Papers by Author: Árpád Kovács

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Authors: Kinga Tomolya, Zoltán Gácsi, Árpád Kovács
Abstract: The central problem of producing of Al/SiCP composites is to avoid the forming of brittle Al4C3, which leads to a poor corrosion resistance and degraded mechanical properties [Mingyuan, 1999]. The possible way is the covering of the SiC particles. This paper deals with the covering of SiC. The coated particles will be applied for producing aluminium matrix composites. We have covered three different grain sizes of particles. We have applied the nonelectrolytic method of deposition from solution for coating. Before the covering the surface needs to be catalysed. We have compared the effects of different type of catalysators, then we have analysed the effects of plating time by means of the scanning electron microscopy.
Authors: Béla Török, Árpád Kovács
Abstract: In the last few years iron slag finds from the Late Avar Period (7-9th cent.), the Period of Hungarian conquest (10th cent.) and the Árpáds (11-13th cent.) uncovered in sites of excavation in the Carpathian Basin had been examined. The pieces of slags are by-products of the metallurgical process of bloomery and forming procedure of iron blooms. The structure of the examined slags was very heterogeneous from the metallographic point of view. The amorphous phase as well as panelled and dendritic crystallization can be found, which was the more frequent. Secondary, nay, tertiary branch of dendrite often can be studied, which was the result of gradual cooling. It was typical for its microstructure that minerals formed from oxides of elements with lower atomic number than iron (Al, Mg, Ca, etc.) surround the fayalite-rich parts. These minerals sometimes also have a high quantity of Fe, sometimes those have a very low Fe-content. The examination of microstructure can help to determine the type of the slag, whether it comes from metallurgical (as a tap-slag or cinder) or forming process, and to specify and reconstruct the metallurgical and physicochemical processes in the medieval bloomery.
Authors: Mária Svéda, András Roósz, Jenő Sólyom, Árpád Kovács, Gábor Buza
Authors: András Roósz, Jenő Kovács, Arnold Rónaföldi, Árpád Kovács
Abstract: Al–7wt.-% Si–1wt.-% Fe alloy was solidified unidirectionally in the Crystallizer with High Rotating Magnetic Field (CHRMF). The diameter of sample was 8 mm and its length was 120 mm. The parameters of solidification were as follows: solid/liquid interface velocity ~0.082 mm/s, temperature gradient 7+/-1 K/mm, magnetic induction 0 and 150 mT, frequency of magnetic field 0 and 50 Hz. The structure solidified without rotating magnetic field (RMF) showed a homogeneous, columnar dendritic one. The structure solidified by using magnetic stirring showed a dual periodicity. On the one hand, the branches of the “Christmas tree”-like structure known from the earlier experiments contained Al+Si binary eutectic. On the other hand, bands with higher Fe- and Si-content formed in the sample, which were at a larger distance from each other than the branches of the “Christmas tree” structure. The developed microstructure was analyzed by SEM with EDS. The average Si- and Fe-concentrations were measured on the longitudinal section at given places along the length of sample. Furthermore the Si- and the Fe-concentrations close to the bands and among the bands as well as the composition of the compound phases were determined.
Authors: Valéria Mertinger, G. Szabó, Pál Bárczy, Árpád Kovács, György Czél
Authors: Kinga Tomolya, Márton Benke, Dóra Janovszky, Árpád Kovács
Abstract: This research work dealt with production of amorphous powder with nominal composition of (Cu55Zr45Al10)97Hf3 (at%). Combining the mechanical milling and alloying, powder of crystalline Cu-Zr-Al alloy mixed with Hf elemental powder were milled in order to produce a homogenous and amorphous alloy powder The master alloy and the powders milled for different time were analyzed by X-Ray Analysis (XRD) and Scanning Electron Microscopy (SEM). Particle size distribution and hardness were controlled during milling and at the end of procedure. The milling caused dissolving of the hafnium. The 25 h milling time was the optimal to obtain the Hf containing powder with amorphous structure. However, elemental Hf traces with size below 3 µm were still observed in the powder. After 50 h of milling, such impurity elements as iron, nickel, chromium originating from milling tools (vial, balls) were detected.
Authors: Erzsebet Nagy, Márton Benke, Árpád Kovács, Valéria Mertinger
Abstract: The crystallographic orientation relations of phases forming during the martensitic transformation determine the properties of alloys. In TRIP/TWIP steels, the circumstances of thermomechanical treatment (e.g. temperature, deformation) define the forming of martensites of different origins. Due to the thermomechanical treatment, thermally induced martensite (εTH), strain induced martensite (εD) and α’ martensite phases are present in the samples besides the austenite. The proportion of martensites in the sample is defined by the parameters of treatment. The thermally and strain induced martensites which are simultaneously present in the alloy at room temperature can be differentiated by the orientation relations.The martensitic transformations were followed by different methods in FeMn alloys with different Cr content. The macroscopic crystallographic anisotropy was measured by X-ray diffraction method; the microscopic one was examined by EBSD. The cognition of phenomenon observed in the texture image in different scales helps determine the possible origin of martensites.
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