Cr-based protective coating with fine columnar crystal structure as well as preparation method and application of Cr-based protective coating

Abstract

The invention relates to the field of protective coatings, in particular to a Cr-based protective coating with a fine columnar crystal structure and a preparation method and application of the Cr-based protective coating. A Cr100-a-bXaMb component (X = Al / Si, M = Y / Ce / La / Nd, a is greater than or equal to 0 and less than or equal to 10, and b is greater than or equal to 0.1 and less than or equal to 8.5) is designed, the vacuum degree and the matrix temperature are controlled, and intermediate-frequency and radio-frequency power supplies are adopted for cooperative sputtering, so that a structure with the columnar crystal width of 5-100 nm is obtained, and M and / or M oxide nanoparticles with the grain boundary being dispersed and distributed at 1-50 nm are obtained. The structure is compact and void-free, has excellent radiation resistance, high-temperature oxidation resistance and structural integrity, and is suitable for nuclear fuel cladding tube protection.

Description

Technical Field

[0001] This invention relates to the field of protective coatings, specifically to a Cr-based protective coating with a fine columnar crystal structure, its preparation method, and its application. Background Technology

[0002] With the increasing importance of nuclear energy as a clean energy source, nuclear reactor safety has become a research hotspot. The development of accident-tolerant fuel (ATF) has become a key focus in the international nuclear energy field. Within the ATF technology roadmap, Cr-based protective coatings are widely used for surface protection of nuclear fuel cladding tubes due to their excellent high-temperature oxidation performance and neutron economy.

[0003] Currently, research on Cr-based protective coatings mainly focuses on coating structure design and preparation process optimization. Existing technologies, such as CN118957527B, propose a method for preparing FeCrAlY wear-resistant corrosion-resistant coatings based on HiPIMS and ion implantation technology, aiming to improve performance stability and self-healing capabilities under extreme environments. To further enhance overall performance, multilayer composite structures have also been extensively explored. For example, CN119082662A discloses a periodic multilayer coating composed of a Cr layer and a Cr-Al-Si-N layer, where the Cr-Al-Si-N layer is a composite structure of dispersed nanocrystals in a dense amorphous matrix; CN112125705B introduces a MexO1-x (Me selected from Cr, CrAl, CrNi) protective coating for SiC ceramics.

[0004] However, existing Cr-based protective coatings still face severe challenges under the harsh irradiation environment of nuclear reactors. Under irradiation conditions, coatings are prone to various defects such as dislocation loops, micropores (cavitation), and phase separation. These defects not only significantly degrade the microstructure and mechanical properties of the coating but also severely impair its critical oxidation resistance. A common limitation of existing technologies is the relatively large grain size, resulting in insufficient grain boundary density, making it difficult to effectively annihilate irradiation-induced point defects and suppress the nucleation and growth of cavitation. Irradiation-induced cavitation, especially its size and density, has been considered a key factor accelerating the corrosion and oxidation of Cr coatings, but in-depth research on this mechanism and material design strategies to effectively suppress cavitation formation are still insufficient. Meanwhile, the oxide layer thickness control of existing coatings under simulated loss-of-coolant (LOCA) conditions (such as 1200°C high-temperature steam) is often inadequate, affecting long-term service reliability. Although multilayer composite structures can improve performance to some extent, their preparation processes are usually complex (involving multiple materials, multiple processes, or special equipment), resulting in high costs and hindering industrial applications.

[0005] Therefore, developing a Cr-based protective coating that combines excellent radiation resistance (especially effective suppression of radiation cavitation formation), superior resistance to high-temperature water vapor oxidation, and relatively simple preparation process suitable for large-scale production has become an urgent need to break through the current bottleneck of core technologies in ATF research and development. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a Cr-based protective coating with a fine columnar crystal structure, its preparation method, and its applications. This invention provides an innovative solution for achieving advanced nuclear fuel cladding protective coatings that combine excellent accident resistance with superior process economy through the synergistic design of fine columnar crystals, grain boundary-dispersed rare-earth nanoparticles, and a dense, void-free structure.

[0007] The first objective of this invention is achieved through the following technical solution:

[0008] A Cr-based protective coating with a fine columnar crystal structure, the composition of which conforms to the chemical formula Cr 100-a-b X a M b Where X is Al or Si or any combination thereof, M is any one or more of Y, Ce, La, Nd, and 0≤a≤10, 0.1≤b≤8.5, the coating has a fine columnar crystal structure with a width of 5-100nm.

[0009] Preferably, 0 < a ≤ 10. a can be any value from 0.1, 0.2, 0.3, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0 or any range between two values.

[0010] Preferably, 0.5 ≤ b ≤ 5.

[0011] Preferably, the coating contains M and / or M oxide nanoparticles dispersed along the columnar grain boundaries.

[0012] More preferably, the particle size of the M and / or M oxide nanoparticles is 1-50 nm.

[0013] More preferably, the spacing between the M and / or M oxide nanoparticles is ≤120 nm.

[0014] More preferably, the spacing between the M and / or M oxide nanoparticles is ≤100 nm.

