Three plants extracts were used for biosynthesis of Ag nanoparticles (AgNPs). AgNPs nucleation process requires effective reduction agents which secure Ag+ to Ag0 reduction and also stabilizing/capping agents. The UV-vis and TEM observation revealed that the best results were obtained by R. officinalis leaf extract. The strong SPR band peak appeared at the wavelength 418 nm. Synthetized AgNPs were globular, fine (~20 nm), uniform and stabile throughout the experiment. A rapid rate of AgNPs synthesis was also significant and economically advantageous factor. Fine (10-20 nm) and globular nanoparticles were synthetized also by U. dioica leaf extract, but the stability of nanoparticles was not permanent. Despite V. vitis-idaea fruit extract contains a lot of reducing agents, UV-vis did not confirm the presence of AgNPs in solution. Synthetized Ag particles were very unstable, Ag particles agglomerated very fast and clearly indicated sediment was formed.
Analytical transmission electron microscopy has been applied to characterize the microstructure, phase and chemical composition of the Ag–Al wear track throughout its thickness down to the atomic level. Microscopy findings have been correlated with Ag–Al film tribological properties to understand the effect of the hexagonal solid solution phase on the tribological properties of this film. Ag–25Al (at.%) films have been produced by simultaneous magnetron sputtering of components in Ar atmosphere under 1 mTorr pressure and subjected to pin-on-disc tribological tests. It has been shown that hcp phase with (001) planes aligned parallel to the film surface dominates both in as-deposited and in tribofilm areas of the Ag–Al alloy film. Possible mechanisms of reduced friction in easily oxidized Ag–Al system are discussed and the mechanism based on readily shearing basal planes of the hcp phase is considered as the most probable one.
The results of structure observations of Ni base superalloy subjected to long-term influence of high pressure hydrogen atmosphere at 750K
and 850K are presented. The structure investigation were carried out using conventional light-, scanning- (SEM) and transmission electron
microscopy (TEM). The results presented here are supplementary to the mechanical studies given in part I of this investigations. The
results of study concerning mechanical properties degradation and structure observations show that the differences in mechanical
properties of alloy subjected different temperature are caused by more advanced processes of structure degradation during long-term aging
at 850K, compare to that at 750K. Higher service temperature leads to formation of large precipitates of δ phase. The nucleation and
growth of needle- and/or plate-like, relative large delta precipitates proceed probably at expense strengthening γ" phases. Moreover, it can't
be excluded that the least stable γ" phase is replaced with more stable γ' precipitates. TEM observations have disclosed differences in
dislocation structure of alloy aged at 750K and 850K. The dislocation observed in alloy subjected to 750K are were seldom observed only,
while in that serviced at high stress and 850K dislocation array and dislocation cell structure was typical.
Mechanical components and tools in modern industry are facing increasing performance requirements leading to the growing need for advanced materials and thus, for modern frictional systems. In the last decades, the Pulsed Laser Deposition (PLD) has emerged as an unique tool to grow high quality mono- as well as multilayers surfaces in metallic/ceramic systems. Building up a knowledge base of tribological properties of industrially-scaled, room temperature deposited PLD hard coatings are the most important step for the application of these coatings in engineering design. Although single-layer coatings find a range of applications, there are an increasing number of applications where the properties of a single material are not sufficient. One way to surmount this problem is to use a multilayer coating. Application of metallic interlayers improves adhesion of nitride hard layer in multilayer systems, which has been used in PVD processes for many years, however, the PLD technique gives new possibilities to produce system comprising many bilayers at room temperature. Tribological coatings consisted of 2, 4 and 16 bilayers of Cr/CrN and Ti/TiN type were fabricated with the Pulsed Laser Deposition (PLD) technique in the presented work. It is found in transmission electron examinations on thin foils prepared from cross-section that both nitride-based multilayer structures studied are characterized by small columnar crystallite sizes and high defect density, what might rise their hardness but compromise coating adhesion. The intermediate metallic layers contained larger sized and less defective columnar structure compared to the nitride layers, which should improve the coatings toughness. Switching from single layer to multi-layer metal/nitride composition improved resistance to delamination.
