Grain boundaries in nanocrystalline tungsten probed by Fe-57 Mossbauer spectroscopy

Iron enriched in the isotope Fe-57 was dispersed in a nanocrystalline tungs ten matrix by mechanical alloying. Mossbauer experiments were performed usi ng as-milled; isochronally and isothermally annealed samples, both at room temperature and as a function of measurement temperature. The spectra were interpreted in terms of quadrupole splitting distributions p(QS). By carefu l analysis of the p(QS) distributions it is possible to deconvolute the spe ctral signatures of Fe-57 atoms on substitutional sites, in the vicinity of lattice defects and in grain boundaries. The Debye-Waller factor of Fe-57 atoms in grain boundaries is found to be enhanced with respect to iron atom s in the crystalline matrix. An interpretation of this result is given that is consistent with the observed hyperfine parameters.