Homogeneous multi-level Cr coating and preparation method thereof

Abstract

The invention discloses a homogeneous multi-level Cr coating and a preparation method thereof, and belongs to the technical field of metal high-temperature protective coatings. The preparation method comprises the following steps: carrying out target material pre-sputtering treatment and argon plasma etching treatment on a zirconium alloy matrix to obtain an etched zirconium alloy; by taking Cr as a target material and argon as sputtering gas, depositing on the etched zirconium alloy under the voltage condition of-200V-0V to obtain a bottoming transition layer; and by taking Cr as a target material and argon as sputtering gas, alternately depositing on the bottoming transition layer under the voltage conditions of-70V to 0V and-250V to-90V, so as to obtain the homogeneous multi-level Cr coating. According to the Cr coating obtained through the preparation method, on the premise that heterogeneous elements and heterogeneous interfaces are not introduced, galvanic corrosion can be avoided, the permeation speed of corrosive ions is effectively increased, the corrosion resistance of the coating is improved, and therefore the serious accident resisting capacity of the zirconium alloy fuel cladding is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal high-temperature protective coatings, and more specifically to a homogeneous multi-level Cr coating and a preparation method thereof. Background Art

[0002] Zirconium alloys have been widely used in nuclear power due to their advantages such as low thermal neutron absorption cross-sectional area, good neutron economy, excellent neutron irradiation resistance, and good compatibility with U-O2 cores. In particular, they are widely used in light water reactors (LWRs). Zirconium alloy cladding tubes have excellent corrosion and oxidation resistance under normal operating conditions, but when accidents such as loss of coolant accidents (LOCA) occur, zirconium alloys will rapidly react with high-temperature water vapor to produce hydrogen and explode, causing nuclear accidents, which poses serious risks to the safe operation of nuclear power plants and the development of social economy and ecology. The ability of zirconium alloy cladding tubes to withstand accident conditions has become an important safety consideration.

[0003] During reactor operation, as fuel consumption increases, fission gas released by fuel pellets will increase the internal pressure of fuel rods. Due to the fluctuation of power grid load and frequency control, the power of nuclear power plant reactors is required to be adjusted accordingly (i.e. load tracking, that is, adjusting the linear power of fuel rods), which will lead to cyclic deformation of cladding. When fuel pellets are in contact with cladding, this cyclic deformation is particularly prominent in the circumferential direction of cladding, so that fatigue damage may occur to cladding before reaching the maximum allowable strain. The magnetron sputtered Cr coating presents a coarse columnar crystal structure and is highly brittle. Under operating conditions, coating peeling and other situations may occur, reducing the fatigue life of zirconium alloy cladding materials. The typical columnar grain boundaries of magnetron sputtered Cr coatings are channels for rapid oxygen diffusion, which is not conducive to the best protection of Cr and is harmful to the mechanical properties of long-term service. Summary of the invention

[0004] In view of the above problems, the present invention provides a homogeneous multi-level Cr coating and a preparation method thereof. The Cr coating obtained by the preparation method of the present invention can limit the continuous growth of columnar crystals. Without introducing heterogeneous elements and heterogeneous interfaces, it can not only avoid the occurrence of galvanic corrosion, but also effectively organize the penetration rate of corrosive ions, thereby improving the corrosion resistance of the coating and effectively improving the ability of the zirconium alloy fuel cladding to resist serious accidents.

[0005] The first object of the present invention is to provide a method for preparing a homogeneous multi-level Cr coating, comprising the following steps: The zirconium alloy substrate is subjected to target material pre-sputtering treatment and argon plasma etching treatment to obtain an etched zirconium alloy.

[0006] Using Cr as the target and argon as the sputtering gas, a bottom transition layer is deposited on the etched zirconium alloy under the voltage condition of -200V to 0V.

[0007] Using Cr as the target and argon as the sputtering gas, alternating depositions are carried out on the bottom transition layer under the voltage conditions of -70V to 0V and -250V to -90V to obtain a homogeneous multi-level Cr coating.

[0008] In a preferred embodiment of the present invention, during the alternating deposition, the gas flow rate is 10 sccm to 40 sccm, the pulse width is 500 ns, the frequency is 25 KHz to 250 KHz, the target current is 2 A to 7 A, and the gas pressure is 8×10 -4 torr to 9×10 -4 torr.

[0009] In a preferred embodiment of the present invention, during the alternating deposition, the deposition time for each time is 60 min to 180 min.

[0010] In a preferred embodiment of the present invention, the number of alternating times is 2 to 5 times.

[0011] In a preferred embodiment of the present invention, when depositing the bottom transition layer, the gas flow rate is 10 sccm to 40 sccm, the pulse width is 500 ns, the frequency is 200 KHz to 250 KHz, the target current is 0.5 A to 2 A, and the gas pressure is 1×10 -4 torr to 1×10 - 3 torr.

