Volume 55, Issue 1

The aluminum metal-matrix composites reinforced with the micro- and nanoparticles of TiO 2 were manufactured in the form of sheets through the accumulative roll bonding (ARB) process which has been lately considered as a novel method under an intense plastic deformation so as to produce particulate-reinforced metal-matrix composites. Themicrostructural examinations via optic microscopy and scanning electron microscopy (SEM) depict that the distribution of TiO 2 particles in the aluminum matrix is almost uniform and also the dispersion of the microparticles of TiO 2 is more homogeneous than that of the nanoparticles one. Furthermore, the tensile tests demonstrate the noteworthy enhancements in the tensile strengths of the composites, compared to the Al 1100 as the virgin metal, however, by attenuating the size of the particles, i.e. from micron to nano, the composite tensile strengths are augmented. The fractographic analysis of the fracture surfaces revealed that the fracture mode in the ARB-processed Al/TiO 2 composite is the shear ductile rupture type.

In the present paper, we report the preparation and characterization of magnetic silica nanostructured materials that were used as ibuprofen drug molecule carriers. This work was aimed at obtaining drug release systems sensitive to a magnetic field to be directed to target sites. The preparation of the silica nanostructuredmaterials started with the synthesis of magnetite (Fe3O4) nanoparticles that were added subsequently during the hydrolysis and condensation of tetraethyl-orthosilicate (TEOS) to obtain SiO2-Fe3O4 nanocomposites. The ibuprofen molecules were added simultaneously with magnetite nanoparticles. The in vitro ibuprofen release profiles were analyzed, showing a typical controlled release for all materials studied. The nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning microscopy (SEM), thermogravimetric analysis (TGA), N2 adsorption-desorption isotherms; magnetic studies were also performed. The obtained materials showed low superparamagnetic values, and saturation behavior was also observed. It was demonstrated that ibuprofen does not affect the magnetic behavior of magnetite, indicating its possible use in medical applications.

Stress-driven grain boundary (GB) migration in ultrafine-grained materials with nanotwinned structure is theoretically described. In the framework of the theoretical model, the stress-driven high-angle GB migration is accompanied by migration of twin boundaries which adjoin this GB. Energetic characteristics and critical stresses of the GB migration accompanied by the twin boundary migration are calculated.

Theoretical model describing stress-driven migration of low-angle grain boundaries (GBs) in the vicinity of growing crack in metal matrix nanocomposites with reinforcing (metallic or ceramic) incoherent nanoinclusions is proposed. Using two-dimensional discrete dislocation dynamics approach profiles of migrating GBs are analytically calculated and critical stress for transition into unstable migration mode is found. It is shown that the presence of crack always promotes stress-driven migration and thus grain growth.

A fuzzy logic-based embedded system to characterize materials and metamaterials is presented. Trapezoidal and Gaussian profiles, used as membership functions, allow to classify materials despite variations on light intensity. The results on various materials show the capacity of the system to calculate the refractive index as a complex number, through a fourth order equation. Since all the roots of the equarion, including imaginary ones, the system allow to characterize metamaterials. The embedded character of the systems allows to use it as an external module for most commercial equipments.

A simple, low-cost and environmentally friendly method has been used to obtain highly porous biomorphic carbon monoliths with a good combination of interconnected macro-, mesoand microporosity, and good electrical conductivity and mechanical strength, making these biocarbon materials interesting for electrochemical applications as binder-free electrodes. Highly porous monolithic biocarbons were obtained from beech wood precursors through pyrolysis and subsequent surface modification in a steam heated to 970°C with different activation times. The obtained biocarbons demonstrated good electrical conductivity and mechanical strength. They were studied as electrodes for supercapacitors in half cell experiments, demonstrating maximum gravimetric capacitance of 200 F g-1 in a basic media at scan rate 1 mV s-1. Galvanostatic charge-discharge experiments showed maximum capacitance of 185 F g-1 at current density of 0.15 A g-1 and ~100 F g-1 at current density of 0.75 A g-1. It has been shown that in addition to the developed porous surface, the micropores with diameters exceeding 1 nm play a key role for the enhanced electrochemical capacity. Long-cycling experiments demonstrated excellent stability of the monolithic biocarbon electrodes with no reduction of the initial capacitance values after 600 cycles in voltammetry.

Solid solution treated Al-Zn alloys with different Zn contents (10 and 30 wt.%) have been nanostructured by severe plastic deformation (SPD) via equal-channel angular pressing method. In-situ transmission electron microscopy observations have been used to follow microstructure evolutions upon annealing. It was shown that SPD leads to the precipitation of Zn particles and that this partial solid solution decomposition was more pronounced in the Al- 30%Zn alloy. Annealing at temperatures in range of 200 to 250 °C led to visible dissolution of Zn particles in both alloys and to formation of extensive grain boundary segregations of Zn. This approach helped to design short term annealing treatments leading to specific ultrafine grain structures that could be achieved by static annealing on bulk samples. Last, the tensile behavior of these materials has been investigated with a special emphasis on the influence of the strain rate on the yield stress and on the elongation to failure. It is shown that in any case the yield stress is mainly controlled by the grain size, while a low volume fraction of Zn phase leads to a relatively modest ductility.

Results of in situ transmission electron microscopic studies of annealing-induced evolution of grain boundary misorientations in ultrafine-grained aluminum alloy Al-4%Cu-0.5%Zr (wt.%) processed by high pressure torsion are presented. An experimental procedure based on the single reflection technique was applied for the measurements of orientations of individual grains before and after annealing that allowed for determining misorientations between them. The measurements revealed that relaxation processes occurring in non-equilibrium grain boundaries during short-time annealing are accompanied by a change of grain boundary misorientations, grain rotation, grain migration as well as grain growth. Obtained results were compared with theoretical studies considering the kinetics of grain rotation in discrete-dislocation as well as continuum approaches.

