Microstructure and stress rupture property of titanium-containing 11Cr ferritic/martensitic steels

The microstructure and stress rupture behavior of 11Cr ferritic/martensitic steels with 0.02 wt.%Ti (low Ti) and 0.14 wt.%Ti (high Ti) have been studied. The steels are prepared by vacuum induction melting followed by hot forging and rolling into plates. The results show that titanium is easy to combine with oxygen and other elements to form complex inclusions. Large MX particles with 1–3 μm are found in the high titanium steel. Most of the large MX particles have a TiO₂ cored structure. After normalizing at 1100 °C for 1 h, cooled in air and tempering at 750 °C for 1 h, nano-sized MX precipitates distribute densely near martenstic lath boundaries in the high titanium steel. The large MX particles cannot be dissolved even at austenitizing temperature up to 1300 °C. Creep cracks nucleate at the interface between matrixes and the large MX particles or titanium-containing oxide inclusions.     

Sintering of Al2O3–TiB2 nano-composite derived from milling assisted sol–gel method

Synthesis and sintering of an alumina /titanium diboride nano-composite have been studied as an alternative for pure titanium diboride for ceramic armor applications. Addition of TiB₂ particles to an Al₂O₃ matrix can improve its fracture toughness, hardness and flexural strength and offer advantages with respect to wear and fracture behavior. This contribution, for the first time, reports the sintering, microstructure, and properties of Al₂O₃–TiB₂ nano-composite densified with no sintering aids. Nano-composite powder was produced by combination of sol–gel and mechano-chemical methods. The densification experiments were carried out using both hot pressing and pressureless sintering routes. In the pressureless sintering route, a maximum of 92.3% of the theoretical density was achieved after sintering at 1850 °C for 2 h under vacuum. However, hot pressing at 1500 °C for 2 h under the same condition led to achieving a 99% of the theoretical density. The hot pressed Al₂O₃–TiB₂ nano-composites exhibit high Vickers hardness (16.1 GPa) and a modest indentation toughness (~ 4.2 MPa.m^1/2).     

Effect of titanium ions on the ion release rate and uptake at the interface of silica based xerogels with simulated body fluid

The dissolution and surface layer changes of new xTiO₂(100 − x)[4SiO₂·CaO·0.3P₂O₅] sol–gel derived xerogels (0 ⩽ x ⩽ 20 mol%) have been investigated in Kokubo’s simulated body fluid (SBF). The ionic leaching rate was analysed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). ICP-AES results showed a relatively fast dissolution of titanium free sample, with a high release of phosphorous and calcium ions in the first hour of incubation while the release of silicon ions continuously increased up to 6 h of immersion. The titanium dioxide addition up to 20 mol% differently influences the release of phosphorus, calcium and silicon ions, i.e. TiO₂ strongly stabilises the phosphorus ions, to a lesser extent the calcium ions, and has almost no effect on the silicon ions release. The structural changes were evaluated using X-ray powder diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The XRD results show that all samples remain mainly amorphous after immersion in SBF. The changes occurred in the surrounding of phosphorous and silicon ions are well reflected in FTIR spectra and they were correlated with the samples stability in SBF.     

Effects of degree of deformation on the microstructure,mechanical properties and texture of hybrid-reinforced titanium matrix composites

Titanium matrix composites reinforced by TiB whiskers and La₂O₃ particles are synthesized in a consumable vacuum arc remelting furnace by an in situ technique based on the reaction between Ti, LaB₆ and oxygen in the raw material. The titanium matrix composites are hot rolled with degrees of deformation of 60%, 80%, 90% and 95%. The effects of the hot rolling degree of deformation on the mechanical properties of the composites are investigated by experiment and modeling. In particular, the variation in the inclination of the TiB whiskers during rolling is quantified in the model. The results show that, with increasing degree of deformation, the mechanical properties of composites are improved. Modeling of the mechanical properties reveals that grain refinement and TiB whisker rotation during rolling contribute to the improvement in the yield strength of the titanium matrix composites. Electron backscatter diffraction and transmission electron microscopy observations are used to study the texture of the composites. It is found that the orientation relationships between Ti matrix and TiB whiskers are [1 1 ?2 0]_Ti || [0 1 0]_TiB, (0 0 0 1)_Ti || (0 0 1)_TiB and (1 ?1 0 0)_Ti || (1 0 0)_TiB. TiB whiskers rotate in the rolling direction (RD) with increasing degree of deformation, which results in a higher intensity [1 1 ?2 0]_Ti || RD fiber due to the special orientation relationship between TiB and the Ti matrix.     

