High-quality Ti Research Articles

Diffusion bonding of Ti—6Al—4V titanium alloy powder and solid by hot isostatic pressing

The Ti—6Al—4V (TC4) alloy powder and forged solid were diffusion bonded by hot isostatic pressing (HIP) to fabricate a powder—solid part. The microstructure of the powder—solid part was observed by scanning electron microscope (SEM). The microhardness and tensile tests were conducted to investigate the mechanical properties. The results showed that the powder compact was near-fully dense, and the powder/solid interface was tight and complete. The microhardness of the interface was higher than that of the powder compact and solid. The fractures of all powder—solid tensile specimens were on the solid side rather than at the interface, which indicated that a good interfacial strength was obtained. The tensile strength and elongation of the powder compact were higher than those of the solid. It is concluded that the HIP process can successfully fabricate high-quality Ti—6Al—4V powder—solid parts, which provides a novel near net shape technology for titanium alloys.

Selective laser melted high Ni content TiNi alloy with superior superelasticity and hardwearing

• High quality Ti 47 Ni 53 alloy is fabricated by the SLM for the first time. • The microstructure of SLM-Ti 47 Ni 53 alloy has been systemically studied. • Compressive deformation behavior is explored by the in-situ HE-XRD. • Synergy relationship between transforming matrix and elastic Ni 4 Ti 3 is revealed. • This work is a favorable reference for preparing other high Ni content TiNi alloys. TiNi alloys with high content Ni (52–55 at.%) are perfectly suitable for preparing wear- and corrosion-resistant parts that service on the space station, spacecraft, and submarine, because of their superior superelasticity, high strength, and hardwearing. However, the fabrication of complicated Ni-rich TiNi parts by the traditional machining method often faces problems of poor precision, low efficiency, and high cost. In this work, we succeed in preparing an excellent Ti 47 Ni 53 alloy by selective laser melting (SLM), and thus, open a new way for the efficient and precise formation of complicated Ni-rich TiNi parts with superelasticity and hardwearing. An optimized processing window for compact parts without defects is reported. The elaborately fabricated Ti 47 Ni 53 alloy exhibited a breaking strain of 11%, a breaking stress of 2.0 GPa, a superelastic strain of 9%, and a better hardwearing than that of casting and quenched Ti 47 Ni 53 alloy. Besides, the microstructure, phase transformation, and deformation, as well as their influence mechanisms are investigated by in situ transmission electron microscope (TEM) and high-energy X-ray diffraction (HE-XRD). The results obtained are of significance for both fundamental research and technological applications of SLM-fabricated high Ni content TiNi alloys.

Theoretical and experimental investigations of magnetic field assisted ultra-precision machining of titanium alloys

Although titanium (Ti) alloys possess unique properties that allow them to compete with many other materials in advanced industries such as aerospace, marine and biomedical, they have poor machining performances. The primary objective of this study is to investigate the distribution of magnetic field intensity at the cutting environment in single-point diamond turning (SPDT) of Ti–6Al–4 V alloy and its influence on the machining performances, with the goal of achieving the desired machining conditions of magnetic field assisted ultra-precision machining, especially magnetic field intensity and the corresponding machining parameters, and to enhance the machinability of Ti–6Al–4 V alloy. In this study, magnetic field-assisted machining (MFAM) system was designed and coupled with ultra-precision machining (UPM) using single-point diamond turning for increasing the machinability and improving the surface quality of Ti6Al4V alloy machined parts. The finite element method (FEM) was developed to demonstrate the influences of the generated magnetic field on the machining processes. The Experimental results showed the capability of magnetic field assistance to enhance the machining performance of Ti–6Al–4 V alloy. These findings provided strong evidence that a magnetic field has the ability to extend cutting tool life, additionally, MFAM achieved the lowest value of surface roughness, representing a 33 percent improvement in surface roughness. This research contributes to the support of the optimum MFAM by FEM and the achievement of high-quality machined Ti alloys in UPM for similar research works, as demonstrated by the experimental results.

