The effect of gravity on the combustion synthesis of advanced materials

Abstract

The effect of gravity on the combustion synthesis characteristics and the resultant microstructures of the synthesized metal matrix composites (MMCs) were studied for the HfB2/Al and Ni3Ti/TiB2 reaction systems conducted under both normal (1 g) and low gravity conditions. Under normal gravity conditions, the pellets were ignited at three orientations to the gravity vector. The low gravity combustion synthesis reactions were conducted on a DC-9 aircraft at NASA Lewis Research Center (NASA-LeRC). It was found that under normal gravity conditions, both the combustion temperature and wave velocity were highest when the pellets were ignited from the bottom. Both the combustion temperature and wave velocity were lower when conducting the reactions under low gravity than under normal gravity conditions. It is believed that the convective flow of argon gas was responsible for this phenomenon. Gravity-induced, density-driven fluid flow (sedimentation) of the heavier phases in the MMCs was also observed for both re...