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Postirradiation annealing behavior of (a) the S parameter, (b) the intensity of the Snoek peak, (c) the W parameter, and (d) the magnitude of phase transition discontinuity.
Source publication
The structure of copper nanoclusters/precipitates formed under neutron irradiation in Fe-0.3 wt. % Cu-C alloy is studied by the internal friction and positron annihilation experiments of postirradiation annealed alloys. The appearance of a carbon-relaxation peak during the first recovery stage at about 723 K reveals the fact that complex carbon-vac...
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Context 1
... change in IF coefficient, e.g., the magnitude of discon- tinuity as a function of the annealing temperature is presented in Fig. 5(d). The behavior of the IF discontinuity related to the phase transition at 122 K resembles the behavior of the W parameter; see Fig. 5(b). The Q −1 exhibits an increase and then a decrease by increasing the annealing temperature, with a peak value at about 823 K. This finding suggests that the dissolution of vacancies from ...
Context 2
... change in IF coefficient, e.g., the magnitude of discon- tinuity as a function of the annealing temperature is presented in Fig. 5(d). The behavior of the IF discontinuity related to the phase transition at 122 K resembles the behavior of the W parameter; see Fig. 5(b). The Q −1 exhibits an increase and then a decrease by increasing the annealing temperature, with a peak value at about 823 K. This finding suggests that the dissolution of vacancies from vacancy-copper(-carbon) clusters is accompanied by the subsequent full crystallization of Cu precipitates. It is indeed plausible that in neutron- ...
Context 3
... of IF discontinuity occurs at temperatures slightly above the first recovery stage (of about 50 K). This could be either the consequence of measurement sensitivity or an indication of the existence of an intermediate state of copper precipitate (this requires further study). At the peak, the magnitude of IF discontinuity Q −1 ∼ 1.5 × 10 −4 [see Fig. 5(d)] is, roughly speaking, 3 times smaller than the Q −1 saturation value obtained in thermally aged Fe-1 wt. % Cu alloys. 22 This result nicely correlates with the difference in copper concentrations in these two alloys. Further increase of the annealing temperature causes the decrease and disappearance of the Q −1 , as a result of the ...
Citations
... 4. It has also been shown that, in addition to small SIA clusters [51], small prismatic loops of self-interstitial nature that may form directly in displacement cascades interact strongly and attractively with solutes, especially with P, Si, Mn, Cu and Ni (in order of strength, from the strongest to the weakest interaction) [52]. The interaction energy depends on whether the solute interacts with the center or the edge of the loop; it ranges between 0.2 and 0.5 eV and can be as high as 1 eV in the case of P. In addition, both experiments and atomistic studies have shown that carbon-vacancy complexes (possibly nitrogen-vacancy and oxygen-vacancy complexes as well [53]) form abundantly under irradiation [54,55] and act as very efficient traps for gliding prismatic loops [56], with interaction energies as high as 1.3 eV [57]. The existence of an affinity between solute atoms and loops, as revealed by DFT, has been extended to atomistic studies with interatomic potentials using Metropolis Monte Carlo techniques. ...
The formation of nano-sized, coherent, solute-rich clusters (NSRC) is known to be an important factor causing the degradation of the macroscopic properties of steels under irradiation. The mechanisms driving their formation are still debated. This work focuses on low-Cu reactor pressure vessel (RPV) steels, where solute species are generally not expected to precipitate. We rationalize the processes that take place at the nanometre scale under irradiation, relying on the latest theoretical and experimental evidence on atomic-level diffusion and transport processes. These are compiled in a new model, based on the object kinetic Monte Carlo (OKMC) technique. We evaluate the relevance of the underlying physical assumptions by applying the model to a large variety of irradiation experiments. Our model predictions are compared with new experimental data obtained with atom probe tomography and small angle neutron scattering, complemented with information from the literature. The results of this study reveal that the role of immobilized self-interstitial atoms (SIA) loops dominates the nucleation process of NSRC.
