Hydrogen permeation behavior and mechanism of multi-layered graphene coatings and mitigation of hydrogen embrittlement of pipe steel

A method for in situ deposition of multi-layered graphene (MLG) coatings is demonstrated to mitigate hydrogen embrittlement of the X70 pipe steel. Carbon is implanted into the nickel catalytic layer pre-deposited by electroplating on the surface of the pipe steel, followed by annealing to segregate and form MLG. The MLG coatings are investigated systematically with respect to the surface morphology, phase structure, hydrogen resistance, corrosion resistance, and molecular dynamics simulation. In the stacked MLG structure, the in situ grown graphene layers interpenetrate each other to boost the coating adhesion and hydrogen resistance. Diffusion and the solid solution formed between the Ni coating and substrate improve the adhesion strength after annealing. The diffusion coefficient and permeability are reduced by 123 times and 48 times, respectively. Slow strain rate tests demonstrate outstanding resistance against hydrogen embrittlement because the MLG coatings inhibit hydrogen evolution, extend the diffusion path, decrease the permeation area, and enhance hydrogen adsorption. Moreover, electrochemical tests indicate that the MLG coatings have better corrosion resistance. These results reveal a viable strategy to use graphene to protect commercial steels from hydrogen embrittlement.