“…Figure 4Results from tensile testing of high purity iron at 200 K with a strain rate of with hydrogen charging () in solution switched on and off. Adapted from [84]…”
Section: Description Of the Failure Mechanisms Affecting Steelsmentioning
Hydrogen embrittlement is a complex phenomenon, involving several lengthand timescales, that affects a large class of metals. It can significantly reduce the ductility and load-bearing capacity and cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Despite a large research effort in attempting to understand the mechanisms of failure and in developing potential mitigating solutions, hydrogen embrittlement mechanisms are still not completely understood. There are controversial opinions in the literature regarding the underlying mechanisms and related experimental evidence supporting each of these theories. The aim of this paper is to provide a detailed review up to the current state of the art on the effect of hydrogen on the degradation of metals, with a particular focus on steels. Here, we describe the effect of hydrogen in steels from the atomistic to the continuum scale by reporting theoretical evidence supported by quantum calculation and modern experimental characterisation methods, macroscopic effects that influence the mechanical properties of steels and established damaging mechanisms for the embrittlement of steels. Furthermore, we give an insight into current approaches and new mitigation strategies used to design new steels resistant to hydrogen embrittlement.
“…Figure 4Results from tensile testing of high purity iron at 200 K with a strain rate of with hydrogen charging () in solution switched on and off. Adapted from [84]…”
Section: Description Of the Failure Mechanisms Affecting Steelsmentioning
Hydrogen embrittlement is a complex phenomenon, involving several lengthand timescales, that affects a large class of metals. It can significantly reduce the ductility and load-bearing capacity and cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Despite a large research effort in attempting to understand the mechanisms of failure and in developing potential mitigating solutions, hydrogen embrittlement mechanisms are still not completely understood. There are controversial opinions in the literature regarding the underlying mechanisms and related experimental evidence supporting each of these theories. The aim of this paper is to provide a detailed review up to the current state of the art on the effect of hydrogen on the degradation of metals, with a particular focus on steels. Here, we describe the effect of hydrogen in steels from the atomistic to the continuum scale by reporting theoretical evidence supported by quantum calculation and modern experimental characterisation methods, macroscopic effects that influence the mechanical properties of steels and established damaging mechanisms for the embrittlement of steels. Furthermore, we give an insight into current approaches and new mitigation strategies used to design new steels resistant to hydrogen embrittlement.
“…Two degradation mechanisms are primarily invoked to frame hydrogen effects in metals where hydride formation is not favorable and the material contains internal hydrogen: hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) [1]. The HELP theory suggests that hydrogen enhances the mobility of dislocations by shielding their interactions, thereby causing localized plasticity in regions of high hydrogen concentration, ultimately resulting in macroscopic brittle fracture via locally ductile processes [3,5]. In contrast, the HEDE mechanism assumes that dissolved hydrogen weakens interatomic bonds, and therefore the cohesive energy, resulting in brittle fracture modes (e.g.…”
Positron annihilation spectroscopy and thermal desorption spectroscopy experiments were combined to ascertain the role of hydrogen on generation of vacancies and vacancy clusters in Ni alloys. The effects of grain size and deformation temperature are emphasized for pure Ni single crystals and polycrystalline Ni-201 alloy samples with two grain sizes that were thermally pre-charged with 3000 appm hydrogen. Variation in positron lifetime and intensity suggests that hydrogen enhances and stabilizes vacancies and vacancy clusters. Additionally, grain boundaries and the regions adjacent to them are preferential sites for vacancy and cluster formation. Hydrogen-altered vacancies and vacancy clusters are manifest in yield behavior differences: uniform vacancy distributions augment strength increases after hydrogen charging; enhanced yield strength during cryogenic deformation is ascribed to an 'Orowan type' strengthening mechanism while cross-slip restriction dominates hardening behavior at room temperature.
“…The internal stress induced by abundant dissolved hydrogen can be estimated by eq. ( 15): (15) where is the bulk modulus of Alloy 718, and is the lattice volume change by hydrogen. The value of cannot be obtained directly from the literature, however, one can estimate it from the bulk modulus of γ'' phase (211 GPa) and γ' phase (229 GPa) in Inconel 718 [69].…”
Section: Pre-damages Induced By Cathodic Chargingmentioning
confidence: 99%
“…Several acceptable mechanisms proposed thus far include hydrogen-enhanced localized plasticity (HELP) [12,14,15], hydrogen-enhanced decohesion (HEDE) [7,[16][17][18], hydrogen adsorption-induced dislocation emission (AIDE) [11,[19][20][21][22], hydrogen-enhanced strain-induced vacancy (HESIV) [23] and crack induction by hydride formation [6,[24][25][26].…”
The susceptibility of age-hardened nickel-based 718 superalloy to hydrogen embrittlement was studied by the controlled electrochemical charging combined with slow strain-rate tensile tests (SSRT) and advanced characterization techniques. We proposed some novel ideas of explaining hydrogen embrittlement mechanisms of the studied material in regard to two cracking morphologies: transgranular and intergranular cracking. It is for the first time to report that electrochemical charging alone could cause slip lines, surface and subsurface cracks on nickel-based superalloys. The formation of pre-damages was discussed by calculating the hydrogen concentration gradient generated during cathodic charging. Predamages were proved to result in transgranular cracks and lead to the evident reduction of mechanical properties. In addition, the STRONG (Slip Transfer Resistance of *Manuscript_clean Click here to download Manuscript: Revised Manuscript_clean_A-19-1789_R1.docx Click here to view linked References Neighbouring Grains) model was used to analyze the dependence of hydrogen-assisted intergranular cracking on the microscopic incompatibility of the grain boundaries. The results show that in the presence of hydrogen, grain boundaries with a lower dislocation slip transmission are more prone to cracking during loading and vice versa.
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