No (1013)
Yes (4)
Number of found documents:
1017
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Compressive creep testing of MoSi2-SiC nanocomposites
Luptáková, Natália; Ballóková, B.; Dymáček, Petr
2015 - English
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.
Keywords:
MoSi2-SiC; creep test; compressive creep; stress exponent; activation energy
Available at various institutes of the ASCR
Compressive creep testing of MoSi2-SiC nanocomposites
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 ...
Stress analysis of modified compact tension specimens: K-calibration curves
Seitl, Stanislav; Viszlay, V.
2015 - English
Compact tension (CT) test is in engineering frequently used test for metallic materials to determiner fracture parameters/properties, e.g. fracture energy, fracture toughness, crack propagation rate, J-R curves etc. [20]. The modified compact tension (MCT) specimen for cement based composites has to be prepared due to negligible concentration around the holes for tenons. An accurate determination of fracture parameters requires the use of a valid calibration curves, there for in this contribution the stress analysis near the crack tip and calibration curve for modified compact tension test are introduced. The calibration curve is introduced for diameter 150 mm (the specimen could be easy made from the specimen for compression test) and includes all theoretical imperfections that results from preparation of the MCT specimens.
Keywords:
Modified compact tension specimen; stress intensity factor; concrete; FEM
Available at various institutes of the ASCR
Stress analysis of modified compact tension specimens: K-calibration curves
Compact tension (CT) test is in engineering frequently used test for metallic materials to determiner fracture parameters/properties, e.g. fracture energy, fracture toughness, crack propagation rate, ...
Stress relaxation in partially pyrolysed SiOC materials
Halasová, Martina; Chlup, Zdeněk; Černý, Martin; Strachota, Adam; Dlouhý, Ivo
2015 - English
This paper focuses on the difficulty with Vickers hardness evaluation of SiOC materials. To evaluate it, diagonals of an indent are crucial. Due to stress relaxation in experimental material it was not possible to evaluate it in the whole range of experimental temperatures. As experimental materials were used two types of commercialy available polysiloxane resins, pyrolysed in range from 400 to 1000°C.
Keywords:
polysiloxane; resin; SiOC; glass; ceramics; Vickers hardness; 3D reconstruction; indent
Available at various institutes of the ASCR
Stress relaxation in partially pyrolysed SiOC materials
This paper focuses on the difficulty with Vickers hardness evaluation of SiOC materials. To evaluate it, diagonals of an indent are crucial. Due to stress relaxation in experimental material it was ...
The Changes in Structure of Steel P91 after Short Annealings
Král, Lubomír; Čermák, Jiří; Král, Petr
2015 - English
Phase composition of the steel P91 during annealing was studied with the aim to reveal the evolution of new phases. In this paper, the precipitation was characterized using energy-dispersive X-ray spectroscopy (EDS) and electron diffraction in transmission microscopy (TEM). Only Nb-rich particles were found in the studied samples austenitized at 1423 °C for 20h and water cooled. After tempering at 673 °C for 2 h, the formation mainly M3C type carbides and after tempering at 873 °C for 2 h, the formation of M7C3 and M23C6 was observed. These structure changes play an important role for stability and also carbon diffusion.
Keywords:
P91; carbides; carbon; precipitation
Available at various institutes of the ASCR
The Changes in Structure of Steel P91 after Short Annealings
Phase composition of the steel P91 during annealing was studied with the aim to reveal the evolution of new phases. In this paper, the precipitation was characterized using energy-dispersive X-ray ...
HYDROGEN STORAGE IN Mg-In-C ALLOYS: EFFECT OF COMPOSITION AND AGEING
Čermák, Jiří; Král, Lubomír
2015 - English
Hydrogen storage in two Mg-In-C alloys with different In concentration, c In , was studied in the temperature range from 250°C to 350°C after five-years-ageing at room temperature. The both alloys show acceptable cycling stability, however, the storage capacity of the alloys decreased from about 5 wt. % H2 to about 2,5 and 3.1 wt. % H 2 by higher c In and lower c In , respectively after 5 years. The sorption kinetics degraded much more by high c In than by c In . PCT isotherms, TPS and DSC patterns were measured for both materials. It was found that the hydrides responsible for hydrogen storage in alloy with higher c In are slightly more stable.
