| In the International Thermonuclear Experimental Reactor (ITER) project, tritium permeation barrier is necessary on the surface of TBM (Test Blanket Module). Al2O3 /Fe-Al layer with self-repairing performance is recognized as the best tritium permeation barrier. But how to prepare tritium permeation barrier on special-shaped surface and maintain mechanical performance of the matrix at the same time is still one of the technical problems. In this paper a new preparation technology of tritium permeation barrier is presented:at first, aluminum is electrodeposited on metal surface at room temperature molten salt; then Fe-Al alloy coating is prepared on the surface through low temperature heat treatment, and further Al2O3 film is prepared on the surface of the Fe-Al coating through low temperature oxidation.By means of the technology of electrodeposition at room temperature molten salt, heat treatment and thermal oxidation and the methods such as CV, XRD, SEM, EDS and XPS, the effects of pretreatment on different metal matrix and electrodeposition parameters at room temperature molten salt on adhesion and morphology are studied, and further the effects of heat treatment temperature, time, matrix composition, matrix structure and surface roughness on phase structure and phase transformation of Fe-Al coating are studied. At the same time the formation mechanism and influence factors of the voids between the coating and matrix are studied. At last the oxidation of Fe-Al coating on different metal matrix is studied and tritium resistivity test is carried out. Through the research, the following conclusion can be concluded:Through anode activation treatment of 1 A/dm2,30 min at AlCl3-EMIC room temperature molten salt on 201, HR-2 austenitic and 1Cr17 ferritic stainless steel matrix, oxide film on the surface is removed; if the activation current density is too low, localized corrosion will be produced on the matrix and higher current density would lead to the plating liquid decomposition. Compact aluminum coating will be electrodeposited with the current density of 0.5-3 A/dm2, and with the increase of current density, grain size become smaller. Dendritic crystal will appear if current density is too high. Current efficiency is close to 100% with the current density of 2 A/dm2, during 5-40 min. Aluminum coating thickness linear increase with the time increase. Through controlling the electrodeposition time, different thickness of aluminum coating can be obtained. After the aluminum coating of 17μm on 201 austenitic stainless steel is heat treated at low temperature of 620℃～680℃, Fe-Al coating with the alloy element of chrome, nickel will form. The aluminum layer gradually disappeared with the heat treatment time increases at the temperature higher than aluminum melting point in 2～240 min range. FeAl3 and Fe2Al5 form in succession; after the aluminum layer disappear completely, diffusion continue with FeAl3 as aluminum source and the thickness of Fe2Al5 phase continues to increase, at the same time FeAl phase forms between the coating and the matrix. Below the melting point of aluminum, the rule of the phase transformation is similar, just the transformation time is longer. When the matrix is 1Cr17 ferrite and HR-2 austenitic stainless steel, the rule is similar. According to the diffusion theory, FeAl layer can be prepared through short time heat treatment at low temperature. After aluminum coating of 4μm on HR-2 is heat treated at 670℃/4h, FeAl layer with uniform thickness can form and there is no defects such as cracks and voids at the interface and FeAl layer.The morphology of Fe-Al layer prepared by low temperature heat treatment is different on different matrix. Alloy elements of chromium, manganese, nickel appears in Fe-Al alloy phase as the solid solution. The exist of chromium, nickel, manganese inhibit the growth of Fe2Al5 phase like tongue, so that the interface between Fe-Al layer and 201, HR-2 austenitic and 1Cr17 ferritic stainless steel is flat. The curve of FeAl layer thickness with heat treatment time is a parabola. The generating speed of FeAl phase is different:FeAl generation rate on 1Cr17 ferrite matrix is the slowest, and the rate on Q235 matrix is the quickest.Voids appears at the interface of FeAl and matrix during the heat treatment. Void formation is related with heat treatment temperature, time, roughness of matrix, crystal structure and alloy elements. At the heat treatment temperature of 640℃below the melting point of aluminum, there is no void on the interface between the FeAl layer and 1Cr17 matrix even the heat treatment time is 100 h, but at 670℃above the melting point of aluminum, voids are observed after 20 h heat treatment. Circular voids are observed after 50 h heat treatment. Rough surface of the matrix increases the aluminum diffusion flux, so voids forms easier. The void morphology of sandblasted 1Cr17 heat treated with 670℃/20 h is similar with polishing 1Cr17 heat treated with 670℃/50. Voids form easier on the interface of HR-2 and 201 austenitic stainless steel with face-centered cubic structure than 1Cr17 with body-centered cubic structure. There is no void even after 740℃/24 h heat treatment on sandblasted HR-2 matrix.In the atmosphere, Al2O3 can be observed after the Fe-Al layer on 1Cr17 thermal oxidized at 740℃, but Fe2O3 is observed too, and there exist voids between Fe-Al and the matrix. The oxide film containing Fe2O3 and Al2O3 after the Fe-Al layer on HR-2 thermal oxidized at 690℃-740℃in the atmosphere and there is no void at the interface. But in 10-2 Pa hypoxia potential environment, intact Al2O3 film can be obtained after thermal oxidation at 700℃/80 h. Hypoxia potential can inhibit iron oxide formation. Chromium in Fe-Al layer promotes the formation of intact Al2O3 film. Tritium resistivity test is carried out at 740℃, the permeability reduction factor PRF is 431.In the base of the successful application of electrodeposition aluminum on prepare tritium permeation barrier at room temperature molten salts in the ITER project, the studied of electrodeposition aluminum on active La-Ce rare earth and AZ91D magnesium alloy in AlCl3-EMIC at room temperature molten salt is carried out which focuses on the adhesion between coating and matrix. The following important conclusions can be drawed:oxide film can be effectively removed after the La-Ce rare earth polished in kerosene and dried in argon atmosphere and this pretreatment can prevent the oxide film to produce. After the AZ91D magnesium alloy etched for 20 seconds in dilute phosphoric acid with concentration of 10 wt.%, phosphate film can be obtained on the surface which can inhibit the formation of oxide film. After the pretreatment, dense and pure aluminum coating with good adhesion can be obtained on the surface of the two kind of active metal.
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