Zirconium alloy surface composite SiC / Cr coating and preparation method thereof

Abstract

The invention discloses a zirconium alloy surface composite SiC / Cr coating and a preparation method thereof, and belongs to the technical field of metal protective coatings. The preparation method comprises the following steps: pretreating a zirconium alloy matrix to obtain a pretreated zirconium alloy matrix; siC is used as a target material, argon-containing gas is used as sputtering gas in a vacuum environment, deposition is carried out on the pretreated zirconium alloy matrix, and a SiC base layer is formed; siC and Cr are used as target materials, SiC layers and Cr layers are alternately deposited on the SiC base layer in a vacuum environment, and a composite barrier layer is formed on the SiC base layer; and with Cr as a target material, depositing a Cr layer on the composite barrier layer in a vacuum environment to form a Cr protective layer, thereby obtaining the zirconium alloy surface composite SiC / Cr coating. According to the method, the thickness of the coating can be accurately controlled, cracks and holes caused by poor bonding force between ceramic and metal and phase change and internal stress at high temperature are avoided, and the compact coating with high bonding strength is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of metal protective coatings, and more particularly to a zirconium alloy surface composite SiC / Cr coating and a preparation method thereof. Background Art

[0002] Zirconium alloy, a high-performance material, is increasingly being used in fields such as nuclear energy and aerospace due to its low neutron absorption cross-section, excellent corrosion resistance, and mechanical properties. However, under loss of coolant accident (LOCA) conditions, zirconium alloy can react with water vapor to produce hydrogen, triggering an explosion and potentially causing an irreversible accident. Therefore, researchers have proposed the concept of accident-tolerant fuel (ATF) to extend accident response time and increase safety margins under LOCA conditions.

[0003] Surface coating treatment of zirconium alloys has been identified as an effective method for significantly improving the performance of zirconium alloy cladding materials. Cr coatings, currently the mainstream development direction for zirconium alloy coatings internationally, still face the problem of ZrCr interdiffusion. ZrCr interdiffusion leads to significant Cr coating loss on the substrate side. Furthermore, Zr diffusion along grain boundaries provides oxygen diffusion pathways, reducing the coating's oxidation resistance. Furthermore, intermetallic compounds formed by ZrCr interdiffusion create numerous pores that affect the coating's oxidation and mechanical properties. At 1350°C, ZrCr eutectics form, rendering it incapable of resisting beyond-design-basis loss-of-coolant accidents (LOCAs). To address the ZrCr interdiffusion issue and extend the service life of chromium-coated zirconium alloy cladding under LOCA conditions, the introduction of diffusion barriers has proven effective. Diffusion barriers offer excellent chemical and physical compatibility and stability, low volatility, good thermal expansion coefficient matching and bonding, high-temperature self-healing capabilities, and the ability to maintain the inherent mechanical properties, low oxygen diffusion capacity, and high radiation resistance of the chromium-coated zirconium alloy cladding.

[0004] Common coating materials include silicon carbide (SiC), MAX phase, chromium (Cr), and FeCrAl. Ceramic materials, due to their excellent corrosion resistance and thermal stability, are preferred materials for preventing the interdiffusion of ZrCr and Cr. Among these materials, SiC is incorporated into the ZrCr system as a diffusion barrier due to its high operating temperature limit, low water vapor reactivity, low water-side corrosion efficiency, and slow radiation growth rate, meeting the basic requirements of cladding materials.

[0005] Currently, researchers are using three technologies: CVD chemical vapor deposition, 3D laser cladding, and reactive magnetron sputtering. While CVD and 3D laser cladding offer advantages such as high processing precision and high coating quality, they suffer from excessively high temperatures during the production process, severely affecting the microstructure and overall performance of the zirconium alloy substrate. Therefore, they cannot be used for coating zirconium alloy surfaces for nuclear applications. While reactive magnetron sputtering meets the temperature requirements for nuclear production, it introduces large amounts of flammable and explosive gases such as hydrogen and methane during the production process, posing potential risks to the environment and production safety. Summary of the Invention

[0006] In response to the above problems, the present invention provides a composite SiC / Cr coating on the surface of a zirconium alloy and a preparation method thereof, using argon-containing gas as the sputtering gas, avoiding the use of hazardous gases such as hydrogen and methane, and under conditions below 400°C. A method for depositing a multi-unit composite structure SiC / Cr composite coating on the surface of a zirconium alloy. This method can not only accurately control the coating thickness, avoid poor bonding between ceramic and metal, and avoid cracks and holes caused by phase transformation and internal stress at high temperatures, thereby obtaining a dense coating with high bonding strength, but also avoid damage to the zirconium alloy cladding caused by excessively high production temperatures, improve the safety of the production process, and avoid safety hazards caused by flammable and explosive gases in the production process. It has the advantages of simple operation, high cost-effectiveness, and environmental friendliness. The introduction of the barrier layer enhances the oxidation resistance of the chromium-coated zirconium alloy cladding, effectively prolongs the emergency treatment time of the coated cladding under accident conditions, and significantly improves the operating safety of nuclear power units under accident conditions.

