The strain rate dependent plastic flow behavior of zirconium and its alloys

Abstract

The effect of strain rate (10⁻⁵ {$\sim$} 10⁻¹ min⁻¹) on the plastic flow behavior was examined by means of tension tests over a range of temperatures (RT {$\sim$} 500°C). The principal material examined was Zircaloy-2, and the others were iodide zirconium and binary alloys of Zr-0.1 pct O and Zr-1.5 pct Sn by weight. In Zircaloy-2, the behavior was characterized by a sudden increase of flow strength with decreasing strain rate; concurrently the ductility decreased. Other interrupted and hold time experiments showed that the process is essentially that of a strain rate-induced strengthening phenomenon, with several features which could be identified with the strain aging process. It was further shown that the critical range of strain rates and temperatures at which the anomalous behavior took place could be correlated with the minimum in the strain rate sensitivity of flow stress. A similar but less pronounced flow behavior was observed with pure zirconium and its binary alloys, but with no marked change in the tensile ductility. From these results, the role of oxygen and tin on the early stage of plastic flow behavior was discussed in terms of dislocation-impurity interaction mechanisms. It was however concluded that these elements are not directly responsible for the ductility loss at slow strain rate in Zircaloy-2.