Superior hydrogen storage kinetics of MgH2 nanoparticles doped with TiF3

MgH₂ nanoparticles were obtained by hydriding ultrafine magnesium particles which were prepared by hydrogen plasma–metal reaction. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that the obtained sample is almost pure MgH₂ phase, without residual magnesium and with an average particle size of ∼300 nm. Milled with 5 wt.% TiF₃ as a doping precursor in a hydrogen atmosphere, the sample desorbed 4.5 wt.% hydrogen in 6 min under an initial hydrogen pressure of ∼0.001 bar at 573 K and absorbed 4.2 wt.% hydrogen in 1 min under ∼20 bar hydrogen at room temperature. Compared with MgH₂ micrometer particles doped with 5 wt.% TiF₃ under the same conditions as the MgH₂ nanoparticles, it is suggested that decrease of particle size is beneficial for enhancing absorption capacity at low temperatures, but has no effect on desorption. In addition, the catalyst was mainly responsible for improving the sorption kinetics and its catalytic mechanism is discussed.     

Viscoelastic and conductivity properties of thermoreversible polyaniline–DNNSA gel in m-cresol

The rheological behavior of polyaniline (PANI)–dinonylnaphthalene sulfonic acid (DNNSA) in m-cresol is studied for different weight percent (w/v) of PANI–DNNSA_0.5. From rheological viewpoint the sample behaves like viscous fluid at low concentration (2 wt%) and gel at the concentration ≥8 wt%. The 4 wt% PANI–DNNSA_0.5 in m-cresol is at typical viscoelastic percolation region which is sol in the absence of shear but show invariant storage modulus with frequency at 30 °C. SEM picture indicates fibrillar network structure in the gel and the doped polyaniline remain as nanofiber at ≤2 wt% concentrations. The complete doping of PANI in all the systems is confirmed from UV–vis spectra. The dc conductivity of the gel increases with increasing the concentration of PANI–DNNSA_0.5 in m-cresol showing a jump at ～4% concentration (percolation threshold). ac-Conductivity increases with increase in PANI–DNNSA_0.5 concentration studied here for each frequency. At lower frequency (<10⁵ Hz) ac-conductivity increase slowly with frequency but at higher frequency (>10⁵ Hz) the increase is large having a curve like behavior. The gel state shows an increase of module by ～5 orders and also an increase of ～3 orders in ac-conductivity at the same frequency. The impedance spectroscopy results suggest the formation of combined resistance and capacitance (R–C) circuits in the gel and the increase of PANI–DNNSA_0.5 in the gel increases the capacitive feature more dominantly though the path becomes less resistive. The process also signifies the preparation of DNNSA doped PANI nanofiber in the gel medium.     

Microstructure and properties of intermetallic composite coatings fabricated by selective laser melting of Ti–SiC powder mixtures

Transition metal silicides and carbides are attractive advanced materials possessing unique combinations of physical and mechanical properties. However, conventional synthesis of bulk intermetallics is a challenging task because of their high melting point. In the present research, titanium carbides and silicides composites were fabricated on the titanium substrate by a selective laser melting (SLM) of Ti–(20,30,40 wt.%)SiC powder mixtures by an Ytterbium fiber laser with 1.075 μm wavelength, operating at 50 W power, with the laser scanning speed of 120 mm/s. Phase analysis of the fabricated coatings showed that the initial powders remelted and new multiphase structures containing TiC_x, Ti₅Si₃C_x, TiSi₂ and SiC phases in situ formed. Investigation of the microstructure revealed two main types of inhomogeneities in the composites, (i) SiC particles at the interlayer interfaces and, (ii) chemical segregation of the elements in the central areas of the tracks. It was suggested and experimentally proven that an increase in laser power to 80 W was an efficient way to improve the laser penetration depth and the mass transport in the liquid phase, and therefore, to fabricate more homogeneous composite. The SLM Ti–(20,30,40 wt.%)SiC composites demonstrated high hardness (11–17 GPa) and high abrasive wear resistance (3.99 × 10⁻⁷–9.51 × 10⁻⁷ g/Nm) properties, promising for the applications involving abrasive wear.     

