Nanostructured Fe obtained by high-energy ball milling

A detailed microstructural study of nanocrystalline Fe powder samples, obtained by mechanical attrition, was carried out by X-ray diffraction experiments as a function of the milling time. During the process, the exchange energy between the vessels, balls and Fe powders leads to a change of the Fe microstructure: in particular, a significant decrease in the size of the coherent diffraction domains and the creation of a large number of linear defects which induces microstrains. This microstructure seems to be responsible for the distinct magnetic behaviour of the samples. In addition, on heating, the sample produces the relaxation of the nanostructure, recovering the initial magnetic properties; this process has been followed on the sample with larger milling time by neutron thermo-diffraction from room temperature up to 1200 K. The analysis of the diffraction patterns by the Rietveld method allows determining the microstructure at each stage. (C) 2005 Elsevier B. V. All rights reserved.