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In this research, dense TiAl and fimctionally gradient TiAlx-Ti-Al composite materials were fabricated using a one-step, self-propagating high-temperature synthesis (SHS) and densification method (pseudo-hot isostatic pressing, P-HIP).
In this process, Ti and Al powders were used as the reactants. These two powders were thoroughly mixed at appropriate ratios and then pressed into reactant compacts with cylindrical shapes. The reactant compact and a heating element were placed in a mold which was filled with casting sand. The combustion synthesis reaction was ignited by heating by the heating element. A mechanical pressure was applied to the mold during propagation of the combustion wave. Due to the transmission of pressure by the casting sand, densification of the product was achieved. Besides, because of the enhanced heat loss by densification, the combustion wave ceased resulting in a gradient distribution of the conversion of the TiAlx compounds along the propagating direction of the combustion wave. Dense and functionally gradient TiAlx-Ti-Al composite materials were therefore produced. On the other hand, dense TiAl material was fabricated applying a mechanical pressure to the mold after combustion wave passed over and while the compact was still at high temperature.
The operating parameters of the designed process were changed to fabricate the final produets. Properties of products were affected by heating ways, heating power, applied pressure, reactant particle sizes and composition, the time of applied pressure and spots of thermocouple. The results showed that dense TiAl and functionally gradient TiAlx-Ti-Al composite materials could be produced by chosing the right time of applied pressure.
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