Combustion synthesis of Ni3Al intermetallic compound in self-propagating mode

The production of Ni3Al intermetallic compound from elemental powder compacts was conducted by self-propagating high-temperature synthesis (SHS) in this study. Effects of initial sample density, preheating temperature, and particle size of the reactants on the combustion characteristics, as well as on the composition and morphology of final products were studied. Experimental observation indicated that the combustion process was preceded by the propagation of the flame-front, followed by prolonged bulk combustion. It was found that the flame-front propagation velocity was significantly higher for the sample using fine particles of Ni (3-7 mum) when compared to that with coarse Ni particles (-325 mesh). The use of small particles of Ni (3-7 mum) and Al (10 mum) resulted in the formation of dense single-phase products made up of Ni3Al from preheated sample compacts with a green density equal to 65% theoretical maximum density (TMD). However, highly porous products composed of Ni3Al,NiAl, and unreacted Ni were produced from 60% TMD samples using large particles of Ni (-325 mesh) at a low preheating temperature of 200degreesC. Even with the use of coarse Ni powders, a complete reaction yielding the single-phase product Ni3Al was achieved by increasing the preheating temperature and the sample green density. The increase of preheating temperature and initial sample density also led to an increase in the product density up to above 90% relative to the density of the Ni3Al compound. Based upon the measured data obtained in this study, the activation energy of about 92-98 kj/mol was deduced for the combustion synthesis of Ni-3,Al. (C) 2004 Elsevier B.V. All rights reserved.