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The as-cast microstructure of ductile cast iron (DI) was investigated using light microscopy (LM) and SEM techniques. Further the influence of hot plastic extrusion at 1000°C with plastic strain in the range of 20-60-80% on the transformation of the as-cast microstructure and on the mechanical properties was studied. Besides this, the microstructure of DI subjected to hot extrusion after the fracture of the corresponding samples induced by compression tests was thoroughly investigated. It was found that compression had a dramatic influence on a shear deformation and hence shear fracture of the compressed samples. It was shown that the shear fracture of the hot deformed ductile iron is accompanied by the occurrence of a narrow zone of severe plastic deformation. The fracture surfaces of the extruded samples subjected to the tensile tests and the compression tests were examined. [ABSTRACT FROM AUTHOR]

Electron beam welded joints made on AW2099 aluminium lithium alloy with the thickness of 4 mm were analysed. The third generation of aluminium lithium alloys was developed to improve the drawbacks of the second one. Various electron beam welding parameters (beam current, welding speed) were tested. Accelerating voltage was constant, i.e., 55 kV. Defect free welded joints were produced under optimized welding parameters. Weld metal microstructure and welded joints mechanical properties were investigated. Microstructure of weld metal matrix consists of α-aluminium solid solution. Inter-dendrite areas were enriched in alloying elements due to segregation. Narrow equiaxed zone was observed at the location close to the fusion boundary being characteristic for welded joints made on aluminium lithium alloys. The character of the grains changed in the direction towards weld metal centre to columnar dendritic and equiaxed dendritic. Microhardness values reduction in the weld metal was observed which is associated to the dissolution of strengthening precipitates. 22 Ref., 1 Tabl., 9 Fig. [ABSTRACT FROM AUTHOR]

Abstract: Nanosized titania photocatalysts were prepared from a TiOSO4·2H2O–Na2CO3 mixture via high-energy milling for 5min, and subsequent annealing at a temperature range of 300–700°C/1h. Photoactivity of all samples monitored by electron paramagnetic resonance (EPR) spectroscopy was correlated with phase composition, crystallinity, crystal size and morphology of the annealed products. The anatase nanocrystals with an XRD average size of 24nm and well-faceted bipyramidal morphology exposed mainly by {101} type planes obtained on heating at 700°C, exhibited markedly higher photoactivity than the Aeroxide® P25 TiO2 standard and sample annealed at 600°C. The rapid increase in photoactivity was assigned to complete crystallization of the sample, optimal size, but mainly to the well-developed bipyramidal morphology of anatase nanocrystals and enlargement of the {101} type plane area due to final growth of bipyramids in the 〈001〉 direction. The weak beam dark field (WBDF) transmission electron microscopy (TEM) method was used to characterize morphology of the nanocrystals. Based on the thickness changes along the electron beam incidence inside the individual nanocrystals yielded by WBDF images, it was demonstrated that the mixture of polyhedral shaped anatase projections, such as square-like, hexagonal-like, rhomboid-like, rhombic-like, and rectangular-like prevailing in bright-field (BF) images, corresponds exclusively to tetragonal bipyramidal shape projected along different crystallographic directions. WBDF images of the most often occurring anatase nanocrystal projections are summarized and compared with both the schematic depictions of similarly oriented anatase bipyramids and that recorded in BF images. The difficulties of 3D morphology assessment from the projected nanocrystal shapes are highlighted. Attention is paid to the determination of facets limiting the nanocrystals, using the high resolution (HR)TEM method. [Copyright &y& Elsevier]

This study investigates the phase composition, microstructure, and their influence on the properties of Mo-W-C nanocomposite films deposited by dual-source magnetron sputtering. The synthesised films consist of metal carbide nanograins embedded in an amorphous carbon matrix. It has been found that nanograins are composed of the hexagonal β-(Mo 2 + W 2 )C phase at a low carbon source power. An increase in the power results in the change in the structure of the carbide nanoparticles from a single-phase to a mixture of the β-(Mo 2 + W 2 )C and NaCl-type α-(Mo + W)C (0.65≤ k ≤1) solid-solution phases. The analysis of electrical properties demonstrates that the nanograin structure of the films favours the occurrence of hopping conductivity. The double-phase structure leads to a twofold increase in the relaxation time compared to the single-phase one. Films with both types of nanograin structures exhibit tunnelling conductance without the need for thermal activation. The average distance between the potential wells produced by the carbide nanograins in nanocomposite films is approximately 3.4 ± 0.2 nm. A study of tribomechanical properties showed that Mo-W-C films composed of a mixture of the β-(Mo 2 + W 2 )C and α-(Mo + W)C (0.65≤ k ≤1) phases have the highest hardness (19-22 GPa) and the lowest friction coefficient (0.15-0.24) and wear volume (0.00302-0.00381 mm 2 ). Such a combination of electrical and tribomechanical properties demonstrates the suitability of Mo-W-C nanocomposite films for various micromechanical devices and power electronics.

