DS03 - Stimuler le renouveau industriel

Crack initiation in Ni under fatigue and hydrogen flux – CRACKHINIT

Submission summary

One of the elementary physical mechanisms implied at the first stage of corrosion fatigue processes in presence of hydrogen in nickel is investigated during the CRACKHINIT project. Here, we focus on the hydrogen embrittlement phenomenon during fatigue, which has many implications for the durability of metallic structures in the industry and for the sustainable development societal field. The investigated processes are related to the hydrogen-vacancy-surface interactions under stress, which remain unclear. In particular, these interactions can deeply affect the solubility and the diffusion of the solute, but also the formation and the mobility of the vacancies during fatigue through the formation of slip bands at the surface. The study implements both a theoretical approach based on atomic scale calculations conducted within DFT and an experimental part performed on single crystals with cyclic deformation tests under an in situ hydrogen flux or on ex situ H charged materials. Here, the chosen material is fcc nickel for its common applications in the industry and it is widely studied in our laboratory. The surface and the subsurface layers of the material after fatigue tests are characterized in terms of density of defects and roughness (i.e, the height of the slip band at the surface). The vacancy and hydrogen concentrations and the diffusion coefficients of the particles are determined for several deformation states and/or hydrogen fluxes in the subsurface layers within calorimetric and electrochemical techniques. The atomic scale calculations are conducted at finite temperature on supercells based on the lattice repetition of the conventional Ni fcc structure to investigate the energetics of H and vacancy concentrations and diffusion on the (100), (110) and (111) surfaces and on their subsurface layers. The temperature is taken into account from the calculations of the free energy from a sum of vibration and electronic excitations contributions. Additional calculations are conducted to take into account the effects of a stress state and the formation of steps at the surface, which represent the first stage of the emergence of the slip bands. The comparison between the experiments and the DFT calculations put in forward the most influent parameter (surface state, stress state, height of the slip band) affecting the H diffusion and solubility but also the formation and mobility of vacancies during fatigue. The expected results can be used to develop new macroscopic models and to define criteria on the initiation of cracks and damage in situations of corrosion – fatigue in presence of hydrogen. These models and criteria help to define new metallurgical states tolerant to H embrittlement and can be transferred to the industry in the future.

Project coordinator

Monsieur Arnaud METSUE (Laboratoire des Sciences de l'Ingénieur pour l'Environnement)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LaSIE Laboratoire des Sciences de l'Ingénieur pour l'Environnement

Help of the ANR 207,360 euros
Beginning and duration of the scientific project: - 48 Months

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