| 1. |
- Ding, Yu, et al.
(författare)
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Hydrogen-enhanced grain boundary vacancy stockpiling causes transgranular to intergranular fracture transition
- 2022
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Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 239
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Tidskriftsartikel (refereegranskat)abstract
- The attention to hydrogen embrittlement (HE) has been intensified recently in the light of hydrogen as a carbon-free energy carrier. Despite worldwide research, the multifaceted HE mechanism remains a mat-ter of debate. Here we report an atomistic study of the coupled effect of hydrogen and deformation temperature on the pathway to intergranular fracture of nickel. Uniaxial straining is applied to nickel E5(210)[001] and E9(1-10)[22-1] grain boundaries with or without pre-charged hydrogen at various temperatures. Without hydrogen, vacancy generation at grain boundary is limited and transgranular frac-ture mode dominates. When charged, hydrogen as a booster can enhance strain-induced vacancy genera-tion by up to ten times. This leads to the superabundant vacancy stockpiling at the grain boundary, which agglomerates and nucleates intergranular nanovoids eventually causing intergranular fracture. While hy-drogen tends to persistently enhance vacancy concentration, temperature plays an intriguing dual role as either an enhancer or an inhibitor for vacancy stockpiling. These results show good agreement with recent positron annihilation spectroscopy experiments. An S-shaped quantitative correlation between the proportion of intergranular fracture and vacancy concentration was for the first time derived, highlight-ing the existence of a critical vacancy concentration, beyond which fracture mode will be completely intergranular.
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| 2. |
- Ding, Yu, et al.
(författare)
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Hydrogen-induced transgranular to intergranular fracture transition in bi-crystalline nickel
- 2021
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Ingår i: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 204
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Tidskriftsartikel (refereegranskat)abstract
- It is known that hydrogen can influence the dislocation plasticity and fracture mode transition of metallic materials, however, the nanoscale interaction mechanism between hydrogen and grain boundary largely remains illusive. By uniaxial straining of bi-crystalline Ni with a Σ5(210)[001] grain boundary, a transgranular to intergranular fracture transition facilitated by hydrogen is elucidated by atomistic modeling, and a specific hydrogen-controlled plasticity mechanism is revealed. Hydrogen is found to form a local atmosphere in the vicinity of grain boundary, which induces a local stress concentration and inhibits the subsequent stress relaxation at the grain boundary during deformation. It is this local stress concentration that promotes earlier dislocation emission, twinning evolution, and generation of more vacancies that facilitate nanovoiding. The nucleation and growth of nanovoids finally leads to intergranular fracture at the grain boundary, in contrast to the transgranular fracture of hydrogen-free sample.
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| 3. |
- Ding, Yu, et al.
(författare)
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Hydrogen trapping and diffusion in polycrystalline nickel : The spectrum of grain boundary segregation
- 2024
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Ingår i: Journal of Materials Science & Technology. - : Elsevier. - 1005-0302. ; 173, s. 225-236
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen as an interstitial solute at grain boundaries (GBs) can have a catastrophic impact on the mechanical properties of many metals. Despite the global research effort, the underlying hydrogen-GB interactions in polycrystals remain inadequately understood. In this study, using Voronoi tessellations and atomistic simulations, we elucidate the hydrogen segregation energy spectrum at the GBs of polycrystalline nickel by exploring all the topologically favorable segregation sites. Three distinct peaks in the energy spectrum are identified, corresponding to different structural fingerprints. The first peak ( -0.205 eV) represents the most favorable segregation sites at GB core, while the second and third peaks account for the sites at GB surface. By incorporating a thermodynamic model, the spectrum enables the determination of the equilibrium hydrogen concentrations at GBs, unveiling a remarkable two to three orders of magnitude increase compared to the bulk hydrogen concentration reported in experimental studies. The identified structures from the GB spectrum exhibit vastly different behaviors in hydrogen segregation and diffusion, with the low-barrier channels inside GB core contributing to short-circuit diffusion, while the high energy gaps between GB and neighboring lattice serving as on-plane diffusion barriers. Mean square displacement analysis further confirms the findings, and shows that the calculated GB diffusion coefficient is three orders of magnitude greater than that of lattice. The present study has a significant implication for practical applications since it offers a tool to bridge the gap between atomic-scale interactions and macroscopic behaviors in engineering materials.& COPY; 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )
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| 4. |
- Ding, Yu, et al.
