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Abstract:
Fluorescent carbon dots (CDs) synthesized by pulsed laser ablation in liquid (PLAL) are still interesting materials due to their possible applications. However, unlike CDs produced by the hydrothermal method, CDs produced the synthesis products by the PLAL method were never separated by dialysis, which differentiates the synthesis products and allows the identification of the main source of fluorescence. In this work, the synthesis of fluorescent carbon dots (CDs) was performed by nanosecond laser ablation of a graphite target immersed in polyethyleneimine (PEI) and ethylenediamine (EDA), and the synthesis products were separated by dialysis. The results of optical measurements showed that the main source of luminescence of the obtained nanostructures are fluorescent particles or quasi-molecular fluorophores created in the ablation process. In the case of ablation in PEI, most of the produced molecular fluorophores are associated with carbogenic nanostructures, while in the case of EDA, free fluorescent molecules dominate.

Keywords:
carbon dots, photoluminescence, laser ablation

Abstract:
In the search for a remedy to increase the fracture toughness of NiAl, the effect of rhenium and aluminum oxide addition is explored. Using a powder metallurgy processing route an optimum composition of NiAl-Re-Al2O3 material is found which manifests KIC over two times higher than as-received NiAl sintered under the same conditions.

Keywords:
fracture behavior, stress/strain measurements, intermetallics, composites, powder metallurgy, grains and interfaces

Abstract:
The search for new materials capable of replacing nickel-based superalloys in aerospace applications has increased rapidly in the recent years. One of the candidates for this purpose is nickel aluminide NiAl provided that its main drawback, namely the inferior fracture toughness at room temperature is overcome. We propose rhenium as an addition to NiAl to improve its mechanical properties without compromising on the oxidation resistance. Two powder metallurgy techniques (HP and SPS) were used to obtain NiAl/Re sinters. Small amounts of rhenium (0.6 at.%; 1.25at.%; 1.5 at.%) almost doubled the flexural strength of NiAl and improved its fracture toughness by 60%. Microscopic investigations revealed rhenium particles at the boundaries of NiAl grains resulting in an enhanced fracture toughness. Mass changes during oxidation at 900 oC, 1100 oC and 1300 oC were relatively low. Plausible mechanisms of the fracture toughness enhancement and the oxidation behavior are discussed.

Keywords:
nickel aluminide, rhenium, fracture toughness, oxidation resistance, powder metallurgy, grain boundary strengthening

Abstract:
The Ni/Al multilayer coating of λ ≈100 nm was deposited onto (001)-oriented monocrystalline silicon substrate using double target magnetron sputtering system equipped with rotating sample holder. The thicknesses of alternating layers were adjusted in the way to preserve the chemical composition ratio close to 50%Al:50%Ni (at.%). The in situ X-ray diffraction and in situ transmission electron microscopy heating experiments were carried out at relatively low heating rates (20°C/min) in order to study the phase transformation sequence. The investigations revealed that the reaction between Ni and Al multilayers starts at ≈200°C with precipitation of Al₃Ni phase, while above 300°C dominates precipitation of Ni₃Al and NiAl intermetallic phases. Both the X-ray and electron diffractions acquired at 450°C confirmed presence of the Ni₃Al and NiAl intermetallics, but the former pointed at still lasting traces of Ni(Al) solid solution.

Keywords:
transmission electron microscopy, multilayers

Abstract:
Alumina/copper composites have been used where high thermal conductivity, high absorption and dissipation of heat, high resistance to thermal fatigue and good frictional wear resistance are required. This kind of composites may be applied in medicine, electronic and automotive industry. Both the physical and mechanical properties of this type of composites are strongly influenced by the properties of its individual constituents and, also, by the properties of interface layer between ceramic and metal. One of the solution, from the point of view of the best properties’ achievements (especially thermal, structural and shape stability), is the production of ceramic-metal composites with interpenetrating networks structure. They can be produced using porous alumina performs, which are infiltrated (pressure or pressureless) by molten metal or sintered with metallic powders. The subject of the presented paper is the development of the interpenetrating network Al2O3-Cu composites, processed by sintering porous ceramic perform (85 and 90% porosity) with copper powder. The paper presents the new developed technology, results of microstructure investigations, measurements of the selected physical and mechanical properties and the analysis of the influence of the processing conditions on the properties and interface morphology between ceramic and copper