Preparation method of high-temperature butterfly valve cobalt-based alloy PVD composite coating

Abstract

This invention relates to the field of valve surface treatment technology and discloses a method for preparing a cobalt-based alloy PVD composite coating for high-temperature butterfly valves. The method includes: laser-coating identical cobalt-based alloy powder onto the sealing surfaces of mating butterfly plates and valve seats; forming a cobalt-based alloy support layer through grinding, polishing, cleaning, and ion activation; and sequentially depositing a cobalt-based alloy matching layer, a nitrogen-containing cobalt-based alloy connecting layer, and a composite transition layer using a cobalt-based matching target that matches the main metal elements of the cobalt-based alloy powder. An AlCrSiN working layer is formed on the butterfly plate sealing surface, and an AlCrSiN working layer and an AlCrSiON surface layer are formed on the valve seat sealing surface, ensuring that the total thickness difference between the two working layers does not exceed 0.2 μm. This invention reduces adhesive tearing and material transfer during high-temperature opening and closing by using the same support interface system, the mating of heterogeneous surface layers in a specified direction, and the matching of the total thickness of the working layers, thus maintaining opening, closing, and sealing performance.

Description

Technical Field

[0001] This invention relates to the field of valve surface treatment technology, and more specifically, to a method for preparing a cobalt-based alloy PVD composite coating for a high-temperature butterfly valve. Background Technology

[0002] High-temperature butterfly valves typically employ a hard metal seal between the butterfly plate sealing surface and the valve seat sealing surface. During the opening and closing process, the butterfly plate sealing surface and the valve seat sealing surface repeatedly undergo compression, relative sliding, and separation. Under the combined effects of high-temperature media, contact loads, and temperature cycling, the sealing surface is prone to oxidation, wear, localized adhesion, material transfer, and scratches. Long-term operation may lead to problems such as increased opening and closing torque, sealing surface damage, and increased leakage. Using a cobalt-based alloy layer can improve the sealing surface's load-bearing capacity and high-temperature wear resistance. Further deposition of a PVD hard coating on the cobalt-based alloy layer surface can further improve the surface wear resistance and oxidation resistance of the sealing surface.

[0003] Chinese invention patent application CN103060751A discloses an ultra-hard corrosion-resistant PVD coating for valve sealing components and its coating process. It forms a metal nitride, metal carbide, or metal carbonitride coating on the surface of the valve sealing component, and employs pretreatment, a metal transition layer, and ion bombardment processes to improve the coating performance. Chinese invention patent application CN108130533A discloses a high-wear-resistant and corrosion-resistant hard-seal ball valve and its manufacturing method. It sequentially forms a carbide metal-ceramic inner coating and a PVD nitride ceramic coating on the surfaces of the ball and valve seat. The inner coating provides hardness support, and the PVD coating enhances surface wear and corrosion resistance.

[0004] The aforementioned existing technologies primarily focus on improving the hardness, wear resistance, and corrosion resistance of the sealing component surface, without addressing the correlation between the working layer composition and total thickness of the contact mating pair formed by the butterfly plate sealing surface and the valve seat sealing surface. When both sealing surfaces use hard working layers with the same or similar compositions, the two working layers remain in a homogeneous contact state for a long time, and local adhesion and material transfer are still possible during repeated opening and closing at high temperatures. If an additional oxidation-resistant surface layer is added to only one sealing surface, it will increase the total thickness of the working layer on the corresponding sealing surface, causing changes in working layer composition and coating thickness to coexist, making it difficult to balance the heterogeneous mating effect and the original sealing mating state. Furthermore, there is a compositional difference between the cobalt-based alloy support layer and the aluminum-chromium-silicon nitride working layer. Using direct deposition or a single transition layer makes it difficult to simultaneously achieve the supporting role of the cobalt-based alloy support layer and the bonding stability of the PVD working layer during high-temperature cycling. Therefore, there is a need to provide a method for preparing a cobalt-based alloy PVD composite coating for high-temperature butterfly valves, which forms a stable transition between the cobalt-based alloy bearing layer and the PVD working layer, and coordinates the surface composition and total thickness of the working layer of the butterfly plate sealing surface and the valve seat sealing surface, thereby reducing the possibility of local adhesion, material transfer and sealing failure during repeated opening and closing at high temperatures. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a cobalt-based alloy PVD composite coating for high-temperature butterfly valves, so as to solve the above-mentioned technical problems.

