Anti-oxidation coating and manufacturing method thereof

Abstract

The invention discloses an anti-oxidation coating and a manufacturing method thereof, and belongs to the field of coatings. The anti-oxidation coating is arranged on the surface of a zirconium alloy matrix, the anti-oxidation coating is a pure Cr coating, the hardness of the anti-oxidation coating is in gradient distribution in the thickness direction, the hardness of a surface layer is larger than that of a bottom layer, and the hardness gt of the bottom layer of the anti-oxidation coating is larger than that of gt; the hardness gt at the 1 / 2 thickness is 4GPa; the hardness of the surface layer is gt; and 6 GPa. Good bonding strength is achieved between the anti-oxidation coating and the zirconium alloy matrix, cracks are not prone to being generated on a bonding interface when the anti-oxidation coating serves in a long-term high-temperature and high-pressure corrosion environment, the service life of the zirconium alloy matrix can be effectively prolonged, and the reliability of the zirconium alloy matrix can be effectively improved.

Description

TECHNICAL FIELD

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

[0002] At present, the zirconium alloy is generally used to manufacture the fuel rod cladding of the pressurized water reactor. The zirconium alloy cladding tube is prone to breakage due to water corrosion and fretting wear in a high-temperature and high-pressure corrosive environment. The service life of the zirconium alloy can be improved to a certain extent by setting a coating with high hardness and oxidation resistance on the surface of the zirconium alloy. However, the bonding strength between the protective coating and the zirconium alloy substrate is insufficient in the prior art, and the coating is prone to cracking and peeling due to the mismatch of the thermal expansion coefficient or the elastic modulus. Therefore, it is of positive significance to provide an oxidation-resistant coating with optimized fatigue performance for improving the service life and reliability of the zirconium alloy parts used in nuclear power under a water corrosion environment. SUMMARY

[0003] The present application aims to provide an oxidation-resistant coating and improve the service life of the oxidation-resistant coating under a high-temperature and high-pressure water corrosion environment. The present application also provides a manufacturing method of the oxidation-resistant coating.

[0004] According to an embodiment of one aspect of the present application, an oxidation-resistant coating is provided, which is arranged on the surface of a zirconium alloy substrate, wherein the oxidation-resistant coating is configured as a pure Cr coating, the hardness of the oxidation-resistant coating is gradiently distributed along the thickness direction, and the hardness of the surface layer is greater than that of the bottom layer.

[0005] The hardness of the oxidation-resistant coating is gradiently set along the thickness direction, the surface layer has high hardness, and the wear resistance of the coating is improved. The coating of the bottom layer has low hardness, and the elastic modulus matching of the zirconium alloy substrate is good, so that the fatigue failure, cracking and other problems of the bonding interface are prevented.

[0006] Further, in some embodiments, the hardness of the bottom layer of the oxidation-resistant coating is greater than 4 GPa, the hardness at 1 / 2 thickness is greater than 5 GPa, and the hardness of the surface layer is greater than 6 GPa.

[0007] Further, in some embodiments, the thickness of the oxidation-resistant coating is 15-30 microns.

[0008] Further, in some embodiments, the fatigue cycle life of the oxidation-resistant coating is greater than 50,000 times under the air environment with a temperature of 316 DEG C and a pressure of 240 MPa.

[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, there is provided a method for manufacturing an oxidation-resistant coating, which is used to manufacture the oxidation-resistant coating provided in any of the preceding embodiments, and comprises the following steps:

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

[0012] Step b) keeping the zirconium alloy workpiece at 70-90℃ for at least 1 hour;

[0013] Step c) performing a laser remelting modification treatment on the pure Cr layer, wherein the laser remelting modification treatment satisfies T=(120D+115)±5℃, wherein T is the surface temperature of the pure Cr layer, and D is the thickness of the pure Cr layer in μm.