The present work investigates the influence of isothermal annealing on the microstructure and oxidation behavior of nanocomposite coatings. AlTiSiN/TiSiN coatings with TiSiN adhesive layer were deposited onto a high-speed steel substrate via physical vapor deposition. The coatings were investigated in the as-deposited state as well as after annealing in air at 700, 800, 900 and 1000 °C, respectively. The microstructure and morphology of the coatings were observed using scanning electron microscopy and transmission electron microscopy. The chemical composition and presence of oxidation products were studied by energy-dispersive X-ray spectroscopy. The phase identification was performed by means of X-ray diffraction. In the microstructure of the as-deposited coating, the (Ti 1-x Al x )N particles were embedded in an amorphous Si 3 N 4 matrix. TiO 2 and SiO 2 were found at all annealing temperatures, and Al 2 O 3 was additionally identified at 1000 °C. It was found that, with increasing annealing temperature, the thickness of the oxide layer increased, and its morphology and chemical composition changed. At 700 and 800 °C, a Ti-Si-rich surface oxide layer was formed. At 900 and 1000 °C, an oxidized part of the coating was observed in addition to the surface oxide layer. Compared to the as-deposited sample, the oxidized samples exhibited considerably worse mechanical properties.

Magnetic separation of microalgae using magnetite is a promising harvesting method as it is fast, reliable, low cost, energy-efficient, and environmentally friendly. In the present work, magnetic harvesting of three green algae ( Chlorella vulgaris, Chlorella ellipsoidea, and Auxenochlorella protothecoides ) and one cyanobacteria ( Microcystis aeruginosa ) has been studied. The biomass was flushed with clean air using a 0.22 μm filter and fed CO 2 for accelerated growth and faster reach of the exponential growth phase. The microalgae were harvested with magnetite nanoparticles. The nanoparticles were prepared by controlled co-precipitation of Fe 2+ and Fe 3+ cations in ammonia at room temperature. Subsequently, the prepared Fe 3 O 4 nanoparticles were coated with polyethyleneimine (PEI). The prepared materials were characterized by high-resolution transmission electron microscopy, X-ray diffraction, magnetometry, and zeta potential measurements. The prepared nanomaterials were used for magnetic harvesting of microalgae. The highest harvesting efficiencies were found for PEI-coated Fe 3 O 4 . The efficiency was pH-dependent. Higher harvesting efficiencies, up to 99%, were obtained in acidic solutions. The results show that magnetic harvesting can be significantly enhanced by PEI coating, as it increases the positive electrical charge of the nanoparticles. Most importantly, the flocculants can be prepared at room temperature, thereby reducing the production costs.

Due to the increased demands for drilling and cutting tools working at extreme machining conditions, protective coatings are extensively utilized to prolong the tool life and eliminate the need for lubricants. The present work reports on the effect of a second MeN (Me = Zr, Cr, Mo, Nb) layer in WN-based nanocomposite multilayers on microstructure, phase composition, and mechanical and tribological properties. The WN/MoN multilayers have not been studied yet, and cathodic-arc physical vapor deposition (CA-PVD) has been used to fabricate studied coating systems for the first time. Moreover, first-principles calculations were performed to gain more insight into the properties of deposited multilayers. Two types of coating microstructure with different kinds of lattices were observed: (i) face-centered cubic (fcc) on fcc-W 2 N (WN/CrN and WN/ZrN) and (ii) a combination of hexagonal and fcc on fcc-W 2 N (WN/MoN and WN/NbN). Among the four studied systems, the WN/NbN had superior properties: the lowest specific wear rate (1.7 × 10 -6 mm 3 /Nm) and high hardness (36 GPa) and plasticity index H/E (0.93). Low surface roughness, high elastic strain to failure, Nb 2 O 5 and WO 3 tribofilms forming during sliding, ductile behavior of NbN, and nanocomposite structure contributed to high tribological performance. The results indicated the suitability of WN/NbN as a protective coating operating in challenging conditions.

The microstructure, phase constitution, and corrosion performance of as-solidified Al 70 Pd 25 Co 5 and Al 74 Pd 12 Co 14 alloys (element concentrations in at.%) have been investigated in the present work. The alloys were prepared by arc-melting of Al, Pd, and Co lumps in argon. The Al 74 Pd 12 Co 14 alloy was composed of structurally complex ε n phase, while the Al 70 Pd 25 Co 5 alloy was composed of ε n and δ phases. The corrosion performance was studied by open circuit potential measurements and potentiodynamic polarization in aqueous NaCl solution (3.5 wt.%). Marked open circuit potential oscillations of the Al 70 Pd 25 Co 5 alloy have been observed, indicating individual breakdown and re-passivation events on the sample surface. A preferential corrosion attack of ε n was found, while the binary δ phase (Al 3 Pd 2 ) remained free of corrosion. A de-alloying of Al from ε n and formation of intermittent interpenetrating channel networks occurred in both alloys. The corrosion behavior of ε n is discussed in terms of its chemical composition and crystal structure. The corrosion activity of ε n could be further exploited in preparation of porous Pd-Co networks with possible catalytic activity.