Papers by Author: Mohammad Reza Aboutalebi

Abstract: Hot dip aluminizing of low carbon steel followed by high temperature oxidation in air was carried out to evaluate the dissolution rate of coated sample in molten aluminum. The microstructure of oxide and aluminide layers was investigated using scanning electron microscopy and X-ray diffraction methods. The characterization of the coating showed that Fe₂Al₅ has been the major phase formed on the surface of specimen before high temperature oxidation. Isothermal oxidation of the coating as resulted in the formation of Al₂O₃ while Fe₂Al₅ phase transformed into FeAl and Fe₃Al phases. The coated samples were further subjected to corrosion in molten aluminum. It was proved that the oxide layer formed on the coating and developed FeAl and Fe₃Al intermetallic phases play the major role in protecting the specimen from corrosion in molten aluminum.

Abstract: In continuous casting process, tundish operates as a refining finisher. Different flow modifiers can be used in order to optimize cleanliness of liquid steel. To study the effect of various flow modifiers such as dam, weir, inlet shroud and etc., a three dimensional mathematical model was developed to simulate turbulent flow inside the tundish. The computed flow field was further used to model the transient mass transfer in the melt flowing in the tundish. The residence time distribution (RTD) of particles was determined by mass transfer model. The performance of the model was evaluated by experimental data obtained by a physical model. The verified model was used to evaluate the effect of location and size of different flow modifiers on flow pattern and particles residence time and consequently on tundish performance.

Abstract: The starting reaction in the combustion synthesis process in TiO2-Al-C system leading to TiC+Al2O3 composite was evaluated using a combination of Differential Thermal Analysis (DTA), X-Ray Diffraction (XRD) and Transmission Electron Microscope (TEM). Double phases in 3TiO2- 4Al-3C system were milled separately and then the third phase was added according to the stoichiometric reaction for 3TiC+2Al2O3 composite formation. The combustion synthesis temperature was observed to decrease from 962 °C to 649 °C after mechanical activation of TiO2/Al mixture for 16 hr. On the contrary, the mechanical activation of Al/C and TiO2/C mixtures for 16 hr made the reaction temperature increase to 995 °C and 1024 °C, respectively. TEM and XRD patterns of as-milled powders showed that the reaction temperature changes could be due to increased TiO2 and Al interface area. In addition, DTA experiments showed that for the sample in which TiO2 and Al were mechanically activated the reaction occurred at the temperature even lower than the aluminum melting point.

Abstract: A mechanism for the combustion synthesis of TiC+Al2O3 was proposed in a mechanically activated TiO2-Al-C system. As-milled powder mixture was analyzed using XRD and TEM techniques where no chemical reaction and/or inter-particle diffusion were identified. The results obtained from DTA tests on unmilled powder revealed that the combustion synthesis occurred in a single step at 962 °C while the synthesis of mechanically activated powder mixture occurred in three different stages. The XRD analysis on the synthesized samples of 8 hour premilled powder at different temperatures showed that the three stages were as follows: First the reaction between Al and TiO2 takes place forming Al3Ti, Ti2O3, and Al2O3 at 700 °C. In the second step, Ti-rich titanium aluminides (AlTi, AlTi2, and AlTi3) and TiO, are formed at 923 °C, and finally the formation of TiC+Al2O3 is completed at 1329 °C.