Radiation Effects in Metals and Ceramics: Chemical and Phase Stability under Irradiation
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: Djamel Kaoumi, North Carolina State University; Thak Sang Byun, Oak Ridge National Laboratory; Dane Morgan, University of Wisconsin-Madison; Maria Okuniewski, Purdue University; Mahmood Mamivand; Geoffrey Beausoleil, Idaho National Laboratory; Philip Edmondson, The University Of Manchester; Khalid Hattar, University of Tennessee Knoxville; Aurelie Gentils, Université Paris-Saclay; Joel Ribis, Cea
Tuesday 2:00 PM
February 25, 2020
Room: Theater A-7
Location: San Diego Convention Ctr
Session Chair: Mahmood Mamivand, Boise State University; Djamel Kaoumi, North Carolina State University
2:00 PM
BCC-FCC Interface Leading to Ni Precipitation under Irradiation in a FeNi Alloy: Estelle Meslin1; Lisa Belkacémi1; Brigitte Décamps2; Marie Loyer-Prost1; Maylise Nastar1; 1CEA; 2CSNSM Orsay University
A bcc Fe-3%at. Ni ferritic alloy has been irradiated with 27 MeV Fe9+ ions at 673 K to a damage rate of 10-6 dpa.s-1 within the Jannus Saclay facility, up to a displacement damage of 1.2 dpa. We recently report the formation of a fcc phase in this purely bcc matrix [1]. Since the alloy was initially undersaturated, the out-of-equilibrium fcc phase formation was radiation induced. In this presentation, we will focus on the atomic scale description of the fcc/bcc interface (HR-TEM). There is a Kurdjumov-Sachs (KS) relationships: {111}γ(fcc)//{110}α(bcc) between the bcc matrix and the fcc precipitate. The later are grouped by blocks of 2 variants exhibiting a twin relationships. Explanations about the formation mechanism of these precipitates, involving the defects created under irradiation, will be given.[1] L.T. Belkacemi, E. Meslin, B. Décamps, B. Radiguet, J. Henry, Acta Materialia Vol. 161 (2018)) 61-72.
2:20 PM
Enhanced Austenite Stability in Nanostructured Steels During Ion Irradiation: Andrew Hoffman1; Maalavan Arivu1; Haiming Wen1; 1Missouri University of Science and Technology
The formation of ferrite in austenitic steels during irradiation has been documented for decades, and typically occurs at temperatures above 400 °C. Because this transformation does not typically occur at lower temperatures, this transformation has been attributed greatly to the chemical segregation of Ni (an austenite stabilizer) towards grain boundaries and dislocations, therefore reducing the austenite stability of the matrix. Some studies, however, claim that this transformation is due to the high strain accumulated in the material, causing a strain induced martensite transformation. In this study, we show that in the case of 304L steel ion irradiated at 500 °C, both chemical segregation and strain contribute to the ferrite formation. Additionally, we show that ultrafine-grained and nanocrystalline 304L steels possess significant resistance to the ferritic transformation during irradiation. This enhanced phase stability has been attributed to both reduced radiation induced segregation and resistance to radiation induced strain from defect accumulation.
2:40 PM
Solute Stabilization of Two-phase Microstructures in Irradiated Alloys: Soumyajit Jana1; Pascal Bellon1; Robert Averback1; 1University of Illinois Urbana Champaign
Competition between ballistic mixing and thermal diffusion often leads to self-organized compositional patterning in two-phase binary alloys during irradiation. These compositional patterns are steady-state structures and thus provide radiation resistance. In order to extend their stability to higher temperatures, we consider here dilute additions of a second solute, C, to a patterning A-B alloy. We show using KMC simulations that the solute C, when binding to vacancies, can suppress diffusion of the precipitating solute B, thus promoting defect recombination and extending the patterning regime. However the effects introduced by the two solutes, patterning and enhanced recombination, are not additive, but rather there are complex couplings between alloy concentration, atomic interactions and sink density. For example, if the heat of mixing of the B-C system is lower than that of A-B, precipitation of the B solute removes the C solute from the matrix, thereby reducing its efficiency.