[0007] The first object of the present invention is to provide a method for preparing a composite SiC / Cr coating on a zirconium alloy surface, comprising the following steps: The zirconium alloy substrate is pretreated to obtain a pretreated zirconium alloy substrate.

[0008] Using SiC as the target material, in a vacuum environment, using argon-containing gas as the sputtering gas, and under the gradient condition of bias voltage of -500V~-100V, deposition is carried out on the pretreated zirconium alloy substrate to form a SiC base layer; when preparing the SiC base layer, the bias voltage is gradually reduced. This is to gradually transition to the voltage of the preparation stage. Gradually reducing the bias voltage will obtain a coating interface with better quality than a sudden change in voltage.

[0009] Using SiC and Cr as target materials, under the conditions of -350V~0V in a vacuum environment, SiC layers and Cr layers are alternately deposited on the SiC base layer to form a composite barrier layer on the SiC base layer.

[0010] Using Cr as the target, a Cr layer was deposited on the composite barrier layer under the conditions of -350V~0V in a vacuum environment to form a Cr protective layer, thereby obtaining a composite SiC / Cr coating on the surface of the zirconium alloy.

[0011] The zirconium alloy substrate may be a zirconium alloy cladding tube, in particular a cladding tube used for nuclear fuel rods.

[0012] When the zirconium alloy substrate is plate-shaped, and the deposition step is carried out in a manner such that the deposition rates of the SiC and Cr layers in the composite coating on the substrate are between 50 nm / h and 50 μm / h; When the zirconium alloy substrate is a tube having a central axis, and the deposition step is performed by rotating the substrate about its central axis and the deposition rate of the SiC and Cr layers in the composite coating on the substrate is between 50 / π nm / h and 50 / π μm / h.

[0013] In a preferred embodiment of the present invention, during the alternating deposition, the sputtering power of SiC is 20W-500W, and the sputtering power of Cr is 5W-500W.

[0014] In a preferred embodiment of the present invention, a SiC layer is deposited once, and the deposition thickness of the SiC layer is 1 nm-5 μm.

[0015] In a preferred embodiment of the present invention, a Cr layer is deposited once, and the deposition thickness is 1 nm to 20 μm.

[0016] In a preferred embodiment of the present invention, the number of alternating depositions is 1 to 500 times.

[0017] In a preferred embodiment of the present invention, in a vacuum environment, the background vacuum degree is 1×10 -4 ~9.9×10 -4 Pa.

[0018] In a preferred embodiment of the present invention, the argon-containing gas is argon or a mixture of argon and nitrogen; the flow rate of argon is 5 sccm~50 sccm, and when depositing the SiC base layer and the SiC layer in the composite barrier layer, the flow rate of nitrogen is 0~50 sccm.

[0019] When forming the SiC base layer, the sputtering power is 20W~500W, and the working gas pressure is 0.02Pa~2.0Pa.

[0020] When forming the composite barrier layer, the sputtering power is 20W~500W, and the working gas pressure is 0.02Pa~2.0Pa.

[0021] When forming the Cr protective layer, the sputtering power is 20W~500W and the working gas pressure is 0.02Pa~2.0Pa.

[0022] In a preferred embodiment of the present invention, the deposition thickness of the SiC base layer is between 1 nm and 1 μm.

[0023] In a preferred embodiment of the present invention, the deposition thickness of the Cr protective layer is between 1 nm and 20 μm.

[0024] The second object of the present invention is to provide a composite SiC / Cr coating on the surface of a zirconium alloy prepared by the above preparation method.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses magnetron sputtering technology to prepare SiC coatings. Compared with traditional coatings, the present invention does not require an additional heating source during the preparation process. In addition, compared with the traditional preparation of SiC coatings using Si targets and introducing gases such as hydrogen and methane for reactive sputtering in a vacuum chamber, the present invention directly sputters using SiC targets and introducing argon gas, effectively improving the safety of the operation process and avoiding safety risks. During the magnetron sputtering process, C or Si ions are sputtered by bombarding the target material with argon ions, which are quickly injected into the sample surface with a negative bias applied, resulting in a strong film-base bonding force, thereby effectively solving the problem of high-temperature preparation of SiC coatings changing the zirconium alloy matrix structure. At the same time, it solves the problem of poor interface bonding between SiC ceramics and metals, and improves the bonding force between zirconium alloy and SiC ceramic coating without changing the matrix structure.