[0006] To achieve the above objectives, the present invention provides the following solution: A method for preparing a cobalt-based alloy PVD composite coating for a high-temperature butterfly valve includes the following steps: Using the same Co-Cr-W-Ni-B-Si-C cobalt-based alloy powder, laser cladding is performed on the mating butterfly plate sealing surface and valve seat sealing surface, respectively. After grinding and polishing, a cobalt-based alloy bearing layer with a thickness of 0.6-1.2 mm is formed, and then the layers are cleaned and ion activated. At 380–450 °C and 0.6–1.2 Pa, the same PVD interface deposition was performed on two cobalt-based alloy support layers: a Co-Cr-W-Ni cobalt-based matching target was used for magnetron sputtering in argon gas to form a cobalt-based alloy matching layer with a thickness of 0.2–0.5 μm; after normalizing the total mass of Co, Cr, W and Ni of the cobalt-based matching target and the cobalt-based alloy powder, the mass percentage difference of each corresponding element did not exceed 1.0 percentage point; While keeping the cobalt-based matching target in operation, the nitrogen flow rate was sequentially set to 20%, 40%, and 60% of the total flow rate of argon and nitrogen, and each deposition lasted for 5 to 10 minutes to form a nitrogen-containing cobalt-based alloy bonding layer. With the nitrogen ratio maintained at 60%, the aluminum-chromium-silicon target was started, and the cobalt-based matching target and the aluminum-chromium-silicon target were co-sputtered sequentially at target surface power density ratios of 75:25, 50:50 and 25:75, respectively, for 8 to 12 minutes each, and the sum of the target surface power densities of the two targets remained constant, forming a composite transition layer. The cobalt-based matching target is turned off, while the aluminum-chromium-silicon target remains operational. An AlCrSiN working layer with a thickness of 2.5–4.0 μm is deposited on the butterfly plate side, and an AlCrSiN working layer and an AlCrSiON surface layer with a thickness of 0.2–0.5 μm are sequentially deposited on the valve seat side. The total thickness of the two layers on the valve seat side is 2.5–4.0 μm, and the thickness difference between the two layers and the AlCrSiN working layer on the butterfly plate side does not exceed 0.2 μm.

[0007] Preferably, the cobalt-based alloy powder comprises, by mass percentage, 24%–30% Cr, 6%–10% W, 7%–12% Ni, 1.0%–2.5% B, 1.5%–3.0% Si, 0.5%–1.5% C, with the balance being Co and unavoidable impurities.

[0008] Preferably, the cobalt-based matching target is prepared according to the normalized mass percentages of Co, Cr, W and Ni in the cobalt-based alloy powder, wherein the difference between the normalized mass percentage of each element in the cobalt-based matching target and the normalized mass percentage of the corresponding element in the cobalt-based alloy powder does not exceed 0.5 percentage points, and the total unavoidable impurity content in the cobalt-based matching target does not exceed 0.5%.

[0009] Preferably, the aluminum-chromium-silicon target comprises 55%–62% Al, 4%–8% Si, and the balance being Cr and unavoidable impurities, with the total content of unavoidable impurities in the aluminum-chromium-silicon target not exceeding 0.5% by atomic percentage.

[0010] Preferably, when forming the cobalt-based alloy support layer, the cobalt-based alloy powder is preheated to 100-180°C, and argon gas is used to transport the cobalt-based alloy powder to the laser cladding area. The laser power is 1.4-2.2kW, the scanning speed is 4-10mm / s, the powder feeding rate is 8-18g / min, and the overlap rate of adjacent cladding channels is 30%-50%. The cobalt-based alloy support layer formed by laser cladding is ground and polished so that the surface roughness Ra of the ground and polished cobalt-based alloy support layer is 0.05-0.4μm.

[0011] Preferably, when cleaning and ion-activating the cobalt-based alloy carrier layer, alkaline degreasing, deionized water cleaning, and ethanol ultrasonic cleaning are performed sequentially. The cleaned high-temperature butterfly valve is placed in a vacuum chamber and vacuum-heated at 250–350°C for 30–60 minutes. Then, argon gas is introduced, and argon ion etching is performed at a negative bias voltage of 400–700V for 15–30 minutes.

[0012] Preferably, before performing the PVD interface deposition process, the background pressure of the vacuum chamber is evacuated to no more than 5 × 10⁻⁶. - 3 Pa; When the cobalt-based alloy matching layer is formed, the target surface power density of the cobalt-based matching target is 4-8 W / cm². 2 The base negative bias voltage applied to the butterfly plate or valve seat is 80-150V.

[0013] Preferably, when forming the nitrogen-containing cobalt-based alloy connecting layer, the total flow rate of argon and nitrogen is maintained at 200-400 sccm, and the ratio of nitrogen flow rate to the total flow rate of argon and nitrogen is adjusted to 20%, 40% and 60% in turn by reducing the argon flow rate by an equal amount; the thickness of the formed nitrogen-containing cobalt-based alloy connecting layer is 0.3-0.8 μm.

[0014] Preferably, when forming the composite transition layer, the sum of the target surface power densities of the cobalt-based matching target and the aluminum-chromium-silicon target is maintained at 8–12 W / cm². 2 The thickness of the composite transition layer is 0.6–1.5 μm; when forming the AlCrSiN working layer, the target surface power density of the aluminum-chromium-silicon target is 4–8 W / cm². 2 The base negative bias voltage applied to the butterfly plate or valve seat is 60-120V.