Density compatibility of encapsulation of white inorganic TiO2 particles using dispersion polymerization technique for electrophoretic display

The polymer encapsulated TiO₂ particles with negative charge surface functionality were prepared by a two-stage dispersion polymerization technique for applications in electrophoretic displays (EPDs). In order to give the functionality for inorganic pigment particles in the EPDs, we have investigated the density of the polymer encapsulation of TiO₂ particles with the density of 4.0 g/ml. The density of the polymer encapsulated TiO₂ particles is suitable to 1.7 g/ml, due to density matching with suspending media. In results, the obtained particles showed the average densities in the range 1.5–2.5 g/ml at 25 °C. The polymer encapsulation of TiO₂ particles was confirmed with scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The TGA results showed that the initial weight loss of the encapsulated particles occurred near 400 °C in nitrogen, due to the degradation of the encapsulating polymer of TiO₂ particles.     

Synthesis of nano-structured titanium carbide by Mg-thermal reduction

Nano-structured titanium carbides were synthesized by liquid-magnesium reduction of vaporized TiCl₄ + CCl₄ solution. Fine TiC particles were produced by the reaction of released Ti and C atoms, and vacuum was used to remove the residual phases of MgCl₂ and excess Mg. Characterization of products was performed with various reaction parameters.     

XPS study of the initial stages of oxidation of α2-Ti3Al and γ-TiAl intermetallic alloys

The initial stages of oxidation of α₂-Ti₃Al and γ-TiAl alloys at 650 °C under low oxygen pressure are shown to be characterized by three stages using XPS. Stage I is a pre-oxidation stage characterized by the adsorption and absorption of oxygen species. When the subsurface is saturated with dissolved oxygen (16 and 2 at.% on α₂-Ti₃Al and γ-TiAl, respectively), the selective oxidation of the alloy leads to the nucleation and growth of ultrathin (∼0.5 and ∼1.2 nm on α₂-Ti₃Al and γ-TiAl, respectively) alumina layers (stage II). The growth kinetics of the alumina layers is limited by the transport of Al in the alloy, leading to Al-depletion in the metallic phase underneath the oxide. When a critical concentration is reached (Ti₈₂Al₁₈ and Ti₇₅Al₂₅ on α₂-Ti₃Al and γ-TiAl, respectively), titanium oxidation occurs (stage III). Ti(III) and Ti(IV) oxide particles are formed at the surface of the still growing alumina layer.     

Synthesis,morphology, microstructure and magnetic properties of hematite submicron particles

We report on hydrothermal synthesis, plate-like morphology, microstructure and magnetic properties of hematite (α-Fe₂O₃) plate-like particles. The sample is obtained immediately after the hydrothermal process without using any template and without further heat treatment. The so-obtained sample is characterized by X-ray powder diffraction (XRPD), energy-dispersive X-ray spectroscopy (EDX), field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and superconducting quantum interference device (SQUID) magnetometer. XRPD confirms the formation of a single-phase hematite sample whereas EDX reveals that iron and oxygen are the only components of the sample. SEM, FE-SEM, TEM and HRTEM show that the sample is composed of plate-like particles. The width of the particles is ～500 nm whereas thickness is ～100 nm (aspect ratio 5:1). The HRTEM images exhibit well defined lattice fringes of α-Fe₂O₃ particles that confirm their high crystallinity. Moreover, the HRTEM analysis indicates the plate-like particles preferring crystal growth along [0 1 2] direction. Magnetic measurements display significant hysteretic behavior at room temperature with coercivity H_C = 1140 Oe, remanent magnetization M_r = 0.125 emu/g and saturation magnetization M_S = 2.15 emu/g as well as the Morin transition at T_M ～ 250 K. The magnetic properties are discussed with respect to morphology and microstructure of the particles. The results and comparison with urchin-like, rods, spherical, hexagonal, star-like, dendrites, platelets, irregular, nanoplatelets, nanocolumns and nanospheres hematites reveal that the plate-like particles possess good magnetic properties. One may conjecture that the shape anisotropy plays an important role in the magnetic properties of the sample.     

