Ti Melt Research Articles

Nitrogen-doped TiO2 mesosponge layers formed by anodization of nitrogen-containing Ti alloys

An alloy containing 5 at.% of N was produced by arc melting of Ti and TiN powders. By anodization of the alloy in a 10 wt.% K2HPO4/glycerol electrolyte at 140 °C, oxide mesosponge layers can be formed with thickness as up to several micrometers. X-ray photoelectron spectroscopy confirms nitrogen uptake in the oxide. Photoelectrochemical measurements show successful N-doping of these mesoporous anodic layers with a significant visible light photoresponse.

Silicate Liquid Immiscibility within the Crystal Mush: Evidence from Ti in Plagioclase from the Skaergaard Intrusion

A key target in the study of layered intrusions is to constrain the liquid line of descent of the magma. However, the evolution of the interstitial liquid is rarely considered, and its liquid line of descent is often assumed to be equivalent to that of the bulk magma. Because of extensive sub-solidus and diffusional changes that occur in slowly cooled rocks, clues to the composition of the interstitial liquid can only be obtained using very slowly diffusing trace elements and components. This study uses the Ti concentrations and anorthite contents of interstitial plagioclase to consider the compositional evolution of the interstitial liquid in the Skaergaard Intrusion. Ti-XAn zoning of interstitial plagioclase does not follow the same cryptic variations that develop in plagioclase primocrysts as a function of stratigraphic height, demonstrating that the bulk and interstitial liquid lines of descent are not equivalent. After Fe-Ti oxides start to crystallize, Ti concentrations decrease in both primocryst and interstitial plagioclase as a result of decreasing melt Ti. However, in the interstitial plagioclase within a single thin section, divergent trends develop adjacent to fine-grained interstitial pockets containing diverse mineral assemblages, which are interpreted to represent the crystallized products of late-stage immiscible liquids. These trends vary systematically as a function of stratigraphic height and spatial location within the intrusion. The distribution and compositions of these plagioclase zoning trends are used to comment on the spatial distribution and differential movement of interstitial immiscible liquids within the intrusion. © The Author 2010. Published by Oxford University Press. All rights reserved.

Electron beam melting of Ti–48Al–2Cr–2Nb alloy: Microstructure and mechanical properties investigation

Gas atomized Ti–48Al–2Cr–2Nb powders have been used as precursor material in order to evaluate additive manufacturing for the production of near-net-shape γ-TiAl specimens to be employed in the field of aero-engines. In particular electron beam melting (EBM) is used to realize a selective densification of metal powder by melting it in a layerwise manner following a CAD design. The microstructure, the residual porosity and the chemical composition of the samples have been investigated both immediately after EBM and after heat treatments. High homogeneity of the samples, very low pickup of impurities (oxygen and nitrogen) with respect to the starting powders have been observed and due to an extremely low level of internal defects, intrinsic to EBM process, the tensile properties of the EBM γ-TiAl appear very consistent with a small scatter.

First direct comparison of platelet reactivity and thrombolytic status between Japanese and Western volunteers: Possible relationship to the “Japanese paradox”

ObjectiveTo determine and compare thrombotic and endogenous thrombolytic status in Japanese and Western populations. BackgroundIncidence of coronary heart disease (CHD) and AMI in Japan remains lower than in Western countries. Primary genetic effects are unlikely, given the increased CHD in Japanese migrants. For men, cholesterol and blood pressure have been similar in Japan and the U.S. Dietary factors are implicated, but how these effect CHD is unclear. We postulated that differences in thrombotic and/or thrombolytic status may contribute. MethodsWe measured thrombotic and thrombolytic status in 100 healthy Japanese (J) from Japan and 100 healthy Westerners (W) from the U.K. using the Global Thrombosis Test (GTT). The GTT employs non-anticoagulated blood to create platelet-rich thrombi under high shear (occlusion time OT; seconds), and then measures the restart of blood flow, due to spontaneous thrombolysis (lysis time LT; seconds). ResultsOT was longer in (J) compared to (W) (545 vs. 364, p<0.0001). LT was longer in (J) than in (W) (1753 vs. 1052, p<0.0001). Distribution of LT in (J) did not conform to a normal population, with markedly impaired thrombolytic status (LT>3000s) in 18%, compared to none of the Westerners (p<0.0001). ConclusionsThere are marked differences in thrombotic and thrombolytic status, with (J) having less prothrombotic (longer OT) but less favourable endogenous thrombolytic profile (longer LT). This may be important in the aetiology of thrombotic events. Since platelets and thrombolysis were both inhibited in (J) and yet incidence of AMI is lower, OT would seem more important than LT as a determinant of overall thrombotic risk in this population.