[0014] The high-power magnetron pulsed sputtering process can form a uniform and dense pure Cr layer on the surface of the zirconium alloy workpiece, and can accurately control the thickness D of the coating. In the subsequent step of laser remelting modification treatment, the instantaneous maximum temperature of the surface of the pure Cr layer is accurately controlled, so that about 1 / 3 thickness of the pure Cr layer is melted and rapidly solidified, forming a gradient hardness distribution along the thickness direction, and obtaining a coating surface with high hardness, which effectively improves the service life of the oxidation-resistant coating.

[0015] Further, in some embodiments, in the step c), the laser pulse width used in the laser remelting modification treatment is 10-50 nanoseconds, and the repetition frequency is not less than 4 MHz.

[0016] Further, in some embodiments, in the step a), the zirconium alloy workpiece is subjected to pickling treatment. The pickling treatment can remove the oxide layer on the surface of the zirconium alloy workpiece, and improve the bonding strength of the pure Cr layer.

[0017] Further, in some embodiments, in the step a), in the magnetron pulsed sputtering process, the temperature is 200-400℃, the vacuum degree is 3×10 -4 Pa-4×10 -4 Pa, the power is 300-400W, and the sputtering time is 15-20 minutes.

[0018] Further, in some embodiments, in the step c), after the laser remelting modification, a step d) is further included, which is keeping the zirconium alloy workpiece at 70-90℃ for at least 1 hour. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 FIG. 2 is a scanning electron microscope photo of the coating bottom layer interface region in the first embodiment;

[0020] Figure 2A scanning electron microscope photograph of the interface region between the coating and the substrate in the second example;

[0021] Figure 3 A scanning electron microscope photograph of the interface region between the coating and the substrate in the third example;

[0022] Figure 4 A scanning electron microscope photograph of the interface region between the coating and the substrate in the comparative example.

[0023] 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 not to limit the present application. DETAILED DESCRIPTION

[0024] The present application will be further described in detail below with reference to specific examples in conjunction with the drawings.

[0025] Reference herein to "an example" means that a particular feature, structure, or characteristic described in connection with the example can be included in at least one example herein. The phrase "in various examples" appearing at various locations in the specification does not necessarily refer to the same example, nor is it limited to a single or alternative example. Those skilled in the art will appreciate that examples herein can be combined with other examples without structural conflict.

[0026] In the description herein, the terms "first", "second", etc. 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, "a plurality of" means at least two.

[0027] With the development of nuclear power technology, the safety of nuclear power facilities is increasingly improved. At present, the zirconium alloy fuel rod cladding, which is widely used, is prone to damage and even failure due to fretting wear caused by oxidation corrosion or coolant impact under the long-term service in the high-temperature and high-pressure water corrosion environment in the reactor core, which restricts the further improvement of the safety of nuclear power facilities. In order to improve the service life of the zirconium alloy fuel rod cladding, some technical solutions set a pure Cr coating or a FeCrAl coating with high hardness and good oxidation resistance on the surface of the zirconium alloy cladding tube to improve the wear resistance and oxidation resistance of the zirconium alloy cladding tube. However, due to the high hardness of these coatings, cracks inevitably occur at the bonding surface between the coating and the zirconium alloy substrate due to the mismatch of the thermal expansion coefficient or the elastic modulus under long-term service conditions, and even the coating cracks and peels off.

[0028] In order to overcome the above-mentioned deficiencies of the prior art, an embodiment of one aspect of the present application provides an oxidation-resistant coating, which can effectively improve the service life and reliability of zirconium alloy parts in a high-temperature and high-pressure corrosion environment.

[0029] Specifically, the coating is arranged on the surface of a zirconium alloy base, and in a preferred embodiment, the zirconium alloy base is configured as a zirconium alloy fuel rod cladding. The oxidation-resistant coating is configured as a pure Cr coating, and along the thickness direction of the coating, the hardness is distributed in a gradient manner, with the surface layer hardness being greater than the bottom layer hardness. In a preferred embodiment, the hardness of the bottom layer of the oxidation-resistant coating is > 4 GPa, the hardness at 1 / 2 thickness is > 5 GPa, and the hardness of the surface layer is > 6 GPa; the thickness of the oxidation-resistant coating is 15-30 μm. The coating is subjected to a fatigue cycle test in an air environment at 316 ℃ and 240 MPa, and the service life is > 50,000 times; and no cracking or peeling occurs after serving for 4,000 h under a high-temperature high-pressure water dynamic load simulation working condition.