Fabrication of spherical Ti–6Al–4V powder for additive manufacturing by radio frequency plasma spheroidization and deoxidation using calcium

Commercial hydride-dehydride Ti–6Al–4V powder was used as raw material to fabricate high-quality spherical Ti–6Al–4V powder by radio frequency (RF) plasma spheroidization and calcium deoxidation in this work. The spheroidized and deoxidized Ti–6Al–4V powder were examined by X-ray diffraction, scanning electron microscopy and O/N/H analyzer, respectively. Effects of feeding rate on spheroidization of Ti–6Al–4V powder were investigated. Effects of calcium reduction on microstructure and oxygen content of spheroidized Ti–6Al–4V powder was also studied. Results show that better flowability of 28.01 s/50 g and higher apparent density of 2.43 g/cm3 can be obtained when feeding rate is 80 g/min. However, the appropriate feeding rate for higher spheroidization ratio and lower mass loss ratio is 140 g/min. Oxygen content of Ti–6Al–4V powder can be reduced to 1240 ppm by deoxidation without phase transformation.

Deposition and characterization for high-quality Ti–Ni–Cu thin films with higher Cu content

In order to attain high-quality Ti–Ni–Cu film, the surface morphologies, chemical compositions and mechanical properties of Ti–Ni–Cu thin films prepared by direct current (DC) magnetron sputtering at various processes were characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and tensile tests. The type of substrates, Ar pressure and sputtering power had significant effects on the quality and chemical composition of Ti–Ni–Cu thin film. Compared with Si and SiO2 slides, it was easier to obtain freestanding films by adopting glass or piezoid slide as substrates. The Ti–Ni–Cu thin film deposited at lower pressure (0.10 Pa) had a better density. The surface was featured with porous structure in the Ti–Ni–Cu thin film prepared by higher Ar pressure of 0.36 Pa. In addition, both the tensile strength and strain of annealed Ti–Ni–Cu thin film continuously increased with Ar pressure decreasing. Higher density contributed to the superior mechanical properties. The deposition rate firstly increased and then decreased with Ar pressure and sputtering power increasing. The composition of deposited Ti–Ni–Cu film can be tailored by changing sputter power. The deposited Ti–Ni–Cu thin films at different processing parameters were in amorphous state. In short, the present study offered the important theoretical basis for the preparation of Ti–Ni–Cu thin film with higher quality and performance.

High-quality Ti(C,N)-based cermets via solid-state nitrogen-pressure sintering: Influence of the sintering atmosphere

Owing to the denitrification behavior of Ti(C,N)-based cermets during the sintering process, nitrogen atmosphere sintering is essential for the fabrication of high-quality products. Disclosing the roles of the sintering atmosphere on the microstructure and properties of cermet is of significance. Herein, Ti(C,N)-based cermets were fabricated under six types of sintering atmosphere. Effects of sintering atmosphere on the microstructure, coercive force (Hc), specific saturation magnetization (Ms (%)), and mechanical properties of cermets were investigated. More rimless Ti(C,N) grains with increased fraction of black cores were formed with increasing the nitrogen partial pressure. Three types of gradient structure of cermets were confirmed caused by the different nitrogen activity at the liquid sintering state. Vacuum sintering induced the formation of thicker rims on smaller Ti(C,N) cores at the surface due to the low nitrogen potential, while fcc solid solutions rich in N was formed in nitrogen atmosphere. Vacuum sintered cermets showed the lowest Hc and Ms. (%) of 3.66 KA/m and 2.13%, owing to the denitrification process. High-quality Ti(C,N)-based cermets were achieved via the solid-state nitrogen atmosphere sintering, benefiting from the optimized core-rim structure, i.e. moderate thickness of rims and certain amount of black Ti(C,N) cores.

