Role of external impacts in nanostructured titanium alloys

Specifics of the effects of electroplastic deformation, ion implantation (II), and ultrasonic treatment (UST) on the structure and characteristics of coarse-grained (CG) and ultrafine-grained (UFG) VT1-0, VT6 and TiNi titanium alloys are investigated. The introduction of pulse current during cold rolling promotes increased deformability and causes stress jumps during tension that result from phase transformations or the electroplastic effect (EPE). It is shown that EPE is a structurally sensitive property dependent on the size of grains. Methods of surface II and UST change the phase composition and lead to additional structural refinement in layers with a thickness of 0.1–10 microns.     

The influence of the initial structural state of armco iron on the ultrasonic treatment effect

Methods of diffraction electron microscopy have been used to examine the types of dislocation substructures formed in the surface layer of armco-iron specimens subjected to ultrasonic treatment. It is shown that banded or equiaxed ultrafine-grained structure can be generated in the material depending on its initial structural state. The special features of the plastic deformation and fracture of the ultrafine-grained surface layers of the specimens under uniaxial tension are described. The extent to which the mechanical properties of the examined material are improved by ultrasonic treatment has been found to depend on its initial state. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 74–82, January, 2009.     

Structure and mechanical and electrochemical properties of ultrafine-grained Ti

A study is conducted into the microstructure and physico-mechanical properties of ultrafine-grained titanium produced by severe plastic deformation using the method of equichannel angular pressing. The effects of thermal and mechanical treatment on these characteristics are investigated. The possibility of forming mechanical properties in titanium that compare well with those of highly doped titanium alloys is shown. Institute for Strength Physics and Materials Science; Siberian Physical-Technical Institute at Tomsk State University; Institute of Physics of Advanced Materials at UFA Aviation Technology University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 77–85, January, 2000.     

True Grain-Boundary Slipping in Coarse- and Ultrafine-Grained Titanium

The temperature dependence of internal grain-boundary friction in coarse- and ultrafine-grained titanium is investigated. It is demonstrated that true grain-boundary slipping causes internal grain-boundary friction in ultrafine-grained titanium, as in coarse-grained metals. It is established that when going from the coarse-grained structure with perfect grain boundaries to ultrafine-grained structure with imperfect grain boundaries, the temperatures of the beginning and intense development of true grain-boundary slipping decrease together with the activation energy of this process. The diffusion mechanism of true grain-boundary slipping is justified for both structural states.     

Structure,unelastic properties,and deformation behavior of ultrafine-grained titanium

The results of investigations into the structure, unelastic properties, deformation behavior, strength, and plasticity of ultrafine-grained titanium produced by equichannel angular pressing are discussed. Particlular emphasis has been placed on the grain-boundary unelasticity and the effects of external thermal and thermal-force actions on the deformation behavior and plastic deformation localization at the meso- and macroscale levels. The influence of cold plastic deformation of ultrafine-grained titanium on the grain-boundary unelasticity and temperature dependence of the mechanical properties is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 33–43, September, 2004.     

High-rate erosion of Ti–6Al–4V ultrafine-grained titanium alloy obtained via intensive plastic torsional deformation

Testing results for Ti–6Al–4V ultrafine-grained titanium alloy obtained via intensive plastic torsional deformation (IPTD) are presented. To estimate the effect of IPTD treatment on the behavior of this material under erosion conditions, special experimental techniques were developed. The ultrafine-grained alloy was tested alongside with the traditional coarse-grained titanium alloy in an erosion wind tunnel in an air flow with corundum particles as an abrasive material. The erosion resistance of the material was estimated from the mass loss of specimens. Despite a considerable increase in the static strength characteristics, the nanostructured material did not demonstrate any increase in its erosion resistance in comparison with the initial alloy.     

Low-temperature plasticity in nanocrystalline titanium and copper

The stress-strain compressive curves, temperature dependences of the yield stress, and small-inelastic-strain rate spectra of coarse-grained and ultrafine-grained (produced by equal-channel angular pressing) titanium and copper are compared in the temperature range 4.2–300 K. As the temperature decreases, copper undergoes mainly strain hardening and titanium undergoes thermal hardening. The temperature dependences of the yield stress of titanium and copper have specific features which correlate with the behavior of their small-inelastic-strain rate spectra. Under the same loading conditions, the rate of microplastic deformation of ultrafine-grained titanium is lower than that of coarse-grained titanium and the rate peaks shift toward high temperatures. The deformation activation volumes of titanium samples differing in terms of their grain size are (10–35)b ³, where b is the Burgers vector magnitude. The dependences of the yield stress on the grain size at various temperatures are satisfactorily described by the Hall-Petch relation.     

