Ultra-fine grained copper prepared by high pressure torsion: spatial distribution of defects


Ultra-fine grained copper prepared by high pressure torsion: spatial distribution of defects

Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.; Kuzel, R.; Cieslar, M.; Islamgaliev, R. K.

High-purity bulk ultra-fine grained (UFG) metals of grain size of " 100 nm and of no porosity can be produced by high-pressure torsion (HPT) technique. In the present contribution a study of spatial distribution of defects in HPT made UFG copper is reported. Positron annihilation spectroscopy (slow-positron implantation, lifetime and Doppler broadening spectroscopies) was utilized together with transmission electron microscopy, x-ray diffraction and microhard-ness measurements to investigate lateral distributions as well as depth profiles of defects.
Two types of defects were identified: dislocations situated in distorted regions along grain boundaries and microvoids of size comparable to 3-5 vacancies inside grains. No lateral changes in grain size and mean dislocation density were observed. Close to the specimen sur-face, the mean coherent domain size was found to be 80±20nm and it slightly increased with depth. As a consequence, a decrease in volume fraction of distorted regions takes place, which results in a decrease of the mean dislocation density with depth. These changes were observed at depths below 35 mm. At higher depths, the mean dislocation density tends to independence of depth. Contrary to lateral behavior of dislocations, concentration of microvoids was found to vary with distance from center of the specimen disk.

Keywords: High-pressure torsion; ultra-fine grained copper; spatial distribution of defects; positron annihilation

  • Contribution to external collection
    Proc. Second Int. Conf. on Nanomaterials by Severe Plastic Deformation: Fundamentals - Processing - Applications, Vienna 2002, eds. M.J. Zehetbauer, R.Z. Valiev (Wiley, Weinheim, 2003) pp. 407-412

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Publ.-Id: 6010