[0026] (2) The introduction of the SiC diffusion barrier layer effectively blocks the interdiffusion between the Zr and Cr interfaces, solves the problems of increased coating oxidation caused by interdiffusion and the formation of Kirkendall effect holes in intermetallic compounds, improves the service life of the chromium-coated zirconium alloy cladding under LOCA conditions, and prolongs the emergency response time after an accident.

[0027] (3) A multi-unit composite structure SiC / Cr coating was prepared by magnetron sputtering technology. Compared with traditional coatings, the composite gradient coating effectively solved the problems of unstable thermal expansion coefficient and large residual internal stress of SiC coating, improved the service life of SiC barrier layer chromium coating zirconium alloy cladding under LOCA conditions, and extended the emergency response time after the accident.

[0028] (4) During the preparation process, due to the use of magnetron sputtering technology, the morphology, structure and thickness of the coating can be precisely controlled, and the gradient structure design of the coating can be realized. The multi-layer composite diffusion barrier layer prevents the diffusion of the Zr element in the matrix and the Cr element in the coating, thereby improving the service life of the chromium-coated zirconium alloy cladding. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a cross-sectional morphology diagram of the film prepared in Example 1 of the present invention.

[0030] Figure 2 This is the longitudinal depth element distribution GDOES diagram of the surface film prepared in Example 1 of the present invention.

[0031] Figure 3 This is the steam oxidation weight gain curve at 1200℃.

[0032] Figure 4 These are SEM images of Example 1 and Comparative Example 1 after steam oxidation at 1200°C for 15 min, where (a) is a cross-sectional SEM image of Cr@Zr, (b) is a cross-sectional SEM image of Cr / SiC@Zr, (c) is a SEM image of the interface of Cr@Zr, and (d) is a SEM image of the interface of Cr / SiC@Zr. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] To address the intermetallic compound, Kirkendall voids, and ZrCr eutectic at 1350°C caused by interdiffusion between Zr and Cr, a Cr-coated zirconium alloy cladding system was developed. This invention introduces a SiC ceramic coating as a diffusion barrier. This coating reacts with the Zr and Cr elements on both sides of the interface at high temperatures, preventing contact between the Zr and Cr elements and thus preventing cross-sectional interdiffusion. This extends the service life of the Cr-coated zirconium alloy cladding and broadens the applicable temperature range of the system. Specifically, the service operating temperature is between 280°C and 400°C. Accident operating temperatures can reach as high as 1500°C.

[0035] During preparation, the present invention utilizes radio frequency current in the SiC ceramic target to avoid the problem of weak conductivity preventing normal sputtering. A SiC ceramic diffusion barrier layer is directly introduced into the Cr-coated Zr alloy cladding via the SiC ceramic target, where the Cr coating still comprises a single-component Cr structure. The introduction of this barrier layer inhibits the interdiffusion reaction between Zr and Cr, slowing the consumption of the Cr coating on the substrate side to optimize the high-temperature oxidation performance of the coated cladding and extend the cladding's service life under operating conditions. The present invention also optimizes the structural design of the SiC / Cr layer to improve the cladding's mechanical properties and service life. The preparation method of the present invention maintains a temperature below 400°C during the sputtering process, preventing any impact on the substrate.

[0036] Under the high temperature oxidation conditions of LOCA working conditions, the Si and C elements in the SiC coating react with the Zr and Cr on both sides to generate Zr2Si and Cr respectively. 9.1 Si 0.9At the same time, a part of ZrC is generated, which prevents the mutual diffusion of ZrCr and slows down the consumption of the substrate side of the Cr coating to optimize the high temperature oxidation performance. Example 1 A single-unit composite SiC / Cr coating is prepared on the surface of a zirconium alloy sheet substrate using magnetron sputtering technology, comprising the following steps: Step 1: Use 400#, 800#, 1500#, 2000#, and 3000# sandpaper to polish the Zr-4 alloy sheet in sequence, and then use 0.5μm, 0.25μm and 0.05μm diamond polishing agents and 0.02μm silicon oxide polishing agents for mechanical polishing. Then, use acetone and anhydrous ethanol to heat ultrasonic cleaning for 20 minutes and dry. The sample is mounted on the workpiece turntable in the vacuum chamber of the magnetron sputtering equipment, the Cr target is mounted on the DC target position, and the SiC target is mounted on the RF target position.

[0037] Step 2: Introduce argon gas into the vacuum chamber and perform glow sputtering cleaning on the substrate surface with a bias voltage of -400 V and sputtering for 30 minutes.

