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Title: Dimensional Stability and Microstructure Evolution in Irradiated Systems with Complex Kinetics

Abstract

We use a combination of molecular dynamics and kinetic Monte Carlo simulations to explore the role of temperature and dose rate on damage accumulation in a model system with complex kinetics. We describe the accumulation of He-vacancy (HeV) complexes as well as vacancy and interstitial clusters as a function of irradiation temperature, dose, and dose rate. We show that nucleation of stable HeV complexes (voids and bubbles) at low temperature and flux takes place at extremely low doses. We also describe the effect of temperature on the HeV complex size distribution and show that growth beyond a critical nucleation size is not possible in this system at temperatures above 300 K for dose rates smaller than 10{sup -8} dpa/s. We further demonstrate that a temperature shift of 25 K per decade of flux scales the dose rate dependence of He-vacancy complex (voids and bubbles) accumulation when irradiation is carried out to low doses (0.03-0.06 dpa) at temperatures between 150 K and 300 K and dose rates of 10{sup -6}, 10{sup -7}, l0{sup -8}, and 10{sup -9} dpa/s. The results provide an atomistic description of microstructure evolution including void nucleation and the early stages of growth, and should be useful inmore » designing and interpreting accelerated aging experiments.« less

Authors:
; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab., Livermore, CA (US)
Sponsoring Org.:
USDOE Office of Defense Programs (DP) (US)
OSTI Identifier:
793932
Report Number(s):
UCRL-ID-136235
TRN: US200301%%240
DOE Contract Number:
W-7405-Eng-48
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 11 Oct 1999
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; AGING; BUBBLES; DISTRIBUTION; DOSE RATES; INTERSTITIALS; IRRADIATION; KINETICS; MICROSTRUCTURE; NUCLEATION; STABILITY

Citation Formats

Diaz de la Rubia, T., Caturla, M., and Fluss, M.J. Dimensional Stability and Microstructure Evolution in Irradiated Systems with Complex Kinetics. United States: N. p., 1999. Web. doi:10.2172/793932.
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Diaz de la Rubia, T., Caturla, M., & Fluss, M.J. Dimensional Stability and Microstructure Evolution in Irradiated Systems with Complex Kinetics. United States. doi:10.2172/793932.
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Diaz de la Rubia, T., Caturla, M., and Fluss, M.J. Mon . "Dimensional Stability and Microstructure Evolution in Irradiated Systems with Complex Kinetics". United States. doi:10.2172/793932. https://www.osti.gov/servlets/purl/793932.
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@article{osti_793932,
title = {Dimensional Stability and Microstructure Evolution in Irradiated Systems with Complex Kinetics},
author = {Diaz de la Rubia, T. and Caturla, M. and Fluss, M.J.},
abstractNote = {We use a combination of molecular dynamics and kinetic Monte Carlo simulations to explore the role of temperature and dose rate on damage accumulation in a model system with complex kinetics. We describe the accumulation of He-vacancy (HeV) complexes as well as vacancy and interstitial clusters as a function of irradiation temperature, dose, and dose rate. We show that nucleation of stable HeV complexes (voids and bubbles) at low temperature and flux takes place at extremely low doses. We also describe the effect of temperature on the HeV complex size distribution and show that growth beyond a critical nucleation size is not possible in this system at temperatures above 300 K for dose rates smaller than 10{sup -8} dpa/s. We further demonstrate that a temperature shift of 25 K per decade of flux scales the dose rate dependence of He-vacancy complex (voids and bubbles) accumulation when irradiation is carried out to low doses (0.03-0.06 dpa) at temperatures between 150 K and 300 K and dose rates of 10{sup -6}, 10{sup -7}, l0{sup -8}, and 10{sup -9} dpa/s. The results provide an atomistic description of microstructure evolution including void nucleation and the early stages of growth, and should be useful in designing and interpreting accelerated aging experiments.},
doi = {10.2172/793932},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Oct 11 00:00:00 EDT 1999},
month = {Mon Oct 11 00:00:00 EDT 1999}
}
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DOI:  10.2172/793932
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  • ; ;
    We use a combination of molecular dynamics and kinetic Monte Carlo simulations to explore the role of temperature and dose rate on damage accumulation in a model system with complex kinetics. We describe the accumulation of He-vacancy (HeV) complexes as well as vacancy and interstitial clusters as a function of irradiation temperature, dose, and dose rate. We show that nucleation of stable HeV complexes (voids and bubbles) at low temperature and flux takes place at extremely low doses. We also describe the effect of temperature on the HeV complex size distribution and show that growth beyond a critical nucleation sizemore » is not possible in this system at temperatures above 300 K for dose rates smaller than 10{sup -8} dpa/s. We further demonstrate that a temperature shift of 25 K per decade of flux scales the dose rate dependence of He-vacancy complex (voids and bubbles) accumulation when irradiation is carried out to low doses (0.03-0.06 dpa) at temperatures between 150 K and 300 K and dose rates of 10{sup -6}, 10{sup -7}, 10{sup -8}, and 10{sup -9} dpa/s. The results provide an atomistic description of microstructure evolution including void nucleation and the early stages of growth, and should be useful in designing and interpreting accelerated aging experiments.« less

  • Study the interaction of defects produced during irradiation or deformation of a metal with the microstructure of that particular material, such as dislocations and grain boundaries. In particular we will study the interaction of dislocation with interstitial loops and stacking fault tetrahedral, and the production of displacement cascades close to dislocations and grain boundaries. The data obtained from these simulations will be used as input to diffusion models and dislocation dynamics models.

