In situ synchrotron characterization of mechanically activated self-propagating high-temperature synthesis applied in Mo-Si system

An original experiment was designed to monitor structural and thermal evolutions during the MASHS (Mechanically Activated Self-propagating High-temperature Synthesis) process in the Mo-Si system. Time-Resolved X-Ray Diffraction (TRXRD) coupled with an infrared imaging technique was performed to study, in situ, the formation of the alpha-MoSi2 phase in the combustion front. Despite a temporal resolution of 50 ms between two consecutive diffractograms, no intermediate phase was observed during the passage of the combustion front. The only reaction responsible for the self-sustentation is Mo + 2Si-->MoSi2 in the primary zone inside the combustion wave. The mechanical activation was found to influence Self-propagation High-temperature Synthesis (SHS) parameters such as the propagation front velocity (>13 mm/s), the maximal combustion temperature and the local thermal gradient. After the MASHS process, the alpha-MoSi2 compound is nanostructured (D-MoSi2 = 88 nm) and some explanations are expressed in order to understand why the nanostructure of the as-milled powders can be maintained during the combustion reaction. (C) 1999 Published by Elsevier Science Ltd. On behalf of Acta Metallurgica Inc. All rights reserved.