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Atomistic models of triple junctions and the origin of topological changes in microstructural evolution

Published online by Cambridge University Press:  21 March 2011

Alessandra Satta
Affiliation:
Istituto Nazionale per la Fisica della Materia and Dipartimento di Fisica, Università di CagliariCittadella Universitaria, I-09042, Monserrato - Cagliari, Italy
Luciano Colombo
Affiliation:
Istituto Nazionale per la Fisica della Materia and Dipartimento di Fisica, Università di CagliariCittadella Universitaria, I-09042, Monserrato - Cagliari, Italy
Fabrizio Cleri
Affiliation:
Ente Nuove Tecnologie, Energia e Ambiente, Divisione Materiali, Centro Ricerche Casaccia, CP 2400, I-00100 Roma, Italy, and Istituto Nazionale per la Fisica della Materia, Roma, Italy
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Abstract

Triple junctions are crucial elements in microstructural evolution: for example, their mobility can be rate-limiting if lower than that of grain boundaries. However, very little is known about their atomic-level structure and properties. We studied the atomic structure of multiple-twin triple junctions in silicon, formed by the convergence of two {111} and one {221} symmetric-tilt grain boundaries. Molecular dynamics simulations with the Stillinger-Weber potential and constant-traction border conditions were performed on several triple junction configurations, obtained by different combinations of the three grain boundaries. All the configurations have a positive excess line energy, a measurable volume contraction and display regions of opposite, tensile and compressive, residual stress. Moreover, we tried to elucidate the role of triple junctions as being the seeds of the only microscopic events that can lead to topological changes in the microstructure. Such events, usually dubbed T1 and T2 in mesoscopic models, correspond to grain switching (in the Ashby-Verrall sense) and grain-disappearance events, respectively. We present preliminary results for the atomic-scale modelling of both classes of topological events and discuss the connection between atomistic and mesoscopic modelling of microstructural evolution.

Type
Research Article
Copyright
Copyright © Materials Research Society 2001

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