[0015] Preferably, the set thickness of the AlCrSiON surface layer on the valve seat sealing surface is predetermined. When the AlCrSiN working layer on the valve seat sealing surface is deposited to the difference between the set total thickness of the working layer on the valve seat sealing surface and the set thickness of the AlCrSiON surface layer, the target power density, argon flow rate and total flow rate of the reaction gas of the aluminum chromium silicon target are kept constant. Oxygen is introduced and nitrogen is reduced by an equal amount, so that the oxygen flow rate accounts for 3% to 8% of the total flow rate of nitrogen and oxygen, and the AlCrSiON surface layer continues to be deposited.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In this invention, a cobalt-based alloy bearing layer is first formed on the butterfly plate sealing surface and the valve seat sealing surface, and then a cobalt-based alloy matching layer is formed using a cobalt-based matching target. The Co, Cr, W and Ni in the cobalt-based matching target are configured according to the normalized mass percentage of the corresponding elements in the cobalt-based alloy powder, so that the cobalt-based alloy bearing layer and the cobalt-based alloy matching layer have corresponding main metal element compositions. On this basis, a nitrogen-containing cobalt-based alloy connecting layer is formed sequentially with nitrogen ratios of 20%, 40% and 60%, and a composite transition layer is formed according to the target surface power density ratios of 75:25, 50:50 and 25:75, transitioning from cobalt-based composition to aluminum chromium silicon nitride composition. The cobalt-based alloy bearing layer is used to bear the sealing contact load, and the cobalt-based alloy matching layer, the nitrogen-containing cobalt-based alloy connecting layer and the composite transition layer are used to connect the cobalt-based alloy bearing layer and the AlCrSiN working layer, thereby mitigating the abrupt changes in composition and performance between adjacent layers and improving the bonding stability of the composite coating during high-temperature start-up and shut-down cycles.

[0017] (2) The butterfly plate sealing surface and the valve seat sealing surface adopt the same cobalt-based alloy bearing layer, cobalt-based alloy matching layer, nitrogen-containing cobalt-based alloy connecting layer and composite transition layer, so that the two sealing surfaces have corresponding bearing and interface transition systems. The butterfly plate sealing surface adopts an AlCrSiN working layer, and the valve seat sealing surface adopts a working layer composed of an AlCrSiN layer and an AlCrSiON surface layer, so that the two sealing surfaces in contact form a specified non-homogeneous surface layer fit between AlCrSiN and AlCrSiON. The AlCrSiN working layer on the butterfly plate side is used to maintain wear-resistant bearing capacity, and the AlCrSiON surface layer on the valve seat side is used to improve the high-temperature surface chemical stability and change the contact interface state of the two sealing surfaces. When the two sealing surfaces are in contact, a direct fit between the homogeneous surface layers of AlCrSiN and AlCrSiN is no longer formed, thereby reducing the tendency of local adhesion, material transfer and scratching during repeated opening and closing at high temperature.

[0018] (3) The AlCrSiON surface layer on the valve seat side is used to replace part of the AlCrSiN layer, instead of adding more coating on the AlCrSiN layer that has already reached the set thickness. This ensures that the sum of the thicknesses of the AlCrSiN layer and the AlCrSiON surface layer on the valve seat side is no more than 0.2 μm thicker than the thickness of the AlCrSiN working layer on the butterfly plate side. This allows for the introduction of a heterogeneous surface layer mating relationship while maintaining a basically consistent total thickness of the working layers on both sealing surfaces, reducing the impact of adding a surface protective layer on one side on the sealing mating state. When forming the AlCrSiON surface layer, oxygen is introduced and nitrogen is reduced by an equal amount after the AlCrSiN layer has been deposited to 80%–95% of the set thickness. At the same time, the target power density and the total flow rate of the reaction gas are kept constant. This allows for the continuous conversion of the AlCrSiN layer to the AlCrSiON surface layer in the same deposition process, reducing fluctuations in deposition conditions and making the preparation process of the composite coating stable and repeatable. The aforementioned matching of the bearing layer, phased transition, pairing of heterogeneous surface layers, and matching of total thickness work together to help suppress the increase of opening and closing torque and damage to the sealing surface of the high-temperature butterfly valve, and maintain the sealing performance after high-temperature cycling. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise specified, the content of each element in the cobalt-based alloy powder is a mass percentage, and the content of each element in the aluminum-chromium-silicon target is an atomic percentage. Nitrogen ratio refers to the percentage of nitrogen flow rate relative to the total flow rate of argon and nitrogen; oxygen ratio refers to the percentage of oxygen flow rate relative to the total flow rate of nitrogen and oxygen. The total thickness of the working layer on the butterfly plate side refers to the thickness of the AlCrSiN working layer on the butterfly plate sealing surface, and the total thickness of the working layer on the valve seat side refers to the sum of the thickness of the AlCrSiN layer and the thickness of the AlCrSiON surface layer on the valve seat sealing surface.

[0021] The high-temperature butterfly valve used in this embodiment is a DN100 metal hard-seal butterfly valve, with both the butterfly plate and valve seat made of 06Cr19Ni10 stainless steel. The cobalt-based alloy powder is gas-atomized powder with a particle size of 45–105 μm. The reactive magnetron sputtering equipment is equipped with a cobalt-based matched target and an aluminum-chromium-silicon target, both with an effective sputtering area of ​​200 cm². 2 The butterfly plate and valve seat are PVD deposited separately. Except for the gas composition at the end of the working layer, the cobalt-based alloy matching layer, nitrogen-containing cobalt-based alloy connecting layer and composite transition layer on the two sealing surfaces use the same deposition parameters.

