High Purity Ti Research Articles

Single-Step Pressureless Synthesis of the High-Purity Ti$_{3}$AlC$_{2}$ MAX-Phase by Fast Heating

Single-Step Pressureless Synthesis of the High-Purity Ti$_{3}$AlC$_{2}$ MAX-Phase by Fast Heating

Evaluation of thermal conductivities and thermal expansion coefficients of TiSi2 and Ti5Si3 ceramics prepared from Ti- and Si-rich wastes

TiSi2 and Ti5Si3 ceramics are high-temperature coating materials that are mainly synthesized using high-purity Ti and Si. In this study, to determine the application potential of TiSi2 and Ti5Si3 ceramics prepared through Al reduction-electromagnetic directional crystallization (AR-EDC) from Ti-bearing blast furnace slag (TBFS), spent SCR catalysts (SSCs), and diamond wire saw Si powder (DWSSP) for high-temperature coating, the thermal conductivity of AR-EDC-prepared TiSi2 and Ti5Si3 ceramics was measured. In addition, the effect of dissolved W and Al on the thermal conductivities of TiSi2 and Ti5Si3 ceramics was investigated. Meanwhile, the thermal conductivities of AR-EDC-prepared TiSi2 and Ti5Si3 ceramics were compared with those of commercial TiSi2 and Ti5Si3 ceramics and typical high-temperature coating materials. Additionally, the thermal coefficient expansions of AR-EDC-prepared TiSi2 and Ti5Si3 ceramics were compared with those of typical high-temperature Ti alloys. The results showed that the heat transfer mode of TiSi2 ceramics was phonon heat transfer, while that of the Ti5Si3 ceramics was radiation heat transfer, and dissolved W and Al reduced their thermal conductivities. At the temperature range of 298–873K, the thermal conductivities of the TiSi2 and Ti5Si3 ceramics were 29–35 W/(m·K) and 6–11 W/(m·K), respectively, and their thermal expansion coefficients were 8 × 10−6–12 × 10−6 K−1 and 5 × 10−6 –10 × 10−6 K−1, respectively. These results indicate that the thermal conductivity and thermal expansion coefficient of AR-EDC-prepared TiSi2 and Ti5Si3 meet the requirements for high-temperature coating. This study shows that Ti5Si3 and TiSi2 ceramics prepared from Ti- and Si-rich wastes are promising high-temperature coating materials.

Thermal Stability and Mechanical Behavior of Ultrafine-Grained Titanium with Different Impurity Content

Ultrafine-grained (UFG) commercially pure (Ti Grade 2) and high-purity (Ti 99.99%) titanium can be a good alternative to less biocompatible Ti alloys in many biomedical applications. Their severe plastic deformation may lead to a substantial increase of strength, but their highly refined microstructure show a lower thermal stability which may limit their range of applications. The purpose of this study was to investigate the effect of interstitial elements on the thermal stability of UFG Ti Grade 2 and high-purity Ti 99.99% processed by a multi-pass cold rolling to the total thickness reduction of 90%. The severely cold rolled Ti sheets were annealed at temperature in the range of 100-600 °C for 1 h and, subsequently, they were evaluated in terms of microstructure stability, mechanical performance as well as heat effects measured by differential scanning calorimetry (DSC). It was found that the microstructure and mechanical properties were relatively stable up to 200 and 400 °C in the case of UFG Ti 99.99% and Ti Grade 2, respectively. DSC measurements confirmed the aforementioned results about lower temperature of recovery and recrystallization processes in the high-purity titanium. Surprisingly, the discontinuous yielding phenomenon occurred in both investigated materials after annealing above their thermal stability range, which was further discussed based on their microstructural characteristics. Additionally, the so-called hardening by annealing effect was observed within their thermal stability range (i.e., at 100-400 °C for UFG Ti Grade 2 and 100 °C for UFG Ti 99.99%).

Deuteron and α-particle-induced nuclear reactions on 45Sc: activation cross section measurement and thick target yield evaluation

Systematic measurements of nuclear reaction cross sections were done in the low energy range for the two reactions 45Sc(d,p)46Sc and 45Sc(α,n)48V. Thin foils of high-purity (99.95%) natural Sc targets (100% 45Sc), purchased from Good-Fellow, were irradiated with 10 and 20 MeV incident deuteron and α-particle energies, respectively, at beam current of 100 nA using MGC-20 cyclotron. For precise measurements, high-purity Ti and Cu foils were used for monitoring the actual deuteron and α-particle beam intensities, respectively. The conventional stacked-foil technique was applied for measurement and calculation of the cross section values using a high-resolution γ-ray spectrometer for measuring the radioactivity. Nuclear model code EMPIRE-3.2 was used for calculation of the investigated excitation functions. The obtained results were compared with the experimental values and TENDEL-2021 data which are based on TALYS-1.96 code calculations. The integrated yields for the two reactions, based on the proposed average excitation functions, were estimated.