Thermodynamics, surface properties and microscopic functions of liquid Al–Nb and Nb–Ti alloys

The energetics of mixing in Al–Nb and Nb–Ti liquid alloys have been analysed through the study of surface properties (surface tension and surface segregation), dynamic properties (chemical diffusion) and microscopic functions (concentration fluctuations in the long-wavelength limit and chemical short-range order parameter) in the frame of statistical mechanical theory in conjunction with quasi-lattice theory (QLT). The phase diagram of the Al–Nb system exhibits three intermetallic compounds in the solid state, while a relatively simple phase diagram of the Nb–Ti system indicates nearly ideal mixing behaviour in the liquid phase and two stable solid phases. Since the structure of a liquid alloy is in some respects similar to that of a crystal, the complex formation phenomenon in Al–Nb melts has been analysed by a quasi-lattice structural model for chemical complexes. The energetics and structural arrangement in Nb–Ti melts have been studied by the quasi-chemical approximation (QCA) for the regular solution model.

Crystallographic oxide phase identification of char deposits obtained from space shuttle Columbia window debris

Char deposits on recovered fragments of space shuttle Columbia windowpanes were analyzed to further understand the events that occurred during orbiter reentry and breakup. The TEM analysis demonstrated that oxides of aluminum and titanium mixed with silicon oxides to preserve a history of thermal conditions to which portions of the vehicle were exposed. The presence of Ti during the beginning of the deposition process, along with the thermodynamic phase precipitation upon cool down, indicated that temperatures well above the Ti melt point were experienced. The stratified observations implied that additional exothermic reactions, expectedly metal combustion of a Ti–6Al–4V structure, had to occur for oxide formation. Results are significant for aerospace vehicles, where thermal protection system (TPS) breaches could cause material originally designed for substructural applications to be in direct path with reentry plasma.

Liquid phase separation in Gd–Ti and Gd–Zr melts

Liquid phase separation in two binary melt systems, Gd–Zr and Gd–Ti, related to phase separated metallic glasses are investigated by electromagnetic levitation experiments. Gd–Ti samples quenched onto a copper chill substrate from temperatures below the binodal line exhibit typical coarse phase separated microstructures, assigning melt immiscibility. The miscibility gap of Gd–Ti melts extends at least from 10 to 80 at.% Gd, much wider than reported previously. The critical temperature is about 1580 °C at Gd 20Ti 80. In the Gd–Zr system no indication of a stable liquid miscibility gap was detected. However, melt droplets quenched from the undercooled state exhibit concurrent coarse Gd and Zr primary phase constituents suggesting a metastable miscibility gap.

A study of the microstructural evolution during selective laser melting of Ti–6Al–4V

Selective laser melting (SLM) is an additive manufacturing technique in which functional, complex parts can be created directly by selectively melting layers of powder. This process is characterized by highly localized high heat inputs during very short interaction times and will therefore significantly affect the microstructure. In this research, the development of the microstructure of the Ti–6Al–4V alloy processed by SLM and the influence of the scanning parameters and scanning strategy on this microstructure are studied by light optical microscopy. The martensitic phase is present, and due to the occurrence of epitaxial growth, elongated grains emerge. The direction of these grains is directly related to the process parameters. At high heat inputs it was also found that the intermetallic phase Ti 3Al is precipitated during the process.

