Papers by Author: Kinga Tomolya

Abstract: The effect of Ni or Zr addition to Ti-Cu alloy was studied on the microstructure evolution during mechanical milling regarding to dependence of the amorphous transformation on the various composition elements. The microstructure of initial crystalline alloys and the remained phases after few hours of milling were investigated. The milling process lasted to the full amorphization of the powders. The results show that amorphous Ti₄₈Cu₄₂Ni₁₀ and Ti₄₈Cu₄₂Zr₁₀ powders are obtained after 13 h and 14 h of milling.

Abstract: The effect of nickel addition was studied in the CuZr system creating alloys with near eutectic composition. Nickel and aluminum have been regarded as useful elements to improve the plasticity, thermal stability of the CuZr-based amorphous alloys. Cu₄₉Zr₄₅Al₆ and (Cu₄₉Zr₄₅Al₆)₉₅Ni₅ were selected because of the good glass-forming ability. After 15 h of milling the structure of the powders was amorphous based on the XRD analysis. By adding nickel, the crystallization temperature (T_x) shifted to higher temperatures compared to CuZrAl alloy. The value of supercooled liquid region was 64 K, which means CuZrAl has a comparatively high glass forming ability.

Abstract: The Cu-Zr-Ag system is characterized by a miscibility gap. The liquid separates into Ag-rich and Cu-Zr rich liquids. Yttrium was added to the Cu-Zr-Ag and Cu-Zr-Ag-Al systems and its influence on liquid immiscibility was studied. This alloying element has been chosen to check the effect of the heat of mixing between silver and the given element. In the case of Ag-Y system it is highly negative (-29 kJ/mol). The liquid becomes immiscible in the Cu-Zr-Ag-Y system. To the effect of Y addition the quaternary liquid decomposed into Ag-Y rich and Cu-Zr rich liquids. The Y addition increased the field of miscibility gap. An amorphous/crystalline composite with 6 mm thickness has been successfully produced by liquid-liquid separation based on preliminary calculation of its composition. The matrix was Cu₃₈Zr₄₈Al₆Ag₈ and the crystalline phases were Ag-Y rich separate spherical droplets.

Abstract: This research work dealt with production of amorphous powder with nominal composition of (Cu₅₅Zr₄₅Al₁₀)₉₇Hf₃ (at%). Combining the mechanical milling and alloying, powder of crystalline Cu-Zr-Al alloy mixed with Hf elemental powder were milled in order to produce a homogenous and amorphous alloy powder The master alloy and the powders milled for different time were analyzed by X-Ray Analysis (XRD) and Scanning Electron Microscopy (SEM). Particle size distribution and hardness were controlled during milling and at the end of procedure. The milling caused dissolving of the hafnium. The 25 h milling time was the optimal to obtain the Hf containing powder with amorphous structure. However, elemental Hf traces with size below 3 µm were still observed in the powder. After 50 h of milling, such impurity elements as iron, nickel, chromium originating from milling tools (vial, balls) were detected.

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: In this paper CuZrAl amorphous alloys with different Al content were prepared by centrifugal casting. The master alloy ingots were prepared by arc melting the mixture of the constituents on a water cooled copper boat in argon atmosphere. Wedge-shaped samples were prepared from the ingots by centrifugal casting into copper mold. The microstructure of the samples was examined by Scanning Electron Microscope (SEM) and the phases were analyzed by X-ray diffractometry (XRD) to define the amorphous fraction.

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: 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: 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.

Abstract: The central problem of producing of Al/SiCP composites is to avoid the forming of brittle Al4C3, which leads to a poor corrosion resistance and degraded mechanical properties [Mingyuan, 1999]. The possible way is the covering of the SiC particles. This paper deals with the covering of SiC. The coated particles will be applied for producing aluminium matrix composites. We have covered three different grain sizes of particles. We have applied the nonelectrolytic method of deposition from solution for coating. Before the covering the surface needs to be catalysed. We have compared the effects of different type of catalysators, then we have analysed the effects of plating time by means of the scanning electron microscopy.