Solid State Phenomena Vols. 203-204

Abstract: Charge density wave (CDW) ordering in NbSe3 and the structurally related quasi one-dimensional compounds is reconsidered. Since the modulated ground state is characterized by unstable nano-domains, the structural information obtained from diffraction experiments is to be supplemented by some additional information from a method, able to reveal details on a unit cell level. Low-temperature (LT) scanning tunneling microscopy (STM) can resolve both, the local atomic structure and the superimposed charge density modulation. It is shown that the established model for NbSe3 with two incommensurate (IC) modes, q1 = (0,0.241,0) and q2 = (0.5,0.260,0.5), locked in at T1=144K and T2=59K and separately confined to two of the three available types of bi-capped trigonal prismatic (BCTP) columns, must be modified. The alternative explanation is based on the existence of modulated layered nano-domains and is in good accord with the available LT STM results. These confirm i.a. the presence of both IC modes above the lower CDW transition temperature. Two BCTP columns, belonging to a symmetry-related pair, are as a rule alternatively modulated by the two modes. Such pairs of columns are ordered into unstable layered nano-domains, whose q1 and q2 sub-layers are easily interchanged. The mutually interchangeable sections of the two unstable IC modes keep a temperature dependent long-range ordering. Both modes can formally be replaced by a single highly inharmonic long-period commensurate CDW.

Abstract: The composites of Al₆₁Cu₂₇Fe₁₂ alloys containing quasicrystalline and crystalline phases (CQ composites) were obtained by the Bridgman method. The morphology of composites crystallized with different solidification rates was studied. The solidification rate influence on fibrous reinforcement morphology was analyzed. The microsections for analysis were prepared parallel and perpendicular to the direction of crystallization. The optical and the scanning electron microscope were used for metallographic observation. Obtained composites were examined by X-ray powder diffraction and reflective X-ray topography. The Laue method enabled to conclude that the matrix is singlecrystalline. The different level of structural perfection of reinforcement fibres was presented at various solidification rates.

Abstract: Ir-Re alloys were synthesized from nanocrystalline iridium and rhenium powders under high pressure (4 GPa) und temperature (2000° C). They were characterized using powder X-ray diffraction and scanning electron microscopy.

Abstract: Stainless steels are used widely in many industries. A duplex microstructure offers a combination of advantages, including resistance to crevice and stress corrosion, reduced susceptibility to hot cracking in comparison with fully austenitic structures and excellent tensile strength. The paper discusses the effect of aging on the microstructure and corrosion resistance of X2CrNiMoN25-7-4 super duplex stainless steel. Low and predictable corrosion rate is an important parameter for steels operating in aggressive environments. Resistance to intergranular corrosion expressed by corrosion rate (mm/year) was determined in accordance with standard PN-EN ISO 3651-1. Metallographic studies were carried out to evaluate surface degradation and intergranular corrosion. The results support an evaluation of the impact that phase fraction changes caused by aging have on resistance to intergranular corrosion. The results of the corrosion analysis were used to develop mathematical models describing changes in corrosion rate over time for different phase fractions.

Abstract: Characterization of structure defects in turbine blades is the basis for determination of the overall crystalline perfections. This work presents the possibilities of identifying casting defects by combining different X-ray diffraction techniques. The investigation was conducted on samples prepared from as-cast turbine blades airfoil and tips. It was found that X-ray topograms revealed dendritic structure and macro strain areas. The defects areas which have appeared on topograms were also investigated by X-ray diffraction mapping technique by EFG diffractometer. Additionally, the X-ray investigation was complemented by macro SEM images obtained by stitching several images of microstructure. The X-ray maps of misorientation angle and X-ray topograms revealed deviation between the γ’ direction and the blade axis and rotation of the primary dendrite arm around this axis.

Abstract: The work includes the studies of the first stage tempering of the medium carbon Cr-Mn-Mo alloy steel, and occurredprecipitations of carbides. Dilatometric analysis allowed to trace precisely the changes that occur during the first stage of tempering and associate them with the various phase transformations. With the use of the high resolution scanning electron microscope it was able to photograph very small precipitation occurred in the investigated steel after low tempering. Analysis of these images allowed to determined the crystallographic plane in which the precipitation increases, and angles between these planes. With these obtained information it was able to identifiedthe precipitations, as a cementite carbides.

Abstract: The aim of this work was the microstructure and texture analysis of a deformed via cold-rolling 24.5Mn-3.5Si-1.5Al-Ti-Nb TWIP/TRIP type steel. It was found, that during cold plastic deformation a phase transformation of austenite into martensite takes place. The transformation progress was confirmed by the microscopic investigations. The texture of austenite is characterized by a limited α₁=||RD fibre and the γ=||ND fibre. The texture of austenite changed with increasing deformation rate. In the texture of deformed austenite the strongest orientation is the {110} Goss orientation, which belongs to the α=||ND orientation fibre. During cold plastic deformation γ→ε and γ→ε→α’ phase transformations as well as the deformation of γ, ε and α’ phases are taking place in the steel. The formed ε phase (hexagonal structure) also possesses a distinct texture.

Abstract: Single crystals of Sr_xBa_1-xNb₂O₆ (0.26 a parameter monotonically increases with increasing of temperature, while the c parameter decreases up to the phase transition temperature T_C, and the next it begins increasing slowly. It was ascertained that with the increase of the Sr concentration in the studied crystals the changes of the lattice parameters were observed. They can be described according to the following relations: a = - 2.418 • 10-5 x² + 1.050 • 10-3 x + 12.479 Å and c = - 0.0015 x + 4.0216 Å. Basing on the obtained results the character of the phase transition was able to do.

Abstract: This paper reports, for the first time, synthesis and characterization of new bifunctional materials containing platinum and silver ions deposited on mesoporous ordered silica SBA-15. Both types of ions were incorporated on silica surface during adsorption from water solutions containing various amounts of dissolved tetraamineplatinum(II) dichloride and diamminesilver(I) hydroxide or tetraamineplatinum(II) dichloride and diamminesilver(I) chloride complexes. The silanol groups on silica surface play important role in adsorption mechanism and one of the most commonly used technique for their characterization is photoacoustic spectroscopy. This technique provides clear evidence of successfully incorporation two types of precious metal ions (Pt and Ag) on SBA-15 surface. The decomposition process of absorbed complexes was investigated according to high temperature in helium. The products of decomposition were analyzed by mass spectrometer. Obtained results show that decomposition temperature of platinum and silver complexes are quite vary. Similarly mechanisms of decomposition of ligands from silver and platinum complexes are also different. Moreover, the structural and chemical properties of Pt,Ag-SBA-15 samples were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS).

Abstract: This study discusses changes in the value of fractal parameters determined based on functions of structure S(t), generated in different directions of anisotropy of the examined surfaces. The analyzed material consisted of AFM calibration standards TGT1, PG and TGZ1 which were used as models of strongly isotropic and anisotropic surfaces. The topography of the examined surfaces was imaged by atomic force microscopy. The obtained results indicate that all surfaces can be described mathematically to identify fractal parameters in any anisotropic direction.