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Abstract: Al2O3/TiC composites are used as cutting tools for machining gray cast iron and steels. The addition of iron improves the toughness of Al2O3/TiC composites. Ilmenite, aluminum and graphite can be used to produce in-situ Al2O3/TiC–Fe composites. However the formation mechanism and reaction sequences of the system are not clear enough. Therefore, the present research is designed to determine the formation mechanism and the reaction sequences of the foresaid system. In this research, ilmenite was synthesized to prevent the presence of impurities in the system and then the critical temperatures of ilmenite, aluminum and graphite powder mixture were determined by DTA analysis. The milled and pressed samples, prepared from this mixture, were heat treated at the critical temperatures. The final products were analyzed with XRD. It was found that at the first exothermic peak of DTA curve (720°C), aluminum reacts with FeTiO3, forming Fe, TiO2, Al2O3 and Fe2Al5. Further increase in the temperature, up to 930°C, results not only in the transformation of TiO2 to Ti2O3 and TiO, but also in the conversion of Fe2Al5 to FeAl. Moreover, titanium carbide will also be formed. With the rise in temperature, Ti2O3, TiO and iron aluminides disappear and TiC, Al2O3 and Fe will be the final compounds. [Copyright &y& Elsevier]

Metallic-intermetallic laminate composites are promising materials for many applications, namely, in the aerospace industry. Ti/TiAl laminates are one of the interesting laminate composites, which are mostly used in aerospace applications. In this work, commercially pure aluminum and titanium sheets were explosively joined. The multilayer samples were annealed between 1 and 260 hours at 903 K (630 °C) in ambient atmosphere, and the formation and growth of the intermetallic compound at the Ti/Al interface were monitored. Microstructural investigations were carried out using optical and scanning electron microscopes equipped with energy-dispersive spectroscopy and the X-ray diffraction technique. The microhardness profile of the layers was also determined. The thickness and type of Al-Ti intermetallics were determined. It was found that the only intermetallic phase observed in the interfaces was TiAl. It was also shown that two mechanisms for TiAl growth exist: reaction and diffusion controlled. The growth exponent was equal to 0.94 for the reaction-controlled mechanism (first step) and 0.31 for the diffusion-controlled mechanism (second step). These values were in good agreement with theoretical values (1 and 0.5 for the first and second steps, respectively). Based on the results of this research, a kinetic model for the formation and growth of TiAl intermetallic phase was proposed. [ABSTRACT FROM AUTHOR]

Abstract: Titanium–aluminum diffusion couples were prepared using pure titanium and aluminum sheets in the form of a tri-layer sandwich. The Ti–Al interface was investigated after heating the specimens at 550, 575, 600, 625, 640 and 650 °C. EPMA results indicated that TiAl3 intermetallic layer is the only phase that can form and grow at the Ti–Al interface. Evidences from the SEM observations showed that aluminum is the dominant diffusing component through the TiAl3 layer which reacts with titanium at the Ti–TiAl3 interface. According to the normal parabolic behavior of the layer thickening, activation energies of 33.1 kJ mol−1 and 296.2 kJ mol−1 were calculated for the low temperature grain boundary diffusion controlled growth and the high temperature bulk diffusion controlled growth, respectively. Overall activation energy of 76.8 kJ mol−1 is calculated for the diffusion-controlled growth of the TiAl3 layer at all applied annealing temperatures. [Copyright &y& Elsevier]