The interaction of hydrogen with dislocation in iron (original) (raw)
Related papers
Quantitative tests revealing hydrogenenhanced dislocation motion in α-iron
Nature Materials, 2023
Hydrogen embrittlement jeopardizes the use of high-strength steels in critical load-bearing applications. However, uncertainty regarding how hydrogen affects dislocation motion, owing to the lack of quantitative experimental evidence, hinders our understanding of hydrogen embrittlement. Here, by studying the well-controlled, cyclic, bow-out motions of individual screw dislocations in α-iron, we find that the critical stress for initiating dislocation motion in a 2 Pa electron-beam-excited H2 atmosphere is 27–43% lower than that in a vacuum environment, proving that hydrogen enhances screw dislocation motion. Moreover, we find that aside from vacuum degassing, cyclic loading and unloading facilitates the de-trapping of hydrogen, allowing the dislocation to regain its hydrogen-free behaviour. These findings at the individual dislocation level can inform hydrogen embrittlement modelling and guide the design of hydrogen-resistant steels.
ISIJ International
Explaining the hydrogen effect on dislocation mobility is crucial to revealing the mechanisms of hydrogen-related fracture phenomena. According to the general perspective, reducing the speed of dislocation can give enough time to hydrogen to catch up with the dislocation migration. In this research, we conducted molecular dynamics (MD) simulations to investigate the impact of hydrogen on the edge-dislocation motion in α-iron at various dislocation speeds and temperatures. It was discovered that, for all hydrogen concentrations evaluated in this paper, the hydrogen effect on dislocation transition from pinning to dragging occurs at a dislocation speed of around 0.1 m/s at 300 K. When the dislocation velocity is reduced to 0.01 m/s employing long timescale MD simulations over 1 μs, it is observed that hydrogen follows dislocation motion with small jumps in the dislocation core. The required stress to migrate the edge dislocation at a speed of 0.01 m/s was discovered to be 400 MPa, even at a lower hydrogen concentration, which was achieved in a gaseous hydrogen environment with lower pressure than atmospheric pressure. Although the dislocation still traps hydrogen at 500 K, as temperature increases, the impact of hydrogen on the shear stress required for dislocation glide becomes negligibly small. The required shear stress at lower dislocation speeds was predicted by employing the stress-dependent thermal activation model assuming the hydrogen diffusion rate-determining. The finding demonstrated that the edge dislocation should slow down until 1 mm/s order or less in the presence of hydrogen and suitable stress for α-iron.
Scientific reports, 2013
Employing the empirical embedded-atom method potentials, the evolution of edge and screw dislocation core structure is calculated at different hydrogen concentrations. With hydrogen, the core energy and Peierls potential are reduced for all dislocations. A broaden-core and a quasi-split core structure are observed for edge and screw dislocation respectively. The screw dislocation and hydrogen interaction in body-centred cubic iron is found to be not mainly due to the change of elastic modulus, but the variation of dislocation core structure.
Hydrogen detrapping from grain boundaries and dislocations in high purity iron
Acta Metallurgica et Materialia, 1992
Aima'act-Hydrogen detrapping in high purity iron was studied by measuring evolution rates of quenched-in hydrogen from 80 to 800 K using a quadrupole mass spectrometer in an ultra high vacuum system. The peak of the evolution rate was observed at 395 K in single crystal specimens and 415 K in polycrystalline specimens with a heating rate of 1 K min-i. Effects of grain size and deformation on the evolution rate was also studied. It was shown that the results are consistent with the evolution rates calculated with the binding energy B = 0.51 + 0.02 eV and the trap density term)'Cr = (4 ~ 15) x 10-5 in polycrystalline iron, and B = 0.47 +0.02eV and yCr = (2 ~ 13)x 10-5 in single crystal iron. The dominant traps are considered to be grain boundaries in polycrystalline specimens and dislocations in single crystal specimens. R~sumr-4)n 6tudie le drpart de l'hydrogrne pirg6 dans un fer de haute puret6 en mesurant les vitesses d'rvolution de t'hydrog/:ne fix6 par la trempe entre 80 et 800 K, en utilisant un spectromrtre de masse quadrupolaire dans un systrme ~ ultra vide. Un pic de la vitesse d'rvolution est observ6 ~ 395 K dans les 6chantillons monocristallins et ~i 415 K dans les polycristaux pour une vitesse de chauffage de 1 K min-1 Les effets de la taille du grain et de la drformation sur la vitesse d'rvolution sont aussi 6tudirs. On montre que les rrsultats sont en accord avec les vitesses d'rvolution calculres avee une 6nergie de liaison et un terme de densit6 de pirges de B = 0,51 + 0,02 eV et 7 C:r = (4 ~ 15) x 10-5 dans le fer polycristallin et de B = 0,47 _ 0,02 eV et)'Cr = (2 ~ 13) x 10-5 dans le fer monocristallin respectivement. On considrre que les pirges dominants sont les joints de grains dans les 6chantillons polycristallins et les dislocations dans les monocristaux. Zusammenfassung-Die Freigabe von Wasserstoff aus Fallen in hochreinem Eisen wird mit der Messung der Freigaberaten des eingeschreckten Wasserstoffes zwischen 80 und 800 K mittels eines Quadrupol-Massenspektrometers in einem ultrahohen Vakuum untersucht. Das Maximum der Freigaberate wird bei einer Aufheizrate yon 1 K min-~ an einkristallinen Proben bei 395 K und an polykristallinen Proben bei 415 K beobachtet. Der EinfluB von Korngr6Be und Verformung auf die Freigaberate wird ebenfalls untersucht. Die Ergebnisse sind vertr~iglich mit den Freigaberaten, die sich mit einer Bindungsenergle B = 0,51 + 0,02 eV und dem Term der Fallendichte }'Cr = (4 ~ 15) x 10-5 fiir polykristallines Eisen und mit B = 0,47 __+ 0,02 eV und ~,C T = (2 ~ 13) x 10-5 fiir einkristallines Eisen ergibt. Als vorherrschender Fallentyp werden die Korngrenzen in polykristallinen Proben und Versetzungen in einkristallinen Proben angesehen.
