Pure Ti Substrate Research Articles

Comparison of oxidation resistance of Al–Ti and Al–Ni intermetallic formed in situ by thermal spraying

A pure Al coating and an Al/Ni composite coating were deposited on the surface of a pure Ti substrate by thermal spraying. To enable the in situ reaction between the coatings and the substrate, the specimens were heated to 800 °C. Furthermore, the high-temperature oxidation resistance and the protection mechanism of the Ti–Al and Ni–Al intermetallic compounds were compared. The results showed that after heating to 800 °C, the diffusion region of the Al/Ti specimen mainly comprised the TiAl3 phase, and the thickness of the diffusion region first increased and then decreased as the reaction time was extended. The diffusion region of the Al/Ni/Ti specimen consisted of the Ni2Al3 and NiAl phases after heating to 800 °C, and the thickness of the Al/Ni diffusion layer showed parabolic growth as the reaction time was extended. After the oxidation treatment (800 °C for 100 h), oxygen diffused not only into the Al/Ti diffusion region, but also into the Ti substrate. For the NiAl intermetallic coating, no elemental Ti was found on the surface of the specimen and no oxygen was found in the Ti substrate after the oxidation treatment. The NiAl intermetallic coating had better oxidation resistance than the TiAl3 intermetallic coating.

Mechanical and biological properties of ZnO, SiO2, and Ag2O doped plasma sprayed hydroxyapatite coating for orthopaedic and dental applications

In this study, we explored a ternary dopant system utilizing 0.25 wt% ZnO to induce osteogenesis, 0.5 wt% SiO2 to induce angiogenesis, and 2.0 wt% Ag2O to provide secondary infection control within a plasma assisted hydroxyapatite coating for orthopaedic or dental applications. The objective of this study was to understand the effects of ZnO, SiO2, and Ag2O dopants on the mechanical and biological properties of hydroxyapatite (HA) coatings on titanium (Ti). Coatings were deposited using a 30 kW plasma spray system equipped with a supersonic nozzle to produce above standard coating bond strengths of 24 ± 2 MPa on Ti6Al4V and 22 ± 1 MPa on commercially pure Ti substrates. Antibacterial properties were revealed in vitro against E. coli and S. aureus. The ternary dopant system was implanted in 18 male Sprague-Dawley rats with timepoints of 5 and 10 weeks. By week 5, ZnSiAg-HA produced 32% bone mineralization of 68% total bone formation compared to only 11% bone mineralization of 55% total bone formation in the undoped coating. This system can be employed for replacement surgeries and revision surgeries to reduce healing time and enhance osseointegration. Statement of SignificanceTotal hip replacements increased 124% from 2000 to 2010 with an ever-increasing rate due to the rise in average life span and an escalation in surgeries for young patients. Replacement surgeries come with the risk of rejection, poor integration, and infection. This study incorporates biologically relevant metallic oxides of ZnO, SiO2, and Ag2O within a hydroxyapatite coating on titanium deposited using a radio frequency induction plasma spray. A ternary dopant system has not been explored in the current literature and little is known about these particular dopants in vivo. This proposed system can be employed for replacement surgeries to lower healing time and enhance osseointegration between implant and host tissue.

Influence of different sodium-based additives on corrosion resistance of PEO coatings on pure Ti

ABSTRACTIn the present study, the plasma electrolytic oxidation method was used to form ceramic coatings on pure Ti substrates. For this purpose, five different aluminate-based electrolytes containing various sodium-based additives (sodium hydroxide, sodium phosphate, sodium silicate, sodium tetraborate and sodium fluoride) were used. The role of additives in the growth, macrostructure, surface and cross-sectional microstructure, phase composition and corrosion resistance of the coatings was evaluated. An X-ray diffractometer and scanning electron microscope were used to study the microstructure and phase composition of the coatings, respectively. The corrosion resistance of the coatings was investigated by applying electrochemical impedance spectroscopy and potentiodynamic polarization tests in a 3.5 wt. % NaCl solution. The results revealed that use of a sodium phosphate additive led to formation of a coating (4.33 µm thick) with the most suitable microstructure and highest corrosion resistance (4.36 × 106 Ω cm2), which was 53 times higher than that of uncoated Ti.

