Kinga Tomolya

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.

Evaluation of XRD analysis of amorphous alloys

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.

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.

Ti-Cu-Based Amorphous Powders Produced by Ball-Milling

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.

Amorphization of CuZr Based Alloy Powders by Mechanical Milling

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 (Tx) 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.

Designing Amorphous/Crystalline Composites by Liquid-Liquid Phase Separation

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.

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.

Copper Coating by Electroless Process for Aluminium Matrix Composite

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.

Hf particles reinforced Cu-Zr-Al amorphous powder produced by milling

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.