(författare)
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The dual role of hydrogen in grain boundary mobility
- 2023
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 133:4
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Tidskriftsartikel (refereegranskat)abstract
- The effect of solute hydrogen on shear-coupled grain boundary (GB) migration is investigated with the dislocation-array type sigma 25(430)[001] GB and a dual role of hydrogen on GB mobility is unraveled. In the low temperature and high loading rate regime, where hydrogen diffusion is substantially slower than GB motion, GB breaks away from the hydrogen atmosphere and transforms into a new stable phase with highly enhanced mobility. In the reverse regime, hydrogen atoms move along with GB, exerting a drag force on GB and decreasing its mobility. These findings provide rationale for the coexistence of hydrogen hardening and softening observed experimentally in polycrystalline materials.
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| 5. |
- Lin, Meichao, et al.
(författare)
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A microstructure informed and mixed-mode cohesive zone approach to simulating hydrogen embrittlement
- 2022
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Ingår i: International journal of hydrogen energy. - : Elsevier. - 0360-3199 .- 1879-3487. ; 47:39, s. 17479-17493
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen induced failure under uniaxial tension is simulated in a duplex stainless steel considering microstructural feature of the material. There are three key ingredients in the modelling approach: image processing and finite element representation of the experimentally observed microstructure, stress driven hydrogen diffusion and diffusion coupled cohesive zone modelling of fracture considering mixed failure mode. The microstructure used as basis for the modelling work is obtained from specimens cut in the transverse and longitudinal directions. It is found that the microstructure significantly influences hydrogen diffusion and fracture. The austenite phase is polygonal and randomly distributed in the transverse direction, where a larger effective hydrogen diffusion coefficient and a lower hydrogen fracture resistance is found, compared to the specimen in the longitudinal direction, where the austenite phase is slender and laminated. This indicates that the proper design and control of the austenite phase help improve hydrogen resistance of duplex stainless steel. The strength of the interface in the shear direction is found to dominate the fracture mode and initiation site, which reveals the importance of considering mixed failure mode and calibrating the hydrogen induced strength reduction in shear.
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| 6. |
- Lin, Meichao, et al.
(författare)
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A predictive model unifying hydrogen enhanced plasticity and decohesion
- 2022
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Ingår i: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 215
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Tidskriftsartikel (refereegranskat)abstract
- The detrimental effect of hydrogen on metals which manifests itself as a transition from a ductile to a brittle failure mode is, for the first time, incorporated into a unified continuum-scale predictive framework. The complete Gurson model, designed to predict ductile failure by voiding, is extended to include failure by deco-hesion. Hydrogen enhanced plasticity is accounted for through acceleration of the voiding process while hydrogen induced decohesion is realized by a degradation of the decohesion threshold. The interplay between these two failure modes driven by hydrogen concentration are well captured. This model can predict a realistic level of embrittlement as well as the suppression of dimples in a hydrogen induced fracture surface. Being generic, versatile, and easy to implement, the model may serve as a basis for interpretation of laboratory ex-periments and enable the transferability of the laboratory results to the integrity assessment of engineering components in hydrogen environment.
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| 7. |
- Lin, Meichao, et al.
(författare)
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Experimental and numerical study on hydrogen-induced failure of X65 pipeline steel
- 2024
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 894
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen-induced fracture of X65 pipeline steel under in -situ electrochemical charging is investigated by using slow strain-rate tensile (SSRT) test, hydrogen diffusion test, fractography analysis, and finite element simulation. Smooth and notched tensile specimens with varying notch radii are utilized to ascertain the impact of stress triaxiality on hydrogen embrittlement (HE) susceptibility. A fully coupled model, H-CGM+, capable of simulating the synergy between hydrogen-enhanced plasticity and decohesion, is employed. The simulation proficiently replicates both the global stress-strain trajectories and the local failure initiation sites of the in -situ SSRT tests. The findings indicate a predominance of dislocation trapping hydrogen mechanism in HE, with crack inception at the notch surface where local plastic strain peaks, subsequently advancing towards the center of the specimen. Notably, an inverse relationship is observed between HE susceptibility and stress triaxiality. A hydrogen-induced failure criterion, defined as a critical combination of local hydrogen concentration and plastic strain, is derived. The failure criterion is found to be independent of stress triaxiality, which serves as a good reference for safety assessment of hydrogen pipelines.
