Reactive processing of titanium carbide with titanium

The reactive sintering of titanium carbide with titanium metal was studied using mechanical mixtures of fine-grained powders heated in vacuum above the TiC-Ti eutectic temperature. Mixtures with bulk compositions of TiC_0.94 to TiC_0.63 yielded nonstoichiometric carbide with less than 0.5 wt% residual titanium metal after sintering, while residual metal was observed at higher titanium concentrations. The effects of time, temperature, and composition on Mohs hardness, final porosity and final grain-size were determined using a Box-Wilson experimental design. The experimental ranges studied were sintering times of 10 to 100 min, sintering temperatures of 1650 to 1850° C, and compositions from TiC_0.94 to TiC_0.58. Over these experimental ranges, the effects of time and temperature were small compared with those of composition. The Mohs hardness increased approximately linearly from two to nine with increasing percentage of titanium metal in the starting powder. The average grain size ranged from 15 to 70μm, increasing with increasing time and temperature. For bulk compositions TiC_0.94 to TiC_0.70 grain growth was largely due to the conversion of titanium to substoichiometric carbide which grows epitaxially on the carbide grains. Substantial grain growth occurred for higher metal concentrations. The open porosity decreased from 28% to 16% as the amount of titanium metal in the starting powders was increased. Both the grain growth and the densification during reactive sintering of titanium-titanium-carbide mixtures were analysed in terms of a sintering model adapted from Kuczynski. A factor which empirically describes the behaviour of the system over a range of compositions was incorporated into the equations proposed by Kuczynski. Microstructural evidence and the activation energies for grain growth and densification all indicate that the rapid reaction between titanium metal and titanium carbide to form substoichiometric carbide occurs via short-circuit diffusion of carbon out of the carbide grains along Ti₂C platelets. Low sintered densities are attributed to the rapid formation of a solid titanium-carbide skeleton which prevents significant particle rearrangement in the eutectic liquid. Solution-precipitation processes do not appear to contribute significantly to the densification in this system.     

Interaction of hydroxyapatite with titanium nickelide and titanium

It has been established that the interaction of hydroxyapatite with titanium nickelide and titanium results in the formation of new phases whose physicomechanical properties and biocompatibility are unknown. After hydroxyapatite has been resorbed, these phases come in contact with tissue and near-tissue fluids and influence the result of the implant. Pis’ma Zh. Tekh. Fiz. 24, 41–44 (December 26, 1998)     

Inductive hot-pressing of titanium and titanium alloy powders

Inductive hot-pressing is a field-assisted sintering process (FAST) in which an electrical current is used to enhance the densification of the powder. Inductive hot-pressing could be employed to enable titanium powder to reach a higher density in less time than the pressing and sintering process. In this study, titanium and titanium alloy powders with different features were processed by means of inductive hot-pressing. The influence of processing temperature on density, microstructure, quantity of interstitial elements and hardness was investigated. Generally, practically fully dense materials were obtained without any carbon pick-up, even if the materials were in contact with the graphite matrix during processing. Nevertheless, there was an increment of the nitrogen content and some oxygen pick-up, especially for the powders with smaller particle size. Hardness is not significantly affected by the pressing temperature, but it strongly depends on the amount of interstitials.     

Ion beam nitriding of titanium and titanium alloy

Titanium and Ti8A/1Mo1V alloy have been nitrided with an ion beam source of nitrogen or agon and nitrogen, at a total pressure of 2?10×10^?4 torr. The treated surface has been characterized by surface profilometry, X-ray diffractometry, Auger Electron Spectroscopy (AES), and microhardness measurements. It was found that tetragonal Ti₂N phase forms in pure titanium and Ti8A/2Mo1V alloy with traces of AIN in the alloy. Two opposite processes were found to compete during the ion beam nitriding: (a) formation of nitrides in the surface layers; (b) sputtering of the nitrided layers by the ion beam. The highest surface hardness, of about 500 kg mm^?2 in titanium and 800 kg mm^?2 in Ti8A/1Mo1V, was obtained by nitriding with an ion beam of pure nitrogen at 4.2×10^?4 torr, at beam voltage of 1000 V.     

