Structural Effects on the Kinetics of Mechanically Induced Nitriding.

M. A. BAB; L. A. MENDOZA-ZELIS

JOURNAL OF METASTABLE AND NANOCRYSTALLINE MATERIALS

Trans Tech Publications (ttp)

Año: 2004 vol. 20-2 p. 511 - 516

1422-6375

It is well known that milling of Zr, Hf and other refractory metals under nitrogen atmosphere induce the formation of nanocrystalline nitride phases. Previous kinetics studies have shown that the absorption curve follows a single sigmoidal shape irrespective of the milling intensity, which in turns strongly influence the reaction rate. In this work we explore the effect of structure on the kinetics, by means of a detailed study of the nitriding of cubic Hf2Fe compound and its comparison with hexagonal Hf and Zr and tetragonal Zr2Fe. The absorption curve shown a slight shoulder at n=0.25 followed by a second acceleratory stage that didn´t saturate after 10 hours of milling. The structural characterization indicated that under milling, Hf2Fe forms an interstitial solid solution ( -phase), with N atoms occupying the octahedral interstices, delimited by Hf atoms, before its transformation to the cubic-HfN structure. It is worth to note that the number of octahedral interstices per Hf atom is 0.25 and 1 in the   and   structures respectively, evidencing clearly the influence of structure on the nitriding rate.