Enhanced hydrogen resistance of X70 pipeline steels by adaptive growth of NiCr composite coatings with Cr/Fe_xNi_y inlaid structures

Elucidating the relationship between the structure of metallic hydrogen permeation barriers and their hydrogen resistance is crucial to reducing hydrogen embrittlement. In this study, four groups of NiCr coatings with different ratios of Ni and Cr are fabricated on X70 pipeline steels by magnetron co-sputtering and annealing. The diffusion behavior of the coating elements, microstructure of the NiCr coatings, and coating formation mechanism are investigated. An adaptively grown structure with an upper Cr₂O₃ layer, outer Fe-Ni-Cr layer, and inner Fe-Ni layer is formed after annealing. The Fe-Ni-Cr layer has a Cr/Fe_xNi_y inlaid structure, and the Cr/Fe_xNi_y interfaces form hydrogen traps to reduce the hydrogen permeability by 204 times compared to the uncoated substrate. The evolution of microstructure after electrochemical hydrogen charging proves that the NiCr coatings have excellent resistance against hydrogen-induced cracking. A larger Cr concentration improves the mechanical properties and corrosion resistance of the NiCr coatings. The results reveal the effects of the Cr/Fe_xNi_y interfaces and metal-H bonds with regard to hydrogen resistance and also provide insights into the design and preparation of metallic hydrogen permeation barriers on steels. © 2024 Elsevier B.V.