[0038] Step 3: Open the SiC target and introduce argon gas with a purity of not less than 99.9%. The flow rate of the introduced argon gas is 20 sccm and the working pressure is 0.5 Pa to prepare a SiC base layer, wherein the sputtering power is 250 W and the substrate bias voltage is gradually reduced to prepare a SiC base layer of about 200 nm; specifically, the substrate bias voltage is -400 V and the deposition thickness is about 60 nm; then the bias voltage is reduced to -300 V and the deposition thickness is about 50 nm; the bias voltage is reduced to -200 V and the deposition thickness is about 50 nm; finally, the bias voltage is reduced to -100 V and the deposition thickness is about 40 nm.

[0039] Step 4: introduce argon gas with a purity of not less than 99.9%, a flow rate of 20 sccm, a working pressure of 0.5 Pa, a bias voltage of -150 V applied to the substrate, a SiC target sputtering power of 250 W, and deposit a 1 μm SiC diffusion barrier layer on the SiC base layer.

[0040] Step 5: Introduce argon gas with a purity of not less than 99.9% and a flow rate of 20 sccm. Turn off the SiC target and turn on the Cr target. The working pressure is 0.5 Pa, the substrate bias is -150 V, the Cr target sputtering power is 250 W, and a 1 μm Cr layer is deposited on the SiC diffusion barrier layer.

[0041] Step 6: introduce argon gas with a purity of not less than 99.9%, a flow rate of 20 sccm, a working pressure of 0.5 Pa, a substrate bias of -150 V, maintain the Cr target sputtering power at 250 W, and continue to deposit a 1 μm Cr protective layer on the Cr layer.

[0042] Example 2 A dual-unit composite SiC / Cr coating is prepared on the surface of a zirconium alloy sheet substrate using magnetron sputtering technology, comprising the following steps: Step 1: Use 400#, 800#, 1500#, 2000#, and 3000# sandpaper to polish the Zr-4 alloy sheet in sequence, and then use 0.5μm, 0.25μm and 0.05μm diamond polishing agents and 0.02μm silicon oxide polishing agents for mechanical polishing. Then, use acetone and anhydrous ethanol to heat ultrasonic cleaning for 20 minutes and dry. The sample is mounted on the workpiece turntable in the vacuum chamber of the magnetron sputtering equipment, the Cr target is mounted on the DC target position, and the SiC target is mounted on the RF target position.

[0043] Step 2: Introduce argon gas into the vacuum chamber and perform glow sputtering cleaning on the substrate surface with a bias voltage of -400 V and sputtering for 30 minutes.

[0044] Step 3: Open the SiC target and introduce argon gas with a purity of not less than 99.9% at a flow rate of 20 sccm and a working pressure of 0.5 Pa to prepare a SiC base layer, wherein the sputtering power is 250 W and the substrate bias voltage is gradually reduced to prepare a SiC base layer of about 200 nm; specifically, the substrate bias voltage is -400 V and the deposition thickness is about 60 nm; then the bias voltage is reduced to -300 V and the deposition thickness is about 50 nm; the bias voltage is reduced to -200 V and the deposition thickness is about 50 nm; finally, the bias voltage is reduced to -100 V and the deposition thickness is about 40 nm.

[0045] Step 4: The working gas pressure is 0.5 Pa, the bias voltage applied to the substrate is -150 V, the SiC target sputtering power is 250 W, and a 1 μm SiC diffusion barrier layer is deposited on the SiC base layer.

[0046] Step 5: Turn off the SiC target and turn on the Cr target. The working gas pressure is 0.5 Pa, the substrate bias is -150 V, the Cr target sputtering power is 250 W, and a 1 μm Cr layer is deposited on the SiC diffusion barrier layer.

[0047] Step 6: Turn off the Cr target and turn on the SiC target. The working gas pressure is 0.5 Pa, the substrate bias is -150 V, the SiC target sputtering power is 250 W, and a 1 μm SiC diffusion barrier layer is deposited on the Cr layer.

[0048] Step 7: Turn off the SiC target and turn on the Cr target. The working gas pressure is 0.5 Pa, the substrate bias is -150 V, the Cr target sputtering power is 250 W, and a 1 μm Cr layer is deposited on the SiC diffusion barrier layer.

[0049] Step 8: The working gas pressure is 0.5 Pa, the substrate bias voltage is -150 V, the Cr target sputtering power is maintained at 250 W, and a 5 μm Cr protective layer is continuously deposited on the Cr layer.

