Papers by Author: Gábor Buza

Abstract: Composites of ceramic particle reinforcement (such as alumina) have potential for high temperature structural applications. In contrast to conventional processing methods (e.g. mechanical alloying), in situ processing techniques can be inexpensive and can also lead to unique microstructures, such as very fine dispersions of the reinforcements or interconnecting phases. The feasibility of processing Fe/Al₂O₃ composites layer by an in situ displacement reaction between Fe₂O₃ and Al by using laser beam pre-experiments were carried out and the results are presented in this paper.

Abstract: Titanium and its compounds are one of the most frequently used reinforcing particles in iron ceramic composite materials. These materials have special characteristics because they are quenchable, their hardness can be increased by heat treatment and they can be quite easily machined. The point of the technology developed in the Bay Zoltán Institute of Materials Sciences and Technology is to form the reinforcing layer on the surface of the sample in an in situ way by melting the surface of the low carbon steel and the laminar carbon felt using laser beam while the titanium metal powder is simultaneously added to the melt. Several methods (metallographic examinations, selective area hardness measurements, SEM, and XRD) were applied to answer the questions about the optimal conditions for the in situ synthesis of a wear resistant layer.

Abstract: In the steel-work the rolled coils of low carbon steel plates must be unended before pickling on the continuous mill. This was solved with butt welded joint by laser beam welding at ISD DUNAFERR Dunai Vasmő ZRt. The 8 kW light power, near TEM00 mode laser beam’s final part of optical system is a divided parabolic mirror, which creates two focal spot in the welding region. In the interest of productivity rising, the rolled bands’ ends have to be welded at the highest speed as far as possible. The welded seams have to tolerate the repeated bends on the pickling mill without cracking. The optimum parameters of laser welding technology were determined by metallography and calculation of energetic efficiency.

Abstract: In order to perform a continuous cold rolling of steel sheets, hot rolled coils need to be attached to each other in order to get an endless sheet. This process can be achieved by laser key-hole welding as well. The structure and mechanical properties (e.g. hardness) of the welded joint without added metal, as well its heat affected zone differs significantly from the base metal. During our laboratory experiments the aptitude of cold rolling of joints and their environment, as well as the change in the features of materials was analyzed. During the rolling phases the hardness of the joint is higher than the ground structure, the strip thickness is modified depending on the difference of the hardness during the passes. According to our findings, the significant difference in measured hardness profile and texture structure prior to cold rolling and during cold rolling is minimized due to a recrystallisation annealing treatment following the cold rolling procedure. It is obvious that the normalization before cold rolling has advantageous effect to the properties of the welded joint. Elongation of the normalized samples is bigger than elongation of the non normalized samples.

Abstract: The aim of our research was to comparatively examine Ni content surface layers on amorphisable Cu base alloy produced by different laser surface treatments. Laser surface treatment (LST) techniques, such as laser surface melting, laser alloying and laser cladding, provide a wide range of interesting solutions for the production of wear and corrosion resistant surfaces. [1,2] With LST techniques, the surface can be: i) coated with a layer of another material by laser cladding, ii) the composition of the matrix can be modified by laser alloying. [3] Two kinds of laser surface treatment technologies were used. In the case of coating-melting technology a Ni content surface layer was first developed by galvanization, and then the Ni content layer was melted together with the matrix. In the case of powder blowing technology Ni3Al powder was blown into the layer melted by laser beam and Argon gas. LST was performed using an impulse mode Nd:YAG laser. The laser power and the interaction time were 2 kW and 20÷60 ms. The characterization of the surface layer microstructure was performed by XRD, scanning electron microscopy and microhardness measurements.

Abstract: Tungsten (W) based alloy composite layer reinforced with TiC particles has been successfully prepared on unalloyed steel sample by LMI technology. In order to obtain in situ produced TiC reinforcement, pure titanium has been introduced to the melt pool. WC powder was added for increasing the carbon content of the layer in order to avoid the softening of the matrix (with low carbon content) during TiC formation. The present study aims to investigate the optimum amount of injected WC and Ti powder to improve wear resistance and hardness of the layer. Samples were investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The maximum hardness of the layer has been reached ~900HV in case of 2-4wt% of titanium content. Ti has been collected all of the carbon from the matrix when titanium content was 9,6wt%, which resulted that the austenite and (Fe,W)6C phases have been disappeared. Only α-Fe and TiC phases were presented in the layer. The hardness of the layer reduced to the hardness of the base material.

Abstract: In the present study the analysis of 5 different mechanisms of porosity formation during laser melt injection (LMI) technology were performed. Experiments were supported by thermodynamic and fluid-flow analysis. Special attention should be paid to i. clean the surface of the substrate, ii. use inert shielding gas, iii. use proper particle size and gas velocity, iv. use proper laser power and laser beam velocity to control bath temperature and v. deoxidize the surface of the added particles.

Abstract: Diverse technologies in domestic enamelling production for machining, cutting and joining process are applied. The experiments presented in this paper focused on the opportunities of replacement of the drawn tubes built in heat exchangers longitudinal seam pipes produced by DUNAFERR Co. Ltd. The steel grade which satisfies the requirement of two-side enamelling, formability and after-fire sag resistance has been investigated. It has been shown that the coldrolled DC 04 EK-B steel grades stand all demands needed and therefore are able to replace the imported drawn tubes presently used.

Abstract: The aim of the present work is to investigate the microstructure of Al-Pb monotectic surface layers generated by a laser surface alloying technique on the surface of an Al-4Cu-1.5Si-0.5Mg alloy. Monotectic alloys are generally used as materials for sliding bearings. Layers of a monotectic alloy generated by laser surface alloying have a potential for superior properties, because the rapid solidification during this process results in fine precipitation structures which can act as solid lubricant. The structure of the Al-Pb monotectic surface layers was observed in the light microscope and the scanning electron microscope. Volume fraction and size distribution of lead particles were determined by quantitative image analysis. Pin-on-disc experiments were carried out to characterize and compare the tribological properties of the Al-Pb monotecitc layers and cast Al-Cu-Si-Mg alloys.

Abstract: The aim of this research work is to investigate the sliding properties of the monotectic surface layers developed by a laser surface-treatment technology. The coatings-remelting technology has been chosen from the laser surface treatment methods. The surface of Al-Si alloy was coated with a lead layer by galvanizing, then the basic material and the surface layer were remelted together by using laser beam produced a monotectic Al- Pb surface layer. The structure of monotectic surface layer has been determined by means of a light microscope and scanning electron microscope. The sliding properties of the basic material (as cast, nearly eutectic Al-Si alloy), the Al-Si-Pb monotectic surface layer as well as the Al-Cu-Sn sliding bearing (Al-Cu matrix and Sn sliding layer) used in the gas industry have been investigated.