Inhomogeneous Swelling Near Grain Boundaries in Irradiated Materials: Cavity Nucleation and Growth Saturation Effects

2000 ◽  
Vol 650 ◽  
Author(s):  
S. L. Dudarev
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Nucleation And Growth ◽  
Homogeneous Distribution ◽  
Rate Theory ◽  
Diffusional Growth ◽  
Standard Rate ◽  
Saturation Effects ◽  
Kinetics Of ◽  
Cascade Damage

ABSTRACTThe effect of inhomogeneous nucleation and growth of cavities near grain boundaries illustrates the failure of the standard rate theory to describe the kinetics of phase transformations in irradiated materials under cascade damage conditions. The enhanced swelling observed near grain boundaries is believed to result from the competition between the diffusional growth of cavities and their shrinkage due to the interaction with mobile interstitial clusters. Swelling rates associated with the two processes behave in a radically different way as a function of the size of growing cavities. For a spatially homogeneous distribution of cavities this gives rise to the saturation of swelling in the limit of large irradiation doses.We investigate the evolution of the population of cavities nucleating and growing near a planar grain boundary. We show that a cavity growing near the boundary is able to reach a size that is substantially larger than the size of a cavity growing in the interior region of the grain. For a planar grain boundary the magnitude of swelling at maximum is found to be up to eight times higher than the magnitude of swelling in the grain interior.

scholarly journals Cloud droplet diffusional growth in homogeneous isotropic turbulence: bin microphysics versus Lagrangian superdroplet simulations

2020 ◽  
Author(s):  
Wojciech W. Grabowski ◽  
Lois Thomas
Keyword(s):  
Fluid Flow ◽  
Time Scale ◽  
Isotropic Turbulence ◽  
Spectral Width ◽  
Small Scale ◽  
Computational Domain ◽  
Homogeneous Isotropic Turbulence ◽  
Diffusional Growth ◽  
Droplet Concentration ◽  
Bin Microphysics

Abstract. Increase of the spectral width of initially monodisperse population of cloud droplets in homogeneous isotropic turbulence is investigated applying a finite-difference fluid flow model combined with either Eulerian bin microphysics or Lagrangian particle-based scheme. The turbulence is forced applying a variant of the so-called linear forcing method that maintains the mean turbulent kinetic energy (TKE) and the TKE partitioning between velocity components. The latter is important for maintaining the quasi-steady forcing of the supersaturation fluctuations that drive the increase of the spectral width. We apply a large computational domain, 643 m3, one of the domains considered in Thomas et al. (2020). The simulations apply 1 m grid length and are in the spirit of the implicit large eddy simulation (ILES), that is, with explicit small-scale dissipation provided by the model numerics. This is in contrast to the scaled-up direct numerical simulation (DNS) applied in Thomas et al. (2020). Two TKE intensities and three different droplet concentrations are considered. Analytic solutions derived in Sardina et al. (2015), valid for the case when the turbulence time scale is much larger than the droplet phase relaxation time scale, are used to guide the comparison between the two microphysics simulation techniques. The Lagrangian approach reproduces the scalings relatively well. Representing the spectral width increase in time is more challenging for the bin microphysics because appropriately high resolution in the bin space is needed. The bin width of 0.5 μm is only sufficient for the lowest droplet concentration, 26 cm−3. For the highest droplet concentration, 650 cm−3, even an order of magnitude smaller bin size is not sufficient. The scalings are not expected to be valid for the lowest droplet concentration and the high TKE case, and the two microphysics schemes represent similar departures. Finally, because the fluid flow is the same for all simulations featuring either low or high TKE, one can compare point-by-point simulation results. Such a comparison shows very close temperature and water vapor point-by-point values across the computational domain, and larger differences between simulated mean droplet radii and spectral width. The latter are explained by fundamental differences in the two simulation methodologies, numerical diffusion in the Eulerian bin approach and relatively small number of Lagrangian particles that are used in the particle-based microphysics.

