Materials Science Forum Vol. 729

Abstract: Silicon nitride-based nanocomposites with different quantities (0, 1, 2 wt%) of multiwall carbon nanotubes (MWCNT) have been prepared by isostatic pressing. Abrasive tribological tests were carried out at room temperature in ambient atmosphere with various types of abrasives (different material and grain size) and lubricants respectively. Worn surfaces were characterized by surface roughness parameters, surface topography and scanning electron microscope while wear rate was featured by the worn mass. Results indicate that increase in MWCNT-content leads to decrease of abrasive wear resistance which is proven by increase of R_a and R_z roughness parameters and SEM-analyses of the abrasive worn surfaces.

Abstract: Nowadays the most commonly used baths for hot-dip galvanizing are the ones which contain about 0.1 ... 0.2% of aluminium. Besides aluminium, the effects of the addition of small quantities of titanium (up to 0.0005%) to the bath have recently been studied in detail by Culcasi et al. [2]. They proved the strong impact of adding a small amount of titanium on the development of the iron-zinc layer, which influences primarily the building up of the intermetallic compound film Fe₂Al₅ on the surface of the steel piece in contact with the molten zinc. This aluminium-alloyed hot-dip bath with titanium usually does not form a nicely coloured surface [. Therefore, our experiments were limited to test only the effect of adding titanium to the molten zinc which contains only traces of aluminium in order to study the impact of titanium on surface colouring using GD-OES spectrometry.

Abstract: The most promising process for metal matrix syntactic foam (MMSF) production is pressure infiltration. In case if it can be advanced to die casting the cost of the MMSFs will drop significantly. The first step on this road is to characterize the kinetics of the pressure infiltration with respect to infiltration pressure and time. Experimental infiltration equipment was built and many preliminary tests were performed on the AlSi12 + SLG system. The load bearing capacity is also important, therefore the compressive behaviour of MMSFs were investigated. According to the results engineering factors (matrix material, size of the microballoons, applied heat treatment, temperature of the tests) have significant effects on the compressive properties.

Abstract: Melt-spun amorphous Mg₆₅Ni₂₀Cu₅Y₁₀ metallic glass compacts were subjected to severe shear deformation by high-pressure torsion. High-resolution X-ray diffraction analysis and scanning electron microscopy revealed that high-pressure torsion resulted in a deformation dependent microstructure. Nanoindentation measurements indicated that the heavy shear deformation yields an increase in hardness. High-pressure calorimetry measurements revealed that hydrogen uptake in the fully amorphous alloy occurs at a significantly lower temperature compared to the fully crystallized state, while the amount of absorbed hydrogen increased considerably after shear strain due to the formation of Mg₂Ni crystals.

Abstract: In the recent years a remarkable development can be observed in the electronics. New products of electronic industry generate more and more heat. To dissipate this heat, thermally conductive polymers offer new possibilities. The goal of this work was to develop a novel polymer based material, which has a good thermal conduction. The main purpose during the development was that this material can be processed easily with injection molding. To eliminate the weaknesses of the traditional conductive composites low-melting-point alloy was applied as filler. Furthermore in this work the effect of the filler content on thermal conductivity, on structure and on mechanical properties was investigated.

Abstract: The need for flexible forming processes is of utmost importance in the recent years. Therefore, it is very important to develop new innovative technologies and processes. This is particularly valid for small batch and prototype production. Incremental sheet metal forming may be regarded as one of the promising developments for these purposes. In this paper, first a general overview of main process characteristics of the incremental sheet metal forming will be given. Then some recent results of a joint Eureka project launched by two universities and two SME companies in Hungary and Slovenia will be presented.

Abstract: Automotive castings have to meet more and more versatile requirements these days. One of the most important requirements towards suppliers and foundries is producing parts of better quality, higher performance but at the same time of less weight. In order to couple this small weight with high performance and excellent quality these products should meet very strict mechanical standards of automotive parts. There is a constant need for production engineering developments ranging from purity degree - that is producing molten metal with high cleanness - to grain refinement and alloy improving including heat treatment technologies.

Abstract: In the current paper a new method is presented that determines the five macroscopic parameters of a grain boundary (GB) from electron diffraction patterns and bright field (BF) images in a transmission electron microscope. Usefulness of the method is demonstrated on a set of GBs measured in laser crystallized Si thin films. To characterize the geometry of a grain boundary, we have to determine the misorientation between the neighboring grains, and the direction of the GB-plane. The misorientation is calculated from two convergent beam electron diffraction (CBED) patterns taken on the neighboring grains, and the plane-normal can be calculated from bright field (BF) images of the GB. The thickness of the sample is also needed and it is measured from a CBED pattern taken in two-beam condition. It has been previously observed in metallic thin films, that the GBs can minimize their energy in two alternative ways in thin films: either forming a GB plane with low energy density or minimizing the area of the plane. In the last case the GB plane is almost normal to the surface of the specimen and has a general index. We found, that boundaries with exact Σ3 misorientation generally adopted low energy-density {111} boundary planes and formed coherent twins. The rest of the boundaries adopted general index planes and minimized the surface area of the boundary. The last group included boundaries with small deviation from 3 misorientation, other special high-angle boundaries with-value>3 and boundaries with general misorientation.

Abstract: The research work aimed to present the usability of the cracked round bar (CRB) specimen type for the determination of the linear-elastic plain strain fracture toughness values (K_Ic or K_Q) on steels; and to demonstrate the applicability of the testing results for the reliability assessment of structural elements having cracks or crack like defects. Micro-alloyed structural steel and heat resistant steel were tested at elevated temperatures, at 260 °C and 410 °C, respectively, using small-sized specimens with small diameters. Four different equations were used for the evaluation of the tests, and the determined fracture toughness values were compared with one another. Reliability assessment calculations were realised on two structural element models, critical crack sizes and safety factors were determined for all cases.

Abstract: The aim of this work is to study the microstructural changes in 2507 type superduplex stainless steel due to heat treatments. Two series of specimens were studied. The first series were heat treated isothermally at 800 °C for different times up to 42 minutes. The second ones were heat treated isochronically for 20 minutes in the temperature range of 720-900 °C. The microstuctural changes were investigated by metallography and by magnetic tests. The first magnetization curves and the saturation magnetization loops were measured by a double yoke DC magnetometer.