Number of found documents: 971
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W-B-C Nanostructured Layers - Microstructure and Mechanical Properties
Buršík, Jiří; Kuběna, Ivo; Buršíková, V.; Souček, P.; Zábranský, L.; Mirzaei, S.; Vašina, P.
2017 - English
Several W-B-C layers were prepared by magnetron sputtering. The microstructure of thin layers was observed by means of scanning and transmission electron microscopy on cross sections prepared using a focused ion beam. Both undisturbed layers and the volume under indentation prints were inspected. Keywords: coating; nanostructure; electron microscopy Available at various institutes of the ASCR
W-B-C Nanostructured Layers - Microstructure and Mechanical Properties

Several W-B-C layers were prepared by magnetron sputtering. The microstructure of thin layers was observed by means of scanning and transmission electron microscopy on cross sections prepared using a ...

Buršík, Jiří; Kuběna, Ivo; Buršíková, V.; Souček, P.; Zábranský, L.; Mirzaei, S.; Vašina, P.
Ústav fyziky materiálů, 2017

Spin-dependent electrical transport at finite temperatures from the first principles
Wagenknecht, David; Carva, K.; Turek, Ilja
2017 - English
A theoretical method for finite-temperature electronic transport properties of metallic systems is presented. The developed formalism is applied to pure platinum and to random Cu-Ni alloys. Keywords: elektrical transport; finite temperature; ferromagnetic alloys Available at various institutes of the ASCR
Spin-dependent electrical transport at finite temperatures from the first principles

A theoretical method for finite-temperature electronic transport properties of metallic systems is presented. The developed formalism is applied to pure platinum and to random Cu-Ni alloys.

Wagenknecht, David; Carva, K.; Turek, Ilja
Ústav fyziky materiálů, 2017

Quantum-mechanical study of tensorial elastic and high-temperature thermodynamic properties of grain boundary states in superalloy-phase Ni3Al
Friák, Martin; Všianská, Monika; Holec, D.; Šob, Mojmír
2017 - English
Grain boundaries (GBs), the most important defects in solids and their properties are crucial for many materials properties including (in-)stability. Quantum-mechanical methods can reliably compute properties of GBs and we use them to analyze (tensorial) anisotropic elastic properties of interface states associated with GBs in one of the most important intermetallic compounds for industrial applications, Ni3Al. Selecting the Sigma 5(210) GBs as a case study because of its significant extra volume, we address the mechanical stability of the GB interface states by checking elasticity-based Born stability criteria. One critically important elastic constant, C 55, is found nearly three times smaller at the GB compared with the bulk, contributing thus to the reduction of the mechanical stability of Ni3Al polycrystals. Next, comparing properties of Sigma 5(210) GB state which is fully relaxed with those of a Sigma 5(210) GB state when the supercell dimensions are kept equal to those in the bulk we conclude that lateral relaxations have only marginal impact on the studied properties. Having the complete elastic tensor of Sigma 5(210) GB states we combine Green's-function based homogenization techniques and an approximative approach to the Debye model to compare thermodynamic properties of a perfect Ni3Al bulk and the Sigma 5(210) GB states. In particular, significant reduction of the melting temperature (to 79-81% of the bulk value) is predicted for nanometer-size grains. Keywords: Anisotropic elastic properties; Defects in solids; Elastic tensors Available at various institutes of the ASCR
Quantum-mechanical study of tensorial elastic and high-temperature thermodynamic properties of grain boundary states in superalloy-phase Ni3Al

Grain boundaries (GBs), the most important defects in solids and their properties are crucial for many materials properties including (in-)stability. Quantum-mechanical methods can reliably compute ...

Friák, Martin; Všianská, Monika; Holec, D.; Šob, Mojmír
Ústav fyziky materiálů, 2017

Comparison of calibration functions for short edge cracks under selected loads
Seitl, Stanislav; Miarka, Petr; Malíková, Lucie; Krejsa, M.
2017 - English
Attention to the fatigue cracks in steel structures and bridges has been paid for long time. In spite to efforts to eliminate the creation and propagation of fatigue cracks throughout the designed service life, cracks are still revealed during inspections. Note, that depending on location of initial crack, the crack may propagate from the edge or from the surface. The theoretical model of fatigue crack progression is based on linear fracture mechanics. Steel specimens are subjected to various load (tension, three- and four-point bending, pure bending etc.). The calibration functions for short edge cracks are compared for various load and the discrepancies are discussed. Keywords: Calibration curve; Edge crack; Fracture mechanics; Paris-erdogan law; Stress intensity factors Available at various institutes of the ASCR
Comparison of calibration functions for short edge cracks under selected loads

Attention to the fatigue cracks in steel structures and bridges has been paid for long time. In spite to efforts to eliminate the creation and propagation of fatigue cracks throughout the designed ...

