Preparation of CoTi intermetallics by self-propagating combustion synthesis

The production of B2-type cobalt titanide (CoTi) from elemental powder compacts was conducted by self-propagating high-temperature synthesis (SHS) in this study. Effects of the initial sample density, particle size of the reactants, and initial sample temperature on the combustion characteristics, as well as on the composition of final products were studied. Unlike most of the intermetallic reactions, the combustion of the Co-Ti powder compact is self-sustained upon initiation even without any preheating prior to ignition, implying that the reaction is highly exothermic. The combustion process was preceded by fast propagation of the flame front, followed by vigorous bulk combustion. The flame-front propagation velocity and combustion temperature were found to increase with increasing sample green density and initial sample temperature. The degree of conversion to produce the CoTi phase was enhanced by increasing the sample green density or by preheating the sample prior to ignition. The use of fine particles of Co (2 mu m) in the green compact was also proved to be beneficial in improving the phase conversion, in comparison with the coarse Co powders (-325 mesh). Based upon the measured data of this study, the activation energy with a value of 67.95 kJ/mol was deduced for the synthesis of CoTi by SHS. (c) 2005 Elsevier B.V. All rights reserved.