Abstract

The ternary carbide η-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 Mössbauer 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 η-Fe₃Mo₃C and Mo₂C occurs. The ball-milled samples are composed of η-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 η-Fe₃Mo₃C to form Fe₃W₃C at high temperatures. The samples annealed at high temperatures (>1073 K) are composed of crystalline η-Fe₃Mo₃C-type phases (η-Fe₃Mo₃C with an isomorphous substitution of W for Mo) with a lattice constant of 11.117(8) Å and an isomer shift of −0.21(1) mm s⁻¹.