Single crystalline specimens of L12 ordered binary Ni3Al and Ni3(Al,B) with single slip [1̄23] and multiple slip [001] orientations were deformed in compression within the anomalous temperature regime. In all cases the TEM investigations show that dipoles of locked screws were a dominant feature of the dislocation structure. This was of special interest since screw dipoles were not observed in disordered face-centered cubic structures. The results indicate that screws interact and form long sessile dipoles even when their heights was much larger (> factor of 10) than that given by the passing stress. The minimum height of the screw dipoles was about 16±4 nm and seems to be given when the interaction stress corresponds to the saturation stress. In the dipoles the locked screws were very difficult to unlock since the external stress was screened to a large extent. Therefore the deformation has to occur by the movement of edge segments. It was suggested that based on this exhaustion of the screws steady state conditions do not always apply on a local scale.

Screw Dipoles Acting as Strong Locks in Ni3Al. Karnthaler, H.P., Rentenberger, C., Yu, H.: Materials Research Society Symposium – Proceedings, 1995, 364[1], 315-20