Interactions between TiAl alloys and yttria refractory material in casting process

In this work, U-shaped yttria ceramic crucibles have been prepared to melt Ti–47Al (at.%) alloy in a vacuum induction furnace, in order to simulate the worst practical situation with respect to the interactions between TiAl alloy and yttria refractory material. The effects of superheating temperature and cooling media on the metal–crucible interface, microstructure, chemical composition and microhardness have been evaluated. The investigation demonstrates that interactions between the yttria crucible and the molten TiAl consist of slight chemical dissolution and some physical erosion and the extent of the dissolution and erosion depend on the superheating temperature. The thermodynamics of TiAl–Y 2O 3 reactions have been investigated according to the calculation of the Gibbs free energy change of the yttria dissolution reaction. The possibilities of melting and casting TiAl alloys by the use of yttria refractory material are also discussed.

Wettability of Ti3SiC2 by Ag–Cu and Ag–Cu–Ti melts

Recently, the ternary carbide Ti3SiC2 has gained much attention due to its unique characteristics combining the properties of metals and ceramics (i.e., a low density, decent thermal and electrical conductivities, an excellent thermal shock resistance, a good machinability, damage tolerance, low friction, and so on). This study describes an investigation of the wettability in high vacuum of bulk Ti3SiC2 by a classical braze alloy based on the Ag–Cu–Ti system. Two techniques, i.e., the sessile drop and dispensed drop methods, were utilized. The results indicated that spreading kinetics is controlled by deoxidation kinetics of Ti3SiC2 surface under vacuum. The final contact angle on clean Ti3SiC2 is very small (~10°), testifying the development of strong, metallic interactions across the liquid–solid interface. The reactivity between the ternary carbide and the liquid phase during isothermal heating at 800 °C was also considered.

Advanced metal powder based manufacturing of complex components by electron beam melting

Electron beam melting of Ti–6Al–4V powder (∼30 μm diameter) to create complex, three-dimensional components layer by layer using CAD is described along with the characterisation of these products (builds) by optical and electron microscopy, and mechanical testing. Build defects, including porous (unmelted or unsintered) zones, inclusions and gas bubbles trapped in the atomised powder particles and retained in the build, are illustrated. Reticulated mesh geometries and their applications are described along with examples having biomedical applications. Microstructures of solid components and mesh arrays are described. Powder chemistries and solid build chemistries are also examined and shown to be constant for up to 40 cycles of powder reuse, but there was a 10–15% reduction in Al content in the solid builds at optimised build conditions. Quality control and related issues are also described using duplicate products for destructive testing correlated with removable quality control tabs on the builds.

Growth morphologies and mechanisms of TiC grains during Selective Laser Melting of Ti–Al–C composite powder

Selective Laser Melting (SLM) was used to consolidate the high-energy ball milled Ti–Al–C composite powder. The morphologies of the in-situ formed TiC grains under different laser processing parameters were investigated. It showed that with increasing the applied laser powers, the TiC grain morphologies experienced successive changes from a laminated shape to an octahedron shape, and then to a truncated near-octahedron shape, and finally to a near-spherical shape. It was believed that the continuously elevated SLM operating temperatures induced by the increasing laser powers played an important role in determining the TiC grain morphologies. Reasonable metallurgical mechanisms for grain growth behind the microstructural developments were proposed.

Thermal Explosion Reaction in the Ti-C System under Air Atmosphere

The ignition temperature of the thermal explosion reaction from the Ti-C system under air is much lower than that under Ar atmosphere. The ignition mechanism for the Ti-C system under air is determined to be a mechanism of chemical oven, and the reaction mechanism is dissolution, reaction, and precipitation. Namely, the heat generated from the oxidation and nitrification of Ti and C can promote the melting of Ti inside the compact; subsequently, the carbon atoms dissolve into the Ti melt and TiC precipitate.

