The determination of the atomic configuration of metallic glasses is a long-standing problem in materials science and solid-state physics. So far, only average structural information derived from diffraction and spectroscopic methods has been obtained. Although various atomic models have been proposed in the past fifty years, a direct observation of the local atomic structure in disordered materials has not been achieved. Here we report local atomic configurations of a metallic glass investigated by nanobeam electron diffraction combined with ab initio molecular dynamics simulation. Distinct diffraction patterns from individual atomic clusters and their assemblies, which have been theoretically predicted as short- and medium-range order, can be experimentally observed. This study provides compelling evidence of the local atomic order in the disordered material and has important implications in understanding the atomic mechanisms of metallic-glass formation and properties.

Fig. l(a).This structure is consistent with that obtained by slow cooling in Fe-20Mn alloy.3) On the other hand, alloys A2 and A4 gave birth to a fully austenitic structure as rcpresented by Fig. I (b A typical example is shownin Fig. 3 for alloy A2.The yield stress at zero plastic strain is plotted as a function of aluminumconcentration for the 20 and The phase boundary of T/((~+T) for the 20 ryo Mn allovs wcre estimated and marked in the Fig. 4~a).

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