Characterization of Point Defect Generation, Migration and Coalescence in Irradiated SiC by Atomistic Simulation
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1043-T02-04
Characterization of Point Defect Generation, Migration and Coalescence in Irradiated SiC by Atomistic Simulation
© 2008 Materials Research Society Dave Farrell Prof. Wing Kam Liu Department of Mechanical Engineering Northwestern University
In Collaboration With: Dr. Noam Bernstein Center for Computational Materials Science Naval Research Laboratory
Overview Brief motivation, background Motivating application Overall goal of work
© 2008 Materials Research Society
Overview of preliminary simulations, results Conclusions, future work
Motivation
© 2008 Materials Research Society Inside of tokamak
an
operating
spherical
Schematic of the Aries-AT reactor From Najmabadi et al FED 2006
Image from UKAEA MAST reactor
Nuclear fusion promising for future energy production Fewer hazardous bi-products than current fission systems Many materials design problems remain ! ‘Nice’ environment for creating point defects
Goal of Work Study void initiation in 3C-SiC due to the generation, diffusion and coalescence of point defects under fusion-reactor relevant conditions via multiscale atomistic and continuum simulations What does this mean and why does it matter? Interested in: Vacancies to voids and all the stuff in-between! Understanding how voids form from point defect clusters can provide useful models for continuum studies (predictive system simulations!)
© 2008 Materials Research Society What are ‘voids’ ? Depends on who you ask…
Katz & Wiedersich JCP 1971: any cluster of vacancies Some authors (e.g. Woo and co-workers JNM 1990, Prasad & Sinno PRB 2003) say large clusters/voids interchangeable & typically immobile
SiC not as widely studied as metals, of interest technologically
Overview of Model Based on Devanathan et al NIMPRB 1998 10 keV SiC model Rectangular prism shape.. varied to test size dependence
© 2008 Materials Research Society
Tersoff w/ Devanathan et al JNM 1998 parameters used Periodic BCs applied to all sides of prism
z 4 cell ‘thermostat zone’ applied by simple velocity scaling on all sides but ‘top’ (otherwise NVE)
y x
Si PKA simulated by applying an initial velocity to a Si atom near the center/top of the simulation cell PKA KE: 5.5 keV (after thermal equilibration) Temp: 1200 K Lattice param: 4.037685 Å (pressure ~ 100 MPa)
Overview of Model (con’t) Simulation broken down into 4 phases: Thermal equilibration phase System equilibriated for 2k steps @ 1 fs/step… all systems are ‘close’ to desired starting temp/pressure of 1200 K / 50-175 MPa by the end
Initial collision phase (labeled in diagrams as I)
PKA velocity applied along ~ © 2008 Materials Research Society (5.5 keV -> ~1952 Å/ps = 195200 m/s!) Allowed to evolve for 10k steps @ 10 attoseconds/step (.01 fs/step) - .1 ps total time
Intermediate evolution phase (labeled in diagrams as II) Timestep increased to .1 fs and system allowed to evolve for 10k steps (1 ps total)
Final evolution phase (labeled in diagrams as III) Timestep increased to 1 fs and system allowed to evolve for 10k steps (10 ps total)
Total simu
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