Effect of Precursor's Composition and Thickness on Foaming Behavior of Al-Tiintermetallics in Volume Combustion and Self-propagating High-temperature Synthesis Modes

摘要

Sheet type precursors made of aluminum, titanium, and boron carbide (B 4 C) powders were prepared by rolling, and porous Al-Ti intermetallics were fabricated by a combustion reaction in volume combustion synthesis (VCS) and self-propagating high-temperature synthesis (SHS) modes. The effects of precursor's composition and thickness on the foaming behavior were investigated.The microstructure of the precursor was not affected by rolling. In the VCS mode, the thin precursor (1 mm) with a high Al/Ti blending ratio (Al/Ti = 7.0) did not expand sufficiently. The microstructure of the specimen after the reaction revealed that the reaction between titanium and aluminum was not completed in this specimen. This means that the maximum temperature during the reaction decreased by decreasing the thickness and increasing the Al/Ti blending ratio. The self-propagating high-temperature synthesis mode combustion reaction propagated through the whole specimen when the Al/Ti ratio was 4.0 and the thickness of the precursor was 4 mm or more. However, by reducing the thickness of the precursors to 2 mm or less, the reaction front did not propagate through the whole specimen. The self-propagation also became difficult by increasing the Al/Ti ratio to 7.0. Theseresults imply that the SHS mode reaction was more susceptible to precursor's composition and thickness than the VCS mode reaction. Fine pores with diameters below 1 mm are dispersed in the specimen by the SHS mode reaction.