Infrasonic Nanocrystal Formation in Amorphous NiTi Film: Physical Mechanism, Reasons and Conditions

Evgeny E Slyadnikov

doi:10.3390/met11091390

Abstract

The physical mechanism, reasons and conditions of nanocrystal formation in an amorphous NiTi metal film, stimulated by infrasonic action, are formulated. Nanostructural elements of an amorphous medium (relaxation centers) containing disordered nanoregions with two-level systems are considered to be responsible for this process. When exposed to infrasound, a large number of two-level systems are excited, significantly contributing to inelastic deformation and the formation of nanocrystals. The physical mechanism of the nanocrystallization of metallic glass under mechanical action includes both local thermal fluctuations and the additional quantum tunneling of atoms stimulated by shear deformation. A crystalline nanocluster appears as a result of local atomic rearrangement growing increasingly exposed to infrasound. It is possibly unstable in the absence of infrasound. When the radius of the nanocluster reaches a critical value, a potential well appears, in which a conducting electron is localized to form a phason (stable nanocrystal). Estimated values of the phason’s radius and the depth of the nanometer potential well is about 0.5 nm and 1 eV, respectively. It forms a condition of stable phason formation. The occurrence of the instability of the amorphous state and following transformation to the nanostructured state is based on the accumulation of the potential energy of inelastic deformation to a critical value equal to the latent heat of the transformation of the amorphous state into the nanostructured state.

Highlights

Amorphous metal alloys with a nanostructure are possessed by unique mechanical properties occurring due to intensive mechanical processing [1]
As we found in the literature, there is no consideration of the effect of infrasound nanocrystal formation, and its physical mechanisms and possible conditions are not established
Metallic glass contains a large number of relaxation centers containing two-level systems, which are described by a double-well potential, resonance detuning ∆, and tunnel transition frequency ωK

Summary

Introduction

Amorphous metal alloys with a nanostructure are possessed by unique mechanical properties occurring due to intensive mechanical processing [1]. In the structure of the sample subjected to mechanical vibrations with an amplitude of 4 mkm, nonspherical clusters with correct atomic positions and sizes of 3–5 nm appear in an amorphous matrix. It has been established [2] that, under mechanical action, the latent heat of crystallization decreases slightly. The analytical formulation of the problem is of two objectives: (1) in the framework of the model to formulate the equations of the density operator, taking into account the relaxation term and the field of static shear deformation; (2) to determine the probabilities of transitions of an atom in a double-well potential by thermal and athermal, i.e., quantum, mechanisms. There is a need in quantitative estimations of the critical values of the potential well depth and the radius of a stable nanocrystal

Physical Mechanism of Inelastic Deformation of Metal Glasses

Electron Localized States in Potential Nanometer Well and Phason Formation

Findings

Discussion

Conclusions