PLASTIC-FLOW IN HCP METALS AND SOLID-SOLUTIONS

The temperature and concentration dependences of the critical resolved shear stress (CRSS) and of the associated activation volume in binary solid solutions based on cadmium and magnesium are analysed in terms of the kink-pair nucleation model of solid-solution hardening (SSH). Numerical calculations of the activation parameters of plastic deformation show that in alloy crystals containing 0.005 to 15 at% solute, the dislocation segment involved in the activation process gets unpinned from several solute atoms simultaneously. A single mechanism of SSH is therefore operative in dilute as well as in concentrated hexagonal close-packed alloys. It is also inferred that the CRSS of solute-free magnesium crystal is determined by a slip nucleation process, similar to the kink-pair nucleation at barriers of aligned solute atoms in the magnesium-based alloy crystals.