Strain-induced metal-hydrogen interactions across the 1st transition series: An ab initio study of hydrogen embrittlement (original) (raw)
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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.
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.
Engineering Fracture Mechanics, 2019
Component failures due to the hydrogen embrittlement (HE) were observed in different industrial systems, including high-pressure hydrogen storage tanks, aircraft components, high-strength alloy components, and high-strength steel fasteners. The contemporary approach in studying the effects of hydrogen on the mechanical properties of steels and iron at different scales is based on the implementation of various multiscale (macro, micro-meso, and nano-atomic) modeling approaches and the applications of advanced experimental methods. A large number of contemporary studies confirmed the multiple effects and activity of different HE mechanisms in steels and iron. The coexistence and synergistic activity-concurrent action and effects in a cooperative manner of different HE mechanisms, including the hydrogen-enhanced localized plasticity (HELP) and the hydrogen-enhanced decohesion (HEDE), were recently detected and confirmed through computations-simulations, as well as experimentally in different grades of steel. However, the critical evaluation and quantification of synergy between the HELP and HEDE mechanisms, enhanced plasticity and decohesion, hydrogen-deformation/dislocation interactions and their simultaneous effect on the mechanical properties (hardening and softening), still do not exist. In this review paper, the multifaceted nature of the synergistic interplay of HE mechanisms is covered through extensive literature overview regarding the chronological development of ideas related to the HELP + HEDE concept and HELP mediated HEDE model. The particular emphasis is given to the proposal of the novel and unified HELP + HEDE model based on the specific microstructural mapping of the dominant HE mechanisms with implications on the fracture process and resulting hydrogen-assisted fracture modes. Most of up-to-date experimental and modeling approaches, current trends and future challenges in the investigation of the synergistic interplay of HE mechanisms in different grades of steel, including the most advanced, and iron, are also included and critically discussed.
Acta Materialia, 2004
We propose that the ideal fracture energy of a material with mobile bulk impurities can be obtained within the framework of a Born-Haber thermodynamic cycle. We show that such a definition has the advantage of initial and final states at equilibrium, connected by well-defined and measurable energetic quantities, which can also be calculated from first principles. Using this approach, we calculate the ideal fracture energy of metals (Fe and Al) in the presence of varying amounts of hydrogen, using periodic density functional theory. We find that the metal ideal fracture energy decreases almost linearly with increasing hydrogen coverage, dropping by $45% at one-half monolayer of hydrogen, indicating a substantial reduction of metal crystal cohesion in the presence of hydrogen atoms and providing some insight into the cohesion-reduction mechanism of hydrogen embrittlement in metals.
Hydride-induced embrittlement and fracture in metals—effect of stress and temperature distribution
Journal of the Mechanics and Physics of Solids, 2002
A mathematical model for the hydrogen embrittlement of hydride forming metals has been developed. The model takes into account the coupling of the operating physical processes, namely: (i) hydrogen di usion, (ii) hydride precipitation, (iii) non-mechanical energy ow and (iv) hydride=solid-solution deformation. Material damage and crack growth are also simulated by using de-cohesion model, which takes into account the time variation of energy of de-cohesion, due to the time-dependent process of hydride precipitation. The bulk of the material, outside the de-cohesion layer, is assumed to behave elastically. The hydrogen embrittlement model has been implemented numerically into a ÿnite element framework and tested successfully against experimental data and analytical solutions on hydrogen thermal transport (in: Wunderlich, W.
DEFORMATION BEHAVIOR IN MATERIALS SUSCEPTIBLE TO HYDROGEN EMBRITTLEMENT
ABSTRACT The effects of dissolved hydrogen on dislocation motion in stainless steel have been studied in an attempt to understand how hydrogen impacts deformation, which is important for understanding hydrogen embrittlement in these alloys. Indentation tests of stainless steels before and immediately after exposure to high hydrogen gas pressures have been conducted to examine the effects of dissolved hydrogen on indentation induced slip steps.
