Hydrogen Embrittlement Along Grain Boundaries in Nickel Based on MD Simulation PDF Download
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Author:
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Languages : en
Pages : 17
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Author:
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Languages : en
Pages : 17
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Author: Wesley Allen Barrows
Publisher:
ISBN: 9781321959956
Category : Fracture mechanics
Languages : en
Pages : 136
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Book Description
The deleterious effects of atomic and molecular hydrogen on the mechanical properties of metals have long been observed. Although several theories exist describing the mechanisms by which hydrogen negatively influences the failure of materials, a consensus has yet to be reached regarding the exact mechanism or combination of mechanisms. Two mechanisms have gained support in explaining hydrogen's degradative role in non-hydride forming metals: hydrogen-enhanced localized plasticity and hydrogen-enhanced decohesion. Yet, the interplay between these mechanisms and microstructure in metallic materials has not been explained. Accordingly, for this thesis, the three main objectives are: (i) to develop a numerical methodology to extract traction-separation relationships from atomistic simulation data during steady-state crack propagation along a grain boundary, building upon prior work employing atomistic cohesive zone volume elements (CZVEs); (ii) to apply the numerical methodology to specific grain boundary systems with different amounts of hydrogen located at the grain boundary interface; (iii) to further the understanding, based on the traction-separation relationships, of the mechanisms by which hydrogen effects the decohesion of a grain boundary system. A range of symmetric tilt grain boundaries in Ni are studied, with hydrogen coverages and favorable sites for hydrogen segregation motivated by Monte Carlo calculations. A sensitivity analysis is performed on the CZVE approach, clarifying the role of CZVE size and numerical parameters necessary to differentiate elastic and decohesion data. Results show that increasing hydrogen coverage can asymmetrically influence crack tip velocity during propagation, leads to a general decrease in the work of separation and promotes a reduction in the peak stress in the extracted traction-separation relationships, though these trends are dependent on the grain boundary structures.
Author:
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Category :
Languages : en
Pages : 14
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Author:
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Category :
Languages : en
Pages : 11
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Author:
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ISBN:
Category :
Languages : en
Pages : 11
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Book Description
A statistical approach combined with molecular dynamics simulations is used to study the influence of hydrogen on intergranular decohesion. This methodology is applied to a Ni ?3(112)[11¯0] symmetric tilt grain boundary. Hydrogenated grain boundaries with different H concentrations are constructed using an energy minimization technique with initial H atom positions guided by Monte Carlo simulation results. Decohesion behavior is assessed through extraction of a traction–separation relationship during steady-state crack propagation in a statistically meaningful approach, building upon prior work employing atomistic cohesive zone volume elements (CZVEs). A sensitivity analysis is performed on the numerical approach used to extract the traction–separation relationships, clarifying the role of CZVE size, threshold parameters necessary to differentiate elastic and decohesion responses, and the numerical averaging technique. Results show that increasing H coverage at the Ni ?3(112)[11¯0] grain boundary asymmetrically influences the crack tip velocity during propagation, leads to a general decrease in the work of separation required for crack propagation, and provides a reduction in the peak stress in the extracted traction–separation relationship. Furthermore the present framework offers a meaningful vehicle to pass atomistically derived interfacial behavior to higher length scale formulations for intergranular fracture.
Author: Siegfried Schmauder
Publisher: Springer
ISBN: 9789811068836
Category : Science
Languages : en
Pages : 0
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Book Description
This book provides a comprehensive reference for the studies of mechanical properties of materials over multiple length and time scales. The topics include nanomechanics, micromechanics, continuum mechanics, mechanical property measurements, and materials design. The handbook employs a consistent and systematic approach offering readers a user friendly reference ideal for frequent consultation. It is appropriate for an audience at of graduate students, faculties, researchers, and professionals in the fields of Materials Science, Mechanical Engineering, Civil Engineering, Engineering Mechanics, and Aerospace Engineering.
Author: Anthony W. Thompson
Publisher: John Wiley & Sons
ISBN: 1118803272
Category : Technology & Engineering
Languages : en
Pages : 1090
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Book Description
Proceedings of the Fifth International Conference on the Effect of Hydrogen on the Behavior of Materials sponsored by the Structural Materials Division (SMD) Mechanical Metallurgy and Corrosion & Environmental Effects Committees of The Minerals, Metals & Materials Society held at Jackson Lake Lodge, Moran, Wyoming, September 11-14, 1994.
Author: John Paul Hanson (Ph. D.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 196
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Book Description
Hydrogen embrittlement of engineering alloys is characterized by a loss of ductility and unpredictable failure. These failures affect numerous industries, including nuclear power, oil and gas exploration, and hydrogen transportation and storage. In face-centered cubic alloys, the resultant fracture is intergranular and very sensitive to grain boundary character. We study this behavior in alloy 725, a popular nickel-iron superalloy with high strength and corrosion resistance. Using a suite of complementary experimental techniques we reveal the fracture behavior of individual grain boundaries in hydrogen embrittlement for the first time, providing critical understanding of the role of grain boundary character and informing improved microstructure design. We study crack propagation in hydrogen embrittled tensile test specimens using highenergy diffraction-microscopy, a non-destructive X-ray synchrotron technique capable of mapping grain boundaries in 3-D. We find that boundaries with low-index planes (BLIPs), defined as planes within 10° of [111], [110] or [100], resist crack propagation and improve toughness. We show that coherent twin boundaries (CTBs), a subset of BLIPs, also indirectly improve toughness by increasing the heterogeneity of the grain boundaries they intersect. In addition, we use electron backscatter diffraction and scanning electron microscopy to identify the grain boundaries along which cracks initiate and propagate on the sample surface. We unambiguously show that grain boundaries are the source of crack initiation, and we study a statistically significant number of cracking events, providing the ability to determine the role of grain boundary character. Surprisingly, we find that while CTBs resist crack propagation, they preferentially initiate cracks. These results inform a more nuanced approach to microstructure design. Typically grain boundary engineering techniques aim to maximize the fraction of low-S boundaries as designated by the coincident site lattice model. Our results suggest that these techniques should maximize the fraction of BLIPs instead. In addition, the dual nature of CTBs suggests the development of graded microstructures, with high concentrations of CTBs in the interior to resist crack propagation and reduced concentrations at the surface to limit crack initiation.
Author: Pavel Lejcek
Publisher: Springer Science & Business Media
ISBN: 3642125050
Category : Technology & Engineering
Languages : en
Pages : 249
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Book Description
Grain boundaries are important structural components of polycrystalline materials used in the vast majority of technical applications. Because grain boundaries form a continuous network throughout such materials, their properties may limit their practical use. One of the serious phenomena which evoke these limitations is the grain boundary segregation of impurities. It results in the loss of grain boundary cohesion and consequently, in brittle fracture of the materials. The current book deals with fundamentals of grain boundary segregation in metallic materials and its relationship to the grain boundary structure, classification and other materials properties.
Author: D. H. Lassila
Publisher:
ISBN:
Category :
Languages : en
Pages : 15
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Book Description
Grain boundary fracture of hydrogen-charged nickel was studied under test conditions where hydrogen is essentially immobile. Prior to testing, hydrogen was allowed to diffuse during aging treatments. Experimental results show that the transition in the fracture mode from ductile rupture to intergranular is strongly dependent on aging temperature an time as well as initial bulk hydrogen concentration. Analytical modeling of these dependencies using established thermodynamic and kinetic relationships, indicates that grain boundary hydrogen concentration controls the fracture mode of hydrogen-charged nickel at low temperatures.
