valve stems are protected by an electroplated chromium coating, they are still prone to wear failure under nuclear power plant operating conditions. Nuclear power plants need to replace many failed valve stem components annually, undoubtedly increasing operating costs; furthermore, plant shutdowns and reactor shutdowns caused by valve stem replacement result in even greater economic losses. Therefore, improving the wear resistance of the valve stem surface coating is an effective way to extend the service life of worn components.

[0003] Currently, there are two methods to improve the wear resistance of valve stems: one is to apply a coating to the valve stem surface before service; the other is to repair the surface of failed valve stems. Compared with surface repair after valve stem wear, improving the wear resistance of the valve stem surface before service is more economical as it extends the service life of the valve stem from the source and avoids repair after damage. Therefore, it is necessary to develop a coating for control valve stems that meets the usage requirements of control valve stems and has low production costs. Summary of the Invention

[0004] In view of this, in order to overcome the shortcomings of the prior art, the present invention provides a coating structure for a nuclear power plant valve stem and a valve stem and its preparation method, which solves the problems of insufficient strength and toughness, corrosion resistance and wear resistance of the valve stem in the prior art, as well as the increased production cost caused by frequent valve stem replacement.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] One object of the present invention is to provide a coating structure for a valve stem in a nuclear power plant, comprising a transition layer and a hydrogen-free diamond-like carbon layer arranged sequentially from the inside out. The microstructure of the transition layer is nanotwinned, and the coating structure uniformly covers the surface of the valve stem. Furthermore, the valve stem surface itself also has a layer of chromium.

[0007] The transition layer has a nanotwinned microstructure. The numerous nanotwin grain boundaries facilitate dislocation absorption, coordinate crystal deformation, and alleviate stress concentration, thus improving the coating's toughness. The hydrogen-free diamond-like carbon layer on the transition layer surface is a tetrahedral amorphous carbon (ta-C) film, characterized by high hardness and a low coefficient of friction. It exhibits excellent corrosion resistance and wear resistance, ultimately reducing frictional losses in the valve stem.

[0008] According to some preferred embodiments of the present invention, the transition layer is a TiBN layer and / or an AlN layer. In some embodiments of the present invention, the transition layer may be a single TiBN layer or an AlN layer; it may also be a composite layer of TiBN and AlN layers.

[0009] According to some preferred embodiments of the present invention, when the transition layer is a TiBN layer and an AlN layer, the thickness ratio of the TiBN layer to the AlN layer is 1:0.8 to 1:1.5. In some embodiments of the present invention, the thickness ratio of the TiBN layer to the AlN layer is preferably 1:1.

[0010] According to some preferred embodiments of the present invention, the thickness of the transition layer is 0.5 to 1 μm, and the thickness of the hydrogen-free diamond-like layer is 1.5 to 3 μm.

[0011] According to some preferred embodiments of the present invention, the hardness of the hydrogen-free diamond-like layer is 3000-3600 HV.

[0012] According to some preferred embodiments of the invention, the fracture toughness of the hydrogen-free diamond-like carbon layer is greater than 3.5 MPa / m. 1 / 2 .

[0013] Another object of the present invention is to provide a valve stem comprising the coating structure described above, wherein the valve stem has a hardness greater than or equal to 3000 HV and a fracture toughness greater than or equal to 3.5 MPa / m. 1 / 2 Furthermore, after the aforementioned coating is grown on the surface of the control valve stem, the high-temperature resistance of the stem is improved by approximately 100°C compared to traditional valve stems with only a single layer of chromium coating. It can withstand high-temperature environments of 400–450°C, which helps to extend the service life of the valve stem.

[0014] The present invention also provides a method for preparing a valve stem as described above, comprising the following steps:

[0015] After cleaning the valve stem, the valve stem is subjected to plasma surface activation, and then a transition layer and a hydrogen-free diamond-like carbon layer are deposited sequentially to obtain the valve stem.

[0016] In order to prepare a transition layer with a nanotwin structure, in some embodiments of the present invention, the relevant experimental parameters in the preparation method of the transition layer are adjusted, including controlling the target sputtering power to be 2000-2500W, the bias voltage to be -100-300V, and the temperature to be 100-200℃, so as to obtain a transition layer with a nanotwin structure.

[0017] Specifically, the valve stem is prepared as follows:

[0018] (1) Clean the valve stem surface with ultrasonic petroleum ether for 1 hour to remove hydraulic valve stem oil stains, then clean it with anhydrous ethanol for 30 minutes, and finally dry it in a 45°C drying oven for 1 hour.

