A high toughness coating and method of making the same

Abstract

The application relates to 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, which comprises a substrate layer and a modified region, wherein the average grain size of the substrate layer is 0.1-0.8 mu m, the average grain size in the modified region is 1-2 mu m, the average diameter of the modified region is 5-15 mu m, and the interval is 0.5-1.5 mm. The high-toughness coating has good toughness and oxidation resistance, and can effectively improve the service life and reliability of a zirconium alloy in a high-temperature and high-pressure corrosion environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of coating, and particularly relates to a high-toughness coating and a manufacturing method thereof. BACKGROUND

[0002] Zirconium alloy fuel rod cladding used in nuclear power plants usually needs to be provided with a protective coating on the surface to improve the oxidation resistance and wear resistance of the zirconium alloy. Among them, the Cr coating is one of the coatings widely used at present, which has good hardness and can form a dense oxide film to inhibit the oxidation of the zirconium alloy substrate. However, in the existing Cr coating, the fine-grained coating with columnar crystal as the main organizational feature has high hardness but insufficient toughness, and is prone to intergranular brittle fracture under thermal cycling or mechanical load, resulting in cracking or failure of the coating; and the coarse-grained coating has low grain boundary density, and it is difficult to act as a barrier to oxygen diffusion, and the oxidation rate is significantly increased under high temperature conditions. Therefore, providing a coating with good oxidation resistance and good toughness has a positive significance for improving the service life and reliability of zirconium alloy components in nuclear power plants. SUMMARY

[0003] The purpose of the present application is to provide a high-toughness coating to improve the service life and reliability of zirconium alloy in the reactor core. The present application also provides a manufacturing method of the high-toughness coating.

[0004] According to an embodiment of one aspect of the present application, a high-toughness coating is provided, which is arranged on the surface of a zirconium alloy substrate, the high-toughness coating is configured as a pure Cr layer, and the high-toughness coating comprises a substrate layer and a modified region; wherein the average grain size of the substrate layer is 0.1-0.8 μm; the modified region is uniformly distributed on the surface of the substrate layer, the average grain size in the modified region is 1-2 μm, the average diameter of the modified region is 5-15 μm, and the interval between adjacent modified regions is 0.5-1.5 mm.

[0005] The high-toughness coating comprises a substrate layer with fine-grained structure and coarse-grained modified regions uniformly distributed in the substrate layer. The substrate layer has high hardness due to fine-grain strengthening, 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, which can effectively relieve stress concentration in the coating and reduce the risk of crack initiation under long-term service conditions, thereby effectively improving the service life of the coating.

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

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

[0008] Further, in some embodiments, the high-toughness coating has a room-temperature fracture strain threshold of no less than 1.5%, and a time for oxygen to diffuse through the high-toughness coating to the surface of the zirconium alloy substrate under a water vapor environment at 1200°C is no less than 10h.

[0009] Further, in some embodiments, the zirconium alloy substrate is configured as a zirconium alloy fuel rod cladding.

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

[0011] Step a): providing a zirconium alloy workpiece as a substrate, and coating a pure Cr layer on the surface of the zirconium alloy workpiece by a magnetron pulsed sputtering process;

[0012] Step b): heat treating the zirconium alloy workpiece at 70-90°C for at least 1h;

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

[0014] The laser remelting modification process forms a generally conical remelting region in the substrate layer, and strict limitation of the remelting depth can ensure accurate control of the size of the modified region, ensure that the modified region effectively absorbs stress and strain in the high-toughness coating, prevent the initiation of cracks, and at the same time not affect the blocking effect of the coating itself on oxygen permeation.

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

[0016] Further, in some embodiments, in the step a), in the magnetron pulsed sputtering process, the heating temperature is 300-400°C, the vacuum degree is 3x10 -4 Pa-4x10 -4 Pa, the power is 300-400W, and the sputtering time is 15-20min.

[0017] Further, in some embodiments, after the step c), there is further a step d) of holding the zirconium alloy piece at 70-90 °C for at least 1 h.

