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Brno, Czech Republic

Saada G.,ONERA | Kruml T.,CEITEC IPM
Philosophical Magazine | Year: 2013

This paper presents experiments showing that the inversion of the sense of the applied stress on a specimen deformed in tension (respectively compression) results in the removal of mechanical instabilities such as the yield point and the Lüders band in a ferritic steel or serrations in an Al-Mg alloy. We show that this behaviour is connected neither to the mechanical set-up (tension, torsion,.), nor to the crystal geometry, but to the development of antagonist internal stresses during plastic flow. We develop a multi-domain analysis of the effect of these stresses and emphasize the importance of the analysis of the elastic-plastic transition. © 2013 Copyright Taylor and Francis Group, LLC. Source

Nemcova A.,University of Manchester | Kubena I.,CEITEC IPM | Smid M.,Academy of Sciences of the Czech Republic | Habazaki H.,Hokkaido University | And 2 more authors.
Journal of Solid State Electrochemistry | Year: 2015

Anodizing of a Mg-Zn-RE alloy was carried out at constant current densities from 0.1 to 10 mA cm−2 in a fluoride/glycerol/water electrolyte. Rutherford backscattering spectroscopy, nuclear reaction analysis and analytical transmission electron microscopy revealed barrier-type films composed of oxide and fluoride species. The films were formed by outward migration of cations and inward migration of anions. The transport number of cations in the film above the matrix was in the range ∼0.5 to 0.6, and ∼0.1 in the film above the grain boundary Mg-Zn-RE phase. From the oxidation behaviour of the Zn-Zr phases, it is suggested that anions and cations migrate through short-circuit paths in the film. © 2015 The Author(s) Source

Dobes F.,Academy of Sciences of the Czech Republic | Dymacek P.,CEITEC IPM
Key Engineering Materials | Year: 2014

Several possible routes are available for estimation of fracture behaviour from the results of small punch tests performed at constant rate of deflection. The routes include: (i) measurement of relevant dimensions directly on ruptured specimens, (ii) determination of critical deflections on the load vs. deflection curves and (iii) integration of these curves up to specific points. Equivalent fracture strain, fracture energy or fracture toughness are then evaluated from the obtained quantities. The mutual relations among the quantities are demonstrated by the results of small punch tests performed on a Fe-Al-based alloy in the temperature range extending from brittle up to ductile fracture appearance. © (2014) Trans Tech Publications. Source

Kruml T.,CEITEC IPM | Obrtlik K.,Academy of Sciences of the Czech Republic
International Journal of Fatigue | Year: 2014

Low cycle fatigue properties of lamellar TiAl with 8 at.% Nb were studied at four temperatures: room temperature, 700, 750 and 800 °C. Up to 750 °C, stable cyclic behaviour is observed while cyclic softening is characteristic for 800 °C. The strength of the alloy is still high even at 800 °C. The TEM observation did not reveal any substantial changes in the microstructure due to the cycling at RT. At 750 °C, the lamellar structure was in some places destroyed by cyclic plastic straining and pure γ-phase islands with high density of dislocation debris were formed. At 800 °C, the domains without lamellar structure cover about 10% of volume and are almost dislocation free. The destruction of lamellar microstructure and possible annealing of dislocation debris is the reason for marked cyclic softening at 800 °C. © 2013 Elsevier Ltd. All rights reserved. Source

Kubena I.,Academy of Sciences of the Czech Republic | Kruml T.,CEITEC IPM
Engineering Fracture Mechanics | Year: 2013

Three high Cr steels prepared by powder metallurgy and strengthened by fine oxide particles were subjected to low cycle fatigue testing at room temperature and microstructural characterisation. While the strength of the three materials is roughly comparable, the strong variance in the fatigue life of studied materials was measured. The reasons for this difference are discussed in terms of microstructure and differences in the crack nucleation mechanisms and early crack growth. © 2012 Elsevier Ltd. Source

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