Surface Morphology and Formation of Nanocrystals in an Amorphous Zr55Cu30Al10Ni5 Alloy under High-Pressure Torsion

Abstract

A change in the structure of an amorphous Zr55Cu30Al10Ni5 alloy under deformation by high-pressure torsion (HPT) was studied by X-ray diffraction, high-resolution electron microscopy, scanning electron microscopy, and atomic force microscopy. It was found that the uneven distribution of deformation along the radius of the sample, characteristic of deformation by high-pressure torsion, led to the formation of an inhomogeneous structure. The formation of nanocrystals begins at the periphery of the sample. The threshold value of deformation required for crystallization onset was established; the formation of nanocrystals begins in areas with true deformation e = 4.83 or more. An increase in the deformation degree led to an increase in the height of steps on the deformed sample surface and an increase in the roughness of the surface. The thickness of an elementary step that was formed when one shear band came out to the surface was 10 nm, and its height was about 1 nm. It was found that large steps on the deformed surface of the sample had a complex structure and consisted of a large number of elementary steps. The results obtained are important for analyzing the stress distribution and the concentration of free volume in a deformed material, which affect the parameters of the amorphous-nanocrystalline structure formed.