[0030] Embodiments of another aspect of the present application provide a method for manufacturing an oxidation-resistant coating, which is used to manufacture the oxidation-resistant coating provided in the foregoing embodiments, and specifically includes the following steps:

[0031] Step a): providing a zirconium alloy workpiece, preferably the surface of the zirconium alloy workpiece is subjected to pickling treatment to remove surface stains and oxide layers, and a pure Cr layer is coated on the surface of the zirconium alloy workpiece by using a high-power magnetron pulse sputtering process. In a preferred embodiment, during the magnetron pulse sputtering treatment process, the temperature of the magnetron pulse cavity is controlled to be 200-400 ℃, the vacuum degree is controlled to be 3×10 -4 Pa-4×10 -4 Pa, the power is 300-400 W, and the sputtering time is 15-20 min. Step b): after the magnetron pulse sputtering treatment is completed, the zirconium alloy workpiece is loaded into a muffle furnace, and is kept at a temperature of 70-90 ℃ for at least 1 h to obtain a pure Cr layer with stable organization.

[0032] Step c): laser remelting modification treatment is performed on the pure Cr layer, and by controlling the laser parameters, the surface instantaneous maximum temperature T of the pure Cr layer should satisfy the formula T=(120D+115)±5℃ based on the laser remelting modification process obtained based on a large number of research tests of the application, wherein T is the surface temperature of the pure Cr layer, D is the thickness of the pure Cr layer in μm, 115℃ is the basic temperature compensation provided based on the heat capacity of the material and the environmental heat dissipation under the laser remelting modification process, and ±5℃ is the process tolerance. Specifically, the laser pulse width is 10-50 nanoseconds, and the repetition frequency is not less than 4 MHz, thereby ensuring that the temperature of the laser reaching the coating surface can rapidly exceed the melting point (1907℃) of pure Cr metal. During the laser remelting modification process, the heat input of the laser is controlled to make the melting depth of the pure Cr layer reach about 1 / 3D, so that the pure Cr layer generates a hardness distribution gradient along the thickness direction in the process of rapid melting and rapid condensation. The Cr on the surface layer has a significantly improved hardness due to rapid cooling, while the Cr on the bottom layer is hardly affected by the heat input and maintains a low hardness, which can coordinate with the stress and strain of the zirconium alloy substrate and reduce the risk of crack initiation during long-term service.

[0033] In the preferred embodiment, after the laser remelting modification treatment is completed, step d) is further included: the zirconium alloy part is loaded into a muffle furnace and kept at 70-90℃ for at least 1h to realize the microstructure stabilization of the modified pure Cr layer.

[0034] The oxidation-resistant coating prepared by the oxidation-resistant coating manufacturing method provided in the above embodiments has good bonding strength with the zirconium alloy substrate and good service life and reliability in high-temperature and high-pressure corrosion environments. Compared with other processes such as direct current magnetron sputtering and multi-arc ion plating, the magnetron pulse sputtering process has a more suitable coating microstructure and density for the laser remelting process. The use of other processes to prepare Cr coating not only makes it difficult to achieve a gradient distribution of hardness, but also may cause problems such as coating cracking, peeling or fatigue performance degradation.

[0035] In the first embodiment, the oxidation-resistant coating is prepared by the following process:

[0036] The zirconium alloy pipe is used as the substrate, and the zirconium alloy pipe is subjected to pickling treatment to remove oil stains, dust and oxide layers on the surface. The zirconium alloy pipe is loaded into a magnetron pulse sputtering device, the cavity temperature is controlled at 350℃, the vacuum degree is controlled at 4×10 -4 Pa, the power is 400W, and the sputtering treatment is performed for 15min to coat a 15μm-thick pure Cr layer on the surface of the zirconium alloy pipe.