[0022] The PVD coating thickness was controlled using a quartz crystal film thickness monitor, which controlled the thickness of each individual layer based on a pre-calibrated deposition rate. Film thickness test pieces from the same batch were installed in fixtures adjacent to the corresponding sealing surfaces, ensuring that the test pieces maintained the same target distance, orientation, and movement pattern with the corresponding sealing surfaces. A 3mm wide measurement area was pre-shielded from each test piece. After deposition, the shielding was removed, and a contact profilometer was used to measure the height difference between the deposited area and the shielded area. Five measurements were taken from each test piece in the batch, and the average of the five measurements was used to verify the total thickness of the corresponding PVD composite coating. Example 1

[0023] This embodiment provides a method for preparing a cobalt-based alloy PVD composite coating for a high-temperature butterfly valve, including the following steps.

[0024] (1) Formation of a cobalt-based alloy support layer The cobalt-based alloy powder used includes 27.0% Cr, 8.0% W, 9.5% Ni, 1.8% B, 2.2% Si, and 1.0% C, with the balance being Co. The Co content is 50.5%.

[0025] Rust removal and ethanol cleaning were performed on the butterfly plate sealing surface and valve seat sealing surface. Cobalt-based alloy powder was preheated at 140℃ for 30 minutes. Coaxial powder feeding laser cladding equipment was used to perform cladding along the circumference of the butterfly plate sealing surface and valve seat sealing surface. The laser spot diameter was 3.0 mm, the laser power was 1.8 kW, the scanning speed was 7 mm / s, the powder feeding rate was 12 g / min, the overlap rate of adjacent cladding channels was 40%, the argon powder feeding flow rate was 8 L / min, and the protective argon flow rate in the cladding area was 15 L / min.

[0026] After cladding, the cobalt-based alloy cladding area was ground and polished using a diamond grinding wheel to ensure that the thickness of the cobalt-based alloy bearing layer on both the butterfly plate sealing surface and the valve seat sealing surface was 0.90 mm and the surface roughness Ra was 0.30 μm. The thickness of the cobalt-based alloy bearing layer was determined by comparing the height difference between the sealing surfaces before and after cladding at the same measurement position. Eight measurement positions were selected at equal intervals along the circumference of the sealing surface, and the thickness at each of the eight measurement positions was controlled within the range of 0.90 mm ± 0.05 mm.

[0027] (2) Preparation of cobalt-based matching target The total mass of Co, Cr, W, and Ni in the cobalt-based alloy powder is 95.0%. Using 95.0% as the normalized baseline, the normalized mass percentages of Co, Cr, W, and Ni are 53.16%, 28.42%, 8.42%, and 10.00%, respectively.

[0028] A cobalt-based matching target was prepared using a vacuum melting method. The cobalt-based matching target consisted of 53.2% Co, 28.4% Cr, 8.4% W, and 10.0% Ni. The difference between the mass percentage of each element in the cobalt-based matching target and its corresponding normalized mass percentage did not exceed 0.1 percentage points.

[0029] The B, Si, and C elements in the cobalt-based alloy powder are used to improve the melting and spreading properties during laser cladding and the performance of the cobalt-based alloy support layer; these are not included in the normalized composition of the cobalt-based matching target. The cobalt-based matching target is used to match the main metallic element composition in the cobalt-based alloy support layer.

[0030] (3) Cleaning and ion activation The butterfly plate and valve seat, after grinding and polishing, are sequentially subjected to alkaline degreasing, deionized water cleaning, ethanol ultrasonic cleaning, and vacuum heating.

[0031] The alkaline degreasing solution consists of 25 g / L sodium carbonate, 20 g / L trisodium phosphate, 10 g / L sodium silicate, and 2 g / L nonionic surfactant. The alkaline degreasing temperature is 60℃, and the degreasing time is 10 min. After degreasing, the solution is rinsed twice with deionized water for 3 min each time, and then ultrasonically cleaned in ethanol for 15 min.

[0032] Install the cleaned butterfly plate or valve seat onto the rotating fixture of the PVD equipment, with the sealing surface facing the target material. The target-base distance should be 100 mm, and the fixture rotation speed should be 5 r / min. Evacuate the vacuum chamber to 5 × 10⁻⁶. -3 Below Pa, vacuum heating was performed at 300℃ for 45 min, followed by a further increase to 420℃. Argon gas was introduced and the pressure was adjusted to 0.8 Pa, and argon ion etching was performed for 20 min under a substrate bias of -550V.

[0033] (4) Formation of cobalt-based alloy matching layer After ion etching, the deposition temperature is maintained at 420℃, the working pressure is adjusted to 0.9 Pa, and argon gas with a purity of not less than 99.999% is introduced. The cobalt-based matching target is then activated, with a target surface power density of 6 W / cm². 2 The substrate negative bias voltage is -110V. A cobalt-based alloy matching layer with a thickness of 0.35μm is deposited on the surface of the cobalt-based alloy carrier layer.

[0034] (5) Formation of a nitrogen-containing cobalt-based alloy bonding layer With the cobalt-based matching target in operation and the total flow rate of argon and nitrogen maintained at 300 sccm, the following three nitriding stages were performed sequentially: First nitriding stage: Argon flow rate 240 sccm, nitrogen flow rate 60 sccm, nitrogen ratio 20%, deposition time 8 min; Second nitriding stage: Argon flow rate 180 sccm, nitrogen flow rate 120 sccm, nitrogen ratio 40%, deposition for 8 min; Third nitriding stage: Argon flow rate is 120 sccm, nitrogen flow rate is 180 sccm, nitrogen ratio is 60%, deposition time is 8 min.

