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.     

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.     

Structure and properties of the bronze laser alloyed with titanium

The paper describes the microstructure and properties (microhardness and wear resistance) of the bronze laser alloyed with titanium. The laser alloying was done using a pulsed Nd:YAG laser with a generated beam energy of 25-35 J. A very fine microstructure was formed under such rapid solidification conditions like laser treatment. The high chemical homogeneity and fine structure of the melted zone were attributed to high cooling rates due to the short interaction time with Nd:YAG pulsed laser radiation and relatively small volume of the melted material. The structure obtained in the surface layer after laser alloying permits to get a high level of hardness and an improved wear resistance.     

Structure and physical properties of titanium diselenide intercalated with nickel

The structure, electrical resistivity, thermopower, and magnetic susceptibility of titanium diselenide intercalated with nickel (N_xTiSe₂) are studied systematically in the nickel concentration range x=0–0.5. In accordance with a model proposed earlier, strong hybridization of the Ni3d/Ti3d states is observed, giving rise to suppression of the magnetic moment because of delocalization of the nickel d electrons. It is shown that the strain caused by the Ni3d/Ti3d hybridization does not change the local coordination of a titanium atom.     

Enhanced in vitro biocompatibility of ultrafine-grained titanium with hierarchical porous surface

Bulk ultrafine-grained Ti (UFG Ti) was successfully fabricated by equal-channel angular pressing (ECAP) technique in the present study, and to further improve its surface biocompatibility, surface modification techniques including sandblasting, acid etching and alkali treatment were employed to produce a hierarchical porous surface. The effect of the above surface treatments on the surface roughness, wettability, electrochemical corrosion behavior, apatite forming ability and cellular behavior of UFG Ti were systematically investigated with the coarse-grained Ti as control. Results show that UFG-Ti with surface modification had no pitting corrosion and presented low corrosion rate in simulated body fluids (SBF). The hierarchical porous surface yielded by surface modification enhanced the ability of UFG Ti to form a complete apatite layer when soaked in SBF and promoted osteoblast-like cells attachment and proliferation in vitro, which promises to have a significant impact on increasing bone-bonding ability and reducing healing time when implanted due to faster tissue integration.     

Structure and mechanical properties of titanium nitride/carbon nitride multilayers

The structure and mechanical properties of the multilayers consisting of 5-73 nm thick titanium nitride (TiN) and 4.6 nm thick carbon nitride (CN) have been investigated. It has been found that the CN layers are amorphous and the TiN layers thinner than 17 nm are amorphous. The TiN layers become crystallized as the thickness is increased to 30 nm or thicker. The hardness from the composite response of the multilayered films and their substrates determined using continuous stiff measurement is smaller than the film-only hardness (without substrate effects) calculated using Bhattacharya-Nix empirical equation. The hardness increases with raising the thickness of TiN layers. With the crystallization of the TiN layer, the multilayers become even harder than that calculated based on the rule of mixtures. However, no enhancement in hardness has been observed when the TiN layers are amorphous.     

Structure and optical properties of chemically synthesized titanium oxide deposited by evaporation technique

Titanium oxide inorganic ion exchange material was synthesized by hydrolysis with water and ammonia solution. Structural feature of the synthesized titanium oxide was analyzed using X-ray diffraction, X-ray fluorescence and infrared spectrometer technique. Tentative formula of titanium oxide was determined and written as TiO₂·0.58H₂O. Titanium oxide films were deposited on glass substrates by means of an electron beam evaporation technique at room temperature from bulk sample. The films were annealed at 250, 350, 450, and 550 °C temperatures. Transmittance, reflectance, optical energy gap, refractive index and extinction coefficient were investigated. The transmittance values of 85% in the visible region and 88% in the near infrared region have been obtained for titanium oxide film annealed at 550 °C. Kubelka-Munk function was used to evaluate the absorption coefficient which was used to determine the optical band gap. It was found that the optical band gap increases with increasing annealing temperature whereas the refractive index and extinction coefficient decreases.     

