Nanoparticles of NaAlH(4) have been infiltrated in nanoporous carbon aerogel with TiCl(3) nanoparticles in order to explore possible synergetic effects between nanoconfinement and a functionalized catalytic scaffold. Resorcinol formaldehyde carbon aerogels with an average pore size of 17 nm and total pore volume of 1.26 mL/g were infiltrated with TiCl(3) to obtain an aerogel doped with 3.0 wt % TiCl(3) nanoparticles. NaAlH(4) was melt-infiltrated into the functionalized carbon aerogel at 189 °C and p(H(2)) ∼ 186-199 bar. Energy-dispersive spectrometry (EDS) combined with focused ion beam (FIB) techniques revealed the presence of Na, Al, Ti, and Cl inside the aerogel scaffold material. The infiltrated NaAlH(4) was X-ray amorphous, whereas (27)Al magic-angle spinning (MAS) NMR spectroscopy confirmed the presence of nanoconfined NaAlH(4). Temperature-programmed desorption mass spectroscopy (TPD-MS) and Sieverts' measurements demonstrated significantly improved hydrogen desorption kinetics for this new nanoconfined NaAlH(4)-TiCl(3) material as compared to nanoconfined NaAlH(4) without the catalysts TiCl(3) and to bulk ball-milled samples of NaAlH(4)-TiCl(3). We find that the onset temperature for hydrogen release was close to room temperature (T(onset) = 33 °C), and the hydrogen release rate reached a maximum value at 125 °C, which demonstrates favorable synergetic effects between nanoconfinement and catalyst addition.
This paper presents a characterization study of specimens manufactured from Ti-6Al-4V powder with the use of laser engineered net shaping technology (LENS). Two different orientations of the specimens were considered to analyze the loading direction influence on the material mechanical properties. Moreover, two sets of specimens, as-built (without heat treatment) and after heat treatment, were used. An optical measurement system was also adopted for determining deformation of the specimen, areas of minimum and the maximum principal strain, and an effective plastic strain value at failure. The loading direction dependence on the material properties was observed with a significant influence of the orientation on the stress and strain level. Microstructure characterization was examined with the use of optical and scanning electron microscopes (SEM); in addition, the electron backscatter diffraction (EBSD) was also used. The fracture mechanism was discussed based on the fractography analysis. The presented comprehensive methodology proved to be effective and it could be implemented for different materials in additive technologies. The material data was used to obtain parameters for the selected constitutive model to simulate the energy absorbing structures manufactured with LENS technology. Therefore, a brief discussion related to numerical modelling of the LENS Ti-6Al-4V alloy was also included in the paper. The numerical modelling confirmed the correctness of the acquired material data resulting in a reasonable reproduction of the material behavior during the cellular structure deformation process.
In this paper, the effect of applied multi-variant heat treatment on microstructure, phase composition and mechanical response of Haynes 282 nickel-based superalloy was investigated. For this reason, temperatures of both stages of standard two-stage aging treatment (i.e., 1010°C/2 h + 780°C/8 h) were extended to 900-1100°C/2 h and 680-880°C/8 h ranges, respectively. Consequently, 30 different variants of heat treatment were applied. The microstructural features of heat-treated samples were investigated by means of light microscopy and SEM/EDS methods, while mechanical properties were examined via microhardness measurements. It was found that by using various combinations of temperatures of the first and second stage of aging, the room temperature hardness of Haynes 282 alloy can be decreased by 100 HV units or increased by up to 25 HV units as compared to that of the alloy subjected to the standard heat treatment schedule. The mechanical response of the alloy is determined by a complex structural evolution involving the secondary precipitation of c¢, M 23 C 6 and M 6 C phases, as well as their interaction with the fcc c matrix.
A thermodynamic justification for the joint formation is developed on the basis of the diffusion brazing of the Ni/Al/Ni system. The phenomena of dissolution and solidification were included into the description. The first solid/solid transformation is also discussed. Mainly, a description for the isothermal brazing occurrence in the meta-stable conditions is developed. It involves the application of the criterion of higher temperature of the solid / liquid (s/l) interface. The dissolution of the filler metal in the substrate is described by the N 0 -solute concentration within the dissolution zone (liquid film) distinguished at the substrate surface. The selection of the N 0 − parameter by the dissolution is justified by the Thermocalc calculation of the Ni-Al phase diagram for meta-stable equilibrium. According to the model assumptions, the solidification is accompanied by partitioning or by undercooled peritectic reaction resulting in formation of the intermetallic phase. The average Al -solute concentration measured across some Al 3 Ni 2 /Al 3 Ni/Al 3 Ni 2 joints confirms that the N 0 -solute concentration is conserved within the analyzed joint sub-layers. The Ni-Al phase diagram for meta-stable equilibrium referred to the solidification is also calculated by means of the Thermocalc Software. It allows locating the solidification path, s/l interface path and redistribution path onto the mentioned diagram. Superposition of both calculated phase diagrams is also given to show that the joint formation occurs cyclically under the meta-stable conditions.Keywords: meta-stable equilibrium, joint formation model, dissolution, solidificationZaproponowano termodynamiczne uzasadnienie dla kształtowania się złącza na przykładzie spajania dyfuzyjnego systemu Ni/Al/Ni. Do proponowanego opisu włączono zjawiska rozpuszczania i krystalizacji. Pierwsza przemiana w stanie stałym również poddana jest dyskusji. Głównie, opis dotyczy przebiegu spajania dyfuzyjnego w warunkach metastabilnych. Wymaga on zastosowania kryterium wyższej temperatury frontu krystalizacji. Rozpuszczanie składnika łączącego (Al) w podłożu (Ni) jest opisane stężeniem N 0 w strefie rozpuszczania (w ciekłej błonce wyróżnionej tuż przy powierzchni podłoża). Selekcja parametru N 0 jest uzasadniona obliczeniami z użyciem program Thermocalc Software Programem tym wyznaczono diagram fazowy Ni-Al dla równowagi metastabilnej odniesiony do zjawiska rozpuszczania. Zgodnie z założeniami proponowanego opisu krystalizacji towarzyszą rozdział składnika lub przechłodzona reakcja perytektyczna skutkujące formowaniem się fazy międzymetalicznej. Średnie stężenie Al zmierzone w złączach Al 3 Ni 2 /Al 3 Ni/Al 3 Ni 2 potwierdza, że stężenie N 0 jest zachowane w podwarstwach analizowanych złącz. Również, wyznaczono diagram fazowy Ni-Al dla równowagi metastabilnej odniesiony do krystalizacji. Wykorzystano ponownie program Thermocalc Software. Pozwoliło to na zlokalizowanie ścieżki krystalizacji, ścieżki frontów krystalizacji, ścieżki redystrybucji na diagramie fazowym równowagi m...
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