Diffusional Growth Kinetics of Boride Layers on Iron-Chromium Alloys

2008 ◽  
pp. 181-188 ◽  
Author(s):  
V.I. Dybkov ◽  
L.V. Goncharuk ◽  
V.G. Khoruzha ◽  
K.A. Meleshevich ◽  
A.V. Samelyuk ◽  
...  
Keyword(s):  
Growth Kinetics ◽  
Diffusional Growth ◽  
Chromium Alloys ◽  
Kinetics Of ◽  
Iron Chromium

scholarly journals A Gibbs Energy Balance Model for Growth Via Diffusional Growth-Ledges

2019 ◽  
Vol 59 (3) ◽  
pp. 573-582 ◽  
Author(s):  
Samuel James Clark ◽  
Yongjun Lan ◽  
Alireza Rahnama ◽  
Vit Janik ◽  
Seetharaman Sridhar
Keyword(s):  
Energy Balance ◽  
Gibbs Energy ◽  
Energy Balance Model ◽  
Balance Model ◽  
Diffusional Growth

Precipitation of Oxygen and Mechanism of Stacking Fault Formation in Czochralski Silicon Bulk Crystals

1982 ◽  
Vol 14 ◽  
Author(s):  
Kazumi Wada ◽  
Naohisa Inoue ◽  
Jiro Osaka
Keyword(s):  
Growth Model ◽  
Growth Kinetics ◽  
Stacking Faults ◽  
Diffusional Growth ◽  
Czochralski Silicon ◽  
Self Diffusion ◽  
Diffusion Limited ◽  
Silicon Bulk ◽  
Precipitate Growth ◽  
Kinetics Of

ABSTRACTThis paper describes recent progress on nucleation and growth of oxide precipitates and stacking faults in Czochralski silicon. Conclusions on the growth kinetics of oxide precipitates are drawn from the experiments and analysis of growth kinetics of two-dimensional precipitates: The experimentally obtained growth kinetics, three-quarter power law is theoretically derived and the precipitate growth is demonstrated to be diffusion-limited by oxygen interstitials. The formation mechanism of stacking faults is the Bardeen-Herring mechanism. Based on diffusional growth model, the growth kinetics of stacking faults are analyzed, assuming a coexistence of self-interstitial supersaturation and vacancy undersaturation. It is found that the growth is driven by vacancies in undersaturation. Vacancy component of self-diffusion has been determined and found to be predominant at low temperature. The possibility of growth model proposed for increase of oxide precipitate density during annealing has been excluded. Both processes, homogeneous and heterogeneous nucleation, have been taking place during annealing.

Multilayer diffusional growth in silicon–molybdenum interactions

2002 ◽  
Vol 405 (1-2) ◽  
pp. 170-178 ◽  
Author(s):  
Jin-Kook Yoon ◽  
Ji-Young Byun ◽  
Gyeung-Ho Kim ◽  
Jae-Soo Kim ◽  
Chong-Sool Choi
Keyword(s):  
Diffusional Growth

Broadening of the Cloud Droplet Size Distribution due to Thermal Radiative Cooling: Turbulent Parcel Simulations

2020 ◽  
Vol 77 (6) ◽  
pp. 1993-2010
Author(s):  
Mares Barekzai ◽  
Bernhard Mayer
Keyword(s):  
Thermal Radiation ◽  
Droplet Size ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Growth Efficiency ◽  
Droplet Growth ◽  
Radiative Cooling ◽  
Radiative Effect ◽  
Diffusional Growth ◽  
The Impact

Abstract Despite impressive advances in rain forecasts over the past decades, our understanding of rain formation on a microphysical scale is still poor. Droplet growth initially occurs through diffusion and, for sufficiently large radii, through the collision of droplets. However, there is no consensus on the mechanism to bridge the condensation coalescence bottleneck. We extend the analysis of prior methods by including radiatively enhanced diffusional growth (RAD) to a Markovian turbulence parameterization. This addition increases the diffusional growth efficiency by allowing for emission and absorption of thermal radiation. Specifically, we quantify an upper estimate for the radiative effect by focusing on droplets close to the cloud boundary. The strength of this simple model is that it determines growth-rate dependencies on a number of parameters, like updraft speed and the radiative effect, in a deterministic way. Realistic calculations with a cloud-resolving model are sensitive to parameter changes, which may cause completely different cloud realizations and thus it requires considerable computational power to obtain statistically significant results. The simulations suggest that the addition of radiative cooling can lead to a doubling of the droplet size standard deviation. However, the magnitude of the increase depends strongly on the broadening established by turbulence, due to an increase in the maximum droplet size, which accelerates the production of drizzle. Furthermore, the broadening caused by the combination of turbulence and thermal radiation is largest for small updrafts and the impact of radiation increases with time until it becomes dominant for slow synoptic updrafts.

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