Microstructure, adhesion, in vitro corrosion resistance and tribological behavior of (Si:N)-DLC coated pure Ti

(Si:N)-DLC, Si/(Si:N)-DLC, Si3N4/(Si:N)-DLC and Si/Si3N4/(Si:N)-DLC four films were deposited on the pure Ti substrates, using a hybrid ion beam deposition system consisting of a DC magnetron sputtering and linear anode-layer ion sources, to improve the adhesion and in vitro protective performance. The microstructures and thicknesses of the (Si:N)-DLC film with different interlayers were investigated by Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and scanning electron microscopy. The mechanical and adhesion properties were evaluated by indentation and scratch tests. The corrosion resistance and wear resistance of the coated pure Ti samples were characterized by electrochemical test and friction test in the SBF solution, respectively. The results showed that the (Si:N)-DLC film containing Si3N4 structure was obtained. This (Si:N)-DLC film interacted with the Si or Si3N4 interlayer, showing an obvious transition boundary, which resulted in an increasing binding force. As a result, the Si/Si3N4/(Si:N)-DLC film showed the highest critical loads. Furthermore, it was found that the Si/(Si:N)-DLC film had excellent in vitro corrosion resistance and tribological behavior in the SBF solution.

High-Temperature Oxidation Resistance of NiAl Intermetallic Formed In Situ by Thermal Spraying

An Al/Ni composite coating was deposited on the surface of a pure Ti substrate by arc spray technology and plasma spray technology. In order to enable the in-situ reaction between the Al/Ni composite coating and the specimen, they were heated under different conditions. In addition, oxidation testing was conducted to test the oxidation-resistant property of the coating. The phase transition regulation of the coating after heating, the influence of heating at different temperatures and time on the reaction depth, and the correlated theory of the in-situ formation of the NiAl intermetallic compounds were studied and analyzed. The results showed that after the heat treatment, a ragged wave-like morphology was exhibited in the diffusion front of Al, and a small amount of the Ni in the diffusion region did not participate in the reaction. The growth of the NiAl intermetallic layer in the diffusion region of the Al/Ni/Ti specimen was obviously slower compared with the Al/Ni specimen.

The correlation between substrate and deposited biocompatible layer microstructures on different substrates

The biocompatibility is essential for the so called biomaterials used for medical devices (e.g. artificial implants, implants). It is determined mainly by the surface chemical composition and the environment in which the implant is used. The implant materials used till the date have limited biocompatibility. On the other hand newly developed biocompatible materials are usually more expensive. The biocompatibility of currently used materials can be improved via deposition of thin biocompatible layer on the substrate. This layer may be further improved (or used as interlayer) introducing hydroxyapatite, BaTiO3 or other surface treatments. The microstructure of deposited layers has to be known in such cases as it can influence properties of the surface. Various substrates (pure titanium, Ti6Al4V alloy and Ti-39Nb alloy) were used for biocompatible Ti-39Nb layer sputtering deposition in current paper. The microstructure of substrates has been characterized using electron microscopy techniques. The correlation between substrate and layer microstructures could have been revealed, because both microstructures were studied at the same area of the substrate. Significant differences in grain size have been observed on various substrates. Also the microstructure of deposited layer can be distinguished into two types. These are pure β-Ti phase probably on the grains where the surface diffusivity is high enough (locally observed on Ti-39Nb and pure Ti substrates) and mixture of α″ martensitic and β-Ti phase columns.

Plasma Electrolytic Oxidation (PEO) Process on Commercially Pure Ti Surface: Effects of Electrolyte on the Microstructure and Corrosion Behavior of Coatings

