Search NASA⌕ Search

Engineering topics

Weber, William

Publications and source records attributed to Weber, William.

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

High Entropy Alloys: Irradiation

High entropy alloys (HEAs) have been considered as structural materials for nuclear applications due to their promising mechanical properties and radiation resistance. For this purpose, irradiation-induced defect evolution and microstructure change have been characterized to evaluate the irradiation performance of different HEAs. This article reviews recent advances in understanding the irradiation response of HEAs, including the effect of disordered states on the defect energy landscape and defect evolution, irradiation-induced microstructure changes, void swelling, phase stability, mechanical properties under irradiation, as well as the He irradiation effects.

Zhao, Shijun↗
DOE OSTI2021

Origin of increased helium density inside bubbles in Ni (1–$x$) Fe $x$ alloys

Due to virtually no solubility, He atoms implanted or created inside materials tend to form bubbles, which are known to damage material properties through embrittlement. Higher He density in nano-sized bub- bles was observed both experimentally and computationally in Ni (1–$x$) Fe $x$ -alloy samples compared to Ni. The bubbles in the Ni (1–$x$) Fe $x$ -alloys were observed to be faceted, whereas in elemental Ni they were more spherical. Molecular dynamics simulations showed that stacking fault structures formed around bubbles at maximum He density. Higher Fe concentrations stabilize stacking fault structures, suppress evolution of dislocation network around bubbles and suppress complete dislocation emission, leading to higher He density.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Dislocation loop evolution and radiation hardening in nickel-based concentrated solid solution alloys

Effects of chemical composition, ion irradiation dose and temperature on unfaulting of irradiation induced Frank dislocation loops to perfect loops in two nickel based single-phase solid solution alloys, Ni–20Fe and NiFe–20Cr, have been studied. The fraction of Frank loops decreases with irradiation dose from 7.2 to 38.4 dpa at 500°C, but with more Frank loops remaining in the ternary alloy. However, perfect loops and dislocation networks become the dominant features of defects at 580°C in both alloys. The results indicate a thermally assisted loop unfaulting process that may be hindered by more sluggish defect motion in the alloy with more chemical components. Nano-indentation with both continuous stiffness method and single indentation method are used to measure radiation hardening. Loop unfaulting in both alloys irradiated at 580°C reduced radiation hardening while significant hardening is observed after irradiation at 500°C. The quasi-static single indentation method exhibits lower hardness results compared to continuous stiffness method, because dislocations induced from the cyclic loading in the latter method get relaxed and stabilized, resulting in higher resistance to the indenter.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Electronic stopping in molecular dynamics simulations of cascades in 3C–SiC

Here, we investigate the effect of the electronic stopping power on defect production due to ion irradiation of cubic silicon carbide using molecular dynamics simulations. We simulate 20 keV and 30 keV Si and C ions, with and without the electronic energy loss. The results show that the electronic stopping effects are more profound in the case of C irradiation, where the ratio of the electronic energy loss S e to the nuclear energy loss S n is much larger compared to the ratio for Si ions. These findings indicate that this ratio plays a role in the effect of the electronic stopping on ion irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Symmetry degeneration and room temperature ferroelectricity in ion-irradiated SrTiO 3

Polar phonon modes associated with room temperature ferroelectricity are observed in SrTiO 3 single crystals irradiated with Ti ions. Quantitative strain analysis reveals that irradiation-induced out-of-plane strain drives the centrosymmetric cubic SrTiO 3 to a tetragonal-like structure in the maximum damaged region. Energy transfer from ions to electrons during ion irradiation yields defects in SrTiO 3 that also plays an important role for the room temperature ferroelectricity. Different from thin film techniques, the ferroelectricity in the ion irradiated SrTiO 3 can occur for much larger thicknesses, depending on the energy and type of ion.

36 MATERIALS SCIENCE↗
DOE OSTI2020

From suppressed void growth to significant void swelling in NiCoFeCr complex concentrated solid-solution alloy

Void swelling can result in dimensional instability and undermine the safe operation of nuclear reactors. Current strategies to inhibit void swelling mainly focus on enhancing defect absorption and recombination by introducing high-density defect sinks. Complex concentrated solid-solution alloys (CSAs), including high-entropy alloys, can withstand severe radiation damage due to their inherent chemical complexity without interfaces. However, the underlying mechanisms for void suppression in CSAs are far from clear. In this research, we studied the void evolution with respect to irradiation depths, doses, and temperatures in equiatomic NiCoFeCr under 3 MeV Ni ion irradiations. At relatively low doses (16 and 54 displacements per atom, dpa), voids form mainly outside of the ion-damaged region, and void formation in the peak damage region is suppressed, leading to negligible swelling. However, with further increase of dose (86 up to 250 dpa), significant void growth occurs in the peak damage region and extended dislocation lines dominate instead of short dislocation lines and loops formed at lower doses. From 500 to 700 °C, the dislocation density decreases while dislocations grow. Although the overall void swelling increases dramatically from 500 to 580 °C at 54 dpa, void growth in the peak damage region is still suppressed. The transition from suppressed void growth to significant void swelling is attributed to dislocation evolution and local chemical inhomogeneity (enrichment of Fe/Cr in the matrix) at higher doses. Our study shows that controlling element diffusion and defect evolution through tuning chemical complexity can further enhance the swelling resistance of CSAs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Interpreting nanovoids in atom probe tomography data for accurate local compositional measurements

Quantifying chemical compositions around nanovoids is a fundamental task for research and development of various materials. Atom probe tomography (APT) and scanning transmission electron microscopy (STEM) are currently the most suitable tools because of their ability to probe materials at the nanoscale. Both techniques have limitations, particularly APT, because of insufficient understanding of void imaging. Here, we employ a correlative APT and STEM approach to investigate the APT imaging process and reveal that voids can lead to either an increase or a decrease in local atomic densities in the APT reconstruction. Simulated APT experiments demonstrate the local density variations near voids are controlled by the unique ring structures as voids open and the different evaporation fields of the surrounding atoms. We provide a general approach for quantifying chemical segregations near voids within an APT dataset, in which the composition can be directly determined with a higher accuracy than STEM-based techniques.

36 MATERIALS SCIENCE↗
NASA NTRS1991

Estimating Liquid And Gas Contents In A Tank

General approach to estimation of amounts of liquid and gas in tank based on measurements of pressure perturbations and temperatures and use of thermodynamic relationships among pressures, temperatures, and volumes. Although approach approximate and indirect, advantageous where such direct and precise methods as observation of stationary liquid/gas interface in gravitational field cannot be used. Used in presence or absence of gravitation or acceleration, and regardless of numbers, shapes, and movements of liquid/gas interfaces in tank. Also useful where liquid stationary but too hazardous to permit direct observation. Implemented in variety of ways, depending on type of liquid and conditions of operation and design of tank system.

Walter, Richard T.↗