[0037] Next, the zirconium alloy pipe is loaded into a muffle furnace and kept at 80℃ for 1h to obtain a pure Cr layer with stable microstructure.

[0038] The nanosecond high repetition rate laser with pulse width of 45 nanoseconds and repetition frequency of 4.2 MHz is used to perform remelting modification treatment on the surface of the coating, and through control of the pulse width and the repetition frequency, the instantaneous maximum temperature T of the pure Cr layer surface satisfies T=(120D+115)±5℃ (1917℃ measured), and the remelting depth of the pure Cr layer reaches 1 / 3 (5 μm) of the total thickness.

[0039] Finally, the zirconium alloy pipe is loaded into a muffle furnace, and is kept at 80℃ for 1h to obtain the zirconium alloy pipe with the oxidation-resistant coating on the surface.

[0040] The interface structure between the bottom layer of the oxidation-resistant coating and the zirconium alloy substrate is shown in FIG. 1. Figure 1 As shown in FIG. 1, the interface region between the oxidation-resistant coating 1 and the zirconium alloy substrate 2 is tightly combined, and has no defects such as pores and cracks. The surface hardness of the coating is 6.7 GPa, the hardness at 1 / 2 thickness position is 5.1 GPa, and the hardness of the bottom layer in contact with the zirconium alloy substrate is 4.2 GPa. The fatigue cycle life of the oxidation-resistant coating is 51500 times under the air environment of 316℃ and 240 MPa, and the coating does not crack or peel off after serving for 4000h under the high-temperature high-pressure water dynamic load simulation working condition.

[0041] In the second embodiment, the oxidation-resistant coating is prepared by the following process:

[0042] The zirconium alloy pipe is used as the substrate, and the zirconium alloy pipe is subjected to pickling treatment to remove oil stains, dust and oxide layers on the surface. The zirconium alloy pipe is loaded into a magnetron pulse sputtering device, the cavity temperature is controlled at 350℃, the vacuum degree is controlled at 4×10 -4 Pa, the power is controlled at 400W, and the sputtering treatment is performed for 18min to coat a pure Cr layer with a thickness of 18μm on the surface of the zirconium alloy pipe.

[0043] Next, the zirconium alloy pipe is loaded into a muffle furnace, and is kept at 80℃ for 1h to obtain the pure Cr layer with stable structure.

[0044] The nanosecond high repetition rate laser with pulse width of 25 nanoseconds and repetition frequency of 4.5 MHz is used to perform remelting modification treatment on the surface of the coating, and through control of the pulse width and the repetition frequency, the instantaneous maximum temperature T of the pure Cr layer surface satisfies T=(120D+115)±5℃ (2275℃ measured), and the remelting depth of the pure Cr layer reaches 1 / 3 (6 μm) of the total thickness.

[0045] Finally, the zirconium alloy pipe is loaded into a muffle furnace, and is kept at 80℃ for 1h to obtain the zirconium alloy pipe with the oxidation-resistant coating on the surface.

[0046] The interface structure between the bottom layer of the oxidation-resistant coating and the zirconium alloy substrate is shown in FIG. 1. Figure 2As shown, the interface between the anti-oxidation coating 1 and the zirconium alloy substrate 2 is tightly bonded, without defects such as pores or cracks. Measurements show that the surface hardness of the coating is 6.8 GPa, the hardness at half the thickness is 5.5 GPa, and the hardness of the bottom layer in contact with the zirconium alloy substrate is 4.3 GPa. The anti-oxidation coating exhibits a fatigue cycle life of 50,500 cycles in an air environment at 316℃ and 240 MPa. After 4,000 hours of service under simulated high-temperature and high-pressure water dynamic load conditions, no coating cracking or peeling occurred.

