High-toughness coating and manufacturing method thereof

Abstract

The invention discloses a high-toughness coating and a manufacturing method thereof, and belongs to the field of coatings. The high-toughness coating is a pure Cr layer and comprises a matrix layer and modified areas, the average grain size of the matrix layer ranges from 0.1 micrometer to 0.8 micrometer, the average grain size of the modified areas ranges from 1 micrometer to 2 micrometers, the average diameter of the modified areas ranges from 5 micrometers to 15 micrometers, and the interval between every two adjacent modified areas ranges from 0.5 mm to 1.5 mm. The high-toughness coating has good toughness and oxidation resistance, and can effectively prolong the service life and improve the reliability of the zirconium alloy in a high-temperature and high-pressure corrosion environment.

Description

Technical Field

[0001] This invention belongs to the field of coatings, and specifically relates to a high-toughness coating and its manufacturing method. Background Technology

[0002] The cladding of zirconium alloy fuel rods used in nuclear power plant reactors typically requires a protective coating to improve the oxidation and wear resistance of the zirconium alloy. Cr coating is one of the most widely used coatings, possessing good hardness and the ability to form a dense oxide film to inhibit the oxidation of the zirconium alloy substrate. However, existing Cr coatings, particularly fine-grained coatings characterized by columnar crystals, exhibit high hardness but insufficient toughness, making them prone to intergranular brittle fracture under thermal cycling or mechanical loading, leading to coating cracking or failure. Conversely, coarse-grained coatings have low grain boundary density, failing to effectively barrier oxygen diffusion, resulting in a significantly increased oxidation rate at high temperatures. Therefore, providing a coating with both good oxidation resistance and good toughness is crucial for improving the service life and reliability of zirconium alloy components in nuclear power plants. Summary of the Invention

[0003] The purpose of this invention is to provide a high-toughness coating to improve the service life and reliability of zirconium alloys in reactor cores. This invention also provides a method for manufacturing the high-toughness coating.

[0004] According to one aspect of the present invention, a high-toughness coating is provided, which is disposed on the surface of a zirconium alloy substrate. The high-toughness coating is configured as a pure Cr layer and includes a substrate layer and modified regions. The substrate layer has an average grain size of 0.1 μm-0.8 μm. The modified regions are uniformly distributed on the surface of the substrate layer, with an average grain size of 1 μm-2 μm and an average diameter of 5 μm-15 μm. The spacing between adjacent modified regions is 0.5 mm-1.5 mm.

[0005] The high-toughness coating comprises a matrix layer with a fine-grained structure and a coarse-grained modified region uniformly distributed in the matrix layer. The matrix layer has high hardness due to the strengthening effect of fine grains, and the dense grain boundaries can effectively block the diffusion of oxygen in the coating. The coarse-grained modified region has low hardness and good plasticity. Under long-term service conditions, it can effectively alleviate stress concentration in the coating and reduce the risk of crack initiation in the coating, thereby effectively improving the service life of the coating.

[0006] Furthermore, in some embodiments, the depth of the modified zone is 20%-40% of the average thickness of the high-toughness coating. If the modified zone is too shallow, it will not be able to effectively absorb the stress and strain within the coating, while if it is too deep, it will cause the overall hardness of the coating to decrease and form a rapid oxygen diffusion channel.

[0007] Furthermore, in some embodiments, within the high-toughness coating, the diameter of the modified region decreases with increasing depth.

[0008] Furthermore, in some embodiments, the high-toughness coating has a room temperature fracture strain threshold of not less than 1.5%, and the time for oxygen to diffuse through the high-toughness coating to the surface of the zirconium alloy substrate in a water vapor environment at 1200°C is not less than 10 hours.

[0009] Furthermore, in some embodiments, the zirconium alloy matrix is ​​configured as a zirconium alloy fuel rod cladding.