Microstructure and mechanical properties of ZrB2–SiC composites prepared by gelcasting and pressureless sintering

ZrB₂–SiC ceramic composites were prepared through water-based gelcasting and pressureless sintering. Effects of the pressureless sintering temperature (1500–2000 °C), heating rate (5–15 °C/min) and soaking time (0.5–2 h) on the relative density, microstructure and mechanical properties of the ZrB₂–SiC composites were investigated in detail. A sintering temperature of 2000 °C, a heating rate of 5 °C/min and a soaking time of 2 h were found to be the optimal pressureless sintering procedure. The relative density, flexural strength and fracture toughness of the ZrB₂–SiC composite prepared under the optimum condition were 97.8%, 403.1 ± 27.8 MPa and 4.05 ± 0.42 MPa·m^1/2, respectively.     

Kinetics and microstructure of laser chemical vapor deposition of titanium nitride

Titanium nitride (TiN) films were deposited onto Ti–6Al–4V substrates by laser chemical vapor deposition using a cw CO₂ laser and TiCl₄, N₂ and H₂ reactant gases. Laser-induced fluorescence (LIF) and pyrometry determined relative titanium gas phase atomic number density and deposition temperature, respectively. Auger electron spectroscopy found substoichiometric films, caused by diffusion of nitrogen through TiN grain boundaries to the titanium alloy substrate. The morphology is a polyhedral structure with crystallite sizes ranging from 10 to 1000 nm. The activation energy was calculated to be 122 ± 9 kJ mol⁻¹ using growth rates measured by film height and 117 ± 23 kJ mol⁻¹ using growth rates measured by LIF signals. Above N₂ and H₂ levels of 1.25% and below TiCl₄ input of 4.5%, the growth rate has a half-order dependence on nitrogen and a linear dependence on hydrogen. The rate-determining steps of TiN growth are discussed.     

Effect of the Cr content on the sintering behaviour of TiCN–WC–Ni–Cr3C2 powder mixtures

In TiCN–W–Cr–Ni cermets produced by liquid phase sintering melting occurs at lower temperatures as their Cr content increases. For low Cr additions (up to 4 wt.%) eutectic temperatures are close to those found in the TiC–WC–Ni system. For 8 wt.% Cr and above, temperatures are similar to those found in the Cr–Ni–C system. The precipitation of M₇C₃ carbides is observed to start at 8 wt.% Cr in samples sintered at 1425 °C for 1 h. This sets a limit for the Cr solubility in the binder phase of these cermets around 18 wt.%. The dissolution of WC and Cr₃C₂ particles starts at temperatures as low as 1150 °C, but that the homogenization of the binder phase is only achieved after melting. The carbonitride phase exhibits the typical precipitation of inner and outer rims onto Ti(C,N) cores. However, a fine precipitation of Ni-rich particles is found inside Ti(C,N) cores, likely related to coalescence phenomena.     

Carbothermal synthesis of ZrC powders using a combustion synthesis precursor

ZrC powders were synthesized by carbothermal reduction of a combustion synthesized precursor derived from zirconium nitrate, urea, and glucose mixed solution. The results showed that the obtained precursor was comprised of polyporous blocky particles. The precursor powders were subsequently calcined under argon at 1200–1600 °C for 3 h. The transformation of ZrO₂ to ZrC, by adopting this route, occurred at 1300 °C. The preparation of ZrC experienced an intermediate phase of ZrOxCy. ZrC powders synthesized at 1500 °C are characterized by the spherical shape, small particle size (120–180 nm in diameter), low oxygen content (1.4 wt.%) and non-aggregated particles.     

Elaboration and characterization of nanocrystalline TiO2 thin films prepared by sol–gel dip-coating

Nanocrystalline TiO₂ thin films were deposited on a ITO coated glass substrate by sol–gel dip coating technique, the layers undergo a heat treatment at temperatures varying from 300 to 450 °C. The structural, morphological and optical characterizations of the as deposited and annealed films were carried out using X-ray diffraction (XRD), Raman spectroscopy, Atomic Force Microscopy (AFM), visible, (Fourier-Transform) infrared and ultraviolet spectroscopy, Fluorescence and spectroscopic ellipsometry. The results indicate that an anatase phase structure TiO₂ thin film with nanocrystallite size of about 15 nm can be obtained at the heat treatment temperature of 350 °C or above, that is to say, at the heat treatment temperature below 300 °C, the thin films grow in amorphous phase; while the heat treatment temperature is increased up to 400 °C or above, the thin film develops a crystalline phase corresponding to the titanium oxide anatase phase. We have accurately determined the layer thickness, refractive index and extinction coefficient of the TiO₂ thin films by the ellipsometric analysis. The optical gap decreases from 3.9 to 3.5 eV when the annealing temperature increases. Photocatalytic activity of the TiO₂ films was studied by monitoring the degradation of aqueous methylene blue under UV light irradiation and was observed that films annealed above 350 °C had good photocatalytic activity which is explained as due to the structural and morphological properties of the films.     

