SEDL / STP / STP1492-EB / STP46572S

Kinetics of the Migration and Clustering of Extrinsic Gas in bcc Metals

Deo, C. S.
Georgia Institute of Technology, Atlanta, Georgia

Srinivasan, S. G.
Los Alamos National Laboratory, Los Alamos, New Mexico

Baskes, M. I.
Los Alamos National Laboratory, Los Alamos, New Mexico

Maloy, S. A.
Los Alamos National Laboratory, Los Alamos, New Mexico

James, M. R.
Los Alamos National Laboratory, Los Alamos, New Mexico

Okuniewski, M.
University of Illinois, Urbana, Illinois

Stubbins, J.
University of Illinois, Urbana, Illinois

Pages: 13    Published: Jan 2008

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Abstract

We study the mechanisms by which gas atoms such as helium and hydrogen diffuse and interact with other defects in bcc metals and investigate the effect of these mechanisms on the nucleation of embryonic gas bubbles. Large quantities of helium and hydrogen are produced due to spallation and transmutation in structural materials in fusion and accelerator-driven reactors. The long time evolution of the extrinsic gas atoms and their accumulation at vacancies is studied using a kinetic Monte Carlo algorithm that is parameterized by the migration energies of the point defect entities. First-order reaction kinetics are observed when gas clusters with vacancies. If gas-gas clustering is allowed, mixed-order diffusion limited kinetics are observed. When dissociation of gas from clusters is allowed, gas-vacancy clusters survive to steady state while gas-gas clusters dissolve. We obtain cluster size distributions and reaction rate constants that can be used to quantify microstructural evolution of the irradiated metal.