[0015] More preferably, the spacing between the M and / or M oxide nanoparticles is ≥5nm and ≤50nm.

[0016] Preferably, the coating has no voids in its growth direction, has a dense structure, and the columnar crystals have a preferred orientation of

[110] .

[0017] Preferably, the coating is a single alloy layer.

[0018] Preferably, the total thickness of the coating is 8-15 μm.

[0019] Preferably, the thickness of the Cr2O3 layer formed on the surface of the coating after oxidation under water vapor at 1200°C for 15 minutes is 0–700 nm. A thickness of 0 nm indicates that no Cr2O3 layer is formed. When a Cr2O3 layer is formed on the surface, it has a continuous and dense structure.

[0020] This method introduces rare earth elements (M) such as Y, La, Ce, and Nd into Cr-based coatings, utilizing their dual-action mechanism to synergistically regulate the microstructure: On the one hand, rare earth elements provide extremely high-density non-spontaneous nucleation sites during deposition, significantly increasing the nucleation rate; and on the other hand, their tendency to aggregate at grain boundaries reduces grain boundary energy, thereby effectively inhibiting grain growth, ultimately forming fine columnar crystals with a width of only 5-100 nm and ≥1×10⁻⁶ grains. 5 cm -1 High-density grain boundaries; on the other hand, these high-density grain boundaries and rare earth elements generated in situ at the grain boundaries form MO. x The nanoparticle clusters collectively construct a composite defect annihilation trap. When interstitial atoms and vacancies generated by irradiation separate due to differences in migration rates, the interstitial atoms preferentially escape to the surface or dislocations, while the retained vacancies are rapidly recombinated and annihilated at grain boundaries and nanophase interfaces, thereby blocking the aggregation and growth of cavitation bubbles and significantly inhibiting irradiation damage. At the same time, rare earth oxide nanoparticles resist the destruction of irradiation cascade collisions due to strong covalent bonds and high displacement energy, further improving the long-term stability of the coating. In addition, trace amounts of Al / Si elements preferentially diffuse outward in high-temperature water vapor to form a continuous and dense Al2O3 / SiO2 oxide film. This barrier layer significantly inhibits the inward diffusion of oxygen and synergistically endows the coating with excellent high-temperature oxidation resistance.

[0021] The second objective of this invention is achieved through the following technical solution:

[0022] A method for preparing the above-mentioned coating includes the following steps:

[0023] (1) Prepare the substrate and polish and clean it;

[0024] (2) Install Cr c X 100-c The target and the M target are used to evacuate the vacuum chamber to a background vacuum and then heat and bake it.

[0025] (3) Introduce Ar gas into the cavity, set the Ar flow rate and working pressure, and use an RF power supply to perform ion etching on the substrate;

[0026] (4) Heating the matrix and applying it to Cr c X100-c An intermediate frequency power supply is applied to the target, an radio frequency power supply is applied to the M target, a bias voltage is applied to the substrate and the working distance is set, the target baffle is opened under cooling conditions, the sample stage is controlled to rotate, and sputtering deposition is performed.

[0027] Preferably, in step (1), the matrix is ​​Zr or a Zr alloy.

[0028] This invention does not impose any particular restrictions on the shape of the substrate and can be applied to workpieces of any shape.

[0029] More preferably, the substrate coating surface is polished to Ra < 100 nm.

[0030] More preferably, the polishing process uses sandpaper of grits of [200, 400], (400, 600], (600, 1000], and (1000, 2000) and polishing paste of grit ≥6000 in sequence.

[0031] In this scheme, square brackets “[]” indicate that the endpoint value is included, and parentheses “()” indicate that the endpoint value is not included.

[0032] A further preferred method is to use alcohol, acetone, and deionized water for ultrasonic cleaning for 5-20 minutes each in sequence.

[0033] Even more preferably, after cleaning, it is dried with high-purity N2 with a purity of ≥99.99%.

[0034] Preferably, in step (2), the purity of the M target is ≥99.9%.

[0035] Preferably, in step (2), the Cr c X 100-c The target satisfies 70≤c≤100.

[0036] More preferably, in step (2), the Cr c X 100-c The target satisfies 70≤c≤97.

[0037] Preferably, in step (2), the background vacuum is evacuated to ≤1×10⁻⁶. -4 Pa.

[0038] Preferably, in step (2), the heating and baking temperature is 500-600℃.

[0039] More preferably, the heating and baking time is 1-3 hours.

[0040] Preferably, in step (3), the Ar flow rate is 20-30 sccm.

[0041] Preferably, in step (3), the working air pressure is 0.8-1.2 Pa.

[0042] Preferably, in step (3), the ion etching power of the radio frequency power supply is 40-100W.

[0043] More preferably, the ion etching time is 5-15 minutes, ensuring that water molecules, gas molecules, or dust particles adsorbed on the substrate surface are completely removed.

[0044] Preferably, in step (4), the substrate heating temperature is 200-450℃.

[0045] Preferably, in step (4), the pulse width of the intermediate frequency power supply is 2.0-4.0 μs.