Superior strength-ductility balance in hot pressed swarf-Ti-6Al–4V alloy

Ti–6Al–4V alloys were successfully fabricated by directly hot processing of the alloy swarf materials (having a size of 3 mm and 15 mm). The microstructure and mechanical properties of the hot-pressed swarf Ti-64 alloy and influence of starting swarf materials and heat treatment on the hot-pressed alloys were investigated. The hot-pressed swarf-Ti-64, made from 15 mm swarf that has a lamellar structure and 0.16% O, shows excellent strength-ductility balance, having a yield strength (YS) of 902 MPa, ultimate tensile strength (UTS) of 1016 MPa, and strain to fracture of 8.6%. After STA (solution treatment at 980 °C for 1 h, and then aging at 500 °C for 6 h), both alloy's strength and ductility were improved to a YS of 992 MPa, UTS of 1077 MPa, and strain to fracture of 17.3%. The strength-ductility combination of swarf-Ti-64 alloys is comparable or even better than the Ti–6Al–4V alloys manufactured by other approaches. It demonstrates that the hot processing is a promising process to produce high-quality Ti–6Al–4V alloy from the swarf materials.

Fabrication of high-quality Ti joint with ultrafine grains using submerged friction stirring technology and its microstructural evolution mechanism

It is rather challenging to obtain high-quality Ti joints by conventional friction stir welding because of the problem of over-heating. The welding process and final microstructures and properties of the joints are controlled by both plastic deformation and recrystallization. However, for a long time, studies have only focused on recrystallization mechanisms but ignored deformation modes. In this study, a defect-free ultrafine-grained Ti joint with a joint efficiency of 100% was for the first time produced by submerged friction stirring (SFS) technology. We utilized transmission electron microscopy with a two-beam diffraction technique and electron backscatter diffraction to systematically investigate the deformation mode versus the grain refinement mechanism. The finite element method was utilized to simulate the temperature field throughout the joint for the microstructural explanation. During the whole SFS, prismatic slip occurred, and the other dominant deformation mechanisms changed from {101¯2} twinning and basal slip to pyramidal <a + c> slip. The variation of slip modes was largely dependent on the twinning and temperature rise. The ultrafine-grained microstructure was attributed to the successive refinement effect of the twin-dislocation interaction, dislocation absorption, dynamic grain boundary migration and texture-induced grain convergence. The effect of the temperature, strain and strain rate on the microstructural evolution mechanisms was discussed. Based on our work, we expect the wide application of SFS in producing ultrafine-grained bulk Ti materials and high-quality joints.

Effect of vacuum level on microstructure and mechanical properties of titanium–steel vacuum roll clad plates

Vacuum roll cladding (VRC) was used to bond pure titanium (Ti) plate to a plain low carbon steel (Q345) with the aim of obtaining a high-quality Ti–steel clad plate. The effect of interfacial compound on the microstructure and mechanical properties of Ti–steel clad plate was studied by electron probe microanalysis, scanning electron microscopy, X-ray diffraction and shear test. The clad plates were heated at 850 °C for 120 min and welded at different levels of vacuum. The results indicated that the cracked zone of the bonded interface decreased significantly with the increase in the level of vacuum during welding. Welding at atmospheric pressure, the randomly distributed TiN damaged the continuity of TiC and the uniformly diffused region of Ti and Fe at the bonded interface, while welding in vacuum of 1 × 10−2 Pa, maximum shear strength of 298 MPa was obtained because of the decrease in TiN content.

Surface functionalization of titanium implants with chitosan-catechol conjugate for suppression of ROS-induced cells damage and improvement of osteogenesis.

