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Příprava Fe-Ti kompozitů mletím v kulovém mlýnku
Roupcová, Pavla ; Schneeweiss, Oldřich
The materials were prepared by mechanical alloying in the ball mill. The first type of sample consists of pure commercial precursors (TiH2 and ferrihydride). The slightly changes of phase composition of the powder were under the detection limit of X-ray powder diffraction. The MS determined the changes from the first step of milling. The second type of sample was prepared from turnings. The reduction of the splinters volume and the mechanical alloying was running simultaneously. The huge crystalline size differences decreased the credibility of computation of phase composition by XRD. MS was able determined phase composition more exactly and in additional to differentiate crystalline and amorphous FeTi phase.
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Microstructure Stability and Creep Behaviour of Alloys Processed by ECAP
Dvořák, Jiří ; Král, Petr ; Svoboda, Milan ; Kvapilová, Marie ; Sklenička, Václav
Coarse-grained binary Cu and Al alloys were processed by equal-channel angular pressing (ECAP) in order to evaluate the effect of severe plastic deformation on the thermal stability of resulting ultrafine-grained microstructure after ECAP followed by creep loading of the pressed alloys. ECAP was conducted at room temperature with a die that had an internal angle of 90° between the two parts of the channel. The subsequent extrusion passes were performed by route Bc. Microstructure of samples up to 12 ECAP passes was characterized by transmission electron microscope (TEM) and scanning electron microscope (SEM) equipped with the electron backscatter diffraction (EBSD) unit. Constant load creep tests in tension were performed at 0.3 - 0.5 Tm and at different applied stresses. It was found that the creep behaviour is influenced by high-angle grain boundaries created by ECAP and creep fracture occurred along the shear bands which are situated near shear plane of the last ECAP pass.
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Studium vlivu segregovaných nečistot na magnetismus hranic zrn a povrchů v FCC niklu a kobaltu
Všianská, Monika ; Vémolová, H. ; Šob, Mojmír
Na základě výpočtů elektronové struktury z prvních principů studujeme vliv segregovaných sp nečistot (Al, Si, P, S, Ga, Ge, As, Se, In, Sn, Sb a Te) na hranici zrn (GB) 5(210) a na volném povrchu (FS) (210) fcc niklu a kobaltu. Provádíme přitom úplnou relaxaci atomové konfigurace GB a FS bez nečistot i se substitučně a intersticiálně vloženými nečistotami. Analyzujeme vliv studovaných nemagnetických nečistot na rozložení magnetického momentu, geometrické uspořádání atomů v okolí GB a FS a hustoty elektronových stavů. Vysvětlujeme také, proč při segregaci studovaných nečistot mohou být magneticky mrtvé vrstvy přítomny v niklu, ale nikoliv v kobaltu.
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Influence of atmosphere on small punch testing of P91 steel
Dymáček, Petr ; Dobeš, Ferdinand
The small punch testing (SPT) under constant force condition was performed in various atmospheres: air, hydrogen and argon. The material selected for the study was P91 steel and testing temperature 873 K. The effect of atmosphere on the test results such as time to rupture, minimum deflection rate and other parameters was measured and evaluated. The results show that there is not very strong but definite effect of atmosphere on SPT creep rupture time. The longest times to rupture were obtained in hydrogen atmosphere for whole range of tested forces. However the difference between tests in hydrogen and tests in air or in argon diminished with decreasing force and longer time to rupture.
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Comparison of Creep Behaviour and Microstructural Changes in Electrodeposited Ultrafine-grained Nickel and its Particle-reinforced Nanocomposite
Kvapilová, Marie ; Sklenička, Václav ; Kuchařová, Květa ; Vidrich, G.
On the basic of the creep experimental results the paper reports comparison creep behaviour of electrodeposited ultrafine-grained nickel and its particle-reinforced nanocomposite. The objective of this research was to further improve the knowledge of the creep behaviour of monolithic nickel and to explore the role of nano-sized SiO2 particles in the potential creep strengthening of electrodeposited Ni nanocomposite. The creep behaviour and microstructure of the pure ultrafine-grained nickel and its nanocomposite reinforced by 2 vol.% nano-sized SiO2 particles were studied at temperatures in the range from 293 to 573 K and at the tensile stresses between 100 to 800 MPa. It was found that the creep resistance of the nanocomposite might be noticeably improved compared to the monolithic nickel. Possible creep mechanisms controlling the creep rate during the creep loading were discussed. The Coble creep as creep rate controlling mechanism was founded improbable.
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Hydrogen Storage Capacity of Mg/Mg2Ni Eutectic Doped with Elements from Groups XIII and XIV
Čermák, Jiří ; Král, Lubomír
In the present paper, the chemical composition of Mg-8.5 at.% Ni-2.7at.%X alloys (X – elements of the 13th and 14th groups) as prospective hydrogen storage was investigated. Experimental alloys were studied in three states: (i) after stabilization anneal, (ii) after stabilization anneal and hydrogen charging, and (iii) after stabilization anneal, hydrogen charging and hydrogen desorption. It was ascertained that a ratio of concentration of X in two principal phases – Mg2NiH4(-X) and MgH2(-X) – was a decreasing function of the ionization potential of X. The stronger the preference of X for Mg2NiH4-X phase, the higher the hydrogen storage capacity of Mg-Ni-X alloy was. For X = In, the hydrogen storage capacity was slightly higher than the capacity of an un-alloyed binary eutectic Mg-Ni alloy.
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Improvement of Hydrogen Desorption Characteristics of Eutectic Mg/Mg2NiH4 and Mg2NiH4 by In addition
Čermák, Jiří ; Král, Lubomír
Mg-xNi alloys are known as perspective hydrogen storage materials [1,2]. Hydrogen storage capacity and hydrogen desorption rate of binary alloys Mg-Ni are, however, still unsatisfactory and therefore, improvements are sought, e.g., by introduction of a proper catalyst [3]. As candidate elements, transition metals [4] are often used that attract bonding valence electrons and, hence, destabilize the hydrides. However, also elements with weaker bond to H than that of Mg, or even non-hydride forming elements show a beneficial effect upon the hydrogen desorption rate [5,6]. The present investigation continues our previous work [7,8]. Here we investigate the resistance of eutectic Mg/Mg2Ni against the poisoning by residual air and possible ways how to improve the hydrogen desorption kinetics of Mg2NiH4 by doping. As dopants, elements of the 13th and the 14th group were tested that do not form stable hydrides.
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Changes of Phase Composition of NaAlH4 Based Complex Hydrides
Roupcová, Pavla ; Schneeweiss, Oldřich
The Mössbauer study is target to valence of Fe-doped phase and its changes during preparation by mixing with NaAlH4 and charging and discharging cycles. The 2 mol % FeCl2·4H2O powder was contained in the asmixing material. The dry milled sample did not transformed during the milling in the protective atmosphere. The significant change was approved in the firstly hydrogenation step only. The analysis shows FeClO which released the most significant component in the dehydrogenation and hydrogenation steps. The amount of FeClO was decreased with the all following step of hydrogenation and dehydrogenation. The fine paramagnetic particles of iron oxides were detected and their amount increased influenced of gas impurities. The longer period of heat treatment shows the agglomeration of iron oxides and their magnetic effect.
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