Dresden 2006 – wissenschaftliches Programm
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MM: Metall- und Materialphysik
MM 27: Diffusion I
MM 27.2: Vortrag
Donnerstag, 30. März 2006, 10:30–10:45, IFW B
Ordering kinetics is affected when jump barrier heights depend on local environment — •Martin Leitner1, Wolfgang Püschl1, Ferdinand Haider2, and Wolfgang Pfeiler1 — 1Institut für Materialphysik, Universität Wien, Boltzmanng. 5, AT-1090 Vienna, Austria — 2Institut für Physik, Universität Augsburg, Universitätsstrasse 1, D-86159 Augsburg, Germany
Kinetics of order-order transformations in a L12 long-range ordered model crystal was investigated by Monte-Carlo simulation employing a residence-time algorithm. Atoms were supposed to jump into nearest-neighbor vacancies. In doing so, they have to pass through a rectangular window of atoms which are nearest neighbors to both the initial and the final positions. ab initio calculations of jump profiles [Mat. Res. Soc. Symp. Proc. 842, S5.28 (2005)] for Ni3Al show that barrier heights are markedly influenced by the kind of atoms occupying this window as well as their relative position. These results were incorporated as a rule into the MC algorithm, with a parameter characterizing the influence of the window atoms. If this parameter is increased from zero, three regimes of kinetic behavior can be discerned: a regime of finite but small influence below a certain threshold, a critical region where behavior changes quickly and in a qualitative way, an asymptotic region where the kinetics is stable against a further increase. It is discussed under which conditions the usual assumption of constant barrier height made in the literature will have to be modified.