Structural mechanisms of plastic deformation of amorphous alloys containing crystalline nanoparticles

Abstract

Patterns of plastic deformation of amorphous nanocrystalline composites, caused by the local action of an indenter on a thin electron microscopy foil, have been experimentally investigated for the first time in structural analysis. Classification of the observed types of interaction of shear bands with crystalline nano- particles is performed. This classification is in good agreement with the theoretically predicted interaction mechanisms. DOI: 10.3103/S1062873807120106 Amorphous-nanocrystalline alloys form a new class of materials that possess, due to their peculiar structural state, a unique complex of physicomechani- cal properties (1). The unusual feature of such alloys is primarily that their structural (phase) components have radically different atomic structures: the crystalline component has a regular (according to the translational symmetry) atomic arrangement, whereas the amor- phous component is characterized by almost disor- dered, statistical arrangement of atoms in space. Obvi- ously, this uniformity of inconsistencies leads to a num- ber of effects that influence, in particular, the mechanical behavior of such materials. The situation becomes even more dramatic if the crystalline phase in the amorphous-crystalline state is nanoscale (with characteristic sizes less than 100 nm). Let us consider the main methods for obtaining amorphous-nanocrystalline composites. Early nanoc- rystallization stages can be implemented under the con- dition of rapid melt quenching (with a rate close to crit- ical) with effective heat removal from the system crys- tallized. Controlled annealing of the amorphous state facilitates formation of new clearly formed (nanocrys- talline) structural component in the amorphous matrix. In this case, there are certain conditions under which the amorphous state is crystallized through nanocrys- tallization, i.e., formation of nanocrystals in the amor- phous matrix in the long-term crystallization stage (2). Recently, much attention has been paid to the fabrica- tion of amorphous-nanocrystalline composites using the so-called severe plastic deformation or pulsed laser irradiation of a material in the amorphous state (3-5). Two limiting cases of formation of amorphous nanocrystalline structures can be arbitrarily distin- guished. First type. A nanocrystalline material with nan- ograins separated by thin amorphous intercrystallite interlayers.