(Cr / CrNb) / CrNb composite structure coating with high-temperature steam oxidation resistance and diffusion resistance and preparation method of (Cr / CrNb) / CrNb composite structure coating

Abstract

The invention discloses a (Cr / CrNb) / CrNb composite structure coating with high-temperature steam oxidation resistance and diffusion resistance, the composite structure coating comprises a Cr / CrNb transition layer deposited on the surface of a zirconium alloy substrate and a CrNb alloy coating deposited on the surface of the Cr / CrNb transition layer, and the CrNb alloy coating is composed of nanocrystals with the particle size of 500-800 nm; the invention further discloses a preparation method of the composite structure coating. According to the coating with the composite structure, the CrNb alloy coating with the Nb element with stable chemical properties and good compatibility is selected, the characteristic that the Nb element tends to be segregated at the interface of the coating and the substrate is utilized, mutual diffusion of Cr atoms and Zr atoms is greatly inhibited, the stability of the interface is kept, and the coating is suitable for preparing the nuclear reactor fuel cladding material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature region structure coating of pressurized water reactor, and particularly relates to a (Cr / CrNb) / CrNb composite structure coating with high-temperature steam oxidation resistance and diffusion resistance and a preparation method thereof. BACKGROUND

[0002] With the rapid development of society, the supply of fossil energy in China is becoming increasingly tight, and the environmental pollution problem caused by it is becoming increasingly serious. Under the background of China's vigorous promotion of green development, nuclear energy, as a highly efficient and stable clean energy, has irreplaceable advantages in terms of cost, carbon emission and operation, and is an inevitable choice for China to enter the era of clean energy. However, during the rapid development of nuclear energy, the three major nuclear accidents in history have brought great hidden dangers to environmental safety and seriously damaged the confidence of most countries in the development of nuclear energy. Therefore, the safety of nuclear energy has become the primary factor restricting the sustainable development of energy.

[0003] Fuel cladding is the first safety barrier to prevent nuclear leakage and is crucial to the safe operation of nuclear power plants. Zirconium alloy is a key material for nuclear reactor fuel cladding, but the 2011 Fukushima accident in Japan exposed the defects of traditional zirconium alloy fuel cladding in high-temperature steam oxidation and hydrogen generation. Subsequently, the accident-tolerant fuel plan has become a new trend in the field of nuclear fuel to improve the safety of reactors. As a relatively mature key technology of the plan, the accident-tolerant fuel coating has been listed by the international nuclear industry as a short-term plan for the design of accident-tolerant fuel systems, and is one of the key development directions in the next 20 years. Among various coatings considered for the application of enhanced accident-tolerant fuel, metal Cr has become one of the current research hotspots due to its excellent high-temperature oxidation resistance, adhesion, ductility and wear resistance.

[0004] However, the serious problem of rapid mutual diffusion of Cr-Zr at high temperature hinders the wide application of Cr coating on Zr alloy. Under high-temperature service conditions, the outwardly diffusing Zr atoms reach the interface between the Cr2O3 layer and the Cr coating, reducing the Cr2O3 to Cr and ZrO2, resulting in the loss of protection of the Cr coating. Cr-Zr interdiffusion is closely related to the preparation process of the Cr coating. Most preparation techniques use physical vapor deposition method, and the coating grows in a columnar crystal structure, with intergranular gaps and internal structural defects providing channels for atomic diffusion. Therefore, the "short board" of Cr coating and zirconium alloy substrate interdiffusion problem seriously restricts its application.

[0005] Therefore, in view of the limitations of the existing Cr coating structure and preparation process, a (Cr / CrNb) / CrNb composite structure coating with high-temperature steam oxidation resistance and diffusion resistance and a preparation method thereof are needed. SUMMARY