[0050] Example 3 A multi-unit gradient composite SiC / Cr coating is prepared on the surface of a zirconium alloy sheet substrate using magnetron sputtering technology, comprising the following steps: Step 1: Use 400#, 800#, 1500#, 2000#, and 3000# sandpaper to polish the Zr-4 alloy sheet in sequence, and then use 0.5μm, 0.25μm and 0.05μm diamond polishing agents and 0.02μm silicon oxide polishing agents for mechanical polishing. Then, use acetone and anhydrous ethanol to heat ultrasonic cleaning for 20 minutes and dry. The sample is mounted on the workpiece turntable in the vacuum chamber of the magnetron sputtering equipment, the Cr target is mounted on the DC target position, and the SiC target is mounted on the RF target position.

[0051] Step 2: Introduce argon gas into the vacuum chamber and perform glow sputtering cleaning on the substrate surface with a bias voltage of -400 V and sputtering for 30 minutes.

[0052] Step 3: Open the SiC target and introduce argon gas with a purity of not less than 99.9% at a flow rate of 20 sccm and a working pressure of 0.5 Pa to prepare a SiC base layer, wherein the sputtering power is 250 W and the substrate bias voltage is gradually reduced to prepare a SiC base layer of about 200 nm; specifically, the substrate bias voltage is -400 V and the deposition thickness is about 60 nm; then the bias voltage is reduced to -300 V and the deposition thickness is about 50 nm; the bias voltage is reduced to -200 V and the deposition thickness is about 50 nm; finally, the bias voltage is reduced to -100 V and the deposition thickness is about 40 nm.

[0053] Step 4: The working gas pressure is 0.5 Pa, the bias voltage applied to the substrate is -150 V, the SiC target sputtering power is 250 W, and a 1 μm SiC diffusion barrier layer is deposited on the SiC base layer.

[0054] Step 5: Turn off the SiC target and turn on the Cr target. The working gas pressure is 0.5 Pa, the substrate bias is -150 V, the Cr target sputtering power is 250 W, and a 1 μm Cr layer is deposited on the SiC diffusion barrier layer.

[0055] Step 6: Turn off the Cr target and turn on the SiC target. The working gas pressure is 0.5 Pa, the substrate bias is -150 V, the SiC target sputtering power is 250 W, and a 500 nm SiC diffusion barrier layer is deposited on the Cr layer.

[0056] Step 7: Turn off the SiC target and turn on the Cr target. The working gas pressure is 0.5 Pa, the substrate bias is -150 V, the Cr target sputtering power is 250 W, and a 500 nm Cr layer is deposited on the SiC diffusion barrier layer.

[0057] Step 8: Turn off the Cr target and turn on the SiC target. The working gas pressure is 0.5 Pa, the substrate bias is -150 V, the SiC target sputtering power is 250 W, and a 200 nm SiC diffusion barrier layer is deposited on the Cr layer.

[0058] Step 9: Turn off the SiC target and turn on the Cr target. The working gas pressure is 0.5 Pa, the substrate bias is -150 V, the Cr target sputtering power is 250 W, and a 200 nm Cr layer is deposited on the SiC diffusion barrier layer.

[0059] Step 10: Turn off the Cr target and turn on the SiC target. The working gas pressure is 0.5 Pa, the substrate bias is -150 V, the SiC target sputtering power is 250 W, and a 100 nm SiC diffusion barrier layer is deposited on the Cr layer.

[0060] Step 11: Turn off the SiC target and turn on the Cr target. The working gas pressure is 0.5 Pa, the substrate bias is -150 V, the Cr target sputtering power is 250 W, and a 100 nm Cr layer is deposited on the SiC diffusion barrier layer.

[0061] Step 12: The working gas pressure is 0.5 Pa, the substrate bias voltage is -150 V, the Cr target sputtering power is maintained at 250 W, and a 5 μm Cr protective layer is continuously deposited on the Cr layer.

[0062] Example 4 A single unit composite N-SiC / Cr coating is prepared on the surface of a zirconium alloy sheet substrate using magnetron sputtering technology, comprising the following steps: Step 1: Use 400#, 800#, 1500#, 2000#, and 3000# sandpaper to polish the Zr-4 alloy sheet in sequence, and then use 0.5μm, 0.25μm and 0.05μm diamond polishing agents and 0.02μm silicon oxide polishing agents for mechanical polishing. Then, use acetone and anhydrous ethanol to heat ultrasonic cleaning for 20 minutes and dry. The sample is mounted on the workpiece turntable in the vacuum chamber of the magnetron sputtering equipment, the Cr target is mounted on the DC target position, and the SiC target is mounted on the RF target position.

[0063] Step 2: Introduce argon gas into the vacuum chamber and perform glow sputtering cleaning on the substrate surface with a bias voltage of -400 V and sputtering for 30 minutes.