The current study investigates the ceramic oxide coatings formed on commercially pure Ti substrate via plasma electrolytic oxidation (PEO) technique in electrolytes with different chemical compositions. The effects of electrolyte on the discharge characteristics, macro- and micro-structure, thickness, phase compositions, and corrosion behaviors of coatings were evaluated. Five kinds of electrolytes based on the sodium salt compounds including aluminate, phosphate, silicate, aluminate-phosphate, and aluminate-silicate were used. The PEO processes were carried out at fixed voltage (420 V) for 180 seconds. The morphology and phase composition of samples were investigated using scanning electron microscope (SEM) and X-ray diffractometer (XRD), respectively. The corrosion behavior of specimens was analyzed in a 3.5 wt pct NaCl solution using the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. The results showed that the most uniform and dense structure with less porosity was obtained in the coating prepared in aluminate-phosphate-based electrolyte. This coating consisted of TiO2 (Rutile and Anatase) and TiAl2O5 phases. Also, it was confirmed that the noblest corrosion potential and lowest corrosion current density, and consequently, the best corrosion behavior (22.96 × 107 Ω cm2), were observed for aluminate-phosphate-based electrolyte. The Mott–Schottky analysis exhibited that all samples had n-type semiconducting behavior. The coating prepared in aluminate-phosphate-based electrolyte possessed the lowest donor densities.

Synthesis, structure and mechanical properties of Ti-Al-Nb coatings formed by electron beam additive technique

We present a detailed investigation of the synthesis and mechanical properties of Ti-Al-Nb coatings, formed by alloying of Ti substrates with Al and Nb films by selective electron-beam melting (SEBM) via continuous electron beam. A cycling mixing of pre-deposited bilayer Al/Nb films with a Ti substrate is realized, where the maximum number of the cycles is 3. The first one is a SEBM of a bilayer Al/Nb coating deposited on pure Ti substrate. The obtained after the first cycle specimen is further coated with the same bilayer coating and then subjected to a second SEBM cycle; the same procedure is repeated for the third cycle. The alloyed layers are characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), and X-ray Diffraction (XRD). The microhardness is also studied. The thickness of the coatings obtained after each cycle is in the range from 20 μm to 24 μm. The specimen obtained after the first cycle exhibits an alloyed zone consisting of pure Ti with a small content of Al and Nb, while those manufactured by the following cycles represent Ti2AlNb based phases. The microhardness increases from 180 HV0.03 for the pure Ti substrate to 570 HV0.03 after the third cycle.

Influence of electrolyte composition on microstructure and properties of coatings formed on pure Ti substrate by micro arc oxidation

The aim of this work is to study how electrolyte composition incorporates into the prepared micro arc oxidation (MAO) coatings on titanium in electrolytes containing K2ZrF6 or K2TiF6 and modify the surface characteristics. The microstructure of MAO coatings were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDS) and X-Ray Diffractometer (XRD). Vickers hardness, corrosion resistance and wear resistance of these coatings were evaluated. The obtained results showed that arcing phenomenon could be affected by the electrolyte composition, and it occurred with short arc starting time and low arc starting voltage in the solution with K2TiF6 addition, resulting in an increasing growth rate of the coating. Compared with the MAO coating prepared in the base solution, the MAO coating formed in electrolyte with K2ZrF6 or K2TiF6 additives showed a self-sealing microstructure, exhibiting improved hardness. The ZrO2-modified MAO coating showed an excellent tribological behavior and the coating with K2TiF6 addition exhibited the best corrosion resistance. Furthermore, the correlation of the electrolyte composition, microstructure and properties had been revealed.

Plasma Electrolytic Oxidation Coatings on Pure Ti Substrate: Effects of Na3PO4 Concentration on Morphology and Corrosion Behavior of Coatings in Ringer’s Physiological Solution

Plasma electrolytic oxidation has been used as a relatively new method for applying ceramic coatings having different features. In the present study, commercially pure titanium is used as substrate, and effects of trisodium phosphate electrolyte concentration on the microstructure, as well as corrosion behavior of the coating in Ringer’s physiological solution are investigated. The morphology and phase compositions of coatings were analyzed by using scanning electron microscopy (SEM) and x-ray diffraction patterns. The study on the corrosion behavior of samples in a Ringer’s physiological solution was carried out using open-circuit potential potentiodynamic polarization and electrochemical impedance spectroscopy. The results of electrochemical analysis proved that higher concentration of phosphate electrolyte leads to increase in the corrosion resistance of applied coatings. Accordingly, obtained results revealed that the optimum electrolyte concentration for the best corrosion behavior was 20 g L−1. Furthermore, SEM images and reduction in the dielectric breakdown potential indicated that increase in the electrolyte concentration leads to morphological improvement and smoothening of the surface.

