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Stoller, Roger E

Publications and source records attributed to Stoller, Roger E.

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Primary Radiation Damage Formation in Metals in State-of-the-art Report on Structural Materials Modelling

The processes that give rise to changes in the microstructure and the physical and mechanical properties of materials exposed to energetic particles are initiated by essentially elastic collisions between atoms in what has been called an atomic displacement cascade. The formation and evolution of this primary radiation damage mechanism are described to provide an overview of how stable defects are formed by displacement cascades, as well as the nature and morphology of the defects themselves. The impact of the primary variables cascade energy and irradiation temperature are discussed, along with a range of secondary factors that can influence damage formation.Radiation-induced changes in microstructure and mechanical properties in structural materials are the result of a complex set of physical processes initiated by the collision between an energetic particle (neutron or ion) and an atom in the lattice. This primary damage event is called an atomic displacement cascade. The simplest description of a displacement cascade is to view it as a series of many billiard-ball-like elastic collisions among the atoms in the material. This chapter describes the formation and evolution of this primary radiation damage mechanism to provide an overview of how stable defects are formed by displacement cascades, as well as the nature and morphology of the defects themselves. The impact of the relevant variables such as cascade energy and irradiation temperature is discussed, and defect formation in different materials is compared.

atomic displacement cascades↗
DOE OSTI2015

Effect of helium on irradiation creep behavior of B-doped F82H irradiated in HFIR

The diameter of pressurized tubes of F82H and B-doped F82H irradiated up to similar to 6 dpa have been measured by a non-contacting laser profilometer. The irradiation creep strains of F82H irradiated at 573 and 673K were almost linearly dependent on the effective stress level for stresses below 260 MPa and 170 MPa, respectively. The creep strain of (BN)-B-10-F82H was similar to that of F82H IEA at each effective stress level except 294 MPa at 573K irradiation. For 673K irradiation, the creep strain of some (BN)-B-10-F82H tubes was larger than that of F82H tubes. However, the generation of similar to 300 appm He did not cause a large difference in the irradiation creep behavior at 6 dpa.

Ando, M.↗
DOE OSTI2015

Displacement Cascade Damage Production in Metals

Radiation-induced changes in microstructure and mechanical properties in structural materials are the result of a complex set of physical processes initiated by the collision between an energetic particle (neutron or ion) and an atom in the lattice. This primary damage event is called an atomic displacement cascade. The simplest description of a displacement cascade is to view it as a series of many billiard-ball-like elastic collisions among the atoms in the material. This chapter describes the formation and evolution of this primary radiation damage mechanism to provide an overview of how stable defects are formed by displacement cascades, as well as the nature and morphology of the defects themselves. The impact of the relevant variables such as cascade energy and irradiation temperature is discussed, and defect formation in different materials is compared.

defect creation↗
DOE OSTI2014

Breakthrough in Understanding Radiation Growth of Zirconiu

The efforts of many scientists for more than a half of a century have resulted in a substantial understanding of the response of Zr-based materials to irradiation. However, the models of radiation growth proposed to date have not played a decisive role in creating radiation-resistant materials and cannot predict strain rates at high irradiation doses. The main reason for this is the common assumption that, regardless of the incident particle mass and energy, the primary damage consists of single vacancies and self-interstitial atoms (SIAs), both diffusing three-dimensionally. Thus, the models ignore the distinguishing features of the damage production in displacement cascades during fastparticle, e.g., neutron, irradiation; namely, the intra-cascade clustering of vacancies and SIAs and one-dimensional diffusion of SIA clusters. Over the last twenty years or so, the production bias model (PBM) has been developed, which accounts for these features and explains many observations in cubic crystals. The cascades in hcp crystals are found to be similar to those in cubic crystals; hence one can expect that the PBM will provide a realistic framework for the hcp metals as well. It is shown in this paper that it reproduces all the growth stages observed in annealed materials under neutron irradiation, such as the high strain rate at low, strain saturation at intermediate, and breakaway growth at relatively high doses. It accounts for the striking observations of negative strains in prismatic directions and co-existence of vacancy- and interstitial-type prismatic loops, which have never been explained before. It reveals the role of cold work in the radiation growth behavior and the reasons for the alignment of basal vacancy-type loops along the basal planes. The critical parameters determining the high-dose behavior are revealed and the maximum growth rate is estimated.

Golubov, Stanislav I↗
DOE OSTI2013

Irradiation response in weldment and HIP joint of reduced activation ferritic/martensitic steel, F82H

This work investigates irradiation response in the joints of F82H employed for a fusion breeding blanket. The joints, which were prepared using welding and diffusion welding, were irradiated up to 6 dpa in the High Flux Isotope Reactor at the Oak Ridge National Laboratory. Post-irradiation tests revealed hardening in weldment (WM) and base metal (BM) greater than 300 MPa. However, the heat affected zones (HAZ) exhibit about half that of WM and BM. Therefore, neutron irradiation decreased the strength of the HAZ, leaving it in danger of local deformation in this region. Further the hardening in WM made with an electron beam was larger than that in WM made with tungsten inert gas welding. However the mechanical properties of the diffusion-welded joint were very similar to those of BM even after the irradiation.

Hirose, Takanori↗
DOE OSTI2013

Cascade Defect Evolution Processes: Comparison of Atomistic Methods

Determining the defect evolution beyond the molecular dynamics (MD) time scale is critical in bridging the gap between atomistic simulations and experiments. The recently developed self-evolving atomistic kinetic Monte Carlo (SEAKMC) method provides new opportunities to simulate long-term defect evolution with MD-like fidelity. In this study, SEAKMC is applied to investigate the cascade defect evolution in bcc iron. First, the evolution of a vacancy rich region is simulated and compared with results obtained using autonomous basin climbing (ABC) +KMC and kinetic activation-relaxation technique (kART) simulations. Previously, it is found the results from kART are orders of magnitude faster than ABC+KMC. The results obtained from SEAKMC are similar to kART but the time predicted is about one order of magnitude faster than kART. The fidelity of SEAKMC is confirmed by statistically relevant MD simulations at multiple higher temperatures, which proves that the saddle point sampling is close to complete in SEAKMC. The second is the irradiation-induced formation of C15 Laves phase nano-size defect clusters. In contrast to previous studies, which claim the defects can grow by capturing self-interstitials, we found these highly stable clusters can transform to <111> glissile configuration on a much longer time scale. Finally, cascade-annealing simulations using SEAKMC is compared with traditional object KMC (OKMC) method. SEAKMC predicts substantially fewer surviving defects compared with OKMC. The possible origin of this difference is discussed and a possible way to improve the accuracy of OKMC based on SEAKMC results is outlined. These studies demonstrate the atomistic fidelity of SEAKMC in comparison with other on-the-fly KMC methods and provide new information on long-term defect evolution in iron.

Xu, Haixuan↗