  • ; ;
    Irradiation effects in materials depend in a complex way on the form of the as-produced primary damage state and its spatial and temporal evolution. Thus, while collision cascades produce defects on a time scale of tens of picosecond, diffusion occurs over much longer time scales, of the order of seconds, and microstructure evolution over even longer time scales. In this report the authors present work aimed at describing damage production and evolution in metals across all the relevant time and length scales. They discuss results of molecular dynamics simulations of displacement cascades in Fe and V. They show that interstitialmore » clusters are produced in cascades above 5 keV, but not vacancy clusters. Next, they discuss the development of a kinetic Monte Carlo model that enables calculations of damage evolution over much longer time scales (1000`s of s) than the picosecond lifetime of the cascade. They demonstrate the applicability of the method by presenting predictions on the fraction of freely migrating defects in {alpha}Fe during irradiation at 600 K.« less

  • The main goal of the proposed project is the development of validated nondestructive evaluation (NDE) techniques for in situ monitoring of ferritic-martensitic steels like Grade 91 9Cr-1Mo, which are candidate materials for Generation IV nuclear energy structural components operating at temperatures up to ~650{degree}C and for steam-generator tubing for sodium-cooled fast reactors. Full assessment of thermomechanical damage requires a clear separation between thermally activated microstructural evolution and creep damage caused by simultaneous mechanical stress. Creep damage can be classified as "negligible" creep without significant plastic strain and "ordinary" creep of the primary, secondary, and tertiary kind that is accompanied bymore » significant plastic deformation and/or cavity nucleation and growth. Under negligible creep conditions of interest in this project, minimal or no plastic strain occurs, and the accumulation of creep damage does not significantly reduce the fatigue life of a structural component so that low-temperature design rules, such as the ASME Section III, Subsection NB, can be applied with confidence. The proposed research project will utilize a multifaceted approach in which the feasibility of electrical conductivity and thermo-electric monitoring methods is researched and coupled with detailed post-thermal/creep exposure characterization of microstructural changes and damage processes using state-of-the-art electron microscopy techniques, with the aim of establishing the most effective nondestructive materials evaluation technique for particular degradation modes in high-temperature alloys that are candidates for use in the Next Generation Nuclear Plant (NGNP) as well as providing the necessary mechanism-based underpinnings for relating the two. Only techniques suitable for practical application in situ will be considered. As the project evolves and results accumulate, we will also study the use of this technique for monitoring other GEN IV materials. Through the results obtained from this integrated materials behavior and NDE study, new insight will be gained into the best nondestructive creep and microstructure monitoring methods for the particular mechanisms identified in these materials. The proposed project includes collaboration with a national laboratory partner and the results will also serve as a foundation to guide the efforts of scientists in the DOE laboratory, university, and industrial communities concerned with the technological challenges of monitoring creep and microstructural evolution in materials planned to be used in Generation IV Nuclear Energy Systems.« less

  • A three-dimensional finite difference numerical methodology was developed for self-gravitating, rotating gaseous systems. The fully nonlinear equations for time-varying fluid dynamics are solved by high speed computer in a cylindrical coordinate system rotating with an instantaneous angular velocity, selected such that the net angular momentum relative to the rotating frame is zero. The time-dependent adiabatic collapse of gravitationally bound, rotating, protostellar clouds is studied for specified uniform and nonuniform initial conditions. Uniform clouds can form axisymmetric, rotating toroidal configurations. If the thermal pressure is high, nonuniform clouds can also collapse to axisymmetric toroids. For low thermal pressures, however, the collapsingmore » cloud is unstable to initial perturbations. The fragmentation of protostellar clouds is investigated by studying the response of rotating, self-gravitating, equilibrium toroids to non-axisymmetric perturbations. The detailed evolution of the fragmenting toroid depends upon a non-dimensional function of the initial entropy, the total mass in the toroid, the angular velocity of rotation, and the number of perturbation wavelengths around the circumference of the toroid. For low and intermediate entropies, the configuration develops into co-rotating components with spiral streamers. In the spiral regions retrograde vortices are observed in some examples. For high levels of entropy, barred spirals can exist as intermediate states of the fragmentation.« less