DYNAMIC DISLOCATION EFFECTS IN PRECIPITATION-HARDENED MATERIALS

The critical resolved shear stress tau(t) of copper-single crystals strengthened by cobalt-rich precipitates has been measured in the temperature range 12-500 K. The radius of the particles was about 3 nm, their volume fraction went up to 0.022. Below 200 K, partial derivative tau(t)/partial derivative T, T = temperature, was found to be positive. This is interpreted as a manifestation of dynamic dislocation effects. At the lowest temperatures damping of the dislocation motion is so low that dislocations acquire kinetic energy while gliding in between the cobalt-rich particles. This energy helps dislocations to overcome the particles. As T is raised, phonon damping increases and finally suppresses the dynamic effects. The same can be achieved by solving gold-atoms in the matrix: they too lead to over-damping of the dislocation motion.