[0010] According to another aspect of the present invention, a method for manufacturing a high-toughness coating is provided, for manufacturing the high-toughness coating provided in any of the foregoing embodiments, and includes the following steps:

[0011] Step a): Provide a zirconium alloy part as a substrate, and coat the surface of the zirconium alloy part with a pure Cr layer by magnetron pulse sputtering process;

[0012] Step b): Hold the zirconium alloy part at 70℃-90℃ for at least 1 hour;

[0013] Step c): The pure Cr layer is modified by laser remelting to form the modified region; wherein the maximum depth D of the laser remelting and the thickness d of the pure Cr layer satisfy D=1 / 3d±2μm.

[0014] Laser remelting modification creates a roughly conical remelting zone in the substrate layer. Strictly limiting the remelting depth ensures accurate control of the modified zone's size, effectively absorbing stress and strain within the high-toughness coating and preventing crack initiation, while not affecting the coating's ability to block oxygen penetration.

[0015] Furthermore, in some embodiments, in step c), the surface energy density of the laser remelting modification is 1.2 J / cm². 2 -3J / cm 2 The scanning speed is 0.5m / s-1m / s, the pulse width is 15 nanoseconds-30 nanoseconds, and the repetition frequency is 250kHz-350kHz.

[0016] Furthermore, in some embodiments, in step a), the magnetron pulse sputtering process involves a heating temperature of 300℃-400℃ and a vacuum degree of 3×10⁻⁶. -4 Pa-4×10 -4 Pa, power 300W-400W, sputtering time 15min-20min.

[0017] Furthermore, in some embodiments, step d) is included after step c): the zirconium alloy part is kept at 70°C-90°C for at least 1 hour.

[0018] Furthermore, in some embodiments, in step a), the zirconium alloy part undergoes surface pickling treatment. Attached Figure Description

[0019] Figure 1 This is a partial scanning electron microscope image of the high-toughness coating in one embodiment;

[0020] Figure 2 This is a local EBSD image of a high-toughness coating in one embodiment;

[0021] Figure 3 This is an image showing the local stress distribution of a high-toughness coating in one embodiment.

[0022] The purpose of the above figures is to provide a detailed description of the invention so that those skilled in the art can understand the technical concept of the invention, and not to limit the invention. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0024] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment herein. The phrase appearing in various places in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive, independent, or alternative embodiments. Those skilled in the art will understand that the embodiments herein can be combined with other embodiments without causing structural conflicts.

[0025] In this description, terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating relative importance or limiting the number, specific order, or primary / secondary relationship of the described technical features. In this description, "multiple" means at least two.

[0026] Currently, nuclear power plants commonly use zirconium alloys, which possess good neutron permeability and radiation resistance, as structural components within the reactor core, such as fuel rod cladding and guide tube cladding. Because zirconium alloys are prone to oxidation at high temperatures and lack sufficient hardness, a hard, anti-oxidation coating is typically applied to the surface of the zirconium alloy to improve the service life of the components. Pure Cr coatings have high hardness, and the grain boundaries within the Cr coating can restrict oxygen diffusion. Furthermore, Cr oxidation can form a dense oxide layer, further enhancing the coating's oxidation resistance, thus making it considered a promising candidate for application. However, while fine-grained pure Cr coatings have high hardness, they lack toughness, making them prone to brittle fracture along grain boundaries under long-term service conditions, leading to coating cracking and spalling. Coarse-grained pure Cr coatings, although possessing better plastic deformation capabilities, suffer from reduced grain boundary density, weakening the shielding effect against oxygen diffusion and resulting in a significantly increased oxidation rate. Existing technologies struggle to overcome the contradiction between the toughness and oxidation resistance of pure Cr coatings, hindering further improvements in the overall performance of zirconium alloy components.