[0006] The present application aims to overcome the deficiencies in the prior art, and provides a (Cr / CrNb) / CrNb composite structure coating with high-temperature steam oxidation resistance and diffusion resistance. The (Cr / CrNb) / CrNb composite structure coating uses a CrNb alloy coating with stable chemical properties and good compatibility of Nb element, and utilizes the characteristics of Nb element tending to segregate at the interface between the coating and the substrate, greatly inhibits the mutual diffusion of Cr atoms and Zr atoms, maintains the stability of the interface, and solves the problem of rapid mutual diffusion between the Cr coating and the zirconium alloy substrate at high temperature.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is: a (Cr / CrNb) / CrNb composite structure coating with high-temperature steam oxidation resistance and diffusion resistance, characterized in that the (Cr / CrNb) / CrNb composite structure coating comprises a Cr / CrNb transition layer deposited on the surface of a zirconium alloy substrate and a CrNb alloy coating deposited on the surface of the Cr / CrNb transition layer, the CrNb alloy coating is composed of nanocrystalline grains with a particle size of 500nm-800nm, the thickness of the CrNb alloy coating is 8μm-10μm, and the thickness of the Cr / CrNb transition layer is 0.5μm-1μm.

[0008] The present application designs a CrNb alloy coating with a Cr / CrNb transition layer on the surface of a Zr-4 alloy substrate. A Cr / CrNb transition layer is designed between the Zr-4 alloy substrate and the CrNb alloy coating, which increases the interface bonding strength of the coating and improves the anti-peeling ability of the coating in a high-temperature steam environment, and can also delay the service life of the coating. Nb has good high-temperature corrosion resistance, can maintain the stability and integrity of the material in a high-temperature environment, and effectively prevents further corrosion; the surface grains of the CrNb alloy coating are nanocrystallized by the nanocrystallization method, which reduces the pores in the CrNb alloy coating and further inhibits the penetration of oxygen elements in a high-temperature steam medium; the thickness of the Cr / CrNb transition layer is designed to be smaller than that of the CrNb alloy coating, which is used to improve the stability of the CrNb alloy coating.

[0009] The (Cr / CrNb) / CrNb composite structure coating with high-temperature steam oxidation resistance and diffusion resistance is characterized in that the atomic percentage of Nb element in the CrNb alloy coating is 5%-10%.

[0010] The present application also discloses a preparation method of a (Cr / CrNb) / CrNb composite structure coating with high-temperature steam oxidation resistance and diffusion resistance, characterized in that the preparation method comprises the following steps: Step one, ion source cleaning: the pretreated zirconium alloy substrate is fixed on the sample table of the vacuum chamber of the equipment, the Nb target and the Cr target are placed on the target position in the center of the sputtering source, and the position of the zirconium alloy substrate and the target is determined, the ion source cleaning is started to the zirconium alloy substrate, and the heater is started to heat the zirconium alloy substrate; Step two, Cr / CrNb transition layer preparation: Ar gas is used as the sputtering gas, and the Cr / CrNb transition layer is deposited on the surface of the zirconium alloy substrate heated in step one by pulse magnetron sputtering. Step three, (Cr / CrNb) / CrNb composite structure coating preparation: Ar gas is used as the sputtering gas, the Cr / CrNb transition layer deposited in step two is ion source cleaned, then CrNb alloy coating is deposited by pulse magnetron sputtering, and (Cr / CrNb) / CrNb composite structure coating is obtained after laser nanocrystallization.

[0011] The preparation method of the (Cr / CrNb) / CrNb composite structure coating with high-temperature steam oxidation resistance and diffusion resistance, wherein the zirconium alloy substrate in step one is Zr-4 alloy, and the pretreatment method comprises acid pickling, grinding, polishing and ultrasonic cleaning in sequence.

[0012] The preparation method of the (Cr / CrNb) / CrNb composite structure coating with high-temperature steam oxidation resistance and diffusion resistance, wherein the distance between the zirconium alloy substrate and the target in step one is 10cm~15cm, and the heating temperature is 230℃~300℃.

[0013] The preparation method of the (Cr / CrNb) / CrNb composite structure coating with high-temperature steam oxidation resistance and diffusion resistance, wherein the flow rate of Ar gas in the ion source cleaning in step one is 45mL / min~60mL / min.

[0014] The preparation method of the (Cr / CrNb) / CrNb composite structure coating with high-temperature steam oxidation resistance and diffusion resistance, wherein the parameters of the pulse magnetron sputtering in steps two and three are as follows: vacuum degree 8×10 -4 Pa~1×10 -5 Pa, working gas pressure 0.3Pa~0.6Pa, Ar gas flow rate 20mL / min~40mL / min, pulse frequency 50kHZ~100kHZ, duty cycle 30%~80%, Nb target sputtering power 80W~100W, reverse voltage 20V~50V, and bias voltage-50V~-150V.

