Preparation of tritium permeation barrier consisting of titanium by the pack cementation method

•Tritium permeation barriers were prepared simultaneously with the heat treatment of matrix steels.•A three-layered structure coating was obtained.•The three-layered structure coating exhibited a good barrier properties against hydrogen penetration.

In this work, tritium permeation barriers were prepared on the surface of super-clean reduced activation martensitic (SCRAM) steel by the pack cementation method. The pack cementation process was conducted by packing samples in a powder mixture consisting of titanium, ammonium chloride and alumina powder at 1000 °C for 30 min to form a titanized coating. Subsequently, the samples were nitrided in an ammonium atmosphere and then oxidized in air at 760 °C for 1 h to obtain a multilayered structure. The results showed that the as-prepared titanized coatings consisted of two layers. The exterior layer was made of TiN and the interior layer was a diffusion layer resulting from titanium atoms diffusing into the substrate. After being nitrided and then oxidized, the coatings were discovered to have transformed into a three-layered structure. The outer layer was rutile TiO2, the middle layer was Ti-N and the inner layer was Ti-C. Hydrogen permeation tests were performed on the coatings and pure matrix steels at room temperature. The results revealed that the three-layered structure coatings exhibited good barrier properties against hydrogen penetration. This three-layered structure coating may be a good material to increase the hydrogen permeation resistance of SCRAM steel.