Oxidation Resistance and Modification Reaction Mechanism of Al Coating Sprayed on Pure Ti Substrate

An Al coating was deposited on the surface of pure Ti substrate by arc spray technology. In order to enable the modification reaction between the Al coating and Ti substrate, the specimen was heated to a temperature above the melting point of Al. Oxidation testing of the uncoated Ti and coated specimen was conducted at 1073 K under an air atmosphere. The microstructure, chemical composition, and phase determination of the coatings and interfaces, before and after modification treatment, were done using SEM, EDS, and XRD methods. The relationships between the modification results and time and temperature were discussed. The results showed that, after heating at 973 K for 5 hours, there was still sufficient Al on the surface of the specimen. Only intermetallic TiAl3 was formed in the diffusion region. After heating at 1073 K for 5 hours, all the Al elements diffused into the Ti substrate. Intermetallics TiAl2 and Ti3Al were also formed in the diffusion front of Al, in addition to TiAl3. After heating at 1173 K for 5 hours, a new intermetallic TiAl phase was formed at the interface of TiAl2 and Ti3Al. As the modification reaction time was prolonged at 1173 K, the formation of intermetallics TiAl2, TiAl, and Ti3Al were all increased. Among them, the formation amount of TiAl2 > Ti3Al > TiAl. The specimen after modification treatment had better high temperature oxidation resistance than the pure Ti substrate without coating.

The Photocatalytic Properties and Mechanistic Study of ZnO,Ag Multiphase Co-Composited TiO2 Nanotube Arrays Film Prepared by One-Step Anodization Method

ZnO/Ag multi-phase composited TiO2 nanotube arrays (TiO2 TNAs) films were prepared on pure Ti substrate through one-step anodizing method using double pulse plating power supply. The deposition amount of Ag and ZnO were adjusted by changing the concentration of Zn(NO3)2·6H2O and AgNO3 and reverse voltage. The results showed that ZnO deposited in the wall of TiO2 NTAs dispersedly; sedimentary phase and dispersed phase are the two forms of deposited Ag in TiO2 NTAs. The bandgap narrowed 0.33 eV, and the recombination rate of photo-generated electron-hole pairs also decreased obviously due to the doping energy level synergistic effect of ZnO and the Surface Plasmon Resonance (SPR) effect of Ag. Furthermore, the sample with 1 mM ZnO+0.4 mM Ag and 5 V reverse voltage has the best photocatalytic properties, the degradation rate of Methylene blue (MB) reached 86% which improved 15% compared with undoped TiO2 NTAs.

A comparison of electrochemical behavior of coated nanostructured Ta on Ti substrate with pure uncoated Ta in Ringer's physiological solution

In the current investigation, direct current magnetron sputtering (DCMS) provided nanostructured (NS) α-Ta coating on pure Ti substrate as an effective coating technique. Microstructural observations revealed that a dense and homogeneous coating exhibiting (110) preferred orientation could be achieved. Different electrochemical experiments were performed to study the electrochemical and passive behaviors of α-Ta coating and uncoated commercially pure Ta in the Ringer's physiological electrolyte at 37 °C. Interestingly, the electrochemical response and semiconducting behavior of α-Ta coating and pure Ta were different in several aspects. α-Ta coating showed a superior passive behavior and higher level of protection in Ringer's physiological electrolyte at 37 °C compared to pure Ta. Mott–Schottky (M–S) analysis clearly showed that a less defective passive film forms on α-Ta coating due to its lower levels of donor densities compared to what could be estimated for the case of pure Ta. α-Ta coating offered a considerably improved corrosion resistance in the aforementioned physiological environment, owing to its nano-scale features that have facilitated the formation of less defective and thicker protective passive films.

