Molybdenum-Nitride Precipitation in Recrystallized and Cold-Rolled Fe-1 at. pct Mo Alloy

Nitriding of recrystallized and cold-rolled Fe-1 at. pct Mo alloy at 853 K (580 °C) in a NH₃/H₂ gas mixture leads to the formation of cubic nanometer-sized Mo₂N-type precipitate platelets. These platelets obey a Baker–Nutting orientation relationship with the ferrite matrix. After prolonged nitriding, micrometer-sized colonies of lamellae consisting of a hexagonal MoN-type nitride and ferrite develop in a discontinuous precipitation reaction. These nitride lamellae have a Burgers-type orientation relationship with the ferrite lamellae. As compared to the recrystallized specimens, in the cold-rolled specimens, the precipitation of the initial Mo₂N-type platelets occurs much faster and moreover leads to incoherently diffracting precipitates; upon continued nitriding, a much earlier but only partially occurring transition of Mo₂N-type to MoN-type precipitates is observed. The results indicate that incorporation of iron in the nitrides can occur, if at all, only up till a negligible level, thereby invalidating earlier data.