Number of found documents: 977
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Study of mechanical properties of nanolayered Ti/Ni coatings
Zábranský, L.; Václavík, R.; Přibyl, R.; Ženíšek, J.; Souček, P.; Buršík, Jiří; Fořt, Tomáš; Buršíková, V.
2018 - English
The aim of the present work was to study the dependence of mechanical properties of Ti/Ni multilayer thin films on the thicknesses of constituent Ti and Ni layers. The multilayer thin films were synthesized by deposition of Ti and Ni layers alternately on single crystalline silicon substrates using direct current magnetron sputtering method. Thicknesses of Ti and Ni layers varied from 1.7 nm to 100 nm. The micro-structure of the multilayer films was studied using X-ray diffraction technique, scanning electron microscopy with focused ion beam technique and transmission electron microscopy. Mechanical properties obtained from nanoindentation experiments were discussed in relation to microstructural observations. Keywords: Ti/Ni; multilayers; magnetron sputtering; nanoindentation; TEM Available at various institutes of the ASCR
Study of mechanical properties of nanolayered Ti/Ni coatings

The aim of the present work was to study the dependence of mechanical properties of Ti/Ni multilayer thin films on the thicknesses of constituent Ti and Ni layers. The multilayer thin films were ...

Zábranský, L.; Václavík, R.; Přibyl, R.; Ženíšek, J.; Souček, P.; Buršík, Jiří; Fořt, Tomáš; Buršíková, V.
Ústav fyziky materiálů, 2018

HIGH - TEMPERATURE CREEP BEHAVIOUR OF CAST COBALT-BASE SUPERALLOYS
Dvořák, Jiří; Král, Petr; Kvapilová, Marie; Hrbáček, Karel; Sklenička, Václav
2018 - English
Two cast and heat-treated NbC and TaC – strengthened cobalt superalloys have been developed for a precision casting of spinner discs for glass wool industry. In this work constant load creep tests in tension were carried out in argon atmosphere at three testing temperature 900, 950 and 1000 °C and at the initial applied stresses ranged from 40 to 200 MPa. All the tests were continued until the final fracture. The results of creep testing were combined with microstructural and fractographic examinations by means of light and scanning electron microscopy. A mutual comparison of creep characteristics of the investigated superalloys under comparable creep loading conditions showed that NbC-strengthened superalloy exhibited longer creep life than TaC-strengthened one. Further, it was found that carbide precipitation is the primary strengthening mechanism in both cobalt-base superalloys under investigation and the amount, morphology\nand type of carbides have the decisive effect on the creep properties including creep damage and fracture processes. By contrast, NbC-superalloy exhibited a more brittle character of creep fracture mode than TaCstrengthened superalloy. This study was initiated to investigate in more details creep deformation processes and the effect of the creep microstructure and damage evolution on both investigated superalloys. The different behaviour and properties of studied superalloys were explained based on the received results of this study. Keywords: Co-based superalloys; creep tests; microstructure evolution; carbide precipitation; damage process Available at various institutes of the ASCR
HIGH - TEMPERATURE CREEP BEHAVIOUR OF CAST COBALT-BASE SUPERALLOYS

Two cast and heat-treated NbC and TaC – strengthened cobalt superalloys have been developed for a precision casting of spinner discs for glass wool industry. In this work constant load creep tests in ...

Dvořák, Jiří; Král, Petr; Kvapilová, Marie; Hrbáček, Karel; Sklenička, Václav
Ústav fyziky materiálů, 2018

HYDROGEN SORPTION BEHAVIOR OF CHOSEN BINARY MAGNESIUM-CONTAINING INTERMETALLICS
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2018 - English
Hydrogen absorption in chosen binary Mg-X (X-Al, Ga, In, Si and Sn) intermetallics was studied. These compounds are prospective as additives in other Mg-based hydrogen storage materials. From this point of view it is desirable to know the hydrogen solubility in Mg-X and their resistivity against hydride formation. The present study was carried out at temperatures up to 623 K. Keywords: Hydrogen storage; magnesium alloys; Mg-based intermetallics Available at various institutes of the ASCR
HYDROGEN SORPTION BEHAVIOR OF CHOSEN BINARY MAGNESIUM-CONTAINING INTERMETALLICS

Hydrogen absorption in chosen binary Mg-X (X-Al, Ga, In, Si and Sn) intermetallics was studied. These compounds are prospective as additives in other Mg-based hydrogen storage materials. From this ...

Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
Ústav fyziky materiálů, 2018

Quantum-mechanical study of magnetic properties of superalloy nanocomposite phase Fe2AlTi
Slávik, Anton; Miháliková, Ivana; Friák, Martin; Všianská, Monika; Šob, Mojmír
2018 - English
The L21-structure Fe2AlTi intermetallic compound is one of the two phases identified in Fe-Al-Ti superalloy nanocomposites. Experimental data related to low-temperature magnetic properties of this Heusler compound indicate that magnetic moment is about 0.1 Bohr magneton per formula unit. In contrast, previous quantum-mechanical calculations predicted Fe2AlTi to have much higher magnetic moment, 0.9 Bohr magneton per formula unit. In order to solve this discrepancy between the theory and experiment we have performed a series of quantum-mechanical fix-spin-moment calculations and compared our results with those for non-magnetic state. It turns out that the total energy of the non-magnetic state is only by 10.73 meV/atom higher than that of the magnetic state. When applying Boltzmann statistics to this very small energy difference we predict that the non-magnetic state appears at non-zero temperatures with significant probabilities (for instance, 22.36 % at T = 100 K) and reduces the overall magnetic moment. As another mechanism lowering the magnetization we studied selected shape deformations, in particular trigonal shearing. Fe2AlTi exhibits a compression-tension asymmetry with respect to these strains and, for example, the strain 0.08 destabilizes the spin-polarized state, leaving the non-magnetic state as the only stable one. Keywords: Ab initio calculations; Fe-Al based superalloys; Fixed-spin-moment; Nanocomposites Available at various institutes of the ASCR
Quantum-mechanical study of magnetic properties of superalloy nanocomposite phase Fe2AlTi

The L21-structure Fe2AlTi intermetallic compound is one of the two phases identified in Fe-Al-Ti superalloy nanocomposites. Experimental data related to low-temperature magnetic properties of this ...

Slávik, Anton; Miháliková, Ivana; Friák, Martin; Všianská, Monika; Šob, Mojmír
Ústav fyziky materiálů, 2018

LOW CYCLE FATIGUE BEHAVIOR AND FATIGUE CRACK INITIATION IN MAR-M247 AT 700 °C
Šulák, Ivo; Obrtlík, Karel; Hrbáček, K.
2018 - English
The second generation nickel-based superalloy MAR-M247 offers a satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that are required for application at elevated temperatures in hostile environments. The microstructure consists mainly of the face centred cubic γ matrix and ordered γ´ strengthening precipitates (L12 crystal structure). The present work focuses on low cycle fatigue (LCF) behaviour of polycrystalline nickel-based superalloy MAR-M247 at high temperature. LCF tests were conducted on cylindrical specimens in a symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 700 °C in ambient air. Cyclic stress-strain curves and fatigue life curves in the representation of plastic strain amplitude vs. stress amplitude and stress amplitude vs. the number of cycles to failure, respectively, were plotted and compared with data obtained on Inconel 713LC. Special attention was paid to the investigation of crack initiation in MAR-M247 during low cycle fatigue. Crack initiation sites were studied by means of scanning electron microscopy (SEM) in dual beam microscope TESCAN LYRA 3 XMU FESEM equipped with focus ion beam (FIB). Specimens’ surface observations revealed the formation of pronounced surface relief indicating localisation of plastic deformation. Observations in transmission electron microscope (TEM) confirmed localisation of cyclic plastic deformation in persistent slip bands along {111} slip planes. Fractographic analysis revealed fatigue crack initiation sites. Fatigue crack propagation in stage I was typical of smooth facets up to 500 μm long. Keywords: Nickel-based superalloy; cyclic stress-strain curve; Fatigue life; fatigue crack initiation; focus ion beam Available at various institutes of the ASCR
LOW CYCLE FATIGUE BEHAVIOR AND FATIGUE CRACK INITIATION IN MAR-M247 AT 700 °C

The second generation nickel-based superalloy MAR-M247 offers a satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that are required for application at ...