[0019] (2) Place the valve stem in the vacuum vapor deposition chamber, with a chamber temperature of 100–200°C, and evacuate to 5 × 10⁻⁶. -3 ~8×10 -3 Pa, then high-purity argon gas with a purity of 99.99% and a flow rate of 100-200 sccm is introduced into the chamber through the anolyte ion source. The chamber pressure is maintained at 0.2-0.7 Pa, the anolyte ion source discharge voltage is 750-1000V, the discharge current is 0.2-0.7A, and a bias voltage of -300 to -550V is applied to the valve stem to clean the regulating valve stem for 40-50 minutes;

[0020] (3) In the vacuum vapor deposition chamber, adjust the negative bias voltage of the valve rod after plasma surface activation to -100 to -300V, introduce nitrogen gas at a flow rate of 100 to 200 sccm, and continue to introduce argon gas to keep the gas pressure in the deposition chamber at 1.0 to 1.5 Pa. Turn on the magnetron sputtering target, adjust the power of the magnetron sputtering target to 2000 to 2500W, and the deposition time to 20 to 30 minutes. After the deposition is completed, turn off the magnetron sputtering power supply to complete the deposition of the transition layer.

[0021] (4) Adjust the negative bias voltage of the valve stem to -100 to -200V, shut off nitrogen and argon gas, and maintain a vacuum of 5×10⁻⁶. -4 ~7×10 -4 Pa, the pulsed laser power supply is turned on and focused on the carbon target. The laser pulse energy is 400-500 mJ, the repetition rate is 30-45 Hz, and the deposition time is 1-2 hours; finally, the valve stem is obtained. The carbon target is evaporated and ionized into carbon ions by laser. Under the action of negative bias voltage on the substrate, the carbon ions bombard the substrate at high speed and deposit into a hydrogen-free diamond-like carbon layer.

[0022] Compared with the prior art, the advantages of this invention due to the adoption of the above technical solution are as follows: The coating structure of the nuclear power plant valve stem and the valve stem and its preparation method of this invention combine a transition layer with a nanotwin structure and a hydrogen-free diamond-like carbon layer with high hardness, low friction coefficient and high temperature resistance, and grow it on the surface of the valve stem of the regulating valve used in nuclear power plants. This increases the surface hardness of the valve stem, improves its wear resistance, reduces the friction coefficient, reduces the friction loss of the valve stem, improves operating efficiency, and thus increases the service life of the valve stem. It can meet the technical performance requirements of valve stem impact toughness, corrosion resistance and wear resistance under high temperature and high pressure water environment, and effectively reduce production costs. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0024] Example 1

[0025] This embodiment provides a valve stem for a nuclear power plant. The valve stem includes a coating structure and an existing chromium layer. The coating structure uniformly covers the surface of the chromium coating on the valve stem itself. The coating structure of this embodiment includes a transition layer and a hydrogen-free diamond-like carbon layer arranged sequentially from the inside out.

[0026] In this embodiment, the transition layer has a nanotwinned microstructure and is configured as a TiBN layer and / or an AlN layer. The thickness of the transition layer is 0.5–1 μm, and the thickness of the hydrogen-free diamond-like carbon (DLC) layer is 1.5–3 μm. The hardness of the hydrogen-free DLC layer is 3000–3600 HV, and the fracture toughness is greater than 3.5 MPa / m. 1 / 2 In this embodiment, the valve stem has a hardness greater than or equal to 3000 HV; the valve stem's fracture toughness is greater than or equal to 3.5 MPa / m. 1 / 2 .

[0027] Example 2

[0028] This embodiment provides a method for preparing the valve stem in Embodiment 1 above, including the following steps:

[0029] (1) Clean the valve stem surface with ultrasonic petroleum ether solvent for 1 hour to remove hydraulic valve stem oil stains, then put it into anhydrous ethanol for ultrasonic cleaning for 30 minutes, and finally put it into a 45℃ drying oven for 1 hour.

[0030] (2) Place the valve stem in the vacuum vapor deposition chamber, with the chamber temperature at 100℃, and evacuate to 5×10⁻⁶. -3 Pa, then high-purity argon gas with a purity of 99.99% and a flow rate of 100 sccm is introduced into the chamber through the anodic layer ion source. The chamber pressure is maintained at 0.35 Pa, the anodic layer ion source discharge voltage is 825 V, the discharge current is 0.4 A, and a bias voltage of -500 V is applied to the valve stem to clean the regulating valve stem for 45 minutes.