[0027] To overcome the aforementioned shortcomings of the prior art, one embodiment of the present invention provides a high-toughness coating that possesses both good toughness and oxidation resistance. Specifically, the high-toughness coating is disposed on the surface of a zirconium alloy substrate. In a preferred embodiment, the zirconium alloy substrate can be a zirconium alloy fuel rod or a zirconium alloy guide tube. The high-toughness coating is a pure Cr layer, comprising a fine-grained substrate layer and a modified region with a coarse-grained structure. The average grain size of the substrate layer is 0.1 μm-0.8 μm, and the average grain size of the modified region is 1 μm-2 μm. The modified regions are uniformly distributed on the surface of the substrate layer, with an average diameter of 5 μm-15 μm, and the spacing between adjacent modified regions is 0.5 mm-1.5 mm. The substrate layer has a fine-grained structure, which results in higher hardness due to the strengthening effect of the fine grains. At the same time, the dense grain boundaries can form a barrier against oxygen diffusion in the coating thickness direction, ensuring that the high-toughness coating has good strength and oxidation resistance. The modified zone has a larger grain size and a relatively softer structure, thus exhibiting better plastic deformation capacity. Under high temperature and high pressure corrosion environment, the modified zone can effectively absorb stress and strain within the coating, prevent stress concentration within the substrate layer, reduce the risk of crack initiation, and improve coating life.

[0028] In a preferred embodiment, the depth of the modified zone is 20%-40% of the average thickness of the high-toughness coating. If the thickness of the modified zone is too small, it will be difficult to fully absorb the stress and strain within the high-toughness coating; while if the thickness of the modified zone is too large, it will provide a rapid penetration channel for oxygen to penetrate the coating. Within the high-toughness coating, the diameter of the modified zone decreases with increasing depth, and the overall structure approximates a cone.

[0029] The high-toughness coating has good toughness and oxidation resistance, and the fracture strain threshold is not less than 1.5% at room temperature; in a water vapor environment at 1200℃, the time for oxygen to diffuse through the high-toughness coating to the surface of the zirconium alloy substrate is not less than 10 hours.

[0030] Another aspect of the present invention provides a method for manufacturing a high-toughness coating, used to prepare the high-toughness coating provided in the foregoing embodiments. Specifically, the method includes the following steps:

[0031] Step a): Provide a zirconium alloy component as a substrate. In different embodiments, the zirconium alloy component can be a fuel rod cladding tube, a control rod guide tube, or other core component. In a preferred embodiment, the zirconium alloy component undergoes surface pickling to remove dirt and surface oxide layers. Using the zirconium alloy component as a substrate, a pure Cr layer is coated on the surface of the zirconium alloy component using a magnetron pulse sputtering process.

[0032] Specifically, in a preferred embodiment, the magnetron pulse sputtering process is configured with a pulse cavity temperature of 300°C-400°C and a vacuum degree of 3×10⁻⁶. -4 Pa-4×10 -4 Pa, power 300W-400W, sputtering time 15min-20min.

[0033] Step b): Load the zirconium alloy part into a muffle furnace and hold it at 70℃-90℃ for at least 1 hour to obtain a stable pure Cr layer structure.

[0034] Step c): Localized laser remelting modification of the pure Cr layer is performed to form uniformly distributed modified regions. During the laser remelting modification process, the maximum laser remelting depth D and the pure Cr layer thickness d satisfy D = 1 / 3d ± 2 μm. The prepared modified regions have an average diameter of 5 μm-15 μm and are uniformly distributed on the surface of the zirconium alloy part at intervals of 0.5 mm-1.5 mm. Specifically, the surface energy density of the laser remelting modification is 1.2 J / cm². 2 -3J / cm 2 The scanning speed is 0.5 m / s-1 m / s, the pulse width is 15 nanoseconds-30 nanoseconds, and the repetition frequency is 250 kHz-350 kHz. The spot size of the laser remelting modification process affects the surface diameter of the modified zone, while the laser input energy density and scanning speed jointly affect the remelting depth.

[0035] In a preferred embodiment, step d) is further included: the zirconium alloy part that has undergone laser remelting modification is loaded into a muffle furnace and held at a temperature of 70°C-90°C for at least 1 hour to obtain a stable high-toughness coating structure.