3:00 PM
Alpha-alpha' Decomposition at Grain Boundaries in Annealed and Irradiated ODS Steels: Joel Ribis1; Amal Issaoui1; Joel Malaplate1; Marie Loyer-Prost1; Alexandre Legris2; 1Commissariat a l'Energie Atomic CEA; 2University of Lille
Cr-rich ferritic Oxide Dispersion Strengthened (ODS) steels are envisaged as cladding materials in Generation IV fission nuclear reactors due to their good radiation resistance and improved high-temperature mechanical properties. However, these alloys, whose service temperature is in the range of 400-700°C, face severe embrittlement problems owing to the decomposition of the matrix into the alpha (Fe-rich) and alpha’ (Cr-rich) phases. Thus, the aim of our study is to analyse the chemical response of the grain boundaries under both sollicitation: thermal aging and irradiation. We showed that under thermal aging, the low angle grain boundaries present a slight segregation of Cr while the large angle grain boundaries present a high Cr segregation. Further we reported spinodal decomposition solely at high angle grain boundaries while a classic nucleation/growth is observed for the alpha-alpha’ decomposition within the matrix. Under irradiation, Cr segregation is observed at dislocations while grain boundaries are systematically depleted.
3:20 PM
Dose Rate and Temperature Effect on the Stability of Alpha Prime Precipitates in Ultra-high Purity Fe-Cr Alloys: Yajie Zhao1; Arunodaya Bhattacharya2; Philip Edmondson2; Caleb Massey2; Jean Henry3; Steven Zinkle1; 1University of Tennessee; 2Oak Ridge National Laboratory; 3CEA, DEN, Service de Recherches Métallurgiques Appliquées, Laboratoire d’Analyse Microstructurale des Matériaux, Université Paris-Saclay
Cr-rich alpha prime (α’) precipitates are detrimental to the mechanical properties of FeCr based ferritic-martensitic steels. Understanding α’ precipitation under irradiation conditions is essential for application of this steel in nuclear reactor environments. To study the effect of dose rate (ballistic dissolution) and irradiation temperature (radiation-enhanced diffusion) on α’ formation, ultra-high purity Fe-Cr alloys with 12-18 wt.% Cr (in either solid solution or thermally aged to form pre-existing α’precipitates) were irradiated with 8 MeV Fe ions to a midrange (~1 um) dose of 0.35-3.5 displacements per atom (dpa) between 300-450 °C at 10^-3, 10^-4 and 10^-5 dpa/s. Following irradiation, atom probe tomography (APT) was employed to characterize the number density, radius and Cr concentration of Cr-rich clusters. Homogeneously distributed α’ precipitates were revealed when radiation-enhanced diffusion dominates over ballistic dissolution (>350°C). The segregation of Cr, C and N atoms to dislocation loops was also observed.
3:40 PM Break
4:00 PM Invited
The Effect of Point Defects on the Thermodynamics and Kinetics of Irradiated Materials: Thomas Schuler1; Maylise Nastar1; 1DEN-Service de Recherches de Métallurgie Physique, CEA, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France
Irradiation creates a supersaturation of point defects in materials, and their interaction with atoms leads to various phenomena that we are now able to understand and quantify using state-of-the art modeling tools. For instance, irradiation can trigger precipitate dissolution when point defects stabilize solutes in the solid solution. This thermodynamic mechanism is very different from the well-known kinetic “ballistic” dissolution mechanism. When the precipitate density differs significantly from the matrix density, point defects will have a huge effect on precipitation sequences as they provide the additional space or lattice sites required to grow the precipitate phase. These two examples show that thermodynamics under irradiation is far more subtle than equilibrium thermodynamics. Also, kinetic effects must not be neglected. For instance solute-point defect flux coupling can, over time, suppress the recombination enhancement due to solute addition. We will discuss these phenomena and how we model them.