[0046] Preferably, in step (4), the intermediate frequency power supply pulse frequency is 100-200kHz.

[0047] Preferably, in step (4), the radio frequency power supply is configured to output a continuous wave radio frequency signal.

[0048] More preferably, in step (4), the radio frequency power supply is a continuous wave radio frequency power supply with a frequency of 11-15MHz.

[0049] More preferably, in step (4), the radio frequency power supply is a continuous wave radio frequency power supply with a frequency of 13.56MHz.

[0050] Preferably, in step (4), the Cr c X 100-c The target power density is 1.5-3.6 W / cm³. 2 .

[0051] Preferably, in step (4), the power density of the M target is 0.1-1.2 W / cm². 2 .

[0052] Preferably, in step (4), the bias voltage is -15V to -80V.

[0053] Preferably, in step (4), the working distance is 80-90mm.

[0054] Preferably, in step (4), the cooling condition is cooling in water at a temperature ≤ 20°C.

[0055] Preferably, in step (4), after turning on the power, pre-sputter for 10-15 minutes before opening the target baffle.

[0056] Preferably, in step (4), the sample stage rotation speed is 10-20 rpm.

[0057] Preferably, in step (4), the deposition time is 6-12 hours.

[0058] Preferably, the method for preparing the Cr-based protective coating specifically includes the following steps:

[0059] The coating was prepared on a magnetron sputtering device with two targets. A Zr or Zr alloy substrate was prepared, and the substrate surface was polished to a mirror finish with Ra < 100 nm using a metallographic polishing machine. Polishing was performed sequentially using [200, 400] grit, (400, 600] grit, (600, 1000] grit, and (1000, 2000] grit sandpaper, followed by polishing paste with a grit ≥ 6000 grit. The substrate was ultrasonically cleaned with alcohol, acetone, and deionized water for 5-20 minutes each. After ultrasonic cleaning, the substrate was dried with high-purity N2 (≥ 99.99%). Cr was then installed. c X 100-c The target and the M target material with a purity of 99.9% were used, and the background vacuum was evacuated to ≤1×10⁻⁶. -4 Pa, and start heating and baking, setting the temperature to 500-600℃ for 1-3 hours, introducing Ar gas with a flow rate of 20-30 sccm and controlling the working pressure to 0.8-1.2 Pa. Use an RF power supply for ion etching, setting the RF power supply ion etching power to 40-100W for 5-15 minutes, to completely bombard and remove water molecules, gas molecules, or micro-dust particles adsorbed on the substrate surface. Set the power supply parameters and apply the intermediate frequency power supply to the Cr... c X 100-c On the target, an RF power supply is applied to the M target, Cr c X 100-c The target's carbon content (c) must satisfy 70 ≤ c ≤ 100 to ensure an Al or Si content of 0-10 at% and prevent the formation of brittle phases in the coating. The substrate is heated to 200-450℃, with a medium-frequency power supply pulse width of 2.0-4.0 μs and a pulse frequency of 100-200 kHz. (Cr...) c X 100-c The target power density is 1.5-3.6 W / cm³. 2 The RF power supply is a continuous wave RF power supply with a frequency of 11-15MHz, and the M-target power density is 0.1-1.2W / cm². 2 The bias voltage is set to [-15, -80]V, the working distance is adjusted to 80-90mm, and the target is cooled in water at a temperature ≤20 degrees. The target baffle is opened, and the coating deposition begins. The coating deposition time is 6-12 hours.

[0060] This scheme employs techniques such as low background vacuum, substrate heating, working gas pressure control, sample stage rotation, and coordinated regulation of intermediate frequency / radio frequency power supply parameters (power / voltage / pulse width / frequency) to achieve controllable fabrication of fine columnar crystal structures (width 5-100 nm) and grain boundary dispersed nanophases (particle size 1-50 nm). Specifically, in an Ar plasma environment, Cr and rare earth elements (M) are co-sputtered and reach the substrate at high energy. Because the atomic radius of M is larger than that of Cr and the surface migration activation energy is lower than that of bulk diffusion activation energy, the deposition temperature of 200-450℃ corresponds to 0.22-0.33T. m Under (Cr) conditions, M atoms are instantaneously "frozen" in the Cr matrix to form a supersaturated solid solution and random nanoclusters; at this point, the grain boundary diffusion coefficient reaches 10 times that of bulk diffusion. 3 -10 4 The process forces grains to grow vertically, forming a columnar structure. M atoms rapidly accumulate along grain boundaries, and when the local concentration exceeds the solid solubility limit, M nanoparticles are precipitated through heterogeneous nucleation at the grain boundaries. During cooling, residual M atoms continue to agglomerate, while excess M grows as a pure M phase, but is restricted by grain boundary pinning, ultimately forming dispersed nanoparticles that are coherent / semi-coherent with the matrix. Simultaneously, an 80-90 mm working distance and a 10-20 rpm sample stage rotation eliminate the "shadowing effect," and pre-sputtering for 10-15 minutes avoids large particle contamination, jointly ensuring the high density and structural uniformity of the coating.