[0012] In a preferred embodiment of the present invention, when depositing the bottom transition layer, the duration is 1 min to 40 min.

[0013] In a preferred embodiment of the present invention, the pre-sputtering treatment conditions are: the argon flow rate is 50 sccm to 60 sccm, the bias voltage is 60 V to 70 V, the pulse width is 500 ns, the frequency is 25 KHz to 100 KHz, the target current is 0.5 A to 1 A, and the gas pressure is 8×10 -4 torrr to 9×10 -4 torr, and the duration is 20 min to 40 min.

[0014] In a preferred embodiment of the present invention, the conditions for argon plasma etching are: the argon flow rate is 25 sccm to 30 sccm, the bias voltage is -500 V to -400 V, the voltage pulse width is 500 ns, the frequency is 250 KHz to 300 KHz, the target current is 0.5 A to 1 A, and the gas pressure is 8×10 -4 torr to 9×10 -4 torr, and the duration is 40 min to 50 min.

[0015] The second object of the present invention is to provide a homogeneous multi-level Cr coating prepared by the above preparation method.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses a method of depositing a single-oriented Cr coating in a staggered laminated manner to prepare a homogeneous multi-level Cr coating with good matching with the substrate on the surface of a zirconium alloy cladding tube. Without introducing heterogeneous elements and heterogeneous interfaces, it can not only avoid the occurrence of galvanic corrosion, effectively organize the penetration rate of erosive ions, and improve the corrosion resistance of the coating. It effectively solves the problem that the Cr coating prepared by the existing DC magnetron sputtering shows a coarse columnar crystal structure. This coating has excellent high-temperature oxidation resistance and water corrosion resistance.

[0017] (2) By alternately working at high negative bias and low negative bias, the densification of the coating is guaranteed. The high density of the Cr coating can significantly improve its corrosion resistance and oxidation resistance. The dense structure reduces the existence of pores and microcracks, effectively hinders the penetration and diffusion of oxygen, water vapor and corrosive media, thereby delaying the oxidation rate and corrosion process of the coating. In a high-temperature oxidation environment, the dense coating helps to form a continuous and stable Cr2O3 oxide film, further enhancing the protection effect.

[0018] (3) The coating has a preferred orientation of (110) and an obvious 101 texture. The (110) crystal plane is the most dense and has the smallest diffusion coefficient in the body-centered cubic structure, which can effectively inhibit the diffusion channels of oxygen and corrosive media, and helps to form a uniform and dense oxide film structure. At the same time, this crystal orientation is also more stable and has strong intergranular corrosion resistance, so it can maintain better structural stability and protection performance in extreme environments. Description of the Drawings

[0019] Figure 1 It is an EBSD result diagram of the product prepared in Example 1.

[0020] Figure 2 It is a cross-sectional scanning diagram of the product prepared in Example 1 after oxidation, where a is the oxidation for 1800 s and b is the oxidation for 2700 s.

[0021] Figure 3 It is an xrd comparison diagram of the product prepared in Example 1 before and after oxidation.

[0022] Figure 4 It is an EBSD result diagram of the product prepared in Example 2.

[0023] Figure 5 It is a cross-sectional scanning diagram of the product prepared in Example 2 after oxidation, where a is the oxidation for 1800 s and b is the oxidation for 2700 s.

[0024] Figure 6 XRD comparison diagrams of the product prepared in Example 2 before and after oxidation.

[0025] Figure 7 Scanning diagram of the sample with a coating on one side prepared in Example 2.

[0026] Figure 8 EBSD result diagram of the product prepared in Example 3.

[0027] Figure 9 EBSD result diagram of the product prepared in Comparative Example 1.

[0028] Figure 10 Cross-sectional morphology diagram of the product prepared in Comparative Example 1 after oxidation.

[0029] Figure 11 EDS surface scan diagram and element distribution diagram of the cross-section of the product prepared in Comparative Example 1 after oxidation. Among them, (a) is the EDS surface scan diagram, (b) is the O element distribution diagram, (c) is the Zr element distribution diagram, and (d) is the Cr element distribution diagram. Detailed implementation manners

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0031] Introducing an alternating strategy of high and low bias voltages during physical vapor deposition is an effective means to achieve the densification of the Cr coating structure and the synergistic optimization of its properties. Its mechanism of action is mainly reflected in the periodic regulation of the ion bombardment energy and the film growth kinetics: during the high bias voltage stage, the bombardment of high-energy ions in the plasma is enhanced, significantly improving the mobility and rearrangement ability of the deposited particles on the substrate surface, which helps to break up the columnar growth structure, fill the voids, and promote the transformation of the film layer into a denser and more continuous morphology. In addition, the high-energy bombardment can also introduce an appropriate amount of compressive stress to enhance the mechanical strength of the film layer; however, if it lasts for too long, it may lead to the accumulation of internal stress, crack formation, or a decrease in adhesion. Therefore, during the low bias voltage stage, by reducing the ion kinetic energy, the stress introduced in the previous stage can be effectively relieved, promoting stress release and structural stability, while maintaining the deposition rate and the orderly growth of grains, and avoiding the formation of large particles or pore structures. This periodic deposition mode of alternating high and low bias voltages macroscopically realizes the synergistic evolution process of "densification-regulation-stability" of the film microstructure. The finally obtained Cr coating not only has a lower porosity and a higher density, but also has excellent bonding strength and thermal stress resistance, thus significantly improving its oxidation resistance and corrosion resistance in high-temperature environments.

