Microstructural evolution and deuterium permeation resistance of an Al2O3/SiO2/Cr2O3/CaO composite coating on 304 stainless steel under high-temperature permeation conditions

Abstract

To address radioactive safety risks caused by tritium permeation in liquid metal-cooled fast reactors, an Al 2 O 3 /SiO 2 /Cr 2 O 3 /CaO composite tritium permeation barrier coating was fabricated on the surface of 304 stainless steel by a slurry method combined with high-temperature sintering. Surface structural characteristics of the coating were systematically investigated. The chemical composition, phase structure, and micro-morphology of the coating were analyzed using XPS, XRD, SEM-EDS, and its tritium permeation resistance was evaluated through deuterium gas-phase permeation experiments. The results show that the coating was mainly composed of α- Al 2 O 3 , SiO 2 , Cr 2 O 3 , and CaO, and exhibited continuous coverage on the substrate. The coating achieved an initial permeation reduction factor of two orders of magnitude at 500 °C. After high-temperature deuterium permeation, the PRF increased to three to four orders of magnitude, with a maximum value exceeding 13,000 at 650 °C. XRD analysis indicated that the characteristic crystallite size increased from approximately 35.4 nm before permeation to 57.2 nm after high-temperature deuterium permeation, suggesting grain coarsening during the experiment. TEM observations provided additional local morphological evidence for structural evolution of the coating. Cross-sectional SEM observations further indicated a more compact coating structure and improved interfacial bonding after high-temperature deuterium permeation. The enhanced deuterium permeation resistance is therefore interpreted as the combined result of high-temperature-induced microstructural evolution, including crystallite/grain coarsening, coating densification or re-sintering, partial reduction of pores and micro-defects, and the improved coating/substrate interfacial bonding. After 50 thermal cycles at 600 °C, the coating remained intact without obvious cracking or spallation, demonstrating good thermal shock resistance. These findings provide useful guidance for the development of oxide composite coatings for hydrogen isotope permeation mitigation.

The authors' abstract, as published at the source. International Journal of Hydrogen Energy, 2026 · DOI ↗