HYDROGEN AND MATERIALS - Fragility, Stresses and Corrosion
MORE THAN 130 PARTICIPANTS!
H, so small and still so exciting, HYDROGENE was the central axis of the days organized by the office of A3TS Ile de France on February 3 and 4, 2016, at the Lycée technique Diderot, which we thank in passing for the technical support it has shown. This event brought together 130 people from very diverse backgrounds (Aerospace, Fasteners, Automotive, Energy, Armament, Contract caterers, Steel industry, TS Formulators, Experts, Technical Center, the University world, ...) in the image of the topics addressed during the three half-days each devoted to the interaction hydrogen and metallic materials for different approaches.
We would like to thank all of the speakers for the quality and content of their presentations, which made this conference a success.
These ½ days allowed us to address:
1 . The embrittlement of metallic materials in a hydrogenated environment with the presentations of :
O. BARDOU (AIR LIQUIDE) devoted to the characterization of the behavior of hydrogen storage materials under pressure. This characterization for pressures ranging from 500 to 1000 bar, is obtained by comparing the behavior under the same helium pressures. The fracture surfaces are analyzed and show the embrittling effect of hydrogen.
C. DURET (IFC St Etienne) dealing with the embrittlement associated with the corrosion, in a sulphide environment (H2S) of low alloy steels, stainless steels and nickel base alloys, characterized by the HIC (Hydrogen Induced Cracking) behaviors where, in the absence of stress, the embrittlement is linked to the production of hydrogen by cathodic dissociation of H2S and SSC (Sulphide Stress Cracking) . Under stress, a corrosion effect due to sulfur leads to a reduction of the K1C. The test methods are presented and the mechanisms explained.
F. VUCKO (IFC Brest) considering the CSC stress corrosion behavior of galvanized high yield strength steels (up to Rm =1000 MPa) intended for the realization of car bodies, on which hydrogen can come from the implementation conditions (welding, surface treatments). The hydrogen entry process is characterized by a Kelvin probe. The sensitivity to hydrogen embrittlement from either galvanic coupling with the sacrificial coating (Zn) and the accumulation of iron corrosion products with local acidification is demonstrated. This finding reinforces the need for effective reinforcement solutions against corrosion.
A. DI RIENZO (SNCT) was interested in the specifications of pressure equipment codes, their monitoring and identification of damage related to hydrogenation.
L. GAILLET (IFSTTAR) approached corrosion under stress in civil engineering with the problem of the embrittlement of prestressed cables, the influence of the composition of concrete is described as well as the modes of degradation in particular in CSC according to the coupling material-protection-medium.
2 . Hydrogen in crystal lattices other than cubic-centered :
J. CREUS (LaSIE University of La Rochelle) in a lecture exposed a method of investigation and understanding of the mechanisms at the crystalline scale of cfc metals such as copper and nickel, from a critical experimental approach associating electrochemical permeation (EP) with thermal desorption spectroscopy (TDS) in order to access to the hydrogen trapping energies and the concentrations of hydrogen trapped and desorbed. The author develops the influence of grain boundaries on hydrogen diffusivity and the effects on gap creation and dislocation evolution.
S. PUYDEBOIS (SNECMA ) showed the influence of hydrogen on a nickel alloy, Inconel 718, produced by additive metallurgy, by carrying out electrochemical and gaseous permeations in order to determine the diffusion and solubility coefficients for different temperatures and pressures. Slow tensile and low cycle fatigue behaviors were compared between tests in air and under 300 bar of hydrogen.
C. BLANC (ENSIACET ) considers the FPH of an aluminum alloy of the 7000 family without copper (all. AlMgZn, 7046 in T4 condition Rm = 600 MPa) The study concerns the influence of microstructural parameters (nature of intermetallic precipitates Al3Fe, Al3Ti, dispersoids Al3Zr, intergranular MgZn2) on stress corrosion and sensitivity to FPH in 0.6M NaCl medium under tensile stress at 80%Rp0.2 for different durations prior to tensile fracture in air. The fractographies are identified in relation with the chemical and microstructural phenomena. The study is extended by the same study of the alloy in the T7 state.
V. DUQUESNES (VALLOUREC) described the hydrogenation of a T40 titanium alloy (hc structure) leading to the formation of a TiH2 hydride layer on the surface and to hydride precipitation from the hydrogen solubility in titanium. Tests of CSC behaviour are carried out on U-bent specimens maintained in an autoclave (350°C, 150 bar) with or without prehydriding, by cathodic permeation. The mechanical and microstructural behaviors are analyzed.
E. LEGRAND (Mc Gill University) concludes this session with a modeling approach of hydrogen diffusion on notched 4-point bending specimens (ASTM F519), combining the knowledge of mathematical expressions of Fick's laws of diffusion and finite element modeling.
3 . Chemical and electrolytic surface treatments and FPH in high strength steels.
E. LEGRAND and S. BRAHIMI (MC GILL University) have characterized the hydrogen diffusion during zinc deposition and its mechanical consequences in the perspective of cadmium substitution.
F. RAULIN (COVENTYA) presented the state of standardization related to hydrogen in electrolytic coatings for corrosion protection.
V. ROSCOL (MESSIER BUGATTI), still with a view to replacing cadmium deposits, discusses H loading during the production of a 12-16% Zn-Ni deposit observed using the characterization techniques already mentioned by the other speakers: electrochemical permeation, thermodesorption spectroscopy, mechanical tests. The interest of a degassing treatment at 190°C for 23 h is explored for Cd.
A. FLEURENTIN (METALLO CORNER) has shown that the susceptibility to brittle intergranular failure by FHP of a material is enhanced by all the parameters intervening throughout the manufacturing process of a product, such as chemical composition, heat treatment. All conditions affecting the ductility have a direct effect on the FHP.
H. MORILLOT and A. OUDRISS (CETIM and LaSIE) have characterized the hydrogen damage on 6 martensitic steel grades by observing the different fracture faces according to the degassing conditions and the stress concentration values (Kt) of the tested specimens. An embrittlement index is defined from the section at fracture, directly correlated to the maximum of the degassed hydrogen flux suggesting that the damage vector is not only dependent on the concentration but also on its mobility.
The first feedback that we have been able to have allows us to say that these days are a success both at the technical level and at the level of human meetings that have animated this event, so we give you an appointment in 3 to 4 years for a new session on this subject.
But in the meantime, in February 2017, we will organize days on the theme of residual stresses both in forming processes and in thermal and mechanical operations to strengthen the fatigue life of mechanical parts.
