In-situ oxidation of aluminized stainless-steel to form alumina as tritium permeation barrier coating

Tritium permeation barrier (TPB) coating technology is one of the most effective methods to solve the problem of permeation and leakage of tritium through the structural materials to the coolant, environment, and other functional components in tritium breeder blanket modules (TBMs). Alumina coatings prepared by in-situ oxidation of aluminized steel shows a high permeation reduced factor (PRF) and self-healing ability. However, to eliminate the Al5Fe2 phase in the aluminizing process, the stainless-steel substrate is often heat treated under high temperature conditions for a long time which leads to the degeneration of steel. In this work, a gradient alumina TPB coating was prepared on 316 L stainless steel by aluminizing process at low temperature. The influence of Al5Fe2 on the formation of Al2O3 is studied. The mechanism for the different growth behavior of Al2O3 in the polished and unpolished samples is also discussed. Compared to the polished samples, the existence of porous Al5Fe2 layer in unpolished sample changes the diffusion behavior of Al and leads to the formation of an un-continuous and rough Al2O3 layer.