Ultra-high permeation reduction factor obtained by oxidizing a silicon-containing RAFM steel

Developing barrier coatings with high resistance to hydrogen isotope permeation in the structural materials of fusion reactor blankets is a critical priority. In this work, we propose a novel approach to address this challenge by utilize the oxide layer of a modified Reduced Activation Ferritic-Martensitic (RAFM) steel after proper oxidization process. The SIMP steel, which contains 1.43% silicon and 10.8% chromium, is distinguished from the 9% chromium CLF-1 steel by its additional silicon. Gas-driven permeation (GDP) experiments show that, after oxidation at 700 °C in air for 30 h, the SIMP steel forms an oxide layer with a thickness of approximately 100 nm. Deuterium GDP tests reveal a permeation reduction factor (PRF) of 2 × 104 at 560 °C for oxidized SIMP steel, compared to a PRF of approximately 100 for oxidized CLF-1 steel. This high PRF is attributed to the dense Cr–Mn oxide layer due to the presence of Si, independent of the substrate heat treatment, as confirmed by microstructural analysis. Following irradiation with Au ions up to 12 dpa, the PRF of the oxidized SIMP steel decreases by less than one order of magnitude, with partial recovery observed at elevated temperatures. This work provides new insight into the development of tritium permeation barriers, highlighting a promising route that combines low activation, cost-effectiveness, and strong manufacturability.