Materials Science Forum Vol. 752

Abstract: The aim of the research was to develop an amorphous and microstructured layer on non-amorphous alloys by laser surface treatment. The as-prepared Cu based master alloy ingots were imbedded in a metallic sinking with Wood metal to assure the good thermal conductivity during the laser treatment. The laser remelting, alloying and coating techniques were applied from the laser surface treatment techniques. The surface layer production and a subsequent rapid cooling were performed using CO2 laser and pulse and continuous modes of Nd:YAG laser. The characterization of the microstructure of the resulting surface layer was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Actual remelting on substrates showed that the process of laser remelting is a suitable technique for production of metallic glasses as surface layers. The amorphous layer up to 250 m in depth can be produced by laser surface remelting on Cu46Zr42Al7Y5 alloy.

Abstract: The heat balance of a casting cycle can be ensured in short times by the annealing of the die-casting tool, by which the well-constructed and well-functioned cooling system can enhance productivity. Incorrect cooling, however, can lead to heat unbalance in the die casting tool, thus causing the destruction of casting quality, reduction of the lifetime of die casting tool and irreversible production-reduction. Beside the theoretical examination of construction and function of cooling system, the evaluation of the effectively removed heat quantities has great importance. The paper presents an analysis of the function of the cooling system of a scraggy thin casting of AlSi9Cu3 alloy, in case of different cooling parameters. Based on the measured results of the inlet and outlet temperatures and the volume flow of the cooling agents, the heat quantities belonging to the cooling circles are determined and an optimization of the cooling system is proposed. The findings of the analysis can be utilized for the construction and optimum operation of die-casting cooling systems.

Abstract: The softening of Al-Mn base alloys not only depend on the degree of deformation and the parameters of annealing, but the pre-treatment of as-cast alloy. Large extent of the Mn remains in the solid solution during the crystallization process. During a high temperature heat treatment the manganese precipitate from the solid solution phase. The size and amount of the precipitations mainly of the processes takes place during annealing. In this article this effect is studied through the heat treatment and deformation of a specific alloy.

Abstract: The austenitization is a solid phase transformation process accompanied by nucleation and nucleus growth controlled by long-range carbon diffusion. In the course of our work, a method was developed by which spheroidite model structures were constructed such a way that their different parameters (the size of ferrite grains, the average value of carbon concentration, the size of cementite spheroids) could be changed optionally. In addition, a nucleation model of free enthalpy base was created by which the difference between the two different places of nucleation can be distinguished on the basis of their free enthalpy. The effects of structure parameters, interface free enthalpies and temperature on the nucleation rate of austenite were investigated by cellular automaton simulations.

Abstract: The present research work deals with the examination and rheological modelling of flow properties of asphalt mastics which are the most important components of asphalt concretes. Asphalt mastics are mixtures of fine grained mineral filler particles (d<0,063 mm) and bitumen, having a stabilizing role in asphalt mixtures and largely determining the cohesion between mineral particles and bitumen. During our examinations two types of mineral fillers – limestone and dolomite – as well as standard bitumen were tested, which are extensively used in Hungarian road construction. Asphalt mastic mixtures were prepared out of these materials and they were tested with dynamic shear rheometer (DSR). According to the test results, rheological models of mastics were determined. It has been established that at different test temperatures and shear rate ranges asphalt mastics behave as Herschel-Bulkley and Bingham-type materials.

Abstract: Numerous literature [1,4,5] has reported on the effective use of cellular automaton method for the simulation of short-range diffusion. Using this model for the simulation of short-range diffusional phase transformations therefore is a resolved issue. It is proven that two- or three-dimensional automata can reflect the course of the abovementioned processes realistically. What our study demonstrates more than in the past [1] is that two-dimensional stochastic cellular automaton simulation already presented before has been simplified. This time our automaton operates in one dimension [2], which has consequently reduced running time, thus, made it possible to enhance the efficiency of the scaling of simulation. In our previous work the results of scaling of one-dimensional simulation of the recrystallization process [3] were demonstrated, in our current study fitting is performed for measurement results of grain coarsening using one-dimensional cellular automaton.

Abstract: To protect the environment and conserve resources WPC (Wood-Plastic-Composite) materials are gaining foothold. Since in the construction industry both PVC (high weathering resistance, flame retardant, lightweight, long lifetime) and wood (natural, decorative, renewable) are well known and liked materials wood-PVC composites are also sought for. Numerous research and development/improvement efforts are on the way to produce commercially successful systems. The main hindrance is the compatibility issue between the components. This work describes a novel method – a work in progress – applied for a selected wood type, which was processed and validated using physical and mechanical tests. It was found that the prepared composite system is somewhat softer and more flexible than the original matrix PVC composition, but the thermal stability and the application temperature has been improved. It was also found that the PVC encloses the wood particles, shielding them from the environment and the humidity, thus protecting it from mold and microorganisms eve in humid conditions. A further step in the work is performing the tests focusing on the processing behavior of the material.

Abstract: We can encounter products made from UHMWPE in many different areas of utilization. This material is used in plastic bearings, ball-and-socket joints, heavy-duty plastic cog-wheels and joint implants. The UHMWPE is a very particular polymer, the special characteristics of which can be attributed to its molecular structure. The ulra-high molecular weight has an effect on wear-resistance, creep-resistance and hardness. These are the parameters demanded by the highly specialized utilization. On the other hand, this molecular stucture also has disadvantages next to the many advantages. Its greatest disadvantage is that it’s difficult to process. The UHMWPE is a thermoplastic, but because of the long molecular chains its injection molding is impossible. In the course of the present research work we will compare the mechanical and quality properties of products made with lathe machining (RAM extrusion) and direct compression molding. We will examine the impact of the changes of the manufacturing and technological parameters. We will be placing a special emphasis on the surface quality because the quality and life-span of the abovementioned products (bearings, ball-and-socket joints, artficial joints) largely depends on this parameter. Besides this we will examine the changes of hardness and the stability of size. In view of these results we will try to determine what would be the best manufacturing technology that could ensure the maximum performance and life-span of these products. [1,3,6] We are focusing by having the results, to optimizing the manufacturing.

Abstract: Recent work describes changes in polylactic acid samples with different crystallinity during microbiological degradation. We treated PLA at 93°C for different periods of time, which yielded samples with particular crystallinity. The fraction of crystalline phase was determined by differential scanning calorimetry, and the visual effect of crystallinity was measured by colorimetric method with black and white backgrounds. The medium for biological degradation process was living sludge under room temperature and normal atmospheric pressure. Furthermore, the change in mass was also measured. The results show that increased crystallinity reduces the rate of mass lost. The volumetric proportion of crystallinity is in direct correlation with opacity, so checking transparency is also a suitable possibility for estimating crystallinity. DSC, colorimetric method and visual observation experiments confirm that crystallinity has increased proportionally by the time of heat treatment and caused opacity. The experiments show that water uptake happened faster and in much higher volume in polymers having dominantly amorphous structure than in the case of samples with higher crystallinity. In the case of materials with only 2.43% crystallinity, weight lost began later because they had a greater water uptake during the first 7-12 days, while this period took only 7 days with a very low water uptake for samples containing approximately 35% crystalline phase. After swelling, weight loss of the crystalline samples was much slower than that of samples containing more amorphous parts, because crystalline phases inhibit the diffusion of small water molecules and the microbes with it.

Abstract: Ultra high molecular weight polyethylene (UHMWPE) was modified by 20 % methyl-methacrylate (MMA). Specimens were examined by two directional tribological wearing methods. Wear resistance of the modified materials was found to be increased by 38 %. Despite the promising results further experiments are needed to utilize it as human implant.