Materials Science Forum Vol. 589

Abstract: The wetting phenomenon between solids and liquids has an outstanding role in several technological processes [1, 2]. The knowledge of physical and chemical factors acting on the surface tension is needed to ensure the successful processing in casting, brazing and sintering. The surface oxide layer influences the wetting conditions and makes difficult the exact measurement of contact angle [3]. In this paper the effect of oxide layer disruption and recovery was observed using a high speed camera.

Abstract: Silicone rubber is an essential construction material in food industry, medicine and in some fields of mechanical engineering, because it has good mechanical, electrical, biological and other special properties. One needs to know these material properties in order to develop silicone sensors. We performed several standard measurements for rubber, like tensile strength, cyclic tensile, bending, fatiguing, stress relaxation tests etc. To investigate the electrical properties, we measured the resistance of silicone during the mechanical tests. The paper summarizes the newest results of our research in connection with mechanical and electrical properties of conductive silicone rubber.

Abstract: Duplex stainless steels constitute a famous group of the stainless steels. They consist of mainly ferritic and austenitic phases. The ratio between these phases is regulated by numerous alloying elements and low content of carbon. Because of this strong alloying a lot of metallurgical processes can take place at high temperature, e.g. the decomposition of ferritic phase into σ-phase and secondary austenite. In this paper the changes of amounts of these three phases are studied by automated EBSD, saturation magnetization measurement, XRD-analysis and micro-hardness test. Similar results were obtained by the different applied measurements for the change of phase ratios due to the isothermal heat treatment.

Abstract: Silicone rubber is an essential construction material in food industry, medicine and in some fields of mechanical engineering, because it has special mechanical, electrical, biological and other special properties. Over the usage of silicone rubber as structural material, the “intelligent” behaviour is more and more important. In this case the question arises whether its optical properties change by the effect of mechanical load or deformation Can it be used like sensor, utilizing these properties The paper shows the newest result of our optical research in connection with silicone rubber and shows the possibility of its usage for optical strain and force sensor, using its birefringence.

Abstract: After development of the well-known T/P91 steel grade in the early 80’s and its long industrial experience since early 90’s, it has been necessary to develop new martensitic creep resistant steels to answer the demand of the power generation industry. New USC (ultra-super critical) boilers require materials with advanced creep properties to reach severe steam parameters. Addition of W to the steel has been found by many researches to be effective to increase creep rupture strength at high temperatures and already used in some developed steel grades such as T/P92, T/P122 and AISI 422 for the USC boilers. Recently, long-term creep strength of the advanced high Cr ferritic steels has been argued regarding the instability of their microstructures at high temperatures over 600 °C. This microstructural instability seems to be enhanced with increasing Cr content or with substitution of Mo by W in the steels. The aim of this paper is concentrated on the investigation of the microstructural development of the studied steel using the Jominy end-face quench test. Different hardness profiles from this test were introduced.

Abstract: The Si3N4 ceramics are usually known as strongly refractory and enduring materials and they have typical insulating material properties on room temperature. If reinforcing phase of the Si3N4 matrix composite is a good electrical conductor, in that case it is worth to investigate the composite in electrical aspect. In our case carbon nanotubes, black-carbon and graphite with good electrical conductivity were mixed in the base ceramic. During our electrical investigations DC resistivity measurements were used to determine the percolation threshold and the conductivity of the composites. In case of high resistance samples AC impedance spectroscopy was applied. As result of the impedance spectroscopy capacitive properties were found. In some cases of conductor samples combined mechanical – electrical measurements were done to study the integrity of the additions in the matrix.

Abstract: The Si3N4 is one of the leader high-tech ceramic nowadays. As a result of numerous developments excellent mechanical properties of the material are increased by carbon additives. In our previous investigation the electrical effect of the additives was examined. In our work thermo radiation measurements were used by infrared camera technique on conductor Si3N4 ceramic composites in infrared wavelength range. The thermal properties of the developed ceramic composites were determined. This is not easy with the ordinary methods because of the fashioning and geometrical parameters of the material. During the experiments the emissivity of our composites was determined by infrared thermography measurements. Based on a theoretical thermal conductivity model an evaluation method that allows a derivation of thermal conductivities of special geometry conductive materials from results of infrared measurements was established.

Abstract: The paper describes an analysis of the AE signals captured with PZT sensor during and after laser cutting. In the course of cutting the continuous AE signals are treated in a defined time interval. After cutting, bursts of acoustic emission will occur. They are due to solidification of the molten material and cooling of the laser-cut surface. The results shown refer to cutting of steel plate DC04 and of austenitic stainless steel plate X5CrNi18-10. Both plate types are frequently used in automobile industry, where, because of mass production, optimisation of the cutting process is desired. Numerous laser-cutting conditions assuring different quality levels of the cut made were chosen. It was proved that the laser cutting conditions had a significant influence on the amplitude value and intensity of the continuous signal and AE activity after the termination of laser cutting. Separately it was also confirmed that there was a relation between the measured signal and laser-cut quality, which is shown, to a large extent, by the presence of dross at the lower edge of the cut.

Abstract: Poly(vinyl alcohol)/carbon nanotube (CNT) composite nanofibers were processed by both conventional and needleless electrospinning method. The effect of the processing parameters on the possibility of manufacturing was investigated. The results were evaluated by surface tension and conductivity measurements. For the investigation of surface morphology scanning electron microscopy (SEM) was used. It was concluded that surface treatment of carbon nanotubes was necessary for needleless electrospinning. Lower surface tensions were better for this process but the effect of conductivity was not so significant.

Abstract: In this paper glass fibers, chopped roving pieces, and fiber mats were tested in case of emulsion bonded glass fiber mat samples. Relationships between the tensile strength properties of the different structural levels of the fiber mats were studied and fiber bundles as structural elements of fiber mats were modeled by idealized statistical fiber bundles developed by the Department of Polymer Engineering, BUTE. The geometrical and mechanical measurements were carried out by image processing methods and a computer aided tensile tester. The results proved that the modeling method gave a tool in understanding the failure behavior of the fiber mat samples and studying the effect of the structural parameters. The applicability of the modeling method is demonstrated by the good agreement with some measurements.