[0061] The third objective of this invention is achieved through the following technical solution:

[0062] A nuclear reactor fuel cladding tube, the surface of which is coated with the above-mentioned coating.

[0063] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0064] 1. This invention utilizes 5-100 nm fine columnar crystals and high-density grain boundaries, combined with 1-50 nm rare-earth nanoparticles uniformly distributed along the grain boundaries, to provide numerous rapid recombination channels and trapping centers for point defects generated by irradiation, effectively preventing the growth and aggregation of cavitation bubbles. This results in the coating exhibiting strictly controlled cavitation size below 7 nm and a cavitation density not exceeding 4 × 10⁻⁶ after irradiation. 23 Each cubic meter significantly improves the long-term stability of the coating under the strong irradiation environment of a nuclear reactor, preventing the cladding tube from failing due to irradiation damage.

[0065] 2. The dense, gapless structure of the coating in this invention, along with the addition of trace amounts of aluminum (Al) or silicon (Si), allows for the rapid formation of a continuous and dense chromium oxide (Cr2O3) protective layer on the coating surface under high-temperature steam accident conditions of 1200℃. Simultaneously, the preferential outward diffusion of Al or Si elements contributes to the formation of a denser and more firmly adhered alumina (Al2O3) or silicon oxide (SiO2) inner layer, collectively limiting the total oxide layer thickness after 15 minutes of oxidation to within 700 nanometers. This significantly enhances the coating's resistance to high-temperature steam corrosion, protecting the zirconium alloy cladding tube substrate from erosion.

[0066] 3. The coating of this invention adopts a single alloy layer design with uniform thickness controlled between 8 and 15 micrometers. Its growth direction is free of voids and the overall structure is dense, avoiding through-holes or cracks that may become the starting point of failure. The columnar crystals have a specific

[110] crystallographic orientation (preferred orientation), which helps to improve the coating's ability to resist thermal and mechanical stress. These characteristics together ensure the structural integrity of the coating under harsh working conditions, making it less prone to peeling or cracking, and providing a continuous and reliable protective barrier for the cladding tube. Atomic layers are used.

[0067] 4. This invention employs a specific preparation process, which achieves the formation of 5-100 nanometer fine columnar crystals in the coating by precisely controlling key parameters such as low background vacuum, substrate heating temperature, working gas pressure, sample stage rotation speed, and the power, voltage, pulse width, and frequency of the intermediate frequency / radio frequency power supply. At the same time, 1-50 nanometer rare earth phase or oxide particles are precisely dispersed and precipitated at the grain boundaries, ensuring the repeatable and large-scale preparation of the required high-performance nanostructures.

[0068] 5. The method provided by this invention utilizes both intermediate frequency and radio frequency power supplies for sputtering, requiring only a single deposition process to directly obtain a dense, void-free chromium-based protective layer with a thickness of 8-15 micrometers on the surface of the zirconium alloy fuel cladding tube. This process is relatively simple and efficient, and the coating bonds firmly to the zirconium alloy substrate. The resulting coating possesses excellent resistance to radiation damage, outstanding resistance to high-temperature steam oxidation at 1200℃, and reliable structural integrity, providing a high-performance and industrially feasible protection solution for nuclear reactor accident-tolerant fuel (ATF) cladding tubes. Attached Figure Description

[0069] Figure 1 SEM image of the Cr-based protective coating with a fine columnar crystal structure prepared in Example 1 of the present invention;

[0070] Figure 2 This is a TEM image of the Cr-based protective coating with a fine columnar crystal structure prepared in Example 1 of the present invention;

[0071] Figure 3This is a TEM image of the Cr-based protective coating with a fine columnar crystal structure prepared in Example 3 of the present invention;

[0072] Figure 4 This is a cross-sectional morphology image of the Cr-based protective coating with a fine columnar crystal structure prepared in Example 3 of the present invention after irradiation.

[0073] Figure 5 This is a cross-sectional morphology image of the Cr-based protective coating with a fine columnar crystal structure prepared in Example 1 of the present invention after oxidation;

[0074] Figure 6 This is a cross-sectional morphology diagram of the Cr-based protective coating prepared in Comparative Example 1 of the present invention after irradiation;

[0075] Figure 7 This is a cross-sectional morphology diagram of the Cr-based protective coating prepared in Comparative Example 1 of the present invention after oxidation. Detailed Implementation

[0076] The following will provide a clear and complete description of the concept, specific structure, and technical effects of the present invention in conjunction with embodiments and accompanying drawings, so as to fully understand the purpose, solution, and effects of the present invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0077] I. Coating Preparation

