CEITEC IPM

Brno, Czech Republic

CEITEC IPM

Brno, Czech Republic

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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)


Smid M.,CEITEC IPM | Kunz L.,Academy of Sciences of the Czech Republic | Hutar P.,Academy of Sciences of the Czech Republic | Hrbacek K.,PBS Velka Bites
Procedia Engineering | Year: 2014

The nickel-based superalloy MAR-M 247 was experimentally studied in the area of high-cycle fatigue at temperatures 650, 800 and 900 °C. The alloy, a cast polycrystalline material processed by hot isostatic pressing (HIP), was subjected to symmetrical cyclic loading. The fracture surfaces of specimens were studied by scanning electron microscopy from the perspective of the influence of temperature on the fatigue damage mechanism and fatigue crack initiation. The extent of Stage I of crystallographic fatigue crack propagation and non-crystallographic Stage II differs with various test temperatures. Fatigue crack initiation sites were predominantly shrinkage pores inherited from casting. The general description of governing mechanisms of the fatigue crack initiation and the crack propagation are proposed. © 2014 The Authors. Published by Elsevier Ltd.


Kubena I.,Academy of Sciences of the Czech Republic | Polak J.,Academy of Sciences of the Czech Republic | Marmy P.,Belgian Nuclear Research Center | Kruml T.,CEITEC IPM
Procedia Engineering | Year: 2014

The Eurofer 97 steel and its variant strengthened by fine oxide dispersion (ODS Eurofer) were investigated. Both variants were subjected to the cyclic loading at room temperature. Moreover, the Eurofer 97 steel was exposed to the cyclic loading at 550°C and the ODS Eurofer steel at 650 and 750 °C. Continuous cyclic softening was found in both variants. Nevertheless, addition of 0.3 wt% of Y2O3 significantly reduces softening rate in the ODS Eurofer compared with the Eurofer 97 steel. Microstructure evolution and the role of oxide dispersion were investigated by means of transmission electron microscopy. It was observed the oxide dispersion suppresses grain growth in the ODS Eurofer steel and thus possible operating temperature is higher. The oxide particles remain stable up to highest temperature studied. The microstructural aspects are discussed in relation to the cyclic behavior of both steels. © 2014 The Authors. Published by Elsevier Ltd.


Kubena I.,Academy of Sciences of the Czech Republic | Polak J.,Academy of Sciences of the Czech Republic | Plocinski T.P.,Warsaw University of Technology | Hebert C.,Ecole Polytechnique Federale de Lausanne | And 2 more authors.
Fatigue and Fracture of Engineering Materials and Structures | Year: 2015

The remarkable microstructural stability of high chromium steels prepared by powder metallurgy and strengthened by dispersion of nanometric yttrium oxides in cyclic loading at high temperatures is reported. Contrary to the continuous cyclic softening and profound changes in the microstructure during fatigue of common high chromium steels, the addition of 0.3wt% Y2O3 stabilizes the microstructure and significantly reduces cyclic softening of investigated steels. The evolution of microstructure as a result of fatigue loading at room temperature, 650 and 750°C, was examined by means of transmission electron microscopy. Only minor changes in the microstructure were detected. The stability of oxide particles after high-temperature exposure was confirmed by energy dispersion spectroscopy chemical analysis. The microstructural features are discussed in relation to the cyclic behaviour of the oxide dispersion strengthened steels. The analysis of the hysteresis loop indicates that oxide nanoclusters are intersected and dissolved in slip bands of ODS Eurofer steel. This process contributes to cyclic softening. © 2015 Wiley Publishing Ltd.


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.


Luptakova N.,CEITEC IPM | Luptakova N.,Academy of Sciences of the Czech Republic | Ballogova B.,Slovak Academy of Sciences | Dymacek P.,CEITEC IPM | Dymacek P.,Academy of Sciences of the Czech Republic
Manufacturing Technology | Year: 2015

The aim of this study is to investigate the creep resistance of molybdenum disilicide (MoSi2-SiC) based composites with different types of embedded particles. The materials were prepared via powder metallurgy using high temperature controlled reaction sintering (CRS). The creep experiments were performed in uniaxial compression at constant stress in the temperature range from 1273 K (1000 °C) to 1473 K (1200 °C) for applied stress from 50 to 100 MPa. Creep was tested by stepwise loading: in each step, the load was changed to a new value after steady state creep rate had been established. The applied stress dependences of the creep rate at different temperatures were analyzed in terms of stress exponent (n) and activation energy (Q). Possible rate-controlling mechanisms were suggested. © 2015. Published by Manufacturing Technology.


Kruml T.,CEITEC IPM | Chlupova A.,Academy of Sciences of the Czech Republic | Obrtlik K.,Academy of Sciences of the Czech Republic
Advanced Materials Research | Year: 2014

Ternary TiAl alloy with 8 at.% Nb and lamellar microstructure is subjected to low cycle fatigue tests at temperatures ranging from room temperature to 800 °C. The aim of the study is to find limit conditions when the microstructure is still stable and to study mechanisms of microstructural degradation when this limit is exceeded. Up to 750 °C, no cyclic softening or hardening is observed and cyclic stress-strain curve follows the tensile curve. Cyclic softening is characteristic for 800 °C. The TEM observation did not reveal any substantial changes in the microstructure due to the cycling up to 700°C. The lamellar structure is altered by cyclic straining at 750 °C and, to a higher extent, at 800°C. In specimens cycled to fracture at 800 °C, the domains without lamellar structure cover about 10% of volume and are almost dislocation free. The destruction of lamellar microstructure is the reason for the marked cyclic softening at 800 °C. © (2014) Trans Tech Publications, Switzerland.


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.


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.


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.

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