[0015] The application adopts physical vapor deposition and laser nanocrystallization method to prepare (Cr / CrNb) / CrNb composite structure coating on the surface of zirconium alloy base, induces grain refinement, thereby increases the interface bonding strength of the coating and the base and corrosion resistance; through optimizing sputtering parameters, adjusting pulse bias and duty cycle, etc., the columnar crystal structure is broken, and the compactness of the coating is increased. Meanwhile, the influence of Nb element content on the brittleness of the coating is considered, the CrNb coating with high purity, high bonding force and high temperature steam oxidation resistance is prepared through accurate control, which is suitable for complex working conditions in the field of nuclear power, and avoids corrosion failure of parts in high temperature region of pressurized water reactor.

[0016] The preparation method of the (Cr / CrNb) / CrNb composite structure coating with high temperature steam oxidation resistance and diffusion resistance has the characteristics that the ion source cleaning in step three is carried out in the order of glow discharge ion cleaning and metal ion cleaning.

[0017] The application can improve the bonding force between the Cr / CrNb transition layer and the zirconium alloy base through the process of glow discharge ion cleaning + metal ion cleaning, thereby affecting the high temperature oxidation resistance and service life of the (Cr / CrNb) / CrNb composite structure coating.

[0018] The preparation method of the (Cr / CrNb) / CrNb composite structure coating with high temperature steam oxidation resistance and diffusion resistance has the characteristics that the ion source cleaning in step three is carried out in the order of glow discharge ion cleaning and metal ion cleaning.

[0019] The application can control the energy reaching the material by setting the laser nanocrystallization parameters, thereby affecting the grain size.

[0020] Compared with the prior art, the application has the following advantages: 1、The coating system of the application selects the CrNb alloy coating with stable chemical properties and good compatibility of Nb element, fully utilizes the tendency of Nb element to segregate at the interface between the coating and the base, greatly inhibits the mutual diffusion of Cr atoms and Zr atoms, maintains the stability of the interface, and prevents the formation of brittle phase; at the same time, a small amount of Nb is dissolved in Cr, which can refine the grains of Cr2O3 formed by Cr oxidation, and further increase the protection performance.

[0021] 2、The application can improve the high temperature corrosion resistance of the zirconium alloy base by preparing the CrNb alloy coating on the surface of the zirconium alloy base, and can increase the interface bonding strength by designing Cr / CrNb as a transition layer between the zirconium alloy base and the CrNb alloy coating, thereby improving the anti-peeling ability of the (Cr / CrNb) / CrNb composite structure coating in the high temperature steam environment, and delaying the service life of the coating.

[0022] 3、The application prepares the (Cr / CrNb) / CrNb composite structure coating with high density and low defects by the method of pulsed magnetron sputtering and laser nanocrystallization surface treatment, reduces the porosity of the (Cr / CrNb) / CrNb composite structure coating, improves the bonding strength of the (Cr / CrNb) / CrNb composite structure coating and the high-temperature substrate, and inhibits the growth of columnar crystals, avoiding the intercrystalline gap and internal structural defects of the columnar crystals to provide channels for atomic diffusion.

[0023] The technical solutions of the application are described in further detail below with reference to the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The figure is the oxidation rate of the (Cr / CrNb) / CrNb composite structure coating after laser nanocrystallization treatment in the high-temperature steam environment in the embodiment 3 of the application.

[0025] Figure 2 The figure is the micrograph of the (Cr / CrNb) / CrNb composite structure coating before laser nanocrystallization treatment in the embodiment 3 of the application.