[0035] After the three nitriding stages are completed, a nitrogen-containing cobalt-based alloy bonding layer with a thickness of 0.55 μm is formed. The deposition temperature is maintained at 420 °C, the working pressure at 0.9 Pa, and the substrate negative bias voltage at -100 V for all three nitriding stages.

[0036] (6) Formation of a composite transition layer Maintain the argon and nitrogen flow rates during the third nitriding stage and start the aluminum-chromium-silicon target. The aluminum-chromium-silicon target comprises 58% Al, 6% Si, and 36% Cr. The combined target surface power density of the cobalt-based matching target and the aluminum-chromium-silicon target is maintained at 10 W / cm². 2 The total working power of the two targets is 2.0kW. The following three co-sputtering stages are performed sequentially: First co-sputtering stage: cobalt-based matching target power is 1.5kW, aluminum-chromium-silicon target power is 0.5kW, target power density ratio is 75:25, deposition time is 10min; Second co-sputtering stage: cobalt-based matching target power is 1.0kW, aluminum-chromium-silicon target power is 1.0kW, target power density ratio is 50:50, deposition time is 10min; Third co-sputtering stage: cobalt-based matching target power is 0.5kW, aluminum-chromium-silicon target power is 1.5kW, target power density ratio is 25:75, deposition time is 10min.

[0037] The substrate was kept at a negative bias of -90V during all three co-sputtering stages. After the three co-sputtering stages were completed, a composite transition layer with a thickness of 1.05 μm was formed, and then the cobalt-based matching target was turned off.

[0038] (7) Forming the AlCrSiN working layer on the butterfly plate side During PVD deposition on the butterfly plate, the argon flow rate was maintained at 120 sccm, the nitrogen flow rate at 180 sccm, the deposition temperature at 420℃, and the working pressure at 0.9 Pa. The target power density of the aluminum-chromium-silicon target was 6 W / cm². 2 The substrate negative bias voltage is -90V.

[0039] AlCrSiN was deposited on the surface of the composite transition layer until the thickness of the AlCrSiN working layer reached 3.20 μm, at which point deposition was stopped. The total thickness of the working layer on the butterfly plate side was 3.20 μm.

[0040] (8) Forming an AlCrSiN layer and an AlCrSiON surface layer on the valve seat side. When performing PVD deposition on the valve seat, the same gas flow rate, target power density, and substrate negative bias are used to deposit the AlCrSiN layer as on the butterfly plate side. When the AlCrSiN layer thickness reaches 2.80 μm, the argon flow rate is kept constant at 120 sccm, the working power of the AlCrSiN target is kept constant, and the total flow rate of the reaction gas (the total flow rate of the reaction gas refers to the sum of the nitrogen flow rate and the oxygen flow rate). The nitrogen flow rate is adjusted from 180 sccm to 169.2 sccm, while 10.8 sccm of oxygen is introduced.

[0041] Oxygen accounts for 6% of the total volume of nitrogen and oxygen, and continues to deposit to form an AlCrSiN surface layer with a thickness of 0.40 μm. When oxygen is introduced, the thickness of the already formed AlCrSiN layer accounts for 87.5% of the set total thickness of the working layer on the valve seat side.

[0042] The sum of the thicknesses of the AlCrSiN layer and the AlCrSiON surface layer on the valve seat side is 3.20 μm, and the thickness difference between the AlCrSiN working layer on the butterfly plate side is 0 μm.

[0043] During the PVD deposition process on the butterfly plate side and valve seat side, the vacuum chamber is not opened from the beginning of the cobalt-based alloy matching layer until the corresponding working layer is deposited, in order to reduce surface contamination between adjacent layers.

[0044] Example 2 and Example 3 Examples 2 and 3 follow the same preparation sequence as Example 1, except that the cobalt-based alloy powder, cobalt-based matching target, aluminum-chromium-silicon target, and process parameters are set according to Tables 1 and 2.

[0045] Table 1 Material composition of Examples 2 and 3

[0046] Table 2. Process parameters for Examples 2 and 3

[0047] Since the effective sputtering area of ​​both the cobalt-based matching target and the aluminum-chromium-silicon target is 200 cm² 2 In Example 2, the total working power of the two targets is 1.6kW, and the working power of the two targets in the three co-sputtering stages is 1.2kW and 0.4kW, 0.8kW and 0.8kW, and 0.4kW and 1.2kW, respectively. In Example 3, the total working power of the two targets is 2.4kW, and the working power of the two targets in the three co-sputtering stages is 1.8kW and 0.6kW, 1.2kW and 1.2kW, and 0.6kW and 1.8kW, respectively. The target surface power density ratios of the two targets in each co-sputtering stage are 75:25, 50:50, and 25:75, respectively.

[0048] In Example 2, oxygen was introduced when the AlCrSiN layer thickness on the valve seat side reached 2.50 μm, and the AlCrSiN layer thickness accounted for 89.3% of the total set thickness of the working layer on the valve seat side. In Example 3, oxygen was introduced when the AlCrSiN layer thickness on the valve seat side reached 3.30 μm, and the AlCrSiN layer thickness accounted for 86.8% of the total set thickness of the working layer on the valve seat side.

