Transmission electron microscopy observations of dislocations and wins in polycrystalline zirconium

The microstructural characteristics of polycrystalline pure zirconium are studied by means of transmission electron microscopy (TEM), following several thermo-mechanical treatments and internal friction measurements. Dislocations with Burgers vectors (a/3) <1120> arranged in tilt or twist boundary configurations are observed in annealed specimens and following prestraining at room temperature. This type of microstructure is also found following elongations not exceeding 6% at 8 K, whereas larger amounts of deformation (up to 17%) cause heavily twinned structures. Analysis of those twins reveals the presence of primarily the [1121] type. Moreover, other twinning modes, not usually observed in zirconium, are also detected in specimens cold rolled at room temperature. (author)