Microstructure evolution of single crystal WC p reinforced Ti–6Al–4V metal matrix composites produced at different cooling rates

Laser melt injection (LMI) and vacuum arc melting (VAM) were explored to prepare single crystal WC particles (WC p) reinforced Ti–6Al–4V metal matrix composites (MMCs). The microstructure evolution of the produced WC p/Ti–6Al–4V MMCs and the interfacial reaction between WC p and liquid Ti at different cooling conditions were investigated. The interfacial reaction of WC p with Ti was sensitive to the cooling rate of the melt pool. The formation of the compact TiC layer during the rapid cooling rate in LMI intercepted the dissolution of WC p and inhibited the interfacial reaction and consequently resulted in the formation of thin reaction layers around WC p. Under the condition of slow cooling rate in VAM, the reaction between WC p and Ti melt was rather intensive and thick reaction layers consisting of W 2C and TiC were formed.

On the Mechanisms of Titanium Particle Reactions in O2/N2 and O2/Ar Atmospheres

AbstractCombustion of titanium particles in air may potentially be used for the in situ synthesis of nanoscale TiO2 particles, which can photocatalytically degrade chemical and biological air pollutants. The knowledge of Ti particle reactions in O2‐containing atmospheres is required to develop this method. In the present work, large (∼3 mm) single Ti particles were heated by a laser in O2/N2 and O2/Ar environments. High‐speed digital video recording, thermocouple measurements and quenching at different stages of the process were used for diagnostics. Analysis of the obtained temperature‐time curves and quenched particles does not show a significant influence of nitrogen on the oxidation of solid Ti. In all experiments, noticeable surface oxidation started at temperatures between ∼850 and ∼950 °C, leading to a sharp temperature rise at ∼1400 °C. During prolonged heating at the Ti melting point (1670 °C), a liquid TiO2 bead formed and, after an induction period, ejected fragments. It was shown that this phenomenon may result from an excess of oxygen in the liquid bead. Fragment ejection in O2/N2 atmospheres was more intense than in O2/Ar, indicating that N2 accelerates the oxidation of liquid Ti.

Thermodynamic properties of melts in Al–TI(Zr, Hf) binary systems

Aluminum-based alloys are widely used in different industries. We need to know the physical and chemical properties of these materials to improve the methods to produce them and to identify their optimal service conditions. Hence, the objective of this paper is to examine the thermodynamic properties of Al–Ti(Zr, Hf) binary melts by isoperibolic calorimetry at 1770 ± 5 K and 1790 ± 5 K. The experimental and data processing methods are described in [1]. Aluminum AV000 (99.999%), titanium, zirconium, and hafnium (99.9%) were used. Aluminum was placed into an yttria-lined corundum crucible in a massive molybdenum block. The calorimeter was calibrated against aluminum at the beginning of the experiment and against tungsten A2 (99.96%) at the end. Prior to the experiment, the calorimeter was warmed up under constant evacuation using forevacuum and diffusion pumps up to 773 K. After that, the chamber was filled with purified argon. The relative errors of the partial and integral mixing enthalpies were ±10 and ±2%, respectively. The reproducibility of the results is within 3%. During the experiment, we recorded variations in temperature that occurred when group IVb metal samples were introduced into liquid aluminum. The chamber heating rate is limited by the evacuation speed. The temperature variations during the experiment were recorded with a self-recorder and thermal effects were determined with the gravimetric method. The partial mixing enthalpies for Ti, Zr, Hf and integral mixing enthalpies for Al–Ti(Zr, Hf) binary melts are shown in Fig. 1. The thermodynamic properties of Al–Ti(Zr, Hf) binary melts are compared with similar data [2–8]. There are few experimental data on the thermodynamic properties of Al–Ti melts over a wide concentration range. At low concentrations, all mixing enthalpies of Al–Ti melts correlate with each other within experimental errors (Fig. 2a). However, the formation enthalpies turned out to be more exothermal at x Ti > 0.15 than Δ m H [3] determined calorimetrically at 2000 K. This is evidence of the temperature dependence of the mixing enthalpies of

Effect of Yttria on Interfacial Reactions Between Titanium Melt and Hot‐Pressed Yttria/Zirconia Composites at 1700°C