[0026] Figure 3 The figure is the micrograph of the (Cr / CrNb) / CrNb composite structure coating after laser nanocrystallization treatment in the embodiment 3 of the application. DETAILED DESCRIPTION

[0027] Embodiment 1 The (Cr / CrNb) / CrNb composite structure coating of the embodiment includes a Cr / CrNb transition layer deposited on the surface of a Zr-4 alloy substrate and a CrNb alloy coating deposited on the surface of the Cr / CrNb transition layer, the CrNb alloy coating is composed of nanocrystalline grains with a particle size of 800 nm, the thickness of the CrNb alloy coating is 8 μm, the atomic percentage of Nb element is 5%, and the thickness of the Cr / CrNb transition layer is 0.5 μm; the preparation method of the (Cr / CrNb) / CrNb composite structure coating includes the following steps: Step one, ion source cleaning: the Zr-4 alloy substrate is pickled for 55 s, polished by using 800#, 1000#, 1200# and 2000# sandpaper in sequence, polished on a polishing machine by using diamond polishing paste with a particle size of 1.5 μm, and cleaned by ultrasonic wave for 30 min and then dried by air gun; the pickling solution used in the pickling is prepared by mixing 16 mol / L HNO3, 33.3 mol / L HF acid and deionized water in a volume ratio of 45:5:50; Then the Zr-4 alloy substrate is fixed on the sample table of the vacuum chamber of the device, the Nb target and the Cr target are placed on the target position in the center of the sputtering source, and the distance between the zirconium alloy substrate and the target is set to 15 cm; start the ion, and the vacuum degree is 1x10 -3 Under the Pa environment, Ar gas with a flow rate of 45 mL / min is introduced into the vacuum chamber to clean the ion source of the Zr-4 alloy substrate; at the same time, the heater is started to heat the zirconium alloy substrate to 230℃. Step two, Cr / CrNb transition layer preparation: Ar gas is used as the sputtering gas, and the Cr / CrNb transition layer is deposited on the surface of the Zr-4 alloy substrate heated in step one by pulse magnetron sputtering. The parameters of the pulse magnetron sputtering are: vacuum degree 5x10 -4 Pa, working pressure 0.3 Pa, inert gas flow rate 20 mL / min, pulse frequency 50 kHz, duty cycle 30%, Nb target sputtering power 80 W, Cr target sputtering power 120 W, reverse voltage 20 V, and bias voltage -50 V. Step three, (Cr / CrNb) / CrNb composite structure coating preparation: Ar gas is used as the sputtering gas to clean the ion source of the Cr / CrNb transition layer deposited in step two, and then the CrNb alloy coating is deposited by pulse magnetron sputtering. After ultrasonic cleaning and laser nanocrystallization treatment, the (Cr / CrNb) / CrNb composite structure coating is obtained. The process of the ion source cleaning is: after the vacuum degree in the vacuum chamber reaches 5x10 -2 Pa, the Zr-4 alloy substrate is heated to 230℃, then Ar gas is introduced into the vacuum chamber to adjust the vacuum degree to 1 Pa, the Ar gas flow rate is 80 mL / min, then the bias power is turned on and adjusted to 1200 V for glow ion cleaning for 3 min, after the glow ion cleaning is completed, the Ar gas flow rate is reduced to adjust the vacuum degree to 0.1 Pa, and the bias value is reduced to 800 V for metal ion cleaning for 1 min; the parameters of the laser nanocrystallization treatment are: laser power 200 W, scanning speed 10 mm / s, and spot overlap rate 30%.

[0028] As shown in Figure 1 the oxidation rate of the (Cr / CrNb) / CrNb composite structure coating after laser nanocrystallization treatment in this embodiment is 0.0256 mg·mm -2 after 1200℃ high-temperature steam oxidation for 1h.

