Research progress on zirconium alloy cladding surface coatings

　　Over the past few decades, zirconium alloy claddings have been successfully used in light water reactors (LWRs), exhibiting excellent irradiation resistance and corrosion resistance. However, a major issue with the in-reactor application of zirconium alloys is their violent reaction with water vapor at high temperatures, releasing large amounts of hydrogen and heat when the temperature exceeds 1200 ℃. After the Fukushima nuclear accident in Japan, the safety of nuclear power was once again placed before all nuclear workers, and how to further improve the safety and reliability of light water reactor nuclear fuel elements under accident conditions has become a pressing issue to be addressed.

　　The challenge facing light water reactor nuclear fuel elements is the development of accident-tolerant fuel to meet the higher safety margin requirements for fuel performance proposed by reactor design. The research directions for accident-tolerant fuel proposed by scientists include accident-tolerant fuel cores and accident-tolerant cladding materials. Accident-tolerant cladding materials aim to improve the reaction kinetics of zirconium with water vapor, reduce the hydrogen release rate, and the cladding should have good thermodynamic properties. The development of accident-tolerant cladding materials is mainly reflected in two aspects: firstly, improving the high-temperature oxidation resistance and strength of zirconium alloy claddings; secondly, developing non-zirconium alloys with high strength and oxidation resistance. This article discusses the research on zirconium alloy cladding surface coatings aimed at the former.

　　The main advantage of applying coated zirconium cladding is its economic feasibility, as the production capacity of existing equipment can be sustained, making it easy to achieve the commercial application of zirconium-based coated cladding. The technical challenge facing coated zirconium cladding is to meet the various performance requirements of fuel cladding and components, while the coated cladding does not change the dimensions of the fuel cladding, which is crucial for in-reactor performance, especially under normal operating conditions. During long-term operation, the coating should have certain stability under corrosion, creep, and abrasion conditions. Therefore, it is necessary to continuously explore and optimize the preparation technology of zirconium alloy surface coatings.

　　New technologies should be easier to control coating quality, especially coating thickness, and zirconium cladding surface coatings should be able to maintain long-term stability in the in-reactor environment.

　　Currently, international research on zirconium alloy cladding surface coatings is still in the early exploration stage. A series of screening work on coating candidate materials and coating processes has been carried out, and coating performance characterization has also been conducted, achieving some results. The United States mainly focuses on MAX phase and ceramic coating materials, while South Korea and France mainly focus on metallic Cr coating materials. Research on zirconium alloy cladding surface coatings in China is still in its infancy.

 

　　1. Current Status of Research on Zirconium Alloy Cladding Surface Coatings

　　Zirconium alloy surface anti-oxidation coating technology is a major method to improve the anti-oxidation ability of zirconium cladding surfaces. By coating a layer of material on the outer surface of the zirconium alloy to enhance the wear resistance and high-temperature oxidation resistance of the cladding, the accident tolerance of the zirconium cladding under normal and accident conditions can be improved. Currently, some preliminary screening results have been obtained internationally on the research of zirconium alloy cladding surface coatings, and the coating materials mainly involve MAX phases and metallic Cr.

　　1.1 MAX Phase Coatings

　　The US Department of Energy's 2014 research proposal on light water reactor cladding structural materials highlighted the application advantages and research recommendations of MAX phase materials. Benjamin et al. at the University of Wisconsin selected Ti2AlC material from MAX phases as the surface coating material for zirconium cladding. Cold spraying was used for the coating process, and the coating thickness was about 90 μm. The experimental results show that the bonding strength between the coating and the zirconium substrate is greater than 50 N, and the wear resistance of the MAX phase coating surface is better (as shown in Figure 1). After a high-temperature oxidation experiment at 700 ℃ for 60 min, no oxide layer was observed at the interface between the coating and the substrate, only slight oxidation on the surface of the zirconium alloy coating, while the oxide film thickness of Zr-4 alloy under the same conditions reached 10 μm. This is because a dense and stable protective film is formed on the coating surface. The high-temperature oxidation test results under simulated accident conditions show that the coating has a protective effect on the zirconium substrate.

 

 

　　Darin J. Tallman et al. studied the reactivity of MAX phase materials Ti3SiC2 and Ti2AlC with Zr-4 alloy in the temperature range of 1100~1300 ℃. The results show that the diffusion thickness of Si and Al both follow the parabolic law, and both form Zr-Si and Zr-Al intermetallic compounds, but the diffusion rate of Si into the Zr-4 alloy is an order of magnitude less than that of Al.