[0064] Step 3: A nitrogen-argon mixture is introduced, the purity of the argon is not less than 99.9%, the flow rate of the introduced argon is 20 sccm, the flow rate of the introduced nitrogen is 30 sccm, the working pressure is 0.5 Pa, and a SiC base layer is prepared, wherein the sputtering power is 250 W, and the substrate bias voltage is gradually reduced to prepare a SiC base layer of about 200 nm; specifically, the substrate bias voltage is -400 V, and the deposition thickness is about 60 nm; then the bias voltage is reduced to -300 V, and the deposition thickness is about 50 nm; the bias voltage is reduced to -200 V, and the deposition thickness is about 50 nm; finally, the bias voltage is reduced to -100 V, and the deposition thickness is about 40 nm.

[0065] Step 4: A nitrogen-argon mixture is introduced, the purity of the argon is not less than 99.9%, the flow rate of the argon is 20 sccm, the flow rate of the nitrogen is 30 sccm, the working pressure is 0.5 Pa, the bias voltage applied to the substrate is -150 V, the SiC target sputtering power is 250 W, and a 1 μm N-SiC diffusion barrier layer is deposited on the SiC base layer.

[0066] Step 5: Turn off the nitrogen and only introduce argon. The purity of the argon is not less than 99.9%. The flow rate of the introduced argon is 20 sccm. Turn off the SiC target and turn on the Cr target. The working gas pressure is 0.5 Pa, the substrate bias is -150 V, the Cr target sputtering power is 250 W, and a 1 μm Cr layer is deposited on the SiC diffusion barrier layer.

[0067] Step 6: introduce argon gas with a purity of not less than 99.9%, a flow rate of 20 sccm, a working pressure of 0.5 Pa, a substrate bias of -150 V, maintain the Cr target sputtering power at 250 W, and continue to deposit a 1 μm Cr protective layer on the Cr layer.

[0068] Example 5 A multi-unit gradient composite SiC / Cr coating is prepared on the surface of a zirconium alloy sheet substrate using magnetron sputtering technology, comprising the following steps: Step 1: Use 400#, 800#, 1500#, 2000#, and 3000# sandpaper to polish the Zr-4 alloy sheet in sequence, and then use 0.5μm, 0.25μm and 0.05μm diamond polishing agents and 0.02μm silicon oxide polishing agents for mechanical polishing. Then, use acetone and anhydrous ethanol to heat ultrasonic cleaning for 20 minutes and dry. The sample is mounted on the workpiece turntable in the vacuum chamber of the magnetron sputtering equipment, the Cr target is mounted on the DC target position, and the SiC target is mounted on the RF target position.

[0069] Step 2: Introduce argon gas into the vacuum chamber and perform glow sputtering cleaning on the substrate surface with a bias voltage of -400 V and sputtering for 30 minutes.

[0070] Step 3: Open the SiC target, introduce argon gas with a purity of not less than 99.9%, the argon flow rate is 5 sccm, the nitrogen flow rate is 10 sccm, the working pressure is 0.4 Pa, and a SiC base layer is prepared, wherein the sputtering power is 20 W, and the substrate bias voltage is gradually reduced to prepare a SiC base layer of about 200 nm; specifically, the substrate bias voltage is -400 V, and the deposition thickness is about 60 nm; then the bias voltage is reduced to -300 V, and the deposition thickness is about 50 nm; the bias voltage is reduced to -200 V, and the deposition thickness is about 50 nm; finally, the bias voltage is reduced to -100 V, and the deposition thickness is about 40 nm.

[0071] Step 4: The argon flow rate is 20 sccm, the nitrogen flow rate is 5 sccm, the working pressure is 0.02 Pa, the bias voltage applied to the substrate is 100 V, the SiC target sputtering power is 50 W, and a 200 nm SiC diffusion barrier layer is deposited on the SiC base layer.

[0072] Step 5: Turn off the SiC target and turn on the Cr target. The working gas pressure is 0.4 Pa, the bias voltage applied to the substrate is 100 V, the sputtering power of the Cr target is 50 W, and a 200 nm Cr layer is deposited on the SiC diffusion barrier layer.

[0073] Step 6: The working gas pressure is 0.4 Pa, the substrate bias is 100 V, the Cr target sputtering power is maintained at 200 W, and a 1 μm Cr protective layer is continuously deposited on the Cr layer.