[0032] Example 1 A method for preparing a single-orientation homogeneous stratified Cr coating on the surface of a zirconium alloy cladding, comprising the following steps.

[0033] 1) Pretreatment of the substrate: Prepare a Zr-4 alloy tube with an outer diameter of 9.5 mm, a wall thickness of 0.57 mm, and a length of 40 cm. The composition consists of the following elements by mass percentage: Zr 98.3%, Sn 1.3%, Fe 0.25%, Cr 0.15%; successively polish the surface of the Zr-4 alloy tube substrate with 800#, 1200#, 2000#, 3000#, and 5000# sandpapers. Then polish it with a 1-μm diamond suspension and a 0.1-μm silica suspension. Immerse the sample in an alcohol solution and ultrasonically clean it for 20 min, take it out, dry it, and put it in a vacuum chamber for standby.

[0034] 2) Installation and pre-sputtering treatment of the substrate: Place the zirconium alloy tube on the three-axis turntable of the magnetron sputtering chamber, adjust the position of the paddle to ensure that the sample rotates at a constant speed during film deposition. Placement and cleaning of the teer target: The gas flow rate is 50 sccm, the bias voltage is 60 V, the pulse width is 500 ns, the frequency is 100 KHz, evacuate the vacuum of the chamber to 3×10 -5 torr, introduce argon gas into the chamber until the chamber pressure is 8×10 -4 torr, adjust the target current to 0.5 A, and clean for 40 min.

[0035] Add vacuum, air pressure, and glow cleaning: The argon gas flow rate is 25 sccm, the bias voltage is -400 V, the voltage pulse width is 500 ns, the frequency is 250 KHz, the target current is 0.5 A, and the air pressure is 8×10 -4 torr, and the duration is 40 min.

[0036] 3) Sputter the Cr coating: During sputtering, use Cr as the target material, the purity of the target material is 99.99%, the sputtering gas is argon, and the sputtering steps are as follows: 3.1 Primer layer: The gas flow rate is 25 sccm, the bias voltage is -150 V, the pulse width is 500 ns, the frequency is 250 KHz, the target current is 0.5 A, and the air pressure is 8×10 -4 torr, and the duration is 20 min.

[0037] 3.2 First step: Low-energy layer, the gas flow rate is 25 sccm, the bias voltage is -25 V, the pulse width is 500 ns, the frequency is 100 KHz, the target current is 7 A, and the air pressure is 8×10 -4 torr. The duration is 120 min.

[0038] 3.3 Second step: High-energy layer, the gas flow rate is 25 sccm, the bias voltage is -90 V, the pulse width is 500 ns, the frequency is 250 KHz, the target current is 7 A, and the air pressure is 8×10 -4 torr. The duration is 120 min.

[0039] 3.4 Third step: Low-energy layer, the gas flow rate is 25 sccm, the bias voltage is -25 V, the pulse width is 500 ns, the frequency is 100 KHz, the target current is 7 A, and the air pressure is 8×10 -4 torr. The duration is 120 min.

[0040] 3.5 Fourth step: High-energy layer, the gas flow rate is 25 sccm, the bias voltage is -150 V, the pulse width is 500 ns, the frequency is 250 KHz, the target current is 7 A, and the air pressure is 8×10 -4 torr. The duration is 120 min.

[0041] 3.6 Fifth step: Low-energy layer, the gas flow rate is 25 sccm, the bias voltage is -25 V, the pulse width is 500 ns, the frequency is 100 KHz, the target current is 7 A, and the air pressure is 8×10 -4 torr. The duration is 120 min.

[0042] 3.7 Sixth step: High-energy layer, the gas flow rate is 25 sccm, the bias voltage is -150 V, the pulse width is 500 ns, the frequency is 250 KHz, the target current is 7 A, and the air pressure is 8×10 -4 torr. The duration is 120 min.

[0043] The total deposition time in this example is 13 h, and a zirconium alloy sample with a Cr coating deposited thereon is obtained. After testing, the total thickness of the coating is 12.5 μm.

[0044] Example 2 A method for preparing a single-orientation homogeneous stratified Cr coating on the surface of a zirconium alloy cladding includes the following steps.