Unusual work hardening rate of a 3D gradient high purity Ti fabricated by laser surface treatment

Three types of heterogeneously structured high purity Ti samples, containing two iso-strained types and one iso-stressed type, were fabricated by using linear-scanning of laser surface treatment. The distances between the scanning-lines were modified to alter the space between the treated-zone and the matrix, forming a 3D gradient structure. These samples were tensile-tested at ambient temperature to characterize the strength and ductility. Scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM) were employed to characterize the microstructures. Results indicate that the laser-treated zone contains a melting zone (MZ) and a heat affected zone (HAZ). Among all the laser-treated samples, a variant of iso-stress type specimen exhibits the best combination of mechanical properties together with unusual work hardening rate. Microstructure investigation and DAMASK simulation results indicate that a variant of iso-stress type specimen might have lower stress and strain concentrations under unaxial tension than homogenous samples, which explains their unusual performance.

Microstructure and mechanical characterizations of additively manufactured high oxygen-doped titanium

In the present work, an additive manufacturing method of selective laser melting (SLM) was adopted to produce high oxygen-doped commercial purity titanium (Ti-O), with raw materials of high purity Ti and rutile (TiO2) powders. Microstructure and mechanical characterizations were then applied to the materials, which indicates that the TiO2 powders decompose under the SLM process and the oxygen atoms presented as solid solutes. Uniaxial quasi-static and dynamic compressive experiments suggest that the strength of SLM Ti-O drastically increases regardless of loading rate, yet the strain rate sensitivity is quite distinguished for pure Ti and the Ti-O alloy. Namely, strain rate jump tests demonstrated positive values of strain rate sensitivity for both samples, while under dynamic loading the Ti-O alloy and pure Ti exhibit obvious strain rate softening and strain rate hardening, respectively. The difference between these two SLM samples is then found to closely relate with their microstructures. Finally, a theoretical model is proposed to elucidate the abnormal strain rate softening.

Effects of Ti Target Purity and Microstructure on Deposition Rate, Microstructure and Properties of Ti Films.

Three titanium (Ti) targets with different purities were used to prepare Ti films on polyimide substrates by DC magnetron sputtering. The microstructures of Ti films were characterized by a metallographic microscope, X-ray diffractometer, field emission scanning electron microscope and three-dimensional surface topography instrument. In this study, we investigated the effects of Ti target purity and microstructure on film deposition rate, surface roughness, microstructure and resistivity. The results show that the deposition rate increased with increasing Ti target purity. Ti film deposited by the high-purity (99.999%) Ti target has fewer surface particles with smaller size, lower surface roughness and lower resistivity when compared to that prepared by the Ti target of low purity (99.7%). The surface roughness of Ti film prepared by the high-purity Ti target was Sa = 121 nm, the deposition rate was 16.3 nm/min and the resistivity was 6.9 × 10−6 Ω·m. For Ti targets of the same purity, the performance of Ti film prepared by a target with equiaxed α-phase grains is better than that of Ti film prepared by a target with twins and β-phase grains.

Preparation of low-oxygen-containing Ti–48Al–2Cr–2Nb alloy powder by direct reduction of oxides

A high-purity Ti–48Al–2Nb–2Cr alloy powder with an oxygen content as low as 0.0572 wt.% and a particle size of <150 μm was produced from a mixture of TiO2, Al2O3, Nb2O5, and Cr2O3 powders through reduction with magnesium and deoxidation with calcium. The phase and composition of the products were analyzed. The final product mainly included γ-TiAl and minor α2-Ti3Al phases, and Ti, Al, Cr, and Nb were homogenously distributed in the powder with a mole ratio of 49.73:43.51:2.05:1.98. The reduction and deoxidation mechanisms were investigated by thermodynamic modeling using the HSC Chemistry software and Pandat software based on the Ti alloy database.