[0074] Example 6 A multi-unit gradient composite SiC / Cr coating is prepared on the surface of a zirconium alloy sheet substrate using magnetron sputtering technology, comprising the following steps: Step 1: Use 400#, 800#, 1500#, 2000#, and 3000# sandpaper to polish the Zr-4 alloy sheet in sequence, and then use 0.5μm, 0.25μm and 0.05μm diamond polishing agents and 0.02μm silicon oxide polishing agents for mechanical polishing. Then, use acetone and anhydrous ethanol to heat ultrasonic cleaning for 20 minutes and dry. The sample is mounted on the workpiece turntable in the vacuum chamber of the magnetron sputtering equipment, the Cr target is mounted on the DC target position, and the SiC target is mounted on the RF target position.

[0075] Step 2: Introduce argon gas into the vacuum chamber and perform glow sputtering cleaning on the substrate surface with a bias voltage of -400 V and sputtering for 30 minutes.

[0076] Step 3: Open the SiC target, introduce argon with a purity of not less than 99.9%, the argon flow rate is 50 sccm, the nitrogen flow rate is 50 sccm, the working pressure is 1 Pa, and a SiC base layer is prepared, wherein the sputtering power is 500 W, and the substrate bias voltage is gradually reduced to prepare a SiC base layer of about 200 nm; specifically, the substrate bias voltage is -400 V, and the deposition thickness is about 60 nm; then the bias voltage is reduced to -300 V, and the deposition thickness is about 50 nm; the bias voltage is reduced to -200 V, and the deposition thickness is about 50 nm; finally, the bias voltage is reduced to -100 V, and the deposition thickness is about 40 nm.

[0077] Step 4: The argon flow rate is 50 sccm, the nitrogen flow rate is 50 sccm, the working gas pressure is 1 Pa, the bias voltage applied to the substrate is -350 V, the SiC target sputtering power is 500 W, and a 2 μm SiC diffusion barrier layer is deposited on the SiC base layer.

[0078] Step 5: Turn off the SiC target and turn on the Cr target. The argon flow rate is 50 sccm, the working gas pressure is 1 Pa, the bias voltage applied to the substrate is -350 V, the Cr target sputtering power is 500 W, and a 1 μm Cr layer is deposited on the SiC diffusion barrier layer.

[0079] Step 6: The argon flow rate is 50 sccm, the working gas pressure is 1 Pa, the substrate bias is -350 V, the Cr target sputtering power is maintained at 500 W, and a 15 μm Cr protective layer is continuously deposited on the Cr layer.

[0080] Comparative Example 1 The pure Cr coating is prepared on the surface of the zirconium alloy sheet substrate by magnetron sputtering technology, including the following steps: Step 1: Use 400#, 800#, 1500#, 2000#, and 3000# sandpaper to polish the Zr-4 alloy sheet in sequence, and then use 0.5μm, 0.25μm, and 0.05μm diamond polishing agents and 0.02μm silicon oxide polishing agents for mechanical polishing. Then, use acetone and anhydrous ethanol to heat ultrasonic cleaning for 20 minutes and dry. The sample is mounted on the workpiece turntable in the vacuum chamber of the magnetron sputtering equipment, and the Cr target is mounted on the DC target position.

[0081] Step 2: Introduce argon gas into the vacuum chamber and perform glow sputtering cleaning on the substrate surface with a bias voltage of -400 V and sputtering for 30 minutes.

[0082] Step 3: Open the Cr target and introduce argon gas with a purity of not less than 99.9% at a flow rate of 20 sccm and a working pressure of 0.5 Pa to prepare a Cr base layer, wherein the sputtering power is 250 W and the substrate bias voltage is gradually reduced to prepare a Cr base layer of about 200 nm; specifically, the substrate bias voltage is -400 V and the deposition thickness is about 60 nm; then the bias voltage is reduced to -300 V and the deposition thickness is about 50 nm; the bias voltage is reduced to -200 V and the deposition thickness is about 50 nm; finally, the bias voltage is reduced to -100 V and the deposition thickness is about 40 nm.

[0083] Step 4: Introduce argon gas with a purity of not less than 99.9% and a flow rate of 20 sccm. Turn on the Cr target, set the working pressure to 0.5 Pa, the substrate bias to -150 V, and the Cr target sputtering power to 250 W, and deposit a 1 μm Cr layer on the SiC diffusion barrier layer.

[0084] Step 5: introduce argon gas with a purity of not less than 99.9%, a flow rate of 20 sccm, a working pressure of 0.5 Pa, a substrate bias of -150 V, maintain the Cr target sputtering power at 250 W, and continue to deposit a 1 μm Cr protective layer on the Cr layer.

