Transmutation Effects in Fusion Reactor Materials: Critical Challenges & Path Forward: Radiation Damage Characterization, Modeling & Alloy Design II
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: Arunodaya Bhattacharya, Oak Ridge National Laboratory; Steven Zinkle, University of Tennessee; Philip Edmondson, The University Of Manchester; Aurelie Gentils, Université Paris-Saclay; David Sprouster, Stony Brook University; Takashi Nozawa, National Institutes for Quantum and Radiological Science and Technology (QST); Martin Freer, University of Birmingham

Thursday 2:00 PM
March 23, 2023
Room: 27B
Location: SDCC

Session Chair: Thomas Davis, Oxford Sigma; Ling Wang, Stanford Linear Accelerator Centre


2:00 PM  Cancelled
Effect of Elemental Segregation in High-entropy Alloys on Materials Transport Properties: Kai Nordlund1; 1University of Helsinki
    High-entropy alloys are considered to exhibit sluggish diffusion, which may partly explain many of their unusual macroscopic properties. However, the origins of this effect remain unclear, in part because the atom-level modelling of dynamic processes in an alloy with 5 or more elements is challenging. To improve on this, we have developed a machine-learning interatomic potential for the 5-element refractory metal high-entropy alloy VNbTaMoW. Using this potential, it is possible to use molecular dynamics and Metropolis Monte Carlo simulations to examine elemental segregation effects of defects and dislocations in a true high entropy alloy. The simulation results and associated positron annihilation experiments show major elemental segregation effects in the intermediate atomic environment around both vacancy- and interstitial-like defects. The defect migration is then affected by this segregation. This implies that point defect migration cannot be treated in the traditional manner of a certain defect type having a well-defined migration energy.

2:40 PM  
Impact of Pre-existing Damage on He Irradiated Sintered 3C-SiC: Nabil Daghbouj1; Bingsheng Li1; Miroslav Karlik1; Mauro Callisti1; Tomas Polcar1; Huseyin Sener1; 1Czech Technical University in Prague
    Helium platelets are created in He irradiated sintered 3C-SiC at high temperature with high fluence. These platelets are the precursor of blisters and exfoliation, and in order to prevent their formation, pre-existing damage is induced in sintered SiC. The irradiation of He under the same condition (high temperature and high fluence) induce only nanobubbles. These samples are studied using the combination of energy recoil detection analysis (ERDA), and transmission electron microscopy (TEM) characterization. Our finding demonstrated that SiC contains damage such as vacancies that are dispersed in a wide region and play as a trapping center for He which can lead to decreased He diffusivity (prevent Ostwald repining) and avoid coalescence phenomena. A detailed analysis using ab initio simulation (DFT) revealed that it is energetically very expensive for He atoms to leave a void making Ostwald and coalescence phenomena unlikely.

3:00 PM  
Molecular Dynamics Simulations of Mixed Materials Effects in Tungsten: Mary Alice Cusentino1; Megan McCarthy1; Ember Sikorski1; Mitchell Wood1; Aidan Thompson1; 1Sandia National Laboratories
    Tungsten is the candidate material for the divertor component of fusion reactors. However, the divertor surface will be impacted by a high flux of a variety of plasma species including hydrogen, helium, beryllium, and nitrogen. These plasma species can alter the tungsten microstructure, creating bubbles, blisters, and fuzz as well as mixed materials layers. Molecular dynamics simulations can provide insight into the physical mechanisms behind material degradation and synergistic effects between multiple plasma species in the tungsten divertor. However, developing interatomic potentials for these types of complex interactions is difficult. In this work we will discuss the development of machine learning interatomic potentials to describe these complex material interactions as well as molecular dynamics simulations of mixed materials effects at the divertor surface. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

3:20 PM  
Ultrafast Measurement of Microscopic Energy Flow in He-implanted W: Mianzhen Mo1; Artur Tamm2; Zhijiang Chen1; Erki Metsanurk3; Ling Wang1; Yongqiang Wang4; Mungo Frost1; Nicholas Hartley1; Fuhao Ji1; Samuel Murphy5; Silvia Pandolfi1; Peihao Sun1; Xiaozhe Shen1; Correa Alfredo6; Siegfried Glenzer1; 1SLAC National Accelerator Laboratory; 2University of Tartu; 3Uppsala University; 4Los Alamos National Laboratory; 5Lancaster University; 6Lawrence Livermore National Laboratory
    Tungsten (W) is a plasma-facing material for ITER and will be subject to radiation damage under reactor operating conditions. Among many others, He-induced damage is one of the severe issues and can change drastically the material properties. To understand the materials degradation of W from He effect, we employed the technique of ultrafast electron diffuse scattering to directly measure the electron-phonon and phonon-phonon dynamics in He-implanted W. These couplings play a determining role in properties including electrical and thermal conductivity. From the time-resolved diffuse scattering measurement, we obtained momentum-dependent information on electron-phonon and phonon-phonon interactions at femtosecond temporal resolutions. The experimental results show a clear signature of non-equilibrium phonon dynamics in pristine W, with faster energy transferred from laser-excited electrons to higher-energy phonons. The results further show that the implantation of He ions considerably changes the phonon-phonon coupling process and hence the microscopic energy flow in W.