4:30 PM
Influence of an Addition of Titanium and Carbon on the Microstructural Evolution under Irradiation of Nickel as Model Alloy for Austenitic Steels: Marie Loyer-Prost1; Kan Ma1; Brigitte Décamps2; Robin Schaeublin3; Fréderic Prima4; 1DEN-Service de Recherches de Métallurgie Physique, CEA; 2CNRS, IN2P3, CSNSM; 3ETH Zürich; 4CNRS UMR 8247-Institut de Recherche de Chimie Paris
Austenitic Stainless Steels (ASSs) are foreseen as cladding material for next generation reactors even though their swelling under irradiation will limit the fuel burnup. Solute elements, such as titanium and carbon, efficiently reduce this swelling but the mechanism is still unexplained. Here we focus on the effect of an addition of titanium and carbon on the microstructure evolution of nickel at small irradiation dose. Nickel is considered as a model alloy for ASSs (same crystallographic structure). Ni alloys (Ni, Ni-Ti, Ni-Ti-C) were irradiated at 510°C in a TEM using the JANNuS-Orsay facility up to 0,06 dpa. The microstructure evolution of samples was recorded and analyzed. Results will be presented in details and discussed during the presentation. For example, we will describe the microstructure evolution (dislocation loop growth) in the three samples and compare the effect of an addition of titanium alone with that of titanium coupled to carbon.
4:50 PM
Investigation of the Stability of Irradiation Induced MnNi Clusters by Post Irradiation Annealing: Bertrand Radiguet1; Milan Konstantinovic2; Philippe Pareige1; 1University Of Rouen; 2SCK-CEN
In order to get a better understanding and a more accurate anticipation of the neutron fluence dependence of the microstructure of reactor pressure vessel steels, it is important to determine unambiguously the nature of the irradiation induced features usually observed by APT (solute rich clusters, solutes-point defects complex clusters, thermodynamically stable phases….). Post irradiation annealing can bring information about the stability and the nature of these features. In this work, a FeMnNi model alloy was neutron irradiated at a dose of 0.2dpa at 300°C. Post irradiations annealing during 30’ were performed at 400, 500 and 600°C. In order to investigate the irradiated microstructure and the stability of irradiation induced features, materials were characterized by atom probe tomography. Results will be described and compared with positon annihilation data obtained on the same samples at SCK.CEN.
5:10 PM
Investigating the Influence of Cu Rich Precipitates (CRPs) on the Formation of Complex Mn-Ni-Si Rich Precipitate Phases using Density Functional Theory (DFT): Alexander Garrett1; Christopher Race1; 1University of Manchester
It is suggested that when subjected to elevated temperatures and very high neutron fluences low-alloy reactor pressure vessel (RPV) steels could experience anomalous embrittlement due to the formation of complex Mn-Ni-Si precipitates (MNSPs). Cu rich precipitates (CRPs) are suspected of assisting the formation of these MNSPs by acting as sites of segregation for the constituent solute species.This work utilises multi-scale modelling to investigate the morphology of CRPs, using this information to provide insights into the role of CRPs in the formation of complex precipitate phases. Specifically, we have used density functional theory (DFT) in combination with particle swarm optimisation (PSO) and molecular statics to predict the geometries and strain states of CRPs. With these calculated geometries and strains we then investigated the segregation (and co-segregation) of Mn, Ni and Si to CRPs of different radii with DFT, allowing segregation behaviour predictions to be made.
5:30 PM
Atomistic Modeling of Radiation Resistance in Concentrated Alloys: Craig Daniels1; Pascal Bellon1; Robert Averback1; 1University of Illinois
A long-considered strategy for designing radiation-resistant alloys is adding solutes that trap point defects, thus inhibiting their diffusion. These solutes promote vacancy-interstitial recombination and reduce the deleterious effects of defect and solute fluxes on the microstructure. These benefits usually have a limited lifespan as solutes that trap point defects are often dragged by defect fluxes to nearby sinks. We recently introduced a hybrid kinetic Monte Carlo algorithm specifically designed to be computationally efficient in alloys with trapping solutes. This algorithm makes it possible to go beyond the limit of infinite solute dilution, and thus to treat trapping by solute clusters. We apply our KMC code to a model alloy system that mimics Cu-Ag. As the Ag solute concentration increases, most of the trapping takes place on solute clusters, and therefore solute-solute interactions play a determinant role in the defect kinetics.