The Effect of Severe Plastic Deformation on the Structure and Mechanical Properties of Al–Mg–Li Alloys

The structural-phase state and mechanical properties of commercial aluminum alloys produced by severe plastic deformation are studied and compared to the initial polycrystalline state. This kind of treatment is found to give rise to the formation of a homogeneous ultrafine-grained structure with second-phase particles occurring predominantly along grain boundaries. With this structure, the strain-temperature and strain-rate intervals wherein the superplastic properties of the alloys under study are observed are shifted to lower temperatures and higher rates.     

Microstructural analysis by scanning thermal microscopy of a nanocrystalline Fe surface induced by ultrasonic shot peening

Experiments were carried out using a scanning thermal microscope (SThM) to investigate the ultrafine-grained microstructures in the surface layer of a pure iron sample produced by ultrasonic shot peening. The analysis of thermal properties by SThM shows that the thermal conductivity strongly depends on the grain size of the microstructure. The different contrasts on the thermal conductivity images are used to estimate the thickness of the affected surface layer produced by ultrasonic shot peening. The results demonstrate that the SThM can be used as a powerful tool for the microstructural analysis of the ultrafine-grained surface layer.     

Optical characteristics of titanium with a natural surface layer

We discuss the solutions of the inverse problem of multiangle ellipsometry for titanium with a natural surface layer, namely, the determination of the thickness of the near-surface layer and optical characteristics by use of which one can interpret the titanium structure. It turned out that the studied samples of pure polycrystalline titanium have a rather thick inhomogeneous layer of polycrystalline titanium with oxygen and, on this layer, there is a surface layer similar to titanium oxide. The data on the optical characteristics of pure polycrystalline titanium agree well with those determined earlier by other optical methods.     

Peculiarities in the thermal and elastic properties of polycrystalline titanium near the electronic topological transition

Temperature dependences of the photoacoustic signal magnitude and the relative velocity variation of longitudinal ultrasound in polycrystalline titanium are measured. Anomalous behavior of these quantities is observed in the temperature region corresponding to the electronic topological transition in a titanium single crystal. The results of measurements are interpreted as an experimental verification of the possibility for the anomalies associated with the electronic topological transition to “survive” in a polycrystalline metal.     

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.     

Optical,structural, and photocatalytic properties of the nanosized titanium dioxide films deposited in magnetron discharge plasma

The conditions of the optimum and controlled deposition of titanium dioxide nanolayers in the cylindrical gas discharge plasma of a magnetron having a unique design are found and described. The examination of the grown films by Raman spectroscopy is used to determine the conditions of deposition of the amorphous and polycrystalline phases of titanium dioxide. The films deposited on a cold substrate are amorphous, and the films deposited on a heated substrate consist of polycrystalline anatase. The evolution of the spectral lines of argon, oxygen, and titanium and the discharge voltage drop are studied as a function of the magnitude and the direction of changing the discharge current. The results obtained are shown to be applied for contactless optical monitoring. The refractive index of the films n is shown to have a nonlinear dependence on the layer thickness, and the layers that have a high photocatalytic activity and can be used to remove inorganic pollutants from the environment are shown to be grown.     

Ultrasonic effects on titanium tanning of leather

The effects of ultrasound on titanium tanning of leather were investigated. Either 20 or 40 kHz ultrasound was applied to the titanium tanning of pigskins. Five different treatment conditions were carried out and the effects were examined, such as leather shrinkage temperature (T(s)), titanium content and titanium distribution in the leather. Overall heat loading was carefully controlled. Results showed that 20 kHz ultrasound effectively improves titanium agent penetration into the hide and increases the leather's shrinkage temperature. Doubling the frequency to 40 kHz produced negligible enhancements. An impressive 105.6 degrees C T(s) was achieved using 20 kHz ultrasound pretreatment of the tanning liquor followed by 20 kHz ultrasound in the tanning mixture (liquor plus pigskins) in a special salt-free medium. Finally, using a unique ultrasonic tanning drum with 26.5 kHz ultrasound, the T(s) reached a record level of 106.5 degrees C, a value not achieved in conventional (no ultrasound) titanium tanning. The ultrasonic effects on titanium tanning of leather are judged to make a superior mineral tanned leather.     

Theoretical examination of ultrasonic pole figures via comparison with the results analyzed by finite element polycrystal model

The ultrasonic wave velocities in a polycrystalline aggregate are sensitively influenced by texture development due to plastic deformation. According to Sayer's model, it is possible to construct ultrasonic pole figures via the crystallite orientation distribution function (CODF), which can be calculated by using ultrasonic wave velocities. In the previous papers, the theoretical modeling to simulate ultrasonic wave velocities propagating in solid materials under plastic deformation has been proposed by the authors and proved to be a good agreement with experimental results. Generally, wave velocities are dependent upon the propagating wave frequency; hence to evaluate texture development via ultrasonic pole figures it is necessary to examine an influence of frequency dependence on the ultrasonic wave velocities. In the present paper, the proposed theoretical modeling is applied to the texture characterization in polycrystalline aggregates of FCC metals under various plastic strain histories via ultrasonic pole figures, and also the frequency dependence is examined by using Granato-Lücke's dislocation strings model. Then the simulated ultrasonic pole figures are compared with the pole figures analyzed by the finite element polycrystal model (FEPM). The good qualitative agreement between both results suggests the sufficient accuracy of our proposed theoretical modeling.     

