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 evolu tions during the MASHS (Mechanically Activated Self-propagating High-temper ature Synthesis) process in the Mo-Si system. Time-Resolved X-Ray Diffracti on (TRXRD) coupled with an infrared imaging technique was performed to stud y, in situ, the formation of the alpha-MoSi2 phase in the combustion front. Despite a temporal resolution of 50 ms between two consecutive diffractogr ams, no intermediate phase was observed during the passage of the combustio n front. The only reaction responsible for the self-sustentation is Mo + 2S i-->MoSi2 in the primary zone inside the combustion wave. The mechanical ac tivation was found to influence Self-propagation High-temperature Synthesis (SHS) parameters such as the propagation front velocity (>13 mm/s), the ma ximal combustion temperature and the local thermal gradient. After the MASH S process, the alpha-MoSi2 compound is nanostructured (D-MoSi2 = 88 nm) and some explanations are expressed in order to understand why the nanostructu re of the as-milled powders can be maintained during the combustion reactio n. (C) 1999 Published by Elsevier Science Ltd. On behalf of Acta Metallurgi ca Inc. All rights reserved.