　　The Ningbo Institute of Materials Science, Chinese Academy of Sciences, has also conducted research on MAX phase coatings, carrying out preliminary exploratory experiments on different coating materials and different coating processes. The institute focuses more on the discussion of coating mechanisms, pointing out that the essence of MAX phase coatings is a "clothing" effect, and the key is to solve the diffusion of oxygen atoms to the zirconium substrate. Zongjian Feng et al. at the Ningbo Institute of Materials Science, Chinese Academy of Sciences, prepared Ti2AlC coatings using direct current magnetron sputtering and conducted research on coating composition control. The substrate material selected was 316L austenitic stainless steel, and the coating thickness was about 10 μm. High-temperature oxidation tests of Ti2AlC coating samples were then carried out at 750 ℃ in air or pure water vapor environments, and the layered oxidation phenomenon and oxidation mechanism were discussed. The results of the oxidation test of the Ti2AlC coating in air show that four layers were formed in total: the outermost layer is a thick mixture of Al2O3 and TiO2 oxides, followed by a thin α- (Al, Cr) 2O3 layer, a thick mixture of Fe2O3 and TiO2 oxides in the middle, and a thin Al2O3 enriched layer in the inner layer. However, the oxidation results in pure water vapor show that oxidation occurred inside the sample, and no clear oxide layer was formed in the Ti2AlC coating, which may be related to coating quality control. Therefore, further research is needed on the preparation of alloy surface coatings using magnetron sputtering.

　　E.N. Hoffman et al. [6] analyzed the application of MAX carbide materials in the reactor core of future nuclear power plants and their neutron transmutation performance. Commercial-purity MAX phase materials were placed in fast neutron reactors and thermal neutron reactors for 10, 30, and 60 years, respectively, to simulate their neutron activity. The simulation analysis results show that under the three activation time conditions, in both fast neutron reactors and thermal neutron reactors, the activity of MAX phase materials is similar to that of SiC, but three orders of magnitude lower than that of 617 alloy.

　　Neutron irradiation test results of three MAX phase materials, Ti3SiC2, Ti3AlC2, and Ti2AlC, also verify the rationality of the neutron irradiation simulation analysis results. Ian Younker et al. evaluated the neutron properties of coating candidate materials for accident-tolerant fuel, and the results showed that the thickness of the MAX phase coating should be controlled at 10-30 μm to limit neutron loss. Darin J. Tallman et al. studied the defect evolution behavior of Ti3SiC2 and Ti2AlC materials during neutron irradiation, indicating that Ti3SiC2 shows better prospects than Ti2AlC as a candidate MAX phase coating material for high-temperature nuclear energy applications. Qing Huang et al. [9] also studied the irradiation resistance of MAX phase materials Ti3SiC2 and Ti3AlC2, and the results showed that at room temperature, Ti3AlC2 has better irradiation resistance than Ti3SiC2, and both MAX phase materials have better irradiation stability at 600 ℃ than at room temperature.

　　Existing reports have shown that MAX phase is a promising candidate material for accident-tolerant cladding coatings, but its coating preparation process needs further screening and optimization. Further research on the in-pile application performance of MAX phase cladding coatings is also needed.

　　1.2 Metal Cr Coating

　　In order to reduce the oxidation rate of zirconium-based alloys in a high-temperature steam environment, Hyun-Gil Kim et al. of the Korea Atomic Energy Research Institute (KAERI) explored related coating materials and coating technologies. A Cr coating was prepared on the surface of the zirconium alloy using 3D laser cladding technology, with a coating thickness of 90 μm. The adhesion of the coating on the surface of the zirconium alloy was tested, and high-temperature oxidation tests were carried out. The results showed that due to the formation of an intermediate diffusion layer, the Zr-4 alloy and the Cr coating have excellent adhesion. The Cr-coated cladding did not show cracks until 4% strain (as shown in Figure 2), meeting the 1% strain requirement of the fuel cladding. Oxidation test data showed that the high-temperature oxidation resistance of the coated zirconium alloy is significantly better than that of the Zr-4 matrix.

