Elastic and microplastic properties of titanium in different structural states

The behavior of elastic (Young’s modulus) and microplastic properties of titanium depending on the initial structure and subsequent severe plastic deformation that transforms the material (concerning the grain size) into the submicrocrystalline structural state has been studied. It has been shown that, to a great extent, different initial structures of the metal predetermine its elastic properties after deformation.     

Modification of structural states in titanium nickelide under severe deformation

X-ray diffraction, electron microscopy, and thermal analysis are used to study the effects of high degrees of deformation on the structural state of titanium nickelide. It is established that nearly amorphous regions are formed along with defective fine-grained structure in strongly deformed titanium nickelide.Tomsk Construction Engineering Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 3–7, December, 1992.     

The role of curvature of the crystal structure in the formation of micropores and crack development under fatigue fracture of commercial titanium

The multiscale mechanism of fatigue fracture of titanium with the surface layer hydrogenated under alternating bending at room temperature is studied. It is shown that the generation of the fatigue fracture occurs in the surface layer subjected to plastic deformation in conjunction with an elastically loaded substrate. The latter causes the appearance of a strong curvature of the material and the appearance of micropores in these areas along with any fatigue cracks. The emergence of the local curvature of the crystal structure plays a central role in the origin and the development of the fatigue fracture as the structural phase decomposition of the material under cyclic loading.     

The structure and fatigue life of titanium alloys processed by electrical pulses

The structure and properties of VT3-1 titanium alloy processed by electrical pulses are investigated. The electric pulse processing improves the fatigue life of titanium specimens, as follows from high-cycle fatigue tests.     

Theory of shallow donor impurity near-surface states in Si and Ge

Previously developed methods for determining the wave functions and energy levels of shallow donor impurities on the surface or in the bulk of a semiconductor have been extended to the case of impurities at a finite depth from the surface. Calculations were performed for impurities near either a (100) or (111) surface in Sci and for a (111) surface in Ge. The ground state and the excited state having the largest electric dipole coupling to the ground state wete determined. In addition, the optical absorption cross section for transitions from the ground state to this excited state were calculated for surface and near surface states. These results were used to calculate a theoretical absorption spectrum for Si doped uniformly to a depth of 10 atomic layers.     

Crystallographic properties and mechanical behaviour of titanium hydride layers grown on titanium implants

Commercially pure titanium for bone-anchored dental implants, subjected to a sand-blasting and acid-etching surface treatment, has been mechanically tested and analysed by scanning electron microscopy and transmission electron microscopy observations. A fcc titanium hydride layer grows on the polycrystalline titanium substrate with various epitaxial relationships, whose grains also show epitaxial relationships with each other. Indentations, flexion tests and dislocation analyses indicate that this hydride layer can be plastically deformed.     

Effect of ambient gas on structural and optical properties of titanium oxynitride films

Titanium oxynitride films have been deposited on glass substrates by reactive RF magnetron sputtering of titanium target. The influence of oxygen partial pressure in N₂ + Ar and N₂ + He mixtures was examined on structural and optical properties of titanium oxynitride films. The prepared samples were characterized by X-ray diffraction, EDS, surface profilometer, AFM and contact angle measurement system. With increase in oxygen partial pressure, the grain size decreases from ∼70 nm to ∼50 nm in N₂ + Ar mixture, while from ∼60 nm to ∼37 nm in N₂ + He mixture. The thickness calculated from optical transmission data and surface profilometer is in good agreement with each other. The deposited samples are hydrophobic by nature and the contact angle was found to decrease with increase in oxygen partial pressure. Samples prepared in oxygen partial pressure ≥5.5% show transmittance of about 97% in the visible region of the spectrum in both N₂ + Ar and N₂ + He mixtures. The atomic mass of the sputtering gas (Ar and He) significantly affects the primary crystallite size, orientation as well as band gap. We were able to relate the better crystallisation of titanium atoms with low partial pressure of oxygen when films are deposited in helium instead of argon due to Penning ionization.     

Metastable states,relaxation mechanisms,and fracture of liquids under severe loading conditions

The relaxation properties and fracture of glycerol, silicone oil, transformer oil, and water have been studied experimentally under shock wave loading. The power-law strain rate dependences of the stress amplitude and spall strength were found for the compression and rarefaction fronts, respectively. It was shown that temperature has a strong influence on the spall strength of glycerol near the phase transformation temperature. The power laws reflect a self-similar nature of the momentum transfer and fracture mechanisms of liquids that are conventionally observed in solids and governed by the mechanisms of defect-induced structural relaxation. The mechanisms of viscoelasticity are related to the metastable states that may give rise to a collective behavior of displacement field fluctuations (microshearing) in liquids and thus provide a viscoplastic response of liquids under high strain rate loading.     

Effect of structural heterogeneity on the fatigue strength of a dispersion-hardened alloy

A study is made of the fatigue strength of alloy 36NKhTYu in relation to its structural state. It is shown that the highest strengths, with good fracture toughness, are obtained with a disperse structure containing regions of high ductility.Deceased.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 86–91, February, 1989.     