[0078] The coating was prepared on a magnetron sputtering device with two targets. A Zr or Zr alloy substrate was prepared, and the substrate surface was polished to a mirror finish with Ra < 100 nm using a metallographic polishing machine. Polishing was performed sequentially using [200, 400] grit, (400, 600] grit, (600, 1000] grit, and (1000, 2000] grit sandpaper, followed by polishing paste with a grit ≥ 6000 grit. The substrate was ultrasonically cleaned with alcohol, acetone, and deionized water for 5-20 minutes each. After ultrasonic cleaning, the substrate was dried with high-purity N2 (≥ 99.99%). Cr was then installed. c X 100-c The target and the M target material with a purity of 99.9% were used, and the background vacuum was evacuated to ≤1×10⁻⁶. -4 Pa, and start heating and baking, setting the temperature to 500-600℃ for 1-3 hours, introducing Ar gas with a flow rate of 20-30 sccm and controlling the working pressure to 0.8-1.2 Pa. Use an RF power supply for ion etching, setting the RF power supply ion etching power to 40-100W for 5-15 minutes, to completely bombard and remove water molecules, gas molecules, or micro-dust particles adsorbed on the substrate surface. Set the power supply parameters and apply the intermediate frequency power supply to the Cr... c X 100-c On the target, an RF power supply is applied to the M target, Crc X 100-c The target's carbon content (c) must satisfy 70 ≤ c ≤ 97% to ensure an Al or Si content of 0-10 at% and prevent the formation of brittle phases in the coating. The substrate is heated to 200-450℃, with a medium-frequency power supply pulse width of 2.0-4.0 μs and a pulse frequency of 100-200 kHz. (Cr...) c X 100-c The target power density is 1.5-3.6 W / cm³. 2 The RF power supply is a continuous wave RF power supply with a frequency of 13.56MHz, and the M-target power density is 0.1-1.2W / cm². 2 The bias voltage was set to [-15, -80]V, the working distance was adjusted to 80-90mm, and the target was cooled in water at a temperature ≤20 degrees Celsius. With the baffle closed, pre-sputtering was performed on the Cr and Y targets for 10-15 minutes. Afterward, the target baffle was opened, and coating deposition began, with a deposition time of 6-12 hours. Specific coating structures were obtained by controlling the sputtering power density, frequency, and deposition time of each target according to different operating conditions. The preparation parameters for specific embodiments are shown in Table 1.

[0079] Table 1. Preparation parameters of samples from Examples 1-6 and Comparative Example 1

[0080] II. Coating Structure Characterization

[0081] 1. Coating phase

[0082] The phase composition of the coatings in each embodiment was analyzed using a Brucker AXSD8 Advance X-ray diffractometer (XRD). The coatings in the prepared state and after irradiation and high-temperature steam oxidation were characterized. The phase composition of the prepared coating and the phase composition of the oxidation products formed after high-temperature steam oxidation were determined, and the coating's resistance to high-temperature steam oxidation was judged based on the phase composition.

[0083] 2. Morphology and composition analysis of the coating

[0084] The surface and cross-sectional morphology of the coating, as well as its morphology after high-temperature water vapor oxidation, were observed using a Hitachi S-4800 scanning electron microscope (SEM, emission gun voltage 8 kV). EDX was used in area scanning mode to perform compositional analysis of the oxidized coating morphology for qualitative evaluation of its protective capability. A Talos F200x transmission electron microscope (TEM) was used to observe the cross-sectional morphology of the oxidized coating at a lower microscale using bright-field imaging, and selective diffraction was used to determine the crystal structure of the oxide layer. Cross-sectional TEM samples were obtained using focused ion beam (FIB) methods. A nanoscale Pt layer was deposited on the sample surface before oxidation to improve conductivity and prevent charge accumulation. The sample was then placed in a Helios G4-CX dual-beam SEM, and the entire region was cut, extracted, and thinned using a focused ion beam to obtain the cross-sectional TEM samples. Statistical analysis of TEM images, including grain size and number density, was performed using Nano Measurer software. Before the statistical analysis, the scale bar of the TEM image was set, followed by grain labeling and statistical analysis. The statistical results were plotted using Origin plotting software.

[0085] III. Coating Performance Testing

[0086] 1. Ion irradiation test of coating

[0087] The ion irradiation experiments in each embodiment were conducted using the Lanzhou Heavy Ion Research Facility (HIRFL) at the Lanzhou Heavy Ion Accelerator National Laboratory of the Institute of Modern Physics, Chinese Academy of Sciences.

[0088] 2. High-temperature water vapor oxidation test of the coating

[0089] The high-temperature steam oxidation experiment was conducted in a tube furnace with a steam generator connected to one end, and the furnace temperature was set to 1200℃. After the furnace tube temperature reached the set temperature, the steam generator was turned on, and steam at a uniform flow rate was introduced into the furnace tube. Once the steam flow rate stabilized, the sample was moved from the open end of the furnace tube to the center position, and the port was sealed with a corundum plug for insulation. After continuous oxidation for different times, the sample was slowly removed and cooled to room temperature in air. After cooling, the sample was sealed in epoxy resin, and the cross-section was polished. The cross-sectional morphology and composition were analyzed under SEM to evaluate the coating's resistance to high-temperature steam oxidation.

[0090] The following describes the preparation method, structural characteristics, and performance testing of the Cr-based protective coating with ultrafine grain structure in each embodiment.

