The Climb of Dislocation Loops in Zinc

The annealing behaviour of faulted dislocation loops in quenched zinc has been studied with the aid of the electron microscope. On annealing, it is observed that some of the loops grow rather than shrink, and this has been attributed to the growth of zinc oxide on the foil surface, which results in the formation of vacancies. Loops which shrink on annealing are considered to lie beneath breaks in the surface oxide layer such that these regions are able to act in the normal manner as vacancy sinks. An estimation of the vacancy supersaturation near such shrinking loops shows that the chemical stress is low, and the climb rate of loops shrinking in the presence of a negligible chemical stress has been analysed to give a value for the stacking fault energy, y. An analysis of the climb rate of a faulted loop based on the emission of vacancies as the controlling process gives a value of 290 erg/cm2. A more reliable value of y, which is thought to be independent of the rate-controlling process, is obtained by comparing the climb rate of a faulted loop with that of a prismatic loop. A stacking fault energy value for zinc of 220 erg/cm2 is deduced.