Determining the deformation resistance of metals in nonisothermal deformation

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 3, pp. 120–123, May–June, 1992.     

Nanoscale deformation analysis near crack-tip under residual stress in Si by high-resolution transmission electron microscopy

A micro-crack in single-crystal silicon was experimentally observed using a high-resolution transmission electron microscopy. The localized elasticity deformation zone, along the fault line, was found ahead of its tip by numerical moiré, and the features of the deformation zone were further investigated by use of geometric phase analysis (GPA). The GPA measurements indicate that there are deformation and strain convergence only in long and narrow zone ahead of crack-tip. The deformation zone, whose width is only 1.7 nm, stretches intermittently from the crack-tip. Nevertheless, it’s worth noting that there are not only tensile strains but also compression strains in the deformation zone, where the maxima and minimum of the strain components ε_yy can reach 9.3 and ?3.7 %, respectively. In addition, the maxima of the shear strain ε_xy can reach 3.6 % in the deformation zone. The sketch of the deformation distribution near crack-tip is also provided.     

Effect of deformation on electrochemical properties of the double layer and surface charge of metals

Electrochemical measurements on plastically deformed metals revealed the previously predicted [1] deformation-induced shifts toward positive surface charge values and clarified the character of the intensification of the electrochemical heterogeneity of deformed metal surfaces (localization of activated anodes as a result of mechanochemical phenomena). The deformation-induced increase in the differential capacitance of the double layer is attributable to an increase in the intensity of physical (electrostatic) adsorption of SO ₄ ^2– and HSO ₄ ^– HSO ₄ ^– anions on a positively charged surface in sulfuric acid solutions. A necessary (but not always sufficient) condition of the effectiveness of cation-active inhibitors of corrosion of plastically deformed metals is their stable chemisorption at potentials in the range of deformation-induced changes in the surface charge (of the order of tenths of a volt on the -scale).     

Determination of the length of deformation waves in the high-rate deformation of metals

A simple method has been devised for determining the length of a deformation wave in a solid. The method is based on the phenomenon of metalcutting and makes use of the interference of coherent waves. A hypothesis regarding the wave propagation of mechanical and thermal energy is proven experimentally, and it is established that the frequency of these oscillations increases with an increase in deformation rate.Translated from Problemy Prochnosti, No. 3, pp. 88–95, March, 1996.     

Revealing the atomistic deformation mechanisms of face-centered cubic nanocrystalline metals with atomic-scale mechanical microscopy: A review

Nanocrystalline metals have many functional and structural applications due to their excellent mechanical properties compared to their coarse-grained counterparts. The atomic-scale understanding of the deformation mechanisms of nanocrystalline metals is important for designing new materials, novel structures and applications. The review presents recent developments in the methods and techniques for in situ deformation mechanism investigations on face-centered-cubic nanocrystalline metals. In the first part, we will briefly introduce some important techniques that have been used for investigating the deformation behaviors of nanomaterials. Then, the size effects and the plasticity behaviors in nanocrystalline metals are discussed as a basis for comparison with the plasticity in bulk materials. In the last part, we show the atomic-scale and time-resolved dynamic deformation processes of nanocrystalline metals using our in-lab developed deformation device.     

Some effects of an electric field on the plastic deformation of metals and ceramics

 The external parameters generally considered in the plastic deformation of metals and ceramics are the temperature, pressure or stress and time. Usually neglected are the effects of electric and magnetic fields. However, such fields can often have a significant influence, especially when applied concurrently with the more common parameters. Some examples of the effects of an electric field on the plastic deformation of metals and ceramics found by the author and his coworkers are presented. Included are the following: (a) the influence of electropulsing on the flow stress of metals at 78–300 K, (b) the effect of an external electric field (surface charge) on the superplastic deformation of the 74754 Al alloy, (c) the influence of an electric field on the flow stress and ductility of polycrystalline NaCl at 0.28–0.75 T_M and (d) the effect of an electric field on the superplastic deformation of 3Y-TZP. Mechanisms responsible for the observed effects are considered. Received: 1 January 1998 / Accepted: 1 March 1998     

Tribological effects of polymer surface modification through plastic deformation

The efficacy of using polymers in cylindrical applications depends closely on its surface friction and wear characteristics. In this regard, a surface modification technique through plastic deformation has been implemented. Roller burnishing is commonly used to improve the surface quality of non-ferrous surfaces, but no work showed concern about roller burnishing as a polymer surface treatment process. The objective of the present work is to investigate the influence of burnishing force and burnishing speed on the friction and wear performance of acetal homopolymer and polyurethane under dry and lubricated sliding conditions. The results reveal that the coefficient of friction and wear rate decreased to a minimum value and then increased as higher burnishing force and speed were applied. It was shown that roller burnishing had favourable prospective to be utilized as a valuable polymer surface treatment technique.     