Dynamic pressing of titanium for producing an ultrafine-grained structure

Dynamic equal-channel angular pressing, a new method for the intense plastic deformation of materials, was developed and applied to titanium, as an example. A sample, accelerated in a gun to a velocity of 300 m/s, impinged on a matrix with intesecting channels. The deformation of titanium occurred at a shear-deformation rate of 10⁴–10⁵ s^?1 and pressure of several GPa. Upon deformation, the strength of titanium increased by a factor of 2, with the plasticity remaining at an acceptable level. Metallographic and electron microscopy analyses demonstrated that, under the action of intense deformation, the initial course-grained structure of titanium transforms into an ultrafine-grained one.     

Directional Young’s modulus of single-crystal and cold-rolled titanium from ab initio calculations: Preferred crystal orientation due to cold rolling

Titanium is a strong, corrosion resistant metal with low mass density, making it ideal for various purposes, including aviation and medical applications. In the present work, the elastic properties of titanium have been investigated using the first principles Exact Muffin-Tin Orbitals method. The focus of our study is the anisotropic elasticity of single-crystal and cold-rolled titanium. Both types of titanium are used in industrial applications because of their special mechanical properties compared to randomly ordered polycrystalline alloys. Single crystals have better creep resistance compared to polycrystalline metals, while cold-rolled ones, on the other hand, possess more strength. Here cold-rolled titanium is investigated for the first time using ab initio calculations. Single-crystal results are obtained directly from first principles total energy calculations, whereas the elasticity of the cold-rolled structure is estimated from the single-crystal data. The elasticity of cold-rolled titanium has previously been investigated only experimentally, and thus the present computational approach provides new insight and valuable complementary information, not only for cold-rolled titanium, but also for more complex structures. Our results are found to be in good agreement with experimental findings and therefore serve as a starting point for investigating the elasticity of titanium alloys, which, using our method, can be accomplished as easily as the pure titanium case.     

Diffuse scattering of polarized neutrons from a Ni 2% Ti alloy

The diffuse scattering of long wavelength polarized neutrons from a polycrystalline alloy of nickel containing 2% of titanium has been measured at 2, 70 K and at room temperature. The results show that the moment on the titanium atom is nearly zero and the magnetic effects around an impurity are limited to the second nearest neighbours at 2 K. The disturbance is more widespread at higher temperatures.     

Micromechanical model of deformation-induced surface roughening in polycrystalline materials

A micromechanical model has been developed to describe deformation-induced surface roughening in polycrystalline materials. The three-dimensional polycrystalline structure is taken into account in an explicit form with regard to the crystallographic orientation of grains to simulate the micro- and mesoscale deformation processes. Constitutive relations for describing the grain response are derived on the basis of crystal plasticity theory that accounts for the anisotropy of elastic-plastic properties governed by the crystal lattice structure. The micromechanical model is used to numerically study surface roughening in microvolumes of polycrystalline aluminum and titanium under uniaxial tensile deformation. Two characteristic roughness scales are distinguished in the both cases. At the microscale, normal displacements relative to the free surface are caused by the formation of dislocation steps in grains emerging on the surface and by the displacement of neighboring grains relative to each other. Microscale roughness is more pronounced in titanium, which is due to the high level of elastic-plastic anisotropy typical of hcp crystals. The mesoscale roughness includes undulations and cluster structures formed with the involvement of groups of grains. The roughness is quantitatively evaluated using a dimensionless parameter, called the degree of roughness, which reflects the degree of surface shape deviation from a plane. An exponential dependence of the roughness degree on the strain degree is obtained.     

Ultrasonic irradiation assisted surface modification of titanium plates to improve MC3T3-E1 cell proliferation

The surface modification of titanium implants by NaOH has been widely investigated to improve their biocompatibility and bioactivity. It is very important to prepare an even network structure on titanium implants. In this work, ultrasonic irradiation (UI) is used along two different routes to obtain several modified surfaces on titanium plates: (1) the plates are first treated by a NaOH solution, and then UI is used to wash them in double distilled water; (2) the plates are modified by a NaOH solution in an ultrasonic cleaner with UI at 50 W. It is demonstrated that the UI energy can easily remove any weakly bound layers (WBL) on the titanium surface, leaving a strongly bound layer (SBL). The SBL is shown to enhance the proliferation of MC3T3-E1 preosteoblasts in comparison with the WBL. A dense and uniformly distributed nanostructure layer can be synthesized in situ on the surface of metallic titanium through a reaction between a NaOH solution and titanium under UI. The titanium plates prepared with NaOH and UI show better proliferation of preosteoblasts than titanium without UI.