Sonochemical method for producing titanium metal powder

We demonstrate a sonochemical method for producing titanium metal powder. The method uses low intensity ultrasound in a hydrocarbon solvent at near-ambient temperatures to first create a colloidal suspension of liquid sodium–potassium alloy in the solvent and then to reduce liquid titanium tetrachloride to titanium metal under cavitation conditions. XRD data collected for the reaction products after the solvent removal show only NaCl and KCl, with no diffraction peaks attributable to titanium metal or other titanium compounds, indicating either the formation of amorphous metal or extremely small crystallite size. TEM micrographs show that hollow spheres formed of halide salts and titanium metal, with diameters with diameters ranging from 100 to 500 nm and a shell thickness of 20 to 40 nm form during the synthesis, suggesting that the sonochemical reaction occurs inside the liquid shell surrounding the cavitation bubbles. Metal particle sizes are estimated to be significantly smaller than 40 nm from TEM data. XRD data of the powder after annealing and prior to removal of the alkali chloride salts provides direct evidence that titanium metal was formed during the sonochemical synthesis.     

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.     

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.     

Accelerated formation of an ultrafine-grained structure in a two-phase Ti alloy during compression with decreasing temperatures

ABSTRACT

Ultrafine-grained (UFG) structure is beneficial for overcoming the strength-ductility trade-off and enhancing the superplasticity of two-phase Ti alloys. Recently, it has been demonstrated that compression with decreasing temperatures is effective for producing UFG two-phase Ti alloys initially with lamellar microstructures. However, the effect of lamellar thickness on the microstructural evolution during this process has not yet been fully elucidated. In this study, Ti-6Al-4V alloys with different lamellar thicknesses were compressed while the processing temperature was decreased from 800°C to 600°C. The thinner lamellar microstructure was preferable for preventing void/crack formation, while accelerating the continuous dynamic recrystallisation, thus providing a fully UFG structure at a relatively low strain of 1.4. In addition, the origin of different plastic flows in each sample was analysed in detail by analysing the microstructural evolution. These findings demonstrate that the processing method is effective for reducing the grain size of a two-phase Ti alloy without severe plastic deformation techniques, which require large strain (≥4). A reduction in the strain required to achieve the UFG structure would be beneficial because conventional metal-forming processes, i.e. rolling, extrusion, or forging, which are suitable for mass production, could be used.     

Dynamic compression of titanium mononickelide

In this work, the behavior of powdered titanium mononickelide in static and shock compression and subsequent heating of the molds was studied using the methods of x-ray and dilatometric analysis. It was shown that during static compression, in distinction from shock compression, the phase transition B2 B19 takes place to a significant degree in the powder. At the same time, shock compression causes significantly more lattice defects in comparison with static compression, which the process of subsequent sintering activates. During the sintering of the pressings produced by static compression, the reverse transformation takes place in them accompanied by the effect of shape memory and causing the distension of the molds, which complicates the production of high-density sintered material.Translated from Izvestiya Vysshikh Uchebenykh Zavedenii, Fizika, No. 9, pp. 35–39, September, 1987.     

The formation of an ultrafine-grained structure in long-range order metals and alloys subjected to phase transformations and irradiation

The generation of an ultrafine-grained structure in long-range order metals and alloys by phase transformations and ion irradiation is studied. It is shown that the structure of pure iridium can be significantly refined under certain regimes of ion irradiation, and a microduplex structure possessing high mechanical properties can be produced in binary and ternary alloys, combining the processes of atomic ordering, aging, and phase recrystallization.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 81–89, August, 2004.     

Annealing behaviour of ultrafine-grained aluminium

Ultrafine-grained (UFG) aluminium, processed under fast cooling rate conditions (12?K?s^?1) following hot rolling (water quenched) exhibits enhanced thermal stability due to an increase in concentration of solid solution atoms, relative to the furnace cooled material. The influence of fraction recrystallized on yield stress and uniform elongation is reported to exhibit a slight deviation from the linear behaviour that is anticipated on the basis of the rule-of-mixtures. This result was rationalized on the basis of differences in the spatial distributions of the UFG and coarse grains and/or dislocation recovery mechanisms.     

Study of the grain-boundary structure in submicrocrystalline niobium after equal-channel angular pressing

The method of Mössbauer emission spectroscopy on ^119m Sn nuclei was used to study grain boundaries in submicrocrystalline Nb produced by the method of equal-channel angular pressing (ECAP) of poly-crystalline Nb (99.9%). ECAP included 16 passes at room temperature.     

