Phase Stability in Extreme Environments: Phase Stability in Nuclear Environments III
Sponsored by: TMS Structural Materials Division, TMS Materials Processing and Manufacturing Division, TMS: Corrosion and Environmental Effects Committee, TMS: Nuclear Materials Committee, TMS: Phase Transformations Committee
Program Organizers: Andrew Hoffman, Catalyst Science Solutions; Kinga Unocic, Oak Ridge National Laboratory; Janelle Wharry, Purdue University; Kaila Bertsch, Lawrence Livermore National Laboratory; Raul Rebak, GE Global Research

Tuesday 8:00 AM
March 21, 2023
Room: 28C
Location: SDCC

Session Chair: Tiankai Yao, Idaho National Laboratory; Stephen Taller, Oak Ridge National Laboratory


8:00 AM  Invited
Phase Stability of δ-U-50wt%Zr under Thermal Treatment and Irradiation: Amrita Sen1; Tiankai Yao2; Mukesh Bachhav2; Janelle Wharry1; 1Purdue University; 2Idaho National Laboratory
    The objective of this study is to investigate the influence of temperature and irradiation on phase stability in δ-U-50wt%Zr. U-Zr based metallic fuels are being considered for advanced nuclear reactor applications for their superior performance and recyclability compared with conventional oxide fuels. But due to sluggish diffusion of U in Zr, complex phase evolution under extreme conditions can occur. Amongst the stable room temperature phases of U-Zr, δ-UZr2 is the least well understood. In this study, we investigate the microstructural evolution of δ-U-50wt%Zr under thermal and irradiation treatments, using a combination of TEM and APT methods. High temperature thermal annealing on this material results in spinodal-like decomposition, whereas room temperature proton irradiation results in the formation of needle-like precipitates. These results suggest unique phase evolution of δ-U-50wt%Zr under extreme conditions that deviate from that predicted by the conventional thermodynamic U-Zr phase diagram and implications of such will be discussed.

8:30 AM  
Precipitate Evolution in Post-AM Heat Treated and HFIR Irradiated Inconel 718 Alloys: Stephen Taller1; Lukas Metzger2; Matthew Lynch3; 1Oak Ridge National Laboratory; 2Virginia Polytechnic Institute and State University; 3University of Michigan
    Ni-based superalloys are a candidate alloy class for high temperature applications because of their intrinsic resistance to creep, their adequate resistance to corrosion and their high strength gained through secondary phases. Because nickel alloys work harden extensively, additive manufacturing can produce geometrically complex components traditionally unavailable through conventional machining. Three heat treatments of additively manufactured superalloy 718, two with distinct mixtures of δ ,γʹ and γʹʹ precipitates, and one completely homogenized, were irradiated in the High Flux Isotope Reactor (HFIR) nominally to 2 DPA at either 300°C or 600°C to represent current and advanced reactor temperatures. The microstructure was characterized for precipitates, cavities, and dislocations using Scanning Transmission Electron Microscopy and Energy-Dispersive X-ray Spectroscopy. Molecular statics and dynamics calculations of Ni-Nb precipitate-defect interactions at multiple temperatures informed a rate theory Nelson-Hudson-Mazey based model using calculated sink strengths of each microstructural feature to interpret the observed precipitate sizes and densities.

8:50 AM  
Long-range Ordering in Alloy 690 via Isothermal Aging and Irradiation: Julie Tucker1; Cole Evered1; Nicholas Aerne1; Luanne Rolly1; David Sprouster2; 1Oregon State University; 2Stony Brook University
    The formation of long-range ordered phase Ni2Cr in commercial alloy 690 has long been debated as a potential concern in nuclear power applications. The ordered phase is known to cause hardening, embrittlement and lattice contraction but the timescale associated with its formation in commercial alloys has been unclear. In this work, we isothermally aged commercial alloys up to 30,000 hours at 360-475°C and then quantify the Ni2Cr precipitates with synchrotron x-ray diffraction. We find that Ni2Cr forms in Alloy 690 by 20,000 hours 418°C. Additionally, we study the role of P impurities as a potential accelerating factor in Ni2Cr formation by irradiating Alloy 690 with and without 0.01wt.% P additions. The P containing alloy forms Ni2Cr precipitates while the pure 690 alloy does not when irradiated at 350°C to 1.5dpa. Lastly, we compare irradiated and isothermally aged Ni-Cr-Fe model alloys to quantify the acceleration in ordering provided by proton irradiation.

9:10 AM  
Quantitative Phase Field Modeling of Morphological Evolution of Voids under Ion Irradiation: Sreekar Rayaprolu1; Cuncai Fan1; Xinghang Zhang1; Anter El-Azab1; 1Purdue University
    A quantitative diffuse interface model based on KKS formalism has been developed to describe the void evolution under irradiation. The model considers both vacancies and interstitials in the description of void evolution. Unique to the present model is the accurate description of the chemical potentials of defects in the void and matrix, as well as the presence of two mobility parameters in the equation of motion of the phase-field variable. Recent in situ experimental studies revealed the shrinkage, spheroidization, and migration of pre-existing voids in a Cu sample subjected to ion irradiation. Moreover, it was observed that the migration and morphology evolution of these pre-existing voids were highly dependent on the irradiation temperature. In this communication, we explain the underlying mechanisms for the change of void morphology including size, shape, and position using the novel phase-field model.

