A contribution to the resolution of purity and grain-size effects on the relaxation strength of interstitial nitrogen in α-Iron

An analysis of the experimental data published on the inelastic behaviour of the interstitial N-αFe solid solution shows that grain-size and purity effects on the stress-induced ordering relaxation strength can be resolved into two independent phenomena. The grainsize effect is discussed in terms of grain boundary segregation: the necessity of assuming a strong enrichment of interstitials at intercrystalline ridges is proved. The influence exerted by purity on the relaxation strength is quantitatively analysed on the basis of the strain produced by substitutional impurities in the parent lattice. The results obtained make it possible to evaluatea priori the inelastic reponse of a N-αFe solid solution of known chemical composition and grain size. The distortion of the Snoek-peak profile, experienced in less pure materials, is to be connected with a relaxation-time spectrum.