[0091] Example 1

[0092] The Cr-based protective coating with a fine columnar crystal structure in Example 1 was prepared on a magnetron sputtering apparatus with two targets. The specific preparation method is as follows:

[0093] (1) Prepare the Zr alloy substrate. Use a metallographic polishing machine to mechanically polish the substrate coating surface with 200 grit, 400 grit, 600 grit, 1000 grit, and 2000 grit sandpaper and 6000 grit polishing paste in sequence until the surface reaches a mirror state. Then, use alcohol, acetone, and deionized water to ultrasonically clean the substrate for 10 minutes each time. After cleaning, blow dry with high-purity N2 with a purity of 99.99%.

[0094] (2) Install the Cr target (99.99% purity) and Y target (99.99% purity) into the corresponding target positions of the magnetron sputtering coating equipment, close the vacuum chamber and evacuate the base vacuum to ≤1×10⁻⁶. -4 Pa, turn on the heating and baking, set the baking temperature to 500℃, and keep warm for 2 hours;

[0095] (3) High-purity Ar gas is introduced into the vacuum chamber. The Ar gas flow rate is set to 20 sccm and the working pressure is controlled to 0.8 Pa. The radio frequency power supply is turned on to perform ion etching on the substrate surface. The etching power is 40W and the processing time is 10 minutes to remove water molecules, gas molecules and particulate contaminants adsorbed on the surface.

[0096] (4) Turn on the substrate heating system and raise the substrate temperature to 380℃; apply intermediate frequency power to the Cr target, set the pulse width to 2.0μs, the pulse frequency to 100kHz, and the target power density to 3.2W / cm². 2 A radio frequency (RF) power supply was applied to the Y target. The RF power supply was a continuous wave RF power supply with a frequency of 13.56 MHz, and the target power density was 1.2 W / cm². 2 A negative bias voltage of -20V was applied to the substrate, the working distance was adjusted to 80mm, and the cooling water temperature was set to 15℃. Then, with the baffle closed, pre-sputtering was performed on the Cr and Y targets for 10 minutes. Afterward, the target baffle was opened, and the sample stage was started to rotate at 15 rpm to begin sputtering deposition. The deposition time was 6 hours, yielding a Cr-containing target. 96 The protective coating of Y4 has a thickness of 10μm.

[0097] The structure of the coating in Example 1 was observed using a scanning electron microscope (SEM), and the results were obtained. Figure 1 . Figure 1 The coating exhibits a fibrous columnar growth structure with dense boundaries between adjacent fibrous columnar structures and no through-holes.

[0098] The microstructure of the Cr-based protective coating with a fine columnar crystal structure prepared in Example 1 was characterized by transmission electron microscopy (TEM) and statistical analysis was performed. The results are as follows: Figure 2 As shown.

[0099] Figure 2 (a) shows the TEM morphology of the coating, which is composed of fine columnar crystals; (b) and (c) are the corresponding O and Y element mapping distribution diagrams, respectively, confirming that the Y-rich nano-oxide particles are dispersed along the grain boundaries; (d) is a statistical diagram of the size of the nanoparticles in the above morphology diagram; (e) is a statistical diagram of the spacing between nanoparticles.

[0100] Analysis results show that the coating exhibits a fine columnar crystal growth morphology, with Y-rich nano-oxide particles selectively distributed along the grain boundaries. Quantitative statistics confirm that the size of these nanoparticles is mainly concentrated in the 10-25 nm range, with an interparticle spacing ≤100 nm. This composite structure, consisting of fine columnar crystals and ultrafine nano-reinforcing phases dispersed along grain boundaries, effectively pins grain boundaries and hinders dislocation movement through both grain refinement and dispersion reinforcement mechanisms. This is a key microstructural feature contributing to the coating's excellent toughening effect.

[0101] Morphology analysis was performed on the cross-section of the coating from Example 1 after oxidation with water vapor at 1200°C for 15 minutes, and the results were obtained. Figure 5 . Figure 5 The surface forms a uniform, dense, and continuous Cr2O3 oxide layer with a thickness of 600-700nm, which can inhibit the further diffusion of oxygen and corrosive media inward, prevent further oxidation of residual coatings and zirconium alloy substrate, and play an excellent protective role.

[0102] Example 2

[0103] In the preparation method of the Cr-based protective coating with a fine columnar crystal structure in Example 2, step (1) is the same as in Example 1, and steps (2)-(4) are as follows:

[0104] (2) Install Cr 77.6 Si 22.4 The target and the Y target (purity 99.99%) were used as sputtering targets. The vacuum chamber was closed and the background vacuum was evacuated to ≤1×10⁻⁶. -4 Pa, turn on the heating and baking, set the baking temperature to 600℃, and keep warm for 2 hours;

[0105] (3) Introduce high-purity Ar gas into the vacuum chamber. Set the Ar gas flow rate to 20 sccm and control the working pressure to 0.8 Pa. Turn on the radio frequency power supply and perform ion etching on the substrate. The etching power is 65 W and the processing time is 15 minutes to thoroughly remove the adsorbed substances on the substrate surface.