Distinctive features of physical fields near the edge of a composite piezoceramic wedge (antiplane deformation)

We consider a composition in the form of a wedge made of two different conjugate piezoceramic or anisotropic piezopassive wedges and study the distinctive features of the behavior of physical fields in the vicinity of the edge of this composite wedge under homogenous boundary conditions imposed on its external faces. The problem is solved by the method of complex representations of the components of electroelastic fields for two principal types of mechanical and electrical boundary conditions. The results of numerical computations are also presented. Sumy State University, Sumy. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 2, pp. 27–32, March–April, 1999.     

First-principles study of near surface point defects stability in Si (100) and SiGe(100)

Calculations based on Density Functional Theory are carried out to study interstitial generation close to the Si(100) surface with further consideration of effects related to the presence of substitutional Ge atoms on the surface. Defect structures, vacancy and Si interstitial, and associated energies are calculated. We observe that germanium atoms tend to increase the stability of created defects, promote the generation of interstitials through drastic structural changes and blocks the climb of Si interstitials towards the surface.     

Dynamic probe of ZnTe(110) surface by scanning tunneling microscopy

The reconstructed surface structure of the II–VI semiconductor ZnTe (110), which is a promising material in the research field of semiconductor spintronics, was studied by scanning tunneling microscopy/spectroscopy (STM/STS). First, the surface states formed by reconstruction by the charge transfer of dangling bond electrons from cationic Zn to anionic Te atoms, which are similar to those of IV and III–V semiconductors, were confirmed in real space. Secondly, oscillation in tunneling current between binary states, which is considered to reflect a conformational change in the topmost Zn–Te structure between the reconstructed and bulk-like ideal structures, was directly observed by STM. Third, using the technique of charge injection, a surface atomic structure was successfully fabricated, suggesting the possibility of atomic-scale manipulation of this widely applicable surface of ZnTe.     

Dynamic probe of ZnTe(110) surface by scanning tunneling microscopy

Abstract

The reconstructed surface structure of the II–VI semiconductor ZnTe (110), which is a promising material in the research field of semiconductor spintronics, was studied by scanning tunneling microscopy/spectroscopy (STM/STS). First, the surface states formed by reconstruction by the charge transfer of dangling bond electrons from cationic Zn to anionic Te atoms, which are similar to those of IV and III–V semiconductors, were confirmed in real space. Secondly, oscillation in tunneling current between binary states, which is considered to reflect a conformational change in the topmost Zn–Te structure between the reconstructed and bulk-like ideal structures, was directly observed by STM. Third, using the technique of charge injection, a surface atomic structure was successfully fabricated, suggesting the possibility of atomic-scale manipulation of this widely applicable surface of ZnTe.     

Toward the description of uniaxial deformation of metals

Effectiveness of using the endochronic theory of plasticity for describing unidimensional deformation processes under cyclic loading is investigated. A method is developed for determining parameters of the equations of state which depend on the amplitude of plastic deformation and length of strain path. A sufficiently good agreement is shown between calculated and experimental data in describing the kinetics of the stress-strain state of specimens of steels 316 and 45 subjected to variable loads.Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev Polytechnic Institute. Translated from Problemy Prochnosti, No. 11, pp. 65–69, November, 1989.     

Effects of erosion surface on near wall conductivity (NWC) in the Hall-type stationary plasma thrusters

The effect of erosion structure of the wall surface on near wall conductivity was studied in this paper. The electron dynamics process in the plasma was described by the test particle method where electrons were randomly injected into the wall. Monte Carlo method was used to calculate the model. The simulation results showed that the axial current density increased in the case of erosion. Furthermore, the current layers were observed and the layer thickness was approximately equal to the radical electron motion in a half of the electron Larmor period. Also, the current density increases as the erosion structure gradually growed.