Microstructure, Texture, and Hardness Evolution of Cold-Rolled High-Purity Ti Sheet During Annealing at 350 °C to 550 °C

Microstructure, Texture, and Hardness Evolution of Cold-Rolled High-Purity Ti Sheet During Annealing at 350 °C to 550 °C

Unique Work Hardening Rate of a Heterogeneous Structured High Purity Ti Subjected to Laser Surface Treatment

Unique Work Hardening Rate of a Heterogeneous Structured High Purity Ti Subjected to Laser Surface Treatment

Unusual Work Hardening Rate of a 3d Gradient High Purity Ti

Unusual Work Hardening Rate of a 3d Gradient High Purity Ti

Micro-compression of high oxygen doped single-crystal titanium along different orientations

To explore the deformation mechanism of α-Ti with high oxygen doping, micro-pillars of single crystal with orientations of near 0°, 45°, and 90° inclined to c-axis were fabricated via focused ion beam (FIB) milling from a high oxygen content commercial purity Ti (CP–Ti). The micro-pillars were loaded under quasi-static compression. Post-mortem analysis reveals that only prismatic slip activated for 45° and 90° oriented samples with their critical resolved shear stress (CRSS) values of about 457 MPa and 596 MPa, and only {10–11}<c+a> the first-order pyramidal slip activated on the 0° sample with a CRSS of around 1019 MPa. The results suggest that the oxygen addition remarkably reduces the CRSS ratio between non-prismatic and prismatic slips of α-Ti. In addition, the results indicate that the Schmid law may not be applicable for α-Ti single crystal at micro-size level.

Quantitative study of microstructural, textural and hardness evolution of high-purity Ti sheet during rolling from low to medium strains

Many Ti-base products are made of sheets/plates processed by rolling and strong crystallographic textures are often developed, especially for those with α-Ti as the major phase. Compared to intensive explorations of deformation behaviors of low alloyed Ti (including commercial-purity Ti) during rolling, much less has been made for high-purity Ti (HP-Ti), in spite of acknowledged important effects of some impurities on deformation modes of α-Ti. To clearly reveal microstructural, textural and hardness evolution of HP-Ti during rolling from low to medium strains, a typical HP-Ti sheet after 10–50% cold rolling was subjected to quantitative characterization by jointly using electron backscatter diffraction, electron channel contrast imaging, X-ray diffraction and hardness test. Results show that plastic deformation readily occurs through the active operation of both slip and twinning (mainly {112¯2}<112¯3¯> and {101¯2}<101¯1¯>) during 10–30% rolling. As a result of massive twinning, initial grain structures are markedly refined along with significant grain reorientation, leading to largely reduced textural intensity and the presence of new components. At higher strains (>30%), slip becomes the only deformation mode with new twins no longer appearing. In the 50%-rolled specimen, a bimodal basal texture similar to the initial one is formed along with a weak component of c//TD. The HP-Ti sheet is always hardened with increasing strains (from 120.8 ± 5.7 HV to 234.3 ± 5.8 HV). Quantitative analyses reveal that the grain refinement caused by dense twins at low strain (10% rolling) can lead to significant hardening contribution, which keeps relatively stable during subsequent rolling. Since slip can play a more important role with increasing strains, denser low angle boundaries are produced and gradually make larger contributions to hardening. As the rolling reduction increases to 50%, the contribution from low angle grain boundaries to hardness exceeds that from high angle grain boundaries (Hall-Petch hardening). The results documented in this work should not only be able to help clarify specific deformation mechanisms of HP-Ti, but also provide important implications for improving their properties.

Revealing the effect of local stresses on twin growth mechanisms in titanium using synchrotron X-ray diffraction

Deformation twinning has a significant impact on the evolution of microstructure and mechanical response in hexagonal close packed (hcp) metals. Understanding the physical mechanisms associated with twin nucleation and growth processes is important to enable the broad use of hcp metals. While both nucleation and growth are conditioned by the local stress state, few studies have quantified it in bulk deformed samples. In this study, we reveal the effects of local stresses on twin thickening using in-situ synchrotron experiments with differential aperture X-ray microscopy. High purity Ti is deformed under four-point bending to activate {1012} tensile twins. 3D stress fields with a spatial resolution of 0.5μm are mapped in the vicinity of low and high macroscopic Schmid factor (MSF) twins growing inside a grain. Reconciling this experimental analysis with recent twin growth models reveals that the growth of low MSF twins is limited by the nucleation of twin growth defects in the high-purity Ti sample. While growth-inducing defect nucleation may occur in many places on the interface of the high resolved shear stress (RSS)/MSF twin, the nucleation rate of twinning disconnections for the low MSF twin is high only at the end of the twin near a stress concentration. Once nucleated, these defects easily propagate into lower RSS regions of the grain resulting in twin growth. This work highlights the importance of stress concentrations not only for twin (embryo) nucleation, but also to the growth process of twins, particularly in low MSF twins.