[0031] (3) Adjust the negative bias voltage of the valve stem obtained in step (2) to -150V. The target material is TiB. Nitrogen gas with a flow rate of 150sccm is introduced. Argon gas is introduced to keep the gas pressure in the deposition chamber at 1.1Pa. Two sets of magnetron sputtering targets are turned on. The power of each magnetron sputtering target is 2350W. The deposition time is 20 minutes. After the deposition is completed, the magnetron sputtering power supply is turned off to complete the deposition of the TiBN layer. The thickness of the obtained TiBN is 600nm.

[0032] (4) Adjust the valve stem negative bias to -100V, shut off nitrogen and argon gas, and maintain the vacuum at 6.5×10⁻⁶. -4 Pa, turn on the pulsed laser power supply and focus it on the carbon target. The laser pulse energy is 400mJ, the repetition rate is 40Hz, the deposition time is 2 hours, and the thickness of the hydrogen-free diamond-like coating obtained is 2μm.

[0033] Example 3

[0034] This embodiment provides a method for preparing the valve stem in Embodiment 1 above, including the following steps:

[0035] (1) Clean the valve stem surface with ultrasonic petroleum ether solvent for 1 hour to remove hydraulic valve stem oil stains, then put it into anhydrous ethanol for ultrasonic cleaning for 30 minutes, and finally put it into a 45℃ drying oven for 1 hour.

[0036] (2) Place the valve stem in the vacuum vapor deposition chamber, with the chamber temperature at 150℃ and the vacuum level reduced to 6×10⁻⁶. -3 Pa, then high-purity argon gas with a purity of 99.99% and a flow rate of 150 sccm is introduced into the chamber through the anodic layer ion source. The chamber pressure is maintained at 0.45 Pa, the anodic layer ion source discharge voltage is 925 V, the discharge current is 0.45 A, a bias voltage of -400 V is applied to the valve stem, and the regulating valve stem is cleaned for 45 minutes.

[0037] (3) Adjust the negative bias voltage of the valve stem obtained in step (2) to -180V. The target material is 99.99% Al target. Introduce nitrogen gas with a flow rate of 150sccm. Continue to introduce argon gas to keep the gas pressure in the deposition chamber at 1.15Pa. Turn on two sets of magnetron sputtering targets. The power of each magnetron sputtering target is 2050W. The deposition time is 25 minutes. After the deposition is completed, turn off the magnetron sputtering power supply to complete the deposition of the AlN layer. The thickness of the AlN layer obtained is 550nm.

[0038] (4) Adjust the valve stem negative bias to -100V, shut off nitrogen and argon gas, and maintain the vacuum at 5.5×10⁻⁶. -4 Pa, turn on the pulsed laser power supply and focus it on the carbon target. The laser pulse energy is 500mJ, the repetition rate is 30Hz, the deposition time is 2 hours, and the thickness of the hydrogen-free diamond-like coating obtained is 2.4μm.

[0039] Example 4

[0040] This embodiment provides a method for preparing the valve stem in Embodiment 1 above, including the following steps:

[0041] (1) Clean the valve stem surface with ultrasonic petroleum ether solvent for 1 hour to remove hydraulic valve stem oil stains, then put it into anhydrous ethanol for ultrasonic cleaning for 30 minutes, and finally put it into a 45℃ drying oven for 1 hour.

[0042] (2) Place the valve stem in the vacuum deposition chamber, with the chamber temperature at 180℃ and the vacuum level reduced to 7.3×10⁻⁶. -3 Pa, then high-purity argon gas with a purity of 99.99% and a flow rate of 135 sccm is introduced into the chamber through the anodic layer ion source. The chamber pressure is maintained at 0.55 Pa, the anodic layer ion source discharge voltage is 875 V, the discharge current is 0.55 A, and a bias voltage of -350 V is applied to the valve stem to clean the regulating valve stem for 40 minutes.

