Papers by Author: Enikő Bitay

Abstract: In case of traditional surface-hardening processes (e.g. carburization), the wear resistance usually correlates with hardness, which means optimising these technologies could be based on testing the achieved hardness. In case of modern laser treatment technologies however – e.g. surface melting combined with surface alloys or laser scanning surface treatment followed by nitridation – it is unlikely to conclude wear resistance from the value of hardness. The reasons are the following: the hardness of surface melting combined with surface alloys (especially if alloyage is made using high hardness compound powders) depends on the remelting of the material and the particle size and distribution of the dispersed alloy. These same properties define wear resistance, but the values don’t necessarily correlate. In case of a compound phase dispersion in a softer base material, we can have outstanding wear resistance with moderate hardness. (e.g. bearing metals) The case is similar with scanning treatment combined with nitridation, which results in complicated structures. Due to the above, it is possible that in order to optimise these aforementioned technologies, we have to rely on examining wear resistance. In order to back this statement, we show the results of two typical experiments concerning these technologies.

Abstract: In several fields of materials science space-filling polyhedral systems are generally used for modeling and characterizing the microstructure of polycrystalline and cellular materials. In this paper a simple quantitative method designated to classify 3D triply periodic, space-filling, cellular systems is outlined. The concept of the proposed method is based on the known analogy between the combinatorial structure of 3D space-filling polyhedral systems and of 4D polytopes. For classification purposes various topological shape indices are defined and tested. It is demonstrated that using two appropriately selected shape factors (asymmetry and compactness coefficients) a global combinatorial classification of cellular systems can be performed.

Abstract: In recent years, several attempts have been made to characterize the geometric structure of fullerenes by means of topological shape factors in order to predict their physical properties and stability. In this paper, we present a simple method to estimate the stability of fullerenes on the basis of quantitative topological criteria. This approach is based on the concept of the generalized combinatorial curvatures defined on the set of simple graphs embedded on a closed surface without boundary (sphere, torus, projective plane, Klein bottle). It is shown that starting with the computed generalized combinatorial curvatures several novel topological indices can be generated. From computations performed on a set of C40 and C60 fullerenes, we concluded that the four topological shape factors tested (Λ(-1), (-1), Λ(1) and (1)) could be successfully used to preselect the most stable fullerene isomers.

Abstract: The laser surface-treatment methods have been quickly developed by appearing of lasers with high power beam and can increase the hardness, of the surface. A very hard, wear-resisting layer can be produced by the dispersing of ceramic grains. The essence of the technology is, that such a material (compound-phase, e.g.: metal-oxide, carbide, nitride, etc.) is added to the surface layer melted by laser, which does not solve or solves only partly in the metal-melt. This work studies the effect of the different technological parameter (such as, power of the laserbeam, motion speed, amount of the ceramic particles etc.) on the different microstructure accrued during the laser surface alloying. The desired microstructure has homogeneous carbide distribution in the matrix. But it is embarrassed by several conditions. The aim of this present work is to find out the reasons for the inhomogeneous ceramic particle distribution inside the matrix and to discover these embarrassing conditions.

Abstract: The present work aims to analyze the dispersion process (path) of the solid particles by moving a spherical particle from the feeding-nozzle outlet till the penetration of the melted surface (by the laser beam) and then its path in the metal bath. In laser surface treatment technologies with injection of hard particles in the melting bath it is necessary for the particles to work against the surface stress to penetrate through the surface of the bath into the melt. The theory shown was used in precalculations for the experiments carried out dispersing carbide particles (WC, TaC, NbC). Powder of particles of all three types were dispersed by means of the Ar carrying gas into an C15 steel melt by CO₂ laser. Evaluating the results of this process taking into consideration different specific technological parameters (speed of the beam, powder feeding speed) one can conclude that all three carbide types can penetrate into the melt.