Microstructure control and deuterium permeability of erbium oxide coating on ferritic/martensitic steels by metal-organic decomposition

The development of a tritium permeation barrier is essential for building a tritium recovery system in fusion power plants. Toward realizing this application, the fabrication of erbium oxide coatings by metal-organic decomposition has been carried out on reduced activation ferritic/martensitic steels. The coated samples exhibit different surface structures after they are heat-treated under different conditions. A sample that is heat-treated in high-purity argon produces an oxide layer between the erbium oxide coating and the substrate. It is believed that the presence of this oxide layer causes defects in the coating and degradation of the samples during deuterium permeation measurements. The sample heat-treated in high-purity hydrogen with moisture exhibits a thinner oxide layer and improved stability during measurements. A 0.3-μm-thick coating yields a permeation reduction factor of 500–700 at 773–973 K, which is comparable to the coating deposited by the physical vapor deposition technique.