[0018] Further, in some embodiments, in the step a), the zirconium alloy piece is subjected to surface pickling treatment. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A local SEM image of the high toughness coating in one embodiment;

[0020] Figure 2 A local EBSD image of the high toughness coating in one embodiment;

[0021] Figure 3 A local stress distribution image of the high toughness coating in one embodiment.

[0022] The purpose of the above drawings is to make a detailed description of the present application so that those skilled in the art can understand the technical concept of the present application, and is not intended to limit the present application. DETAILED DESCRIPTION

[0023] The present application will be further described in detail below with reference to specific embodiments in conjunction with the accompanying drawings.

[0024] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment. The appearances of the phrase that the phrase in various places in the specification are not necessarily referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of one another. Those skilled in the art will appreciate that embodiments of the present application can be combined with other embodiments in a manner not specifically stated in the description.

[0025] In the description herein, the terms "first", "second", and the like are used only to distinguish different objects, and cannot be understood as indicating relative importance or limiting the number, specific order, or primary and secondary relationship of the described technical features. In the description herein, the meaning of "a plurality of" is at least two.

[0026] Currently, zirconium alloy with good neutron transparency and radiation resistance is widely used as the structural member in the reactor core of nuclear power plant, such as fuel rod cladding, guide tube cladding, etc. Since zirconium alloy is prone to oxidation under high temperature conditions, and the hardness is insufficient, it is usually necessary to set a hard oxidation-resistant coating on the surface of the zirconium alloy to improve the service life of the zirconium alloy parts. Pure Cr coating has high hardness, the grain boundaries in the Cr coating can limit the diffusion of oxygen, and the Cr can form a dense oxide layer after oxidation, further improving the oxidation resistance of the coating, so it is considered to have good application prospect. However, the fine-grained pure Cr coating has high hardness but insufficient toughness, and is prone to brittle fracture along the grain boundary under long-term service conditions, resulting in cracking and peeling of the coating; while the coarse-grained pure Cr coating has better plastic deformation ability, but the reduction of grain boundary density weakens the shielding effect on oxygen diffusion, resulting in a significant increase in oxidation rate. The technical solutions of the prior art cannot overcome the contradiction between the toughness and oxidation resistance of the pure Cr coating, which restricts the further improvement of the comprehensive performance of the zirconium alloy parts.

[0027] In order to overcome the above shortcomings of the prior art, one embodiment of the present application provides a high-toughness coating with good toughness and oxidation resistance. Specifically, the high-toughness coating is arranged on the surface of a zirconium alloy substrate, and in preferred embodiments, 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, which includes a substrate layer with a fine-grained structure and a modified region with a coarse-grained structure, the average grain size of the substrate layer is 0.1-0.8 μm, and the average grain size in the modified region is 1-2 μm. The modified region is uniformly distributed on the surface of the substrate layer, with an average diameter of 5-15 μm, and the spacing between adjacent modified regions is 0.5-1.5 mm. The substrate layer has a fine-grained structure, which has higher hardness due to fine-grain strengthening, and the dense grain boundaries can form a barrier to the diffusion of oxygen in the thickness direction of the coating, ensuring that the high-toughness coating has good strength and oxidation resistance. The modified region has larger grain size and relatively soft structure, so it has better plastic deformation ability. In a high-temperature and high-pressure corrosive environment, the modified region can effectively absorb the stress and strain in the coating, prevent stress concentration in the substrate layer, reduce the risk of crack initiation, and improve the service life of the coating.

[0028] In preferred embodiments, the depth of the modified region is 20-40% of the average thickness of the high-toughness coating. When the thickness of the modified region is too small, it will be difficult to fully absorb the stress and strain in the high-toughness coating; and when the thickness of the modified region is too large, it will provide a fast penetration channel for oxygen to penetrate the coating. In the high-toughness coating, the diameter of the modified region decreases with increasing depth, and the overall structure is approximately conical.

