Materials Science Forum Vol. 729

Abstract: Microhardness and sound velocity were measured in case of differently prepared solder samples. The used Pb-10Sn solder samples were melted then cooled down applying different cooling rates. These procedures caused variant microstructure thus different microhardness and sound velocity values. The sound velocity was measured by means of scanning acoustic microscopy. Characterization of solder materials by acoustic microscopy gives the possibility to non-destructively estimate mechanical and reliability parameters of the given material.

Abstract: The material aspects of a polymer based microfluidic structure were characterised considering the compatibility of the system with bioanalytical applications. The polydimethylsiloxane (PDMS) based channel system is to be integrated in a full polymer photonic biosensor device developed within the European Union project P3SENS (FP7-ICT4-248304). This work is intended to define a modified material composition, which is appropriate to improve both the wettability and the non-specific protein binding characteristics of the PDMS significantly. Triton X-100 (Sigma-Aldrich) surfactant was added to the raw PDMS before polymerisation. The influence of the tenside was studied considering the polymerisation reaction, the surface characteristics and the functional applicability. To test the hydrodynamic behaviour and non-specific protein adsorption on the surfaces, phosphate buffered saline (PBS) solution and fluorescent labelled human serum albumin (HSA) was applied in a microfluidic capillary system.

Abstract: The microstructure of the commonly used SnAgCu (SAC) lead free solder alloy was investigated. SAC solder bumps were soldered by two different soldering techniques (Vapor Phase Soldering (VPS), Laser reflow). Since the soldering profile of the VPS method is considerably different from the temperature profile of the laser reflow soldering, the created microstructures are expected to be diverse. Selective electrochemical etching was applied on cross sectional samples in order to extract the tin from the cross sectioning plane. In this manner the spatial structure of Cu₆Sn₅ and the Ag₃Sn intermetllic compounds (IMCs) was highlighted. The microstructures of the samples were analyzed with optical microscopy and Scanning Electron Microscope (SEM) on cross-section samples. The composing elements were identified by SEM-EDS.

Abstract: The glass forming ability (GFA) of the Cu-Zr-Ag alloy system was investigated on the basis of the thermal stability, and the structural, thermodynamic and kinetic properties of the material. We changed the concentration of the alloys, as we departed from the Cu58Zr42 composition and produced three different eutectic points in the Cu-Zr-Ag ternary system, in accordance with the results published in the respective literature. We produced various test pieces of Cu-Zr-Ag amorphous alloys with different Ag contents (0-70%), by casting the material into wedge-shaped copper moulds. In such ternary alloy system there is only a limited concentration range where amorphous materials can be produced: in the event that the Ag content of the material exceeds 35 at%, no amorphous material structure will develop. In our experiment the maximum temperature range of the supercooled liquid region (ΔTx) was 75 K. The calculated four GFA parameter values are not in perfect harmony and fail to point out the optimal composition available; however, based on γ and the reciprocal value of ω, the best compositions from the GFA aspect are Cu_42.5Zr_37.5Ag₂₀ and Cu₄₀Zr_37.5Ag_22.5. The decrease of the maximum thickness of the bulk metallic glasses is influenced more by the oxygen content than the composition changes within the Cu-Zr-Ag system.

Abstract: Our aim was to develop initial structures similar to the real structures of unalloyed steels that could later be used for simulating austenitization. Both simple models and models that can be compared to the real structures were developed. In our paper, it is described how the initial structures were developed by using digitalized microscopic images.

Abstract: In the course of our experiments we have developed an etching process by means of which the austenite grains formed subsequent to roughing can be made visible in the case of Grade X80Mo0 and X80Mo2 microalloyed steels. The definition of the size and elongation of the grains enables the production process to be optimized and the microstructure features associated with the desired mechanical properties attained thereby.

Abstract: Almost half of the deaths in the European Union are a consequence of cardiovascular diseases, which can be reduced significantly by dietary changes, physical activity and suitable medications. Since changing lifestyle and healthcare is a slow process, a more efficient and quicker solution is to improve medical devices. Stents are mesh-structured implants, which support arterial wall and allow dilatation of the narrowed section. The material analyses of stents removed from cadavers allow further development and improvement of these special devices. Despite of the widespread application of stents, not many publications deal with their technical analysis and most of them have a medical approach. This paper presents a technical analysis of three stents removed from cadavers. The results may promote the evaluation of the stent development. Until now these kind of feedback was missing from the improvement cycle.

Abstract: Conducting composites based on graphite, carbon black and polypropylene have been prepared and the effect of composition on the flexural modulus and electrical conductivity has been studied. The conductivity of polymers containing only one kind of filler did not increase significantly, their modulus of elasticity was the highest for graphite filling, and the lowest for nanotube filling. The conductivity of dual filler hybrids increased significantly due to the synergetic interaction between the two fillers. At lower graphite contents, because of the better dispersion of graphite, the material became more flexible, but at higher carbon black contents the stiffness increased significantly. In the case of triple filler hybrids, if keeping the graphite content at a certain level and varying only the carbon black/nanotube ratio, the conductivity and the flexural modulus varied according to exponential and linear rules respectively.

Abstract: In the traditional heavy-clay industry, compounds are usually prepared by the addition of organic waste material. These additives originate mainly from the wood, food or paper industries. The purpose of this study is to present the results of the examination of friction contact between the wall of the forming die and the clay compounds containing organic additives. Saw dust and ground sunflower seed shell were mixed to clay in 0 wt%, 3 wt% and 5 wt%. The water content of compounds was also varied. The clay and the additives were described by morphology, XRD, bulk density and equivalent diameter. Friction tests were carried out on a special tribometer up to plastic deformation of the sample. The coefficient of friction decreased when normal stress was increased for all the ten compounds. Average results showed that the tendency of change in the value of the coefficient of friction could be divided into three sections: a decreasing, a quasi constant and a shearing section. It follows from this that the coefficient of friction can be characterized with a number only inside the quasi constant section, i.e. between two definable normal stress values. Averaged coefficient of friction was between 0.17 and 0.21 for saw dust and between 0.19 and 0.21 for the compounds with ground sunflower seed shell.

Abstract: In this paper, the correlation between structural and mechanical properties of nanostructured austenitic oxide dispersion strengthened (ODS) steel prepared by powder metallurgy were studied. High efficient milling process was applied to achive an optimal dispersion of ceramic oxide particles in the steel matrix. The austenitic powder with or without Y₂O₃ addition was milled by two different milling process (wet and dry). Spark plasma sintering as a fast and effective compaction method was used as sintering equipment. The morphology and structural properties of ODS were studied by X-ray diffraction and scanning electron microscopy. Mechanical properties, such as microhardness, bending strength and modulus of nanostructured ODS were also determined.