Pyramidal flow stress of single crystal zinc

Abstract

The pyramidal flow stress of single crystal zinc was determined over a temperature range of 77–298 K and a strain rate range of ∼10 −5−10 −1s −1. Tensile and strain-rate cycling tests were performed using bar-shaped grown single crystal specimens. The pyramidal flow stress is divided into two regions: low temperature thermally activated, and higher temperature athermally activated. Activation volume determination and the effect of temperature, strain rate, and dislocation density on flow stress has led to the conclusion that the thermally activated mechanism most likely controlling is the intersection of forest dislocations. The prediction of Friedel that the activation volume is inversely proportional to the cube root of effective stress was found to hold in form but was inconsistent in regard to the coefficient. However, by using the experimentally determined constants, it was possible to obtain reasonable comparisons between predicted and experimental flow stresses as a function of dislocation density with changes in temperature.