Papers by Author: Jenő Sólyom

Abstract: Ti₆₀(Ni_xCu_40-x)₄₀ x = 5 - 40 at% ternary alloys were prepared by arc-melting followed by a centrifugal casting into a wedge-shaped copper mould in order to examine glass forming of these compositions. Microstructure of the master alloys and wedge-shaped samples were studied. Among the master alloys, which solidified under non-equilibrium conditions, the sample with 15 at% Ni content displayed clear eutectic structure and its wedge-shaped sample had the finest structure but still crystalline. Microstructure of the other compositions was far from amorphous state.

Abstract: There is an active research work in the field of amorphous alloys since the discovery of metallic glasses, half a century ago [. In contrast with crystalline alloys, amorphous one have unique material properties, e.g. high yield strength, superior elastic limit, high corrosion resistance, unique acoustical properties [2,. Producing amorphous alloys, it is first necessary to quantify the forming of structure and define the amorphous amount. All of the methods to determine the structure have advantages and disadvantages. An accurate determination of amorphous volume fraction can be accomplished by transmission electron microscopy (TEM), this observation is much localized [ and the evaluation is difficult. The most common techniques to determine the amorphous fraction are XRD and DSC methods, which reflect the entire sample [. However, XRD has a detection limit depending on the type of equipment. Apart from this fact, it is an admitted method in researches, if the XRD reflexion shows an amorphous halo. Amorphous fraction transformed to crystalline can be measured by DSC. This method is much sensitive to impurities, especially oxygen, which can influence on the results.

Abstract: There are no data about the equilibrium phases in the Cu-Hf-Ti system, in the Cu-rich corner which is a glass former region. Phases and solidifying microstructures were examined in the master alloy (cooling rate: ~150 K/s) and in slowly cooled (5 K/min) samples in case of different compositions. Unknown ternary phases were found by SEM and XRD analysis and one of them with the highest Ti content could be identified by TEM study.

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: Cu-Hf-Al alloys are considered to be relatively new ones among Cu-based bulk amorphous alloys. Cu-Hf-Al alloys have high strength in amorphous state and this property makes many applications feasible for the industry. During the production of amorphous alloys the most important purpose is to produce them in the biggest diameter to make them suitable for a wide range of applications. The circumstances of the production process have a great influence on the developing structure. In the present work solidification of Cu-Hf-Al alloys were investigated. The alloys were cast into different shapes with different Al contents with special regard to the appearance of the amorphous/crystalline structure. The appearance and the structure of crystalline phases were determined by X-ray diffraction and X-ray, DSC and metallographic measurements were used to investigate the developing structure.

Abstract: 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.

Abstract: The comparison of the phase transformations going on due to high energy ball milling (HEBM) and produced by pressure-less Direct Metal Laser Sintering (DMLS developed by EOS company) was carried out, by using an α-Fe, Ni and Cu3P powder mixture. It could be shown by X-ray diffractograms (XRD) of the two type of products, that by mechanical alloying a similar phase transformation occurs due to solid state reactions between the metal partners as in the case of laser sintering, in a given range of laser scanning speed in a laboratory laser equipment. According to the XRD evaluation the same metastable, γ-steel like phases were formed.

Abstract: Recently one of the most significant research-field in the development of amorphous alloys is the research of the Cu-based amorphous alloys. The Zr-based alloys developed earlier can be replaced by the newly developed Cu-based alloys as the high price of the Zr-based alloys limits their utilization in spite of their favourable properties. Production of Cu-based alloys having the same or more favourite properties than Zr-based alloys is cheaper and this fact can promote their increasing utilization. Cu-Zr-Ti and Cu-Hf-Ti alloy systems – they are Cu-based alloys – have excellent mechanical properties. In this paper investigations of crystallization of amorphous Cu44,25Zr36Ag14,75Ti5 powder produced by ball milling (these processes have not been investigated yet according to the reference data) are described. In the course of investigation of the crystallization process, samples were heated to a temperature of investigation by means of a DSC equipment and the developed state was frozen by chilling. The investigation of the developed structure and to identify the phases formed during heat treatment, X-ray diffraction method was used.

Abstract: Results of the X-ray diffraction (done by computer quantitative phase analysis) and metallographic miscroscopy (colour etching and computer image analysis) inspections aimed at determining the residual austenite content of modern TRIP steel sheets produced at Dunaferr.

Abstract: The devitrification of the Fe-Ni-B-Si amorphous ribbon was investigated by the differential scanning calorimetry (DSC) with scanning and isothermal methods. The devitrification of rapidly quenched ribbons is a multilevel process. On the basis of DSC investigations it was determined that crystallization occurs in three processes up to 700°C in the Fe40Ni40B16Si4 alloy. In the present work the first and second steps have been discussed. The first crystallization step involves the segregation of the Fe-Ni crystalline solid solution from the amorphous matrix. During the second crystallization phase, in addition to austenite, nickel silicide and two types of iron borides crystallize as well. The ribbons were relaxed at 380°C for 2 hours, following the pre-annealing at different temperatures. Pre-annealing was performed in the DSC within the temperature range elapsing from 395°C to 420°C. The preannealing at temperatures below the first exothermal DSC peak has an effect on the crystallization processes. After the pre-annealing the samples were investigated by DSC. The DSC peak of the first crystallization step shifts to higher temperatures and decrease its enthalpy. The scanning DSC measurements, applied after the isothermal pre-annealing, were performed in order to determine the fraction of the ribbon transformed in the primary crystallization step. The second DSC peak shifts to lower temperatures with a maximum of 4°C. The X-ray diffraction (XRD) analyses reveal that the lattice constant changes with the pre-annealing temperatures. Such observation was also supported by the circumstance that the composition of the Fe-Ni solid solution undergoes certain modifications.