Scaling response of the amorphous alloy surface on loading and extrinsic crystallization

Ioffe Physico-Technical Institute, Russian Academy of Sciences - 194021 St. Petersburg, Russia

Received: 9 March 2010
Accepted: 7 April 2010

Abstract

The surface nano-topography of the amorphous alloy Fe₇₇Ni₁Si₉B₁₃ was found to be anisotropic and fractal with the absolute values of Hurst exponent and fractal dimension close to those known for fracture surfaces of both conventional and amorphous metals. The tensile stress application causes the formation of shear bands (SBs), the highly prevailing orientation of which is normal to the stress applied. However, in very few cases, the SBs oriented at 45° to the stress direction detected. The latter SB orientation is typical for conventional (crystalline) metals where a specific dislocation mechanism determines the SBs orientation; the occurrence of 45°-oriented SBs in the amorphous alloy was attributed to the local, stress-induced extrinsic crystallization at the sample surface. In the region of heterogeneity of this kind, the scaling properties of surface relief were fully disturbed. The mechanism of the fractal roughness formation was related to the fractal geometry of thermal vibrations of walls of primary cavities during the new surface formation under critical conditions, such as that take place at fracturing or ultra high cooling.