Preparing low-oxygen titanium powder by calcium reductant from titanium hydride

In a previous study, we prepared a low-oxygen titanium powder from titanium scrap through Hydrogenation-Dehydrogenation and deoxidation in a solid-state (DOSS) process with calcium. In this study, an advanced deoxidation in a solid-state process applied titanium hydride as a raw material is proposed to shorten the time of the previous DOSS process. Compared to the previous DOSS process, the total process time was shortened, and the same oxygen reduction rate was obtained. In addition, it was confirmed that the low-oxygen titanium powder prepared this by advanced DOSS process has a superior oxidation resistance than the titanium powder obtained by the previous study.     

Growth of titanium oxide overlayers by thermal oxidation of titanium

This paper describes a theoretical model for the growth of titanium oxide by thermal oxidation of titanium. It is shown that this model can explain the formation of layers of different oxides of titanium and the changes in these layers with variations in the conditions of oxidation. Some experimental X-ray diffraction results which support the model are also given.     

Explosive shock-compression processing of titanium aluminide/titanium diboride composites

Explosive shock-compression processing is used to fabricate Ti₃Al and TiAl composites reinforced with TiB₂. The reinforcement ceramic phase is either added as TiB₂ particulates or as an elemental mixture of Ti + B or both TiB₂ + Ti + B. In the case of fine TiB₂ particulates added to TiAl and Ti₃Al powders, the shock energy is localized at the fine particles, which undergo extensive plastic deformation thereby assisting in bonding the coarse aluminide powders. With the addition of elemental titanium and boron powder mixtures, the passage of the shock wave triggers an exothermic combustion reaction between titanium and boron. The resulting ceramic-based reaction product provides a chemically compatible binder phase, and the heat generated assists in the consolidation process. In these composites the reinforcement phase has a microhardness value significantly greater than that of the intermetallic matrix. Furthermore, no obvious interface reaction is observed between the intermetallic matrix and the ceramic reinforcement.     

Surface engineering and chemical characterization in ion-nitrided titanium and titanium alloys

The chemical and physical characteristics of ion-nitrided surface layers, obtained on - titanium alloys, are examined and correlated both with the working conditions adopted in the ion-nitriding process and with the alloy chemical composition. Besides the influence of the working parameters on the morphology and on the microstructures of the ion-nitrided surface layers, mainly the alloy element distributions both in surface coatings and in the substrate are analysed for five - titanium alloys of industrial use, and for titanium c,p. as reference, ionnitrided at various treatment temperatures. The nitriding process forms, on titanium alloy parts, high-hardness surface layers consisting of TiN ( phase) and Ti₂N ( phase) nitrides and an interstitial solid solution of nitrogen in the close-packed hexagonal lattice of titanium ( phase). The presence and the extent of these phases as well as the ion-nitrided layer morphology are essentially determined by the alloy chemical composition and the working parameters. In particular a low-temperature treatment produces an extended nitrogen diffusion in the matrix beneath a thin continuous nitrided layer, while a high-temperature treatment produces prevalently a continuous nitrided surface layer. The alloy element distribution appears differentiated in the various phases and may be correlated with the different affinity of these elements with nitrogen.     

Spongy titanium alloyed with oxygen for the production of titanium alloys

We study the influence of alloying of spongy titanium with oxygen on the structure, mechanisms of fracture, and mechanical properties of titanium. It is shown that, within the range of concentrations 0.05–0.30%, oxygen insignificantly affects both the structure and the mechanism of fracture of cast titanium but strongly increases its strength with preservation of plasticity within the admissible range specified for standard titanium alloys of this grade. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 3, pp. 78–80, May–June, 2008.     

The structure of porous nickel titanium reinforced by monolithic nickel titanium

The structure and elemental composition of a composite representing porous nickel titanium reinforced by a monolithic nickel titanium rod (TN-10 alloy) have been studied. The structures of the initial TiNi powder (PN55T45S grade), the porous and monolithic parts of this composite, and the transition regions between these parts have been studied using a scanning electron microscope (SEM 515). Elemental compositions of the TiNi matrix phase and secondary phase inclusions were determined using an electron probe microanalyzer (JEOL JSM 840). It is established that there is no clear interface between the sintered porous and monolithic parts of the composite. Instead, the TiNi particles and monolithic TN-10 alloy rod exhibit complete mutual dissolution. The elemental composition of the TiNi matrix region exhibits rather insignificant variations between monolithic and porous parts.     

