Papers by Keyword: Microscopy

Abstract: Steel 22MnB5 is widely used in the automotive industry for manufacturing high-strength structural car body parts. To achieve desired mechanical properties, hot-stamping is used, during which the Al-Si coating plays a critical protective role against oxidation. This study investigates the structural evolution of the Al-Si coating under various austenitization durations at 920 °C. Intermetallic phase formation and coating morphology are analyzed.

Abstract: The Stable Isotope Unit of the National Centre of Scientific Research and the Ephorate of Kavala and Thasos collaborated on a project to investigate construction materials from the Ancient Theatre on Thasos Island, which was funded by NSRF European funds (2007-2013 and 2014-2020). Bulk samples of marble were collected to determine their provenance, technology, degradation features, and mechanical and physicochemical properties, with the ultimate goal of developing a conservation plan. By utilizing novel scientific techniques, the research team was able to date constructions discovered within excavations and establish remedial and preventive conservation plans using marble technology. The samples were characterized in terms of their isotopic, chemical, and mineralogical composition. Additionally, extended physicochemical and mechanical testing was applied to estimate the current condition of the Ancient Thasos Theatre. The ¹³C and ¹⁸O isotopic composition of the calcitic marbles was analysed to determine the environmental conditions during calcite formation, making it possible to define the marble provenance. Compositional and morphological analyses were achieved using energy-dispersive X-ray analysis by scanning electron microscopy, while the mineralogical phases were detected using X-ray diffraction and petrographic (polarized optical microscopy) analysis. Mechanical testing according to European Standards was achieved through the examination of compressive tensile strength and grain size distribution.

Abstract: This paper aims to analyse in detail a structural support steel beam from the years 1920 which has been in-use since then. Some tests will show that the steels from the analysed beams are not consistent, which given the time it was manufactured it does make sense since the metallurgy was not nearly as developed as it is now. It will present the analysis of the beam’s chemical composition; tensile and impact properties as well as the hardness of the material.

Abstract: In this article Therban AT 5065 VP, Therban AT 5005 VP - HBNR elastomers of different unsaturation degrees and their combined compositions research results (using optical and atomic force microscopy, DSC, DMA) are described. With these results structure and functional properties operational data of nitrile elastomers was obtained with no need of durable tests under different temperatures. It was found out that filler dispersion rises from 61.8 to 90.5 % and decomposition temperature grows from 261.9 to 275.3 °C while Therban AT 5005 VP share is increased from 20 to 50 weight parts. It is shown that elastomers with rubber ratio of 50:50 within temperature range from minus 30 to plus 150 °C have the lowest elasticity coefficient (from 311 to 1.6 MPa) and mechanical loss tangent (0.20) at the end of the test.

Abstract: In-situ Al_xNi_y reinforced aluminium matrix composites (AMCs) were produced by stir-casting route by adding 5, 10 and 15 weight percentage (wt.%) of Ni to AA6061 aluminum alloy. The density, porosity, microstructure, hardness and corrosion behaviour of the as-cast AMCs was studied and compared with that of the as-cast AA6061 alloy. The porosity in all the castings was found to be less than 0.1%. Further, the porosity was found to decrease with increase in Ni addition. Optical microscopy studies showed that in-situ formed Al_xNi_y was distributed along the dendritic arms. The distribution became non-homogeneous and coarse with increase in Al_xNi_y content. The coarse distribution of Al_xNi_y in the AA6061 matrix also resulted in the decrease in hardness of the composite, after an initial increase in hardness till 10 wt.% Ni addition. The open circuit potential (OCP) and corrosion potential (E_corr) of the AMCs with 5, 10 and 15 wt. of % Ni addition was noble than that of the AA6061 alloy. This was understood to be due to the presence of Al_xNi_y intermetallic which is known to have a noble corrosion potential than the aluminium alloy. However, the corrosion current (i_corr) increased while the polarization resistance (R_p) decreased with increase in Ni addition in the AMC. This indicates that the coarse non-homogeneous distribution of in-situ Al_xNi_y had a detrimental effect on the corrosion performance of the AMCs.

