IN-SITU TEM OBSERVATIONS OF DISLOCATION PROCESSES IN IRON-ALUMINIDES WITH 25 AND 30 AT-PERCENT ALUMINUM

Thin single crystal foils of long-range ordered binary iron-aluminium alloys with 25 and 30 at.% aluminium have been tensile tested inside o f a transmission electron microscope. The motion of dislocations has b een recorded under full load al temperatures ranging from 300 to 970 K . These experiments yield information pertaining to: i) the activated glide planes; ii) the mode of glide (viscous versus jerky and planar v ersus cross-slip); iii) the dissociation of perfect dislocations into partials and the magnitude of the partial Burgers vectors; and iv) the widths and specific energies of the antiphase boundaries between the partial dislocations. The results are discussed with a view to elucida ting the well-known anomalous, positive temperature dependence of the critical resolved shear stress of these intermetallic compounds betwee n 500 and 780 K.