[0029] Example 2 The (Cr / CrNb) / CrNb composite structure coating of the embodiment comprises a Cr / CrNb transition layer deposited on the surface of a Zr-4 alloy substrate and a CrNb alloy coating deposited on the surface of the Cr / CrNb transition layer, the CrNb alloy coating is composed of nanocrystalline grains with a particle size of 650 nm, the thickness of the CrNb alloy coating is 9 μm, the atomic percentage of Nb element is 8%, and the thickness of the Cr / CrNb transition layer is 0.8 μm; the preparation method of the (Cr / CrNb) / CrNb composite structure coating comprises the following steps: Step one, ion source cleaning: the Zr-4 alloy substrate is pickled for 55 s, polished by using 800#, 1000#, 1200# and 2000# sandpaper, polished on a polishing machine by using diamond polishing paste with a particle size of 1.5 μm, and cleaned by ultrasonic wave for 30 min and then dried by air gun; the pickling solution is prepared by using 16 mol / L HNO3, 33.3 mol / L HF acid and deionized water in a volume ratio of 45:5:50; Then, the Zr-4 alloy substrate is fixed on the sample table of the vacuum chamber of the equipment, the Nb target and the Cr target are placed on the target position at the center of the sputtering source, and the distance between the zirconium alloy substrate and the target is set to 12 cm; the ion is started, and the vacuum degree is 1×10 -3 Pa, Ar gas with a flow rate of 55 mL / min is introduced into the vacuum chamber to clean the ion source of the Zr-4 alloy substrate; at the same time, the heater is started to heat the zirconium alloy substrate to 280℃; Step two, preparation of Cr / CrNb transition layer: Ar gas is used as the sputtering gas, and the Cr / CrNb transition layer is deposited on the surface of the Zr-4 alloy substrate heated in step one by using pulsed magnetron sputtering, and the parameters of the pulsed magnetron sputtering are as follows: vacuum degree 8×10 -4 Pa, working pressure 0.5 Pa, inert gas flow rate 30 mL / min, pulse frequency 80 kHZ, duty cycle 50%, Nb target sputtering power 90 W, Cr target sputtering power 120 W, reverse voltage 30 V, and bias voltage -100 V; Step three, preparation of (Cr / CrNb) / CrNb composite structure coating: Ar gas is used as the sputtering gas to clean the ion source of the Cr / CrNb transition layer deposited in step two, and then the CrNb alloy coating is deposited by using pulsed magnetron sputtering, ultrasonic cleaning and laser nanocrystallization treatment to obtain the (Cr / CrNb) / CrNb composite structure coating; The process of the ion source cleaning is as follows: the vacuum degree in the vacuum chamber reaches 5×10 -2After Pa, the heating system is started, the Zr-4 alloy substrate is heated to 280℃, then Ar gas is introduced into the vacuum chamber to adjust the vacuum degree to 1Pa, the Ar gas flow is 80mL / min, then the bias power supply is started and adjusted to 1200V for glow discharge ion cleaning for 3min, after the glow discharge ion cleaning is completed, the Ar gas flow is reduced to adjust the vacuum degree to 0.1Pa, and the bias value is reduced to 800V for metal ion cleaning for 1min; the parameters of the laser nanocrystallization treatment are: the laser power is 300W, the scanning speed is 15mm / s, and the spot overlap rate is 40%.

[0030] It is detected that, as shown in Figure 1 the oxidation rate of the (Cr / CrNb) / CrNb composite structure coating after laser nanocrystallization treatment in the embodiment is 0.0184mg·mm -2 .

