Combustion synthesis of mechanically activated powders in the Ta-Si system

The effect of mechanical activation of reactants on the self-propagating high-temperature synthesis of TaSi2 and Ta5Si3 was investigated. SHS experiments were performed on mixtures of compositions Ta:Si = 1:2 and Ta:Si = 5:3 which had been milled for various times. For both compositions, mechanical activation had a large influence on the characteristics of the combustion process, particularly on the combustion peak temperature and wave velocity. The product composition depended on the initial stoichiometry and milling time. For the 5:3 stoichiometry, the product was single phase Ta 5Si3 (in its hexagonal and tetragonal forms) only when the powders were milled for sufficiently long milling times (>120 min). The 1:2 stoichiometry produced TaSi2 in a pure form, regardless of milling conditions. A mechanism for the combustion process is proposed on the basis of the microstructural evolution in quenched reactions.