Densification of combustion/micropyretic synthesized products by heating treatment of green compacts

The effect of the heating treatment on the green compact has been studied in this article. In the heating treatment, the green compacts are placed in the high temperature air furnace for the different times and temperatures. After the heating treatment, the unreacted compacts are further combustion synthesized. Appropriate heating treatment is noted to eliminate the volatile impurities and moisture prior to the combustion reaction. The amount of gases vaporized from the impurities during the course of combustion synthesis is correspondingly decreased and the effect of gas rejection is thus reduced. It has been reported that the gases are normally released in the direction of the front propagation, further facilitating the propagation of combustion front and expanding the synthesized products. The propagation velocity and expansion are thus noted to decrease for the specimens with the heating treatment. It has been found that the synthesized products do not have significant change at the heating treatment temperature of 250 °C. At the heating treatment temperature of 400 °C, however, the synthesized products with 1–5 h heating treatment time display the dense microstructures. In this study, the influence of the heating treatment temperature and time on the Ni–Al combustion synthesized products has been systematically studied. It is found that the correct heating treatment may aid synthesis in a manner to reduce the final porosity of the NiAl product to ∼5%.