Viktória Rontó

Investigation of new type Cu-Hf-Al bulk glassy alloys

In the last years new type Cu-Hf-Al ternary alloys were developed with high glass forming ability and ductility. The addition of Al to Cu-Hf alloys results in improvements in glass formation, thermal stability and mechanical properties of these alloys. We have investigated new Cu-based bulk amorphous alloys in Cu-Hf-Al ternary system. The alloys with Cu49Hf42Al9, Cu46Hf45Al9, Cu50Hf42.5Al7.5 and Cu50Hf45Al5 compositions were prepared by arc melting. The samples were made by centrifugal casting and were investigated by X-ray diffraction method. Thermodynamic properties were examined by differential scanning calorimetry and the structure of the crystallising phases by scanning electron microscopy. The determination of liquidus temperatures of alloys were measured by differential thermal analysis.

The effect of the cooling rate or the local solidification time and composition on the secondary dendrite arm spacing during solidification PART II: Al—Mg—Si alloys

In our previous work1 Al—Cu—Si alloys were investigated by DTA method and the secondary dendrite arm spacing was written as a function of the composition. The same method of examination was carried out on Al—Mg—Si alloys and is reported in this work. The evaluation was done in the same way and as a result, the secondary dendrite arm spacing can be written by these two equations:

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.

Investigation of secondary dendrite arm coarsening of Al-Cu-Si alloy

Changing of dendritic structure was investigated during isothermal coarsening. A simple equation λ m 2 - λ m 2.0 = K.(t-t 0 ), describes the isothermal coarsening. In this equation λ 2.0 was determined by interrupted solidification than m and K were calculated by Csebisev approximation method The average coarsening parameter was calculated by the method of Tensi and Fuchs and was compared with our results.

Characterization of the Solidifying Microstructure in Ti60(NixCu40-x)40 Alloys

Ti60(NixCu40-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.

Microstructure and Phase Analysis by TEM in Cu-Hf-Ti Alloys

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.

Investigation of solidification behaviour in Cu-based Cu-Hf-Ti alloy system

Solidified microstructures and phases have been investigated at three compositions in the Cu-Hf-Ti alloy system The examined compositions were found to be the best glass formers in the ternary Cu-Hf-Ti system. However, neither the stable phases that are suppressed by the amorphous phase during rapid quenching, nor the solidifying structure have been in the focus of interest. Phases and the solidifying structures formed at different cooling rates (5 K/min, ~150 K/s) were examined for different compositions. Solidification sequence, morphology of the phases, and phase analyses were performed by SEM-EDX, XRD and thermal analyses (DSC).

Investigation of the Solidified Structure of Cu-Hf-Ti Alloys

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.

Structural and thermal properties of Cu-Hf-Ti bulk amorphous alloys

Cu-Hf-Ti amorphous alloys are high strength and wear resistant materials. Master alloys of Cu57.5Hf27.5Ti15 and Cu57.5Hf25Ti17.5 ternary alloys have been prepared by arc melting, and wedge and rod shaped samples have been cast by centrifugal casting. Liquidus and solidus temperatures of the alloys were determined by DTA. The fully amorphous size was determined by X-ray diffraction. Thermodynamic properties of the amorphous alloys were studied by DSC measurements and Kissinger analyses were performed.