[0045] 1) Pretreatment of the substrate: Prepare a Zr-4 alloy tube with an outer diameter of 9.5 mm, a wall thickness of 0.57 mm, and a length of 40 cm. The composition consists of elements with the following mass percentages: Zr 98.3%, Sn 1.3%, Fe 0.25%, Cr 0.15%; successively polish the surface of the substrate of the Zr-4 alloy tube with sandpapers of 800#, 1200#, 2000#, 3000#, and 5000#. Then polish with a 1-μm diamond suspension and a 0.1-μm silica suspension. Immerse the sample in an alcohol solution and ultrasonically clean for 20 min, take it out, dry it, and place it in a vacuum chamber for standby.

[0046] 2) Installation and pre-sputtering treatment of the substrate: Place the zirconium alloy tube on the three-axis turntable of the magnetron sputtering chamber, adjust the position of the paddle to ensure that the sample rotates at a constant speed during coating. Placement and cleaning of the teer target: The gas flow rate is 50 sccm, the bias voltage is 60 V, the pulse width is 500 ns, the frequency is 100 KHz, and the vacuum in the chamber is pumped to 3×10 -5 torr, introduce argon gas into the chamber until the chamber pressure is 8 ×10 -4 torr, adjust the target current to 0.5 A, and clean for 40 min.

[0047] Add vacuum degree, air pressure, glow cleaning: The argon gas flow rate is 25 sccm, the bias voltage is -400 v, the voltage pulse width is 500 ns, the frequency is 250 KHz, the target current is 0.5 A, the air pressure is 8×10 -4 torr, and the duration is 40 min.

[0048] 3) Sputter the Cr coating: During sputtering, use Cr as the target material with a purity of 99.99%, and the sputtering gas is argon. The sputtering steps are specifically as follows: 3.1. Bottom layer: The gas flow rate is 25 sccm, the bias voltage is -150 v, the pulse width is 500 ns, the frequency is 250 KHz, the target current is 0.5 A, the air pressure is 8×10 -4 torr, and the duration is 20 min.

[0049] 3.2. Low energy layer, with gas flow rate at 25 sccm, bias voltage of -70 V, pulse width of 500 ns, frequency of 100 kHz, target current of 7 A, and gas pressure at 8×10 -4 torr. The duration is 60 min.

[0050] 3.3. High energy layer, with gas flow rate at 25 sccm, bias voltage of -250 V, pulse width of 500 ns, frequency of 250 kHz, target current of 7 A, and gas pressure at 8×10 -4 torr. The duration is 120 min.

[0051] 3.4. Low energy layer, with gas flow rate at 25 sccm, bias voltage of -70 V, pulse width of 500 ns, frequency of 100 kHz, target current of 7 A, and gas pressure at 8×10 -4 torr. The duration is 60 min.

[0052] 3.5. High energy layer, with gas flow rate at 25 sccm, bias voltage of -250 V, pulse width of 500 ns, frequency of 250 kHz, target current of 7 A, and gas pressure at 8×10 -4 torr. The duration is 120 min.

[0053] 3.6. Low energy layer, with gas flow rate at 25 sccm, bias voltage of -70 V, pulse width of 500 ns, frequency of 100 kHz, target current of 7 A, and gas pressure at 8×10 -4 torr. The duration is 60 min.

[0054] 3.7. High energy layer, with gas flow rate at 25 sccm, bias voltage of -250 V, pulse width of 500 ns, frequency of 250 kHz, target current of 7 A, and gas pressure at 8×10 -4 torr. The duration is 120 min.

[0055] The total deposition time of this embodiment is 13 h, and a zirconium alloy sample with a Cr coating deposited is obtained. After testing, the total thickness of this coating is 13.4 μm.

[0056] Example 3 A preparation method for a single - orientation homogeneous stratified Cr coating on the surface of a zirconium alloy cladding, comprising the following steps.

[0057] 1) Pretreatment of the substrate: Prepare a Zr-4 alloy tube with an outer diameter of 9.5 mm, a wall thickness of 0.57 mm, and a length of 40 cm. The composition consists of elements with the following mass percentages: Zr 98.3%, Sn 1.3%, Fe 0.25%, Cr 0.15%; polish the surface of the Zr-4 alloy tube substrate successively with 800#, 1200#, 2000#, 3000#, and 5000# sandpapers. Then polish it with a 1-μm diamond suspension and a 0.1-μm silica suspension. Immerse the sample in an alcohol solution and ultrasonically clean it for 20 min. After taking it out and drying, put it into a vacuum chamber for standby.

[0058] 2) Installation and pre-sputtering treatment of the substrate: Place the zirconium alloy tube on the three-axis turntable of the magnetron sputtering chamber, and adjust the position of the paddle to ensure that the sample rotates at a constant speed during film coating. Placement and cleaning of the teer target: The gas flow rate is 50 sccm, the bias voltage is 60 V, the pulse width is 500 ns, the frequency is 100 KHz, and the vacuum in the chamber is pumped to 3×10 -5 torr, and argon gas is introduced into the chamber until the chamber pressure is 8 ×10 -4 torr, and the target current is adjusted to 0.5 A and cleaned for 40 min.