Seitl, Stanislav; Miarka, Petr; Malíková, Lucie; Krejsa, M.
Ústav fyziky materiálů, 2017

NUMERICAL SUPPORT FOR STUDY OF STRESS RATIO EFFECT ON FATIGUE CRACK BEHAVIOUR IN THREE POINT BEND SPECIMEN MADE FROM VIBRATED CONCRETE
Seitl, Stanislav; Thienpont, T.
2016 - English
The fatigue behaviour of concrete has become more important for the design of structures due to more slender/slim structures, which are more sensitive to fatigue loading, or due to wind turbines, which are typically exposed to high-fatigue loading. The fatigue behaviour of concrete was investigated with respect to the influence of various stress ratios. Pilot analysis of fatigue crack propagation rate in three-point bend specimens made from ordinary vibrated concrete was done. Keywords: Stress intensity factor; fatigue crack; Paris-Erdogan law; concrete; FEM; stress ratio Available at various institutes of the ASCR
NUMERICAL SUPPORT FOR STUDY OF STRESS RATIO EFFECT ON FATIGUE CRACK BEHAVIOUR IN THREE POINT BEND SPECIMEN MADE FROM VIBRATED CONCRETE

The fatigue behaviour of concrete has become more important for the design of structures due to more slender/slim structures, which are more sensitive to fatigue loading, or due to wind turbines, ...

Seitl, Stanislav; Thienpont, T.
Ústav fyziky materiálů, 2016

HYDROGENATION OF CHOSEN MgMXN INTERMETALLICS (X=Al, Ga, In, Si, Sn)
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2016 - English
Hydrogen sorption in chosen intermetallics MgmXn (Mg17Al12 , Mg2Ga, mixture of beta-Mg-In phases, Mg2Si and Mg2Sn) formed by magnesium and elements from the 13 th (X: Al, Ga, In) and 14 th (X: Si, Sn) groups was studied between the room temperature and T = 350 °C. Hydrogen pressure p varied from 10-3 MPa to 6 MPa.\nHydrogen solubility in alpha phase (solid solution of hydrogen in MgmXn before the hydride phase was nucleated) was close to hydrogen solubility in pure Mg. Concentration cH of hydrogen solved in Mg m X n depended linearly on pressure p , dependence of cH on temperature T was relatively weak. MgH2 was the main hydrogen storage phase in all the compounds MgmXn . Nucleation of MgH2 at 350 °C was observed at pressure above approximately 1 MPa in Mg17Al12 and above 2 Ma in other compounds. Maximum values of c H in hydride-containing compounds MgmXn detected at T = 350 °C depended on the stability of MgmXn . Keywords: Hydrogen; hydrogen storage; Mg alloys; hydrogen solubility; MgH2 Available at various institutes of the ASCR
HYDROGENATION OF CHOSEN MgMXN INTERMETALLICS (X=Al, Ga, In, Si, Sn)

Hydrogen sorption in chosen intermetallics MgmXn (Mg17Al12 , Mg2Ga, mixture of beta-Mg-In phases, Mg2Si and Mg2Sn) formed by magnesium and elements from the 13 th (X: Al, Ga, In) and 14 th (X: Si, Sn) ...

Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
Ústav fyziky materiálů, 2016

Changes in structure and phase composition in the surface of tram rail
Švábenská, Eva; Roupcová, Pavla; Schneeweiss, Oldřich
2016 - English
We have investigated structure and phase composition of surface layer of tram rails after long time running and the results were compared with those obtained on the original part of material. Changes due to effects of severe plastic deformation together with thermal shocks by friction process were expected. The information about structure and phase composition was obtained by optical and scanning electron microscopy, X-Ray Powder Diffraction, Mössbauer Spectroscopy and Glow Discharge Emission Spectroscopy (GDOES) and this was completed by microhardness measurements. The results show that the surface layer in comparison with the original material exhibits important changes in grain structure, an increase in microhardness and high content of iron oxide and hydrooxides. According to the depth profile of the chemical composition measured by GDOES there is an increase in carbon content in the surface layer which can be effect of up-hill diffusion. Keywords: tram rail; microstructure analysis; surface Available at various institutes of the ASCR
Changes in structure and phase composition in the surface of tram rail

We have investigated structure and phase composition of surface layer of tram rails after long time running and the results were compared with those obtained on the original part of material. Changes ...