Ab-initio calculations of hydrogen embrittlement in high strength steels
2011
Hydrogen embrittlement is believed to be one of the main reasons for cracking of metals under stress. High strength steels in these structures often include a ferritic core made of alpha-iron (body centered cubic lattice). Previous work was concerned with the interaction of atomic hydrogen with iron using first principles calculations. We studied the effect of interstitial hydrogen in the iron lattice and the stress induced by the interstitial hydrogen in the host lattice. In this paper we show the dynamical behaviour of hydrogen inside the iron lattice. Using abinitio Molecular Dynamics and by taking statistical averages diffusion coefficients hydrogen diffusion paths are obtained. Depending on temperature, the diffusion path involve going through tetrahedral or octahedral sites. Simulations where a number of hydrogens occasionally meet in one unit cell have been performed to elucidate the effect of interactions between hydrogens. From simulated diffusion path, the diffusion coeffi...
We investigated the hydrogen distribution and desorption behavior in an electrochemically hydrogen-charged binary NieNb model alloy to study the role of d phase in hydrogen embrittlement of alloy 718. We focus on two aspects, namely, (1) mapping the hydrogen distribution with spatial resolution enabling the observation of the relations between desorption profiles and desorption sites; and (2) correlating these observations with mechanical testing results to reveal the degradation mechanisms. The trapping states of hydrogen in the alloy were globally analyzed by Thermal Desorption Spectroscopy (TDS). Additionally, spatially resolved hydrogen mapping was conducted using silver decoration, Scanning Kelvin Probe Force Microscopy (SKPFM) and Secondary Ion Mass Spectrometry (SIMS): The Ag decoration method revealed rapid effusion of hydrogen at room temperature from the g-matrix. The corresponding kinetics was resolved in both, space and time by the SKPFM measurements. At room temperature the hydrogen release from the g-matrix steadily decreased until about 100 h and then was taken over by the d phase from which the hydrogen was released much slower. For avoiding misinterpretation of hydrogen signals stemming from environmental effects we also charged specimens with deuterium. The deuterium distribution in the microstructure was studied by SIMS. The combined results reveal that hydrogen dissolves more preferably inside the g-matrix and is diffusible at room temperature while the d phase acts as a deeper trapping site for hydrogen. With this joint and spatially resolving approach we observed the microstructure-and time-dependent distribution and release rate of hydrogen with high spatial and temporal resolution. Correlating the obtained results with mechanical testing of the hydrogen-charged samples shows that hydrogen enhanced decohesion (HEDE) occurring at the d/matrix interfaces promotes the embrittlement.
Hydride-Induced Embrittlement in Metals — Stress and Temperature Effects
Solid Mechanics and its Applications, 2003
A robust mathematical model for the hydrogen embrittlement of hydride forming metals has been developed. The model takes into account the coupling of the operating physical processes, namely: (i) hydrogen diffusion, (ii) hydride precipitation, (iii) non-mechanical energy flow, and (iv) hydride/solid-solution deformation. Crack growth is simulated by using a new version of de-cohesion model with time-dependent energy of de-cohesion due to the gradual process of hydride formation. Zircaloy-2 hydrogen embrittlement and fracture initiation have been studied by using a finite element implementation of the model. Delayed hydride cracking has been considered in two configurations: (i) a semi-infinite crack, under mode-I K-field dominance and constant temperature, and (ii) a cracked plate, under tensile stress and temperature gradient. The initial and boundary conditions, in case (ii), are those encountered in the fuel cladding of boiling water reactors, during operation, and lead to loss of K-field dominance soon after the application of loading. The numerical simulation predicts hydride precipitation at some distance from the crack tip. The near-tip hydride platelets fracture, when the remote loading is sufficiently strong, and leave behind ligaments, which are stretched plastically, in agreement with experimental observations. The numerical results on hydride size, incubation period and crack growth velocity are compared with experimental data. Further development of the model should be combined with accurate experimental determination of the mechanical and thermal properties of the hydrides.