Keywords:
hydrogen; hydrogen storage; magnesium alloys
Available at various institutes of the ASCR
HYDROGEN STORAGE IN Mg-In-C ALLOYS: EFFECT OF COMPOSITION AND AGEING
Hydrogen storage in two Mg-In-C alloys with different In concentration, c In , was studied in the temperature range from 250°C to 350°C after five-years-ageing at room temperature. The both alloys ...
THE EFFECT OF MO AND/OR C ADDITION ON MICROSTRUCTURE AND PROPERTIES OF TIAL ALLOYS
Chlupová, Alice; Kruml, Tomáš; Roupcová, Pavla; Heczko, Milan; Obrtlík, Karel; Beran, Přemysl
2015 - English
Cast TiAl alloys with high Nb content are subject of extensive research with the aim to develop material with low density, good corrosion resistance and high strength at elevated temperatures. Disadvantage of their broad applications is restricted workability, machinability and low fracture toughness especially at room temperature. Improvement of properties of TiAl based materials can be achieved by tailoring the microstructure by modification of chemical composition. For this purpose 5 types of TiAl alloys with 7 % of Nb were prepared having variable content of Mo and/or C. Addition of Mo and/or C resulted in three types of microstructure and different phase composition. All modified alloys contain colonies consisting of thin lamellae of a and g phases sometimes complemented by g and/or b phase at the grain boundaries. Variable microstructure and phase composition resulted in differences in mechanical behaviour. The most promising tensile properties at both room and elevated temperature were observed for alloy doped with 2 % of Mo having the mixed microstructure containing b phase and for alloy doped with 0.5 % of C with nearly lamellar microstructure without b phase. 2Mo alloy exhibited reasonably good ductility while 0.5C alloy reached the highest tensile strength. Also low cycle fatigue behaviour of these two materials was the best of all five materials under investigation. Fatigue deformation characteristics were better in the case of 2Mo alloy while 0.5C alloy exhibited higher cyclic stresses. Fracture mechanisms were determined using fractographic analysis. The major fracture mode of all alloys was trans-lamellar.
Keywords:
TiAl; microstructure; mechanical properties; effect of alloying; fractography
Available at various institutes of the ASCR
THE EFFECT OF MO AND/OR C ADDITION ON MICROSTRUCTURE AND PROPERTIES OF TIAL ALLOYS
Cast TiAl alloys with high Nb content are subject of extensive research with the aim to develop material with low density, good corrosion resistance and high strength at elevated temperatures. ...
Book of Abstracts: 17th International Conference on the Strength of Materials
Dlouhý, Antonín; Kunz, Ludvík
2015 - English
The Book of Abstracts covers twelve exciting scientific topics addressed by the International Conference on the Strength of Materials 17 (ICSMA 17). Eight excellent plenary speakers were selected based on the discussion and vote within the International Committee of ICSMA. The topics include not only traditional areas like cyclic or high temperature deformation and scale-bridging modeling but also still growing subjects of nano-micro scale experiments and the strength of biological systems. Moreover, the Local Organizing Committee, in cooperation with the Department of Materials Physics, Charles University in Prague, has decided to highlight the 80th anniversary of Prof. Pavel Lukáč, a brilliant international teacher and scientist. The thirteenth topic of the ICSMA 17 is thus dedicated to honour his contribution to materials research. Altogether, the Book presents 376 abstracts evenly distributed among the individual research areas that entered the scope of the conference.