[0106] (4) The temperature for heating the substrate is 380℃; apply a medium-frequency power supply to Cr 77.6 Si 22.4 The target was configured with a pulse width of 2.0 μs, a pulse frequency of 100 kHz, and a target power density of 3.0 W / cm².2 A radio frequency (RF) power supply was applied to the Y target. The RF power supply was a continuous wave RF power supply with a frequency of 13.56 MHz, and the target power density was 0.3 W / cm². 2 A negative bias voltage of -20V was applied to the substrate, the working distance was adjusted to 80mm, and the cooling water temperature was set to 15℃. Then, with the baffle closed, pre-sputtering was performed on the Cr and Y targets for 10 minutes. Afterward, the target baffle was opened, and the sample stage was started to rotate at 15 rpm to begin sputtering deposition. The deposition time was 12 hours, yielding a Cr-containing target. 92.8 Si 7.0 Y 0.2 The protective coating has a thickness of 10μm.

[0107] Transmission electron microscopy (TEM) characterization of the coating prepared in Example 2 showed that the coating grains were fine, the Y element was distributed along the grain boundaries, and the coating also exhibited a fibrous columnar growth structure with dense boundaries between adjacent fibrous columnar structures and no through-holes.

[0108] Irradiation tests were conducted on the coating of Example 2. After irradiation, the cavity size of the coating was small and the number density was reduced, indicating that the coating has good radiation resistance.

[0109] The oxidation performance of the coating in Example 2 was tested. After oxidation at 1200°C for 2 hours, the zirconium alloy substrate was found to be unoxidized, indicating that the coating has good anti-oxidation properties.

[0110] Example 3

[0111] In the preparation method of the Cr-based protective coating with a fine columnar crystal structure in Example 3, steps (1)-(3) are the same as in Example 2, and step (4) is: the temperature of heating the substrate is 380℃; a medium frequency power supply is applied to the Cr... 77.6 Si 22.4 The target was configured with a pulse width of 2.0 μs, a pulse frequency of 100 kHz, and a target power density of 3.2 W / cm². 2 A radio frequency (RF) power supply was applied to the Y target. The RF power supply was a continuous wave RF power supply with a frequency of 13.56 MHz, and the target power density was 1.1 W / cm². 2 Apply a negative bias voltage of -20V to the substrate, adjust the working distance to 80mm, and set the cooling water temperature to 15℃; then, keeping the baffle closed, apply the Cr... 77.6 Si 22.4 The target and Y target were pre-sputtered for 10 minutes; then, the target baffle was opened and the sample stage was started to rotate at 15 rpm to begin sputtering deposition; the deposition time was 12 hours, yielding a Cr composition. 89.6 Si 9.1 Y 1.3 The protective coating has a thickness of 10μm.

[0112] The morphology of the coating in Example 3 was observed by scanning electron microscopy (SEM), which showed that the coating had a fibrous columnar growth structure with dense boundaries between adjacent fibrous columnar structures and no through gaps.

[0113] The microstructure of the Cr-based protective coating with a fine columnar crystal structure prepared in Example 3 was characterized by transmission electron microscopy (TEM), and the results are as follows: Figure 3 As shown. Figure 3 (a) and (b) show the TEM morphology of the coating under different orientations; Figure 3 (c) is the corresponding Y element mapping distribution diagram; Figure 3 (d) is a statistical chart of the size of columnar grains in the coating.

[0114] The morphology images reveal that the coating exhibits fine grains and a dense, columnar fibrous growth structure. The boundaries between adjacent columnar crystals are tightly bonded, without any penetrating pores or defects. Y-element mapping results clearly show that Y is selectively distributed in the grain boundary regions, and statistical results indicate that the columnar crystal size in the coating ranges from 5 to 100 nm. This process successfully prepared a fine-grained coating with a dense structure, clean grain boundaries, and no penetrating defects, providing the coating with excellent overall performance.

[0115] Irradiation tests were conducted on the coating of Example 3, such as... Figure 4 As shown, the cavity size and number density of the coating are significantly reduced after irradiation, indicating that the coating has good radiation resistance.

[0116] The oxidation performance of the coating in Example 3 was tested. After oxidation at 1200°C for 2 hours, it was found that the zirconium alloy substrate was also not oxidized.

[0117] Comparative Example 1

[0118] In the preparation method of the Cr-based protective coating in Comparative Example 1, steps (1) and (3) are the same as in Example 1, and steps (2) and (4) are as follows:

[0119] (2) Install a pure Cr target (99.99% purity) as the sputtering target, close the vacuum chamber and evacuate the background vacuum to ≤1×10⁻⁶. -4 Pa, turn on the heating and baking, set the baking temperature to 500℃, and keep warm for 2 hours.

[0120] (4) The substrate is heated to 380℃; a medium-frequency power supply is applied to the Cr target with a pulse width of 2.0μs, a pulse frequency of 100kHz, and a target power density of 3.6W / cm². 2A negative bias voltage of -20V was applied to the substrate, the working distance was adjusted to 80mm, and the cooling water temperature was set to 15℃. Then, with the baffle closed, the Cr target was pre-sputtered for 10 minutes. After that, the target baffle was opened, and the sample stage was started to rotate at 15rpm to begin sputtering deposition. The deposition time was 6 hours, and a pure Cr coating with a thickness of 10μm was obtained.

