Preparation of Fe-Mo-C ternary carbide by mechanical alloying

The ternary carbide eta -Fe3Mo3C was synthesized by mechanical alloying of elemental Fe, Mo, and graphite and subsequent heat treatment. The alloying process in the Fe-Mo-C system and the thermal stability of the ball-milled sample have been studied by X-ray powder diffraction and Mossbauer spectroscopy. It is found that alloying occurs in the Fe-Mo-C system during ball-milling. Initially, the milling process reduces the grain sizes of the pure elements and Fe-C alloying occurs to form an amorphous Fe3C-type phase. With increasing milling times, Mo diffuses into the Fe-C alloys, which accelerates the formation of the non-magnetic amorphous Mo-Fe-C alloy. The content of Mo in the amorphous Mo-Fe-C alloy increases with milling time. After 60 to 90 hours ball-milling, a crystallization reaction of the amorphous Mo-Fe-C alloy into eta -Fe3Mo3C and Mo2C occurs. The ball-milled samples are composed of eta -Fe3Mo3C, Mo2C, and residual amorphous Mo-Fe-C alloy together with a slight contamination from the WC balls. It is found that the reaction between Mo2C and the residual amorphous Mo-Fe-C phase occurs at low temperatures while WC reacts with eta -Fe3Mo3C to form Fe3W3C at high temperatures. The samples annealed at high temperatures (> 1073 K) are composed of crystalline eta -Fe3Mo3C-type phases (eta -Fe3Mo3C with an isomorphous substitution of W for Mo) with a lattice constant of 11.117(8) Angstrom and an isomer shift of -0.21(1) mm s(-1).