 

 

　　Jung-Hwan Park et al. used arc ion plating technology to prepare a Cr coating on the surface of Zr-4 alloy. The purity of the metal Cr target was 99.9%, and the deposition temperature was controlled at 473 K during the preparation process. Oxidation test results in a steam environment at 1200 ℃ and 2000 s showed that the high-temperature oxidation resistance of the coated zirconium alloy is significantly stronger than that of the zirconium alloy matrix (as shown in Figure 3), and the Cr-coated zirconium cladding has better ductility.

 

 

　　J.C. Brachet et al. in France used PVD to prepare a metal Cr coating on the surface of zirconium alloy. The latest test results show that the prepared Cr coating is very dense and free of defects (as shown in Figure 4). The Cr coating prepared after process optimization improved the high-temperature oxidation resistance of the zirconium cladding, and retained some residual ductility after oxidation quenching under accident conditions (as shown in Figure 5), providing important accident response time for remedial measures.

 

 

 

　　Studies have shown that the metal Cr coating has good high-temperature oxidation resistance and can be used as a candidate coating material for accident-tolerant zirconium alloy cladding.

　　Currently, research on zirconium alloy surface coatings in the United States mainly focuses on MAX phase materials, including coating processes, high-temperature oxidation performance of coated zirconium alloys, and irradiation performance of coating materials. South Korea and France mainly focus on the preparation process and high-temperature oxidation performance of metal Cr coatings. Domestic research has also conducted preliminary explorations on the preparation process and some properties of MAX phase materials. Because the research on zirconium alloy cladding surface coatings is in the feasibility exploration stage, reports on the application performance research of coatings mainly focus on high-temperature oxidation and corrosion performance, and research on other application performances needs further development.

 

　　2. Several Key Issues in the Research of Zirconium Alloy Surface Coatings

　　2.1 Coating Material Selection

　　Considering the special application environment, the selection of cladding coating materials is mainly based on their physical properties. First, the coating material should improve the high-temperature oxidation resistance of the zirconium cladding. Under accident conditions, the coated zirconium cladding should exhibit a significantly lower oxidation rate, forming a dense and stable protective film on its surface to prevent or delay further oxidation, thereby preventing the zirconium cladding from being damaged due to oxidation loosening. When selecting zirconium cladding coating materials, in addition to considering the essential high-temperature oxidation resistance, it is also necessary to examine the melting point, thermal conductivity, and mechanical properties under temperature gradients of the candidate materials, as well as its neutron economy.

　　Considering the above factors comprehensively, Cr2O3 and Al2O3 ceramic materials stand out, with low growth rates at high temperatures and excellent stability. Due to their brittleness, if a ceramic layer is directly formed on the surface of the zirconium alloy, it will easily crack during the mechanical preparation of nuclear fuel. Considering the compatibility with zirconium alloys, if the coating material can form a ceramic oxide film on the surface of the cladding during high-temperature oxidation reaction, it will be more stable. Metal Cr and MAX phase materials can form a dense protective film after high-temperature oxidation, and are promising candidate coating materials for zirconium cladding.

　　2.1.1 MAX Phase

　　Since 2000, the emerging MAX phase materials have combined some excellent properties of metals and ceramics. MAX phase materials have good plasticity, and this microscopic plasticity and good thermal conductivity make the material have good thermal shock resistance, and microscopic plasticity also makes it have good damage resistance. Tables 1 and 2 give the typical physical and mechanical properties of some commonly used MAX phase materials, respectively.

 

 

 

　　It can be seen that the four alloys Ti2AlC, Ti3AlC2, Ti3SiC2, and Cr2AlC combine some excellent properties of metals and ceramics, and have good comprehensive performance.

　　Existing research shows that MAX phase materials are excellent high-temperature structural materials. Table 3 provides the parabolic rate constants of some commonly used MAX phase materials during oxidation at 1000-1300 ℃ in air. It shows that these MAX phase materials have good high-temperature oxidation resistance. Generally speaking, the oxidation resistance of Ti3AlC2 is 2-3 orders of magnitude higher than that of Ti3SiC2. The reason for its good oxidation resistance lies in the formation of a dense Al2O3 protective film after surface oxidation. Ti2AlC also exhibits good oxidation resistance, and its oxidation mechanism is the same as that of Ti3AlC2. Cr2AlC has good high-temperature oxidation resistance, comparable to Ti3AlC2, but its coefficient of thermal expansion (13.3 × 10-6 K) is too different from that of the zirconium matrix (7.2 × 10-6 K), which is not conducive to coating quality control. The high-temperature oxidation resistance of Ti3SiC2 is relatively poor. With the increase of temperature, the oxidation rate increases significantly, and the oxide film formed is SiO2, a ceramic material with very low thermal conductivity, which is not conducive to the heat dissipation inside the cladding. Both Ti3AlC2 and Ti2AlC form dense Al2O3 protective films after oxidation. The difference in the coefficient of thermal expansion of the film (8.4 × 10-6 K) and zirconium alloy (7.2 × 10-6 K) is relatively small. Although Ti3AlC2 has better high-temperature oxidation resistance than Ti2AlC, considering neutron economy, Ti2AlC is a more ideal candidate material for zirconium alloy cladding coatings.

