MATERIALS ENGINEERING, Vol. 18, 2011, No. 1
published on May 2010
CONTENTS and ABSTRACTS
Tillová, E., Ďuriníková, E., Chalupová, M. (pp. 1-7)
CHARACTERIZATION OF PHASES IN SECONDARY AlZn10Si8Mg CAST ALLOY Full text (PDF 1211kB) - Available online 21 April 2011
Using recycled aluminium cast alloys is profitable in many aspects. Requiring only 5 % of the energy to produce secondary metal as compared to primary metal and generates only 5 % of the green house gas emissions, the recycling of aluminium is therefore beneficial of both environmental and economical point of view. Secondary AlZn10Si8Mg (UNIFONT® - 90) cast alloy are used for engine and vehicle constructions, hydraulic unit and mouldmaking without heat treatment. Properties include good castability, very good mechanical strength and elongation, light weight, good wear resistance, low thermal expansion and very good machining. Improved mechanical properties are strongly dependent upon the morphologies, type and distribution of the secondary phases, which are in turn a function of alloy composition and cooling rate. The presence of additional elements as Mg, Mn, Fe, or Cu allows many complex intermetallic phases to form, which make characterisation non-trivial. These include, for example, Mg2Si, Al2CuMg and AlFeMn phases, all of which may have some solubility for additional elements. Phase’s identification in aluminium alloys is often non-trivial due to the fact that some of the phases have either similar crystal structures or only subtle changes in their chemistries. A combination different analytical techniques (light microscopy upon black-white and colour etching, scanning electron microscopy (SEM) upon deep etching, energy dispersive X-ray analysis (EDX) and HV 0.01 microhardness measurement) were therefore been used for the identification of the various phase.
Ostroushko, D., Mazancová, E. (pp. 8-10)
CHOSEN PROPERTIES OF SANDWICH MATERIAL Ti-304 STAINLESS STEEL AFTER EXPLOSIVE WELDING Full text (PDF 283kB) - Available online 5 May 2011
The work deals with evaluation of joint of stainless steel 304 SS (sheet) and commercially pure Ti both after welding explosion and followed-up annealing at 600°C/1.5h/air. The bonding line shows sinusoidal character with curls in crest unlike the trough of the sine curve. The heat treatment does not change the character of the interface. In work amplitude, wave length and the interface thickness were measured. Thickness of compressed cladded matrix of Ti was measured in area of crests and troughs. In crest of joint melted zones were studied, where complex oxides and intermetallic phases were revealed.
Staneková, H. (pp. 11-15)
MICROSTRUCTURAL STABILITY OF Ti-46Al-8Ta DURING CREEP Full text (PDF 778kB) - Available online 5 May 2011
The effect of long-term creep exposure on the microstructure stability of a new cast air-hardenable intermetallic alloy with nominal chemical composition Ti-46Al-8Ta (at .%) was studied. Constat load creep test were performed at the temperature 750°C and at applied stress 250 MPa up to 3479,3 h. The initial gama(TiAl) + alpha2(Ti3Al) microstructure of the alloy is unstable and transforms to alpha2 + gama + tau type. During creep the formation of cavities along the lamellar colony and grain boundaries is observed. The specimens fail by the growth and coalescence of such cavities with intergranular type of fracture.
Cosmi, F. (pp. 16-24)
PRELIMINARY RESULTS IN SYNCHROTRON X-RAY DIFFRACTION MEASUREMENTS OF RUBBER COMPOSITES STRUCTURE BEFORE AND AFTER EXPOSURE TO HYDROGEN Full text (PDF 1544kB) - Available online 5 May 2011
In future years, fuel cells are expected to represent a promising technology as a source of heat and electricity in buildings and of electrical power for vehicles, since fossil fuels are exhausting and significantly degrade air quality. It is well known that, when exposed to a hydrogen environment, hydrogen embrittlerment may affect materials such as iron and steel. But these are not the only materials that are used for hydrogen equipment. In particular, the rubber materials used for O–rings that seal high pressure hydrogen gas equipment show problems of internal fracture, called blister fracture, when the gas is rapidly decompressed. As many different kinds of fillers can be used, in this work we started to investigate the influence of the type of filler on the rubber composites structure, by means of X-ray diffraction measurements performed at the Elettra synchrotron radiation facility in Trieste. In this preliminary study, three kinds of samples were analyzed before and after exposure to hydrogen: Sulphur vulcanized EPDM, Peroxide vulcanized EPDM and Sulphur vulcanized NBR. While Peroxide vulcanized samples did not show significant differences in the diffraction pattern, changes could be detected in the cristalline form of Sulfure vulcanized rubber.
Bakajová, J., Dománková, M., Gogola, P. (pp. 25-29)
STRUCTURAL STABILITY OF HIGH NITROGEN AUSTENITIC STAINLESS STEELS Full text (PDF 1077kB) - Available online 11 May 2011
This paper deals with the structural stability of an austenitic stainless steel with high nitrogen content. The investigated steel was heat treated at 800°C using different annealing times. Investigation was carried out using light microscopy, transmission electron microscopy and thermodynamic calculations. Three phases were identified by electron diffraction: Cr2N, sigma – phase and M23C6. The thermodynamic prediction is in good agreement with the experimental result. The only is the M23C6 carbide phase which is not thermodynamically predicted. Cr2N is the majority secondary phase and occurs in the form of discrete particles or cells (lamellas of Cr2N and austenite).
Steinhaus, J., Moeginger, B., Großgarten, M., Hausnerova, B. (pp. 30-35)
EVALUATION OF DIELECTRIC CURING MONITORING INVESTIGATING LIGHT-CURING DENTAL FILLING COMPOSITES Full text (PDF 296kB) - Available online 13 May 2011
The aim of this study is the evaluation of a dielectric analysis (DEA) method monitoring the curing behaviour of a light curing dental filling material in real-time. The evaluation is to extract the influence of light intensity on the photo-curing process of dental composite filling materials. The intensity change is obtained by measuring the curing process at different sample depth. It could be shown that increasing sample thickness, and therefore exponentially decreasing light intensity, causes a proportional decrease in the initial curing rate. Nevertheless, the results give rise to the assumption that lower illumination intensities over a long period cause higher overall conversion, and thus better mechanical properties. This would allow for predictions of the impact of different curing-rates on the final mechanical properties.
© University of Žilina, Faculty of Mechanical Engineering, ISSN 1335-0803