Scripta Materialia, 2013
Effect of hydrogen in body-centered cubic iron is explored by using the density function theory. Hydrogen atoms increase the concentration of free electrons in the simulation cell and have bonding interaction with Fe atom. Caused by anisotropic strain components of hydrogen atoms in the tetrahedral sites, elastic interaction for hydrogen with screw dislocation has been found. The dependence of hydrogen-screw dislocation interaction on hydrogen concentration is confirmed by repeated stress relaxation tests.
Hydrogen effects on tensile property of pure iron with deformed surface
Materials Science and Engineering: A, 2013
To study the interaction of hydrogen and surface structure of iron, two types of tensile test are carried out under hydrogen gas environment and cathodic hydrogen charging condition. According to the tensile tests, hydrogen induces reduction of flow stress (softening) for the specimens without deformed surface, but increase of flow stress (hardening) for the one with deformed surface. The results of jump tests signify that hydrogen enhances the dislocation mobility by reducing the thermal activation volume for overcoming barriers, and because of this, in the samples with smooth surface, homogeneously distributed hydrogen leads to the softening effect. On the other hand, the deformed layer just under the surface has larger solubility of H due to trap sites provided by dislocation cell structures. As a result of hydrogen shielding effect, the strong interaction between dislocations in surface layer and multiplication of new defects causes the hardening effect.
Hydrogen-dislocation interactions and their role in HELP mechanism of hydrogen embrittlement
Effects of hydrogen on elastic interactions in single dislocation dipole and dipole-like dislocation pile-up (DDP) were analysed. It was shown that there is no significant hydrogen shielding of elastic forces in the case of a single dislocation dipole, while hydrogen induces a notable effect on the elastic equilibrium of the DDP. Accumulation of hydrogen between adjacent dislocation pile-ups results in a reduction of external stresses which stabilises DDP. The tensile tests of hydrogen-charged austenitic stainless steel single crystals oriented for easy glide and observed hydrogen-induced strain localization are discussed in terms of such a dynamic softening. It is concluded that HELP takes place at the initial stages of plastic deformation.
Acta Materialia, 2010
This paper summarizes recent work at the University of Illinois on the fundamental mechanisms of hydrogen embrittlement. Our approach combines experimental and theoretical methods. We describe the theoretical work on hydride formation and its application to hydrogen embrittlement of Ti alloys through the stress-induced hydride formation and cleavage mechanism, the localization of shear due to solute hydrogen, and finally, we present experimental evidence that favors the decohesion mechanism of hydrogen embrittlement in a β-Ti alloy.
Numerical simulations of hydrogen–dislocation interactions in fcc stainless steels
Acta Materialia, 2002
The discrete simulation method for hydrogen-dislocation interactions is applied to the study of Stress Corrosion Cracking (SCC). We recall the main results of the experimental study of the fracture micro-crystallography in austenitic stainless steels, along with the successive stages of the Corrosion Enhanced Plasticity Model. Numerical simulations allow the assessment of the critical parameters affecting the model stages. Solute hydrogen promotes the formation of dense dislocation pile-ups, and a 'zigzag' type of fracture along alternating slip planes at the SC crack tip. We provide an analytical expression for the stress field of a dilatation line in the vicinity of a crack, from which we derive all the hydrogen-crack-dislocation elastic interactions terms. Diffusing hydrogen also has a marked pinning effect on a dislocation source at a crack tip. This effect exhibits a strong dependence on the crystal orientation. These results are discussed from the viewpoint of SCC fracture mechanisms.