Stereo transmission electron microscopy was used to characterize the depth distributions of disordered zones and associated dislocation loops in these ordered alloys after heavy-ion irradiation. The Ni3Al was irradiated with 50keV Ta+ ions at a temperature of 573K. The Cu3Au was irradiated with 50keV Ni+ ions at a temperature of 373K, using an ion beam which was inclined at 45° in order to emphasize the shapes and sizes of cascades parallel to the beam direction. In the case of Ni3Al, the probability that a disordered zone contained a loop was found to be strongly dependent upon the depth of the zone in the foil, and varied from about 0.7 for near-surface zones to about 0.2 in the bulk. The sizes and shapes of the disordered zones were independent of the depths of the zones in the foil; except for a small population of zones which was very near to the surface. These were strongly elongated parallel to the incident ion beam. In the case of Cu3Au, the surface had a smaller effect; with the yield falling from about 0.7, close to the surface, to 0.5 for deeper zones. These depth dependences were explained in terms of the annihilation of freely migrating point defects at the surface.

S.Müller, M.L.Jenkins, C.Abromeit, H.Wollenberger: Philosophical Magazine A, 1997, 75[6], 1625-40