Spatial Oscillation in SHS of Ni/Al Multilayer Foils: Measurements and Models

Abstract

Spatial oscillations have been observed after self-propagating high temperature synthesis (SHS) of multilayer bi-metallic foils. These oscillations have been correlated with periodic variations in the flame front velocity. Previous researchers have reported oscillation for which the direction of the spatial oscillations coincides with the velocity vector of the flame front. In this study, we find another mechanism for creation of spatial oscillations. Experiments on Ni/Al multilayer foils show oscillations that lie normal to the propagation direction of the flame front. We observe that the effect is consistent with microstructure formation characteristic of directional solidification. The results contribute to increased understanding of SHS combustion mechanisms in thin Ni/Al films, in particular that the combustion temperature exceeds the melting point of all reactants and reaction products, and that the mechanism for formation of reaction products is solidification from a fully molten zone. Previous results from the literature have been inconclusive on these points.