Two-way reversible deformation in titanium nickelide

A systematic study has been made of the shape-memory effects which arise in titanium nickelide after prestraining under isothermal conditions. It has been found that under thermal cycling in the free state a broad spectrum of phenomena is observed — repeatedly reversible shape memory, reversible deformation, deformation of an oriented transformation, etc., each of which can be realized independently of the others in the temperature range of the B2 R and R B19' transformations. When summing up the observed laws of the mechanical behavior of the material we used concepts of heterogeneous development of deformation in crystals, structurally hereditary properties of alloys with a shape-memory effect, as well as the principle of independent initiation of various channels of deformation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 71–76, August, 1988.     

Mechanical properties,density, and defect structure of VT1-0 titanium after intense plastic deformation due to screw and longitudinal rollings

The influence of screw rolling combined with standard methods of mechanothermal treatment on the homogeneity of the forming submicrocrystalline structure, density, and mechanical performance of VT1-0 commercial titanium is studied. It is shown that such a treatment carried out within optimal temperature and strain rate intervals (special deformation conditions) causes minor softening of the material and can be effectively used to form a homogeneous submicrocrystalline structure with high strength and elastoplastic properties.     

Peculiar effects of plastic deformation by cold rolling on structure and mechanical properties of submicrocrystalline and titanium alloys

Using titanium VT1-0 and VT6 alloys as an example, peculiarities of the effect of plastic deformation by rolling at room temperature on the structure and mechanical properties of metallic materials in submicrocrytalline states are investigated. It is shown that this treatment can result in both hardening and softening of these alloys. It is established that variations in the behavior of their mechanical properties is controlled by the relation between structure parameters such as grain size, uniformity of their size distribution, and volume fraction of fine grains in the course of dicreasing dislocation density.     

Severe plastic deformation of amorphous alloys: I. Structure and mechanical properties

The basic regularities of variation in the structure and mechanical properties of amorphous Ni₄₄Fe₂₉Co₁₅Si₂B₁₀ alloy at severe plastic deformation (SPD) in a Bridgman cell at different temperatures are considered. It is shown that SPD is accompanied by homogeneous nanocrystallization, which is caused by the plastic flow mode. The transition from inhomogeneous mode of plastic flow to a qualitatively different one has been detected. The SPD structural model of deformational “dissolving” of crystals is proposed to explain why nanocrystals no more than 10 nm in size are observed during SPD. It is found that thermally activated nanocrystallization may occur at very low temperatures (77 K) under very high stress and with a high concentration of excess free volume.     

Structure and mechanical properties of titanium nickelide obtained by synthesis in the combustion regime

A study was made of the structure and mechanical properties of titanium nickelide obtained by synthesis in the combustion regime with subsequent shaping of the final product heated as a result of chemical reaction. It is shown that a nearly aggregate structure is obtained during synthesis, this structure improving the heat resistance of the alloy in the investigated temperature range. At the same time, dispersion hardening significantly improves the strength characteristics of the alloy.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 49–54, October, 1986.     

On the mechanism of deformation in submicrocrystalline titanium

The mechanical behavior and structural evolution of submicrocrystalline titanium in the course of deformation are investigated at room temperature. The possible mechanisms of deformation are analyzed. It is proved that the dislocation motion inside grains is responsible for the plastic flow.     

Effect of annealing on the microstructure and mechanical properties of ultrafine-grained commercially pure Al

The influence of annealing on the microstructure and mechanical properties of ultrafine-grained (UFG) commercially pure aluminum preliminarily subjected to severe plastic deformation by high pressure torsion has been studied. It is found that annealing of the UFG samples in the temperature range 363–473 K for 1 h leads to increases in the conventional yield strength and ultimate tensile strength, which attained maximum values (50 and 30%, respectively) after annealing at 423 K. A key role of nonequilibrium high-angle grain boundaries in the strengthening effect of UFG-Al due to annealing is discussed. The increase in the strength of UFG-Al is accompanied by a significant decrease in its ductility. A new approach of increasing the ductility of UFG-Al with retaining a high strength is proposed. It is an introduction of additional dislocation density to a UFG structure relaxed by annealing.