Little more than 10
years ago the first paper on molecular dynamics (MD) simulation of displacement cascades in α-Fe using a many-body potential was published by Calder and Bacon J. Nucl. Mater. 207 ...(1993) 25. Since then, a large body of literature data has been produced on the subject using different interatomic potentials. In this review, most of the available data from the literature are compared in order to discuss to what extent they are consistent. It is found that, while the number of Frenkel pairs versus cascade energy is essentially the same for most potentials, yielding a defect production efficiency in agreement with experimental estimates, differences exist concerning the point-defect clustered fractions. In the case of self-interstitial atoms (SIA), the criterion used to define clusters is largely responsible for the discrepancies, but differences also exist as a consequence of the different interatomic potentials. Too few data have been published concerning vacancy clusters to draw definitive conclusions. The existing differences do not correlate in any explicit way with the description that the interatomic potential gives of point-defects and their mobility.
An attempt is made to quantify the contributions of different types of defect-solute clusters to the total irradiation-induced yield stress increase in neutron-irradiated (300°C, 0.6dpa), ...industrial-purity Fe–Cr model alloys (target Cr contents of 2.5, 5, 9 and 12at.% Cr). Former work based on the application of transmission electron microscopy, atom probe tomography, and small-angle neutron scattering revealed the formation of dislocation loops, NiSiPCr-enriched clusters and α′-phase particles, which act as obstacles to dislocation glide. The values of the dimensionless obstacle strength are estimated in the framework of a three-feature dispersed-barrier hardening model. Special attention is paid to the effect of measuring errors, experimental details and model details on the estimates. The three families of obstacles and the hardening model are well capable of reproducing the observed yield stress increase as a function of Cr content, suggesting that the nanostructural features identified experimentally are the main, if not the only, causes of irradiation hardening in these model alloys.
•We can model the accumulation of radiation damage in Fe–C.•The effect of carbon is to form C–vacancy complexes that in turn trap SIA clusters.•The model was successfully used to simulate irradiation ...at <370K and post-irradiation annealing.
Neutron irradiation induces in steels nanostructural changes, which are at the origin of the mechanical degradation that these materials experience during operation in nuclear power plants. Some of these effects can be studied by using as model alloy the iron–carbon system.
The Object Kinetic Monte Carlo technique has proven capable of simulating in a realistic and quantitatively reliable way a whole irradiation process. We have developed a model for simulating Fe–C systems using a physical description of the properties of vacancy and self-interstitial atom (SIA) clusters, based on a selection of the latest data from atomistic studies and other available experimental and theoretical work from the literature. Based on these data, the effect of carbon on radiation defect evolution has been largely understood in terms of formation of immobile complexes with vacancies that in turn act as traps for SIA clusters. It is found that this effect can be introduced using generic traps for SIA and vacancy clusters, with a binding energy that depends on the size of the clusters, also chosen on the basis on previously performed atomistic studies.
The model proved suitable to reproduce the results of low (<350K) temperature neutron irradiation experiments, as well as the corresponding post-irradiation annealing up to 700K, in terms of defect cluster densities and size distribution, when compared to available experimental data from the literature. The use of traps proved instrumental for our model.
We propose an object kinetic Monte Carlo (OKMC) model for describing the microstructural evolution in pure tungsten under neutron irradiation. We here focus on low doses (under 1 dpa), and we neglect ...transmutation in first approximation. The emphasis is mainly centred on an adequate description of neutron irradiation, the subsequent introduction of primary defects, and their thermal diffusion properties. Besides grain boundaries and the dislocation network, our model includes the contribution of carbon impurities, which are shown to have a strong influence on the onset of void swelling. Our parametric study analyses the quality of our model in detail, and confronts its predictions with experimental microstructural observations with satisfactory agreement. We highlight the importance for an accurate determination of the dissolved carbon content in the tungsten matrix, and we advocate for an accurate description of atomic collision cascades, in light of the sensitivity of our results with respect to correlated recombination.
The mechanical properties of neutron irradiated Fe–Cr ferritic model alloys with various concentrations of Cr and minor solutes (Ni, Si and P) were investigated along with high-Cr ...ferritic/martensitic steels. The neutron irradiation was performed in a materials test reactor at two temperatures, 290 ∘C and 450 ∘C, reaching a dose of 0.11 dpa. Tensile tests were subsequently performed on small flat specimens. Significant hardening of about 225 MPa was observed only in model alloys containing Ni, Si and P solute atoms, irrespective of the Cr content and the irradiation temperature. These results suggest that Cr solutes play lesser role in irradiation hardening of ferritic/martensitic alloys steels than previously believed, while minor solutes have a clear effect.
