Nanometer-scale solute segregation at heterophase interfaces and microstructural evolution of molybdenum nitride...

The interrelationship between coherency and solute segregation at metal/metal-nitride heterophase interfaces is studied on a subnanometer scale by both atom-probe field-ion and electron microscopies for molybdenum nitride precipitates in Fe-2 at% Mo-X, where X = 0.4 at% Sb or 0.5 at% Sn. Internal nitridation at 550 degrees C generates thin platelet-shaped molybdenum nitride precipitates, while nitridation at 600 degrees C produces, in addition to the small-scale structure with precipitates of the thin-platelet type, a much coarser structure of thick plates and spheroidal precipitates. The solute species Sn and Sb segregate at the heterophase interfaces of the coarse precipitates and Gibbsian interfacial excesses of up to 7 x 10(18) M(-2) are measured. The segregation is related to the presence of misfit dislocations at the interfaces of the coarse preciptitates, while the thin plates remain coherent with no detectable segregation.