| Fusion Reactors are considered to be one of the important technologies that can solve the shortage of clean energy.Tritium is one of the main fuels of fusion reactors.It is a radionuclide with the smallest atomic radius and has a high permeability in most metallic materials including low activation steels for fusion blanket.Tritium permeation makes the fusion reaction unsustainable,hydrogen embrittlement/helium embrittlement of the structural materials,as well as causes radioactive contamination.The main solution of the problem is to prepare a tritium permeation barrier represented by Al2O3 coating on the surface of structural materials.Although Al2O3 has a strong resistance to hydrogen isotopes permeation,the brittleness of ceramic materials makes it easy to crack and fall off under the harsh service environment of fusion reactor(high temperature,tritium permeation,complex stress,etc.),which seriously affects the performance and service life of the tritium permeation barrier.The latest research shows that the graphene with a dense electron cloud structure has excellent barrier ability on hydrogen isotopes,and the graphene dopped in ceramic materials can also enhance the toughness of the material.Based on the research of ceramic oxide tritium permeation barrier,a graphene/alumina composite coating with both good hydrogen resistance and toughness on the surface of CLAM(China Low Activation Martensitic)steel was designed in this paper.The toughness,deuterium resistance,and thermal cycling resistance of the composite tritium permeation barrier were studied,respectively.The main results of the study are as follows:1)The graphene oxide(GO)film and reduced graphene oxide(RGO)film with multilayer structure on the surface of CLAM steel were prepared by spraying method combined with deuterium thermal reduction.Experiment results indicated that the deuterium permeation reduction factor(PRF)of the unprotected GO and RGO film was 13 and 7 at 350?,respectively.The surface quality of graphene film under the high temperature and pressure gas environment was decreased,and it caused the graphene film partially fell off from the substrate.The reason for the decrease in the surface quality of graphene film was the small amount of gas from the entering through the interlayer defects and the high temperature oxidation accumulation which caused bubbling and cracking of the film.If the graphene film is used in the filed of deuterium resistance in fusion reactor,the surface quality needs to improved to ensure the integrity of the film.2)A new type of tritium permeation barrier of GO/Al2O3 with a layer-by-layer structure was designed and prepared by spraying combined with Sol-Gel method in this paper.The effects of the number of layers,the thickness of GO film,and the type of GO film on the mechanical properties,permeability,and thermal cycling resistance of the composite coating were studied.The PRF of multi-layered composite coating(assembled by a 3-layer GO film with a single layer thickness of 45 nm and an 4-layer Al2O3 film with a single layer thickness of 190 nm)can reach 134 at 550?,which is 5 times that of the pure Al2O3 coating with the same thickness.However,the thermal cycling resistance of the composite coating was poor,and the PRF of the coating dropped about 3 times to 39 after 60 thermal cycles.Studies have shown that the graphene film in the multilayer structure can effectively hinder the diffusion of deuterium atoms and extending its diffusion path to reduce the permeability of the coating;the multilayer structure can deflect the direction of longitudinal microcrack growth and improve the toughness of the coating;the weak bonding of the graphene nanosheets leads to the sliding of the GO films at high temperature,which causes micropores and partial shedding on the surface of the coating,resulting in a decrease in permeability.The layered structure can effectively enhances the toughness and deuterium resistance of the composite coating,but the thermal cycling resistance of the coating needs to be further improved.3)A GO/Al2O3 composite tritium permeation barrier with network structure was prepared by sol-gel method in this paper.The effects of GO content,heat treatment and thermal cycle test on the toughness and permeability of the composite coating were studied.The addition of 0.5 wt%GO increased the deuterium barrier performance of the composite coating by 9 times than the pure Al2O3 coating with the same thickness,and it reached 178.The deuterium resistance of the composite coating can be enhanced by increasing the heat-treament time.The PRF of the coating was increased to 412 after 10 h heat-treament at 650?.At the same time,the toughness of the network composite coating with 0.5 wt%GO was increased by 40%compared with the pure Al2O3 coating,Moreover,the coating has better thermal cycling resistance,and the PRF change is less than 5%after 60 thermal cycles from 650? to room temperature.Studies have shown that GO nanosheets can effectively blocking the diffusion of deuterium atoms and extending the diffusion path to reduce the permeability of the coating.And the deuterium resistance of the coating becomes more stronger with more GO nanosheets.In addition,the ratio of ?-Al2O3 in the coating was increased by adjusting the heat-treatment process to improve the deuterium barrier properties of the coating.GO nanosheets dispersed with network structure in the coating can bridge microcracks to block the crack propagation and improve the toughness of the coating.And the toughness of the composite coating with high content of GO nanosheets becomes stronger.The research on the composite coating with network structure shows that the three-dimensional arrangement of GO nanosheets can effectively enhance the toughness and deuterium resistance of the coating,and the composite coating has good thermal cycling resistance.In summary,the graphene/alumina composite tritium permeation barrier designed and prepared in this paper can improve the toughness and deuterium resistance of the coating at the same time,and the composite coating has simple preparation process,low heat-treatment temperature(650?),and good thermal cycling resistance.In the future,it is necessary to optimize preparation process of the coating,adjust microstructure of the coating,improve the deuterium resistance of the coating at high-temperature,and verify its radiation resistance and corrosion resistance comprehensively. |
PDF Full Text Request