Oxidative stress induced by reactive oxygen species (ROS) overproduction would hinder bone healing process at the interface of bone/implant, yet underlying mechanism remains to be explored. To endow titanium (Ti) substrates with antioxidant activity for enhanced bone formation, multilayered structure composing of chitosan-catechol (Chi-C), gelatin (Gel) and hydroxyapatite (HA) nanofibers was constructed on Ti substrates. Surface wettability and topography of multilayer coated Ti substrates were characterized by water contact angle measurement, scanning electron microscopy and atomic force microscopy, respectively. Chi-C containing multilayer on Ti surface effectively protected osteoblasts from ROS damage, which was revealed by high level of intracellular ROS scavenging activity and reduced oxidative damage on cellular level by regulating the expression of cell adhesion related genes (integrin αv, β3, CDH11 and CDH2). Moreover, it regulated the production of cell adhesive and anti-apoptotic related proteins (p-MYPT1, p-FAK, p-Akt and Bcl-2) and pro-apoptotic critical executioners (Bax and cleaved caspase 3). Beside, the composite multilayer of Chi-C/Gel/HA nanofibers on Ti substrates promoted osteoblasts differentiation, which was evidenced by high expression levels of alkaline phosphatase activity, collagen secretion, ECM mineralization and osteogenesis-related genes expression invitro. The invivo experiments of μ-CT analysis, push out test and histochemistry staining further confirmed that Chi-C multilayered implant had great potential for improved early bone healing. Overall, the study offers an effective strategy for the exploration of high quality Ti implants for orthopedic applications.

Semi-transparent ordered TiO2 nanostructures prepared by anodization of titanium thin films deposited onto the FTO substrate

In a significant amount of cases, the highly ordered TiO2 nanotube arrays grow through anodic oxidation of a titanium metal plate immersed in electrolyte containing fluoride ions. However, for some practical applications, e.g. solar cells or electrochromic windows, the semi-transparent TiO2 formed directly on the transparent, conductive substrate is very much desired. This work shows that high-quality Ti coating could be formed at room temperature using an industrial magnetron sputtering system within 50min. Under optimized conditions, the anodization process was performed on 2μm titanium films deposited onto the FTO (fluorine-tin-oxide) support. Depending on the electrolyte type, highly ordered tubular or porous titania layers were obtained. The fabricated samples, after their thermal annealing, were investigated using scanning electron microscopy, Raman spectroscopy and UV–vis spectroscopy in order to investigate their morphology, crystallinity and absorbance ability. The photocurrent response curves indicate that materials are resistant to the photocorrosion process and their activity is strongly connected to optical properties. The most transparent TiO2 films were fabricated when Ti was anodized in water electrolyte, whereas the highest photocurrent densities (12μAcm−2) were registered for titania received after Ti anodization in ethylene glycol solution. The obtained results are of significant importance in the production of thin, semi-transparent titania nanostructures on a commercial scale.

Mechanism of directional cracking of Ti,C:sapphire crystal

Directional cracking in Ti,C:sapphire crystals grown along [1120] by Vertical Bridgman method often occurs in the cutting and processing process. In this work, we discuss the characteristic and mechanism of directional cracking of Ti,C:sapphire, and find that directional cracking originates from (1100) lattice plane and spreads along [0001] orientation. Through the Crystalmaker Simulation software, we find that atomic arrangement on (1100) lattice plane is the most sparse and adjacent atomic spacing is the largest along vertical [0001] direction, so in the system (1100) [0001] of lattice has a minimum cracking strength. Irregular carbon inclusions in the cracked Ti,C:sapphire are observed with optical microscopy, scanning electron microscopy (SEM), and X-ray diffractometry. These inclusions cause great internal stress in the cooling process due to thermal expansion mismatch and cracking originating from and spreading in the weak system (1100) [0001] of lattice. As a consequence, macroscopic directional cracking is observed in the Ti,C:sapphire. The study has important theoretical and practical significance for growing high-quality Ti,C:sapphire crystal.

