Gábor Buza

Formation of Lead Bearing Surface Layers on Aluminum Alloys by Laser Alloying

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.

On the possible mechanisms of porosity formation during laser melt injection (LMI) technology

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.

Development of monotectic surface layers by CO2 laser

The aim of our work was to develop a monotectic surface layer for be arings by using laser surface-treatment technology. Two kinds of laser surface t reatment technology were used. In case of coating-melting technology a Pb layer was first develope d by galvanization, then the Pb layer was melted together with the matrix. In case of powder bl owing technology Bi powder was blown into the layer melted by laser beam, by Argon gas. The struct ure of monotectic surface layer was investigated by light microscope and a scanning electron micros cope. The volume fraction and size distribution of Pb and Bi particles were determined by image-analyzer. Introduction The essence of laser alloying is that only structure and propertie s of the surface layer of specimen are changed, the structure and properties of the bulk part remains unchang ed. During development of monotectic surface layer, the surface workpiece is heated to a temperature, where only a single homogenous melt remains, in the system after alloying and then – beca use of good heat-extraction ability of the basic material it is quickly cooled. As a conse quence of the high cooling rate (100010000 K/s), a very fine structure develops during solidification. Experiments Laser experiments were performed in the Bay Zoltán Institute of Materials Science and Technology using a CO2 laser with a power of 5 kW. The basic alloy was an Al-11Si eutec tic type alloy. The thickness of specimen was 15 mm and the surface area treated by the laser was 15x130 mm . Two kinds of technologies were used for surface treatment [1-4]. Duri ng the two-step technology (melting of the coating) (Fig. 1) a Pb layer having a thickness of 0.1 mm was taken to the surface by galvanizing, then the Pb layer was melted together with the basic material by using different laser power (2, 2.5, 3, 3.5 kW). The sample was shifted by a scan velocity of 300 mm /min. During the treatment, 8 melted bands were with 50% overlap. Diameter of the foc us was 2 mm. Samples were coated with graphite before treatment to increase the low absorption of aluminium. During the one-step (powder-blowing-in) technology (Fig. 2) Bi grains w ith a diameter of 40-60 μm were blown into the molten layer. The protecting gas was Ar and the laser power wa s chosen (2, 2.5, 3, 3.5 kW). The sample scan velocity was 300, 600 and 900 mm/min respectively. Fi bands were melted on each sample with an overlap of 50%. Materials Science Forum Online: 2003-01-15 ISSN: 1662-9752, Vols. 414-415, pp 147-152 doi:10.4028/www.scientific.net/MSF.414-415.147

Wetting properties of Nd:YAG laser treated copper by SAC solders

Purpose This paper aims to discuss the effect of surface treatment on the wettability between copper and a lead-free solder paste. The industrial applications of laser technologies are increasing constantly. A specific laser treatment can modify the surface energy of copper and affect the wetting properties. Design/methodology/approach The surfaces of copper plates were treated using an Nd:YAG laser with varying laser powers. After laser surface treatment, wetting experiments were performed between the copper plates and SAC305 lead-free solder paste. The effect of laser treatment on copper surface was analysed using optical microscopy and scanning electron microscopy (SEM). Findings The experimental results showed that the wetting contact angles changed with the variation in laser power. Furthermore, it means that the surface energy of copper plates was changed by the laser treatment. The results demonstrated that the contact angles also changed when a different soldering paste was used. Originality/value Previous laser surface treatment can be a possible way to optimize the wettability between solders and substrates and to increase the quality of the soldered joints.

A Comparative Examination of the Friction Coefficient of two Different Sliding Bearing

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.

Tribological Investigations of Parts Sintered and Coated by Laser Beam

In this work we intend to investigate the surface properties of laser sintered and coated parts, by measurement of friction coefficient and wear rate. The main aim of this research is to justify laser sintered prototype tools for injection molding of fibre-reinforced polymers. For increase of wear resistance we used hard Co-based and Fe-based coatings on laser-sintered phosphorous bronze and unalloyed steel substrate. Short carbon- and glass-fibre-reinforced polymers were used as counter bodies. For the tribological laboratory model tests a pin-on-disk test rig was used. In case of coated parts – with higher wear resistance – we used a cylinder-on-cylinder tribometer. The tribological properties were determined at different load conditions. Our results show that the friction coefficient and wear resistance of laser treated surfaces are good. The coefficient of friction of coated specimens is slightly less, but the wear rate is significantly less.

Superficial remelting of cast iron by laser radiation

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.

The Effect of Laser Beam Welding Parameters onto the Evolving Joints Geometry

In our research the effect of a new type of laser beam parameters during the laser welding have been investigated with 80 different welding parameters. The laser welding parameters such as the laser power, laser beam spot size on the surface and feed rate greatly affect the resulting weld geometry. S235 grade steel has been used. The operating equipment was a Trumpf 4001 4 kW disk laser with a diameter of 100 microns optical fiber. The effect of different welding parameters were evaluated from the metallographic cross-section of the welded joints. This article describes the effect of the different laser beam focusing and the welding feed rate.

Residual Stress in Plain Carbon Steel Induced by Laser Hardening

Technological residual stresses have great importance in the manufacturing processes and the lifetime of components. The residual stresses formed by quenching can be very diverse because of its multiple sources. Alternative quenching processes such as laser hardening have a great potential for different applications. The direction of heat transfer during laser hardening is the opposite compared to conventional quenching. This further increases the complexity of the developed stress state. The residual stress profile and the microstructure formed by laser hardening treatment are investigated in the present manuscript.

In Situ Synthesis of a Wear Resistant Layer on the Surface of Low Carbon Steel Produced by Laser Melt Injection Technology

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.