Dynamic strain aging and ductility minima in zirconium

Abstract

Tensile tests using coarse grained zirconium specimens were conducted at two strain rates, differing by 3 orders of magnitude, between 77° and 1032°K. At each strain rate, peaks were observed when the flow stress was plotted against the temperature. The temperature corresponding to a given peak was observed to rise with increasing strain rate. A pronounced minimum in the strain rate sensitivity of zirconium near 675°K can be explained in terms of the strain rate dependence of these peaks. At each strain rate, the zirconium tensile specimens also showed a minimum elongation at the hardening peak temperature. Since the reduction in area did not pass through a corresponding minimum, the elongation minima do not reflect a true ductility loss. What actually takes place is an increased tendency to neck at the hardening peak temperature. This tendency to promote a neck can be rationalized in terms of variations in the strain rate sensitivity caused by dynamic strain aging.