| Reduced activation ferritic martensitic steels (RAFM steels) are considered to be the preferred structural material of future liquid tritium added cladding. However, the RAFM steels have higher tritium penetration than austenitic steels because of its body-centered cubic crystal structure. It is very important to fabricate tritium barrier coatings on the surface of RAFM steels. FeAl/Al2O3 composite coatings are considered to be one of the most practical outlook tritium barrier coatings among so many tritium barrier coating material. So I use ambient temperature ionic liquids anodized aluminum method combine with heat treatment and high temperature oxidation process to fabricate FeAl/Al2O3 composite tritium barrier coatings on the surface of RAFM steels and achieve good results.1) To fabricate tritium penetration barrier of aluminizing coating on Chinese low active martensite (CLAM) steel, electroplating of aluminum on CLAM steel from ambient temperature chloroaluminate ionic liquid AICl3-EMIC (AlCl3-l-ethyl-3-methylimidazoliurn chloride) was carried out. The adhesion of substrates and aluminum coating at different pretreatment of the substrates was examined. The surface morphology,crystal size of aluminum coating at different current densities were examined by SEM and EDS. Comparing the surface morphology of aluminum plated by direct current process with which plated by pulse current process. The results show that the electroplating of aluminum on CLAM steel from AICl3-EMIC is feasible. The current density of electrical pretreatment has influenced to the adhesion of substrates and aluminum coating. Increasing the current density can improve the adherence of substrates and aluminum coating. Using pulse current plating process can improve the compactness of surface morphology. Particle size of aluminum coating decreases with increasing current density. Spherical structure of aluminum coating increases with increasing current density. The deposited aluminum coating is whiter, smooth and uniform at preferable plating techniques. The preferable range of current density is 10-20 mA/cm2.The range of electroplating time is 45-95 min. The pulse current process is better.2) There must be a Fe-Al mutual penetration transition layer between substrate and Al2O3 layer in order to prepare Al2O3 tritium barrier layer which is firmly bonded to the substrate on the CLAM (RAFM) steel. Using electroplating of aluminum in ambient temperature chloroaluminate ionic liquids technique combine with hot mutual penetration technique at high temperatures may become an effective method for preparing the Fe-Al mutual penetration layer. Insulating the sample at 550 ℃-750℃ will make CLAM steel substrate infiltrate with aluminum coating and will form Fe-Al mutual penetration layer of certain thickness after aluminum on CLAM steel substrate surface which studies have shown. The thickness, composition and structure of layer are related with temperature and holding time. Bilayer structure will form at relatively Low temperature. The bilayer structure is consist of a Fe2Al5 outer phase and a gradient composition inner layer. Three-layer structure will form at relatively high temperature. Three-layer structure is consist of a Fe2Al5 outer phase and a (FeCr)Al2 middle phase and a (FeCrMn)Al inner phase. The temperature has big effective to the height of whole layer and the composition of the layer. The holding time of heat treatment has relativity to the height of mutual penetration transition layer.3) By using Standard heat treatment process of CLAM steels(980℃/30min/air cooling +760 ℃/90 min/air cooling), the Al2O3 film which is dense, no obvious defects has been prepared on surface of Fe-Al mutual penetration layer. The thickness of film is about 200-230 nm. The FeAl/Al2O3 composite coatings has been prepared finally. There is no rift between layers. There is no void at the interface of layers. |
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