[0049] Comparative Example 1 A cobalt-based alloy support layer, a cobalt-based alloy matching layer, a nitrogen-containing cobalt-based alloy connecting layer, and a composite transition layer were prepared according to Example 1. A 3.20 μm thick AlCrSiN working layer was deposited on both the butterfly plate sealing surface and the valve seat sealing surface; no AlCrSiON surface layer was formed.

[0050] Comparative Example 2 Each substrate was prepared according to Example 1. A 2.80 μm thick AlCrSiN layer was first deposited on both the butterfly plate sealing surface and the valve seat sealing surface, followed by a 0.40 μm thick AlCrSiON surface layer. The total working layer thickness on both sealing surfaces was 3.20 μm.

[0051] Comparative Example 3 Each bottom layer was prepared according to Example 1. An AlCrSiN layer with a thickness of 2.80 μm and an AlCrSiON surface layer with a thickness of 0.40 μm were sequentially formed on the butterfly plate sealing surface, and an AlCrSiN working layer with a thickness of 3.20 μm was formed on the valve seat sealing surface.

[0052] Comparative Example 4 Each substrate was prepared according to Example 1. A 3.20 μm thick AlCrSiN working layer was formed on the butterfly plate sealing surface; an AlCrSiN layer with a thickness of 3.20 μm was first formed on the valve seat sealing surface, and then an additional AlCrSiON surface layer with a thickness of 0.40 μm was formed.

[0053] The total thickness of the working layer on the valve seat side is 3.60 μm, and the difference in total thickness between the two working layers is 0.40 μm.

[0054] Comparative Example 5 Following Example 1, a cobalt-based alloy support layer was formed, and cleaning and ion activation were completed. After forming a 0.35 μm thick cobalt-based alloy matching layer on the surface of the cobalt-based alloy support layer, the three nitriding stages and three co-sputtering stages were skipped, and the cobalt-based matching target was directly shut down and the aluminum-chromium-silicon target was activated.

[0055] The butterfly plate sealing surface forms an AlCrSiN working layer with a thickness of 3.20 μm; the valve seat sealing surface forms an AlCrSiN layer with a thickness of 2.80 μm and an AlCrSiON surface layer with a thickness of 0.40 μm.

[0056] High temperature start-up and shut-down cycle test Three sets of butterfly plate and valve seat sealing pairs were prepared using the methods of Examples 1-3 and Comparative Examples 1-5, respectively. Each set of sealing pairs was installed in the test valve body of a DN100 butterfly valve of the same specification, and the valve stem, bearing, packing and actuator were all products of the same specification.

[0057] The butterfly valve was placed in a high-temperature opening and closing test apparatus and heated to 650℃ at a rate of 5℃ / min, then held at that temperature for 60 minutes to stabilize the temperature of the sealing pair at 650℃±10℃. The actuator drove the butterfly plate in a sequence of fully closed, fully open, and fully closed. Each time it was fully closed and fully opened, it was held for 5 seconds. One fully open and one fully closed cycle were recorded as one opening and closing cycle. The actuator output torque at the closing endpoint was set to 75 N·m, and a total of 1000 opening and closing cycles were performed.

[0058] During the first, 500th, and 1000th opening and closing operations, a torque sensor installed between the valve stem and the actuator records the peak torque at which the butterfly plate begins to rotate from the fully closed state. The starting torque of the sealing pair is obtained by subtracting the no-load torque of the valve stem, bearing, and packing measured when the butterfly plate is not in contact with the valve seat from the measured peak torque.

[0059] After completing 1000 high-temperature opening and closing cycles, the butterfly valve was allowed to cool naturally to 25℃±2℃. The butterfly valve was then closed, and 0.6MPa nitrogen gas was introduced into the inlet side of the butterfly valve and maintained for 60 seconds. The leakage was measured using a gas flow meter installed on the outlet side, and the average value of the measurement results in the last 30 seconds was taken as the leakage of the sealing pair.

[0060] Disassemble the butterfly plate and valve seat, and remove free abrasive debris from the sealing surface using ethanol. Cover the sealing strip surface with a transparent measuring patch with a 1mm × 1mm grid, and count the number of grids with visible adhesion, smearing, or scratches. The percentage of the area of ​​the grids with adhesion or scratches to the total area of ​​the sealing strip is recorded as the visible adhesion / scratching area ratio. For areas where coating peeling has occurred, intact grids are counted as 1mm. 2 For incomplete meshes, the area of ​​the spalled area is estimated as a proportion of the corresponding mesh area. The visible spalled area of ​​a single sealing pair is recorded to 0.1 mm. 2 The results for each group are the arithmetic mean of the measurement results of three sets of sealing pairs.

[0061] Test results Table 3 Results of High Temperature Start-up and Closing Cycle Test

[0062] The test results of Examples 1-3 show that after 1000 opening and closing cycles at 650℃, the starting torque growth rate of the three sealing pairs was 11.5%-13.3%, the leakage rate was 1.6-2.2 mL / min, and no visible coating peeling was observed on the sealing surface. The starting torque growth rate and leakage rate of Examples 1-3 are similar, indicating that the composite coatings prepared under the three process conditions can maintain stable high-temperature opening and closing performance.