The microstructure of a 9Cr-1W-0.22V-0.09Ta-0.11C reduced activation ferritic/martensitic (RAFM) steel has been investigated after thermo-mechanical rolling with subsequent annealing for 30 min at ...temperatures of 880 °C, 920 °C, 980 °C and 1050 °C, followed by water quenching. Scanning and transmission electron microscopy investigations and electron backscattered diffraction (EBSD) measurements were performed to determine the microstructural features after the different thermal treatments. Additionally, the microstructure and the mechanical properties of the materials were studied after tempering at 750 °C for 2 h. This study aims to understand microstructural processes that occur in the material during thermo-mechanical treatment and to assess the effect of the microstructure on its strength and toughness, with a view on improving its mechanical performance. Microstructural analysis together with the data from mechanical tests identified the beneficial effect of grain refinement obtained with adequate processing on the ductile-to-brittle transition temperature (DBTT) and on the delay of strength degradation at elevated temperatures.
•TM-rolling and micro-alloying with V and Ta lead to alternative precipitation state.•TM-rolling reduces precipitation of carbonitrides at grain boundaries.•The precipitation size and distribution can be optimized by appropriate annealing temperature.•TM-rolling and appropriate Q&T lead to a grain refinement of the martensitic structure.•The obtained refined martensite has improved toughness and a lower DBTT.
Experimental data on partial ordering and α′ precipitation in Fe–Cr alloys and ferritic steels containing up to 15
at.% Cr are summarized. From this data and computer simulations employing the most ...advanced Fe–Cr cohesive models, the Fe-rich phase boundary of the α–α′ miscibility gap is constructed. This boundary is critically compared with the standard (CALPHAD) Fe–Cr phase diagram in the same concentration range and a significant modification of the latter is proposed.
In recent years, the development of atomistic models dealing with microstructure evolution and subsequent mechanical property change in reactor pressure vessel steels has been recognised as an ...important complement to experiments. In this framework, a literature study has shown the necessity of many-body interatomic potentials for multi-component alloys. In this paper, we develop a ternary many-body Fe-Cu-Ni potential for this purpose. As a first validation, we used it to perform a simulated thermal annealing study of the Fe-Cu and Fe-Cu-Ni alloys. Good qualitative agreement with experiments is found, although fully quantitative comparison proved impossible, due to limitations in the used simulation techniques. These limitations are also briefly discussed.
Radiation-induced embrittlement of bainitic steels is the lifetime limiting factor of reactor pressure vessels in existing nuclear light water reactors. The primary mechanism of embrittlement is the ...obstruction of dislocation motion by nano-metric defects in the bulk of the material due to irradiation. Such features are known to be solute clusters that may be attached to point defect clusters. In this work we study the thermal stability of solute clusters near edge dislocation lines and loops with Burgers vector b=½111 and b=100 in FeNiMnCu model alloys by means of Metropolis Monte Carlo simulations. It is concluded that small dislocation loops may indeed act as points for heterogeneous nucleation of solute precipitates in reactor pressure vessel steels and increase their thermodynamic stability up to and above normal reactor operating temperatures. We also found that, in the presence of dislocation-type defects, the Ni content determines the thermodynamic driving force for precipitation, rather than the Mn content.
Reactor pressure vessel steels are well-known to harden and embrittle under neutron irradiation, mainly because of the formation of obstacles to the motion of dislocations, in particular, ...precipitates and clusters composed of Cu, Ni, Mn, Si and P. In this paper, we employ two complementary atomistic modelling techniques to study the heterogeneous precipitation and segregation of these elements and their effects on the edge dislocations in BCC iron. We use a special and highly computationally efficient Monte Carlo algorithm in a constrained semi-grand canonical ensemble to compute the equilibrium configurations for solute clusters around the dislocation core. Next, we use standard molecular dynamics to predict and analyze the effect of this segregation on the dislocation mobility. Consistently with expectations our results confirm that the required stress for dislocation unpinning from the precipitates formed on top of it is quite large. The identification of the precipitate resistance allows a quantitative treatment of atomistic results, enabling scale transition towards larger scale simulations, such as dislocation dynamics or phase field.
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