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Physical mechanisms associated with hydrogen consequences on plasticity mechanisms in nickel single crystals: some antagonists process

le 6 janvier 2022
à 13h30

Xavier Feaugas, Directeur du laboratoire LaSIE

Xavier FEAUGAS

Xavier FEAUGAS

Résumé/Abstract :

One of the fundamental aspects of hydrogen embrittlement is based on the consequences of the solute on the elementary mechanisms of plasticity [1]. Recently we have highlighted that the hydrogen-induced microplasticity antagonistic processes is a key feature to improve the resistance to hydrogen embrittlement [1-5]. In this work, the impact of hydrogen on elastic modulus, elementary processes (emission, mobility etc.) associated with dislocation, global behavior and internal stresses are investigated in nickel single crystals. We focused on the impacts of strain rate and hydrogen concentration on the hardening rate. The impact of hydrogen on the monotonic and cyclic plasticity of <001> oriented nickel single crystal was investigated using loading and unloading tests and nanoindentation. Static and dynamic nanoindentations were performed on undeformed and pre-strained samples with and without hydrogen. The indented surfaces were analyzed by SEM-FIB, EBSD and TEM to characterize the development of dislocation structures and any other defects and hence to establish the hydrogen-plasticity correlation near surface. Hydrogen induced impact on maximum shear stress to activate dislocations, hardness and elastic modulus was observed in static nanoindentation experiment. The long-range internal stresses developed in the hydrogen charged samples during the dynamic nanoindentation were compared to the results of TEM (dislocation density) and cyclic micro-tensile test (effective and back stresses). A competition between cyclic hardening/softening was observed with and without hydrogen, attributed to the hydrogen induced differences in the development of dislocation structures and subsequent internal stresses. Both can be correlated with hydrogen and/or vacancies clusters formation. Based on atomistic calculations we have commented and elucidated some fundamentals mechanisms in relation with experimental results.

Keywords: hardening rate, dislocation pattern, internal stresses, vacancies, nano-indentation.


[1] X. Feaugas, D. Delafosse, chapter 9 - Hydrogen and Crystal Defects Interactions: Effects on Plasticity and Fracture, Editor(s): Christine Blanc, Isabelle Aubert, Mechanics - Microstructure - Corrosion Coupling, Elsevier, (2019) 199-222.
[2] M.A. Ghermaoui, A. Oudriss, A. Metsue, R. Milet, K. Madani, X. Feaugas, A multiscale approach of hydrogen induced softening on f.c.c. nickel single crystal oriented for multi-slips: elastic screening effect, Scientific Report, 9(1) (2019) 13042
[3] G. Hachet, A. Oudriss, A. Barnoush, R. Milet, D. Wan, A. Metsue, X. Feaugas, Impact of hydrogen on the cyclic behaviour of <001> oriented nickel single crystal. Part I: Dislocations organisations and internal stresses, Int.  J. of Plasticity,126 (2020) 102611.
[4] Hachet, A. Metsue, A. Oudriss, X. Feaugas Impact of hydrogen on the cyclic behaviour of <001> oriented nickel single crystal. Part II: Numerical investigation of edge dislocation dipoles stability Int.  J. of Plasticity, 129 (2020) 102667.
[5] G. Hachet, A. Oudriss, A. Barnoush, T. Hajilou, D. Wang, A. Metsue, X. Feaugas, Antagonist softening, and hardening effects of hydrogen investigated using nanoindentation on cyclically pre-strained nickel single crystal, Materials Science and Engineering: A, 803 (2021) 140480.
Type :
Séminaires - conférences
Lieu(x) :
ENS Paris-Saclay
Amphithéâtre  Dorothy Hodgkin - 0I10

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