[0063] Example 1 and Comparative Example 1 have the same underlying structure and total working layer thickness. The difference lies in that Example 1 uses a non-homogeneous surface layer combination of AlCrSiN on the butterfly plate side and AlCrSiON on the valve seat side, while Comparative Example 1 uses AlCrSiN surface layers on both the butterfly plate side and the valve seat side. The starting torque growth rate, leakage rate, and visible adhesive scratch area ratio of Example 1 are 11.5%, 1.8 mL / min, and 0.7%, respectively, while those of Comparative Example 1 are 54.1%, 12.8 mL / min, and 5.9%, respectively. The data show that, under the same underlying structure and total working layer thickness, the non-homogeneous surface layer combination of AlCrSiN and AlCrSiON can reduce adhesive scratches and material transfer caused by repeated high-temperature contact, and reduce the starting torque growth and sealing leakage.

[0064] In Comparative Example 2, both the butterfly plate side and the valve seat side were coated with AlCrSiON. The starting torque growth rate and leakage rate were 34.2% and 7.6 mL / min, respectively, which were lower than those of Comparative Example 1 (54.1% and 12.8 mL / min), but still higher than those of Example 1 (11.5% and 1.8 mL / min). This shows that while using AlCrSiON coatings on both sealing surfaces can improve high-temperature opening and closing performance, it does not achieve the results obtained by combining AlCrSiN and AlCrSiON, which are non-homogeneous coatings.

[0065] Example 1 and Comparative Example 3 used the same coating material, underlayer structure, and working layer thickness, differing only in the reversed placement of the AlCrSiON surface layer. Comparative Example 3 showed a 41.7% increase in starting torque, a leakage rate of 9.4 mL / min, and an adhesion tear area ratio of 4.4%, all higher than Example 1. These data indicate that the placement of the AlCrSiN working layer and the AlCrSiON surface layer between the butterfly plate and the valve seat affects the high-temperature opening and closing performance of the sealing pair. The butterfly plate is a rotating component relative to the valve seat. The AlCrSiN working layer on the butterfly plate side maintains the wear-resistant bearing capacity of the moving side, while the AlCrSiON surface layer on the valve seat side adjusts the high-temperature contact state on the stationary side. The opening and closing performance obtained when both are positioned as described above is better than when reversed.

[0066] In Comparative Example 4, an additional 0.40 μm AlCrSiON surface layer was deposited on the 3.20 μm thick AlCrSiN layer on the valve seat side, bringing the total working layer thickness on the valve seat side to 3.60 μm. The initial starting torque, starting torque after 1000 cycles, and leakage rate of Comparative Example 4 were 45.1 N·m, 58.0 N·m, and 5.8 mL / min, respectively, while those of Example 1 were 42.6 N·m, 47.5 N·m, and 1.8 mL / min, respectively. The results indicate that replacing a portion of the AlCrSiN layer on the valve seat side with an AlCrSiON surface layer, while maintaining a consistent total working layer thickness on both the butterfly plate and valve seat sides, can reduce the impact of the additional coating thickness on one side on the sealing contact state and opening / closing performance.

[0067] Example 1 and Comparative Example 5 use the same heterogeneous working layer mating method and total working layer thickness. In Comparative Example 5, after omitting the nitrogen-containing cobalt-based alloy connecting layer and the composite transition layer, the visible peeling area reaches 9.8 mm. 2 The starting torque growth rate and leakage rate reached 62.4% and 18.9 mL / min, respectively; in Example 1, no visible coating peeling was observed, and the starting torque growth rate and leakage rate were 11.5% and 1.8 mL / min, respectively. These data indicate that the nitrogen-containing cobalt-based alloy connecting layer and the composite transition layer can improve the connection between the cobalt-based alloy matching layer and the AlCrSiN working layer, reducing the possibility of coating peeling during high-temperature cycling.

[0068] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing a cobalt-based alloy PVD composite coating for a high-temperature butterfly valve, characterized in that, Includes the following steps: Using the same Co-Cr-W-Ni-B-Si-C cobalt-based alloy powder, laser cladding is performed on the mating butterfly plate sealing surface and valve seat sealing surface, respectively. After grinding and polishing, a cobalt-based alloy bearing layer with a thickness of 0.6-1.2 mm is formed, and then the layers are cleaned and ion activated. At 380–450 °C and 0.6–1.2 Pa, the same PVD interface deposition was performed on two cobalt-based alloy support layers: a Co-Cr-W-Ni cobalt-based matching target was used for magnetron sputtering in argon gas to form a cobalt-based alloy matching layer with a thickness of 0.2–0.5 μm; after normalizing the total mass of Co, Cr, W and Ni of the cobalt-based matching target and the cobalt-based alloy powder, the mass percentage difference of each corresponding element did not exceed 1.0 percentage point; While keeping the cobalt-based matching target in operation, the nitrogen flow rate was sequentially set to 20%, 40%, and 60% of the total flow rate of argon and nitrogen, and each deposition lasted for 5 to 10 minutes to form a nitrogen-containing cobalt-based alloy bonding layer. With the nitrogen ratio maintained at 60%, the aluminum-chromium-silicon target was started, and the cobalt-based matching target and the aluminum-chromium-silicon target were co-sputtered sequentially at target surface power density ratios of 75:25, 50:50 and 25:75, respectively, for 8 to 12 minutes each, and the sum of the target surface power densities of the two targets remained constant, forming a composite transition layer. The cobalt-based matching target is turned off, while the aluminum-chromium-silicon target remains operational. An AlCrSiN working layer with a thickness of 2.5–4.0 μm is deposited on the butterfly plate side, and an AlCrSiN working layer and an AlCrSiON surface layer with a thickness of 0.2–0.5 μm are sequentially deposited on the valve seat side. The total thickness of the two layers on the valve seat side is 2.5–4.0 μm, and the thickness difference between the two layers and the AlCrSiN working layer on the butterfly plate side does not exceed 0.2 μm.

