Materials Science Forum Vols. 473-474

Abstract: In the heart of Budapest, an ensemble of nearly 40 large size bronze statues and reliefs were restored in the years of 1995 – 2002. In this paper it is shown, how the achievments of materials science were used to restore the original look and ensure long term integrity of the monument.

Abstract: At the beginning of the third millennium, the world’s annual steel production reached 900 million tons. Flat products account for the majority of the production. It is also known that around three times the amount used today would be needed if the mechanical properties of the steels produced would have stagnated on the level characteristic of the 1930s and 40s. The history of the development and production of HSLA steel in Hungary dates back to the beginning of the 1960s. For the construction of the new Erzsébet Bridge, research workers at Danube Steelworks and at Steel Industry Research Institute developed the Ti micro-alloyed steel MTA50. In the study, we will summarise the history of the development of steels of the 700MPa strength category, thereafter we will introduce the main features of the project running within the scope of the National Research and Development Programme aimed at the development of DP- and TRIP-steels, and we will finally report on the results of the first year of the three-year project.

Abstract: In the present paper the chemical interaction between an alumina plate and a one-phase NaCl-KCl-K2TiF6 as well as two-phase NaCl-KCl-K2TiF6/Ti system has been studied experimentally at 700 oC during 2 hours, as function of K2TiF6 content of the melt. In all experiments the reaction product TiO2 of an exchange reaction has been found at the surface of the alumina plate. Its thickness changes through a maximum point as function of the K2TiF6-content of the melt, as a result of the competition of two processes: the exchange reaction leading to the formation of the TiO2 layer, and its dissolution in the melt.

Abstract: A rarely applied technology of surface modifications is the remelting of surfaces by a laser beam. This is so because in the case of laser remelting of surfaces, similarly to other processes used in production, such a competitive alternative surface modification technology is searched for in which the value in use of the component with new properties created by the new procedure is in proportion with the costs and time requirement needed for its production. According to such a point of view, a laser remelting of a surface is in general not worth applying this expensive technology, since the change, the improvement in the properties as a result of remelting is not sufficiently large. However, the laser remelting of cast iron surfaces represents a specific case, since the nature of the surface of this relatively cheap (as compared to cast steel) material of advantageous properties can be changed significantly by this technology. In addition, by the treatment with laser beam, an extraordinarily particular material structure unknown in mass production can be developed. This is why we turned our attention to the specificities and properties of this structure formed during laser beam treatment of cast iron surfaces.

Abstract: A laser rapid-alloy-prototyping technique, was used to produce a number of alloys with compositions lying in the Fe-rich corner of the Fe-Cr-C system. These alloys were prepared in the form of thick coats deposited on a carbon steel by variable powder feed rate laser cladding. The microstructure of the alloys was analyzed by SEM and their mechanical properties were evaluated by microhardness tests, ball-cratering micro-scale abrasive wear tests and scratch tests. Although a poor correlation between the hardness of the alloys and their wear behavior was observed, the correlation between their wear resistance and the fab factor, measured from the scratch tests, is acceptably good. These results are discussed and analyzed on the basis of the microstructural characteristics of the alloys.

Abstract: Short fiber (basalt, carbon, ceramic, and glass) reinforced polypropylene hybrid composites were investigated to determine their mechanical properties in case of different reinforcing fiber types. The composites were reinforced with fibers and were produced by hot pressing after hot mixing techniques. Composite properties such as flexural strength, stiffness, static and dynamic fracture toughness were measured. It was realized that the main damage modes of the composites are fiber pullout and debonding. It was also found that basalt fibers are the most sensitive to the lack of the treatment with additives. These results were supported by scanning electron micrographs taken of the fracture surfaces.

Abstract: CVD diamond layers are often used as protective layers. One of the most important of these applications requires pinhole-free layers to protect against fluid materials, such as found in chemically aggressive environment. These pinholes are present even in very good quality CVD diamond films. In this work we combined the Pulsed Laser Deposition (PLD) technique with Microwave assisted Chemical Vapor Deposition (MW-CVD). We used CVD diamond films prepared under different conditions and layer thicknesses. Both of these proceses produced inperfect protective layers, but we proved that a PLD DLC film over the diamond layer does reduce the number of pinholes in the coating. We used special chemical alcaline etching to detect the remaining pinholes, and to test the corrosion protective properties of the layers. As a result we were able to prepare samples of 1 x 1cm2 with only 0.2 micron thickness without any pinholes, while in CVD diamond layers a thickness of 2,5 micron was needed for the same level of compactness.