Abstract
The evolution of a copper precipitate with a diameter of 3·5 nm containing up to 2.0 at.% of vacancies at different temperatures has been studied by molecular dynamics. The diffusion coefficients were calculated for a single vacancy and vacancy concentrations inside the precipitate of 0.5, 1.0 and 2.0 at. %. The diffusion coefficients for each set of vacancies change with time. During the initial stage, the diffusion of populations of vacancies is very close to that of single vacancy diffusion. The initial stage is interpreted in terms of arrangements of vacancies which contain some clusters and are temperature dependent. For low temperatures (about 600 K) these clusters contain few vacancies whereas for high temperatures (about 1100 K) they are mainly formed by divacancies. These clusters are not stable and change in time quite rapidly. The evolution of larger precipitates with vacancies was followed under ageing at constant temperature followed by cooling at one of several constant speeds. For a precipiate of 7nm diameter containing 6.0 at.% of vacancies and cooled from 1000 K with a speed of 5.0 K ps-1small nuclei of fcc phase were formed. However, the complete bcc→fcc transformation of the precipitate was not obtained, and possible mechanisms of the phase transformation are discussed.
Original language | English |
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Pages (from-to) | 1097-1115 |
Number of pages | 19 |
Journal | Philosophical Magazine A: Physics of Condensed Matter, Structure, Defects and Mechanical Properties |
Volume | 75 |
Issue number | 4 |
DOIs | |
State | Published - Apr 1997 |
Externally published | Yes |
Funding
ACKNOWLEDGEMENTS We gratefully acknowledge Professor D. J. Bacon for invaluable discussions and comments on the manuscript and we also wish to thank Dr S. I. Golubov for numerous discussions. This work was supported by Project No. INTAS-93-3454, a grant from the Catalan Government (Yu.N.0.) and Project No. PB93-0971-Co3 of the Direccion General de Investigacibn Gentifica y Ttcnica.