Papers by Author: Michael Zinigrad

Abstract: Supersaturated titanium-aluminum nitride (Ti_1-xAl_xN) is a very attractive material for a wide range of applications due to its high oxidation and wear resistance accompanied by high strength, hardness, thermal conductivity and thermal shock resistance. Currently, its applications are limited to coatings obtained by physical or chemical deposition. Bulk materials based on Ti_1-xAl_xN may be fabricated by powder metallurgy approach using powders synthesized by high-energy ball milling (HEBM), which composition corresponds to supersaturated Ti_1-xAl_xN solid solution. In the present study, thermal stability of the supersaturated Ti_1-xAl_xN solid solution was investigated. According to the quasi-binary TiN-AlN phase diagram, constructed using density functional theory (DFT) analysis, the concentration ranges, where decomposition takes place through spinodal decomposition or through nucleation and growth, were determined. Experimental study on thermal stability of solid Ti_1-xAl_xN solution powder was conducted by means of differential scanning calorimetry (DSC), Brunauer-Emmited-Teller (BET) and XRD. The results indicated that spinodal decomposition of Ti_1-xAl_xN starts at 800°C, while at temperature higher than 1300°C regular decomposition (nucleation and growth) is occur.

Abstract: In recent years, improvement of metals mechanical properties becomes one of the main challenges in materials and particularly in metallurgical industry. Mostly, an alloying process is typically applied to reach metals enhanced performance. This work, however, describes a different methodology, where WC and TiC nanoparticles used as a modifiers and then gas-dynamic treatment (GDT) are applied. These processes were investigated on a hypoeutectic casting aluminum A356 alloy. Microstructural evaluation illustrated that a coarse Al grains were refined as well as eutectic Si particles were formed. Subsequent mechanical properties tests revealed that aluminum elongation enhanced while strength remained unchanged. Addition of WC and TiC enhanced the elongation by 20-60%, depends on the mold area. A combined treatment, using GDT with addition of TiCN nanoparticles showed even improvement in both, elongation and strength by 18 and 19%, respectively. Moreover, based on the electron microscopy studies, this behavior was attributed to a grain-size strengthening mechanism, where a high concentration of grain boundaries serves as dislocation movement blockers

Abstract: Taguchi’s method was applied to investigate the effect of the main HEBM parameters: milling time (MT), ball to powder weight ratio (BPWR) and milling speed (MS) on the dissolved AlN fraction in TiN. The settings of HEBM parameters were determined by using the orthogonal experiments array (OA). The as-received and milled powders were characterized by X-ray diffraction (XRD). The optimum milling parameter combination was determined by using the analysis of signal-to-noise (S/N) ratio. According to the analysis of variance (ANOVA) the milling speed is the most effective parameter and the optimal conditions for powder synthesis are: MT 20h, MS 600rpm, BPWR 50:1. The result of the experiment conducted under optimal conditions (AlN was completely dissolved during experiment) confirmed the conclusions of the statistical analysis.

Abstract: Mechanochemical activation (MCA) of electrode lignin was performed and the activated lignin was studied by IR-spectroscopy for different activation times. The activated lignin was tested for the ability of binding Cr₂O₇^2-, Cu²⁺, Ni²⁺ ions. It was established that structure deformation, which does not distort the stronger hydrogen bond lattice, but leads to the formation of highly developed surface with active functional groups, occurs in the course of MCA. Weaker inter-layer bonds are broken in the activation process and quickly recovered after the load release. The comparison of the sorption capacity of Cr₂O₇^2-, Cu²⁺, Ni²⁺ ions by the MCA treated vs. inactivated lignin for different activation times was performed.

Abstract: Plasma Electrolytic Oxidation (PEO) is a powerful technique allowing hardening and corrosion protection of valve metals due to formation of an oxide layer on the metal surface. The addition of fluoride ions to the alkaline electrolyte for the PEO processing of aluminum and magnesium alloys produces significant changes in the structure and properties of the coating [1-, however the mechanism of these changes is not clear. A study of the influence of the fluoride concentration on the composition, structure and morphology of thin (to 20 µm) PEO layers was performed. The oxide layer thickness on aluminum is significantly smaller than that on magnesium. Fluorine is detected as an amorphous phase in the vicinity of the base metal.

Abstract: The main issue of the study is aluminum A356 alloy modification by TiC nanoparticles process. Nanoparticles of TiC were especially mechanochemically activated to remove the oxide layer on the particle surface in order to prevent its floating on the molten metal surface. Experimental results indicate that after T6 heat treatment the tensile strength of the modified alloy increased by 6.5%, yield strength increased by 9% and the elongation increased by 22%. A high resolution electron microscopy study shows that dislocation of the modified alloy concentrates near the grain boundary during the crystallization process, and these grain boundaries act as obstacles to dislocation motion. Based on these results, it was found that grain-size aluminum strengthening mechanism occurs in the nanoparticle carbide reinforcement process.

Abstract: The electrodepostion of bi-valent iron, zinc and tungsten (IV) on tungsten electrodes in equimolar NaCl-KCl melt at 700-750oC was studied by Cyclic Voltammetry and Chronoamperometry. While iron (II) and zinc (II) ions demonstrate regular values of diffusion coefficients, which are all in the range of 10-6-10-5 cm2/sec, tungsten (IV) ions diffuse considerably slower. Plausible process mechanisms were proposed, according to which the tungsten (IV) ions form polynuclear ions and these massive species diffuse at considerably more moderate rates.

Abstract: A deterministic computational model of high-temperature heterogeneous re- action between metal and oxide melts has been developed. Transport of reagents and products of reaction occur simultaneously both by diusion and by laminar natural con- vection of the melting metal and oxide uxes. The convection-diusion equations have been numerically solved by a nite-dierences time-implicit discretization scheme. The model was implemented by program which had been written in C# language. The com- putations have been performed for desulfurization reaction between liquid steel and slag phases.The computed results agree well with the results which were found by experimen- tal methods.

Abstract: A mathematical model of sulfur transfer in a moving metal and slag melts has been developed. Sulfur is transported simultaneously both by diffusion and by laminar natural convection of the melting metal and oxide fluxes. The diffusion of sulfur is described by the 2nd Fick's law. We have computed the distribution of sulfur in the metal and slag phases and the concentration changes of sulfur in the volume of the metal and slag phases, both functions of space and time. Numerical results are provided to show the validity of this approach.

Abstract: The purpose of the present work is to investigate the mutual interaction between the melted metal and oxide phases with a small amount of sulfur. In this research, the following phases took part: metallic phase of Fe – C – S and slag CaO–Al2O3 –MgO–S. The mathematical model of sulfur diffusion in the metal and oxide is employed. The experiment was carried out at the temperature of 1773K. The result of the calculation is in qualitative agreement with the experiment. The proposed approach can be applied to the investigations of diffusion processes in molten metal and slag phases.