... 2. It has also been shown that, in addition to small SIA clusters [51], small prismatic loops of self-interstitial nature that may form directly in displacement cascades interact strongly and attractively with solutes, especially with P, Si, Mn, Cu and Ni (in order of strength) [52]. The interaction energy depends on whether the solute interacts with the centre or the edge of the loop; it ranges between 0.2 and 0.5 eV and can be as high as 1 eV in the case of P. In addition, both experiments and atomistic studies have shown that carbon-vacancy complexes (possibly nitrogen-vacancy and oxygen-vacancy complexes as well [53]) form abundantly under irradiation [54,55] and act as very efficient traps for gliding prismatic loops [56], with interaction energies as high as 1.3 eV [57]. The existence of an affinity between solute atoms and loops, as revealed by DFT, has been extended to atomistic studies with interatomic potentials using Metropolis Monte Carlo techniques. ...
The formation of nano-sized, coherent, solute-rich clusters (NSRC) is known to be an important factor degrading the macroscopic properties of steels under irradiation. The mechanisms driving their formation are still debated. This work focuses on low-Cu reactor pressure vessel (RPV) steels, where solute species are generally not expected to precipitate. We rationalize the processes taking place at the nanometre scale under irradiation, relying on the latest theoretical and experimental evidence on atomic-level diffusion and transport processes. These are compiled in a new model, based on the object kinetic Monte Carlo (OKMC) technique. We evaluate the relevance of the underlying physical assumptions by applying the model to a large variety of irradiation experiments. Our model predictions are compared with new experimental data obtained with atom probe tomography and small angle neutron scattering, complemented with information from the literature. The results of this study reveal that the role of immobilized self-interstitial atoms (SIA) loops dominates the nucleation process of NSRC.
... The chemical composition of the investigated RPV steels is given in Table 1. Low Ni, 16MND5 steel samples were neutron irradiated in the Belgian Reactor (BR2) up to 0.1 displacement per atom, dpa, (6:9 Â 10 19 n=cm 2 ), at the temperature and pressure of about 300 C and 150 bar, respectively [13]. Two Ringhals steel samples (weld), Ringhals96 and Ringhals93, with high Ni content were extracted from the surveillance specimens [10] which were irradiated at the temperature of 284 C, reaching the fluence of 6:87 Â 10 19 n=cm 2 and 5:18 Â 10 19 n=cm 2 , respectively. ...
... In Ringhals steel, the W-parameter exhibits a weak peak at the temperature of about 800 K. The peak in the W-parameter typically indicates the existence of Cu-rich precipitates, which were formed under neutron irradiation [13,21,22]. According to previous studies, the peak position of the W-parameter can be correlated to the concentration of copper and corresponding Cu solubility limit (i.e. ...
The thermal stability and the structure of solute-vacancy clusters formed by neutron irradiation are studied by means of positron annihilation spectroscopy and hardness measurements of post-irradiation annealed reactor pressure vessel steels with high and low Ni contents. Two distinct recovery stages were observed and assigned to (a) the dissolution of vacancy clusters at about 650 K, and (b) the dissolution of solute-vacancy clusters at about 750 K. In steels with high Ni content, hardening mainly recovers during the second stage. Atomistic and coarse grain models suggest that during this stage, the removal of vacancies from vacancy-solute clusters leads to complete cluster dissolution, which indicates that solute clusters are radiation induced.
... 2. It has also been shown that, in addition to small SIA clusters [51], small prismatic loops of self-interstitial nature that may form directly in displacement cascades interact strongly and attractively with solutes, especially with P, Si, Mn, Cu and Ni (in order of strength) [52]. The interaction energy depends on whether the solute interacts with the centre or the edge of the loop; it ranges between 0.2 and 0.5 eV and can be as high as 1 eV in the case of P. In addition, both experiments and atomistic studies have shown that carbon-vacancy complexes (possibly nitrogen-vacancy and oxygen-vacancy complexes as well [53]) form abundantly under irradiation [54,55] and act as very efficient traps for gliding prismatic loops [56], with interaction energies as high as 1.3 eV [57]. The existence of an affinity between solute atoms and loops, as revealed by DFT, has been extended to atomistic studies with interatomic potentials using Metropolis Monte Carlo techniques. ...