Proximity effect controlled superconducting behavior of novel biphasic Pb–Sn nanoparticles embedded in an Al matrix

We report the synthesis of biphasic Pb (46 at.%)–Sn (54 at.%) nanoparticles dispersed in an aluminum matrix and explore the nature of the superconducting transition in these particles. The nanoscaled Pb–Sn alloy particles were dispersed in Al by rapid solidification and the two-phase nature of these particles was characterized by transmission electron imaging, diffraction and composition mapping. A weak superconducting transition occurs at 3.1 K in these alloys, which is much lower than the T_C expected for a Pb₄₆Sn₅₄ alloy or that due to the proximity effect between Pb and Sn. We show that it is the superconducting Al matrix with T_C = 1.2 K that plays a major role in determining the effective transition temperature of the system.     

Effect of thermal cycling on the expansion behavior of Al/SiCp composite

The coefficient of thermal expansion (CTE) and accumulated plastic strain of the pure aluminum matrix composite containing 50% SiC particles (Al/SiC_p) during thermal cycling (within temperature range 298–573 K) were investigated. The composite was produced by infiltrating liquid aluminum into a preform made by SiC particles with an average diameter of 14 μm. Experiment results showed that the relationship between the CTE of Al/SiC_p and temperature is nonlinear; CTE could reach a maximum value at about 530 K. The theoretical accumulated plastic strain of Al/SiC_p composites during thermal cycling has also been calculated and compared with the experimental results.     

Synthesis of π-conjugated polymers possessing 1,3-butadiene-1,4-diyl units by reactions of regioregular organometallic polymer having titanacyclopentadiene moieties in the main chain

The synthesis and properties of π-conjugated polymers possessing phenylene-1,4-diyl and 1,3-butadiene-1,4-diyl alternating units in the main chain by reactions of a regioregular organometallic polymer having titanacyclopentadiene-2,5-diyl unit are described. The polymerization of 1,4-diethynyl-2,5-dioctyloxybenzene with a low-valent titanium complex, generated in situ from titanium(IV) isopropoxide and isopropyl magnesium chloride, was carried out at ?78 °C to ?50 °C for 12 h to give the regioregular organotitanium polymer. The diene-containing π-conjugated polymers were obtained by the reactions of the organotitanium polymer with electrophiles such as hydrochloric acid and iodine. For example, the reaction with hydrochloric acid gave a diene-containing polymer in a 61% yield whose M_n and M_w/M_n were estimated as 5700 and 1.61, respectively (by GPC). The π-conjugated character of the resulting polymer could be supported by its UV–vis spectrum. That is, the absorption maximum (λ_max) of the polymer was observable at 470 nm, which was bathochromically shifted by 115 nm compared to that of a model compound (1,4-bis(2-methoxyphenyl)-1,3-butadiene, λ_max = 355 nm).     

Synthesis and hydrogen reduction of nano-sized copper tungstate powders produced by a hydrothermal method

The pure nano-sized copper tungstate (CuWO₄) powders were prepared by hydrothermal method and consequent annealing at 500 °C for 120 min. The thermogravimetric analysis was used to study dehydration processes, and the scanning electron microscopy (SEM) indicated that CuWO₄ particles were mostly spherical in the size range from 60 to 90 nm. Hydrogen reduction at 800 °C for 60 min converted the CuWO₄ to W–Cu composite powders. The hydrogen reduction results showed that nano-sized CuWO₄ particles calcining at 500 °C for 120 min indicated finer microstructure than the other calcination temperatures of 0 °C, 400 °C, 620 °C, 650 °C and 700 °C. W–Cu particles were observed finest and homogeneous in the size range from 90 to 150 nm by SEM images. Homogeneous distribution of W and Cu particles was clearly demonstrated by elemental mapping. Encapsulation of Cu phase by the W phase was observed by EDS and TEM. From FFT and HRTEM images, the orientation relationship of (01-1)_Cu ∥(01-1)_W and a semicoherent interface between W and Cu phases could be observed. A good correlation between the HRTEM image and the calculated lattice misfit (δ) was obtained.