Correlated surface perturbation in stressed foil made of amorphous alloy

A foil strip made of amorphous alloy Fe70Cr15B15 was loaded with the tensile stress ∼500 MPa and remained with the ends kept fixed during 2 h. The statistical characterization of the temporal transformation of the sample surface relief was performed using the autocorrelation functions computed for one-dimensional profiles measured along the axis of loading. The profiles were recorded with the help of the scanning tunneling profilometer. The acquisition time of a single scan was about 0.5 min. The calculated autocorrelation function of the profile depths in the original foil shows a long-range (∼2 × 103 nm) correlation between relief components. The application of the tensile stress causes an immediate, significant increase of the roughness depth from ∼40–50 nm to 100–200 nm with a corresponding drop of the correlation length to 0.7 × 103 nm. The surface relief does not remain stable during loading but varies as a result of the competitive processes, such as microcrack growth, stress-induced flattening, and shearing. The variability of the deformation process in the ‘structureless’ amorphous alloy is due to the dynamical non-uniformity of the multi-focal damage nucleation.