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HYDROGEN SORPTION IN ORDERED Mg-In ALLOYS
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2019 - English
Hydrogen storage (HS) performance of three Mg- x In- y CB alloys (CB - amorphous carbon, x = 55, 64, 73 y =\n10 wt%) was studied. Indium concentration covered an area of ordered β structures. Alloys were prepared by\nball-milling in hydrogen atmosphere. Kinetic curves and PCT isotherms were measured in the temperature\ninterval from 200 °C to 325 °C. X-ray diffraction spectroscopy (XRD) was used for structure investigation. Alloy\nwith x = 73 wt% In ( β ’’ structure) showed reversible amorphization during temperature cycling between about\n100 °C and 350 °C. Hydrogen sorption experiments were done by the Sieverts method under the hydrogen\ngas pressure ranging from 0.1 MPa to 2.5 MPa. It was found that hydrogen sorption capacity varied between\n0.47 and 1.1 wt% H 2 . Hydride formation enthalpy ∆H calculated from desorption PCT experiments was\nsignificantly lower than ∆H , known for pure Mg. This invoked an idea that atomic order of Mg-based HS\nmaterials might decrease the high thermodynamic stability of hydride phase.
Keywords:
Hydrogen storage; Mg alloys; hydride stability; ordering
Available at various institutes of the ASCR
HYDROGEN SORPTION IN ORDERED Mg-In ALLOYS
Hydrogen storage (HS) performance of three Mg- x In- y CB alloys (CB - amorphous carbon, x = 55, 64, 73 y =\n10 wt%) was studied. Indium concentration covered an area of ordered β structures. Alloys ...
Effect of casting conditions and heat treatment on high temperature low cycle fatigue performance of nickel superalloy Inconel 713LC
Šulák, Ivo; Obrtlík, Karel; Hrbáček, Karel
2019 - English
The present work is focused on the study of high temperature low cycle fatigue behaviour of Inconel 713LC produced by a vibratory investment casting (VIC) in as-cast conditions and in the condition after heat treatment (HT) consisting of hot isostatic pressing (HIP) followed by precipitation hardening. Low cycle fatigue tests were carried out on cylindrical specimens in symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 800 °C in air. Hardening/softening curves and fatigue life curves of both materials were assessed and compared with data of Inconel 713LC produced by a conventional investment casting (CIC). Cyclic hardening can be observed in the high amplitude domain while saturated stress response is apparent for low amplitude cycling for all material batches. Data presented in Basquin representation show an increase in fatigue life of both VIC batches compared to the CIC batch, however, no effect of HT on fatigue life of Inconel 713LC produced by VIC was observed. In contrast, the heat treated Inconel 713LC demonstrates slightly higher fatigue life in Coffin-Manson representation. The microstructure of both superalloys was studied by means of scanning electron microscopy (SEM). The microstructure of superalloy is characterized by dendritic grains with casting defects. It comprises the γ matrix, cubic γ´ precipitates, eutectics and carbides. The effect of the VIC and HT on fatigue performance and microstructure of Inconel 713LC is discussed.
Keywords:
Inconel 713LC; vibratory investment casting; hot isostatic pressing; high temperature low cycle fatigue; stress-strain response
Available at various institutes of the ASCR
Effect of casting conditions and heat treatment on high temperature low cycle fatigue performance of nickel superalloy Inconel 713LC
The present work is focused on the study of high temperature low cycle fatigue behaviour of Inconel 713LC produced by a vibratory investment casting (VIC) in as-cast conditions and in the condition ...
PHASE COMPOSITION OF CHOSEN Mg-BASED MATERIALS DURING HYDROGEN SORPTION
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2019 - English
Phase transformation during hydrogen sorption was investigated in ten chosen magnesium-based hydrogen storage (HS) materials. Chemical composition of the materials consisted of Mg, as a principal hydrogen-binding element, additive X and amorphous carbon (CB), as an anti-sticking component. In order to assess the effect of X itself upon the structure, values of concentration of both X and CB were fixed to about 12 wt. %. The influence of X = Mg2Si, Mg2Ge, Mg17Al12, Mg5Ga2, NaCl, LiCl, NaF, LiF and two combinations Ni+Mg17Al12 and Ni+Mg2Si upon the changes in phase composition was tested. Phase content in HS materials was observed (i) after the intensive ball milling (BM), (ii) after the BM followed by hydrogen charging at 623 K and (iii) after the BM and one hydrogen charging/discharging cycle (C/D) at temperature 623 K. The study was carried out by SEM and XRD. It was found that, the C/D is approximately structurally reversible for X = Mg2Ge, Mg17Al12, NaF and LiF. However, additives X = Mg17Al12 and NaF decompose already during the BM. In alloys with combination of Ni with Mg17Al12, new phases NimAln are formed. Phase composition changed during C/D for X = Mg2Si Mg5Ga2 and Ni+Mg2Si due to equilibration of phases composition. Observed structure changes of HS materials with chloride ionic additives NaCl and LiCl are, most likely caused by the relatively strong affinity between Mg and Cl. Hydrogen storage capacity of all studied alloys was 6.0 +/- 0.3 wt. % H-2.
