| 1. |
- Chang, Zhongwen, 1985-, et al.
(författare)
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Anomalous bias factors of dislocations in bcc iron
- 2015
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Ingår i: Journal of Nuclear Materials. - : Elsevier. - 0022-3115 .- 1873-4820. ; 461, s. 221-229
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Tidskriftsartikel (refereegranskat)abstract
- Dislocation bias factors in bcc Fe have been calculated based on atomistic interaction energy maps on three kinds of dislocations, namely the a0/2〈1 1 1〉{1 1 0} screw, a0/2〈1 1 1〉{1 1 0} and a0〈1 0 0〉{0 0 1} edge dislocations. The results show that the dislocation bias is higher for the a0/2〈1 1 1〉 edge dislocation than for the a0〈1 0 0〉 edge dislocation, even though the latter possesses a larger Burgers vector. This indicates the importance of the dislocation core contribution. For the a0/2〈1 1 1〉{1 1 0} screw dislocation, a negative dislocation bias has been obtained, which implies a more efficient absorption of vacancies than of SIAs. The effect of coexistence of both edge- and screw dislocations are assessed by a total bias. A possible complementary mechanism for explaining the long swelling incubation time in bcc metals is suggested and discussed.
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| 2. |
- Chang, Zhongwen, et al.
(författare)
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Assessment of the dislocation bias in fcc metals and extrapolation to austenitic steels
- 2015
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 465
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Tidskriftsartikel (refereegranskat)abstract
- A systematic study of dislocation bias has been performed using a method that combines atomistic and elastic dislocation-point defect interaction models with a numerical solution of the diffusion equation with a drift term. Copper, nickel and aluminium model lattices are used in this study, covering a wide range of shear moduli and stacking fault energies. It is found that the dominant parameter for the dislocation bias in fcc metals is the width of the stacking fault ribbon. The variation in elastic constants does not strongly impact the dislocation bias value. As a result of this analysis and its extrapolation, the dislocation bias of the widely applied austenitic stainless steels of 316 type is predicted to be about 0.1 at temperature close to the swelling peak (815 K) and typical dislocation density of 1014 m-2. This is in line with the bias calculated using the elastic interaction model, which implies that the prediction method can be used readily in other fcc systems even without EAM potentials. By comparing the bias values obtained using atomistic- and elastic interaction energies, about 20% discrepancy is found, therefore a more realistic bias value for the 316 type alloy is 0.08 in these conditions.
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| 3. |
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| 4. |
- Chang, Zhongwen, 1985-, et al.
(författare)
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Dislocation bias factors in fcc copper derived from atomistic calculations
- 2013
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Ingår i: Journal of Nuclear Materials. - : Elsevier. - 0022-3115 .- 1873-4820. ; 441:1-3, s. 357-363
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Tidskriftsartikel (refereegranskat)abstract
- Atomistic calculations were employed in order to calculate the interaction energy of an edge dislocation with different point defects. The bias factor was calculated by applying a finite element method on the interaction energy landscapes obtained from the atomistic calculations. A comparison of the calculated bias factor with a model based on elasticity theory reveals around 30% discrepancy under conditions representative for electron irradiation at 600 degrees C. Possible reasons are discussed. The bias factor dependence on dislocation density and ambient temperature is presented and discussed.
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| 5. |
- Chang, Zhongwen, 1985-, et al.
(författare)
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Interaction Energy Calculations of Edge Dislocation with Point Defects in FCC Cu
- 2013
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Konferensbidrag (refereegranskat)abstract
- In order to improve the dislocation bias (DB) model of swelling under irradiation, a large scale of atomistic simulation of the interaction in face centered cubic (FCC) Cu model lattice between an edge dislocation (ED) and point defects such as a vacancy, a self-interstital atom (SIA) have been performed for various configurations. It is found dislocation core splits into partial cores after energy relaxation. Interactions with any SIA conficurations is one order of magnitute larger than with a vacancy. The reason that SIA creats a larger dilatation volumn than the vacancy is directly observed from calculation. Furthurmore, within the interaction range, an octahedron position rather than dumbbell in <100> direction is observed in the stable state after relaxation in interactions between a edge dislocation and a dumbbell SIA. Comparision of interaction energy in analytical and atomistic calculation shows that analytical one has a stronger interaction in vacancy-ED systems, suggesting that the bias factor (BF) from analytical calculation is larger than from atomistic calculation.
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| 6. |
- Ortiz, Christophe J., et al.
(författare)
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Simulation of defect evolution in electron-irradiated dilute FeCr alloys
- 2011
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 417:1-3, s. 1078-1081
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Tidskriftsartikel (refereegranskat)abstract
- A rate theory model based on ab initio data was used to predict defect evolution in electron-irradiated dilute FeCr alloys during isochronal annealing. A good correlation was found between the prediction of the model and existing isochronal resistivity recovery measurements. In agreement with experimental results, our model predicts a shift of stage IE towards lower temperature with increasing Cr concentration. According to our model, stage II is found to be not only due to the recombination of I2 clusters with vacancies but also due to the annihilation of ICr and I2Cr complexes at vacancies.
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| 7. |
- Terentyev, Dmitry, et al.
(författare)
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Formation of stable sessile interstitial complexes in reactions between glissile dislocation loops in bcc Fe
- 2008
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 382:2-3, s. 126-133
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Tidskriftsartikel (refereegranskat)abstract
- Clusters of self-interstitial atoms (loops) are commonly observed in the microstructure of irradiated metals. These clusters can be formed directly in high-energy displacement cascades or by growth as a result of interaction between individual self interstitials. The majority of these clusters have features of glissile dislocation loops and migrate by fast one-dimensional glide. In this paper, we present results of a systematic molecular dynamics (MD) study of reactions involving glissile interstitial loops. By the example of bcc iron we demonstrate that the reactions can produce a number of specific, stable microstructural features, with different properties compared to the reactants. Namely, the reactions between the most common glissile clusters of < 111 > crowdions can result in coarsening or formation of immobile self interstitial complexes. The coarsening leads to a decrease of the total dislocation line length and therefore is favourable. The structure and stability of the junction formed in the reactions has been studied using many body potentials and density functional theory (DFT) techniques. No evidence of the formation of a < 100 > loop from two glissile < 111 > clusters was found among the studied reactions. The immobile self interstitial complexes that form as a result of these reaction have, however, high binding energies, of the order of tens of eV, implying that a relatively long life time should be assigned to the resulting configurations and therefore that such objects are expected to contribute to the evolution of the microstructure under irradiation.
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| 8. |
- Wallenius, Janne, et al.
(författare)
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Simulation of thermal ageing and radiation damage in Fe-Cr
- 2007
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 255:1, s. 68-74
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Tidskriftsartikel (refereegranskat)abstract
- In recent years substantial progress has been made in the field of multi-scale modelling of radiation damage Fe-Cr alloy. Ab initio calculations have provided a description of point-defect properties for a large number of defect configurations. Empirical potentials for the alloy of EAM and 2nd moment tight binding type have been constructed that reproduce these formation energies, as well as the anomalous shift in sign of mixing enthalpy at a Cr concentration of about 10%. Applying the potentials in simulation of interstitial cluster transport, it has been found that cluster diffusion coefficients have shallow minima corresponding to experimentally measured minima in swelling rates of Fe-Cr alloys. Kinetic Monte Carlo simulation of thermal ageing further show that these potentials correctly reproduce the formation modes of the alpha-prime phase for Cr concentrations above 9%. The present paper is a review of methods used and results achieved within the last couple of years.
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