Solid State Phenomena Vol. 231

Abstract: Early stages of recrystallization were observed for the Al-Mn-Mg-Zr(Sc) aluminium alloy containing a fine second phase particles. The samples were plane strain compressed to 40%, 60% and 83% and then annealed. The processes of the recovery and the nucleation of new grains were analysed with the use of scanning electron microscopy equipped with a high resolution electron backscattered diffraction facility. The deformed alloy contained a structure of flat grains situated parallel to the compression plane. After annealing, the structure coarsened. However, the growth of the new grains was strongly hindered by the presence of particles, and the elongated shape of the deformed grains was conserved up to the later stages of recrystallization. In the case ofthe samples deformed up to 40%, the structure was transformed by the mechanism of continuous recrystallization, whereas, in the case of the samples deformed up to 60% or 83%, both mechanisms- of continuous and discontinuous recrystallization - were valid. A particular role in the rise of thenuclei and the structure spheroidization is attributed to the thermally activated migration of the low-angle grain boundaries and the movement of the dislocations stored inside the cells. This leads to an increase of the misorientation angles across the pre-existing low-angle boundaries.

Abstract: Series of experiments on a series of Al-Fe-Mg alloys were performed to determine the effect of rapid solidification (RS) on the material strengthening, which result from the refining of thegrain size and intermetallic compound. Additionally, an enhancement of the material strengthening due to magnesium addition was also observed. Manufacture of RS Al-Fe-Mg alloys combined a spraydeposition of the molten alloy on the rotating water-cooled copper roll and plastic consolidation bymeans of powders pressing and hot extrusion methods. The results suggest that the rapid solidification provides an effective method of microstructure refinement and, in combination with solid solutionhardening due to Mg, leads to significant improvement of mechanical properties of Al-Fe-Mg based alloys.

Abstract: The aim of the research was to investigate the influence of strontium on the structure thin films La1-x SrxCoO3 (x=0; 0.1, 0.2). The LaCoO3 and LaCoO3 doped by Sr films were grown by pulsed laser deposition (PLD) on Si [100] substrate using an Excimer KrF (= 248 nm). To characterize the structure and morphology of the thin films were used the SEM, AFM and XRD methods. X-Ray Diffraction analysis showed only LaCoO3 phase in the thin film not doped andLa0.1Sr0.9CoO3 and La0.2Sr0.8CoO3 phases in thin films doped by Sr. The crystallites size, calculated by Williamson-Hall plots, was smaller for films doped by Sr. The surface of the thin films was free from the drops. SEM analysis showed change of the shape of thin films as a result of doping by Sr. Highly developed layer surface was observed using the AFM microscope for thin films doped by Sr.

Abstract: Functional nonstoichiometric La_0.6Ca_0.4CoO₃ perovskite thin films were deposited on theepi-polished [001] MgO substrates by the electron ablation process (PED - pulsed electron deposition) in low oxygene pressure conditions (~7 x 10^-3 Torr). Deposition process was performed for about 4 hours with the repetition rate of 5 Hz that gave about 72 000 pulses for each sample. By adjusting both the target-substrate distance in the working chamber (70 - 80 mm) as well as the electron energy (10 - 14 kV) it is possible to affect the microstructure and quality of obtained thin films. This paperrelates to the influence of the single pulse electron energy (discharge) on the structure of La_0.6Ca_0.4CoO₃ thin films investigated by means of scanning electron microscopy, transmission electron microscopy and atomic force microscopy. The chemical compositions were also examined using energy dispersive spectroscopy. Multiple linear scratch tests allowed to determine the thin films adhesion to the substrates.

Abstract: Modern magnesium alloys containing rare earth (RE) elements from the Mg-Y-RE-Zr and Mg-Al-RE systems are characterized by low density and good mechanical properties. Therefore, these alloys are used in the automotive and aerospace industries. However, magnesium alloys offer insufficient corrosion resistance in environments containing electrolyte solutions. Hydrogen is themain corrosive factor appearing during chemical reactions between magnesium and water in anelectrolyte solution. The results showed that when samples were immersed in 0.1M sodium sulfate solution, some cracks were observed inside the Al11RE3 and Al8CeMn4 intermetallic phases. Phase identification was performed by electron backscatter diffraction (EBSD) analysis. The microstructure of the alloys before and after corrosion was observed using a scanning electron microscope (SEM).

Abstract: The Mg-Al alloys are the best-known and most commonly used magnesium alloys (especially AZ91 alloy). However, the AZ91 alloy offers insufficient corrosion resistance. Many investigations show that hydrogen is the main corrosive factor appearing during chemical reactions between magnesium and water in electrolyte solution. The main intermetallic phase in the AZ91alloy is the Mg₁₇Al₁₂ (β phase), which is a hydrogen trap. During corrosion, magnesium hydride forms inside the β phase, and this phase is brittle fractured when the inner stress caused by hydrogen pressure and expansion stress due to the formation of magnesium hydride is higher thanthe fracture strength. We examined the corrosion behaviour of AZ91 and AE44 magnesium alloysin 0.1M Na₂SO₄ solution and 3.5% NaCl solution. We analysed two Mg-Al alloys in order todetermine the various effects of hydrogen on these materials.

Abstract: Copper alloys are characterized by high plasticity and good resistance to corrosion. They are applied in electrical industry, telecommunication, in transport and machine building, particularly in the production of elements for deep drawing. The scope of investigation enclosed production of testing single crystals, determination of their crystallographic orientation, deformation of selected single crystals by compression in a temperature range from 20 °C to 400 °C, applying strain rate from 10^-5 s^-1 to 10^-1 s^-1 as well as microstructure observations. Typical plastic strain effects were observed in the microstructures of studied single crystals in the form of parallel and intersecting lines and slip bands with locally intensified density in different areas of cross section of examined specimen and the deflection bands with slightly marked slip lines in the primary system.

Abstract: The presented paper is a review of own work done on two systems of composites, Al₂O₃‑Ni and Al₂O₃-Fe. The previous own results of research into shape, size and distribution of the metal particles and spinel phase embedded in a ceramic matrix are referred to and new ones are presented. Metal particles as well as spinel can be distributed uniformly in a ceramic matrix or can form graded structures. Most often there are agglomerates of metal or spinel particles rather than separated particles embedded in ceramic grains. In composites the growing spinel forms a thick oval layer around a metal particle, however, separate spinel areas embedded in a ceramic matrix are noticed, too. Also, the characteristic “doughnut” shape of spinel is found. Since the metal and spinel phase influence the mechanical properties, the required properties of ceramic-metal composites can be tailored by changing the size, shape and distribution of the phases.

Abstract: This paper presents the results of an investigation using transmission electron microscopy concerning the structure of AlSi7Cu2 cast aluminium alloy after alloying and remelting with a high power diode laser (HPDL). In particular, the changes in the particle/precipitation type, size and shape were determined, concerning especially the SiC and TiC particles added to the initial material. The aim of this work was also to present the laser treatment technology which will be used for further alloying and remelting with ceramic powders – especially carbides and oxides. The innovatory arrangement of this investigation is based on the mixing of two different powders, which were fed simultaneously to the laser-treated aluminium surface. The overview focuses on the laser power required to achieve good layer hardness to prevent hot work tool steel from losing its work stability and to make the tool surface more resistant to action in external conditions.