[0047] In the third embodiment, the antioxidant coating is prepared by the following process:

[0048] Using a zirconium alloy tube as the substrate, the tube undergoes acid pickling to remove surface oil, dust, and oxide layers. The zirconium alloy tube is then placed into a magnetron pulse sputtering apparatus, with the chamber temperature controlled at 350℃ and the vacuum degree at 4×10⁻⁶. -4 A 21μm thick pure Cr layer was coated on the surface of the zirconium alloy tube by sputtering at 400W for 20 minutes at 400W.

[0049] Next, the zirconium alloy tube was placed into a muffle furnace and held at 80°C for 1 hour to obtain a pure Cr layer with a stable structure.

[0050] The coating surface was remelted and modified by a nanosecond high repetition rate laser with a pulse width of 15 nanoseconds and a repetition frequency of 4.8 MHz. By controlling the pulse width and repetition frequency, the instantaneous maximum temperature T on the surface of the pure Cr layer was made to satisfy T=(120D+115)±5℃ (measured at 2630℃), so that the remelting depth of the pure Cr layer reached 1 / 3 (7μm) of the total thickness.

[0051] Finally, the zirconium alloy tube is placed in a muffle furnace and held at 80°C for 1 hour to obtain a zirconium alloy tube with an anti-oxidation coating on its surface.

[0052] The interface structure between the anti-oxidation coating substrate and the zirconium alloy substrate is as follows: Figure 3 As shown, the interface between the anti-oxidation coating 1 and the zirconium alloy substrate 2 is tightly bonded, without defects such as pores or cracks. Measurements show that the surface hardness of the coating is 6.3 GPa, the hardness at half the thickness is 5.3 GPa, and the hardness of the bottom layer in contact with the zirconium alloy substrate is 4.1 GPa. The anti-oxidation coating exhibits a fatigue cycle life of 53,000 cycles in an air environment at 316℃ and 240 MPa, and after 4,000 hours of service under simulated high-temperature and high-pressure water dynamic load conditions, no coating cracking or peeling occurred.

[0053] In a comparative example, the Cr coating was prepared via the following process:

[0054] The same zirconium alloy tube as in the embodiment is provided, the zirconium alloy tube is acid-washed, and the zirconium alloy tube is loaded into a magnetron pulse sputtering device, with the chamber temperature controlled at 350°C and the vacuum degree at 4×10⁻⁶. -4 A 15μm thick pure Cr layer was coated on the surface of the zirconium alloy tube by sputtering at 400W for 15 minutes at 400W.

[0055] Next, the zirconium alloy tube was placed into a muffle furnace and held at 80°C for 1 hour to obtain a pure Cr layer with a stable structure.

[0056] The coating surface was remelted and modified using a nanosecond high-repetition-rate laser with a pulse width of 65 nanoseconds and a repetition frequency of 3.5 MHz. By controlling the pulse width and repetition frequency, the instantaneous maximum temperature T on the surface of the pure Cr layer was 1900℃, which does not meet the range of T=(120D+115)±5℃ (1910℃-1920℃).

[0057] Finally, the zirconium alloy tube is placed in a muffle furnace and held at 80°C for 1 hour to obtain a zirconium alloy tube with an anti-oxidation coating on its surface.

[0058] The interface structure between the bottom of the Cr coating and the zirconium alloy substrate is as follows: Figure 4 As shown, a relatively obvious interface 4 exists between the Cr coating 3 and the zirconium alloy substrate 2. Measurements show that the surface hardness of the coating is 5.1 GPa, the hardness at half the thickness is 4.6 GPa, and the hardness of the underlying layer in contact with the zirconium alloy substrate is 4.5 GPa. The surface hardness of the Cr coating 4 is insufficient, while the hardness of the underlying layer is too high. The fatigue cycle life of the anti-oxidation coating is only 35,400 cycles in an air environment of 316℃ and 240 MPa. Under simulated high-temperature and high-pressure water dynamic load conditions, localized cracking occurred after 4,000 hours of service.

