Titanium oxide films produced on commercially pure titanium by anodic oxidation with different voltages

Titanium oxide films produced on commercially pure Ti by anodic oxidation with different voltages were analyzed. Anodic oxidation was carried out at room temperature using 1.4 M H₃PO₄ electrolyte and a platinum counter-electrode, in potentiostatic mode under the following conditions: 50 V, 100 V, 150 V, 200 V and 250 V. It was observed that porous titanium layers were formed at all voltage values but morphological differences were observed. Initially, the film was thin but with increasing voltage it broke down locally and porous regions became evident due to the dielectric breakdown. The porosity and the pore size increased with the increasing voltage. The surface morphology in samples formed with 200 V had substantially different porous structures than those formed with other voltage values. The anodic film surface displayed pores and craters formed on the relatively flat ground oxide surface. AFM images showed that higher voltages produced thicker titanium oxide films.     

Anodic oxidation and stress corrosion cracking (SCC) of titanium alloys

Uniform and reproducible oxide films were formed on alloy Ti-6Al-6V-2.5Sn by anodic oxidation in aqueous 0.5% H₃BO₃, at 10 mA cm⁻² and voltages up to 110V; dielectric break down occurred above 120V. A parallelism was found between the effect of environmental factors on stress corrosion cracking (SCC), as reported in the literature and the anodic behaviour, as observed by ourselves: factors that increased susceptibility to SCC (increase in temperature or viscosity, alloying, introductions of CI⁻ or methanol, lowering of pH) reduced passivity under anodic polarization, while factors that inhibited SCC (thicker oxide films, high pH, phosphate ions) increased passivity. The passivity was associated both with the presence of the anodic oxide and with a transitory effect of the electric field across the oxide and the oxide-electrolyte interface.     

Multilayer structure of tantalum anodic oxide films formed in dilute phosphoric acid

An investigation has been made of the multilayer structure of anodic oxide films on pure tantalum, formed up to various voltages with a constant current density of 1.0 mA cm^-2 in 1.0 × 10^-2 N H₃PO₄ at 20°C. For the study, infrared reflectance spectra (IRRS) were recorded and the optical thickness measuring method was successfully applied using the wavelengths of optical interference maxima and a chemical film stripper (concentrated ammonium hydrogen difluoride aqueous solution).The conclusions are that: (1) tantalum anodic oxide films anodized in dilute phosphoric acid consist of three layers, irrespective of the formation voltage; (2) the innermost layer is uniform whatever the anodization voltage; (3) phosphate anions are incorporated in both the outermost and middle layers but not in the innermost layer; (4) all three layers grow from the initial formation stage and the growth rates are nearly equal; (5) for formation voltages below 100 V the middle layer has an unchanging chemical structure, but above 100 V its chemical structure changes with the voltage; (6) the outermost layer appears to vary in chemical structure over all anodization voltages.     

Anodization of evaporated aluminium on Ti-6 wt% Al-4 wt% V

Evaporated aluminium on Ti-6 wt% Al-4 wt% V alloy was anodized in phosphoric acid and other electrolytes. The anodic oxide formed was characterized by various techniques and it was found that a duplex oxide forms in which titanium has diffused through the aluminium oxide film and appears at the surface and throughout the film.     

钛合金表面微弧氧化纳米防污涂层及性能研究

利用微弧氧化技术,在Ti-6Al-3Nb-2Zr合金表面成功制备出纳米防污陶瓷涂层。采用扫描电镜、透射电镜和光学显微镜分析了纳米防污涂层的表面形貌、微观形态和氧化层厚度,采用X射线光电子能谱和X射线能谱仪对防污涂层的元素价态和化学组成进行了分析,采用WS-1型划痕试验机和数字万用表研究了涂层的结合强度和绝缘性,并采用TE66微磨损试验机和进行天然海水挂片试验考察了涂层的摩擦学性能和防污性能。结果表明:防污涂层厚度可达到20μm以上,涂层有非晶和20—50 nm纳米晶TiO2及Cu2O构成,膜基结合强度达到50 MPa,涂层绝缘性和耐磨性良好,防污性能得到明显改善,挂片6个月后涂层表面仅有少量海生物附着,而裸钛合金样品挂片3个月后则完全被海生物附着。     

Influence of noble metals alloying additions on the corrosion behaviour of titanium in a fluoride-containing environment

