Mária Svéda

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

CuZrAl Amorphous Alloys Prepared by Casting and Milling

Several preparation methods are available for the production of amorphous alloys. During the experiment described in this paper (Cu58Zr42)100-xAlx (x = 0-14,8; in at%) amorphous alloys were prepared by casting and ball-milling. The ingots were produced by arc melting. Wedge-shaped samples were prepared from the ingots by centrifugal casting into copper mould. The microstructures of these samples were defined by SEM. The amorphous samples were analysed by DSC and the activation energy of the crystallization processes was calculated from the measured temperatures. The master alloys of identical composition were milled by ball-mill for different periods of time. The powders were analysed by XRD in order to define the amorphous fractions.

The effect of rotating magnetic field on the solidified structure of Sn-Cd peritectic alloys

The peritectic alloys, such as some types of steel, Ni-Al, Fe-Ni, Ti-Al, Cu-Sn, are commercially important. In contrast to other types of alloys, many unique structures (e.g. banded or island ones) can form when peritectic alloys are directionally solidified under various solidification conditions. It can be observed in the course of the directional solidification experiments performed in a rotating magnetic field (RMF) that the melt flow has a significant effect on the solidified structure of Sn-Cd alloys. This effect was investigated experimentally for the case of Sn1.6 wt% Cd peritectic alloy. For this purpose, a Bridgman-type gradient furnace was equipped with an inductor, which generates a rotating magnetic field in order to induce a flow in the melt. As a result, the forced melt flow substantially changes the solidified cellular microstructure. The cell size and the volume fraction of the primary tin phase were measured by an image analyzer on the longitudinal polished sections along the entire length of the samples. The microstructure was investigated by scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS).

Analysis of Cu-Zr-Ag Amorphisable Alloys Produced by Centrifugal Casting

Bulk Metallic Glasses (BMGs) have been widely investigated due to their excellent physical and chemical properties [1]. The copper based BMG occupies a special place in the family of BMGs since they are relatively low priced. The Cu-Zr-Ag ternary system has been examined on the basis of the ternary phase diagram [2]. We have changed the concentration of the alloys from the Cu58Zr42 to the concentration of the deep eutectic point. Wedge-shaped samples have been cast from the master alloys by centrifugal casting into a copper mould, consequently analyse the influence of the cooling rate on the crystallization. The cooling rate has been estimated from the secondary dendrite arm distances by using a Cu-Sn crystalline alloy. Near the tip of the wedge the samples were amorphous and near the base of the wedge the samples were fully or partially crystallized. The structures of the samples have been characterized by scanning electron microscope and X-ray diffraction.

Developing Mechanical Properties and Electrical Conductivity of Cu Alloys by Jominy End-Quench Test

Copper alloys have many properties, which make them suitable in wide-ranging applications in all the engineering industries. For the investigated alloys the most important properties are hardness, strength and electrical conductivity. Precipitation hardenable alloys were studied by Jominy end-quench test, in order to examine the change of hardness, electrical conductivity and microstructure as a length of the test bar (i.e. cooling rate). In the first step samples were solution treated at different temperatures, then water quenched followed by aging. Cold-work after quench was applied in some alloys and improve in the properties was clearly seen. The following Cu-alloys were investigated: Cu-Co-Ni-Be, Cu-2Be-Ni and Cu-2Ni-Be.

Phase Transformation and Morphology Evolution of Ti50Cu25Ni20Sn5 during Mechanical Milling

Nanocrystalline/amorphous powder was produced by ball milling of Ti50Cu25Ni20Sn5 (at.%) master alloy. Both laser diffraction particle size analyzer and scanning electron microscope (SEM) were used to monitor the changes in the particle size as well as in the shape of particles as a function of milling time. During ball milling, the average particle size decreased with milling time from >320 µm to ~38 µm after 180 min of milling. The deformation-induced hardening and phase transformation caused the hardness value to increase from 506 to 779 HV. X-ray diffraction (XRD) analysis was used to observe the changes in the phases/amorphous content as a function of milling time. The amount of amorphous fraction increased continuously until 120 min milling (36 wt % amorphous content). The interval of crystallite size was between 1 and 10 nm after 180 min of milling with 25 wt % amorphous fractions. Cubic Cu(Ni,Cu)Ti2 structure was transformed into the orthorhombic structure owing to the shear/stress, dislocations, and Cu substitution during the milling process.

Development of Amorphous and Microstructured Surface Layer by Laser Surface Treatment

The aim of the research was to develop an amorphous and microstructured layer on non-amorphous alloys by laser surface treatment. The as-prepared Cu based master alloy ingots were imbedded in a metallic sinking with Wood metal to assure the good thermal conductivity during the laser treatment. The laser remelting, alloying and coating techniques were applied from the laser surface treatment techniques. The surface layer production and a subsequent rapid cooling were performed using CO2 laser and pulse and continuous modes of Nd:YAG laser. The characterization of the microstructure of the resulting surface layer was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Actual remelting on substrates showed that the process of laser remelting is a suitable technique for production of metallic glasses as surface layers. The amorphous layer up to 250 m in depth can be produced by laser surface remelting on Cu46Zr42Al7Y5 alloy.

New bulk glassy alloys in Cu-Zr-Ag ternary system prepared by casting and milling

The thermal stability, crystallization behaviour and glass forming ability of Cu-Zr-Ag system have been investigated on the basis of a ternary phase diagram. We altered the concentration of the alloys from the Cu58Zr42 to the concentration of the deep eutectic point of the Cu-Zr-Ag ternary system and we calculated the glass forming ability parameters. This paper summerises the results of the procedure during which Cu-Zr-Ag amorphous alloys with different Ag content (0-25%) were prepared by casting and ball-milling. Wedge-shaped samples were prepared from the ingots by centrifugal casting into copper mold. The supercooled liquid region (ΔTx) exceeded 75K. Following the characterization of the cast alloys, master alloys of identical composition were milled in a Fritsch Pulverisette 2 ball-mill. The powders, milled for various periods of time were analysed by XRD in order to define the amorphous fraction.