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Numerická analýza růstu povrchové trhliny v ochranných vrstvách
Majer, Zdeněk
V práci jsou studovány trhliny v elastické povrchové vrstvě na masivním podkladu. Trhliny jsou iniciovány na volném povrchu a je analyzováno jejich chování s ohledem na možné porušení povrchové vrstvy v závislosti na jejich počáteční velikosti, orientaci a na materiálových parametrech obou složek. Je ukázáno, že v tenké povrchové vrstvě jsou pro chování trhliny rozhodující okrajové podmínky definující namáhání tělesa a vliv materiálových parametrů je druhořadý. V případě, že je těleso namáháno silami rovnoběžnými s rozhraním vrstva-podklad, se trhlina vždy stáčí směrem k rozhraní. Zejména je studován vliv materiálových parametrů obou složek tělesa a způsobu namáhání trhliny na směr jejího šíření. Jsou formulovány obecné závěry týkající se šíření trhliny v blízkosti materiálového rozhraní. Při modelování bi-materiálového tělesa předpokládáme ideální adhesi mezi oběma tělesy a výpočty jsou provedeny metodou konečných prvků (systém ANSYS).
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Comparison of Diffusion Coefficients in Initial Stages of Mutual Diffusion in Layered Structures Carbon/Ferrite and Carbon/Austenite for Chosen Alloys
Čermák, Jiří ; Král, Lubomír
Coefficients of mutual carbon diffusion were measured at initial stages of diffusion for surface thin layer of carbon/ferrite and carbon surface layer/austenite. The aim of the study was to compare the diffusion characteristics obtained at the present strongly non-equilibrium case with those known for carbon mutual diffusion in cases where the carbon concentration does not exceed the solubility limit in the respective substrate. The second goal was to judge, whether the carbon diffusivity is determined by the structure of the substrate matrix (BCC or FCC). As examples of ferrite substrate, pure Fe and chromium steel P91 were chosen, as an example of austenite substrate, AISI316 was taken. It was obtained that – similar to nearequilibrium case – the carbon diffusion measured close to interface C/austenite is significantly lower compared to carbon diffusion near the C/ferrite. Values of carbon diffusion coefficients in cases C/Fe and C/P91 are close one to another. All carbon diffusion coefficients are much lower than those, reported for near-equilibrium conditions; they approach values measured in carbides.
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Intermetallic thin layers deposited by laser method
Jelínek, Miroslav ; Bulíř, Jiří ; Mróz, W. ; Mularczyk-Oliwa, M. ; Prokopiuk, A. ; Bojar, Z. ; Józwiak, S. ; Zasada, D. ; Major, B.
Intermetallic alloys, e.g.: FeAl and Ni.sub.3Al, are commonly regarded as a perspective construction materials for elements working in the extreme conditions. They are often used as the protective coatings on the classical alloys. The pulsed laser deposition method was proposed as the method of creation of the thin intermetallic layers.
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Electrochemical Characterization of TiO2 Blocking Layers for Dye-Sensitized Solar Cells
Kavan, Ladislav
Thin compact layers of TiO2 are grown by thermal oxidation of Ti, by spray pyrolysis, by electrochemical deposition, and by atomic layer deposition. These layers are used in dye-sensitized solar cells to prevent recombination of electrons from the substrate (FTO or Ti) with the hole-conducting medium at this interface. The quality of blocking is evaluated electrochemically by methylviologen, ferro/ferricyanide, and spiro-OMeTAD as the model redox probes. Two types of pinholes in the blocking layers are classified, and their effective area is quantified. Frequency-independent Mott–Schottky plots are fitted from electrochemical impedance spectroscopy. Certain films of the thicknesses of several nanometers allow distinguishing the depletion layer formation both in the TiO2 film and in the FTO substrate underneath the titania film. The excellent blocking function of thermally oxidized Ti, electrodeposited film (60 nm), and atomic-layer-deposited films (>6 nm) is documented by the relative pinhole area of less than 1%. However, the blocking behavior of electrodeposited and atomic-layer-deposited films is strongly reduced upon calcination at 500 °C. The blocking function of spray-pyrolyzed films is less good but also less sensitive to calcination. The thermally oxidized Ti is well blocking and insensitive to calcination.
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