 

 

　　2.1.2 Metallic Cr

　　Metallic Cr has good metallic luster and corrosion resistance and is often used to plate other alloy surfaces. High-purity metallic Cr has advantages such as high-temperature resistance, oxidation resistance, vibration resistance, and creep resistance, and can be used as a target material for various plasma and electron beam sputtering, with wide applications.

　　Hyun-Gil Kim of the Korea Atomic Energy Research Institute studied the high-temperature oxidation performance of candidate coating materials. The experimental results are shown in Table 4.

 

 

　　After oxidation in a 1200 ℃ steam environment, among the four candidate materials, SiO2 showed the best high-temperature oxidation resistance, and Si was more effective in oxidation resistance than Cr. Corrosion tests were also conducted under simulated operating conditions of 360 ℃ and 18.9 MPa. The results showed that metallic Cr exhibited better corrosion resistance than Zr-4 alloy, while Si wafers and SiO2 samples dissolved quickly under corrosive conditions. That is, materials with good oxidation resistance in high-temperature steam environments do not guarantee their corrosion stability under normal operating conditions in the reactor. Therefore, KAERI selected metallic Cr alloy as the coating material for zirconium alloy cladding. The French CAE is also committed to the research of metallic Cr coatings, and has investigated more than 20 coating materials based on Zr-4, including ceramics and metals, and found that metallic Cr coatings have the most potential for development. Existing research shows that metallic Cr is also a promising candidate material for zirconium alloy coatings.

　　2.2 Coating Process Selection

　　In order for the coated zirconium cladding to provide effective protection under accident conditions, the surface coating must be uniform and dense and have good high-temperature oxidation resistance. Therefore, the control of surface coating quality is very important, especially the film-substrate bonding strength and film density, which depend on the deposition technology and process parameters used. The coating preparation process is best carried out under vacuum protection, which has high preparation efficiency and, most importantly, is suitable for fuel assembly coating preparation. Generally speaking, the coating deposition temperature should be lower than the final annealing temperature of the zirconium cladding, about 500 ℃, to avoid changes in the microstructure of the zirconium alloy substrate. By comprehensively comparing the advantages and disadvantages of different surface preparation technologies, arc ion plating technology is a promising zirconium cladding surface coating preparation process.

　　2.2.1 Thermal Spraying

　　Thermal spraying includes flame spraying, arc spraying, plasma spraying, and supersonic flame spraying. The coating and substrate are mainly mechanically bonded, and the bonding strength of the interface is relatively low, so the impact resistance is poor. In the thermal spraying process, there are problems such as powder oxidation, phase transformation, decarbonization, or changes in the physical and chemical properties of the original powder, and it will also have an adverse thermal effect on the substrate. Small-area thermal spraying is uneconomical, and the coating thickness is generally 0.5-5 mm. Coating materials with a thermal expansion coefficient close to that of the substrate should be selected as much as possible.

　　Relatively speaking, plasma spraying has lower porosity and higher bonding strength between the coating and the substrate. However, plasma spraying is more suitable for thick film deposition, and the quality control of zirconium alloy surface coatings with a thickness of tens of micrometers is more difficult. South Korea initially used plasma spraying (PS) technology, but there were some technical problems, such as the formation of pores in the Si coating, and oxidation occurred at the interface due to low bonding strength. After the process was improved, the coating prepared by plasma spraying was then treated by laser beam scanning (LBS), which removed the pores in the Si coating and inhibited its oxidation due to the formation of a diffusion layer at the interface. However, the manufacturing cost of the coating increased sharply, product quality control was difficult, and the PS+LBS preparation process was complex, so this process was not adopted.

