TEM investigations of the superdislocations and their interaction with particles in dispersion strengthened intermetallics

The strategy of oxide-dispersion strengthening has recently been applied to intermetallic compounds in order to improve their creep resistance at high temperatures. In this paper, we describe selected results of an extensive transmission electron microscopy (TEM) study of the dislocation structures and the particle/dislocation configurations in Oxide-dispersion strengthed (ODS) NiAl, Ni3Al and FeAl. High-resolution TEM was employed to characterise the particle/matrix interfaces, and in situ high-temperature deformation in a high-voltage TEM provided insight into the dynamic processes of dislocation detachment from particles. The dissociation of the lattice dislocations into superpartials in FeAl and Ni3Al has important consequences for the particle/dislocation interactions: the superpartials are observed to surmount, and sometimes detach from, the particles separately, which points to a cooperative effect between the partials. The in situ experiments show, in addition, that the climb step is rapid compared with dislocation detachment from the particle. These observations are discussed in the light of our recent theoretical model of creep strength in ordered ODS materials. (C) 1999 Elsevier Science Ltd. All rights reserved.