The effect of deformation mechanisms on the high temperature plasticity of Zircaloy-4

In situ compression and tension tests were performed over a range of temperatures on annealed Zircaloy-4 plate in the rolling and transverse directions (RD and TD) at strain rates ranging from 10−4 s−1 to 10−1 s−1. Post deformation microstructures were indicative of twinning at higher strain rates (10−1 s−1 and 10−2 s−1) with little or no twinning occurring at slower rates. Analysis of post deformation pole figures showed no texture evolution during tensile tests and basal poles remained orientated ±30° between the normal direction (ND) and the transverse direction (TD), as in the as received material. In compression, no evolution was seen in specimens tested in the RD. Those tested in the TD showed a variation in post deformation pole figures as strain rate increased. At slow strain rates a slight rotation of basal poles around the ND was noted, indicative of slip. Increasing the strain rate decreased this effect, and at strain rates of 10−1 s−1 a total reorientation of the basal poles to lie solely in the RD was seen, which is indicative of twinning. Evolution of Kearns’ factors with strain agree with these results. An elasto-plastic self-consistant model was used to analyse the experimental results. The model results indicated that increasing strain rate caused an increase in twinning density, as suggested by the experimental microstructures and pole figures.