A bioactive coating with submicron-sized titania crystallites fabricated by induction heating of titanium after tensile deformations

Thermal oxidation technology was widely investigated as one of effective surface modification method for improving the bioactivity and biocompatibility of titanium and its alloys. In this work, the induction heat oxidization method, a fast, efficient, economical and environmental protective technology, was applied to prepare the submicron-morphological oxide coating with variable rutile TiO2 equiaxed crystallites on the surface of pure Ti substrates after cold-drawing with 10–20% deformations. The results showed the plastic-deformed Ti cylinders recrystallized during induction heating treatment (IHT) for 10–20s which resulted in evolution of microstructures as well as slight improvement of microhardness. The surface characteristics of TiO2 crystallites in oxidation layers were determined by the microstructural evolutions of Ti substrate in terms of the nucleation and growth of TiO2 crystallites. Specially, the oxidized surface with 50–75nm roughness and more uniform and finer equiaxed oxide grains remarkablely improved the apatite deposition after bioactive evaluation in 1.5 × SBF for 7 days. This work provided a potential method to create controlled bioactive oxide coatings with submicro-/nano-scaled TiO2 crystallites on titanium substrate in terms of the role of metallographic microstructure in the formation process of titanium oxides.

Microstructure and Oxidation Behavior of Al and Al/NiCrAlY Coatings on Pure Titanium Alloy

To improve the oxidation resistance of Ti alloys, a NiCrAlY coating was deposited as diffusion barrier between aluminum overlay coating and pure Ti substrate by air plasma spraying method. The microstructure and oxidation behavior of Al coatings with and without NiCrAlY diffusion barrier were investigated in isothermal oxidation tests at 800 °C for 100 h. The results indicate that the weight gain of the Al/NiCrAlY coating was 4.16 × 10−5 mg2 cm−4 s−1, whereas that of the single Al coating was 9.52 × 10−5 mg2 cm−4 s−1 after 100 h oxidation. As compared with single Al coating, the Al/NiCrAlY coating revealed lower oxidation rate and excellent oxidation resistance by forming thin Al2O3 + NiO scales at overlaying coating/diffusion barrier and diffusion barrier/substrate interfaces. Meanwhile, the inward diffusion of Al and the outward diffusion of Ti were inhibited effectively by the NiCrAlY diffusion barrier.

Self-healing effects by the Ce-rich precipitations on completing defective boundaries to manage microstructures and oxidation resistance of Ni-CeO2 coatings

This paper presented an effective approach for electroplating of coatings on the activated surface of pure Ti substrate using pulsed electro deposition. Regarding the ceramic-like TiO2 barrier layer on its surface of Ti substrate to inhibit surface activity, a novel activating solution that composed of HF, HCl, Ce(NO3)2, TiCl3, and bal. DMF dissolvent was applied for surface modifications of Ti substrate in order to increase interfacial bonding strength of surface Ni coatings. Besides a comparative study of Ni nanocrystalline coatings without and with CeO2 addition was carried out for disclosing the role of the Ce-rich phase on managing microstructure and high-temperature oxidation resistance during oxidation at 800 or 1000°C. Results indicated that Ce-rich precipitations, where dispersed along grain boundaries (GBs), were favorable for completing the spalling oxide-layers on Ni-CeO2 nanocomposite coatings during oxidation at 800°C. Furthermore, an analytical modeling was validated for better understanding of Ce-rich precipitations along GBs defects for monitoring oxidation mechanisms. Furthermore, this finding would be therefore leading to the guidelines for Ce-rich precipitations on the strengthening of Ni-based superalloys.

Surface alloying of commercially pure titanium with aluminium and nitrogen using GTAW processing

In the present work, surface modification of pure titanium with aluminium and nitrogen during GTAW processing has been investigated. In this regard, Al wire (grade 1100) was deposited on commercially pure Ti surface by means of GTAW process under various N2/(N2+Ar) ratios (from 1/10 to 2.5/10) in shielding gas. The alloyed layers were characterized using X-ray diffraction (XRD), optical and scanning electron microscopy (OM & SEM). The corrosion behavior of the coatings was also examined in NaCl 3.5% electrolyte by potensiostat analysis. The results indicated that, Al/Ti3Al2N2-Ti3Al composite coating can successfully form on Ti surface during GTAW cladding process. All prepared coatings have much higher hardness (270–460Hv) than pure Ti substrate (160Hv) and the hardness has shown an increasing trend by increasing the N2/(N2+Ar) ratio up to 2.5/10. More increasing in this ratio, lead to the formation of high percentage of defects in alloyed layer. By annealing the produced coatings, the metastable Ti3Al2N2 phase was transformed to Ti2AlN phase and the coating/substrate interface was covered with a smooth and continuous layer of Ti2AlN. The hardness and corrosion resistance of the prepared coatings was also enhanced during annealing process.