[0043] (3) Adjust the negative bias voltage of the valve stem obtained in step (2) to -200V, introduce nitrogen gas with a flow rate of 150sccm, and continue to introduce argon gas to keep the gas pressure in the deposition chamber at 1.15Pa. Turn on one Al magnetron sputtering target with a power of 2050W and a deposition time of 25 minutes. After deposition, turn off the magnetron sputtering power supply to complete the deposition of the AlN layer. Then turn on the TiB target with a power of 2350W and a deposition time of 20 minutes. After deposition, turn off the magnetron sputtering power supply to complete the deposition of the TiBN layer. The thickness of the AlN and TiBN composite transition layer is 500nm, and the thickness ratio of the two is selected as 1:1.

[0044] (4) Adjust the negative bias voltage of the valve stem to -150V, shut off nitrogen and argon gas, and maintain the vacuum at 6.0×10⁻⁶. -4Pa, turn on the pulsed laser power supply and focus it on the carbon target. The laser pulse energy is 500mJ, the repetition rate is 35Hz, the deposition time is 1.5 hours, and the thickness of the hydrogen-free diamond-like coating obtained is 1.8μm.

[0045] Example 5

[0046] This embodiment provides a method for preparing the valve stem in Embodiment 1 above, including the following steps:

[0047] (1) Clean the valve stem surface with ultrasonic petroleum ether solvent for 1 hour to remove hydraulic valve stem oil stains, then put it into anhydrous ethanol for ultrasonic cleaning for 30 minutes, and finally put it into a 45℃ drying oven for 1 hour.

[0048] (2) Place the valve stem in the vacuum vapor deposition chamber, with a chamber temperature of 200℃, and evacuate to 6.5×10⁻⁶. -3 Pa, and then high-purity argon gas with a purity of 99.99% and a flow rate of 120 sccm is introduced into the chamber through the anodic layer ion source. The chamber pressure is maintained at 0.6 Pa, the anodic layer ion source discharge voltage is 910 V, the discharge current is 0.55 A, and a bias voltage of -450 V is applied to the valve stem to clean the regulating valve stem for 50 minutes.

[0049] (3) Adjust the negative bias voltage of the valve stem obtained in step (2) to -240V, then turn on the TiB target with a power of 2150W and a deposition time of 25 minutes. After deposition, turn off the magnetron sputtering power supply to complete the deposition of the TiBN layer. Introduce nitrogen gas with a flow rate of 180sccm and continue to introduce argon gas to keep the gas pressure in the deposition chamber at 1.35Pa. Turn on one Al magnetron sputtering target with a power of 2350W and a deposition time of 20 minutes. After deposition, turn off the magnetron sputtering power supply to complete the deposition of the AlN layer. The thickness of the TiBN and AlN composite transition layer is 550nm, and the thickness ratio of the two is selected as 1:1.

[0050] (4) Adjust the valve stem negative bias to -200V, shut off nitrogen and argon gas, and maintain the vacuum at 5.25×10⁻⁶. -4 Pa, turn on the pulsed laser power supply and focus it on the carbon target. The laser pulse energy is 500mJ, the repetition rate is 45Hz, the deposition time is 2.5 hours, and the thickness of the hydrogen-free diamond-like coating obtained is 2.4μm.

[0051] Comparative Example 1

[0052] The difference between Comparative Example 1 and Example 2 is that the deposited layer in step (4) is a hydrogen-containing diamond-like carbon layer. The hydrogen-containing diamond-like carbon layer is prepared by magnetron sputtering physical vapor deposition technology. The graphite target power is 300W, the bias voltage is 200V, the target-substrate distance is 30cm, and the sputtering pressure is 6×10⁻⁶. -3Pa was used to obtain a hydrogen-containing diamond-like layer, with a deposition time of 3 hours and a coating thickness of 2.8 μm. The rest of the preparation process was the same.

[0053] Comparative Example 2

[0054] The difference between Comparative Example 2 and Example 2 is that the method for depositing the transition layer in step (3) is as follows: the chamber temperature is room temperature, the valve stem is negatively biased to -50V, the target material is TiB, nitrogen gas with a flow rate of 150 sccm is introduced, and argon gas is continued to be introduced to maintain the gas pressure in the deposition chamber at 1.2 Pa. Two sets of magnetron sputtering targets are turned on, each with a power of 1200W, and the deposition time is 20 minutes. After the deposition is completed, the magnetron sputtering power supply is turned off to complete the deposition of the TiBN layer. The thickness of the obtained TiBN layer is 480 nm. The rest of the preparation process is the same.

