Transmission Electron Microscopy Observations of Dislocations and Twins 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 {1012} type and also of the {1012} type. Moreover, other twinning modes, not usually observed in zirconium, are also detected in specimens cold rolled at room temperature. Les caracteristiques microstructurelles d'echantillons de zirconium pure polycrystallin ont ete etudiees par microscopie electronique a transmission, apres des traitements thermo-mecaniques et des mesures de frottement interne. Des dislocations (a/3) 〈1120〉, formant des parois de flexion ou de torsion, ont ete observees dans des echantillons recuits ou deformes a temperature ambiante. Ce type de microstructure est observe aussi apres des elongations inferieures a 6% executees a 8 K, tandis que des deformations plus grandes donnent lieu a des structures forte-ment mǎclees. Ces mǎcles sont essentiellement du type {1012}, parfois du type {1012}. De plus, dans des echantillons ecrouis a temperature ambiante on a pu mettre en evidence aussi d'autres types de mǎcles qui ne sont pas observes generallement dans le zirconium.