Šulák, Ivo; Obrtlík, Karel; Hrbáček, K.
Ústav fyziky materiálů, 2018

First-principles study of interface energies in Fe-Al-based superalloy nanocomposites
Miháliková, Ivana; Slávik, Anton; Friák, Martin; Všianská, Monika; Koutná, N.; Holec, David; Šob, Mojmír
2018 - English
Fe-Al-based nanocomposites with a superalloy-type of microstructure constitute a very promising class of materials. They possess a great potential as an alternative to the currently used steel grades in high temperature applications. Intermetallics-containing nanocomposites, such as those with the Fe3Al compound being one of the phases, may open a way towards future automotive and energy-conversion technologies with lower fuel consumption and reduced environmental impact. We employ quantum-mechanical calculations to analyze relations between ordering tendencies of Al atoms in the disordered Fe-18.75at.%Al phase on one hand and thermodynamic, structural and magnetic properties of Fe-Al-based nanocomposites on the other. When comparing supercells modeling disordered Fe-Al phase with different atomic distribution of atoms we find out that the supercell without 1st and 2nd nearest neighbor Al-Al pairs has a lower energy than that mimicking a perfect disorder (a special quasi-random structure, SQS). Further, coherent interfaces with (001), (110) and (1-10) crystallographic orientations between Fe3Al compound and SQS Fe-Al phase have higher energies than those exhibiting atomic distribution without 1st and 2nd nearest neighbor Al-Al pairs. Keywords: Ab initio calculations; Fe-Al based superalloys; Interface energies; Nanocomposites Available at various institutes of the ASCR
First-principles study of interface energies in Fe-Al-based superalloy nanocomposites

Fe-Al-based nanocomposites with a superalloy-type of microstructure constitute a very promising class of materials. They possess a great potential as an alternative to the currently used steel grades ...

Miháliková, Ivana; Slávik, Anton; Friák, Martin; Všianská, Monika; Koutná, N.; Holec, David; Šob, Mojmír
Ústav fyziky materiálů, 2018

Estimation of equilibrium hydrogen pressure - A new method
Čermák, Jiří; Král, Lubomír
2018 - English
A new method is proposed to estimation of hydrogen pressure in equilibrium with hydride phase in a hydrogen\nstorage material. It is applicable both for hydrogen absorption and desorption in cases where the hydride phase\nis formed by nucleation and growth mechanism. The proposed method saves considerably the experimental\ntime replacing the conventional time consuming measurement of pressure-composition isotherms, the so\ncalled PCT curves. The proposed evaluation procedure is illustrated using hydrogen chemi-sorption at\ntemperatures 623 K, 573 K and 523 K in chosen hydrogen storage alloys Mg-Si-C, Mg-Li-C and Mg-Na-C. Keywords: hydrogen storage; magnesium; new method Available at various institutes of the ASCR
Estimation of equilibrium hydrogen pressure - A new method

A new method is proposed to estimation of hydrogen pressure in equilibrium with hydride phase in a hydrogen\nstorage material. It is applicable both for hydrogen absorption and desorption in cases ...

Čermák, Jiří; Král, Lubomír
Ústav fyziky materiálů, 2018

Evaluation of thin discontinuities in planar conducting materials using the diffraction of electromagnetic field
Savin, A.; Nový, F.; Fintová, Stanislava; Steigmann, R.
2017 - English
The current stage of nondestructive evaluation techniques imposes the development of new electromagnetic (EM) methods that are based on high spatial resolution and increased sensitivity. In order to achieve high performance, the work frequencies must be either radifrequencies or microwaves. At these frequencies, at the dielectric/conductor interface, plasmon polaritons can appear, propagating between conductive regions as evanescent waves. In order to use the evanescent wave that can appear even if the slits width is much smaller that the wavwelength of incident EM wave, a sensor with metamaterial (MM) is used. The study of the EM field diffraction against the edge of long thin discontinuity placed under the inspected surface of a conductive plate has been performed using the geometrical optics principles. This type of sensor having the reception coils shielded by a conductive screen with a circular aperture placed in the front of reception coil of emission reception sensor has been developed and 'transported' information for obtaining of magnified image of the conductive structures inspected. This work presents a sensor, using MM conical Swiss roll type that allows the propagation of evanescent waves and the electromagnetic images are magnified. The test method can be successfully applied in a variety of applications of maxim importance such as defect/damage detection in materials used in automotive and aviation technologies. Applying this testing method, spatial resolution can be improved. Keywords: Electromagnetic fields; Electromagnetic wave reflection; Electromagnetic waves; Geometrical optics; Image resolution; Nondestructive examination; Testing Available at various institutes of the ASCR
Evaluation of thin discontinuities in planar conducting materials using the diffraction of electromagnetic field