[0031] Example 3 The (Cr / CrNb) / CrNb composite structure coating of the embodiment includes a Cr / CrNb transition layer deposited on the surface of the Zr-4 alloy substrate and a CrNb alloy coating deposited on the surface of the Cr / CrNb transition layer, the CrNb alloy coating is composed of nanocrystalline grains with a particle size of 500nm, the thickness of the CrNb alloy coating is 10μm, the atomic percentage of Nb element is 10%, and the thickness of the Cr / CrNb transition layer is 1μm; the preparation method of the (Cr / CrNb) / CrNb composite structure coating includes the following steps: Step one, ion source cleaning: the Zr-4 alloy substrate is pickled for 55s, polished by 800#, 1000#, 1200# and 2000# sandpaper, polished on a polishing machine by diamond polishing paste with a particle size of 1.5μm, and ultrasonic cleaned for 30min and then dried by air gun; the pickling liquid used in the pickling is prepared by mixing 16mol / L HNO3, 33.3mol / L HF acid and deionized water in a volume ratio of 45:5:50; Then the Zr-4 alloy substrate is fixed on the sample table of the vacuum chamber of the equipment, the Nb target and the Cr target are placed on the target position at the center of the sputtering source, and the distance between the zirconium alloy substrate and the target is set to 10cm; start the ion, introduce Ar gas with a flow rate of 60mL / min into the vacuum chamber under the condition of vacuum degree 1×10 -3 Pa, and heat the zirconium alloy substrate to 300℃ by starting the heater; Step two, Cr / CrNb transition layer preparation: with Ar gas as sputtering gas, Cr / CrNb transition layer was deposited on the surface of Zr-4 alloy substrate heated in step one by pulse magnetron sputtering, and the parameters of the pulse magnetron sputtering were as follows: vacuum degree 1x10 -5 Pa, working gas pressure 0.6 Pa, inert gas flow 40 mL / min, pulse frequency 100 kHZ, duty cycle 80%, Nb target sputtering power 100 W, Cr target sputtering power 120 W, reverse voltage 50 V, and bias voltage -150 V. Step three, (Cr / CrNb) / CrNb composite structure coating preparation: with Ar gas as sputtering gas, the Cr / CrNb transition layer deposited in step two was subjected to ion source cleaning, then CrNb alloy coating was deposited by pulse magnetron sputtering, and after ultrasonic cleaning, laser nanocrystallization treatment was performed to obtain (Cr / CrNb) / CrNb composite structure coating. The process of the ion source cleaning was as follows: after the vacuum degree in the vacuum chamber reached 5x10 -2 Pa, the heating system was started to heat the Zr-4 alloy substrate to 280℃, then Ar gas was introduced into the vacuum chamber to adjust the vacuum degree to 1 Pa, the Ar gas flow was 80 mL / min, then the bias power was started and adjusted to 1200 V to perform glow ion cleaning for 3 min, after the glow ion cleaning was completed, the Ar gas flow was reduced to adjust the vacuum degree to 0.1 Pa, and the bias value was reduced to 800 V to perform metal ion cleaning for 1 min; the parameters of the laser nanocrystallization treatment were as follows: laser power was 500 W, scanning speed was 20 mm / s, and spot overlap rate was 50%.

[0032] It was detected that, as shown in Figure 1 , the oxidation rate of the (Cr / CrNb) / CrNb composite structure coating after laser nanocrystallization treatment in the embodiment was 0.0024 mg·mm -2 after high-temperature steam oxidation at 1200℃ for 1 h.

[0033] The (Cr / CrNb) / CrNb composite structure coatings before and after laser nanocrystallization treatment in the embodiment were subjected to microscopic analysis, and as shown in Figure 2 and Figure 3 , both coatings had smooth and dense surfaces and no obvious pore defects; as compared in Figure 2 and Figure 3 , the grains of the (Cr / CrNb) / CrNb composite structure coating after laser nanocrystallization treatment were smaller, indicating that the laser nanocrystallization treatment in the embodiment could effectively reduce the grain size of the coating.

[0034] The above is only the preferred embodiment of the present application, and does not limit the present application, and any simple modification, change and equivalent structure change of the above embodiment according to the technical essence of the present application are still within the protection scope of the technical scheme of the present application.

Claims

1. A (Cr / CrNb) / CrNb composite structured coating with resistance to high temperature steam oxidation and barrier diffusion, characterized in that, The (Cr / CrNb) / CrNb composite structure coating comprises a Cr / CrNb transition layer deposited on the surface of a zirconium alloy substrate and a CrNb alloy coating deposited on the surface of the Cr / CrNb transition layer, the CrNb alloy coating is composed of nanocrystalline grains with a particle size of 500 nm to 800 nm, the thickness of the CrNb alloy coating is 8 μm to 10 μm, and the thickness of the Cr / CrNb transition layer is 0.5 μm to 1 μm.

2. The (Cr / CrNb) / CrNb composite structure coating with high temperature steam oxidation resistance and diffusion barrier according to claim 1, characterized in that, The atomic percentage of the Nb element in the CrNb alloy coating is 5% to 10%.