　　2.2.2 Cold Spraying

　　Cold spraying is a process in which a coating is formed by the strong plastic deformation of high-speed powder particles impacting the substrate at low temperatures. Cold spraying has the advantages of low deposition temperature, small thermal effect on the substrate, uniform distribution, and basically no oxidation phenomenon. Therefore, cold spraying is mainly used for spraying temperature-sensitive, oxidation-sensitive, or phase-change-sensitive materials. The deposition rate of cold spraying is very high, and the coating can obtain a relatively large thickness. Relatively speaking, the bonding strength between the cold-sprayed coating and the substrate is not high, but a lower porosity and higher bonding strength can be achieved by sacrificing a certain deposition rate.

　　Xi'an Jiaotong University and the Ningbo Institute of Materials Science, Chinese Academy of Sciences, both have the foundation for conducting cold spraying process research and coating performance characterization methods. The former's spraying process can be carried out under vacuum or atmosphere protection. It is difficult to achieve a thin coating of tens of micrometers by cold spraying, and the effect of high-speed deposition of coating particles on the deformation of the approximately 0.6 mm thin-walled zirconium tube during cold spraying still needs to be explored. The cold-sprayed film and the substrate are mechanically bonded, and the bonding strength is relatively low, which can be improved by heat treatment. In order to obtain a high-quality coating, cold spraying has certain requirements on the particle size and impurity content of the powder, which also brings about the problem of powder preparation process research. At present, the preparation process of MAX phase material powder is relatively mature at home and abroad, and the cold spraying process can be tried to explore the zirconium alloy surface coating process.

　　2.2.3 Vapor Deposition Method

　　In material surface engineering preparation technology. Vapor deposition methods are divided into physical vapor deposition (PVD) and chemical vapor deposition (CVD). Chemical vapor deposition processes are mostly carried out at relatively high pressure and high deposition temperature (900~1200 ℃). Considering that the coating preparation process should avoid affecting the zirconium matrix structure as much as possible, the deposition temperature should be as low as possible. Therefore, the physical vapor deposition method with a relatively low deposition temperature can be used for the preparation of zirconium alloy surface coatings.

　　At present, the commonly used physical vapor deposition methods are mainly magnetron sputtering and ion plating. Magnetron sputtering has good film-forming effect, low substrate temperature, and strong film adhesion, especially suitable for large-area coating. The substrate temperature in the magnetron sputtering process is the most important influencing factor of the microstructure and properties of the coating. Appropriate substrate temperature can improve the adhesion and deposition rate of the thin film. The film prepared by magnetron sputtering technology has good quality, but the deposition rate is low, and the film is relatively thin. The film thickness can generally reach several micrometers, but it takes a long time to deposit several micrometers of coating, and the residual stress of the film is large. The feasibility of preparing zirconium cladding surface coatings by magnetron sputtering method still needs further exploration.

　　The deposition temperature of ion plating technology is significantly reduced, which is beneficial to reduce or eliminate the thermal stress between the coating and the substrate, and improve the coating bonding force. Arc ion plating has the advantages of good coating quality, high deposition rate, strong diffraction, and large-area deposition. The disadvantage of this process is that the deposition process is prone to jetting particles, which affects the film quality. Magnetic field filtration and other technologies can be used to improve it. As a cathode target material, the coating material must have certain conductivity. MAX phase and metal Cr materials are both conductive, and they can be made into suitable target materials for the preparation of zirconium cladding surface coatings. For the research of zirconium alloy surface coatings, arc ion plating technology is a promising coating preparation technology.

　　2.3 Coating Quality Characterization

　　Candidate materials for high-temperature oxidation coatings, such as MAX phases and metal Cr, have relatively high thermal neutron absorption cross sections. Considering neutron economy, the thickness of the zirconium cladding surface coating should be designed as thin as possible. In the research of coating preparation technology, coating quality characterization is very important. The characterization of coating structure and properties mainly includes chemical composition and phase structure, microstructure, microhardness, coating thickness and coating adhesion.

　　By comparing the results of coating quality characterization, the coating preparation process is optimized. X-ray diffraction (XRD) is generally used to analyze the crystal structure of the coating, the surface phase structure changes between the coating and the substrate, etc. Energy dispersive spectrometer (EDS) is used to analyze the element distribution in the coating, substrate, and interface between the coating and the substrate to determine whether the control of coating composition and phase structure by the preparation process meets the technical requirements.