[0121] For comparison, the cross-sectional morphology of the pure Cr coating in Comparative Example 1 after irradiation under the same conditions was observed. Figure 6 . Figure 6 This indicates the presence of large-area cavities, with cavitation sizes significantly larger than those in the coating of Example 3.

[0122] The cross-sectional morphology of the pure Cr coating in Comparative Example 1 under the same oxidation conditions was observed. Figure 7 . Figure 7 The oxide layer thickness was 2-3 μm, and large voids were observed between the oxide layer and the substrate.

[0123] In summary, this invention successfully achieved a 5-100 nm fine columnar crystal structure and dense, void-free grain boundaries, significantly improving the integrity of the coating structure. Furthermore, by comparing the morphology of the irradiated section of Example 3 with that of Comparative Example 1, it is confirmed that rare earth nanoparticles can effectively suppress the growth of irradiated cavitation, ensuring long-term stability under strong irradiation conditions. The morphology of the oxidation section of Example 1 (…) Figure 5 ) and Comparative Example 1 ( Figure 7 The comparison showed that after oxidation in water vapor at 1200℃ for 15 minutes, the present invention strictly limited the oxide layer thickness to ≤700nm, and the coatings of Examples 2 and 3 still completely protected the zirconium alloy substrate after 2 hours of extreme oxidation, breaking through the existing oxidation resistance limit; at the same time, the coatings of all examples achieved a uniform thickness of 8-15μm and high density through a single deposition process, providing an industrially feasible solution for the protection of nuclear fuel cladding tubes.

[0124] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A Cr-based protective coating having a fine columnar crystal structure, characterized in that: comprising the chemical formula Cr 100-a-b X a M b wherein X is Al or Si or any combination thereof, M is a combination of any one or more of Y, Ce, La, Nd, and 0≤a≤10, 0.1≤b≤8.5; The coating has a fine columnar crystal structure with a columnar crystal width of 5-100 nm; M and / or M oxide nanoparticles are dispersed along the columnar crystal boundaries in the coating.

2. The coating as described in claim 1, characterized in that: The nanoparticles have a particle size of 1-50 nm and a particle spacing of ≤120 nm.

3. The coating of claim 1, wherein: The coating has a dense structure along its growth direction, and the fine columnar crystals have a preferred orientation of [110].

4. The coating of claim 1, wherein: The coating is a single alloy layer.

5. The coating as described in claim 1, characterized in that: The total thickness of the coating is 8-15 μm, and the thickness of the Cr2O3 layer formed on the surface after oxidation with water vapor at 1200℃ for 15 min is 0-700 nm.

6. A method of preparing the coating according to any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Prepare the substrate and polish and clean it; (2) Install Cr c X 100-c The target and M target are vacuum pumped and heated to bake out the vacuum chamber. (3) Introduce Ar gas into the cavity, set the Ar flow rate and working pressure, and use an RF power supply to perform ion etching on the substrate; (4) The substrate is heated, and Cr c X 100-c The target is applied with a medium frequency power source, the M target is applied with a radio frequency power source, the substrate is applied with a bias voltage and the working distance is set, the target material shutter is opened under cooling conditions, the sample table rotation is controlled, and sputter deposition is performed.

7. The method as described in claim 6, characterized in that: In step (2), the background vacuum is drawn to < 1 x 10 -4 Pa; And / or, in step (3), the working air pressure is 0.8-1.2 Pa; And / or, in step (4), the substrate is heated to a temperature of 200-450°C; And / or, in step (4), the rotation speed of the sample stage is 10-20 rpm; And / or, in step (4), the power density of the intermediate frequency power source is 1.5-3.6 W / cm 2 The pulse width is 2.0-4.0 μs, and the pulse frequency is 100-200 kHz. and / or the power density of the radio frequency power source is 0.1-1.2 W / cm 2 ; And / or, the bias voltage is -15V to -80V.

8. The method as described in claim 6, characterized in that: The matrix is ​​Zr or a Zr alloy; The purity of the M target is 99.9%; The Cr c X 100-c The target satisfies 70 ≤ c ≤ 100.

9. The method as described in claim 6, characterized in that: In step (1), the matrix Ra < 100 nm; And / or, in step (2), the heating and baking temperature is 500-600℃ and the time is 1-3h; And / or, in step (3), the Ar flow rate is 20-30 sccm, the ion etching power of the radio frequency power supply is 40-100W, and the etching time is 5-15min; And / or, in step (4), pre-sputter for 10-15 minutes and then open the target baffle, with a working distance of 80-90 mm and a deposition time of 6-12 hours; And / or, in step (4), the cooling condition is cooling in water at a temperature ≤ 20°C.

10. A nuclear reactor fuel cladding tube, characterized in that, The surface is coated with the coating as described in claims 1-6.

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