[0036] The high-toughness coating manufacturing method provided in the above embodiments can form a protective coating with good toughness, hardness, and oxidation resistance on the surface of zirconium alloy parts, effectively improving the service life and reliability of zirconium alloy parts under temperature-sensitive, high-pressure, and corrosive environments. Specifically, the magnetron pulse sputtering process can accurately control the coating thickness, obtaining a uniform, dense, and stable pure Cr layer. Other coating processes, such as electroplating, electroless plating, and ion sputtering, produce Cr coatings whose internal stress state and microstructure characteristics do not meet the requirements of subsequent laser modification. Furthermore, the melting and solidification behavior of the microstructure is uncontrollable during laser modification, making it impossible to obtain coatings that meet performance requirements. After laser remelting modification, the high-toughness coating forms a composite structure with locally coarse grains on the surface and fine grains in the matrix, possessing both good toughness and oxidation resistance.

[0037] In the first preferred embodiment, the manufacturing process of the high-toughness coating is as follows:

[0038] First, a zirconium alloy tube is provided, and the surface oxide layer is removed by acid pickling. The zirconium alloy tube is then installed in a magnetron pulse sputtering apparatus, with the magnetron pulse cavity temperature set to 350℃ and the vacuum degree to 4×10⁻⁶. -4 A pure Cr layer with a thickness d of 15 μm was formed on the surface of a zirconium alloy tube by sputtering at Pa, power of 400 W, and sputtering time of 15 min.

[0039] Next, the zirconium alloy tube is placed into a muffle furnace and held at 80°C for 1 hour to stabilize the pure Cr layer structure.

[0040] The next step is to perform laser remelting modification on the surface of the zirconium alloy tube, with a laser energy density of 1.5 J / cm². 2 The scanning speed was 0.9 m / s, the pulse width was 15 nanoseconds, the repetition frequency was 300 kHz, and the maximum remelting depth D during the remelting modification process met the condition D=1 / 3d±2μm, with an actual measured depth of 4μm.

[0041] Finally, the laser-modified zirconium alloy tube was placed into a muffle furnace and held at 80°C for 1 hour to complete the microstructure stabilization treatment of the high-toughness coating.

[0042] The local microstructure of the high-toughness coating obtained through the above process is as follows: Figure 1 As shown, modified region 1 has a diameter of approximately 10 μm on the surface of the high-toughness coating and extends to a depth of approximately 10 μm within the substrate layer 2. Modified region 1 generally exhibits a cone-shaped structure that is wider at the top and narrower at the bottom. Adjacent modified regions are spaced 1 mm apart and are distributed in a matrix pattern on the surface of the zirconium alloy tube. Backscattered electron diffraction (EBSD) analysis of the region containing modified region 1 is shown below. Figure 2 As shown, the average grain size in modified region 1 is 1 μm, while the grain size in matrix layer 2 ranges from 0.2 μm to 0.6 μm. The stress distribution KAM image of the region where modified region 1 is located is shown below. Figure 3As shown, compressive stress is introduced into the modified zone 1 through remelting modification, which can effectively improve the fracture strain threshold of the high-toughness coating and alleviate the early failure of the coating due to stress concentration under high-frequency fretting wear or thermal shock conditions.

[0043] Tests were conducted on the zirconium alloy tube, and the room temperature fracture strain threshold of the high-toughness coating was measured to be 1.6%. In a 1200℃ water vapor environment, the time for oxygen to diffuse through the high-toughness coating to the surface of the zirconium alloy tube was 24 hours.

[0044] In the second preferred embodiment, the manufacturing process of the high-toughness coating is as follows:

[0045] First, a zirconium alloy tube is provided, and the surface oxide layer is removed by acid pickling. The zirconium alloy tube is then installed in a magnetron pulse sputtering apparatus, with the magnetron pulse cavity temperature set to 350℃ and the vacuum degree to 4×10⁻⁶. -4 A pure Cr layer with a thickness d of 15 μm was formed on the surface of a zirconium alloy tube by sputtering at Pa, power of 400 W, and sputtering time of 15 min.

[0046] Next, the zirconium alloy tube is placed into a muffle furnace and held at 80°C for 1 hour to stabilize the pure Cr layer structure.

