Alexander Katz-Demyanetz

Bulk metallic glass formation in the Mg–Cu–Y system

Abstract The influence of the cooling rate on 80Mg–15Cu–5Y was investigated. Four different cooling rates yielded different microstructures that were characterised by means of X-ray diffraction (XRD), SEM, high-resolution SEM, energy dispersive spectroscopy chemical analysis, TEM and high-resolution TEM. The different casting procedures were gravity castings of 3 mm diameter specimens into a copper mould held at different temperatures (cooled to −195°C with the aid of liquid nitrogen, held at room temperature and heated to 300°C) and melt spinning. Only the melt spun specimen yielded what appeared to be an amorphous XRD spectrum; however, a detailed TEM analysis showed that this specimen was characterised by a micro- or even nanocrystalline rather than amorphous structure.

Microstructure, Tensile and Creep Properties of Ta20Nb20Hf20Zr20Ti20 High Entropy Alloy

This paper examines the microstructure and mechanical properties of Ta20Nb20Hf20Zr20Ti20. Two casting processes, namely, gravity casting and suction-assisted casting, were applied, both followed by Hot Isostatic Pressing (HIP). The aim of the current study was to investigate the creep and tensile properties of the material, since the literature review revealed no data whatsoever regarding these properties. The main findings are that the HIP process is responsible for the appearance of a Hexagonal Close Packed (HCP) phase that is dispersed differently in these two castings. The HIP process also led to a considerable increase in the mechanical properties of both materials under compression, with values found to be higher than those reported in the literature. Contrary to the compression properties, both materials were found to be highly brittle under tension, either during room temperature tension tests or creep tests conducted at 282 °C. Fractography yielded brittle fracture without any evidence of plastic deformation prior to fracture.

Microstructural Evolution and Phase Formation in 2nd-Generation Refractory-Based High Entropy Alloys

Refractory-based high entropy alloys (HEAs) of the 2nd-generation type are new intensively-studied materials with a high potential for structural high-temperature applications. This paper presents investigation results on microstructural evolution and phase formation in as-cast and subsequently heat-treated HEAs at various temperature-time regimes. Microstructural examination was performed by means of scanning electron microscopy (SEM) combined with the energy dispersive spectroscopy (EDS) mode of electron probe microanalysis (EPMA) and qualitative X-ray diffraction (XRD). The primary evolutionary trend observed was the tendency of Zr to gradually segregate as the temperature rises, while all the other elements eventually dissolve in the BCC solid solution phase once the onset of Laves phase complex decomposition is reached. The performed thermodynamic modelling was based on the Calculation of Phase Diagrams method (CALPHAD). The BCC A2 solid solution phase is predicted by the model to contain increasing amounts of Cr as the temperature rises, which is in perfect agreement with the actual results obtained by SEM. However, the model was not able to predict the existence of the Zr-rich phase or the tendency of Zr to segregate and form its own solid solution—most likely as a result of the Zr segregation trend not being an equilibrium phenomenon.

Manufacturing of Aluminum Metal Matrix Cast Composites with Carbon Based Additives for Thermal Management Applications

This work focuses on the production of new high conductive carbon based MMC (Metal Matrix Composites) or co-cast components obtained by casting processes. These novel thermally conductive structures are designed to face modern heat management challenges in critical fields such as power micro-electronics, automotive and aerospace industries, renewable energy generation as well as highest performance combustion engines. The sought parts will be assembled by different heat conductive aluminum-carbon composites and for this reason different heat conductive MMCs have been studied. Their combination into once cast aluminum part may allow the part to meet applicative needs for heat management challenges. The cast production routes as well as thermal behavior of the obtained materials has been studied by means of numerical (Finite Element Methods) approaches in order to determine the effective thermal conductivity in the different directions of heat dissipation. Some kinds of casting methods have been FEM simulated and then performed practically. TPG/aluminum interface microstructure has been studied.

Aluminum/TPG Metal Matrix Composite with Improved Thermal Conductivity

Thermal pyrolytic graphite (TPG) is a material with two-dimensional thermal conductivity of about 1500 W/m·K, which is four times higher than the most thermal conductive metals such as silver (429 W/m·K) and copper (401 W/m·K). This property may enable the usage of TPG’s thermal potential to develop highly thermally conductive composites for devices requiring effective thermal management. In cases of the implementation of TPG parts in liquid metal phases, improvement of aluminum/TPG wetting becomes a main technological task. Obviously, better wetting will result in higher thermal properties of the obtained MMC. In the present research we study the effect various casting techniques as well as various aluminum alloys have on aluminum/TPG interface. Another issue we deal with in this research is the effect of various geometrical designs of TPG on the thermal properties of the MMC.