The effect of changes in Al-based amorphous phase structure on structure forming upon crystallization
The influence of heat treatment and deformation on structural changes of Al-based amorphous alloys in
the amorphous state and at early stages of crystallization has been studied using the methods of X-ray
diffraction, differential scanning calorimetry and transmission electron microscopy. It is shown that
isothermal annealing and multiple cold rolling bring about formation of an inhomogeneous amorphous
phase with the areas of different chemical composition. The formation of an inhomogeneous amorphous
phase accelerates the process of nanocrystallization of Al-based alloys. The conditions of treatment of the
amorphous alloy in the amorphous state affect the size and fraction of nanocrystals forming in the
amorphous phase upon subsequent heating. The size of nanocrystals in the case of preliminary deformation
is smaller than that upon preliminary isothermal annealing. We discuss the reasons for the
formation of nanostructures containing smaller nanocrystals in the case of thermal and deformation
treatments before the onset of crystallization.
Shear bands play a key role in the deformation of amorphous alloys at room, low and elevated (below the glass transition) temperatures. The shear bands in the amorphous Al–Ni–Y are places of nanocrystal formation during the rolling deformation. As Al nanocrystal formation occurs by the diffusion mechanism; their composition is different from the composition of the amorphous matrix. The nanovoids formed by the coalescence of excess free volume during prolonged aging at room temperature were observed in the shear bands by transmission electron microscopy method. The obtained apparent diffusion coefficient in the shear band at room temperature of 10 −22 m 2 s −1 exceeds by 5–6 orders in magnitude the diffusion coefficient in the matrix.
The structure of silicon crystals implanted with protons was studied by methods of high-resolution X-ray diffraction . The distribution of strain in the disturbed layers was analyzed.
Advances in high technologies using nanometer-size structures, such as carbon nanotubes, require calculation of mechanical properties for the objects of the nanosize scale level. Majority of the theoretical mechanical models for nanoobjects is based on the macroscopic equations of theory of elasticity. This gives the questions about applicability of the quantities obtained from the macroscopic experiments to the nanoscale objects or about necessity of corrections taking into account the scale effects. The presented paper is devoted to theoretical investigation of the influence of the scale effects on the bending stiffness of a nanocrystal, which is extended in one direction and has a limited number of atomic layers in another direction. Ambiguity of the bending stiffness due to the ambiguity of the size definition for the nanosize object is discussed. It is shown that appropriate definition of the crystal thickness allows using conventional formula for the bending stiffness, which is known from continuum theory of elasticity.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.