[0059] By comparing the above examples with the comparative examples, it can be known that, by strictly controlling the heat input during the laser remelting process and limiting the laser remelting depth to 1 / 3D, on the one hand, the bonding strength between the bottom layer of the oxidation-resistant coating and the zirconium alloy substrate can be improved, the hardness of the bottom Cr layer can be reduced, and the stress and strain coordination can be improved; on the other hand, the surface hardness of the oxidation-resistant coating can be effectively improved, and the wear resistance of the coating can be improved; in the thickness direction, the hardness of the oxidation-resistant coating changes in a relatively continuous gradient, and the organization form and physical properties in the coating have no obvious mutation; compared with the composite coating, the oxidation-resistant coating provided by the embodiment has higher inter-coating bonding strength. Compared with the composite coating, the oxidation-resistant coating provided by the embodiment has single composition, simple preparation process, high production efficiency, and good industrial application prospect. The oxidation-resistant coating manufacturing method provided by the above embodiment can effectively improve the service life and reliability of the zirconium alloy fuel rod cladding under high temperature and high pressure water corrosion environment for a long time, and improve the safety of nuclear power facilities. In other embodiments, the application of the oxidation-resistant coating is not limited to the pressurized water reactor fuel rod cladding, and can also be used for supercritical water-cooled reactor fuel rod cladding or control rod cladding.

[0060] The purpose of the above examples is to make a further detailed description of the present application combined 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, the technical features involved are optimized or equivalently replaced, and the embodiments in different embodiments are combined without principle conflict, which all fall within the protection scope of the present application.

Claims

1. An anti-oxidation coating, disposed on the surface of a zirconium alloy substrate, characterized in that, The antioxidant coating is configured as a pure Cr coating, and the hardness of the antioxidant coating is distributed in a gradient along the thickness direction, with the surface layer having a higher hardness than the bottom layer; the bottom layer of the antioxidant coating has a hardness >4GPa, the hardness at 1 / 2 thickness has a hardness >5GPa, and the surface layer has a hardness >6GPa.

2. The antioxidant coating according to claim 1, characterized in that, The thickness of the antioxidant coating is 15μm-30μm.

3. The antioxidant coating according to claim 1, characterized in that, The antioxidant coating has a fatigue cycle life of >50,000 cycles in an air environment with a temperature of 316℃ and a pressure of 240MPa.

4. The antioxidant coating according to claim 1, characterized in that, The zirconium alloy matrix is ​​configured as a zirconium alloy fuel rod cladding.

5. A method for manufacturing an antioxidant coating, characterized in that, A method for manufacturing an antioxidant coating as described in any one of claims 1 to 4, the method comprising the following steps: Step a): Provide a zirconium alloy part, and coat the surface of the zirconium alloy part with a pure Cr layer using a 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 subjected to laser remelting modification treatment, wherein the laser remelting modification treatment satisfies T=(120D+115)±5℃, where T is the surface temperature of the pure Cr layer and D is the thickness of the pure Cr layer in μm.

6. The method for manufacturing the antioxidant coating according to claim 5, characterized in that, In step c), the laser pulse width used in the laser remelting modification process is 10-50 nanoseconds, and the repetition frequency is not less than 4MHz.

7. The method for manufacturing the antioxidant coating according to claim 5 or 6, characterized in that, In step a), the zirconium alloy part undergoes pickling treatment.

8. The method for manufacturing the antioxidant coating according to claim 5 or 6, characterized in that, In step a), the magnetron pulse sputtering process is performed at a temperature of 200℃-400℃ and a vacuum level of 3×10⁻⁶. -4 Pa-4×10 -4 Pa, power of 300W-400W, sputtering time of 15min-20min.

9. The method for manufacturing the antioxidant coating according to claim 5 or 6, characterized in that, In step c), after laser remelting modification, step d) is also included: holding the zirconium alloy part at 70℃-90℃ for at least 1 hour.

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