Influence of the nitriding process on the nitrogen distribution in the bulk magnetic compound Sm sub 2 (Fe,Co) sub 17

The bulk magnetic compound Sm sub 2 (Fe sub 0.5 Co sub 0.5 ) sub 17 was nitrided by two different processes: gaseous nitrogenation and fluidized bed nitrogenation. The nitrogen distribution was investigated by scanning electron microscopy, x-ray diffraction and chemical analysis. The cross-sectional nitrogen distribution differed according to the nitrogenation process: (1) nitrogen mainly diffuses along microcracks present in the samples with the gaseous nitrogenation, while it forms a nitrided layer parallel to the surface with the fluidized bed process, (2) the nitriding kinetics is controlled by diffusion (parabolic rate law) for the fluidized bed nitrogenation, whereas it is accelerated in the gaseous process.