非晶氧化钛薄膜形成过程中钛离子能量对表面结构影响的机理

研究了非晶氧化钛薄膜沉积过程中入射钛离子能量对表面结构形成机理以及薄膜特性的影响.模拟结果表明,通过提高入射钛离子能量,可以有效降低成膜表面粗糙度,从而减小薄膜表面的光学散射损耗.研究发现,当入射离子能量提高后,薄膜生长模式从"岛"状生长过渡到了"层"状生长,且离子入射点附近的平均扩散系数也有显著增加,这有利于形成更加平整的高质量薄膜表面.     

Analysis of precipitates in ultrafine-grained metallic materials

In the present work, new possibilities of the X-ray diffraction for investigations of the phase composition, size, shape and volume fraction of particles in ultrafine-grained ferritic/martensitic steel and the Cu-Cr-Zr alloy have been demonstrated. For the first time, the method of X-ray diffraction in the transmission mode was used to identify particles with a volume fraction of less than one percent in the ultrafine-grained materials studied. The small-angle X-ray scattering method was used to estimate the size and shape of dispersed particles. Specific features of the ultrafine-grained structure determined by the X-ray diffraction and transmission electron microscopy studies were used for estimation of dispersion hardening in the samples obtained by equal-channel angular pressing in comparison with the samples subjected to standard treatment.     

The heterogeneity of the aluminum structure and mechanical properties under equal-channel angular pressing

An analysis of the diffraction patterns from backscattered electrons and of measured microhardness has been performed to investigate the distributions of structural parameters (average grain/subgrain size and fraction of high-angle grain boundaries) and of the mechanical properties in the longitudinal section of a pure aluminum billet subjected to severe plastic deformation by equal-channel angular pressing. The distributions of the characteristics under study were found to be nonuniform. A minimum average grain size and a maximum fraction of high-angle boundaries were observed in the core of the billet. As the sample surface was approached, the examined parameters were seen to vary in magnitude through a broad range. Conceivable reasons for the structural heterogeneity of the material are discussed.     

Electronic structure of titanium monoxide with randomly distributed vacancies

The electronic structure of titanium monoxide TiO _y (0.810 ≤ y ≤ 1.262) in the high-temperature cubic phase with vacancies randomly distributed over the titanium and oxygen sublattices is calculated in the coherent potential approximation. The changes in the electronic spectra with the concentration of vacancies are retraced. The calculated spectra are compared to the available experimental data.     

Surface impurity diffusion-induced recrystallization of ultrafine-grained molybdenum

Methods of scanning and transmission electron microscopy are used to perform a comparative analysis of the structur evolution of ultrafine-grained molybdenum subjected to nickel-free annealing and to diffusion annealing accompanied by nickel penetration from the surface into the bulk of Mo(Ni) specimens. The kinetics of nickel diffusion-induced recrystallization of ultrafine-grained molybdenum in the temperature interval 1123–1223 K is investigated and the recrystallization activation energy is determined. Plausible reasons for a decrease in the nickel diffusion-induced recrystallization temperature of ultrafine-grained molybdenum as compared to its fine-grained cousin are discussed. The nickel diffusivity in ultrafine-grained molybdenum along grain boundaries is estimated on the basis of the results obtained. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 37–42, May, 2007.     

Crystal structure of the intermetallide NiMn doped with titanium

By the use of x-ray crystallography and neutron diffraction we have determined the crystal structure of the -and -modifications of titanium doped NiMn. It is shown that the introduction of Ti does not change the structure of -NiMn, in which a B2 type of order is retained. The Ti atoms in this case lie predominantly in the Mn sublattice. In contrast, the titanium doping leads to a change in the stacking order of the close-packed layers in the low temperature -modification of NiMn. As the Ti content is increased from 0 to 15 at. % the stacking order changes from 3R to 4H via a series of intermediate long-period structures. It is proposed that the change in the crystal structure of -NiMn as Ti is introduced facilitates the appearance of the shape memory effect in this intermettalic compound.TsNIIchermet. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 114–122, January, 1994.     

Surface structure of porous titanium nickelide produced by SHS

This work shows that the structure-phase composition of the surface of porous titanium nickelide manufactured using a self-propagating high-temperature synthesis (SHS) under the condition of layerwise combustion considerably changes as a function of the initial synthesis temperature. At low temperature of the powder mixture burning in the mode of pulsed combustion, a large amount of slag is formed on the external surface of the reaction layer, while at high temperature in the mode of continuous combustion the surface is covered with a nanostructured layer of sulfides, silicides, and oxides. The concentrational and structural composition of the master phase undergoing a thermoelastic phase transformation is similar for both synthesis regimes. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 67–72, August, 2008.