The formation of nano-sized, coherent, solute-rich clusters (NSRC) is known to be an important factor causing the degradation of the macroscopic properties of steels under irradiation. The mechanisms
driving their formation are still debated. This work focuses on low-Cu reactor pressure vessel (RPV) steels, where solute species are generally not expected to precipitate. We rationalize the processes that take place at the nanometer scale under irradiation, relying on the latest theoretical and experimental evidence on atomic-level diffusion and transport processes. These are compiled in a new model, based
on the object kinetic Monte Carlo (OKMC) technique. We evaluate the relevance of the underlying physical assumptions by applying the model to a large variety of irradiation experiments. Our model predictions are compared with new experimental data obtained with atom probe tomography and small angle neutron scattering, complemented with information from the literature. The results of this study reveal that the role of immobilized self-interstitial atoms (SIA) loops dominates the nucleation process of NSRC.
... Variety of phases and microstructures which can occur in iron alloys and steels strongly depend on the amount of carbon, heat treatment of the alloy, and distribution of carbon atoms in the lattice, e.g. as an interstitial or in the form of carbides. Moreover, carbon easily segregates at dislocations and grain boundaries, and shows a great affinity to bind with irradiation-induced defects such as vacancies, solute clusters and precipitates 1,2 . Consequently, the carbon distribution has a strong influence on defect formation and mobility, thus affecting the materials mechanical properties including the swelling of irradiated materials. ...
Carbon distribution in Fe-Cr-C alloys with a variety of Cr concentrations is studied based on internal friction, optical and transmission-electron microscopy. It is found that the carbon distribution strongly depends on initial microstructure, being ferritic or ferritic/martensitic, which is determined by the thermal treatment, and Cr and carbon concentrations. In the quenched alloys, carbon is observed in the form of small carbon-vacancy complexes, most probably two carbon - single vacancy cluster, 2CV, that dissolve at about 500 K. In tempered alloys, the carbon atoms are observed to be uniformly distributed only in Fe-2.5Cr-C alloy, which is fully ferrite. In the alloys with 5-12% of Cr, with ferritic/martensitic microstructure, carbon-Snoek relaxation peak is not observed due to the carbon precipitation, as well as due to atomic carbon being trapped at dislocations and grain boundaries. In both quenched and tempered alloys, the plastic deformation causes the appearance of the broad relaxation peak close to 300 K which could be assigned to dissolution of single carbon - single vacancy, CV, complexes.
... These defects are responsible for significant changes in the mechanical properties of RPV steels. In these defects, Cu-rich precipitates as secondary phase precipitates can cause hardening, loss of ductility and an increase of the ductile-to-brittle transition temperature of RPV steels [4][5][6][7]. The interaction between moving dislocations and Cu-rich precipitates is responsible for these effects [8], and an understanding of the atomic-scale mechanisms between dislocations and precipitates is therefore necessary for the development of predictive models to estimate the lifetime of nuclear power plant components. ...
In this paper, we investigated the interaction of an edge dislocation with Cu precipitates with a spherical geometry and with Cu?Ni precipitates that possess a Cu core with an outer Ni shell, commonly observed in reactor pressure vessel (RPV) steels. We applied molecular dynamics techniques to explore the critical stress required to unpin the dislocation (CSRUD), the breakaway dislocation line shape when the dislocation leaves the precipitates and the transition of Cu atoms within precipitates. The results indicate that the CSRUD of the Cu?Ni precipitates with a diameter less than 2.38?nm is larger than that of Cu precipitates that contain the same number of Cu atoms, while for a diameter larger than 2.38?nm, the CSRUD of Cu?Ni precipitates is weaker, which is related to the bcc to fcc-like or hcp-like atoms transformation in precipitates. The dislocations interact with Cu and Cu?Ni precipitates via the cut mechanism.