Titanium alloys exhibit excellent corrosion resistance in most aqueous media due to the formation of a stable oxide film, and some of these alloys (particularly Ti-6Al-7Nb) have been chosen for surgical and odontological implants for their resistance and biocompatibility. Treatment with fluorides (F⁻) is known to be the main method for preventing plaque formation and dental caries. Toothpastes, mouthwashes, and prophylactic gels can contain from 200 to 20,000 ppm F⁻ and can affect the corrosion behaviour of titanium alloy devices present in the oral cavity. In this work, the electrochemical corrosion behaviour of Ti-1M alloys (M = Ag, Au, Pd, Pt) was assessed in artificial saliva of pH = 3.0 containing 910 ppm F⁻ (0.05 M NaF) through open circuit potential, E_OC, and electrochemical impedance spectroscopy (EIS) measurements. The corrosion behaviour of the Ti-6Al-7Nb commercial alloy was also evaluated for comparison. E _OC measurements show an active behaviour for all the titanium alloys in fluoridated acidified saliva due to the presence of significant concentrations of HF and HF₂ ⁻ species that dissolve the spontaneous air-formed oxide film giving rise to surface activation. However, an increase in stability of the passive oxide layer and consequently a decrease in surface activation is observed for the Ti-1M alloys. This behaviour is confirmed by EIS measurements. In fact, the Ti-6Al-7Nb alloy exhibits lower impedance values as compared with Ti-1M alloys, the highest values being measured for the Ti-1Au alloy. The experimental results show that the corrosion resistance of the studied Ti-1M alloys is similar to or better than that of Ti-6Al-7Nb alloy currently used as biomaterial, suggesting their potential for dental applications.     

Fabrication and characterization of self-organized mixed oxide nanotube arrays by electrochemical anodization of Ti-6Al-4V alloy

Self-organized mixed oxide nanotube arrays were fabricated by anodization of Ti-6Al-4V alloy in H₃PO₄/NH₄F aqueous solution. The nanotubes of 90-180 nm in diameter and 10-20 nm in wall thicknesses could be tuned by changing anodization voltages. Whereas, the as-prepared nanotube arrays were amorphous; to induce crystallinity, the products were annealed at 400 °C, 500 °C and 600 °C, respectively. The UV-Vis spectra of samples annealed at 600 °C gives the maximum absorption in the visible spectra range. Various characterization techniques (viz., FESEM, XPS, XRD, and UV-Vis) were used to study the morphology, composition, phase and band gap of the films.     

Substrate bias voltage influenced structural, electrical and optical properties of dc magnetron sputtered Ta2O5 films

Tantalum oxide (Ta₂O₅) films were formed on silicon (111) and quartz substrates by dc reactive magnetron sputtering of tantalum target in the presence of oxygen and argon gases mixture. The influence of substrate bias voltage on the chemical binding configuration, structural, electrical and optical properties was investigated. The unbiased films were amorphous in nature. As the substrate bias voltage increased to −50 V the films were transformed into polycrystalline. Further increase of substrate bias voltage to −200 V the crystallinity of the films increased. Electrical characteristics of Al/Ta₂O₅/Si structured films deposited at different substrate bias voltages in the range from 0 to −200 V were studied. The substrate bias voltage reduced the leakage current density and increased the dielectric constant. The optical transmittance of the films increased with the increase of substrate bias voltage. The unbiased films showed an optical band gap of 4.44 eV and the refractive index of 1.89. When the substrate bias voltage increased to −200 V the optical band gap and refractive index increased to 4.50 eV and 2.14, respectively due to the improvement in the crystallinity and packing density of the films. The crystallization due to the applied voltage was attributed to the interaction of the positive ions in plasma with the growing film.     

The effects of cathodic and anodic voltages on the characteristics of porous nanocrystalline titania coatings fabricated by microarc oxidation

Porous nanocrystalline titania films were prepared by microarc oxidation (MAO) of a titanium alloy keeping anodic voltage at 230–410 V and cathodic voltage at 20–45 V in a Na₂CO₃ and Na₂SiO₃ electrolytic solutions using an asymmetric pulse alternating current power supply. XRD, EDS and SEM were employed to characterize the phase, composition and microstructure of the films. It is found that the films consist of dominant rutile and little anatase phases. The phase, pore size and thickness of the coatings strongly depend on the applied voltage, consistent with the previous reports, and the cathodic voltage has an intense effect on the films' pitting corrosion performance in sodium chloride solution. The films prepared by keeping the anodic and cathodic voltages at 320 and 45 V, respectively, for 30 min were porous, with 200 nm to 4 μm pores and the pore walls composed of 100–300 nm rutile crystallites.     