[0029] The high-toughness coating has good toughness and oxidation resistance, and the threshold value of the fracture strain is not less than 1.5% at room temperature; 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 10h.

[0030] Embodiments of another aspect of the present application provide a method for manufacturing the high-toughness coating provided in the foregoing embodiments. Specifically, the method comprises the following steps:

[0031] Step a): providing a zirconium alloy workpiece as a substrate. In different embodiments, the zirconium alloy workpiece can be a fuel rod cladding tube, a control rod guide tube or other in-core components. In preferred embodiments, the zirconium alloy workpiece is subjected to surface pickling treatment to remove dirt and surface oxide layers. A pure Cr layer is coated on the surface of the zirconium alloy workpiece by using a magnetron pulsed sputtering process.

[0032] Specifically, in preferred embodiments, the temperature in the pulse cavity is set to 300-400°C and the vacuum degree is set to 3x10 -4 Pa-4x10 -4 Pa, the power is 300-400W, and the sputtering time is 15-20min.

[0033] Step b): the zirconium alloy workpiece is loaded into a muffle furnace and is kept at a temperature of 70-90°C for at least 1h to obtain a stable pure Cr layer structure.

[0034] Step c): the pure Cr layer is subjected to local laser remelting modification to form a uniformly distributed modified region. During the laser remelting modification, the maximum depth D of the laser remelting satisfies D=1 / 3d±2μm, where d is the thickness of the pure Cr layer. The prepared modified region has an average diameter of 5-15μm and is uniformly distributed on the surface of the zirconium alloy workpiece at a spacing of 0.5-1.5mm. Specifically, the surface energy density of the laser remelting modification is 1.2-3J / cm 2 -3J / cm 2 , the scanning speed is 0.5-1m / s, the pulse width is 15-30ns, and the repetition frequency is 250-350kHz. The spot size of the laser remelting modification process affects the surface diameter of the modified region, and the energy density of the laser input and the scanning speed jointly affect the remelting depth.

[0035] In preferred embodiments, step d) is further included: the zirconium alloy workpiece subjected to the laser remelting modification is loaded into a muffle furnace and is kept at a temperature of 70-90°C for at least 1h again 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, the compressive stress introduced by the remelting modification in the modified zone 1 can effectively improve the fracture strain threshold of the high toughness coating, and relieve the early failure of the coating due to stress concentration under high frequency fretting wear or thermal vibration working conditions.

[0043] The test on the zirconium alloy tube shows that the fracture strain threshold of the high toughness coating at room temperature is 1.6%, and the time for oxygen to diffuse through the high toughness coating to the surface of the zirconium alloy tube under 1200℃ water vapor environment is 24h.

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

[0045] Firstly, a zirconium alloy tube is provided, and the surface oxide layer of the zirconium alloy tube is removed by pickling treatment; the zirconium alloy tube is loaded into a magnetron pulse sputtering device, the temperature of the magnetron pulse cavity is set to 350℃, the vacuum degree is set to 4×10 -4 Pa, the power is set to 400W, and the sputtering time is set to 15min to form a pure Cr layer with a thickness d of 15μm on the surface of the zirconium alloy tube.

[0046] Next, the zirconium alloy tube is loaded into a muffle furnace, and the temperature is kept at 80℃ for 1h to stabilize the structure of the pure Cr layer.

[0047] Next, the zirconium alloy tube is loaded into a muffle furnace, and the temperature is kept at 80℃ for 1h to stabilize the structure of the pure Cr layer. 2 Next, the zirconium alloy tube is loaded into a muffle furnace, and the temperature is kept at 80℃ for 1h to stabilize the structure of the pure Cr layer.

[0048] Finally, the zirconium alloy tube subjected to the laser remelting modification is loaded into a muffle furnace, and the temperature is kept at 80℃ for 1h to complete the structure stabilization treatment of the high toughness coating.

