Kozubski R. 1, Koz³owski M. 1, Partyka E.1, Pierron-Bohnes V.2, Pfeiler W.3
1M. Smoluchowski Institute of Physics, Jagellonian University, Reymonta 4,
30-059 Krakow, Poland,
2Institut de Physique et Chimie des Matériaux de Strasbourg, 23, rue du Loess, BP43,
67034 Strasbourg CEDEX 2, France
3Institut für Materialphysik, Universität Wien, Strudlhofgasse 4, 1090 Wien, Austria
A number of technologically attractive intermetallic compounds show high stability of crystalline superstructure and, therefore, “order-disorder” transitions in those materials occur at very high temperatures. In many cases the state of chemical long-range order is maintained even up to the melting point. Nevertheless, fine temperature dependence of the degree of long-range order is experimentally observable in so-called “order-order” processes; the phenomena controlled by atomic migration via vacancy mechanism. Atoms migrate, however, in non-steady-state conditions and hence, the corresponding investigation is complementary with respect to standard diffusion studies.
Extensive experimental research of “order-order” kinetics (carried out mainly by means of various resistometric techniques) covered intermetallics with different types of superstructures: Ni3Al (L12), NiAl (B2), FeAl (B2), and FePd (L10). It has been found out that specific features of the observed “order-order” relaxations are due to superstructure geometry. An interest has been focused on the observed correlation between the superlattice stability and the activation energy for ordering. Complete understanding of the observed effects requires, however, a study of vacancy thermodynamics in systems with varying superlattice stability.
In parallel, specific atomistic mechanisms of “order-order” processes are investigated by means of computer simulation.