Deposition of titanium/titanium oxide clusters produced by magnetron sputtering

Titanium clusters of nanometer sizes are produced by magnetron sputtering with subsequent aggregation in an argon gas flow. The produced Ti clusters are directed and deposited on a silicon substrate. Deposited films are analyzed by X-ray photoelectron spectroscopy in order to obtain the chemical composition and by atomic force microscopy and X-ray reflection methods to obtain information about the film structure. Experiments were carried out at different temperatures of the walls of the magnetron chamber. The size and the flux of clusters from the magnetron chamber are obtained by the analysis of the substrate surface with deposited clusters. It is found that the cluster parameters strongly depend on the temperature of the magnetron chamber walls. Molecules of titanium oxides may be nuclei of condensation and accelerate the nucleation process. A theoretical analysis based on experimental results is presented. It allows us to describe various stages of cluster evolution from their formation up to the deposition on the substrate and provides estimations for parameters of the processes involving clusters.     

Mechanical behaviour of SiC fibre-reinforced titanium/titanium aluminide hybrid composites

The viability of developing an SiC fibre-reinforced titanium/titanium aluminide hybrid matrix composite was explored. The hybrid composites are expected to be used at temperatures beyond those attainable in conventional titanium matrix composites while improving the damage tolerance of the titanium aluminide matrix composites. The room-temperature mechanical characteristics studied were tensile strength, fracture toughness, low-cycle fatigue life and fatigue crack growth rate. The mechanisms of damage initiation and propagation under various loading conditions were also characterized. The directions for developing a satisfactory composite with hybrid titanium/titanium aluminide matrix are also addressed.     

Synthesis of nanocrystalline titanium nitride by reacting titanium dioxide with sodium amide

A new method for synthesis of nanocrystalline titanium nitride was developed through the reaction of titanium oxide and sodium amide at 500–600 °C for 12 h in an autoclave. X-ray diffraction (XRD) and electron diffraction (SAED) results indicated the product had a cubic phase with lattice parameter a = 4.242 Å. Transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) revealed that the particle sizes were 10 to 40 nm. Quantitative analysis using X-ray photoelectron spectrum (XPS) showed the atomic ratio Ti:N was 1.03:1.     

Characterization of titanium dioxide atomic layer growth from titanium ethoxide and water

Atomic layer growth of titanium dioxide from titanium ethoxide and water was studied. Real-time quartz crystal microbalance measurements revealed that adsorption of titanium ethoxide is a self-limited process at substrate temperatures 100–250°C. A relatively small amount of precursor ligands was released during titanium ethoxide adsorption while most of them was exchanged during the following water pulse. At temperatures 100–150°C, incomplete reaction between surface intermediates and water hindered the film growth. Nevertheless, the deposition rate reached 0.06 nm per cycle at optimized precursor doses. At substrate temperatures above 250°C, the thermal decomposition of titanium ethoxide markedly influenced the growth process. The growth rate increased with the reactor temperature and titanium ethoxide pulse time but it insignificantly depended on the titanium ethoxide pressure. Therefore reproducible deposition of thin films with uniform thickness was still possible at substrate temperatures up to 350°C. The films grown at 100–150°C were amorphous while those grown at 180°C and higher substrate temperature, contained polycrystalline anatase. The refractive index of polycrystalline films reached 2.5 at the wavelength 580 nm.     

Effect of titanium on copper–titanium/carbon nanofibre composite materials

Copper/carbon nanofibre composites containing titanium varying from 0.3 wt.% to 5 wt.% were made, and their thermal conductivities measured using the laser flash technique. The measured thermal conductivities were much lower than predicted. The difference between measured and predicted values has often been attributed to limited heat flow across the interface. A study has been made of the composite microstructure using X-ray diffraction, transmission electron microscopy and Raman spectroscopy. It is shown in these materials, that the low composite thermal conductivity arises primarily because the highly graphitic carbon nanofibre structure transforms into amorphous carbon during the fabrication process.     

Preparation of titanium diboride powders from titanium alkoxide and boron carbide powder

Titanium diboride powders were prepared through a sol-gel and boron carbide reduction route by using TTIP and B₄C as titanium and boron sources. The influence of TTIP concentration, reaction temperature and molar ratio of precursors on the synthesis of titanium diboride was investigated. Three different concentrations of TTIP solution, 0.033/0.05/0.1, were prepared and the molar ratio of B₄C to TTIP varied from 1.3 to 2.5. The results indicated that as the TTIP concentration had an important role in gel formation, the reaction temperature and B₄C to TTIP molar ratio showed obvious effects on the formation of TiB₂. Pure TiB₂ was prepared using molar composition of Ti: B₄C = 1: 2.3 and the optimum synthesis temperature was 1200°C.