Speaker
Description
To understand and reliably predict the irradiation performance of materials, it is important to understand the fundamental effects of radiation on materials at the atomic scale. At the most basic level, radiation effects are caused by the creation of point defects including interstitial defects, substitutional defects and vacancies. Point defects are created when an incident particle or a displaced atom interacts with an atom located on a lattice position. Incident radiation typically creates a series of atomic displacement events called a displacement cascade. Most of the point defects created during the displacement cascade will be annealed very quickly by finding their way back to appropriate lattice positions, but some of the defects will remain. The motion of the defects through the radiation-damaged lattice is determined by the material characteristics, applied stress, and temperature. A variety of radiation damage microstructures can evolve including radiation-induced segregation, formation of dislocations, creation of voids or bubbles, and changes in phase composition such as second-phase precipitation and amorphization. The resulting microstructures can be evaluated in the irradiated materials by a variety of methods, but most commonly by transmission electron microscopy. The presence of radiation-damaged microstructures will affect the properties and hence the performance of irradiated materials. Changes in material properties can include irradiation hardening and embrittlement, irradiation growth and swelling, enhanced creep rate, irradiation-assisted stress corrosion cracking, and degradation of thermal properties.
Developing computational models to predict the effects of radiation on material properties is a significant challenge. To predict effects from first principles, a variety of tools are needed, operating on multiple scales in both space and time. The initial displacement cascade happens over Angstroms to nanometers and tenths of picoseconds. A few picoseconds after the cascade, there is a thermal spike caused by the motion of the displaced atoms through the lattice on the nanometer scale. After about 100 picoseconds, the defects that have not been annealed will begin to evolve, forming a variety of radiation damage microstructures. As radiation dose proceeds over subsequent hours, days, or years, these microstructures can grow to tens or hundreds of nanometers and significantly affect the bulk properties of the material. At the smallest length scale and shortest time scale, atomistic modeling techniques are typically used, from first-principles density functional theory to molecular dynamics methods that permit larger simulation sizes, albeit at reduced computational accuracy. At the mesoscale, techniques such as kinetic Monte Carlo, phase field and rate theory can be used to describe microstructural evolution. Finally, output from these various techniques can be used as input for continuum modeling methods like finite element or finite volume to evaluate the effects of radiation damage on bulk properties over days to years.
The presentation will include an overview of radiation materials science fundamentals, coupled with a discussion of radiation damage modeling techniques that can be used to inform post-irradiation microstructural characterization, plan experiments, and ultimately, predict irradiation performance of materials at space and time scales relevant to engineering applications.
| Themes for the contribution | 2 Radiation damage in target material and related simulations: |
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