Hank′s溶液中注碳Ti6Al4V合金缝隙试样的电化学行为

为探索碳离子注入Ti-6Al-4V合金在人工模拟体液Hank's溶液中的性能,采用电化学方法、扫描电子显微镜和X射线衍射对其缝隙试样在人工模拟体液Hank's溶液中的电化学行为进行了研究.结果表明:碳离子注入后,Ti-6Al-4V合金缝隙试样的腐蚀电位升高、电荷转移电阻增大,阳极极极化电流密度降低,改善了电化学性能;碳离子注入后,Ti-6Al-4V合金表面形成主要由TiC组成的无序层膜,该膜层阻滞了合金元素的溶解,提高了合金的耐缝隙腐蚀性能.     

Ti-48Al-2Cr-2Nb钝化膜的电化学性能及形成机理

探究Ti-48Al-2Cr-2Nb合金钝化膜的耐腐蚀性和形成机理对提高电解加工过程中的抗杂散腐蚀具有重要意义。通过极化曲线确定了Ti-48Al-2Cr-2Nb合金的钝化电位,采用X射线光电子能谱确定了钝化膜的成分与结构,并运用电化学阻抗谱和Mott-Schottky理论分析了钝化膜的电化学性能。结果表明,Ti-48Al-2Cr-2Nb合金在NaNO3电解液中钝化电位区间为0.079～1.896V,钝化膜主要成分为Al₂O₃、TiO₂及少量的Nb₂O₅,呈双层多孔结构,具有良好的耐腐蚀性。钝化膜具有n型半导体特性,载流子密度随钝化电位的增加而降低。最后,构建了钝化膜形成示意图,揭示了Ti-48Al-2Cr-2Nb合金钝化膜的形成机理与成相膜理论相符,以半球体模型延展并形成独立的相。     

Mechanism of surface modification of a porous-coated Ti-6Al-4V implant fabricated by electrical resistance sintering

A porous-coated Ti-6Al-4V implant was fabricated by electrical resistance sintering, using 480 F capacitance and 1.5 kJ input energy. X-ray photoelectron spectroscopy (XPS) was used to study the surface characteristics of the implant material before and after sintering. There were substantial differences in the content of O and N between as-received atomized Ti-6Al-4V powders and the sintered prototype implant, which indicates that electrical resistance sintering alters the surface composition of Ti-6Al-4V. Whereas the surface of atomized Ti-6Al-4V powders was primarily TiO₂, the surface of the implant consisted of a complex of titanium oxides as well as small amounts of titanium carbide and nitride. It is proposed that the electrical resistance sintering process consists of five stages: stage I – electronic breakdown of oxide film and heat accumulation at the metal-oxide interface; stage II – physical breakdown of oxide film; stage III – neck formation and neck growth; stage IV – oxidation, nitriding, and carburizing; and stage V – heat dissipation. The fourth stage, during which the alloy repassivates, is responsible for the altered surface composition of the implant.     

Formation of amorphous anodic oxide films of controlled composition on aluminium alloys

Binary, non-equilibrium Al-29at%Nb, Al-44at%Ta, Al-19at%Ti, Al-25at%Ti and Al-32at%Zr alloys were prepared by magnetron sputtering and subsequently anodized at high Faradaic efficiency to grow barrier-type anodic films. Examination in the transmission electron microscope revealed amorphous anodic films of relatively uniform compositions across the film thicknesses, except for a layer of relatively pure alumina, of about 5% of the film thickness, present at the film/electrolyte interface of the Al-Ta alloy. The film compositions, from Rutherford backscattering spectroscopy, indicate that the alloy constituents are oxidized in their alloy proportions to form films comprising intimately mixed units of the various oxides, namely alumina, niobia, titania, tantala and zirconia. The films grow by co-operative transport of metal and oxygen ions under the electric field with formation of film material by both migration of metal ions outwards and of oxygen, and possibly hydroxyl, ions inwards. The average migration rates of Al³⁺, Nb⁵⁺, Ti⁴⁺ and Zr⁴⁺ ions are similar, to within 10%, but Ta⁵⁺ ions migrate more slowly than Al³⁺ ions. The results of the study show that a wide range of compositions of amorphous oxide films can be readily formed by anodic oxidation of appropriate alloys, including compositions containing units of normally crystalline anodic oxides, namely TiO₂ and ZrO₂.     

