Browsing by Author "Moreira Jorge, Alberto"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Open Access Metallic iron or a Fe-based glassy alloy to reinforce aluminum: reactions at the interface during spark plasma sintering and mechanical properties of the composites(MDPI, 2023-07-23) Dudina, Dina V.; Kvashnin, Vyacheslav I.; Bokhonov, Boris B.; Legan, Mikhail A.; Novoselov, Aleksey N.; Bespalko, Yuliya N.; Moreira Jorge, Alberto; Koga, Guilherme Y.; Ukhina, Arina V.; Shtertser, Alexandr A.; Anisimov, Alexander G.; Georgarakis, KonstantinosThe microstructural features and mechanical properties of composites formed by spark plasma sintering (SPS) of Al + 20 vol.% Fe and Al + 20 vol.% Fe66Cr10Nb5B19 (glassy alloy) mixtures composed of micrometer-sized particles are presented. The interaction between the mixture components was studied by differential thermal analysis and through examining the microstructure of composites sintered at two different SPS pressures. When the pressure was increased from 40 MPa to 80 MPa, the thickness of the reaction products formed between the iron particles and aluminum increased due to a more intimate contact between the phases established at a higher pressure. When the metallic glass was substituted for iron, the pressure increase had an opposite effect. It was concluded that local overheating at the interface in the case of Al + 20 vol.% Fe66Cr10Nb5B19 composites governed the formation of the product layers at 40 MPa. The influence of the nature of reinforcement on the mechanical properties of the composites was analyzed, for which sintered materials with similar microstructural features were compared. In composites without the reaction products and composites with thin layers of the products, the hardness increased by 13–38% relative to the unreinforced sintered aluminum, the glassy alloy and iron inclusions producing similar outcomes. The effect of the nature of added particles on the hardness and compressive strength of composites was seen when the microstructure of the material was such that an efficient load transfer mechanism was operative. This was possible upon the formation of thick layers of reaction products. Upon compression, the strong glassy cores experienced fracture, the composite with the glassy component showing a higher strength than the composite containing core-shell structures with metallic iron cores.Item Open Access Nanoporous silver for electrocatalysis application in alkaline fuel cells(Elsevier, 2016-09-10) Barsuk, Daria; Zadick, Anicet; Chatenet, Marian; Georgarakis, Konstantinos; Panagiotopoulos, Nikolaos T.; Champion, Yannick; Moreira Jorge, AlbertoSelf-supporting porous silver foils with an average pore size < 100 nm were produced from a crystalline silver-based ternary alloy as a precursor by removing second phases present in the silver matrix. The final Ag-based porous foil shows good mechanical properties when comparing to its previous amorphous analogues. Its activity for direct electrochemical oxidation of ammonia-borane (AB), a fuel of interest for direct liquid fuel cells, has been investigated in alkaline media. The material exhibits promising electrochemical properties in long-term operation; indeed, material composition and nanostructure remain similar after 15,000 cyclic-voltammetries between − 0.3 and 0.5 V vs. RHE in a 0.1 M NaOH + 5 mM AB solution thermostated at 25 °C. Nanoporous materials, and in particular nanoporous silver, can therefore represent a relevant choice as anode in direct ammonia-borane fuel cell.Item Open Access Towards a better understanding of the interaction of Fe66Cr10Nb5B19 metallic glass with aluminum: growth of intermetallics and formation of Kirkendall porosity during sintering(MDPI, 2023-01-15) Dudina, Dina V.; Kvashnin, Vyacheslav I.; Matvienko, Alexander A.; Sidelnikov, Anatoly A.; Gavrilov, Alexander I.; Ukhina, Arina V.; Moreira Jorge, Alberto; Georgarakis, KonstantinosMetallic-glass-reinforced metal matrix composites are a novel class of composite materials, in which particles of alloys with an amorphous structure play the role of reinforcement. During the fabrication of these composites, a crystalline metal is in contact with a multicomponent alloy of an amorphous structure. In the present work, the morphological features of the reaction products formed upon the interaction of Fe66Cr10Nb5B19 metallic glass particles with aluminum were studied. The composites were processed via spark plasma sintering (SPS), hot pressing or a combination of SPS and furnace annealing. The reaction products in composites with different concentrations of the metallic glass and different transformation degrees were examined. The products of the interaction of the Fe66Cr10Nb5B19 metallic glass with Al were observed as dense layers covering the residual alloy cores, needles of FeAl3 protruding from the dense shells as well as needles and platelets of FeAl3 distributed in the residual Al matrix. The possible role of the liquid phase in the structure formation of the reaction products is discussed. The formation of needle- and platelet-shaped particles presumably occurred via crystallization from the Al-Fe-based melt, which formed locally due to the occurrence of the exothermic reactions between aluminum and iron. At the same time, aluminum atoms diffused into the solid Fe-based alloy particles, forming an intermetallic layer, which could grow until the alloy was fully transformed. When aluminum melted throughout the volume of the composite during heating of the sample above 660 °C, a similar microstructure developed. In both Al–Fe66Cr10Nb5B19 and Al–Fe systems, upon the reactive transformation, pores persistently formed in locations occupied by aluminum owing to the occurrence of the Kirkendall effect.