Papers by Author: Viktória Rontó

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 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: 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: Master alloys with different compositions of the Cu-Hf-Ti alloy system were prepared by arc-melting. The pieces were then cast into a wedge- and rod – shaped Cu mould by centrifugal casting. The different mould shapes generated various cooling conditions and produced various microstructures in the samples. Moreover due to the wedge shape, the change of the microstructure can be observed within the samples. The wedge samples became amorphous in 1-1.5 mm thickness, and dendritic structure formed in the thicker parts. The change in the microstructure in the rod samples along the radius can be studied as well. The solidified phases were also investigated by X-ray diffraction and SEM-EDAX.

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.