[0047] The next step is to perform laser remelting modification on the surface of the zirconium alloy tube, with a laser energy density of 2.2 J / cm². 2 The scanning speed was 0.5 m / s, the pulse width was 30 nanoseconds, the repetition frequency was 300 kHz, and the maximum remelting depth D during the remelting modification process met the condition D=1 / 3d±2μm, with a measured depth of 6μm.

[0048] Finally, the laser-modified zirconium alloy tube was placed into a muffle furnace and held at 80°C for 1 hour to complete the microstructure stabilization treatment of the high-toughness coating.

[0049] The modified regions in the high-toughness coating obtained through the above process have a diameter of approximately 10 μm on the coating surface and a depth of approximately 10 μm within the substrate layer. The modified regions generally exhibit a cone-shaped structure that is wider at the top and narrower at the bottom. Adjacent modified regions are spaced 1 mm apart and are distributed in a matrix pattern on the zirconium alloy tube surface. Backscattered electron diffraction (EBSD) analysis of the modified regions revealed an average grain size of 2 μm within the modified regions, while the grain size within the substrate layer 2 ranged from 0.2 μm to 0.6 μm.

[0050] The zirconium alloy tube was tested, and the room temperature fracture strain threshold of the high-toughness coating was measured to be 3.4%. In a 1200℃ water vapor environment, the time for oxygen to diffuse through the high-toughness coating to the surface of the zirconium alloy tube was 16 hours.

[0051] In the third preferred embodiment, the manufacturing process of the high-toughness coating is as follows:

[0052] First, a zirconium alloy tube is provided, and the surface oxide layer is removed by acid pickling. The zirconium alloy tube is then installed in a magnetron pulse sputtering apparatus, with the magnetron pulse cavity temperature set to 350℃ and the vacuum degree to 4×10⁻⁶. -4 A pure Cr layer with a thickness d of 15 μm was formed on the surface of a zirconium alloy tube by sputtering at Pa, power of 400 W, and sputtering time of 15 min.

[0053] Next, the zirconium alloy tube is placed into a muffle furnace and held at 80°C for 1 hour to stabilize the pure Cr layer structure.

[0054] The next step is to perform laser remelting modification on the surface of the zirconium alloy tube, with a laser energy density of 1.8 J / cm². 2 The scanning speed was 0.8 m / s, the pulse width was 20 nanoseconds, the repetition frequency was 300 kHz, and the maximum remelting depth D during the remelting modification process met the requirement of D=1 / 3d±2μm, with an actual measured depth of 5μm.

[0055] Finally, the laser-modified zirconium alloy tube was placed into a muffle furnace and held at 80°C for 1 hour to complete the microstructure stabilization treatment of the high-toughness coating.

[0056] The modified regions in the high-toughness coating obtained through the above process have a diameter of approximately 10 μm on the coating surface and a depth of approximately 10 μm within the substrate layer. The modified regions generally exhibit a cone-shaped structure, wider at the top and narrower at the bottom. Adjacent modified regions are spaced 1 mm apart and are distributed in a matrix pattern on the zirconium alloy tube surface. Backscattered electron diffraction (EBSD) analysis of the modified regions revealed an average grain size of 1.5 μm within the modified regions, while the grain size within the substrate layer 2 ranged from 0.2 μm to 0.6 μm.

[0057] The zirconium alloy tube was tested, and the room temperature fracture strain threshold of the high-toughness coating was measured to be 2.2%. In a 1200℃ water vapor environment, the time for oxygen to diffuse through the high-toughness coating to the surface of the zirconium alloy tube was 20 hours.

[0058] In a comparative example, a pure Cr coating was prepared via the following steps:

[0059] A zirconium alloy tube is provided. After surface pickling, the zirconium alloy tube is installed into a magnetron pulse sputtering device. The magnetron pulse chamber temperature is set to 350℃ and the vacuum degree to 4×10⁻⁶. -4 A pure Cr layer with a thickness d of 15 μm was formed on the surface of a zirconium alloy tube by sputtering at Pa, power of 400 W, and sputtering time of 15 min.