Formation of porous niobium films by oblique angle deposition: Influence of substrate morphology

The present work demonstrates the formation of porous niobium films with separated columnar structures by oblique angle magnetron sputtering for capacitor application. The niobium films deposited on textured aluminium substrates, which had concave cell structures with the cell sizes ranging from 125 nm to 550 nm, consist of isolated columns of niobium with wider gaps between columns developing on the substrates with larger cell sizes. The surface areas of the deposited films, evaluated by the capacitance of the anodic films formed at several voltages, increased with an increase in the cell size of substrate. The surface area decreases with an increase in the formation potential of anodic films from 2 V to 10 V vs Ag/AgCl, because the gaps are filled with anodic oxide as a consequence of the large Pilling-Bedworth ratio of 2.6 for the Nb/Nb₂O₅ system. The reduction of the surface area is suppressed when the substrate with larger cell size is used, due to the formation of niobium columns with wider gaps, which are not filled with anodic oxide. The high surface area even at higher formation voltages of the anodic films is a requisite for capacitor application.     

Thermophysical Properties of Solid and Liquid Ti-6Al-4V (TA6V) Alloy

Ti-6Al-4V (TA6V) titanium alloy is widely used in industrial applications such as aeronautic and aerospace due to its good mechanical properties at high temperatures. Experiments on two different resistive pulse heating devices (CEA Valduc and TU-Graz) have been carried out in order to study thermophysical properties (such as electrical resistivity, volume expansion, heat of fusion, heat capacity, normal spectral emissivity, thermal diffusivity, and thermal conductivity) of both solid and liquid Ti-6Al-4V. Fast time-resolved measurements of current, voltage, and surface radiation and shadowgraphs of the volume have been undertaken. At TU-Graz, a fast laser polarimeter has been used for determining the emissivity of liquid Ti-6Al-4V at 684.5 nm and a differential scanning calorimeter (DSC) for measuring the heat capacity of solid Ti-6Al-4V. This study deals with the specific behavior of the different solid phase transitions (effect of heating rate) and the melting region, and emphasizes the liquid state (T > 2000 K).     

Influences of processing parameters and heat treatment on microstructure and mechanical behavior of Ti-6Al-4V fabricated using selective laser melting

Selective laser melting (SLM) has provided an alternative to the conventional fabrication techniques for Ti-6Al-4V alloy parts because of its flexibility and ease in creating complex features. Therefore, this study investigated the effects of the process parameters and heat treatment on the microstructure and mechanical properties of Ti-6Al-4V fabricated using SLM. The influences of various process parameters on the relative density, tensile properties, impact toughness, and hardness of Ti-6Al-4V alloy parts were studied. By employing parameter optimization, a high-density high-strength Ti-6Al-4V alloy was fabricated by SLM. A relative density of 99.45%, a tensile strength of 1 188 MPa, and an elongation to failure of 9.5% were achieved for the SLM-fabricated Ti-6Al-4V alloy with optimized parameters. The effects of annealing and solution aging heat treatment on the mechanical properties, phase composition, and microstructure of the SLM-fabricated Ti-6Al-4V alloy were also studied. The ductility of the heat-treated Ti-6Al-4V alloy was improved. By applying a heat treatment at 850 ℃ for 2 h, followed by furnace cooling, the elongation to failure and impact toughness were found to be increased from 9.5% to 12.5%, and from 24.13 J/cm² to 47.51 J/cm², respectively.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00389-y     

Structural and mechanical properties of titanium oxide thin films for biomedical application