[0055] Results and Discussion of Example 6

[0056] The valve stems of the control valves prepared according to the methods in Examples 2 to 5 and Comparative Examples 1 and 2 were subjected to relevant physical property tests. The test methods were as follows: hardness was tested using a Vickers hardness tester; fracture toughness was tested using a cantilever beam test. The test results are shown in Table 1.

[0057] Table 1. Test results of valve stems prepared in Examples 2 to 5 and Comparative Examples 1 and 2.

[0058] Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Hardness / HV 3000 3200 3400 3600 2800 2500 <![CDATA[Fracture toughness / MPa / m 1 / 2 > 4 3.8 3.6 3.5 2.5 2.7

[0059] As can be seen from Table 1, the valve stems prepared in Examples 2 to 5 are significantly superior to those prepared in Comparative Examples 1 and 2 in terms of both hardness and fracture toughness. Compared with Comparative Examples 1 and 2, the coating structures of Examples 2 to 5, which have a hydrogen-free diamond-like carbon layer and a transition layer with a nanotwin structure, result in higher hardness and stronger fracture toughness on the valve stem surface. This is beneficial for improving the service life of the valve stem and enabling it to meet the technical performance requirements for impact toughness, corrosion resistance, and wear resistance under high-temperature and high-pressure water environments.

[0060] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A coating structure for the stem of a control valve in a nuclear power plant, characterized in that, The valve stem comprises a transition layer and a hydrogen-free diamond-like carbon (DLC) layer arranged sequentially from the inside out. The transition layer has a nanotwinned microstructure and is a TiBN layer and / or an AlN layer. The transition layer is used to improve the toughness of the valve stem with the coating structure. The valve stem surface itself also has a chromium layer. The coating structure uniformly covers the surface of the chromium coating on the valve stem itself. The hydrogen-free DLC layer is used to improve the hardness of the valve stem with the coating structure. The transition layer with a nanotwinned structure was prepared by the following method: In a vacuum vapor deposition chamber, the negative bias voltage of the valve rod after plasma surface activation was adjusted to -100 to -300V, nitrogen gas with a flow rate of 100 to 200 sccm was introduced, and argon gas was continued to be introduced to maintain the gas pressure in the deposition chamber at 1.0 to 1.5 Pa and the temperature at 100 to 200℃. The magnetron sputtering target was turned on, and the power of the magnetron sputtering target was adjusted to 2000 to 2500W. The deposition time was 20 to 30 minutes. After the deposition was completed, the magnetron sputtering power supply was turned off, and the deposition of the transition layer was completed.

2. The coating structure according to claim 1, characterized in that, When the transition layer is a TiBN layer and an AlN layer, the thickness ratio of the TiBN layer to the AlN layer is 1:0.8 to 1:1.

5.

3. The coating structure according to claim 1, characterized in that, The thickness of the transition layer is 0.5~1μm, and the thickness of the hydrogen-free diamond-like layer is 1.5~3μm.

4. The coating structure according to claim 1, characterized in that, The hardness of the hydrogen-free diamond-like layer is 3000~3600HV.

5. The coating structure according to claim 1, characterized in that, The fracture toughness of the hydrogen-free diamond-like carbon layer is greater than 3.5 MPa·m. 1 / 2 .

6. A valve stem comprising the coating structure as described in any one of claims 1 to 5.

7. The valve stem according to claim 6, characterized in that, The valve stem has a hardness greater than or equal to 3000 HV; the valve stem has a fracture toughness greater than or equal to 3.5 MPa·m. 1 / 2 .

8. A method for preparing a valve stem as described in claim 7, characterized in that, Includes the following steps: After cleaning the valve stem, the valve stem is subjected to plasma surface activation, and then a transition layer and a hydrogen-free diamond-like carbon layer are deposited sequentially to obtain the valve stem.

9. The preparation method according to claim 8, characterized in that, The method for depositing the transition layer is as follows: in a vacuum vapor deposition chamber, the negative bias voltage of the valve rod after plasma surface activation is adjusted, nitrogen and argon are introduced, the magnetron sputtering target is turned on for deposition, and the magnetron sputtering power supply is turned off after deposition is completed to obtain the transition layer. The method for depositing hydrogen-free diamond-like carbon (DLC) layers is as follows: adjust the negative bias voltage of the valve stem, turn off the nitrogen and argon gases, turn on the pulsed laser power supply and focus it on the carbon target for deposition, and turn off the pulsed laser power supply after deposition to obtain a hydrogen-free DLC layer.