Various Y2O3/ZrO2 samples were fabricated by hot pressing, whereby Y2O3 was mutually dissolved or reacted with ZrO2 as a solid solution or Zr3Y4O12. Hot‐pressed samples were allowed to react with Ti melt at 1700°C for 10 min in argon. Microstructural characterization was conducted using X‐ray diffraction and analytical electron microscopy. The Y2O3/ZrO2 samples became more stable with increasing Y2O3 because Y2O3 was hardly reacted and dissolved with Ti melt. The incorporation of more than 30 vol% Y2O3 could effectively suppress the reactions in the Ti side, where only a very small amount of α‐Ti and β′‐Ti was found. When ZrO2 was dissolved into Ti on the zirconia side near the original interfaces, Y2O3 reprecipitated in the samples containing 30%–70 vol% Y2O3, because the solubility of Y2O3 in Ti was very low. In the region far from the original interface, α‐Zr, Y2O3, and/or residual Zr3Y4O12 were found in the samples containing more than 50 vol% Y2O3 and the amount of α‐Zr decreased with increasing Y2O3.

Anomalous modification of the ionospheric total electron content prior to the 26 September 2005 Peru earthquake

This paper investigates the features of pre-earthquake ionospheric anomalies in the total electron content (TEC) data obtained on the basis of regular GPS observations from the International GNSS Service (IGS) network. For the analysis of the ionospheric effects of the 26 September 2005 Peru earthquake, Global Ionospheric Maps (GIMs) of TEC were used. The possible influence of the earthquake preparation processes on the main low-latitude ionosphere peculiarity—the equatorial anomaly—is discussed. Analysis of the TEC maps has shown that modification of the equatorial anomaly occurred a few days before the earthquake. In previous days, during the evening and night hours (local time—LT), a specific transformation of the TEC distribution had taken place. This modification took the shape of a double-crest structure with a trough near the epicenter, though usually in this time the restored normal latitudinal distribution with a maximum near the magnetic equator is observed. Additional measurements (CHAMP satellite) have also confirmed the presence of this structure. To compare the vertical TEC measurements obtained with GPS satellite signals (GPS TEC), the International Reference Ionosphere, IRI-2001, was used for calculating the IRI TEC.

WC p/Ti–6Al–4V graded metal matrix composites layer produced by laser melt injection

The laser melt injection (LMI) process was explored to produce WC particles (WC p) reinforced Ti–6Al–4V metal matrix composites (MMC). In particular monocrystalline WC powder was used as injection particles to avoid the intercrystalline cracking often observed in granular or cast WC p reinforced MMC. WC p were injected into the extended part of the melt pool just behind the laser beam. The process allowed for the minimization of the WC p dissolution caused by the direct irradiation of the laser beam, and the decomposition reaction between WC p and Ti melt. Different parameters were applied, and a processing window of LMI was obtained. WC p exhibit a graded distribution along the depth direction of the MMC layer. New phases such as TiC and W 2C are observed in the MMC layer, in which TiC is the predominant phase. TiC grains present a continuous decrease in both amount and size with the distance from the surface to the bottom of the MMC layer. Two types of reaction layers around WC p can be distinguished, namely an irregular reaction layer and a cellular reaction layer. The growth and final morphology of reaction layers are most likely being dominated by the composition of the neighbouring melt pool. A gradual hardness distribution in the depth direction of the composites layer is observed. Moreover, the transition from the MMC layer to the substrate also exhibits a gradual change in the hardness.

Differential thermal analysis (DTA) on the reaction mechanism in Fe–Ti–B4C system

Abstract Differential thermal analysis (DTA) was undertaken to determine the reaction mechanism in the Fe–Ti–B 4 C system under argon. When the mixtures were heated to about 786 °C, Fe 2 B and C appeared as a result of Fe reacting with B 4 C. As the temperature continued to increase, FeTi formed by an interdiffusion between Fe and Ti. When the mixtures were heated to 1089 °C, FeTi reacted with Ti, leading to the formation of a Fe–Ti melt, into which the displaced C and B from B 4 C dissolve, forming a Fe–Ti–C–B melt. Finally, when the concentration of C and B attained a certain value, Ti reacted with C and B, yielding TiC and TiB 2 in the melt, and simultaneously considerable heat released.