　　Scanning electron microscopy (SEM) is used to observe the surface and interface morphology of the coating, including pores, surface morphology, microstructure and coating thickness, and analyze the uniformity of coating distribution. When measuring the thickness from the cross-section of the coating, it is necessary to prevent the chamfering of the cross-section sample during metallographic polishing. Porosity is a measure of the density of the coating, and it is an important indicator affecting the corrosion resistance of the coating. A hardness tester is used to detect the microhardness that reflects the coating performance.

　　Coating adhesion is the most critical performance indicator for evaluating coating quality. Conventional detection methods include indentation method, scratch method and tensile method. Whether in normal reactor operation or accident conditions, the coating should maintain its integrity when the zirconium cladding tube undergoes circumferential deformation. At room temperature, circumferential tension and compression tests can be used to evaluate the bonding strength between the coating and the substrate for coated zirconium cladding tubes.

　　2.4 Key Application Performance Research of Coated Zirconium Cladding

　　Coating quality has a significant impact on the corrosion resistance of zirconium cladding. For the same coating material, the better the coating density, the lower the porosity, and the better the corrosion resistance of the zirconium cladding. Zirconium cladding materials will undergo creep, fatigue and thermal shock in the reactor. Therefore, the bonding strength between the coating and the substrate will directly affect whether the coating technology can be used in the research of zirconium alloy cladding materials.

　　Good coating quality is to better meet the application performance requirements of zirconium alloy cladding. The results of the application performance research of coated zirconium cladding are fed back to the coating preparation process in time to continuously optimize the preparation process parameters and obtain high-quality surface coatings. Considering the influence of coating quality, it is necessary to study the key application performance of zirconium alloy coatings outside the pile, mainly focusing on whether the coating and zirconium matrix can achieve coordination consistency during the operation of the reactor.

　　2.4.1 High Temperature Oxidation Performance

　　Improving the high-temperature oxidation resistance of zirconium cladding is the key to the development of accident-tolerant fuel cladding. Therefore, it is necessary to study the high-temperature oxidation performance of coated zirconium alloy first. A comprehensive thermal analyzer is used to study the high-temperature oxidation performance of coated zirconium alloy. Water vapor is introduced into the experimental process, and the temperature range is 700~1300 ℃. According to the experimental results, the oxidation kinetic curve of the coated zirconium alloy is analyzed, the microstructure morphology of the oxide film on the sample surface is observed by microscope and scanning electron microscope, and the composition of the oxide film is analyzed by energy dispersive spectrometer.

　　2.4.2 Corrosion Performance

　　Zirconium cladding materials that have been in service in reactors for a long time need to have good corrosion resistance. Corrosion tests of coated zirconium alloys are carried out in a static high-pressure autoclave. The analysis methods of the test results are the same as those described in high-temperature oxidation performance, mainly including the study of oxidation kinetics curves and the analysis of surface morphology and composition of oxide films.

　　2.4.3 Thermal Shock Performance

　　Accident-tolerant cladding materials should have good thermal shock resistance and should not crack under accident conditions to avoid the release of radioactive fission products. The test is to keep the sample in a high-temperature, high-pressure steam environment for a period of time and then quickly cool it down. The microstructure morphology and the bonding situation between the coating and the substrate are observed by optical microscope and scanning electron microscope to analyze the thermal shock resistance of the coated zirconium alloy.

　　2.4.4 Creep Performance

　　Creep performance research of coated zirconium alloys was conducted in comparison with zirconium matrix, analyzing the effects of temperature and stress on the creep resistance of coated zirconium alloys. During the experiment, the peeling and shedding of the coating were observed. Scanning electron microscopy was used to observe the morphology of the port structure and analyze the deformation coordination between the coating and the substrate.

 

　　3. Conclusion

　　Research on surface coatings for zirconium alloy claddings is a major aspect of the development of accident-tolerant fuel, with advantages such as good manufacturing economy and ease of commercialization. Currently, international research on surface coating technology for zirconium alloys is still immature and is in a continuous exploration and verification stage. A systematic investigation of existing coating materials and coating processes lays a good foundation for the research work on zirconium alloy surface coatings in our country. As candidate coating materials, Ti-Al-C based MAX phase materials and metallic Cr have good application prospects. The selection of zirconium alloy cladding coating materials and coating processes is a complex process that requires repeated verification based on the results of subsequent key application performance research. In summary, international research on zirconium alloy surface coating technology is not yet fully mature and is in a stage of multi-party exploration and continuous verification, which also brings opportunities and challenges to the research of zirconium alloy surface coating technology in our country.