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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 - anglický
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.
Klíčová slova:
coating; nanostructure; electron microscopy
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
Spin-dependent electrical transport at finite temperatures from the first principles
Wagenknecht, David; Carva, K.; Turek, Ilja
2017 - anglický
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.
Klíčová slova:
elektrical transport; finite temperature; ferromagnetic alloys
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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.
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 - anglický
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.
Klíčová slova:
Anisotropic elastic properties; Defects in solids; Elastic tensors
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
Comparison of calibration functions for short edge cracks under selected loads
Seitl, Stanislav; Miarka, Petr; Malíková, Lucie; Krejsa, M.
2017 - anglický
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.
Klíčová slova:
Calibration curve; Edge crack; Fracture mechanics; Paris-erdogan law; Stress intensity factors
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
Fatigue crack initiation and growth in 316L steel in torsional cyclic loading
Karol, Michal; Chlupová, Alice; Mazánová, Veronika; Kruml, Tomáš
2017 - anglický
Fatigue crack initiation and growth study in 316L austenitic stainless steel was made in cyclic\ntorsion. The experiments on hollow cylindrical specimens were performed at room temperature using fully reversed shear strain controlled cycles. The specimens used were polished mechanically and electrolytically to enable surface damage and crack propagation observation using optical light microscope, SEM. It was found that high density of extrusions and intrusions are formed on the specimen surface due to cyclic loading. TEM observations revealed that dislocation arrangement in well-known ladder-like structure is responsible for the localization of cyclic plastic deformation and for the origin of surface roughness in which the fatigue crack nucleate. The path of fatigue cracks leading to failure was observed, too. The crack path\nwas found to be dependent upon the applied shear strain amplitude.
Klíčová slova:
316L austenitic steel; fatigue crack initiation; Crack growth; Torsional loading; Crack path
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Fatigue crack initiation and growth in 316L steel in torsional cyclic loading
Fatigue crack initiation and growth study in 316L austenitic stainless steel was made in cyclic\ntorsion. The experiments on hollow cylindrical specimens were performed at room temperature using fully ...
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 - anglický
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.
Klíčová slova:
Stress intensity factor; fatigue crack; Paris-Erdogan law; concrete; FEM; stress ratio
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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, ...
Changes in structure and phase composition in the surface of tram rail
Švábenská, Eva; Roupcová, Pavla; Schneeweiss, Oldřich
2016 - anglický
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.
Klíčová slova:
tram rail; microstructure analysis; surface
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
Fatigue crack growth in 316L under uniaxial and torsional loading
Karol, Michal; Chlupová, Alice; Mazánová, Veronika; Kruml, Tomáš
2016 - anglický
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.
Klíčová slova:
316L austenitic steel; surface relief; fatigue
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
HYDROGEN ABSORPTION IN A-Co30Fe55B15
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2016 - anglický
Hydrogen solved in amorphous alloys (AAs) influences their magnetic characteristics. AAs are also perspective\nas additives that can improve hydrogen storage kinetic in certain types of ball-milled hydrogen storage\nmaterials (HSMs). Therefore, knowledge of hydrogen solubility and hydrogen sorption kinetics in AAs are of a\ngreat importance for aimed design both AAs with optimal magnetic parameters and HSMs with desired sorption\ncharacteristics. In the present paper, amorphous alloy Co30Fe55B15 (an example of the type a-TM1xTM2y Bz ;\nTM - transition metal) was investigated. Hydrogen concentration c H was measured by Sieverts method in\ntemperature interval from T = 150 °C to T = 350 °C under hydrogen pressure p up to 6 MPa. It was found that\nc H was an increasing function of p and its maximum value was typically 0.5 wt.% H2 at 350 °C and 6 MPa.\nHowever, when the alloy was preliminary hydrogen charged (PHC), the pressure dependence of total c Htot in\nthe first absorption cycle(s) is non-monotonous in dependence on PHC conditions. For the sake of comparison,\nthe same absorption characteristics were measured also in Mg2Ni intermetallic that is a common constituent\nin Mg-based HSMs. Comparing Co30Fe55B15 and Mg2Ni, it was concluded that Co30Fe55B15 shows lower\nhydrogen solubility, but much better absorption kinetics.
Klíčová slova:
absorption, Co 30 Fe 55 B 15; Hydrogen; Co30Fe55B15
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
HYDROGEN ABSORPTION IN A-Co30Fe55B15
Hydrogen solved in amorphous alloys (AAs) influences their magnetic characteristics. AAs are also perspective\nas additives that can improve hydrogen storage kinetic in certain types of ball-milled ...
INFLUENCE OF LASER CUTTING AND PUNCHING ON MAGNETIC PROPERTIES\nOF ELECTRICAL STEEL M470-50A
Bulín, Tomáš; Švábenská, Eva; Hapla, Miroslav; Ondrůšek, Č.; Schneeweiss, Oldřich
2016 - anglický
Electrical steel M470-50A belongs to the most often used materials in electrical machines. Due to this fact, it is desirable to know the magnetic parameters after processing raw sheets into the required shape. Basic parameters of mechanical, electrical, and magnetic properties of the sheets are usually obtained from the producer but the magnetic properties are changing in dependence on additional machining processes. The aim of this study is to describe changes in parameters of magnetic behavior after punching, laser and spark cutting of the original sheets. The basic information of structure was obtained by optical and scanning electron microscopy. The magnetic parameters were acquired from the measuring of magnetic hysteresis loops in dependence on saturation fields and frequencies. The results are discussed from the point of view of applied\ncutting technology with the aim to obtain the best magnetic parameters and consequently a higher efficiency of the final product. Results can be used as input parameters in simulation of the electrical machine.
Klíčová slova:
magnetic properties; M470-50A steel; laser cutting; punching; spark cutting
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
INFLUENCE OF LASER CUTTING AND PUNCHING ON MAGNETIC PROPERTIES\nOF ELECTRICAL STEEL M470-50A
Electrical steel M470-50A belongs to the most often used materials in electrical machines. Due to this fact, it is desirable to know the magnetic parameters after processing raw sheets into the ...
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