Modification of structure and magnetic order by mechanically induced nitridation in the Zr–Fe system

Abstract

The structural and magnetic order changes induced by mechanically assisted nitridation of Zr1−xFex alloys and compounds as a function of composition, initial structure and processing time have been studied. It was observed that at the applied conditions, as N is incorporated, phase transformations occur following the schematic sequence: Zr1−xFex→a-(Zr1−xFexNy)→δ-Zr1−xFexN→δ-ZrN+Fe (a = amorphous). In this way, regardless of the initial composition and structure, the final product after prolonged milling was a mixture of nanocrystalline δ-ZrN and almost pure iron and/or Fe–Zr complexes, evidencing the strong tendency of Zr to combine with N and that of transition metals to segregate. The formation of δ-Zr1−xFexN proceeds through the growth of δ-ZrN structure in the amorphous matrix keeping Fe inside, replacing some Zr. For Zr-poor samples the amorphization stage is practically unobservable, obscured by the dominating Fe segregation. This contrasts with the results of milling in Ar, where the steady state is an amorphous phase for Zr1−xFex compounds or mixtures in a wide compositional range. These findings are discussed in terms of possible basic mechanisms for the mechanically activated reaction and keeping in mind its application to the formation of nanoprecipitates of δ-ZrN in various Zr alloys.