[0059] Add vacuum degree, air pressure, glow cleaning: The argon gas flow rate is 25 sccm, the bias voltage is -400 v, the voltage pulse width is 500 ns, the frequency is 250 KHz, the target current is 0.5 A, and the air pressure is 8×10 -4 torr, and the duration is 40 min.

[0060] 3) Sputter the Cr coating: During sputtering, use Cr as the target material with a purity of 99.99%, and the sputtering gas is argon. The sputtering steps are specifically as follows: 3.1 Primer layer: The gas flow rate is 25 sccm, the bias voltage is -150 v, the pulse width is 500 ns, the frequency is 250 KHz, the target current is 0.5 A, and the air pressure is 8×10 -4 torr, and the duration is 20 min.

[0061] 3.2 First step: Low-energy layer, the gas flow rate is 25 sccm, the bias voltage is -25 v, the pulse width is 500 ns, the frequency is 100 KHz, the target current is 7 A, and the air pressure is 8×10 -4 torr. The duration is 90 min.

[0062] 3.3 Second step: High-energy layer, the gas flow rate is 25 sccm, the bias voltage is -90 v, the pulse width is 500 ns, the frequency is 250 KHz, the target current is 7 A, and the air pressure is 8×10 -4 torr. The duration is 90 min.

[0063] 3.4. Third step: Low - energy layer, gas flow rate is 25 sccm, bias voltage is - 25 V, pulse width is 500 ns, frequency is 100 KHz, target current is 7 A, gas pressure is 8×10 -4 torr. The duration is 90 min.

[0064] 3.5. Fourth step: High - energy layer, gas flow rate is 25 sccm, bias voltage is - 150 V, pulse width is 500 ns, frequency is 250 KHz, target current is 7 A, gas pressure is 8×10 -4 torr. The duration is 90 min.

[0065] 3.6. Fifth step: Low - energy layer, gas flow rate is 25 sccm, bias voltage is - 25 V, pulse width is 500 ns, frequency is 100 KHz, target current is 7 A, gas pressure is 8×10 -4 torr. The duration is 90 min.

[0066] 3.7. Sixth step: High - energy layer, gas flow rate is 25 sccm, bias voltage is - 150 V, pulse width is 500 ns, frequency is 250 KHz, target current is 7 A, gas pressure is 8×10 -4 torr. The duration is 90 min.

[0067] 3.8. Seventh step: Low - energy layer, gas flow rate is 25 sccm, bias voltage is - 25 V, pulse width is 500 ns, frequency is 100 KHz, target current is 7 A, gas pressure is 8×10 -4 torr. The duration is 90 min.

[0068] 3.9. Eighth step: High - energy layer, gas flow rate is 25 sccm, bias voltage is - 150 V, pulse width is 500 ns, frequency is 250 KHz, target current is 7 A, gas pressure is 8×10 -4 torr. The duration is 90 min.

[0069] The total deposition time of this embodiment is 13 h, and a zirconium alloy sample with a Cr coating deposited is obtained. After testing, the total thickness of the coating is 12.5 μm.

[0070] Example 4 A preparation method of a single - orientation homogeneous stratified Cr coating on the surface of a zirconium alloy cladding, comprising the following steps.

[0071] 1) Pretreatment of the substrate: Prepare a Zr-4 alloy tube with an outer diameter of 9.5 mm, a wall thickness of 0.57 mm, and a length of 40 cm. The composition consists of elements with the following mass percentages: Zr 98.3%, Sn 1.3%, Fe 0.25%, Cr 0.15%. Polish the surface of the Zr-4 alloy tube substrate successively with 800#, 1200#, 2000#, 3000#, and 5000# sandpapers. Then polish it with a 1-μm diamond suspension and a 0.1-μm silica suspension. Immerse the sample in an alcohol solution and ultrasonically clean it for 20 min. Take it out, dry it, and place it in a vacuum chamber for standby.

[0072] 2) Installation and pre-sputtering treatment of the substrate: Place the zirconium alloy tube on the three-axis turntable of the magnetron sputtering chamber, and adjust the position of the paddle to ensure that the sample rotates at a constant speed during film coating. Placement and cleaning of the teer target: The gas flow rate is 60 sccm, the bias voltage is 70 V, the pulse width is 500 ns, the frequency is 25 kHz, and the vacuum of the chamber is pumped to 3×10 -5 torr. Argon gas is introduced into the chamber until the chamber pressure is 9×10 -4 torr, and the target current is adjusted to 1 A for cleaning for 20 min.