Titanium oxide thin films were deposited by radiofrequency reactive sputtering in Ar-O₂ atmosphere on silicon (100) wafers and titanium alloy plates (Ti-6Al-4V). Thin films structural characterization was carried out by grazing incidence X-ray diffraction, atomic force microscopy, scanning and transmission electron microscopies. Chemical composition was checked by X-ray wavelength dispersive spectroscopy. Mechanical assessment was achieved by nano-indentation and nano-scratch measurements. The films deposited on silicon substrates are over-stoechiometric in oxygen, with an oxygen to titanium ratio of about 2.2. The growth of anatase and rutile phases was promoted by ranging the total and oxygen partial pressures between 0.17-1.47 Pa and 35-85%. The growth rate of films, determined by grazing incidence X-ray reflectivity, was ranging from 35 to 55 nm/h. The rutile single-phased films possess a hardness of about 2.5 times higher and a lower friction coefficient than the anatase films. The films which contain anatase possess a high surface root-mean-square roughness and a reduced elastic modulus of around 120 GPa close to reduced elastic moduli of hydroxyapatite bioceramic and titanium alloy. So the anatase film could be the best candidate as a titanium oxide intermediate layer between hydroxyapatite and titanium alloy in the field of biomedical implants.     

Surface characterization and mechanical property evaluation of thermally oxidized Ti-6Al-4V

The present study concerns development of a thin and adherent oxide film on the surface of Ti-6Al-4V by thermal oxidation. Thermal oxidation was carried out over a range of temperature between 400 to 600 °C and a time from 25 h to 60 h. A detailed characterization of the surface and cross section of the oxidized surface was carried out by optical/scanning electron microscopy and X-ray diffraction techniques. Finally, the mechanical properties of the oxidized surface in terms of microindentation hardness and wear resistance were evaluated as a function of oxidation parameters. Surface oxidation of Ti-6Al-4V at 600 °C for 36 h offered a defect free oxide scale with improved hardness and wear resistance.     

Nanostructured severe plastic deformation processed titanium for orthodontic mini-implants

Titanium mini-implants have been successfully used as anchorage devices in Orthodontics. Commercially pure titanium (cpTi) was recently replaced by Ti-6Al-4 V alloy as the mini-implant material base due to the higher strength properties of the alloy. However, the lower corrosion resistance and the lower biocompatibility have been lowering the success rate of Ti-6Al-4 V mini-implants. Nanostructured titanium (nTi) is commercially pure titanium that was nanostructured by a specific technique of severe plastic deformation. It is bioinert, does not contain potentially toxic or allergic additives, and has higher specific strength properties than any other titanium applied in medical implants. The higher strength properties associated to the higher biocompatibility make nTi potentially useful for orthodontic mini-implant applications, theoretically overcoming cpTi and Ti-6Al-4 V mini-implants. The purposes of the this work were to process nTi, to mechanically compare cpTi, Ti-6Al-4 V, and nTi mini-implants by torque test, and to evaluate both the surface morphology and the fracture surface characteristics of them by SEM. Torque test results showed significant increase in the maximum torque resistance of nTi mini-implants when compared to cpTi mini-implants, and no statistical difference between Ti-6Al-4 V and nTi mini-implants. SEM analysis demonstrated smooth surface morphology and transgranular fracture aspect for nTi mini-implants. Since nanostructured titanium mini-implants have mechanical properties comparable to titanium alloy mini-implants, and biocompatibility comparable to commercially pure titanium mini-implants, it is suggestive that nanostructured titanium can replace Ti-6Al-4 V alloy as the material base for mini-implants.     

Non-sparking anodization process of AZ91D magnesium alloy under low AC voltage

Anodization is widely recognized as one of the most important surface treatments for magnesium alloys. However, since high voltage oxidation films are limited in some applications due to porosity and brittleness, it is worthwhile to explore the non-sparking oxidizing process. In this work, AZ91D was electrochemically anodized at different AC voltages in an electrolyte containing 120 g/L NaOH and 80 g/L Na₂SiO₃·9H₂O. The effects of voltage on the surface morphology, composition and reaction process, especially the non-sparking discharge anodic film formation process, were investigated. The results showed that four different processes would appear according to the applied voltage variation from 6 V to 40 V, and that the non-sparking film formation process occurred in the range of 6–10 V. The film formed on the AZ91D surface under 10 V AC was mainly composed of Mg₂SiO₄ with a lamellar structure. The horizontal and vertical expansion of the lamellar structure resulted in the formation of a multi-layered structure with a stable, linear growth rate for 30 min. The non-sparking film formation process can be considered to be the result of a balance of electrochemical dissolution and chemical deposition reaction.