Modeling and Fabrication of Functionally Graded Materials by the Combustion Synthesis Technique

The combustion characteristics of hypothetical four-layer FGMs (Functionally Graded Materials) were studied using a one-dimensional model. Modeling covered cases of ignition from either the most reactive side, or the least reactive side. It was found that the overall combustion rate was higher when ignited from the least reactive side. Although the combustion wave reached the end of the pellet in relatively short time, it took much longer time to complete the reaction at the end of pellet due to the high rate of heat losses. It was also found that, when ignition was initiated from the least reactive side, the reaction continued even after the combustion wave had passed. Examples of both porous and fully dense FGMs are given. Porous FGMs were fabricated to exhibit a porosity gradient, as well as exhibit both porosity and composition gradients. Fully dense FGMs containing four composition layers were fabricated by in-situ densification immediately following the completion of the combustion synthesis reactions. (Example materials: boron carbide-alumina, titanium carbide cemented by an unspecified metal.)