3. A method for producing a (Cr / CrNb) / CrNb composite structure coating having resistance to high-temperature steam oxidation and diffusion barrier according to claim 1 or 2, characterized in that, The preparation method comprises the following steps: Step one, ion source cleaning: fixing the pretreated zirconium alloy substrate on the sample table of the vacuum chamber of the equipment, placing the Nb target and the Cr target on the target position at the center of the sputtering source, determining the position of the zirconium alloy substrate and the target, starting the ion source to clean the zirconium alloy substrate, and starting the heater to heat the zirconium alloy substrate; Step two, Cr / CrNb transition layer preparation: using Ar gas as the sputtering gas, using pulsed magnetron sputtering to deposit a Cr / CrNb transition layer on the surface of the zirconium alloy substrate heated in step one; Step three, (Cr / CrNb) / CrNb composite structure coating preparation: using Ar gas as the sputtering gas, ion source cleaning is performed on the Cr / CrNb transition layer deposited in step two, then a CrNb alloy coating is deposited by using pulsed magnetron sputtering, and a (Cr / CrNb) / CrNb composite structure coating is obtained after laser nanocrystallization.

4. The method of claim 3, wherein the (Cr / CrNb) / CrNb composite coating layer having resistance to high-temperature steam oxidation and diffusion barrier is prepared by the steps of: The zirconium alloy substrate in step one is Zr-4 alloy, and the pretreatment method comprises the following steps: acid pickling, grinding, polishing and ultrasonic cleaning.

5. The method of claim 3, wherein the (Cr / CrNb) / CrNb composite coating layer having resistance to high-temperature steam oxidation and diffusion barrier is prepared by the steps of: (a) depositing a Cr layer on a substrate; (b) depositing a CrNb layer on the Cr layer; (c) depositing a Cr layer on the CrNb layer; and (d) repeating steps (b) and (c) one or more times. The distance between the zirconium alloy substrate and the target in step one is 10 cm to 15 cm, and the heating temperature is 230°C to 300°C.

6. The method of claim 3, wherein the (Cr / CrNb) / CrNb composite coating layer having resistance to high-temperature steam oxidation and diffusion barrier is prepared by the steps of: (a) depositing a Cr layer on a substrate; (b) depositing a CrNb layer on the Cr layer; (c) depositing a Cr layer on the CrNb layer; and (d) repeating steps (b) and (c) one or more times. The flow rate of Ar gas in the ion source cleaning in step one is 45 mL / min to 60 mL / min.

7. The method of claim 3, wherein the (Cr / CrNb) / CrNb composite coating layer having resistance to high-temperature steam oxidation and diffusion barrier is prepared by the steps of: (a) depositing a Cr layer on a substrate; (b) depositing a CrNb layer on the Cr layer; (c) depositing a Cr layer on the CrNb layer; and (d) repeating steps (b) and (c) one or more times. The parameters of the pulsed magnetron sputtering in step two and step three are as follows: vacuum degree 8x10 -4 Pa, working pressure 0.3 Pa~0.6 Pa, Ar gas flow 20 mL / min~40 mL / min, pulse frequency 50 kHZ~100 kHZ, duty cycle 30%~80%, Nb target sputtering power 80 W~100 W, reverse voltage 20 V~50 V, bias voltage -50 V~-150 V. -5 Pa, working pressure 0.3 Pa~0.6 Pa, Ar gas flow 20 mL / min~40 mL / min, pulse frequency 50 kHZ~100 kHZ, duty cycle 30%~80%, Nb target sputtering power 80 W~100 W, reverse voltage 20 V~50 V, bias voltage -50 V~-150 V.

8. The method of claim 3, wherein the (Cr / CrNb) / CrNb composite coating layer having resistance to high-temperature steam oxidation and diffusion barrier is prepared by the steps of: (a) depositing a Cr layer on a substrate; (b) depositing a CrNb layer on the Cr layer; (c) depositing a Cr layer on the CrNb layer; and (d) repeating steps (b) and (c) one or more times. The ion source cleaning in step three comprises the following steps: glow ion cleaning and metal ion cleaning.

9. The method of claim 3, wherein the (Cr / CrNb) / CrNb composite coating layer having resistance to high-temperature steam oxidation and diffusion barrier is prepared by the steps of: (a) depositing a Cr layer on a substrate; (b) depositing a CrNb layer on the Cr layer; (c) depositing a Cr layer on the CrNb layer; and (d) repeating steps (b) and (c) one or more times. The parameters of the laser nanocrystallization in step three are as follows: laser power 200 W to 500 W, scanning speed 10 mm / s to 20 mm / s, and spot overlap rate 30% to 50%.

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