Abstract: In the restoration field and the cultural heritage, the treatment of colour is very important, being an important factor for the decisions and interventions in historic buildings. However, some of these have not the same recognition and protection by authorities, being really vulnerable, especially against natural phenomena like the earthquakes. After the 2017 Puebla Earthquake, the remainders of the earthen architecture of Jojutla de Juarez were collected to be analysed. Natural clays of the quarries near the town were compared by colorimetry tests with the traditional adobe samples which were collected in the locality. There also were conducted particle size analysis and the Unified Soil Classification System, USCS, to obtain the composition and properties of the soils and the adobe bricks, as well as the additives used, mainly straw as fibre reinforcements of the adobe masonry. One of the factors observed which contributed to change the colorimetric values of the clays was the use of stabilizers like lime, on the other hand, these stabilizers also helped to change the USCS classification of the soils and their cohesive properties.

Abstract: The experimatal alloys were aged at different temperatures of 180°C, 200°C, 220°C, and 240º C with calcium addition levels of (X=0.5, 1, 1.5, 2%) on Mg-6Al-1Zn-XCa alloy were investigated in 3.5% NaCl solution. All the experimatal alloys were immersed in 3.5% NaCl solutions and the resulted surface were analyzed to study the corrosion behaviour and its surface topography by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersed spectroscopy (EDS) and X-ray diffraction (XRD) techniques. The result shows that corrosion attack occurred predominantly on ß phase and α phase exhibit relatively minor corrosion. In addition to that the increased aging temperature coarsens the intermetallic as well as α- Mg grains, which shows adverse effect to corrosion resistances and the best result were obtained at composition of 0.5wt.% Ca aged at 200°C.

Abstract: Digital Image Correlation (DIC) has become more and more important in the field of material characterization and research, especially for strongly anisotropic fiber reinforced materials. Its big advantage over the conventional methods like strain gauges or point based video-extensometers is the full field strain and displacement measurement and the ability to analyze three-dimensional displacements. Although theoretically, the concept of the DIC as a pure image-based method allows it to work on every imaginable scale, its main field of application is in the range, where the region of interest (ROI) has a size between 10 −2 m to 10 −1 m. In this case, imaging is accomplished with the use of high-resolution black and white digital cameras. This work is focused on a smaller scale with ROI sizes between 10 −4 m to 10 −3 m, where a digital microscope is used to create the images. The innovative idea behind this work is using the natural surface structure of a polished carbon fiber reinforced Polyamide-6 sample, produced by automated fiber placement, as a statistical pattern instead of the usual speckle pattern applied to the area to be investigated. This way the stress and strain distributionin different regions of the investigated sample area can be evaluated and displayed, while the sample is exposed to an increasing mechanical load in form of a three-point bending test. The resulting strain and displacement fields are compared to finite element modeling of the ROI. To provide an accurate model, the image of the sample is first segmented into fiber, matrix and voids using “Trainable Weka Segmentation” and the resulting phases mapped with the corresponding material properties. To compute the resulting strains in the sample, the measured displacements from the DIC on the edges of the ROI were used as boundary conditions for the simulation. Simulation and experimental results clearly point out the inhomogeneity of the strain field in these samples. Due to the presence of fiber rovings and the presence of voids, local strain values exceed the global average by up to 4 %.

Abstract: We demonstrate 4^o off-axis 4H-SiC bulk crystal growth using physical vapor transport method (PVT). A radial 6-folded pattern is discovered in the facetted region of the growth surface by differential interference contrast microscopy. SICA88 Wafer Inspection/Review System was used to further inspect such 6-folded pattern with photoluminescence channel for wafers cut from that 4H-SiC crystal. It was found that the 6-folded pattern exists in all the wafers from the bottom to the top of that crystal. Several radial 6-folded patterns are found in the bottom wafer near the seed, but there is only one in the other two wafers. Defects distribution of these wafers after etched were also researched to find out the relationship between the radial 6-folded pattern and the defects. Based on the results, the formation and evolution mechanism of the radial 6-folded pattern on 4o off-axis 4H-SiC crystal is discussed.

Abstract: This document deals with study of nanoand micro particles of artificial corundum in cement mixtures. This inert material with high hardness is usually used as fine-grained additions of concrete mixture. The most important characteristic of corundum is very high hardness (number 9 on Mohr scale). That is the reason, why is mostly added to the cement mixture primary intended for high load flooring. In this paper were studied several type of recycled corundum classified due to its origin. Because it is a recycled material, it was necessary to first examined basic physical properties such as chemical composition or granulometry. We have applied this fine grain material to cement mixes and compared their mechanical properties. For comparison measurement were used a mixture without this admixture and mixture with a corundum with similar granulometry but non-recycled origin.