Positron states on surface and in defective surface layers of semiconductors

The paper discusses the possible spectrum and properties of positron states on the surface of real semiconductors.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 71–75, July, 1979.     

Influence of near-surface graded-gap layers on electrical characteristics of MIS-structures based on MBE grown HgCdTe

The paper examines influence of near-surface graded-gap layers on electrical characteristics of MIS-structures fabricated on heteroepitaxial Hg_1?xCd_xTe films grown by molecular beam epitaxy (MBE). Two types of insulators, i.e., two-layer SiO₂/Si₃N₄ and anodic oxide films were used. As it is seen from the depth and width of the valley on the C-V characteristics, the capacitance is found to vary in a wide range, in contrast to the structures without graded-gap layers. It is shown that the graded-gap layer under MIS-structures with x = 0.22 effectively reduces the tunnelling generation via deep levels and increases a lifetime of minority carriers in the space charge region and its differential resistance. The properties of the HgCdTe-insulator interfaces are studied.     

Influence of thickness on optical properties of titanium layers

Titanium layers with different thicknesses of 21, 83.7, and 133 nm and same other deposition conditions were deposited on glass substrates at 300 K, by physical vapor deposition method under high vacuum conditions. The optical reflectance of the layers was measured in the wave length range of 400–800 nm. The optical properties were calculated by using Kramers-Kronig relations. Relation between the optical properties and nanostructure of the layers was investigated. By using Generalized Gradient Approximations in context of plane wave pseudopotentials (norm conserving and ultrasoft) method, band structure calculated and compared with experimental results.     

Effect of nuclear-reaction mechanisms on the population of excited nuclear states and isomeric ratios

Experimental data on the cross sections for channels of fusion and transfer reactions induced by beams of radioactive halo nuclei and clustered and stable loosely bound nuclei were analyzed, and the results of this analysis were summarized. The interplay of the excitation of single-particle states in reaction-product nuclei and direct reaction channels was established for transfer reactions. Respective experiments were performed in stable (⁶Li) and radioactive (⁶Не) beams of the DRIBs accelerator complex at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, and in deuteron and ³Не beams of the U-120M cyclotron at the Nuclear Physics Institute, Academy Sciences of Czech Republic (?e? and Prague, Czech Republic). Data on subbarrier and near-barrier fusion reactions involving clustered and loosely bound light nuclei (⁶Li and ³He) can be described quite reliably within simple evaporation models with allowance for different reaction Q-values and couple channels. In reactions involving halo nuclei, their structure manifests itself most strongly in the region of energies below the Coulomb barrier. Neutron transfer occurs with a high probability in the interactions of all loosely bound nuclei with light and heavy stable nuclei at positive Q-values. The cross sections for such reactions and the respective isomeric ratios differ drastically for nucleon stripping and nucleon pickup mechanisms. This is due to the difference in the population probabilities for excited single-particle states.     

Annihilation of persistent slip bands and its effect on the fatigue life of copper single crystals

In single-slip-oriented copper single crystals, which were cyclically deformed under constant plastic shear strain amplitude control, a persistent slip band (PSB) was initiated on the persistent slip line (PSL) that first formed in the matrix vein dislocation structure. During intermediate temperature recovery (ITR) treatment in vacuum at 245 to 400°C, the variations in dislocation configurations and other defects of fatigued specimens were studied by using the scanning electron microscopy (SEM) electron channelling contrast (ECC) and the positron annihilation life (PAL) techniques. The results show that the ladders in the PSBs became curved and broken, or escaped locally until the PSBs disappeared completely during ITR treatment. The annihilation of the PSBs and other dislocation structures in the fatigued specimens prolonged the fatigue life to a certain extent.     

Atomistic mechanisms of fatigue in nanocrystalline metals

We investigate the mechanisms of fatigue behavior in nanocrystalline metals at the atomic scale using empirical force laws and molecular level simulations. A combination of molecular statics and molecular dynamics was used to deal with the time scale limitations of molecular dynamics. We show that the main atomistic mechanism of fatigue crack propagation in these materials is the formation of nanovoids ahead of the main crack. The results obtained for crack advance as a function of stress intensity amplitude are consistent with experimental studies and a Paris law exponent of about 2.     

Simulation of transport and relaxation of hot electrons in the near-surface layers of nanostructured and crystalline silicon dioxides

Computer simulation has been performed to investigate the transport and energy relaxation of photoelectrons in the near-surface layers of nanostructured and crystalline silicon dioxides in the presence and absence of an electric field. Calculations have shown that nanostructured samples have a shorter hot-electron thermalization time and exhibit weaker influence of an electric field on the electron energy relaxation process than the bulk crystal. The size effect calculated in terms of electron thermalization time is most pronounced at particle sizes less than 5 nm.