The scope of this work is to investigate the precipitation of two Al-Mg-Si alloys with and without Cu and excess Si by using the differential scanning calorimetry (DSC), transmission electron microscopic (TEM), Vickers hardness measurement and X-ray diffraction. The analysis of the DSC curves found that the excess Si accelerate the precipitation and the alloy contain the excess Si and small addition of copper has higher aging-hardness than that of free alloy (without excess Si and Cu) at the same heat treatment condition. The sufficient holding time for the precipitation of the β'' phase was estimated to be 6 hours for the alloy aged at 100°C and 10 hours for the alloy aged at 180°C. The low Copper containing Al-Mg-Si alloy gives rise to the forming a finer distribution of β (Mg2Si) precipitates which increases the hardness of the alloy. In order to know more about the precipitation reactions, concern the peaks on the DSC curve transmission electron microscopy observation were made on samples annealed at temperatures (250°C, 290°C and 400°C) just above the corresponding peaks of the three phases β'', β' and β respectively.
The state of the dislocation substructure of meteorite in which the history of phenomena accompanying the meteorite during its passage through the Earth’s atmosphere is recorded remains unused. The main goal of the presented work is a comprehensive analysis of the dislocation structure of the iron meteorite from the Morasko reserve (Poland, Wielkopolska Voivodeship) by TEM methods to determine the conditions and mechanism of its formation. The work is cognitive in the field of phenomena related to the destruction and deformation of the material in extreme conditions: space and terrestrial space. It can also be useful in the research on the creation of the material with specific mechanical properties, as well as a unique reference material for earth experiments with low-temperature deformation, high-speed deformation, recrystallization processes with short thermal pulses and structure relaxation in conditions of very long time periods.
The aim of this study is to compare the corrosion resistance of X37CrMoV5-l tool steel after nanostructurization and after a conventional heat treatment. The nanostructuring treatment consisted of austempering at 300°C, which produced a microstructure composed of nanometric carbide-free bainite separated by nanometric layers of retained austenite. The retained austenite occurred also in form of blocks which partially undergo martensitic transformation during final cooling. For comparison, a series of steel samples were subjected to a standard quenching and high tempering treatment, which produced a microstructure of tempered martensite. The obtained results showed that the corrosion resistance of steel after both variants of heat treatment is similar. The results indicate that the nanocrystalline structure with high density of intercrystalline boundaries do not deteriorate the corrosion resistance of steel, which depends to a greater extent on its phase composition.
In this work, the effect of heat transfer during explosive welding (EXW) and post-processing annealing on the microstructural and chemical composition changes have been thoroughly analysed using scanning and transmission electron microscopies and X-ray synchrotron radiation. Several combination of explosively welded metal compositions were studied: Ti with Al, Cu with Al, Ta or stainless steel, stainless steel with Zr or Ta and Ti with carbon steel. It was found that the melted metals exhibit a strong tendency to form brittle crystalline, nano-grained or even amorphous phases during the solidification. For all analysed metal combinations most of the phases formed in the zones of solidified melt do not appear in the equilibrium phase diagrams. Concurrently, the interfacial layers undergo severe plastic deformation forming nano-grained structures. It has been established that these heavily deformed areas can undergo dynamic recovery and recrystallization already during clad processing. This leads to the formation of new stress-free grains near the interface. In the case of low temperature and short time post processing annealing only the melted zones and severely deformed layers undergo recovery and recrystallization. However, drastic changes in the microstructure occurs at higher temperature and for longer annealing times. Applying such conditions leads to diffusion dominant processes across the interface. As a consequence continuous layers of intermetallic phases of equilibrium composition are obtained.