Deformation of single crystals of the L2₁ ordered Ag₂MgZn

Abstract

The orientation and temperature dependence of slip geometry and yield stress in single crystals of the L2₁ ordered Ag₂MgZn has been studied in compression in the temperature range 290 to 580 K. The slip direction in Ag₂MgZn is exclusively 〈1 1 1〉 in this temperature range, but the slip plane varies with crystal orientations; slip occurs on (¯2 1 1) for orientations near the [0 1 1]-[¯1 1 1] boundary, while for the other orientations in the [0 0 1]-[0 1 1]-[¯1 1 1] unit triangle it occurs on the (¯1 0 1). The critical resolved shear stress (CRSS) for slip on both the (¯1 0 1) [1 1 1] and (¯2 1 1) [1 1 1] systems increases abnormally with increasing temperature and reaches a maximum peak at about 0.92 of the critical temperature T _c, for the L2₁-type order. The peak temperature and the shape of the CRSS versus temperature curve are independent not only of crystal orientation but also of the operative slip system. It is suggested that the strength anomaly in Ag₂MgZn be interpreted in terms of the mechanism based on the transition from unit dislocations to superdislocations.