Keywords:
Hydrogen storage; Mg alloys; carbon black
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PHASE COMPOSITION OF CHOSEN Mg-BASED MATERIALS DURING HYDROGEN SORPTION
Phase transformation during hydrogen sorption was investigated in ten chosen magnesium-based hydrogen storage (HS) materials. Chemical composition of the materials consisted of Mg, as a principal ...
PILOT ANALYSIS OF CHEVRON NOTCH LIGAMENT AREA FOR APPLICATION\nON QUASI-BRITTLE MATERIALS
Seitl, Stanislav; Růžička, P.; Miarka, P.; Sobek, J.
2018 - English
Specimens for the bending tests with the chevron notch are standardized for the\nevaluation of the fracture toughness of various materials. The main advantage of this test\nset-up is that no sharp pre-crack has to be introduced, because a sharp crack is formed\nduring loading at the beginning of the test. Furthermore, no crack length measurement is\nrequired, and a stable crack growth can be reached due to geometry of the notch. In this\ncontribution a difference of the ligament area of the specimens with the straight through\nnotch and the chevron notch was investigated
Keywords:
Fracture mechanics; chevron notch; ligament area; work of fracture; straight notch; blunt
Available at various institutes of the ASCR
PILOT ANALYSIS OF CHEVRON NOTCH LIGAMENT AREA FOR APPLICATION\nON QUASI-BRITTLE MATERIALS
Specimens for the bending tests with the chevron notch are standardized for the\nevaluation of the fracture toughness of various materials. The main advantage of this test\nset-up is that no sharp ...
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 ...
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 ...
INFLUENCE OF GRAPHITE UPON THE KINETICS OF HYDROGEN SORPTION IN Mg@Mg17Al12
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2018 - English
Influence of graphite addition to the ball-milling charge composed of Mg splinters and Mg17Al12 particles upon the hydrogen sorption was investigated at sorption temperature 623 K. Measurements were carried out by Sieverts method. Graphite facilitates the ball-milling: It prevents re-agglomeration of crushed particles into large secondary particles. It also suppresses sticking the milled material to the balls and walls of the milling jar. It was found that an increase of carbon concentration up to a certain limit c(L) lying between 14 and 23 wt. % C, carbon increases both the absorption and the desorption rates and hydrogen storage capacity. Above c(L), carbon causes a considerable decrease in HS capacity, which spoils the application potential of Mg@Mg17Al12/C. Crystallite size of the material under study, obtained by XRD, is in the order of tens of nm.
Keywords:
storage; Hydrogen storage; Mg alloys; graphite
Available at various institutes of the ASCR
INFLUENCE OF GRAPHITE UPON THE KINETICS OF HYDROGEN SORPTION IN Mg@Mg17Al12
Influence of graphite addition to the ball-milling charge composed of Mg splinters and Mg17Al12 particles upon the hydrogen sorption was investigated at sorption temperature 623 K. Measurements were ...
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 ...
MICROSTRUCTURE AND COMPOSITION OF FINE PARTICLES RELEASED BY CAR BRAKING
Švábenská, Eva; Roupcová, Pavla; Pizúrová, Naděžda; Schneeweiss, Oldřich
2018 - English
Vehicular traffic is connected with large volume of fine particles released during brake processes of cars. Our research is focused on the phase, structure and chemical analysis of the fine particles taken from some car brake parts by their services. The information on structure and phase composition was obtained by X-Ray Powder Diffraction, Mossbauer Spectroscopy, scanning electron microscopy with EDX and transmission electron microscopy. The results of the wear debris analysis are compared with original brake materials components. Most of recognized particles are based mainly on iron oxides. Wear brake particles are discussed in the relation to the potential risk to the environment and human health.
Keywords:
wear; Nanoparticles; wear debris; environment
Available at various institutes of the ASCR
MICROSTRUCTURE AND COMPOSITION OF FINE PARTICLES RELEASED BY CAR BRAKING
Vehicular traffic is connected with large volume of fine particles released during brake processes of cars. Our research is focused on the phase, structure and chemical analysis of the fine particles ...
HYDROGEN STORAGE PROPERTIES OF GRAPHENE OXIDE MATERIALS PREPARED BY DIFFERENT WAYS
Král, Lubomír; Čermák, Jiří; Bytesnikova, Z.
2018 - English
Graphene-based materials show unique properties. These single layered materials consist of 2D structure of carbon atoms, belong to the strongest known materials, that are very mechanically flexible, optically transparent and that are excellent electrical and thermal conductors. Recently, several studies on these types of materials have highlighted the potential of this material for hydrogen storage (HS) and raised new hopes for the development of an effective solid-state HS media. In the present paper, the structure and HS properties of graphene oxide (GO) and chemically reduced graphene oxide (rGO) produced by different procedures were studied. Hydrogen sorption characteristics of GO and rGO were measured using the Sieverts-type gas sorption analyzer PCT-Pro Setaram Instrumentation. The study of HS was carried out at temperature range from 198 K to 423 K under hydrogen pressure from 1x10(-4) to 4 MPa.
Keywords:
adsorption; reduction; graphite; Graphene oxide; hydrogen storage; adsorption; desorption
Available at various institutes of the ASCR
HYDROGEN STORAGE PROPERTIES OF GRAPHENE OXIDE MATERIALS PREPARED BY DIFFERENT WAYS
Graphene-based materials show unique properties. These single layered materials consist of 2D structure of carbon atoms, belong to the strongest known materials, that are very mechanically flexible, ...
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