[0049] The modified zone in the high toughness coating prepared by the above process has a diameter of about 10μm on the surface of the high toughness coating, and extends to a depth of about 10μm in the substrate layer, and the overall modified zone is roughly in the shape of a wide upper and narrow lower cone structure. The adjacent modified zones are spaced apart by 1mm and are distributed in a matrix form on the surface of the zirconium alloy tube. The backscattered electron diffraction (EBSD) analysis of the region where the modified zone is located shows that the average grain size in the modified zone is 2μm, and the grain size in the substrate layer 2 is 0.2μm-0.6μm.

[0050] The test on the zirconium alloy tube shows that the fracture strain threshold of the high toughness coating at room temperature is 3.4%, and the time for oxygen to diffuse through the high toughness coating to the surface of the zirconium alloy tube under 1200℃ water vapor environment is 16h.

[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 satisfied 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 treatment is 0.2-0.6 μm, and the pure Cr coating has a room temperature fracture strain threshold of only 0.8%.

[0062] It can be seen from the comparison of the above examples and the comparative examples that the high-toughness coating provided by the examples has good toughness, the fracture strain threshold is increased by 87.5% compared with the pure Cr coating without laser remelting modification treatment, the service life of the coating can be effectively improved, the risk of coating failure in the long-term process is reduced, and the service life and reliability of the zirconium alloy part in the high-temperature and high-pressure corrosion environment are effectively improved.

[0063] The above examples are intended to further illustrate the present application in conjunction with the drawings, so that those skilled in the art can understand the technical concept of the present application. Within the scope of the present application, optimization or equivalent replacement of the technical features involved, and combination of the implementation manners in different embodiments without structural and principle conflicts, all fall within the protection scope of the present application.

Claims

1. A high toughness coating disposed on a surface of a zirconium alloy substrate, characterized in that, The high-toughness coating is configured as a pure Cr layer, and includes a base layer and a modified region; wherein the average grain size of the base layer is 0.1-0.8 μm; the modified region is uniformly distributed on the surface of the base layer, the average grain size in the modified region is 1-2 μm, the modified region is distributed in a matrix form, the average diameter of the modified region is 5-15 μm, and the interval between adjacent modified regions is 0.5-1.5 mm. The manufacturing steps of the high-toughness coating are as follows: Step a): providing a zirconium alloy workpiece as a substrate, and coating a pure Cr layer on the surface of the zirconium alloy workpiece by a magnetron pulse sputtering process; Step b): heat treating the zirconium alloy workpiece at 70-90 °C for at least 1 h; Step c): locally laser remelting and modifying the pure Cr layer 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 ± 2 μm.

2. The high toughness coating of claim 1, wherein, The depth of the modified region 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, In the high-toughness coating, the diameter of the modified region decreases with the increase of the depth.

4. The high toughness coating of claim 1 or 2, wherein, The high-toughness coating has a room-temperature fracture strain threshold value of not less than 1.5%, and the time for oxygen to diffuse from 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 h.

5. The high toughness coating of claim 1 or 2, wherein, The zirconium alloy substrate is configured as a zirconium alloy fuel rod cladding.

6. A method of manufacturing a high toughness coating, characterized by, A method for manufacturing the high-toughness coating as claimed in any one of claims 1-5, and comprising the following steps: Step a): providing a zirconium alloy workpiece as a substrate, and coating a pure Cr layer on the surface of the zirconium alloy workpiece by a magnetron pulse sputtering process; Step b): heat treating the zirconium alloy workpiece at 70-90 °C for at least 1 h; Step c): locally laser remelting and modifying the pure Cr layer 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 ± 2 μm.

7. The method of making a high toughness coating of claim 6, wherein, The energy density of the modified surface in the step c) is 1.2 J / cm 2 - 3 J / 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.

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

9. The method of manufacturing a high toughness coating according to claim 6 or 7, characterized in that, After the step c), the method further comprises a step d): heat treating the zirconium alloy workpiece at 70-90 °C for at least 1 h.

10. The method of manufacturing a high toughness coating according to claim 6 or 7, wherein In the step a), the zirconium alloy workpiece is subjected to surface pickling treatment.

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