Materials in Nuclear Energy Systems (MiNES) 2021: Fundamental Irradiation Damage- Session V
Program Organizers: Todd Allen, University of Michigan; Clarissa Yablinsky, Los Alamos National Laboratory; Anne Campbell, Oak Ridge National Laboratory

Wednesday 10:30 AM
November 10, 2021
Room: Urban
Location: Omni William Penn Hotel

Session Chair: Jason Trelewicz, Stony Brook University

10:30 AM  Invited
Radiation Effects and Thermal Stability in Ferritic Steels and High Entropy Alloys: Eda Aydogan¹; O. El-Atwani²; K. Iroc¹; A. Ozalp¹; S.A. Maloy²; Y.E. Kalay¹; ¹Middle East Technical University; ²Los Alamos National Laboratory
    There is a worldwide need of nuclear energy due to the increase in the world’s population and the desire to reduce greenhouse gasses from burning of fossil fuels. However, nuclear energy systems operate under high temperatures and stresses, chemically corrosive environments, and high neutron fluxes. Engineered ferritic alloys are one of the best materials for high temperature and extreme radiation environments. Moreover, new material system of refractory high entropy alloys (RHEAs) have demonstrated great promise. In this study, thermal stability and radiation resistance of nanostructured ferritic alloy (NFA), 14YWT, produced by powder metallurgy methods and TiZrHfNbTa RHEAs produced by vacuum arc melting and additive manufacturing techniques have been investigated. Recently, we have shown that NFAs and RHEAs are extremely stable up to >1000 ⁰C and they show almost zero swelling under high dose irradiation.

11:10 AM
Effect of Damage Rate and Cascade Size on α' Precipitate Stability in Fe-15Cr: Katey Thomas¹; Zhijie Jiao¹; Gary Was¹; ¹University of Michigan
    Fe-Cr ferritic-martensitic (F-M) steels are candidates for nuclear reactor structural components due to their high resistance to swelling and corrosion. However, these steels are susceptible to Cr-rich α’ precipitate formation at low to intermediate temperatures in thermal and irradiation environments. In this study, the effects of damage rate and cascade size on α’ precipitate stability is determined using a steady state α’ precipitate population formed by 2 MeV proton irradiation at 1x10-5 dpa/s to 1 dpa at 400°C. Samples were then subjected to further irradiation, varying the damage rate and cascade size using self-ion, proton, and electron irradiation up to 10 dpa at 400°C. Atom probe tomography (APT) analysis was used to assess precipitate size, number density, volume fraction and Cr content. Results are used to determine the ballistic dissolution factor and to unfold the roles of cascade size and damage rate on α’ stability.

11:30 AM
A New Statistical Approach for Atomistic Calculations of Point Defect Formation Energies in Multicomponent Solid-solution Alloys: Yongfeng Zhang¹; Sean Masengale¹; Anus Manzoor²; Chao Jiang³; Dilpuneet Aidhy⁴; Daniel Schwen⁵; ¹University of Wisconsin-Madison; ²University of Wyoming ; ³Idaho National Laboratory ; ⁴University of Wyoming; ⁵Idaho National Laboratory
    Understanding thermodynamic properties of defects is critical for developing multicomponent alloys for nuclear energy applications. Calculating formation energies of point defects in multicomponent alloys requires calculating chemical potential of each alloying element, which induces additional computation cost and extra uncertainty. This talk presents a new, statistical approach for calculating point defects formation energies in multicomponent alloys. The proposed approach can give the statistical distribution of point defect formation energies without separate calculations for chemical potentials, which can still be derived in a self-consistent manner. It is found that, capturing the distributions of formation energies is of critical importance for estimating thermal equilibrium point defect concentrations. The approach is demonstrated using density functional theory calculations for ternary FeNiCr alloy and molecular dynamics simulations for binary UZr alloy as well as a five-element high-entropy alloy. It is straightforward for alloys with any number of alloying elements.

11:50 AM
Effect of Helium Injection Rate on Cavity Microstructure in Dual Ion Irradiated T91 Steel: Valentin Pauly¹; Stephen Taller²; Zhijie Jiao¹; Gary Was¹; ¹University of Michigan; ²Oak Ridge National Laboratory
    Ferritic-martensitic steel T91 heat 30176 was irradiated using defocused 5.0 MeV Fe²⁺ or 9.0 MeV Fe³⁺ ions up to 100 dpa at 445-460°C with a constant damage rate of 7×10^-4 dpa/s with co-injected He²⁺ ions at a rate varying between 0.22 and 4 appmHe/dpa. Transmission electron microscopy was used to characterize irradiation-induced cavities. For the first 35 dpa, the He injection rate was kept constant at 4 appmHe/dpa. After 35 dpa, the He injection rate was either kept constant or reduced to 0.22 appmHe/dpa. The cavity microstructure at 72 dpa with a reduction in He injection rate was similar to the constant 4 appmHe/dpa. Characterization results were combined with a model based on the cavity growth rate equation and the critical bubble model to better understand the impact of varying He injection rate on the nucleation of bubbles and their transformation to voids.