The combustion synthesis of multilayer NiAl systems

The synthesis of materials by combustion methods, including the self-propagating high-temperature synthesis (SHS) method, involves, typically, the use of powders as reactant materials. The use of particulate materials gives rise to difficulties in experimental and theoretical studies. In the former, the use of powders can result in the introduction of impurities associated with the surface films on the powders. Attempts to provide a fundamental understanding of SHS reactions from model experiments suffer from the same shortcoming as well as the complex nature of the reaction interface in powder systems. In order to provide a simpler geometry for the reaction interface, experimental as well as theoretical research has examined the combustion process between thin reactant layers. Anselmi-Tamburini and Munir investigated the combustion synthesis of nickel aluminides using nickel and aluminum foils as reactants. Because of the high thermal conductivity of the foil ensembles, a self-propagating combustion reaction could not be sustained and the reactants had to be imbedded in a chemical oven. It was observed that a self-sustaining reaction between the foils (which were oriented such that the wave propagated in a parallel direction to the interfaces) does not occur until the temperature is approximately the same as the melting pointmore » of nickel. Significant interfacial reactions, however, took place ahead of the wave resulting in the formation of intermediate nickel-aluminum phases. In this paper, the authors report the results of an investigation on the combustion kinetics of relatively thin (about 200--500 nm) layers in the Ni-Al system.« less