Under high-temperature operating conditions, the tritium would be generated inside the core of thorium-based molten salt reactor (TMSR) and probably diffuse through the structural material into the environment. Establishing an Al2O3/Ni-Al composite tritium permeation barrier coating may help address this issue.
This study aims to explore the optimal preparation process, especially the in-situ oxidation process.
The Al2O3/Ni-Al composite coating was prepared on the surface of GH3535 alloy by pack cementation aluminizing (PCA) followed by vacuum in-situ oxidation, and the effects of oxidation temperature and vacuum on the microstructure of Al2O3 films were analyzed by experiments. Grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM), X-ray energy dispersive spectroscopy (EDS) were used to characterize the phase composition and crystal structure of the alumina film, as well as morphologies of the surface and cross-section.
The experimental results show that the low oxygen partial pressure can increase the forming temperature of alumina film, but can form a more compact film with flat surface. Higher oxidation temperature is conducive to the formation of thicker alumina films, but also greatly increases the surface defects.
By in-situ oxidation process at 1.2 Pa-850 ℃-72 h, alumina thin films with good properties can be obtained on the surface of GH3535 alloy: The phase of film contains γ and α, the thickness is about 0.8 μm, and the surface is compact without defects.