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| 8. |
- Lin, Meichao, et al.
(författare)
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Simulation of ductile-to-brittle transition combining complete Gurson model and CZM with application to hydrogen embrittlement
- 2022
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Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 268
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Tidskriftsartikel (refereegranskat)abstract
- A general simulation framework for modelling ductile-to-brittle transition in metals is proposed. The method combines the complete Gurson model and cohesive zone model, which brings ductile and brittle fracture mechanisms into one play. We found that the transition of failure mode is the result of a competition between fracture due to micro-void growth and coalescence and fracture in the cohesive zone. It is found that the fracture mode is dependent on the ratio between the cohesive strength and the yield strength of the material; brittle fracture only occurs when the strength ratio is below a critical value. This generic rule can be used to rationalize various failure scenarios featured by ductile-to-brittle transition, such as low temperature embrittlement and hydrogen embrittlement. As an application of the general framework, hydrogen embrittlement is simulated. It is revealed that a critical hydrogen concentration has to be achieved in order to trigger brittle fracture, which is consistent with many experimental observations.
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| 9. |
- Yu, Haiyang, PhD, 1989-, et al.
(författare)
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Hydrogen Embrittlement as a Conspicuous Material Challenge : Comprehensive Review and Future Directions
- 2024
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Ingår i: Chemical Reviews. - : American Chemical Society (ACS). - 0009-2665 .- 1520-6890. ; 124:10, s. 6271-6392
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Forskningsöversikt (refereegranskat)abstract
- Hydrogen is considered a clean and efficient energy carrier crucial for shaping the net-zero future. Large-scale production, transportation, storage, and use of green hydrogen are expected to be undertaken in the coming decades. As the smallest element in the universe, however, hydrogen can adsorb on, diffuse into, and interact with many metallic materials, degrading their mechanical properties. This multifaceted phenomenon is generically categorized as hydrogen embrittlement (HE). HE is one of the most complex material problems that arises as an outcome of the intricate interplay across specific spatial and temporal scales between the mechanical driving force and the material resistance fingerprinted by the microstructures and subsequently weakened by the presence of hydrogen. Based on recent developments in the field as well as our collective understanding, this Review is devoted to treating HE as a whole and providing a constructive and systematic discussion on hydrogen entry, diffusion, trapping, hydrogen–microstructure interaction mechanisms, and consequences of HE in steels, nickel alloys, and aluminum alloys used for energy transport and storage. HE in emerging material systems, such as high entropy alloys and additively manufactured materials, is also discussed. Priority has been particularly given to these less understood aspects. Combining perspectives of materials chemistry, materials science, mechanics, and artificial intelligence, this Review aspires to present a comprehensive and impartial viewpoint on the existing knowledge and conclude with our forecasts of various paths forward meant to fuel the exploration of future research regarding hydrogen-induced material challenges.
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| 10. |
- Hesammokri, Parnian, et al.
(författare)
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An extended hydrostatic-deviatoric strain energy density decomposition for phase-field fracture theories
- 2023
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 262-263
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Tidskriftsartikel (refereegranskat)abstract
- The interest in using phase-field theories to numerically analyze fracture has sky-rocketed in the last years. However, in phase-field fracture models are splits, or decompositions, of the strain energy density vital to avoid interpenetration of crack surfaces and to select physically trustworthy crack paths. The most popular decomposition strategies use either a spectral decomposition or a hydrostatic-deviatoric decomposition. Both decompositions have significant disadvantages; the most important is that none of them can handle mixed -mode load scenarios in compression. To circumvent these problems, a generalized decomposition method is derived that unifies some features of the hydrostatic-deviatoric and spectral decompositions, enhanced with a classical Mohr-Coulomb failure criterion. The derived decomposition scheme has the potential to judge whether or not a compressive deformation field will assist in the crack driving process in brittle materials. The enhanced decomposition is scrutinized in numerical models and revealing biaxially loaded crack experiments in global compression. Simulations using the decomposition scheme capture the experiments in a remarkable way: complex crack patterns are reproduced, as well as critical loads. The enhanced decomposition strategy hence provides mechanistic insight into fracture processes in brittle materials subject to mixed-mode loads.
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