[0073] Add vacuum degree, air pressure, and glow cleaning: The argon gas flow rate is 30 sccm, the bias voltage is -500 V, the voltage pulse width is 500 ns, the frequency is 300 kHz, the target current is 1 A, the air pressure is 9×10 -4 torr, and the duration is 50 min.

[0074] 3) Sputter the Cr coating: During sputtering, use Cr as the target material with a purity of 99.99%. The sputtering gas is argon. The sputtering steps are as follows: 3.1 Primer layer: The gas flow rate is 10 sccm, the bias voltage is 0 V, the pulse width is 500 ns, the frequency is 200 kHz, the target current is 1 A, the air pressure is 1×10 -4 torr, and the duration is 40 min.

[0075] 3.2 Low-energy layer: The gas flow rate is 10 sccm, the bias voltage is 0 V, the pulse width is 500 ns, the frequency is 25 kHz, the target current is 2 A, the air pressure is 9×10 -4 torr. The duration is 100 min.

[0076] 3.3 High-energy layer: The gas flow rate is 10 sccm, the bias voltage is -90 V, the pulse width is 500 ns, the frequency is 200 kHz, the target current is 2 A, the air pressure is 9×10 -4 torr. The duration is 100 min.

[0077] 3.4. Low - energy layer, gas flow rate is 10 sccm, bias voltage is 0 V, pulse width is 500 ns, frequency is 25 KHz, target current is 3 A, gas pressure is 9×10 -4 torr. Duration is 100 min.

[0078] 3.5. High - energy layer, gas flow rate is 10 sccm, bias voltage is - 90 V, pulse width is 500 ns, frequency is 200 KHz, target current is 3 A, gas pressure is 9×10 -4 torr. Duration is 180 min.

[0079] Example 5 A preparation method of a single - orientation homogeneous stratified Cr coating on the surface of a zirconium alloy cladding, comprising the following steps.

[0080] 1) Pretreatment of the substrate: Prepare a Zr - 4 alloy tube with an outer diameter of 9.5 mm, a wall thickness of 0.57 mm, and a length of 40 cm. The composition consists of elements with the following mass percentages: Zr 98.3%, Sn 1.3%, Fe 0.25%, Cr 0.15; successively polish the surface of the Zr - 4 alloy tube substrate with 800#, 1200#, 2000#, 3000#, 5000# sandpapers. Then polish with 1 - μm diamond suspension and 0.1 - μm silica suspension. Immerse the sample in an alcohol solution and ultrasonically clean for 20 min, take it out, dry it, and put it in a vacuum chamber for standby.

[0081] 2) Installation and pre - sputtering treatment of the substrate: Place the zirconium alloy tube on the three - axis turntable of the magnetron sputtering chamber, adjust the position of the paddle to ensure that the sample rotates at a constant speed during coating. Placement and cleaning of the teer target: Gas flow rate is 55 sccm, bias voltage is 65 V, pulse width is 500 ns, frequency is 75 KHz, evacuate the chamber to 3×10 -5 torr, introduce argon gas into the chamber until the chamber pressure is 8.5×10 -4 torr, adjust the target current to 0.6 A, and clean for 30 min.

[0082] Add vacuum degree, gas pressure, glow cleaning: Argon gas flow rate is 28 sccm, bias voltage is - 450 V, voltage pulse width is 500 ns, frequency is 280 KHz, target current is 0.6 A, gas pressure is 8.5×10 -4 torr, duration is 45 min.

[0083] 3) Sputter the Cr coating: During sputtering, use Cr as the target material, the purity of the target material is 99.99%, the sputtering gas is argon, and the sputtering steps are specifically as follows: 3.1. Bottom layer: The gas flow rate is 20 sccm, the bias voltage is -100 V, the pulse width is 500 ns, the frequency is 220 KHz, the target current is 1.5 A, and the air pressure is 1×10 -3 torr, and the duration is 1 minute.

[0084] 3.2. Low-energy layer: The gas flow rate is 30 sccm, the bias voltage is -30 V, the pulse width is 500 ns, the frequency is 75 KHz, the target current is 4 A, and the air pressure is 8.5×10 -4 torr. The duration is 60 minutes.

[0085] 3.3. High-energy layer: The gas flow rate is 30 sccm, the bias voltage is -100 V, the pulse width is 500 ns, the frequency is 250 KHz, the target current is 4 A, and the air pressure is 8.5×10 -4 torr. The duration is 120 minutes.

[0086] 3.4. Low-energy layer: The gas flow rate is 30 sccm, the bias voltage is -30 V, the pulse width is 500 ns, the frequency is 75 KHz, the target current is 4 A, and the air pressure is 8.5×10 -4 torr. The duration is 60 minutes.

[0087] 3.5. High-energy layer: The gas flow rate is 30 sccm, the bias voltage is -100 V, the pulse width is 500 ns, the frequency is 250 KHz, the target current is 4 A, and the air pressure is 8.5×10 -4 torr. The duration is 120 minutes.