9:30 AM Break

9:50 AM  
Damage Dependence of Radiation Induced Segregation at Fully Characterized Grain Boundaries in Proton Irradiated 316L Stainless Steel: Sara Wonner1; Pascal Bellon1; 1The University of Illinois, Urbana Champaign
    It has been reported that distinct grain boundaries can exhibit different levels of radiation induced segregation (RIS). RIS studies, however, most often utilized different samples to investigate the evolution of RIS with increasing radiation damage levels, without full determination of the character of the investigated grain boundaries (GBs), thus potentially resulting in uncontrolled RIS variations. In this study, we take advantage of advances in sample preparation and characterization to overcome these limitations. EBSD mapping is combined with focused ion beam for preparing cross-sectional TEM samples across selected GBs, with thin areas extending over ≈ 10 µm in depth, allowing for the determination of the 5 degrees of freedom of each grain boundary. We illustrate the benefits of this approach by quantifying Ni and Si RIS in 2 MeV proton irradiated 316L samples by STEM-EDS, for GBs ranging from large angle ones to special GBs such as twin boundaries.

10:10 AM  
Effect of Dose Rate and Composition on the Precipitation Behavior of RPV Steels: Anshul Kamboj1; Nathan Almirall2; Emmanuelle Marquis1; G. Robert Odette3; 1University of Michigan Ann Arbor; 2General Electric Research; 3University of California, Santa Barbara
    Life extension of light water reactors require that reactor pressure vessels (RPVs) operate within the safety margins of embrittlement under long-term irradiation. The embrittlement results from nanoscale precipitate phases consisting of Cu, Mn, Ni, and Si. Studying the evolution of these phases under actual operating environment is time and cost intensive due to the low neutron dose rate. Therefore, relatively higher dose rate neutrons in test reactors and ion irradiation are often used to study irradiation effects. However, dose rates can significantly influence precipitate evolution and hence the understanding of microstructural evolution as alloy composition as a function of flux is required. Therefore, we studied two sets of six different RPV steel samples with varying Cu and Ni irradiated using medium flux ions (10^-5&10^-6dpa/s) and relatively low flux neutrons (10^-9dpa/s). Atom probe tomography characterization revealed a significant effect of dose rate on precipitate number density, size, volume fraction, and morphology.

10:30 AM  
Synergetic Effects of Mn, Ni, and Si on the Formation of Mn-Ni-Si Clusters in the Reactor Pressure Vessel Model Steels: Deepak Sharma1; Auriane Etienne1; Philippe Pareige1; Bertrand Radiguet1; 1Groupe de Physique des Matériaux, Université et INSA de Rouen, UMR CNRS 6634
    As a part of the STRUMAT-LTO project, we are investigating the synergetic effects of Mn, Ni, and Si on the formation of Mn-Ni-Si clusters at higher neutron fluences. Six reactor pressure vessel model steels, with different content of Mn, Ni, and Si, were produced for this work. The samples were irradiated to a neutron fluence of ~1.11 × 1020 n cm–2 (E > 1 MeV) at 283 °C; with a flux of ~2.75 × 1012 n cm–2 s–1. Atom probe tomography (APT) was used to gather the microstructural information for all the alloys in unirradiated and irradiated conditions. The unirradiated samples do not show any clustering tendency. The hardening of samples after neutron irradiation trends with the increase in Ni content. Mn and Ni show a synergetic effect on hardening. The APT results on the unirradiated and the irradiated samples will be presented and discussed.

10:50 AM  
Fundamental Ionizing and Ballistic Radiation Effects in Multi-component Mineral Phases: Sean Drewry1; Katharine Page1; Kurt Sickafus1; Chris Wetteland1; 1University of Tennessee Knoxville
    Extended operation of light water reactors (LWRs) necessitates the need to assure the durability and reliability of component materials. Concrete structures are ubiquitous to LWRs and, critically, have load bearing as well as radiation shielding functions. Mineral phases within the concrete assemblage can have a substantial sensitivity to ionizing radiation, consequences of which are radiation induced volumetric expansion, structural order-disorder phase transformations, and amorphization. Samples of the plagioclase feldspar anorthite, CaAl2Si2O8, were irradiated with Si+, H+, and Au+ ions to investigate these effects. Disorder of the Si,Al tetrahedra can create a space group transition from P-1 to I-1. The radiation damage profile was characterized using grazing incidence (GI)-XRD along with cross-sectional TEM analysis. Rietveld refinement of the GI-XRD patterns along the damage profile can be used to determine the order to disorder phase transformation and amorphous volume. Diffractograms from the TEM analysis can elucidate the local disorder.