[0060] The zirconium alloy tube was placed in a muffle furnace and held at 80°C for 1 hour to stabilize the pure Cr layer structure.

[0061] The grain size of the pure Cr layer without laser remelting modification is 0.2μm-0.6μm, and the room temperature fracture strain threshold of the pure Cr coating is only 0.8%.

[0062] As can be seen from the comparison of the above embodiments and comparative examples, the high-toughness coating provided by the embodiments of the present invention has good toughness. Compared with the pure Cr coating without laser remelting modification treatment, the fracture strain threshold is increased by 87.5%, which can effectively improve the coating life, reduce the risk of coating failure in the long term, and thus effectively improve the service life and reliability of zirconium alloy parts in high temperature and high pressure corrosion environment.

[0063] The purpose of the above embodiments is to provide a further detailed description of the present invention in conjunction with the accompanying drawings, so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, optimization or equivalent substitution of the technical features involved, as well as combination of implementation methods in different embodiments without causing structural and principle conflicts, all fall within the protection scope of the present invention.

Claims

1. A high-toughness coating disposed on the surface of a zirconium alloy substrate, characterized in that, The high-toughness coating is configured as a pure Cr layer, and the high-toughness coating includes a substrate layer and modified regions; wherein, the average grain size of the substrate layer is 0.1μm-0.8μm; the modified regions are uniformly distributed on the surface of the substrate layer, the average grain size of the modified regions is 1μm-2μm, the average diameter of the modified regions is 5μm-15μm, and the interval between adjacent modified regions is 0.5mm-1.5mm.

2. The high-toughness coating according to claim 1, characterized in that, The depth of the modified zone is 20%-40% of the average thickness of the high-toughness coating.

3. The high-toughness coating according to claim 1 or 2, characterized in that, Within the high-toughness coating, the diameter of the modified region decreases with increasing depth.

4. The high-toughness coating according to claim 1 or 2, characterized in that, The high-toughness coating has a room temperature fracture strain threshold of not less than 1.5%, and the time for oxygen to diffuse through the high-toughness coating to the surface of the zirconium alloy substrate in a water vapor environment at 1200℃ is not less than 10 hours.

5. The high-toughness coating according to claim 1 or 2, characterized in that, The zirconium alloy matrix is ​​configured as a zirconium alloy fuel rod cladding.

6. A method for manufacturing a high-toughness coating, characterized in that, For manufacturing a high-toughness coating as described in any one of claims 1 to 5, and comprising the following steps: Step a): Provide a zirconium alloy part as a substrate, and coat the surface of the zirconium alloy part with a pure Cr layer by magnetron pulse sputtering process; Step b): Hold the zirconium alloy part at 70℃-90℃ for at least 1 hour; Step c): The pure Cr layer is modified by laser remelting to form the modified region; wherein the maximum depth D of the laser remelting and the thickness d of the pure Cr layer satisfy D=1 / 3d±2μm.

7. The method for manufacturing a high-toughness coating according to claim 6, characterized in that, In step c), the surface energy density of the laser remelting modification is 1.2 J / cm². 2 -3J / cm 2 The scanning speed is 0.5m / s-1m / s, the pulse width is 15 nanoseconds-30 nanoseconds, and the repetition frequency is 250kHz-350kHz.

8. The method for manufacturing a high-toughness coating according to claim 6 or 7, characterized in that, In step a), the magnetron pulse sputtering process involves a heating temperature of 300℃-400℃ and a vacuum degree of 3×10⁻⁶. -4 Pa-4×10 -4 Pa, power 300W-400W, sputtering time 15min-20min.

9. The method for manufacturing a high-toughness coating according to claim 6 or 7, characterized in that, The process includes step d) after step c): heat treatment of the zirconium alloy part at 70°C-90°C for at least 1 hour.

10. The method for manufacturing a high-toughness coating according to claim 6 or 7, characterized in that, In step a), the zirconium alloy part undergoes surface pickling treatment.

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