[0088] 3.6. Low-energy layer: The gas flow rate is 30 sccm, the bias voltage is -30 V, the pulse width is 500 ns, the frequency is 75 KHz, the target current is 4 A, and the air pressure is 8.5×10 -4 torr. The duration is 60 minutes.

[0089] 3.7. High-energy layer: The gas flow rate is 30 sccm, the bias voltage is -100 V, the pulse width is 500 ns, the frequency is 250 KHz, the target current is 4 A, and the air pressure is 8.5×10 -4 torr. The duration is 120 minutes.

[0090] 3.8. Low-energy layer: The gas flow rate is 30 sccm, the bias voltage is -30 V, the pulse width is 500 ns, the frequency is 75 KHz, the target current is 4 A, and the air pressure is 8.5×10 -4 torr. The duration is 60 minutes.

[0091] 3.9. High-energy layer: The gas flow rate is 30 sccm, the bias voltage is -100 V, the pulse width is 500 ns, the frequency is 250 KHz, the target current is 4 A, and the air pressure is 8.5×10 -4torr. Duration: 120 min.

[0092] 3.10. Low - energy layer, gas flow rate is 30 sccm, bias voltage is - 30 V, pulse width is 500 ns, frequency is 75 KHz, target current is 4 A, gas pressure is 8.5×10 -4 torr. Duration: 60 min.

[0093] 3.11. High - energy layer, gas flow rate is 30 sccm, bias voltage is - 100 v, pulse width is 500 ns, frequency is 250 KHz, target current is 4 A, gas pressure is 8.5×10 -4 torr. Duration: 120 min.

[0094] Comparative Example 1 A preparation method of a single - orientation homogeneous stratified Cr coating on the surface of a zirconium alloy cladding, comprising the following steps.

[0095] 1) Pretreatment of the substrate: Prepare a Zr - 4 alloy tube with an outer diameter of 9.5 mm, a wall thickness of 0.57 mm, and a length of 40 cm. The composition consists of elements with the following mass percentages: Zr 98.3%, Sn 1.3%, Fe 0.25%, Cr 0.15%; Polish the surface of the Zr - 4 alloy tube substrate with 800#, 1200#, 2000#, 3000#, and 5000# sandpapers in sequence. Then polish it with a 1 - μm diamond suspension and a 0.1 - μm silica suspension. Immerse the sample in an alcohol solution and ultrasonically clean it for 20 min. Take it out, dry it, and put it in a vacuum chamber for standby.

[0096] 2) Installation and pre - sputtering treatment of the substrate: Place the zirconium alloy tube on the three - axis turntable of the magnetron sputtering chamber, adjust the position of the paddle to ensure that the sample rotates at a constant speed during coating. Placement and cleaning of the teer target: Gas flow rate is 50 sccm, bias voltage is 60 V, pulse width is 500 ns, frequency is 100 KHz, evacuate the vacuum of the chamber to 3×10 -5 torr, introduce argon gas into the chamber until the chamber pressure is 8×10 -4 torr, adjust the target current to 0.5 A, and clean for 40 min.

[0097] Add vacuum degree, gas pressure, glow cleaning: Argon gas flow rate is 25 sccm, bias voltage is - 400 v, voltage pulse width is 500 ns, frequency is 250 KHz, target current is 0.5 A, gas pressure is 8×10 -4 torr, duration is 40 min.

[0098] 3) Sputter the Cr coating: During sputtering, use Cr as the target material, the purity of the target material is 99.99%, the sputtering gas is argon, and the sputtering steps are specifically as follows: 3.1. Bottom layer: The gas flow rate is 25 sccm, the bias voltage is -150 V, the pulse width is 500 ns, the frequency is 250 KHz, the target current is 0.5 A, and the air pressure is 8×10 -4 torr, and the duration is 20 min.

[0099] 3.2. The gas flow rate is 25 sccm, the bias voltage is -70 V, the pulse width is 500 ns, the frequency is 250 KHz, the target current is 7 A, and the air pressure is 8×10 -4 torr. The duration is 10 h.

[0100] The total deposition time of this comparative example is 11 h, and a zirconium alloy sample coated with a Cr coating is obtained. After testing, the total thickness of this coating is 11.2 μm.

[0101] According to Figure 1 the Electron Back Scatter Diffraction (EBSD) results, it can be seen that the Cr coating prepared in Example 1 does not have an obvious through-columnar crystal structure, and the overall grain size is between 0.2 - 3.2 microns. There is a certain layered state. Such grains can improve the mechanical properties of the Cr coating and prevent cracks from spreading along the columnar crystal grain boundaries.