The current stage of nondestructive evaluation techniques imposes the development of new electromagnetic (EM) methods that are based on high spatial resolution and increased sensitivity. In order to ...

Savin, A.; Nový, F.; Fintová, Stanislava; Steigmann, R.
Ústav fyziky materiálů, 2017

Crack initiation in austenitic stainless steel sanicro 25 subjected to thermomechanical fatigue
Petráš, Roman; Škorík, Viktor; Polák, Jaroslav
2017 - English
Thermomechanical fatigue experiments were performed with austenitic stainless Sanicro 25 steel. Several amplitudes of mechanical strain in a wide temperature interval (250-700 °C) were applied to the specimens. Mechanical response was recorded and fatigue lives were obtained. Scanning electron microscopy combined with FIB technique was used to study the mechanism of crack initiation in in-phase and in out-of-phase thermomechanical cycling. Different mechanisms of the crack initiation were found in these two types of loading. During in-phase loading fatigue cracks start in grain boundaries by cracking of the oxide. Cracks grew preferentially along grain boundaries which resulted in rapid crack initiation and low fatigue life. In out-of-phase loading multiple cracks perpendicular to the stress axis developed only after sufficiently thick oxide layer was formed and cracked in low temperature loading half-cycle. The cracks in oxide allowed localized repeated oxidation and finally also cracking. The cracks grow transgranularly and result in longer fatigue life. Keywords: Damage mechanism; FIB cutting; Localized oxidation-cracking; Sanicro 25 steel; Thermomechanical fatigue Available at various institutes of the ASCR
Crack initiation in austenitic stainless steel sanicro 25 subjected to thermomechanical fatigue

Thermomechanical fatigue experiments were performed with austenitic stainless Sanicro 25 steel. Several amplitudes of mechanical strain in a wide temperature interval (250-700 °C) were applied to the ...

Petráš, Roman; Škorík, Viktor; Polák, Jaroslav
Ústav fyziky materiálů, 2017

Lifetime Assessment of Particulate Ceramic Composite with Residual Stresses
Náhlík, Luboš; Majer, Zdeněk; Štegnerová, Kateřina; Hutař, Pavel
2017 - English
A micro-crack propagation in particulate ceramic based composite was studied using finite element method (FEM). Subcritical crack growth (SCG) was numerically simulated under complex load conditions (mechanical loading and loading by internal residual stresses). The effect of residual stresses on the crack propagation was studied. Two-dimensional computational model of particulate ceramic composite with material properties corresponding to low temperature co-fired ceramics (LTCC) was developed. The results indicate that the presence of residual stresses significantly reduces values of stress intensity factor in the vicinity of composite surface and the direction of residual stresses around the particles contributes to the micro-crack deflection from the particles. The time to failure of the composite under mechanical loading was determined. Results obtained contribute to a better understanding of the role of residual stresses during micro-crack propagation in ceramic particulate composites. Keywords: ceramic particulate composite; sub-critical crack growth; residual stresses Available at various institutes of the ASCR
Lifetime Assessment of Particulate Ceramic Composite with Residual Stresses

A micro-crack propagation in particulate ceramic based composite was studied using finite element method (FEM). Subcritical crack growth (SCG) was numerically simulated under complex load conditions ...

Náhlík, Luboš; Majer, Zdeněk; Štegnerová, Kateřina; Hutař, Pavel
Ústav fyziky materiálů, 2017

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