Preparation Of Cr₂O₃ And Its Composite Coatings As Tritium Permeation Barriers And Their Properties

Cr₂O₃ coating has been recognized as one of candidate materials in tritium permeation barriers for its excellent high temperature thermal stability,good oxidation resistance,high resistance of tritium permeation factor,and good adhesive with the substrate.At present,Cr₂O₃ coating is generally prepared by chemical densified coating and vapor deposition method.However,there are some disadvantages for these methods,such as difficulty in coating geometrically shaped pipes,poor crystallinity and poor density of the coatings.Therefore,looking for an effective and simple coating preparation technology is one of the most important things that should be solved for tritium permeation barriers.In this paper,Cr₂O₃ coating was successfully prepared on the surface of 321 steel substrate by electroplating-high temperature oxidation technology.Moreover,in order to further improve the comprehensive properties of Cr₂O₃ coating,AlPO₄/Cr₂O₃ and Al₂O₃/Cr₂O₃ composite coating were prepared by impregnation-pulling and electrophoretic deposition technology,respectively.The microstructures,elemental distribution and morphology of the coatings were characterized by XRD,SEM and EDS,respectively.The hardness,corrosion resistance and deuterium resistance of the coatings were tested.The influence of key process parameters of electroplating,oxidation treatment,impregnation-pulling and electrophoresis deposition on the microstructure,morphology and properties of the coatings were also investigated.The results show a homogeneous and dense Cr₂O₃ coating can be obtained on the surface of 321 steel substrate by electroplating and high temperature oxidation.On the optimized process conditions with plating temperature at 72oC,current density at 0.3A/cm²,and the oxidation temperature at 700oC,the obtained Cr₂O₃ coating has tightly combined grains with uniform grain size of about 1?m and low porosity.The existence of a Cr transition layer between Cr₂O₃ coating and the substrate enables interfaces to bond closely.And no holes,cracks and other defects are found in interfaces.The coating exhibits good corrosion resistance,heat resistance of impact performance?300 times?,deuterium permeability?236 at 600oC?.AlPO₄/Cr₂O₃ composite coatings were prepared by impregnation-pulling method.AlPO₄ has a good sealing effect on the surface of Cr₂O₃ coating,which could reduce the porosity of the coating to 0%.The interface of two coatings is combined closely,and the corrosion resistance and deuterium permeability of AlPO₄/Cr₂O₃ coating are better than that of single Cr₂O₃ coating.Al₂O₃/Cr₂O₃ composite coatings were prepared by electrophoretic deposition.Under the optimized process parameters,smooth and dense Al₂O₃/Cr₂O₃ composite coatings are obtained.The two coatings are closely bonded and show excellent corrosion resistance.