Preparation and Properties of Alumina Coatings as Tritium Permeation Barrier by Plasma Electrolytic Oxidation

The alumina coatings as tritium permeation barrier were deposited on 316L stainless steel substrates by plasma electrolytic oxidation. The effects of plasma electrolytic oxidation on the coatings were investigated, and phase, surface morphology and thickness were characterized by XRD, SEM and eddy current method, respectively. After scratch adhesion test, thermal shock resistance test and tritium permeability test, the optimized coatings were obtained. The results show that the phase, the surface morphology and the thickness are affected by current density, voltage and PEO (plasma electrolytic oxidation) duration time. The current density and voltage can change the phase structure of coatings, higher current density propels the transformation of Al→Al2O3 and higher voltage propels the transformation of γ-Al2O3→α-Al2O3. With increasing voltage and duration time, the pore size becomes bigger and the quantity is less so that the surface morphology is worse. With current density increasing to appropriate value (9 A/dm2), surface morphology becomes good. After a series of tests, the coatings, which are obtained at 6 A/dm2, 300 V, 30 min, exhibit good performances with good film-substrate cohesion, thermal shock resistance, and the tritium permeation resistance of coated sample is improved by 3 orders of magnitude higher than that of the 316L stainless steel bulk.