Formation of Ti2AlC-based thin films via magnetron sputtering and annealing under vacuum

High-purity Ti, Al and C targets were used to fabricate Ti2AlC-based thin films on industrial polycrystalline Al2O3 substrates via magnetron sputtering under argon, followed by vacuum annealing. The phase compositions of the Ti2AlC-based thin films were analysed, and scanning electron microscopy was performed to investigate their structures. Grain size and morphology depended on the deposition pattern. A material composed of ∼97.1% Ti2AlC and ∼2.9% TiC was obtained by sputtering Al for thirty minutes, then sputtering four alternating layers of Ti and C for ten minutes each. The thin film was subsequently annealed under vacuum at 900°C for 60 minutes. The samples contained lamellar hexagonal plate-shaped grains structures. The plate-shaped grains ranged from 200 nm to 400 nm in length depending on the sputtering mode. The long sides of the lamellar grains were predominantly oriented perpendicular to the alumina substrates. Regardless of the sputtering conditions, the coherent scattering region of Ti2AlC was ∼64 nm in size after annealing at 900°C. Changes in the size of the coherent scattering region of the TiC phase were non-linear and ranged from 9 to 60 nm.

Solid state processing of titanium chips by an unconventional plastic working

Abstract The aim of this paper is to demonstrate how various titanium chips can be processed into solid bulk materials in the form of rods. In this work, an alternative technology for recycling chips without re-melting is presented. In order to transform chips into a new material, an unconventional plastic working method was applied that involved upsetting, heating and extrusion with a rotating die. Two purities of pure titanium were investigated: Ti Grade4 (the lowest possible purity) and high-purity Ti 99.99 (the highest possible purity). For each of these materials, four geometries of chips were processed, i.e. chips after turning (thin and coarse) and chips after milling (thin and coarse). In this paper, the influence of chip purity and chip geometry on the course and effects of the processing were investigated. In addition, technological aspects such as extrusion force and die wear were analyzed. Independent of the type of chips, the results obtained have proved the efficiency and utility of the applied method. As a result of this processing, solid, bulk products in the form of rods O8 mm in diameter were successfully obtained. The rods were nearly fully consolidated, and their density was practically the same as the density of commercial titanium. The materials obtained exhibited conventional, grained structures. It was also shown that the materials obtained were free from significant structural defects such as porosity and impurities. Additional confirmation of their proper structure and purity was provided by the correct results of hardness (~200 HV10, Ti Gr4, and, ~100 HV10, Ti hp).

Sustainable recovery of ultrafine TiC powders from molten Ti-bearing slag under super-gravity field

Abstract Ultrafine TiC powders possess excellent physicochemical properties, which are mainly synthesized by using high-purity ultrafine Ti or TiO2 powders. In this study, a sustainable method for recovery of ultrafine TiC powders from molten Ti-bearing slag under super-gravity field was proposed. Firstly, the solid-liquid coexistence condition for single TiC powders in molten Ti-bearing slag was acquired. On this basis, the motion mechanism and separation behavior of TiC powders in the molten slag was studied. Under the force of super-gravity, all of TiC powders were efficiently separated from the molten slag along the super-gravity direction, and the Ti recovery ratio reached 96.69%. Moreover, the recovered TiC powders were confirmed to be high purity (w (Ti) = 79.49%) and ultrafine particles (particle size 2.75 μm on average). Compared with synthetic methods, this study provides a sustainable way to produce ultrafine TiC powders for clean utilization of massive Ti-bearing slag.