Keywords:
Materials; Strength; Plasticity; Dislocations
Available at various institutes of the ASCR
Book of Abstracts: 17th International Conference on the Strength of Materials
The Book of Abstracts covers twelve exciting scientific topics addressed by the International Conference on the Strength of Materials 17 (ICSMA 17). Eight excellent plenary speakers were selected ...
The effect of σ-phase formation on long-term durability of SUPER 304H steel
Horváth, J.; Král, Petr; Janovec, J.; Sklenička, Václav
2015 - English
This work presents results of the analysis of phases formed in a SUPER 304H steel during a medium-term static isothermal ageing (675 degrees C/15000 h). The investigations of the precipitates were especially focused on the occurrence of sigma-phase because its formation leads to the serious embrittlement. \nThe evaluation and distribution of brittle sigma-phase were determined on macroscopic level by using light microscopy/colour etching. The microstructure was also investigated on microscopic level by scanning electron microscopes Tescan Lyra 3 and JEOL JSM 5410 equipped by electron backscatter diffraction unit and by transmission electron microscope Jeol 2100F. This work also investigates the effect of sigma-phase formation on the impact strength of an aged state of SUPER 304H steel. For comparison reasons the microstructure and the mechanical properties of the initial as-received) state were also investigated. It was found that the formation of brittle sigma-phase in the aged and therefore degraded microstructure led to the significant decrease of the impact strength. The influence of brittle sigma-phase on long-term durability of the degraded steel regarding its insufficient impact strength is discussed.
Keywords:
austenitic steel; medium-term ageing; SUPER 304H; sigma-phase; impact strength
Available at various institutes of the ASCR
The effect of σ-phase formation on long-term durability of SUPER 304H steel
This work presents results of the analysis of phases formed in a SUPER 304H steel during a medium-term static isothermal ageing (675 degrees C/15000 h). The investigations of the precipitates were ...
Deposition of Hard Yet Moderately Ductile MoBC Coatings by p-DC Magnetron Sputtering
Souček, P.; Buršíková, V.; Zábranský, L.; Buršík, Jiří; Vašina, P.
2015 - English
Novel nanolaminated MoBC coatings were prepared using a combination of non-reactive direct current and pulsed direct current magnetron sputtering. Depending on the deposition conditions the coatings were either of amorphous or of nanocomposite nature. Nanocomposite coatings showed good hardness and Young’s modulus and showed no tendency to form cracks even for high-load nanoindentation testing.
Keywords:
magnetron sputtering; ion flux; nanolaminates
Available at various institutes of the ASCR
Deposition of Hard Yet Moderately Ductile MoBC Coatings by p-DC Magnetron Sputtering
Novel nanolaminated MoBC coatings were prepared using a combination of non-reactive direct current and pulsed direct current magnetron sputtering. Depending on the deposition conditions the coatings ...
Chemical Wet Synthesis and Characterization of Copper-Silver Nanoparticles
Zobač, O.; Sopoušek, J.; Vykoukal, V.; Buršík, Jiří; Roupcová, Pavla
2015 - English
AgCu nanoparticles (NPs) of near-eutectic composition were prepared by various route of wet synthesis. Nanoparticles suspended in nonpolar solvents were synthesized by solvothermal synthesis from metalloorganic precursors. AgCu colloids in aqueous solution were obtained by the hydride reduction of Ag and Cu nitrates under action of different stabilization agents. Chemical characterizations of as-synthesized AgCu NPs were done using inductively-coupled plasma-optical emission spectrometry (ICP-OES). The optical properties of nanoparticles were monitored using UV-Vis spectrophotometer. The size of colloid nanoparticles were measured by both dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) method in some extra cases.
Keywords:
nanoalloy; Ag-Cu; phase transformation
Available at various institutes of the ASCR
Chemical Wet Synthesis and Characterization of Copper-Silver Nanoparticles
AgCu nanoparticles (NPs) of near-eutectic composition were prepared by various route of wet synthesis. Nanoparticles suspended in nonpolar solvents were synthesized by solvothermal synthesis from ...
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