The rate of N diffusion was measured by using an Fe17Sm2N2.4 sample with a particle size of 5. At this N concentration, Fe17Sm2N2 and Fe17Sm2N3 phases were assumed to co-exist. Measurements of the diffusion coefficient yielded a value of 2.7 x 10-12cm2/s at 623K. This value was much higher than those which were found for larger particle sizes. The marked change in diffusivity was attributed to the contribution from the pre-exponential factor. The sample size dependence of the N diffusivity suggested that there were strong interactions between the diffusing N atoms, and defects which were introduced into the nitrided sample. The rate of N diffusion seemed to change, depending upon the ease of strain relief in the sample during nitride formation. This resulted in various diffusion behaviors, depending upon the N concentration and the particle size.

H.Uchida, S.Tachibana, T.Kawanabe, Y.Matsumura, V.Koeninger, H.H.Uchida, H.Kaneko, T.Kurino: Journal of Alloys and Compounds, 1995, 222, 107-12