[0085] Figure 1 Cross-sectional SEM images of samples with Cr coatings introduced into SiC ceramic barrier layers prepared by RF sputtering on silicon wafers, as shown in Figure 2. Figure 1 As shown in the figure, Cr / SiC coatings with thicknesses of 1.98μm and 1.26μm were prepared under the experimental conditions. The SiC ceramic coating is amorphous, while the Cr coating has columnar crystal characteristics. GDOES was used to analyze the atomic distribution of the Cr / SiC coating samples. Figure 2 As shown in Figure 3, the coating thickness is consistent with the SEM results. Due to the heating caused by atomic bombardment during the deposition process, a certain degree of diffusion of Si and C elements occurred during the deposition process.

[0086] The results of the steam oxidation experiment of the pure Cr coating and the Cr coating with SiC ceramic barrier layer after the samples prepared in Example 1 were steam oxidized at 1200°C for 60 minutes are as follows: Figure 3 At the end of the 15-minute holding period at 1200℃, the oxidation weight gain per unit area of ​​the Cr / SiC coating sample is much smaller than that of the pure Cr coating sample.

[0087] Figure 4 The SEM images of the cross section and interface of the pure Cr coating of Comparative Example 1 and the Cr / SiC coating of Example 1 after oxidation weight gain experiment are shown in FIG. Figure 4It can be seen that although the introduction of SiC coating is beneficial to improving the high-temperature oxidation resistance of Cr-coated zirconium alloy cladding, the insufficient thickness of the Cr coating causes rapid failure of the Cr coating during the oxidation process, resulting in oxidation of the substrate. However, the thickness of the ZrO2 oxide layer of the Cr / SiC coating sample (105μm) is much smaller than the oxide layer thickness of the pure Cr coating (128μm).

[0088] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0089] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for preparing a composite SiC / Cr coating on a zirconium alloy surface, characterized in that: The following steps are involved: pretreating the zirconium alloy substrate to obtain a pretreated zirconium alloy substrate; Using SiC as the target, in a vacuum environment, using argon-containing gas as the sputtering gas, and under the gradient condition of -500V~-100V, deposition is carried out on the pretreated zirconium alloy substrate to form a SiC base layer; Using SiC and Cr as targets, under vacuum conditions of -350V to 0V, SiC layers and Cr layers are alternately deposited on the SiC base layer to form a composite barrier layer on the SiC base layer. Using Cr as the target, a Cr layer was deposited on the composite barrier layer under the conditions of -350V~0V in a vacuum environment to form a Cr protective layer, thereby obtaining a composite SiC / Cr coating on the surface of the zirconium alloy.

2. The method for preparing a composite SiC / Cr coating on a zirconium alloy surface according to claim 1, characterized in that: During alternating deposition, the sputtering power of SiC is 20W~500W, and the sputtering power of Cr is 5W~500W.

3. The method for preparing a composite SiC / Cr coating on a zirconium alloy surface according to claim 1, characterized in that: The SiC layer is deposited once, and the deposition thickness of the SiC layer is 1nm~5μm.

4. The method for preparing a composite SiC / Cr coating on a zirconium alloy surface according to claim 1, characterized in that: Deposit a Cr layer once with a thickness of 1nm~20μm.

5. The method for preparing a composite SiC / Cr coating on a zirconium alloy surface according to claim 1, characterized in that: The number of alternating depositions ranges from 1 to 500 times.

6. The method for preparing a composite SiC / Cr coating on a zirconium alloy surface according to claim 1, characterized in that: In a vacuum environment, the background vacuum is 1×10 -4 ~9.9×10 -4 Pa.

7. The method for preparing a composite SiC / Cr coating on a zirconium alloy surface according to claim 1, characterized in that: The argon-containing gas is argon or a mixture of argon and nitrogen; the flow rate of the argon gas is 5 sccm to 50 sccm. When depositing the SiC base layer and the SiC layer in the composite barrier layer, the flow rate of the nitrogen gas is 0 to 50 sccm. When forming the SiC base layer, the sputtering power is 20W~500W, and the working gas pressure is 0.02Pa~2.0Pa; When forming the composite barrier layer, the sputtering power is 20W~500W and the working gas pressure is 0.02Pa~2.0Pa; When forming the Cr protective layer, the sputtering power is 20W~500W and the working gas pressure is 0.02Pa~2.0Pa.

8. The method for preparing a composite SiC / Cr coating on a zirconium alloy surface according to claim 1, characterized in that: The deposition thickness of the SiC base layer is between 1nm and 1μm.

9. The method for preparing a composite SiC / Cr coating on a zirconium alloy surface according to claim 1, characterized in that: The deposition thickness of the Cr protective layer is between 1nm and 20μm.

10. A composite SiC / Cr coating on the surface of a zirconium alloy prepared by the preparation method according to any one of claims 1 to 9.

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