Solid State Phenomena Vol. 197

Abstract: All over the world the investigations of nanophotonic structures called photonic crystals (PCs) are performed. These crystals have potential applications in optoelectronics, e.g. optical filters, antireflective surface coatings, lossless frequency selective mirrors. In Institute of Physics at Silesian Technical University the opal photonic crystals consisting of monodisperse spherical particles, that have diameters of several hundred nanometers, are produced using colloidal self-assembly technics. The main aim of this work is the comparison between pieces of information on morphology of photonic crystals that can be obtained from electron microscopy and from the angular characteristics of optical transmittance and reflectance. The morphology of the samples is characterized by scanning electron microscopy (SEM). Nanosphere diameters are established from statistical analysis of SEM images. The optical properties, which are determined by the photonic band structure, are studied by means of light transmission and reflection measurements. There is a relationship between the wavelength position of transmittance minimum or reflectance maximum and the diameter of the nanospheres. The size of nanospheres obtained from optical measurement results were compared with data obtained from SEM images.

Abstract: Magnesium alloys are widely used in aerospace and automotive industry due to their low density, good mechanical properties and good castability. The paper presents results of the castability tests and microstructural investigations on two unmodified magnesium casting alloys, Elektron 21 and QE22. Spirals for the castability test were poured from three temperatures: 755°C, 800°C and 835°C. Volume fraction of eutectic regions and grain size in both alloys were quantitatively evaluated. Castability increased with increasing pouring temperature. Quantity of eutectics and grain size did not show straight correlation with pouring temperature.

Abstract: Quantitative analysis of γ' and γ" phase nanoparticles in Inconel 718 was performed using FIB-SEM tomography. Three-dimensional visualisation showed that γ' particles are spherical, while γ" precipitates are disc-shaped. The dependence of the particle size of both phases on the heat treatment applied was detected. It was proven that the FIB-SEM tomography is a very precise method for metrology and morphology investigation of nanoparticles precipitated in Inconel 718 superalloy.

Abstract: In this paper the results of microstructural investigations and methodology of detection of intermetallic compounds were reported. The microstructural investigations included the light microscopy, scanning electron microscopy, chemical microanalysis and X-ray diffraction analysis. It was found that the microstructure of Mg-5Al-3Ca-0.7Sr-0.2Mn alloy consists of α-Mg, (Mg,Al)2Ca, Al3Mg13(Sr,Ca), Mg2Ca and Al2Ca intermetallic phases. The correct detection of these phases requires the high magnifications and a large number of measurements fields.

Abstract: Chemical composition and technology of experimental Ni based binder-tungsten carbide particles composite have been worked out to increase corrosion resistance of conventional supercoarse WC-Co type sintered carbides. All the sintered WC cermets, both with Co and Ni-based binding phase have been manufactured using identical supercoarse WC powder. Grain size evaluation was performed using light microscope images and grain chord length measurements, samples of commercial WC-Co coarse and supercoarse grades being included into analysis for comparison purposes. The obtained statistical and geometrical distributions of the chord length revealed certain differences. The performed statistical analysis allowed to state that the investigated experimental grades of Ni-based sintered WC carbides are materials of microstructure significantly more coarse than the reference coarse commercial grade (i.e. they can be classified into supercoarse group of sintered carbides).

Abstract: The work presents the procedure for a quantitative description of the structure of a welded joint of QE22 alloy, welded with TIG method. The developed procedure includes a sampling strategy, methodology of revealing the structure and a set of image conversions necessary to conduct the quantitative assessment. One been observed a repeated fragmentation of the a(Mg) grain and fragmentation of the eutectic areas in the fusion weld, compared to the post-casting material. It results from the conditions of the fusion weld crystallization. The statistical analysis has shown that the developed procedure ensures repeatable and clear presentation of the structure of the QE22 alloy welded joint.

Abstract: Fine Al-Si3N4 composite particles were prepared via mechanochemical processing of the coarse aluminum powder and submicron silicon nitride powder in order to obtain the core-shell structure of composite powder particles. It was expected that soft aluminum particles could form a thin coat on hard silicon nitride particles. The resultant particles were characterized through scanning and transmission electron microscopy and electron spectroscopes. Their particle size distribution, specific surface area, nitrogen/oxygen content and phase composition were also determined. Chemical analysis showed that limited oxidation occurred during mechanochemical processing. It has been found that a thin Al-enriched layer (larger than 10 nm) formed at some Si3N4 particles apart from the opposite effect if Si3N4 particles were occluded in coarser Al items. Discussion of the results is also presented.

Abstract: The ferritic-austenitic stainless steel was obtained by sintering the mixture of ferritic stainless steel AISI 434L powders with different amount of additions: Mn, Ni and Si. The structure of obtained sintered samples was investigated by computer image analysis methods. In porous materials the character of the pore structure strongly effects on its mechanical properties. Accurate information about pores shape is important information for technological process and quality control of produced materials as well. The images of the porous microstructure were analyzed using ADCIS Aphelion analytical software. Analyzed pores have complex and irregular shapes and thus authors decided to appoint different shape factors to obtain its proper quantitative description. Data obtained from image analysis process were statistically analyzed. Authors used a special resampling approach known as smooth bootstrapping to smoothing cumulative empirical distributions. The results obtained during resampling procedure have been compared with raw data from verification set and guidelines for the application of the proposed approach have been formulated. The validity of the proposed approach was positively verified and it significantly improved quality of the results. The smoothing and imputing of data allow to avoid numerical artifacts that may arise during the classical statistical calculations on irregular data originated from image analysis obtained from sintered samples. Efficient, reliable and relatively fast method for accessing the distribution of any others quantitative parameters describing microstructure of the materials is very interesting proposal for wide spectrum of application.

Abstract: Positive nature of the effects of hydrogen on the properties of titanium alloys is manifested in the high temperature hydrogen treatment (HTM - Hydrogen Treatment of Materials), where hydrogen is temporary alloying component. The paper presents the results of the possibilities of hydrogen using as a temporary alloying element in Ti-6Al-4V alloy and titanium Grade 3. Treatment of hydrogen alloy consisted of three stages: hydrogenation in hydrogen gas atmosphere at 650°C, a cyclic hydrogen-treatment (3 cycles 850 °C to 250 °C) and a dehydrogenation in vacuum (550°C). It was shown that hydrogen affects appreciably changes the microstructure of surface layer of the tested titanium alloy. The aim of this work is to determine the effect of hydrogen on the two-phase microstructure in Ti-6Al-4V alloy and Grade 3 titanium and hardness after high temperature hydrogen treatment.

Abstract: Columnar or equiaxed structure selection and particularly the C→E transition in the solidifying massive rolls is shown as the result of changes in heat transfer. The numerical treatment of heat transfer allows to separate the temperature field for columnar structure formation from equiaxed structure formation. An area where transition from columnar into equiaxed structure occurs, C→E≡CET is also distinguished. The current model requires the transformation of the calculated temperature field into the thermal gradients’ field. Thermal gradients are approximately constant during the examined C→E transition according to the numerical simulation. This result is in accordance with the Hunt’s theoretical predictions. The localization of the structural transition (CET) in space and in time is also shown within the map which yields from the temperature field.