Mechanics of hydrogen-dislocation-impurity interactions: part 1- increasing shear modulus

The effect of hydrogen on dislocation-dislocation and dislocation-impurity atom interactions is studied under conditions where hydrogen is in equilibrium with local stresses and in systems where hydrogen increases the shear modulus. In the case of two edge dislocations (plain strain) the effect of hydrogen is modeled through a continous distribution of dilatation lines whose strength depends on the local hydrogen concentration. The hydrogen distribution in the atmospheres is adjusted to minimize the energy of the system as the dislocations approach each other. The iterative finite element analysis used to calculate the hydrogen distribution accounts for the stress relaxation associated with the hydrogen induced volume and the elastic moduli changes due to hydrogen. The interactions between the dislocations are calculated accounting for all the stress fields due to dislocations and hydrogen atmospheres. An analytical formula is suggested for the hydrogen induced reduction in the magnitude of the shear stress exerted between the dislocations along the slip system. Modeling of the hydrogen effect on the edge dislocation-interstitial solute atom interaction is discussed using a finite element analysis and a formula is developed for the calculation of the dislocation-solute atom interaction energy in the presence of hydrogen. In this paper the numerical results are presented for the case where hydrogen increases the shear modulus of the metallic system. A significant decrease of the edge dislocation-intersititial solid atom interaction energy was observed when the dislocation-solute distance is approximately less than 2 Burgers vectors. This can be attributed almost entirely to the modulus change due to hydrogen. The effect of hydrogen on the screw dislocation-intersitial solute interaction was investigated. Numerical results indicate that, depeneding on the orientation of the tetragonal axis of the carbon distortion field, hydrogen may strengthen or weaken the interaction. The present model provides strong support for the hydrogen shielding mechanism wherby hydrogen diminishes the local stress fields from dislocation and solutes which act as barriers to the dislocation motion

Challenges toward achieving a successful hydrogen economy in the US: Potential end-use and infrastructure analysis to the year 2100

Fossil fuels continue to exacerbate climate change due to large carbon emissions resulting from their use across a number of sectors. An energy transition away from fossil fuels seems inevitable, and energy sources such as renewables and hydrogen may provide a low carbon alternative for the future energy system, particularly in large emitting nations such as the United States. This research quantifies and maps potential hydrogen fuel distribution pathways for the continental US, reflecting technological changes, barriers to deployment, and end-use-cases from 2020 to 2100, clarifying the potential role of hydrogen in the US energy transition. The methodology consists of two parts, a linear optimization of the global energy system constrained by carbon reduction targets and system cost, followed by a projection of hydrogen infrastructure development. Key findings include the emergence of trade pattern diversification, with a greater variety of end-uses associated with imported fuels and greater annual hydrogen consumption over time. Further, sensitivity analysis identified the influence of complementary technologies including nuclear power and carbon capture and storage technologies. We conclude that hydrogen penetration into the US energy system is economically viable and can contribute toward achieving Paris Agreement and more aggressive carbon reduction targets in the future

In-Situ TEM study of the effect of hydrogen on crack propagation in steel

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Understanding Fundamental Material Degradation Processes in High Temperature Aggressive Chemomechanical Environments

The objective of this project is to develop a fundamental understanding of the mechanisms that limit materials durability for very high-temperature applications. Current design limitations are based on material strength and corrosion resistance. This project will characterize the interactions of high-temperature creep, fatigue, and environmental attack in structural metallic alloys of interest for the very high-temperature gas-cooled reactor (VHTR) or Next–Generation Nuclear Plant (NGNP) and for the associated thermo-chemical processing systems for hydrogen generation. Each of these degradation processes presents a major materials design challenge on its own, but in combination, they can act synergistically to rapidly degrade materials and limit component lives. This research and development effort will provide experimental results to characterize creep-fatigue-environment interactions and develop predictive models to define operation limits for high-temperature structural material applications. Researchers will study individually and in combination creep-fatigue-environmental attack processes in Alloys 617, 230, and 800H, as well as in an advanced Ni-Cr oxide dispersion strengthened steel (ODS) system. For comparison, the study will also examine basic degradation processes in nichrome (Ni-20Cr), which is a basis for most high-temperature structural materials, as well as many of the superalloys. These materials are selected to represent primary candidate alloys, one advanced developmental alloy that may have superior high-temperature durability, and one model system on which basic performance and modeling efforts can be based. The research program is presented in four parts, which all complement each other. The first three are primarily experimental in nature, and the last will tie the work together in a coordinated modeling effort. The sections are 1) dynamic creep-fatigue-environment process, 2) subcritical crack processes, 3) dynamic corrosion – crack initiation processes, and 4) modeling

Effect of hydrogen on creep properties of SUS304 austenitic stainless steel

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Mechanistic model for hydrogen accelerated fatigue crack growth in a low carbon steel

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A combined micromechanics/materials science approach to understanding high temperature hydrogen attack

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Towards next generation, low cost, hydrogen resilient austenitic steels: Relating composition, microstructure and deformation modes across length

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Atomistic scale experimental observations and micromechanical/continuum models for the effect of hydrogen on the mechanical behavior of metals

In-situ deformation studies in a transmission electron microscope equipped with an environmental cell have shown that solute hydrogen increases the velocity of dislocations, decreases the stacking-fault energy, and increases the stability of edge character dislocations. Theoretical modeling has established that the hydrogen atmospheres formed at dislocations through the elastic interaction cause a change in the stress field of the dislocationhydrogen complex in such a manner as to reduce the interaction energy between it and other elastic obstacles. Consequently, solute hydrogen increases the mobility of dislocations, which will be localized to regions of high hydrogen concentration. On the basis of this material softening at the microscale, a solid mechanics analysis of the hydrogen solute interaction with material elastoplasticity demonstrates that localization of the deformation in the form of bands of intense shear can occur at the microscale. Thus, the present combined experimental and numerical/analytical results provide a clear explanation for the hydrogen-enhanced localized plasticity mechanism of hydrogen embrittlement.published or submitted for publicationis not peer reviewe

Linearized hydrogen elasticity

The general principles of the mechanics and therodynamics of materials are used to describe the effects of interstitial mobile hydrogen on the mechanical behavior of metals and alloys. First the coupled general field equations accounting for hydrogen diffusion and nonlinear deformation are derived and then linearized for the case of small deformation. Linearization reveals that the Laplacian of the hydrostatic stress is related to the Laplacian of the hydrogen concentration in the lattice, and it is not zero, as has often been assumed in calculations involving stress driven diffusion of hydrogen under plane strain conditions. When the hydrogen is in equilibrium with the applied stress, that is, at steady state conditions of hydrogen transport, the linear elastic constitutive response of the solid accounting for the hydrogen effect can be described by the standard Hooke's law of infinitesimal elasticity in which the stiffness moduli are termed moduli at fixed solute chemical potential and are calculated in terms of the moduli at fixed solute composition, the nominal hydrogen concentration, and the material parameters of the system. These moduli at fixed solute chemical potential can be viewed as the corresponding counterparts of those characterizing the drained deformation at constant pressure of fluid-infiltrated porous geomaterials, or the isentropic deformation of thermoelastic materials. Next the linear transient field equations are solved in the case of a dislocation and a line force in an infinite medium under plane strain conditions by using analytic function theory. The range of validity of the solution to the linearized field equations for an isolated edge dislocation is investigated for specific materials. Lastly, the implications of the steady state constitutive behavior of the hydrogen/metal system on the fracture and dislocation behavior are discussed.Energy Department 93/0