Preparation of micro/nano-fibrous brushite coating on titanium via chemical conversion for biomedical applications

Calcium phosphate coatings have been applied on the surface of Ti implants to realize better osseointegration. The formation of dicalcium phosphate dihydrate (CaHPO4·2H2O), mineralogically named brushite on pure Ti substrate has been investigated via chemical conversion method. Coating composition and microstructure have been investigated by X-ray diffractometer, Fourier transform infrared spectrometer and field emission scanning electron microscope. The results reveal that the coatings are composed of high crystalline brushite with minor scholzite (CaZn2(PO4)2·2H2O). A micro/nano-scaled fibrous morphology can be produced in the acidic chemical conversion bath with pH 5.00. The surface of the fibrous brushite coating exhibits high hydrophilicity and corrosion resistance in the simulated body fluid. The osteoblast cells grow and spread actively on the coated samples and the proliferation numbers and alkaline phosphate activities of the cells improve significantly compared to the uncoated Ti. It is suggested that the micro/nano-fibrous brushite coating can be a potential approach to improve the osteoinductivity and osteoconductivity of Ti implant, due to its similarity in morphology and dimension to inorganic components of biological hard tissues, and favorable responses to the osteoblasts.

Effect of anodizing time on the mechanical properties of porous titania coatings formed by micro-arc oxidation

Porous TiO2 coatings were produced on commercially pure Ti substrates by micro-arc oxidation (MAO) in 1.0M H2SO4 electrolyte for different anodizing times. Their mechanical properties were assessed by means of instrumented indentation, XRD residual stress measurements and scratch resistance tests. The rutile/anatase ratio increased from ~0 up to 84% in the 10–360s anodizing time range, with further increase of coating thickness, porosity and roughness. Titania coatings produced for 180 and 360s had poor adhesion and uneven surfaces with spontaneous detachment from the substrate. Coating hardness ranged from 3.5 up to 4.0GPa (close to Ti), whereas the effective elastic modulus varied from 110 up to 120GPa (19% lower than Ti), regardless of the substrate effects. Coatings exhibited tensile residual stresses, while the substrate compressive stress increased forming a plateau at about −110MPa for anodizing time longer than 60s. The presence of such hardened layer beneath the interface improved the coating integrity in the scratch tests under the severe tribological condition, thereby increasing about tenfold the detachment critical load for the samples prepared in the 10–60s MAO time range. Therefore, the 60s anodizing time can be a useful reference line for producing mechanically resistant porous titania coatings.

Cu2O/Ag co-deposited TiO2 nanotube array film prepared by pulse-reversing voltage and photocatalytic properties

In this experiment, Cu2O/Ag co-deposition TiO2 nanotube array (Cu2O-Ag-TNT) film was prepared on pure Ti substrate with the method of combining anodic oxidation and electrodeposition by pulse-reversing voltage power supply in the electrolyte of NH4F, ethylene glycol, CuNO3 · 3H2O and AgNO3. The morphology, phase, chemical composition, photocatalytic property and mechanism of the nanotube array film were studied by means of scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy, UV–vis diffuse reflectance spectra, photoluminescence and photocatalytic degradation under visible light. The results showed that the depositional Cu2O and Ag existed in two forms, being the small-particle dispersion and large-particle sedimentary phase in the nanotube arrays: Cu2O-Ag-TNTs for different doping amounts of Ag could be prepared by adjusting the concentration of AgNO3 and the reverse voltages; with changing of the doping amount of Ag, the band gap and photo-generated electron–hole pair recombination rate also changed, and under the conditions of annealing and the optimized process parameter, the band gap of the nanotube arrays narrowed 0.49 eV and the rate of electron and pair recombination decreased noticeably; the nanotube array film for the concentration of 0.5 cm2 ml−1 degraded the methylene blue of 8 mg L−1, and the degradation rate reached above 98%. The co-deposition Cu2O-Ag-TNT film prepared by the one-step method performed well in the field of photocatalysis under visible light.