Švábenská, Eva; Roupcová, Pavla; Schneeweiss, Oldřich
Ústav fyziky materiálů, 2016

Fatigue crack growth in 316L under uniaxial and torsional loading
Karol, Michal; Chlupová, Alice; Mazánová, Veronika; Kruml, Tomáš
2016 - English
A study of fatigue crack initiation and growth in 316L austenitic stainless steel is reported. Fatigue experiments were performed at room temperature on full cylindrical specimens cycled axially (tension-compression) and on hollow cylindrical specimens tested in reversed torsion. Microstructure and damage evolution (crack initiation and growth) on the surface of mechanically and electrolytically polished specimens were observed using light and electron microscopy. An analysis of the orientation of microcracks and macrocracks which led to failure was made. Axially loaded specimens exhibited presence of several microcracks which resulted in macrocrack propagating perpendicularly to specimen axis. In the case of torsional loading, orientation of macrocrack propagation was dependent on applied load and presence of notches. High amount of short cracks initiated parallel to specimen axis. Long cracks exhibited a tendency to bifurcate with crack branches oriented at approximately 45° to the specimen axis. Keywords: 316L austenitic steel; surface relief; fatigue Available at various institutes of the ASCR
Fatigue crack growth in 316L under uniaxial and torsional loading

A study of fatigue crack initiation and growth in 316L austenitic stainless steel is reported. Fatigue experiments were performed at room temperature on full cylindrical specimens cycled axially ...

Karol, Michal; Chlupová, Alice; Mazánová, Veronika; Kruml, Tomáš
Ústav fyziky materiálů, 2016

Nanoscale phases on surface Fe-6Si magnetic sheets
Švábenská, Eva; Roupcová, Pavla; Král, Lubomír; Bulín, Tomáš; Vondráček, Martin; Foldyna, Josef; Čechal, J.; Schneeweiss, Oldřich
2016 - English
Analysis of the nanoscale phases which appear on the surface Fe-6Si samples were carried out after the various treatments – grinding and etching, annealing, and water jet abrasion. The basic information on structure, chemical and phase composition was obtained by X-Ray Powder Diffraction (XRD), Scanning Electron Microscopy with EDX, Glow Discharge Optical Emission Spectrometry (GDOES), Mössbauer Spectroscopy and X-ray Photoelectron Spectrometry (XPS). The results show high stability of the surface phase composition after the mechanical and heat treatments. Results obtained from the surface analysis in micrometer depth (XRD, EDX, GDOES) do not show any changes after the different treatments. Iron oxides were detected in XPS and conversion electron Mössbauer spectra (CEMS) which analyze the surface composition in a nanometer scale. In addition to, fine changes in atomic ordering on the surface can be observed after mechanical and heat treatments in the CEMS spectra. Keywords: Fe-Si alloy; surface modification; nanostructure Available at various institutes of the ASCR
Nanoscale phases on surface Fe-6Si magnetic sheets

Analysis of the nanoscale phases which appear on the surface Fe-6Si samples were carried out after the various treatments – grinding and etching, annealing, and water jet abrasion. The basic ...

Švábenská, Eva; Roupcová, Pavla; Král, Lubomír; Bulín, Tomáš; Vondráček, Martin; Foldyna, Josef; Čechal, J.; Schneeweiss, Oldřich
Ústav fyziky materiálů, 2016

HYDROGENATION PROPERTIES OF Mg-Al-Ti-Zr-C COMPOSITE
Král, Lubomír; Čermák, Jiří; Roupcová, Pavla
2016 - English
The improvement of hydrogen storage properties of ball-milled Mg-Al-Ti-Zr-C composite was studied in this\npaper. It has been previously shown, that the addition of Ti, Zr, Al and C improves storage properties of Mg.\nThis beneficial effect of additives upon hydrogen storage properties can be explained by catalysis by the\nnanoparticles rich in Ti, Zr or Al located on the surface of Mg grains. They provide effective pathways for the\nhydrogen diffusion into the MgH2. The morphological and microstructural characteristics were investigated by\nscanning electron microscope Tescan Lyra 3 and by X-ray diffraction. The hydrogen sorption was measured\nby Sieverts method using Setaram PCT-Pro device.\nStudied experimental composite absorbed 4.2 wt.% H 2 at 573 K and 3 wt.% H 2 at 523K within 10 min. The\nhydrogen storage capacity of the composite was about 4.6% wt.% H 2 and 4.2% wt.% H 2 at 573K and 523K,\nrespectively. Keywords: Hydrides; hydrogen storage; catalysis; hydrogen; Mg-alloys Available at various institutes of the ASCR
HYDROGENATION PROPERTIES OF Mg-Al-Ti-Zr-C COMPOSITE

The improvement of hydrogen storage properties of ball-milled Mg-Al-Ti-Zr-C composite was studied in this\npaper. It has been previously shown, that the addition of Ti, Zr, Al and C improves storage ...

Král, Lubomír; Čermák, Jiří; Roupcová, Pavla
Ústav fyziky materiálů, 2016

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