... Because of the consequences of Cu precipitation on the mechanical properties of steels used in nuclear power plants, iron-copper (Fe-Cu) alloys have been studied extensively in the past. There is a number of experimental and theoretical studies of Cu nano-precipitates emphasizing the importance of structural transformation on the strength of Fe-Cu alloys [2,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. ...
... coarsening). More recently, this phase transition was also observed in neutron irradiated and annealed Fe-0.3%Cu alloys [18], where Cu precipitation was enhanced by irradiation. ...
Mechanical tests of thermally aged Fe–Cu alloys were performed in the temperature range between 97 K and 297 K in order to investigate their low-temperature mechanical behavior. Tests performed below 122 K have shown that the material breaks in a random fashion already in the elastic region, while above it a clearly pronounced yield point is observed. This sudden change of the mechanical behavior has been rationalized on the basis of atomistic simulations, addressing the interaction of dislocations with Cu precipitates. The latter study has revealed the presence of bcc to fcc transition induced by dislocations which is a temperature dependent process. It is suppressed with increasing temperature and enhanced with increasing a precipitate size. This transition, efficient at low temperature, leads to the transformation of Cu precipitates into non-coherent particles, which act as stronger obstacles and cause the experimentally observed premature failure. The presence of small non-coherent Cu-precipitates, expected to form according to atomistic predictions, and not observed prior to deformation, was confirmed by means of transmission electron microscopy.
Carbon distribution and grain boundary diffusion processes are studied in a variety of FeCr alloys and steels with different chromium content and microstructure, based on magnetic after‐effect measurements performed in a broad temperature range, from 100 K to 1000 K. The existence of three metastable carbon positions in the lattice is revealed in the FeC alloys. Carbon as interstitial in the lattice, segregated at the dislocations and grain boundaries is represented by the relaxation peaks at about 269 K, 432 and 607 K, respectively. The relaxation process due to the grain boundary self‐diffusion is clearly distinguished from those above, and is observed to be at about 643 K and 681 K in low and high carbon Fe, respectively. Addition of Cr has a twofold effect: a) For Cr concentrations higher than about 3 wt% carbon‐related relaxation processes completely disappear from the spectra, most probably due to formation of carbides, b) the solute grain boundary diffusion relaxation peak appears in the spectra at about 800 K, with an activation energy that is directly dependent on the Cr content. Activation energy of the solute grain boundary diffusion is found to be generally smaller in ferrite‐martensite microstructure in comparison with fully ferrite alloys. This article is protected by copyright. All rights reserved.
Cr-rich alpha prime precipitates (CrRP) induce hardening and embrittlement of FeCr alloys, but the kinetics of CrRP formation due to particle irradiation are not well understood. In this study, Fe18wt.%Cr alloy in solid solution state and pre-aged to produce relatively coarse CrRP was irradiated with 8 MeV Fe ions. The irradiation conditions involved two midrange doses of 0.37 and 3.7 displacements per atom (dpa), a wide range of dose rates (10⁻⁵-10⁻³ dpa/s) and temperatures (300-450°C). The distributions of CrRP after irradiation were studied with atom probe tomography (APT). The critical irradiation conditions to suppress CrRP formation were identified as 300°C and 10⁻³ dpa/s; CrRP formation occurred readily at lower dose rates or higher temperatures. From 0.37 to 3.7 dpa, CrRP were observed to slightly grow at 350°C and strongly coarsen at 450°C. Specimens with pre-existing CrRP evolved into a similar precipitate distribution as detected after ion irradiation on solution annealed specimens at 300-350°C to 0.37 dpa, indicating that the precipitate microstructure approaches a quasi-equilibrium for doses <1 dpa. Limited shrinking of pre-existing CrRP was observed after irradiation at 450°C to 0.37 dpa, indicating a higher recovery rate at this temperature. The evolution of CrRP is quantitatively explained by employing corrections to the historic Nelson-Hudson-Mazey precipitate stability model, and a radiation modified precipitation mechanism is proposed to account for the competition between radiation enhanced diffusion and ballistic dissolution which results in the modifications on both size and solute concentration of CrRP.
