Hydrogen-enhanced localized plasticity—a mechanism for hydrogen-related fracture
31 Mar 1994-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing (Elsevier BV)-Vol. 176, pp 191-202
TL;DR: In this article, a theory of hydrogen shielding of the interaction of dislocations with elastic stress centres is outlined, which can account for the observed hydrogen-enhanced dislocation mobility.
Abstract: The mechanisms of hydrogen-related fracture are briefly reviewed and a few evaluative statements are made about the stress-induced hydride formation, decohesion, and hydrogen-enhanced localized plasticity mechanisms. A more complete discussion of the failure mechanism based on hydrogen-enhanced dislocation mobility is presented, and these observations are related to measurements of the macroscopic flow stress. The effects of hydrogen-induced slip localization on the measured flow stress is discussed. A theory of hydrogen shielding of the interaction of dislocations with elastic stress centres is outlined. It is shown that this shielding effect can account for the observed hydrogen-enhanced dislocation mobility.
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Abstract: This article presents an overview of the developments in stainless steels made since the 1990s. Some of the new applications that involve the use of stainless steel are also introduced. A brief introduction to the various classes of stainless steels, their precipitate phases and the status quo of their production around the globe is given first. The advances in a variety of subject areas that have been made recently will then be presented. These recent advances include (1) new findings on the various precipitate phases (the new J phase, new orientation relationships, new phase diagram for the Fe–Cr system, etc.); (2) new suggestions for the prevention/mitigation of the different problems and new methods for their detection/measurement and (3) new techniques for surface/bulk property enhancement (such as laser shot peening, grain boundary engineering and grain refinement). Recent developments in topics like phase prediction, stacking fault energy, superplasticity, metadynamic recrystallisation and the calculation of mechanical properties are introduced, too. In the end of this article, several new applications that involve the use of stainless steels are presented. Some of these are the use of austenitic stainless steels for signature authentication (magnetic recording), the utilisation of the cryogenic magnetic transition of the sigma phase for hot spot detection (the Sigmaplugs), the new Pt-enhanced radiopaque stainless steel (PERSS) coronary stents and stainless steel stents that may be used for magnetic drug targeting. Besides recent developments in conventional stainless steels, those in the high-nitrogen, low-Ni (or Ni-free) varieties are also introduced. These recent developments include new methods for attaining very high nitrogen contents, new guidelines for alloy design, the merits/demerits associated with high nitrogen contents, etc.
1,668 citations
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TL;DR: In this paper, the structure and properties of bearing steels prior to the point of service are first assessed and described in the context of steelmaking, manufacturing and engineering requirements, followed by a thorough critique of the damage mechanisms that operate during service and in accelerated tests.
729 citations
TL;DR: In this paper, the authors performed deformation studies in situ in a transmission electron microscope equipped with an environmental cell to elucidate the mechanisms of hydrogen embrittlement and found that solute hydrogen can increase the velocity of dislocations, increase the crack propagation rate, decrease stacking-fault energy of 310s stainless steel and increase the propensity for edge character dislocation.
546 citations
TL;DR: The effect of hydrogen on the interaction between dislocations and other elastic centers in high-purity aluminum and stainless steel has been directly observed during deformation experiments in situ in an environmental cell transmission electron microscope as discussed by the authors.
442 citations
TL;DR: Parameter-free predictions of embrittlement thresholds in Fe-based steels over a range of H concentrations, mechanical loading rates and H diffusion rates are found to be in excellent agreement with experiments.
Abstract: Hydrogen embrittlement in metals has posed a serious obstacle to designing strong and reliable structural materials for many decades, and predictive physical mechanisms still do not exist. Here, a new H embrittlement mechanism operating at the atomic scale in α-iron is demonstrated. Direct molecular dynamics simulations reveal a ductile-to-brittle transition caused by the suppression of dislocation emission at the crack tip due to aggregation of H, which then permits brittle-cleavage failure followed by slow crack growth. The atomistic embrittlement mechanism is then connected to material states and loading conditions through a kinetic model for H delivery to the crack-tip region. Parameter-free predictions of embrittlement thresholds in Fe-based steels over a range of H concentrations, mechanical loading rates and H diffusion rates are found to be in excellent agreement with experiments. This work provides a mechanistic, predictive framework for interpreting experiments, designing structural components and guiding the design of embrittlement-resistant materials.
420 citations
References
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TL;DR: In this paper, the authors derived an expression for the total energy of a metal using the embedding energy from which they obtained several ground-state properties, such as the lattice constant, elastic constants, sublimation energy, and vacancy-formation energy.
Abstract: We develop the embedded-atom method [Phys. Rev. Lett. 50, 1285 (1983)], based on density-functional theory, as a new means of calculating ground-state properties of realistic metal systems. We derive an expression for the total energy of a metal using the embedding energy from which we obtain several ground-state properties, such as the lattice constant, elastic constants, sublimation energy, and vacancy-formation energy. We obtain the embedding energy and accompanying pair potentials semiempirically for Ni and Pd, and use these to treat several problems: surface energy and relaxation of the (100), (110), and (111) faces; properties of H in bulk metal (H migration, binding of H to vacancies, and lattice expansion in the hydride phase); binding site and adsorption energy of hydrogen on (100), (110), and (111) surfaces; and lastly, fracture of Ni and the effects of hydrogen on the fracture. We emphasize problems with hydrogen and with surfaces because none of these can be treated with pair potentials. The agreement with experiment, the applicability to practical problems, and the simplicity of the technique make it an effective tool for atomistic studies of defects in metals.
5,912 citations
01 Feb 1972-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: A new model for hydrogen-assisted cracking is presented in this article, which explains the observations of decreasing microscopic plasticity and changes of fracture modes with decreasing stress intensities at crack tips during stress-corrosion cracking and HAC of quenched-and tempered steels.
Abstract: A new model is presented for hydrogen-assisted cracking (HAC) which explains the observations of decreasing microscopic plasticity and changes of fracture modes with decreasing stress intensities at crack tips during stress-corrosion cracking and HAC of quenched-and- tempered steels The model suggests that the presence of sufficiently concentrated hydrogen dissolved in the lattice just ahead of the crack tip aids whatever deformation processes the microstructure will allow Intergranular, quasicleavage, or microvoid coalescence fracture modes operate depending upon the microstructure, the crack-tip stress intensity, and the concentration of hydrogen The model unifies several theories but shows how the stress-sorption and lattice embrittlement models are unnecessary The model shows that planar pressure effects are necessary at low stress intensities and are necessary only to augment the driving force from the applied loads The basic hydrogen-steel interaction appears to be an easing of dislocation motion or generation, or both
1,070 citations
TL;DR: In this paper, the threshold pressures, p ∗, of hydrogen and of deuterium gases necessary to cause crack propagation in AISI 4340 steel of 250 ksi yield strength, were determined as functions of plane-strain stress intensity factor K at room temperature.
651 citations
TL;DR: In this paper, a theory of the fracture of metals is presented, which is based on the theory of fracture theory of metal fracture, and it is proved that the theory is correct.
Abstract: (1957). A theory of the fracture of metals. Advances in Physics: Vol. 6, No. 24, pp. 418-465.
619 citations
TL;DR: In this paper, the effect of hydrogen on fracture in the h.c.p. α Ti-4 wt % Al alloy and the role of titanium hydride in the fracture process have been studied by deforming samples in situ in a highvoltage electron microscope equipped with an environmental cell.
437 citations