2. The method for preparing a cobalt-based alloy PVD composite coating for a high-temperature butterfly valve according to claim 1, characterized in that, The cobalt-based alloy powder comprises, by mass percentage, 24%–30% Cr, 6%–10% W, 7%–12% Ni, 1.0%–2.5% B, 1.5%–3.0% Si, 0.5%–1.5% C, with the balance being Co and unavoidable impurities.

3. The method for preparing a cobalt-based alloy PVD composite coating for a high-temperature butterfly valve according to claim 2, characterized in that, The cobalt-based matching target is prepared according to the normalized mass percentages of Co, Cr, W and Ni in the cobalt-based alloy powder. The difference between the normalized mass percentage of each element in the cobalt-based matching target and the normalized mass percentage of the corresponding element in the cobalt-based alloy powder does not exceed 0.5 percentage points, and the total unavoidable impurity content in the cobalt-based matching target does not exceed 0.5%.

4. The method for preparing a cobalt-based alloy PVD composite coating for a high-temperature butterfly valve according to claim 3, characterized in that, The aluminum-chromium-silicon target comprises 55%–62% Al, 4%–8% Si, and the balance being Cr and unavoidable impurities, with the total unavoidable impurities in the aluminum-chromium-silicon target not exceeding 0.5%.

5. The method for preparing a cobalt-based alloy PVD composite coating for a high-temperature butterfly valve according to claim 4, characterized in that, When forming the cobalt-based alloy support layer, the cobalt-based alloy powder is preheated to 100-180°C, and argon gas is used to transport the cobalt-based alloy powder to the laser cladding area. The laser power is 1.4-2.2kW, the scanning speed is 4-10mm / s, the powder feeding rate is 8-18g / min, and the overlap rate of adjacent cladding channels is 30%-50%. The cobalt-based alloy support layer formed by laser cladding is ground and polished so that the surface roughness Ra of the ground and polished cobalt-based alloy support layer is 0.05-0.4μm.

6. The method for preparing a cobalt-based alloy PVD composite coating for a high-temperature butterfly valve according to claim 5, characterized in that, When cleaning and ion-activating the cobalt-based alloy carrier layer, alkaline degreasing, deionized water cleaning, and ethanol ultrasonic cleaning are performed sequentially. The cleaned high-temperature butterfly valve is placed in a vacuum chamber and vacuum-heated at 250–350°C for 30–60 min. Then, argon gas is introduced and argon ion etching is performed at a negative bias voltage of 400–700V for 15–30 min.

7. The method for preparing a cobalt-based alloy PVD composite coating for a high-temperature butterfly valve according to claim 6, characterized in that, Before performing the PVD interface deposition process, the background pressure of the vacuum chamber is evacuated to no more than 5 × 10⁻⁶. -3 Pa; When the cobalt-based alloy matching layer is formed, the target surface power density of the cobalt-based matching target is 4-8 W / cm². 2 The base negative bias voltage applied to the butterfly plate or valve seat is 80-150V.

8. The method for preparing a cobalt-based alloy PVD composite coating for a high-temperature butterfly valve according to claim 7, characterized in that, When forming the nitrogen-containing cobalt-based alloy connecting layer, the total flow rate of argon and nitrogen is maintained at 200-400 sccm, and the ratio of nitrogen flow rate to total flow rate of argon and nitrogen is adjusted to 20%, 40% and 60% respectively by reducing the argon flow rate by an equal amount; the thickness of the formed nitrogen-containing cobalt-based alloy connecting layer is 0.3-0.8 μm.

9. The method for preparing a cobalt-based alloy PVD composite coating for a high-temperature butterfly valve according to claim 8, characterized in that, During the formation of the composite transition layer, the sum of the target surface power densities of the cobalt-based matching target and the aluminum-chromium-silicon target is maintained at 8–12 W / cm². 2 The thickness of the composite transition layer is 0.6–1.5 μm; when forming the AlCrSiN working layer, the target surface power density of the aluminum-chromium-silicon target is 4–8 W / cm². 2 The base negative bias voltage applied to the butterfly plate or valve seat is 60-120V.

10. The method for preparing a cobalt-based alloy PVD composite coating for a high-temperature butterfly valve according to claim 9, characterized in that, The set thickness of the AlCrSiON surface layer on the valve seat sealing surface is predetermined. When the AlCrSiN working layer on the valve seat sealing surface is deposited to the difference between the set total thickness of the working layer on the valve seat sealing surface and the set thickness of the AlCrSiON surface layer, the target power density, argon flow rate and total flow rate of the reaction gas of the aluminum chromium silicon target are kept constant. Oxygen is introduced and nitrogen is reduced by an equal amount so that the oxygen flow rate accounts for 3% to 8% of the total flow rate of nitrogen and oxygen, and the AlCrSiON surface layer continues to be deposited.

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