[0102] Figure 2 The Cr coating prepared in Example 1 was subjected to high-temperature oxidation in steam at 1200°C for 1800 s ( Figure 2 a in Figure 2 ), and 2700 s (

[0103] Figure 3 b in

[0104] ), respectively. Delamination occurred, which were surface chromium oxide, residual chromium, chromium-zirconium diffusion layer, and zirconium substrate respectively. After oxidation, the chromium oxide and the residual chromium coating did not show peeling. Nor did the overall coating fall off, indicating good film-substrate adhesion and that the Cr coating still has a protective effect on the substrate. It improves the service life and usage time of the zirconium alloy at high temperatures. Figure 4 The EBSD results show that the Cr coating prepared in Example 2 does not have an obvious through-columnar crystal structure, and the overall grain size is between 0.2 μm and 3.2 μm. There is a certain layered state. Such grains can improve the mechanical properties of the Cr coating and prevent cracks from spreading along the columnar crystal grain boundaries.

[0105] Figure 5The Cr coating prepared in Example 2 was subjected to high-temperature oxidation in steam at 1200 °C for 1800 s ( Figure 5 a) in Figure 5 and 2700 s (

[0106] Figure 6 b) in

[0107] Figure 7 stratification occurred, which were surface chromium oxide, residual chromium, chromium-zirconium diffusion layer, and zirconium substrate respectively. After oxidation, the chromium oxide and the residual chromium coating did not peel off. Nor did the phenomenon of overall coating peeling off occur, indicating good film-substrate adhesion and that the chromium coating still has a protective effect on the substrate. The service life and usage time of zirconium alloy at high temperature were improved.

[0106] Figure 6

[0107] Figure 7

[0108]

[0109] Figure 8

[0110] Figure 9

[0111] Figure 10Cross-sectional morphology of the sample prepared in Comparative Example 1 after 30 minutes of high-temperature oxidation in steam at 1200 °C. The chromium oxide layer begins to thin, and the residual Cr begins to thicken. Diffusion channels of Zr appear in the Cr layer and redox reactions occur with the chromium oxide, resulting in the loss of the protective effect of the Cr coating.

[0112] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concept. Therefore, the appended claims are intended to be interpreted to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0113] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a homogeneous multi-level Cr coating, characterized in that, It includes the following steps: After subjecting the zirconium alloy substrate to pre-sputtering treatment of the target and argon plasma etching treatment, an etched zirconium alloy is obtained; Using Cr as the target and argon as the sputtering gas, a bottom transition layer is deposited on the etched zirconium alloy under the voltage condition of -200V to 0V; Using Cr as the target and argon as the sputtering gas, alternating depositions are carried out on the bottom transition layer under the voltage conditions of -70V to 0V and -250V to -90V to obtain a homogeneous multi-level Cr coating.

2. The preparation method of a homogeneous multi-level Cr coating according to claim 1, characterized in that, During the alternate deposition, the gas flow rate is 10 sccm to 40 sccm, the pulse width is 500 ns, the frequency is 25 KHz to 250 KHz, the target current is 2 A to 7 A, and the air pressure is 8×10 -4 torr to 9×10 -4 torr.

3. The preparation method of a homogeneous multi-level Cr coating according to claim 1, characterized in that, When carrying out the alternating depositions, the deposition time for each time is 60 min to 180 min.

4. A method for preparing a homogeneous multi-level Cr coating according to claim 1, characterized in that, The number of alternating times is 2 to 5 times.

5. A method for preparing a homogeneous multi-level Cr coating according to claim 1, characterized in that, When depositing the bottom transition layer, the gas flow rate is 10 sccm to 40 sccm, the pulse width is 500 ns, the frequency is 200 KHz to 250 KHz, the target current is 0.5 A to 2 A, and the air pressure is 1×10 -4 torr to 1×10 -3 torr.

6. The preparation method of a homogeneous multi-level Cr coating according to claim 1, characterized in that, When depositing the bottom transition layer, the duration is 1 min to 40 min.

7. The preparation method of a homogeneous multi-level Cr coating according to claim 1, characterized in that The processing conditions for pre-sputtering are as follows: argon gas flow rate is 50 sccm to 60 sccm, bias voltage is 60 V to 70 V, pulse width is 500 ns, frequency is 25 kHz to 100 kHz, target current is 0.5 A to 1 A, air pressure is 8×10 -4 torrr to 9×10 -4 torr, and the duration is 20 min to 40 min.

8. A method for preparing a homogeneous multi-level Cr coating according to claim 1, characterized in that, The conditions for argon plasma etching are as follows: the argon gas flow rate is 25 sccm to 30 sccm, the bias voltage is -500 V to -400 V, the voltage pulse width is 500 ns, the frequency is 250 KHz to 300 KHz, the target current is 0.5 A to 1 A, the gas pressure is 8×10 -4 torr to 9×10 -4 torr, and the duration is 40 min to 50 min.

9. A homogeneous multi-level Cr coating prepared by the preparation method according to any one of claims 1 to 8.

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