Towards a sustainable technology for production of extra-pure Ti metal: Electrolysis of sulfurized Ti(C,N) in molten CaCl2

A new concept for producing highly pure Ti metal powder from ilmenite (FeTiO3) is proposed in this article. Titanium nitride (TiN) or titanium oxycarbonitride (TiOxCyNz) could be synthesized in the first step via the simultaneous carbothermal reduction and nitridation (CTRN) of FeTiO3 to remove oxygen roughly. To separate oxygen completely, high-quality TiS2 samples were then synthesized from TiN and TiC using S2 gas, and the clean sulfides were finally reduced to α-Ti powders with spherical morphology using electrolysis in molten CaCl2. X-ray diffraction (XRD), scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDS), and elemental LECO analysis were used to study the phases and microstructures of the sulfides and the electrochemically reduced powders. The Ti powder showed no carbon contamination and consisted of high-purity foil-like Ti sheets with very low oxygen, carbon, and nitrogen contents of less than 0.15wt% O, 0.02wt% C, and 0.003wt% N, respectively. The quality of the Ti powder was much higher than that of the powder obtained using the conventional OS process (proposed by K. Ono and R.O. Suzuki) starting directly from the oxides.

Titanium isotope fractionation in solar system materials

New methods to determine the titanium (Ti) mass-dependent isotope fractionation of solar system materials to high precision were developed by combining internally normalised Ti isotope data with double-spike analyses utilising a 47Ti-49Ti double spike. The procedure includes a three-stage ion-exchange separation procedure to isolate Ti from the sample matrix that provides high-purity Ti fractions that are necessary for high-precision Ti isotope analyses. Analyses of sample aliquots that were spiked before and after the ion-exchange separation procedure demonstrate that Ti isotope fractionation can be induced by the separation procedure. This outcome requires the addition of the double spike before the ion exchange separation procedure in order to accurately determine the natural mass-dependent Ti isotope fractionation of samples. Multiple double spike analyses of an Alfa Aesar Ti standard performed over eight months yielded a reproducibility (2σ standard deviation) of 0.033‰ for δ49/47Ti (differences in 49Ti/47Ti relative to the OL-Ti standard). Terrestrial sample analyses display a 2σ reproducibility of 0.018 to 0.031‰ for δ49/47Ti. Titanium isotope results for three terrestrial USGS magmatic reference samples (AGV-2, BHVO-2 and BCR-2) agree well with literature data and therefore demonstrate the accuracy and precision of the presented methodologies. Achondritic meteorites display an overall range of 0.75‰ for δ49/47Ti. The ungrouped achondrite NWA 7325 has a more positive composition by 0.64‰ for δ49/47Ti compared to all other investigated samples likely reflecting Ti isotope fractionation induced by magmatic differentiation associated with highly reducing conditions and potentially associated with oxide and plagioclase formation. In contrast, eucrites with δ49/47Ti of -0.020 ± 0.070 and -0.003 ± 0.033 and the first mass-dependent Ti isotope data for an acapulcoite (Dhofar 125; δ49/47Ti = 0.094 ± 0.033) show only limited magmatic Ti isotope fractionation. Chondrites also display a relatively restricted range of 0.085‰ for δ49/47Ti, including one calcium‑aluminum rich inclusion (CAI) from Allende and the first mass-dependent Ti isotope data for two Rumuruti chondrites (NWA 753 and NWA 755). Furthermore, the mass-dependent Ti isotope composition of chondrites overlaps with that of eucrites and the acapulcoite Dhofar 125 indicating that nebular processes induce only limited Ti isotope fractionation. Additionally, the Ti isotope data indicate that thermal metamorphism also produced marginal Ti isotope fractionation at the bulk sample scale for chondrites. Small mass-dependent Ti isotope variations between different bulk meteorite samples are also evident, which might reflect sample heterogeneity. Importantly, the mass-dependent Ti isotope composition of the Earth and Moon overlap with the composition of the investigated chondrites, eucrites and acapulcoites within the 2 standard deviation uncertainties.

A Sustainable Approach for Producing Ti and TiS2 from TiC

TiC was examined as a starting material for Ti metal production by sulfidation and electrochemical reduction in molten salt. The sulfur evaporation temperature, sulfidation temperature, and time were optimized in a dual-zone furnace for the efficient and sustainable formation of TiS2 as well as carbon removal from TiC by S2 gas sulfidation. A mixture of TiS2 and Ti2.45S4 powders was synthesized from TiC at 1200 °C, and a perfect carbon removal was achieved to a very clean level as low as 0.025 mass pct C. The sulfides derived from TiC were then electrochemically reduced in molten CaCl2-0.5 mol pct CaS salt. The spherical shape Ti powder consisting of high-purity Ti sheets was obtained from TiS2 without the carbon contamination. This method might be applied for sustainable recycling of waste carbides and for production of low-cost Ti powders via TiC or TiOxCyNz from the titanium ore.