Progress in the growth of large scale Ti:sapphire crystals by the heat exchanger method (HEM) for petawatt class lasers

In modelocked laser systems, the shortest possible pulse width is determined by the Fourier transform of the spectral bandwidth of the pulse; the wider the spectral bandwidth, the shorter the pulse. Titanium-doped sapphire (Ti:sapphire) offers the widest gain bandwidth of any currently available laser gain material, enabling systems to deliver pulse widths shorter than 10 fs (10 −14 s). Because of the short pulse durations, the peak power can be extremely high, and therefore Ti:sapphire lasers have been at the forefront of research into ultrafast, ultrahigh power lasers. These intense ultrashort laser pulses are the light source for fundamental studies of light–matter interactions. Interesting scientific results have been achieved with these lasers in the fields of high order harmonic and short pulse X-ray generations, high density plasmas, relativistic acceleration, relativistic nonlinear optics, time resolved X-ray diffraction with unprecedented time resolution and others. Researchers have recently achieved near petawatt (10 15 W) peak power laser operation using large diameter Ti:sapphire amplifiers, and are developing higher power lasers for research into high energy physics. However, the saturation fluence of the Ti:sapphire gain medium is limited to about 1 J/cm 2. Thus, continued scale up in peak laser energy requires the scale up of high-quality Ti:sapphire crystals for laser amplifiers. Current demand is for 100 mm diameter crystals, and this requirement is projected to grow up to 250 mm diameter crystals in a few years. To address this technological bottleneck, Crystal Systems has upgraded its heat exchanger method (HEM) furnaces and fabrication and metrology to scale up the production of Ti:sapphire crystals. Currently, 175 mm diameter Ti:sapphire amplifier crystals are being fabricated from high-quality 208 mm boules.

Deposition of dense and smooth Ti films using ECR plasma-assisted magnetron sputtering

We report high quality Ti films grown in a novel electron cyclotron resonance (ECR) plasma-assisted magnetron sputtering (PMS) deposition system. The films are compared with films deposited by conventional direct current (DC) magnetron sputtering. Using ECR-PMS, the argon plasma bombardment energy and Ti film deposition rate can be controlled separately, with the substrate bias voltage under feedback control. Results from SEM, AFM, XRD and PAS (scanning electron microscopy, atomic force microscopy, X-ray diffraction and positron annihilation spectroscopy) show that the properties of Ti films prepared by ECR-PMS are greatly improved compared with conventional sputtering. SEM and AFM confirmed that ECR-PMS Ti films have a dense, smooth, mirror-like surface. Increasing the substrate bias of the ECR plasma from − 23 V to − 120 V while keeping a fixed sputtering bias voltage of − 40 V, the intensity of the (100) reflection of Ti film was a little strengthened, but (002) remained strongly preferred orientation. The XRD peak broadening of ECR-PMS Ti films is more than for conventional magnetron sputtering, due to grain refinement induced by Ar ion bombardment. Doppler broadening of PAS analysis reveals that the Ti films have fewer vacancy defects compared with films prepared by the conventional magnetron.

Effect of milling conditions on structural evolution and phase stability of [Ti(H 2) + Al + Nb] powder mixtures

Mechanical properties of structural intermetallics are very sensitive to chemical composition and to microstructure. Mechanical alloying is here applied to (Ti + 22Al + 23Nb) and (TiH 2 + 22Al + 23Nb) mixtures in order to tailor both chemical and microstructural homogeneity and to refine powder size, for the synthesis of high quality Ti 2AlNb-based intermetallics. Crystal structure and phase evolution during mechanical alloying were investigated by means of X-ray diffraction and Rietveld analysis. It was identified that milling of the (Ti + 22Al + 23Nb) mixture led to the formation of a bcc (Nb, Ti, Al) solid solution, which was further confirmed by TEM analysis. Replacing pure Ti with TiH 2 resulted in the formation of a bcc (Nb, Ti, Al)H x solid solution. Prolonged milling led to the transformation of a mixture of the bcc-(Nb, Ti, Al)H x solid solution and an fcc-TiH 2 into a fully amorphous phase. Selected area electron diffraction confirmed this finding. An EDS analysis showed that the amorphous phase was a (Ti, Nb, Al)H x solid solution.

