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Plasticity in hexagonal close-packed zirconium is mainly controlled by the glide of dislocations with 1/3 Burgers vectors. As these dislocations cannot accommodate deformation in the [0001] direction , twinning or glide of dislocations, i.e. dislocations with 1/3 Burgers vector, have to be activated. We have performed in situ straining experiments in a transmission electron microscope to study the glide of dislocations in two different zirconium samples, pure zirconium and Zircaloy-4, at room temperature. These experiments show that dislocations exclusively glide in first-order pyramidal planes with cross-slip being activated. A much stronger lattice friction is opposing the glide of dislocations when their orientation corresponds to the direction defined by the intersection of their glide plane with the basal plane. This results in long dislocations straightened along which glide either viscously or jerkily. This direction governs the motion of segments with other orientations, whose shape is merely driven by the minimization of the line tension. The friction due to solute atoms is also discussed.

Physical deformation and fracture mechanisms of a duplex high strength, low density steel have been examined, both in individual phases using TEM in-situ tensile tests and in bulk specimens using tensile and impact tests. Deformation in ferrite concentrated into wavy bands. In both ferrite and austenite, strong pinning induced non-continuous motion of dislocations even at low temperature. The stability of austenite against transformation into martensite was varied using either the test temperature or prior low temperature treatment, while keeping the chemistry, processing parameters and microstructural size and morphology constant. It was shown that the brittle-to-ductile transition in this alloy is driven by mechanical interactions between phases, and that cleavage fracture of coarse delta-ferrite is governed by the presence of hard martensite in the fine-grained regions, before or during the mechanical test.

Biomimetic apatite coatings were obtained by soaking chemically treated titanium in SBF with different HCO3- concentration. XRD, FTIR and Raman analyses were used to characterize phase composition and degree of carbonate substitution. The microstructure, elemental composition and preferred alignment of biomimetically precipitated crystallites were characterized by cross-sectional TEM analyses. According to XRD, the phase composition of precipitated coatings on chemically pre-treated titanium after exposure to SBF was identified as hydroxy carbonated apatite (HCA). A preferred c-axis orientation of the deposited crystals can be supposed due to the high relative peak intensities of the (0 0 2) diffraction line at 2 theta = 26 degrees compared to the 100% intensity peak of the (2 1 1) plane at 2 theta = 32 degrees. The crystallite size in direction of the c-axis of HCA decreased from 26 nm in SBF5 with a HCO3- concentration of 5 mmol/l to 19 nm in SBF27 with a HCO3- concentration of 27 mmol/l. Cross-sectional TEM analyses revealed that all distances correspond exactly to the hexagonal structure of hydroxyapatite. The HCO3- content in SBF also influences the composition of precipitated calcium phosphates. Biomimetic apatites were shown to have a general formula of Ca10-x-yMgy(HPO4)(x-z)(CO3)(z)(PO4)(6-x)(OH)(2-x-w)(CO3)(w/2). According to MR and Raman analyses, it can be supposed that as long as the HCO3- concentration in the testing solutions is below 20 mmol/l, only B-type HCA (0 < z < 1; w = 0) precipitates. At higher HCO3- concentration, it can be assumed that AB-type HCA (z = 1;0 < w < 1) is formed. (C) 2007 Elsevier B.V. All rights reserved.