MOLECULAR DYNAMICS STUDY OF DIFFUSIONAL CREEP IN NANOCRYSTALLINE UO2

Journal Article · Mon Sep 01 04:00:00 EDT 2008 · Acta Materialia

DOI:https://doi.org/10.1016/j.actamat.2008.02.052· OSTI ID:939198

Desai, Tapan G; Millett, Paul C; Wolf, Dieter

We present the results of molecular dynamics (MD) simulations to study hightemperature deformation of nanocrystalline UO2. In qualitative agreement with experimental observations, the oxygen sub-lattice undergoes a structural transition at a temperature of about 2200 K (i.e., well below the melting point of 3450 K of our model system), whereas the uranium sub-lattice remains unchanged all the way up to melting. At temperatures well above this structural transition, columnar nanocrystalline model microstructures with a uniform grain size and grain shape were subjected to constantstress loading at levels low enough to avoid microcracking and dislocation nucleation from the GBs. Our simulations reveal that in the absence of grain growth, the material deforms via GB diffusion creep (also known as Coble creep). Analysis of the underlying self-diffusion behavior in undeformed nanocrystalline UO2 reveals that, on our MD time scale, the uranium ions diffuse only via the grain boundaries (GBs) whereas the much faster moving oxygen ions diffuse through both the lattice and the GBs. As expected for the Coble-creep mechanism, the creep activation energy agrees well with that for GB diffusion of the slowest moving species, i.e., of the uranium ions.

• Research Organization: Idaho National Laboratory (INL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC07-99ID13727
• OSTI ID: 939198
• Report Number(s): INL/JOU-07-13473
• Journal Information: Acta Materialia, Journal Name: Acta Materialia Journal Issue: 16 Vol. 56; ISSN 1359-6454; ISSN ACMAFD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ACTIVATION ENERGY
CREEP
DEFORMATION
DIFFUSION
DISLOCATIONS
GRAIN BOUNDARIES
GRAIN GROWTH
GRAIN SIZE
MELTING POINTS
NUCLEATION
OXYGEN
OXYGEN IONS
SELF-DIFFUSION
SHAPE
URANIUM
URANIUM IONS
ceramics
chemical diffusion
creep
molecular dynamics
uranium dioxide