Formation of Low Resistance Nonalloyed Ti∕Au Ohmic Contacts to n-Type ZnO by KrF Excimer Laser Irradiation

We report on the formation of high-quality nonalloyed Ti 30 nm/Au 50 nm ohmic contacts to n-type ZnO:Al using laser irradiation treatment. The electrical characteristics of the Ti/Au contacts are considerably improved when laser-irradiated. The specific contact resistances are measured to be 10 4 cm 2 when the ZnO layers were laser irradiated, which is about two orders of magnitude lower than that of the as-grown sample. Based on electrical and X-ray photoelectron spectroscopy results, a possible mechanism for the laser-irradiation-induced improvement is described.

Optimized lift-off technique for deposition of high-quality Ti strip on LiNbO3 crystal

An optimized lift-off technique for deposition of Ti strips onto Z- or X-cut LiNbO3 crystal surfaces is proposed by comparing several pretreatments on the Ti-sputtered substrate before carrying out the lift-off procedure. The best result is obtained for the pretreatment of preserving the Ti-sputtered substrate in a container at a temperature of 50–90 °C for a duration of several hours. Such a pretreatment can strengthen the adhesion of the Ti metal onto the crystal surface to some extent and hence allow the definition of high-quality Ti strips. The experimental results also revealed that the adhesive force of Ti metal onto the crystal surface depends on the cut version of the crystal.

Gas-phase chemistry in up-scaled plasma enhanced metal-organic chemical-vapor deposition of TiN and Ti(C, N) on tool steel

In this article, the deposition of TiN and Ti(C, N) in a relatively large scale reactor vessel is discussed. Tetrakis(diethylamine)titanium (TDEAT) was used for the deposition of TiN and Ti(C, N) at low temperatures. Favorable gas-phase conditions for deposition of Ti(C, N) in a pulsed direct current plasma have been determined, making use of mass and optical spectroscopy. Decomposition of TDEAT in a pure hydrogen plasma resulted in the favorable cleavage of diethylamine from the precursor but prevents the formation of Ti(C, N) due to the lack of nitrogen and carbon. Addition of N2 to the hydrogen plasma results in the formation of NHx (1⩽x⩽4), opening transamination pathways. Seemingly high quality Ti(C, N) coatings (Hv=1600) were deposited on WN 1.2370 tool steel.

Growth of ferroelectric oxide films on n-GaN/c-sapphire structures

High-quality (Pb, La)(Ti, Zr)O3 films were grown on n-GaN. The film thickness ranged from 0.5 to 5 μm. The material was prepared by a chemical solution method with compositions of 8/65/35 and 0/52/48. The films grown on GaN buffered with a thin layer of indium in oxide were highly textured and exhibited excellent ferroelectric properties with Pr=20–26 μC/cm2. A large field-induced birefringence of 0.025 was measured in the film with a composition of 8/65/35 under a field strength of 2×105 V/cm.

Transamination in Pulsed DC-Plasma Enhanced CVD Of Ti(C,N) From TDMAT

AbstractFavourable gas-phase conditions for deposition of Ti(C,N) from tetrakis(dimethylamine)titanium (TDMAT) in a pulsed DC-plasma have been determined, making use of mass spectroscopy. Decomposition of TDMAT in a pure hydrogen plasma results in the favourable cleavage of dimethylamine from TDMAT but prevents the formation of Ti(C,N) due to the lack of nitrogen and carbon. Addition of N2 to the hydrogen plasma results in the formation of NHx (l&lt;x&lt;4), opening possible transamination pathways. Transamination plays an important role in thermal CVD processes and results in high quality TiN layers. However, an undesired side-effect is the gas-phase particle formation under the conditions used here, possibly due to TDMAT - N2 interactions. The depletion of TDMAT by interaction with nitrogen in a H2(85%) - N2(15%) plasma proceeds in a mechnistic step with a rate constant of k = 4.7 × 10−14 cm3 mol−1sec. Results were compared with those obtained from using ammonia under similar process conditions, and with results from thermal CVD. Seemingly high quality Ti(C,N) coatings were deposited at temperatures between 200°C and 425°C on steel and glass with this simple and, therefore, interesting set-up.