Wyniki 1-10 spośród 33 dla zapytania: authorDesc:"Zbigniew Bojar"

Influence of heat treatment on structure and mechanical properties of Ni3Al (Zr, B) intermetallic alloy

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Results of investigation of as-cast and heat treated Ni3Al phase - based intermetallic with alloying additions Zr and B are presented in the paper. A long-lasting homogenization of the investigated material leads to total homogenizing of a phase composition via ￿ phase ordering (gradual ￿￿￿’ phase transition) and a tendency to the ￿’ monophase s[...]

Influence of sintering process temperature on the formation and final microstructure of FeAl based intermetallics obtained from the elementary Fe and Al powders

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The results of the optimization process of liquid phase sintering of elemental Fe and Al powders in order to fabricate FeAl intermetallic sinters were studied in this paper. The oxidation of Al particles in the sintering process is responsible for the formation of the Al2O3 films in the sintered structure that are mainly located on the interparticle boundaries, which eventually lead to the de[...]

Optimization of Fe and Al elemental powders sintering parameters by DTA analysis

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Sintered iron aluminides are very promising novel structural materials mainly because of their attractive physical and mechanical properties, but also because of the low price of raw materials used for their manufacture [1]. Powder metallurgy (PM) eliminates many of the limitations during the fabrication process [2]. For example, PM enables forming of products with complex shape, choosing almost arbitrary chemical compositions, deals with problem of grain overgrowth, gives better chemical and structure homogeneity as well it is an energy-saving process [3÷5]. However, in case of the Fe-Al phases, the use of this method is limited by the necessity of controlling of the SHS (self-propagating high-temperature synthesis) reaction [3]. SHS occurring during sintering of Fe and Al elemental powders mixture is very rapid and strongly exothermic, which unfortunately may cause unwanted porosity of the sinters [6]. Our previous studies [7÷10] show the great complexity of phenomena taking place during presintering process of Fe and Al powders. These effects correlated with diffusion and phase transformations were also studied by other researchers [1, 3, 4]. It was concluded that the mechanism of exothermic phase transformations is strongly correlated with many factors, such as chemical composition of the sample, elemental powder particles size, atmosphere, and the heating rate. It is important that only the formation of the exothermic Fe2Al5 phase was reported prior to the formation of finally-wanted FeAl phase [1]. Our last investigations show however that not only Fe2Al5 but also other high aluminum phases - FeAl3 and FeAl2 could be found in the samples structure sintered at temperature lower than the SHS reaction temperature. In order to limit unfavorable influence of the SHS on sinter structure, the optimization of the powders particles size, the compact pressure and the heating rate was done in this work. EXPERIMENTAL Investigation[...]

Catalytic activity of Ni3Al foils in decomposition of selected chemical compounds

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Alloys based on the Ni3Al intermetallic phase, as compared to competitive group of nickel-based superalloys, exhibit high strength for high deformation velocity at elevated temperature, high resistance to oxidation and carburization at elevated temperature, and much better fatigue strength (they crack more slowly than other intermetallic phase-based alloys). However, common application of these alloys meets, quite a few technological drawbacks mainly related to insufficient plasticity and a tendency to brittle cracking [1, 2]. Additionally, Ni3Al-based alloys can be used in the form of honeycomb structures, which have an advantage in lightweight, highstiffness and high-strength over bulk Ni-based superalloys. Thus far, we have successfully fabricated Ni3Al thin foils by cold rolling of commonly casted ingots without any additional treatment. The proposed technology allows to obtain foils with thickness even below 50 μm and with micro- and nanograined structure [3, 4]. Methanol is expected to become an alternative energy source (a fuel) in the near future. It can be easily synthesized from biomass, natural gas, coal etc., which are more abundant resources than crude oil [8, 9]. Hexane, as the second analyzed compound in this field of research, is a component of many products related to the petroleum and gasoline industries. Nevertheless, as an effect of these applications, increasing amount of this compound is released to the atmosphere and possibility of hexane deactivations is important for environmental pollution reducing. Above mentioned mechanical properties of Ni3Al thin foils, and their additional good catalytic properties without any coating, allow to build microscale power sources and microreactors for air purification (e.g. MEMS, MECS) [3, 4]. The main purpose of this work was an assessment of catalytic effects observed while thermodecomposition reactions of methanol and hexane run over Ni3Al foil surface. Preli[...]

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