Fractal behavior of amorphous metal structure under the action of tensile stress

We report a series of time-separated topograms of the stressed surface of a foil made of metallic glass Fe70Cr15B15. The numerical analysis of the tortuosity of both normal profiles and horizontal sections of the surface relief demonstrates a fractal/self-affine geometry as beginning from the nanoscopic scale level. Unlike the foils made of convention metals whose surface profile do not exhibit any features of fractality, in the original metallic glass foil the scaling character of the profile depth distribution was revealed. This is a statistical representation of non-equilibrium nanoscopic structure resulting from the highly critical glass forming process in the amorphous alloy. The temporal variation of fractal dimension after applying the 500 MPa tensile stress includes a rise to 1.46 ± 0.06 at the initial stage of loading, dramatic drop to 1.12 + 0.03, and gradual increase to 1.22 ± 0.02 just before the formation of regular shear bands, that is in ∼1.5 h after the stress application. The mechanism of formation of the transient fractal structures is discussed in terms of mid-range order dynamics in disordered media.