The formation of copper pentagonal micropyramids (PMPs) with high (multiatomic) spiral growth steps, which are grown by electrocrystallization with mechanical activation of the cathode, is studied experimentally. A new spiral-layer growth mechanism for the formation of such PMP is proposed. It is shown that PMPs grow on flat pentagonal microcrystals (PMCs) formed initially and containing fivefold twins with one of the twin boundaries being inclined by the angle of 35°16’ to the {110}-type substrate crystallographic plane. Such crystal geometry causes an inclined growth step on the PMC surface. The preferential deposition of metal atoms on this step leads to the spiral-layer PMC growth and the formation of PMPs with a structure inherited from the PMCs.

Intermetallic (Co-Sn, Ni-Sn, Co-Ni) nanoparticles have been synthesized through a borohydride reduction with NaBH4 in aqueous solutions of the chloride salts of Co, Ni, Sn at room temperature using a template technique with a carbon support. As a result nanocomposite materials have been obtained in situ. The ratio of the metallic components has been chosen according the phase diagrams of the relevant binary (Co-Sn, Ni-Sn, Co-Ni) systems: Co:Sn=35:65, Ni:Sn=45:55, Co:Ni=50:50. As carbon supports have been used graphite and carbon powder. To avoid the nanoparticle’s aggregation b-cyclodextrin has been added to the reaction solutions. To study the influence of the supports used on the morphology, specific surface area, elemental and phase composition of the synthesized intermetallic nanoparticles and their carbon nanocomposites SEM, EDS, BET, and XRD investigation techniques have been used. The particle’s morphology varies with the different supports, but in the all cases it is typical for alloyed materials. The nanoparticles are different in shape and size and exhibit a tendency to aggregate. The last-one is due to the unsaturated nanoparticle’s surface and the existing magnetic forces. Regardless of the elemental composition, the nanosized particles are characterized by a relatively high specific surface area (SSA). The Ni-Sn nanoparticle have the largest SSA (80 m2/g), while the Co-Sn particles have the lowest SSA (69 m2/g). The use of a carrier modifies the SSA of the resulting nanocomposites differently depending on the size and shape of the carrier’s particles. The studies conducted on the intermetallic nanoparticles synthesized with various carriers demonstrate that the particle’s morphology, size, and specific surface area for the different supports are suitable for use as catalysts, electrode materials in Li-ion batteries and as magnetic materials for biomedical applications.

Abstract. Microstructure evolution of an Al-0.4Zr(wt.%) alloy after isothermal aging (AG) and subsequent high pressure torsion (HPT) and its impact on strength and electrical conductivity has been investigated. Microstructure was characterized by X-ray diffraction, electron backscatter diffraction, transmission electron microscopy (TEM) and electron energy-dispersive X-ray spectroscopy in TEM. The initial Al-0.4Zr(wt.%) alloy obtained by combined casting and rolling presents solid solution of Zr in Al matrix. Aging at 375 °C for 60 h leads to formation of uniformly distributed metastable Al 3 Zr precipitates with the average diameter of 13 nm, resulting thereby in a decrease of strength s UTS from 128 to 95 MPa and in increase of conductivity from 50.7 to 58.8% IACS at ambient temperature. The subsequent HPT processing leads to grain refinement and partial dissolution of the Al 3 Zr precipitates that is accompanied by enrichment of solid solution by Zr atoms and by coarsening of the remaining Al3Zr precipitates. The combination of AG and HPT provides the strength and the conductivity at ambient temperature which do not decrease under annealing up to 230 °C. Moreover, additional strengthening accompanied by an increase in conductivity was found for AG-HPT samples after annealing at T an =230 °C for 1 h, that provides the best combination of the strength of s UTS =142 MPa and the conductivity of 58.3% IACS. Contribution of different possible mechanisms into strength and charge scattering are analyzed on the basis of specific microstructural features. The analysis indicates a suppression of strengthening by the Orowan mechanism in AG and AG-HPT samples. In all the studied states, i.e. initial, after AG, and subsequent HPT, grain boundary strengthening is found to be the main strengthening mechanism.

A screw dislocation perpendicular to free surfaces and an interface in a two-phase plate, and a screw dislocation piercing a two-phase hollow sphere are considered. The analytical solutions of the boundary-value problems have been found for the first time with the help of the virtual defects technique. Elastic fields of the screw dislocation in the plate are presented in the form of integrals with Bessel functions. Elastic fields of the screw dislocation in the hollow sphere have the form of series with Legendre polynomials. Stress distributions in both of the considered geometries are plotted. The influence of the geometric parameters of the considered solids and the ratio of the shear moduli on the stresses is analyzed. The interaction of a screw dislocation with a parallel edge dislocation is discussed.

Nickel-ceramics composites are very promising materials for various industrial applications. Significant progress was achieved in the field of composite nickel-ceramic coatings development. However, in case of bulk nickel-ceramics composites the available information is quite insufficient. In this study the effect of forging on the microstructure, oxidation resistance, and microhardness of Ni-8Y 2 O 3 -92ZrO 2 (Ni-YSZ) composites was revealed. Nickel-YSZ composites were manufactured by powder metallurgy technique with following vacuum annealing at 1250 °C; in addition, forging at 1000 °C was applied. Oxidation behavior was studied by termogravimetry in air. The microstructure of the composites was investigated via SEM, XRD, and EBSD analysis. It was shown that forged composites do not undergo oxidation in the temperature range 20-950 °C. Forged Ni-YSZ composites exhibited improved Vickers hardness (HV) compared to bulk nickel.