Local structure of metallic glasses

Abstract

In the widely accepted view of the atomic structure of metallic glasses the structure is universal, determined mostly by the atomic size ratio of the constituent transition metal and metalloid atoms via random packing of spheres (DRPS). In this model the chemical interaction between the constituents is restricted only for repulsion of metalloid-metalloid nearest neighbours by excluding their occurrence. Recent Mössbauer [1,2] (ME) and energy dispersive X-ray diffraction [3] (EDXD) studies of (Fe, Ni)B glasses have revealed that none of the above assumptions are fulfilled. Namely: 1. (i) the structure is not universal, the radial distribution functions of amorphous Fe 3B and (Fe 0.33Ni 0.67) 3B measured by EDXD [3] differ significantly, which is not expected in DRPS models because of the similar size of Fe and Ni atoms. The observed differences correlate well with the ME results which suggest [1] the change of the chemical short-range order of these glasses following closely that of the crystalline counterparts. 2. (ii) There are significant chemical interactions between the transition metal atoms and metalloids which are stronger between Ni and B than between Fe and B since the distribution of Ni and Fe on the transition metal sites is not random, Ni prefers neighbourhoods with more B neighbours than Fe as deduced from the Mössbauer studies [2]. These results heavily support and extend structural descriptions based on compound-like building units [4].