Durability of titanium adhesive bonds with surface pretreatments based on alkaline anodisation

The most recent works suggest that the alkaline anodizing process (NaTESi) based in a bath of sodium hydroxide may be an attractive alternative to chromic acid anodizing (CAA) for surface pretreatment of titanium alloys for preparing hybrid adhesive bonds Ti6Al4V/Carbon Fiber Reinforced Composite (CFRC). This work compares several anodizing processes used for surface preparation, such as CAA, NaTESi and two modified NaTESi processes. The surface morphology, roughness, surface free energy and, especially, the initial strength adherence and durability under the wedge crack tests have been characterized. Wedge crack tests were performed in three different ageing media that may be representative of the environment that adhesive joints based upon Ti6Al4V/CFRC have to withstand during aircraft service life environments: hot/wet conditions; CTB3+TS test, that combines wet-dry cycles with exposure to a corrosive environment (CTB3) and thermal shocking (TS); and immersion tests in a Lap Joint Simulant Solution (LJSS). The results indicate that despite the morphological differences of the oxide grown by CAA and NaTESi, the initial adhesive strength with an epoxy adhesive and the durability of the bond are similar for both anodizing processes. Conversely, higher initial adhesive forces are exhibited for both modified NaTESi anodizing processes.     

Ti6Al4V钛合金表面蓝色微弧氧化膜的制备及性能

利用微弧氧化技术在Ti6Al4V钛合金表面制备出蓝色微弧氧化膜。对微弧氧化膜的微观形貌和元素组成进行了分析,并对微弧氧化膜的显微硬度进行了测试。结果表明:微弧氧化膜表面光整,呈均匀深蓝色,其主要由Ti、Mn、O和C四种元素组成,还含有少量的V、Al和Si元素;微弧氧化膜的表面粗糙度约为0.159μm,与钛合金的表面粗糙度相近;微弧氧化膜的显微硬度为5 437.4 MPa,显著高于钛合金的显微硬度。     

Tantalum carbide coating on Ti‐6Al‐4V by electron beam physical vapor deposition method: Study of corrosion and biocompatibility behavior

This study aimed to improve the corrosion resistance and biocompatibility of titanium alloy (Ti‐6Al‐4V) by tantalum carbide (TaC) deposition through electron beam physical vapor deposition (EB‐PVD) method. The physical and chemical characteristics of the coated surface are comprehensively evaluated. The corrosion resistance and ion release are assessed. Cytocompatibility assay and cell morphology observation are performed to assess toxicity and cell interaction, respectively. The TaC‐coated Ti‐6Al‐4V exhibits more resistance to corrosion and ion release. It provides a surface, which is appropriate for cell adhesion, an expansion as well as better biocompatible performance. So, it could improve osseointegration Ti‐alloy implants in clinical applications.     

A study of the potentials achieved during mechanical abrasion and the repassivation rate of titanium and Ti6Al4V in inorganic buffer solutions and bovine serum

Titanium alloys in orthopaedic implants are susceptible to mechanical disruption of the passive film (fretting corrosion). To study this effect, open-circuit potential (ocp) measurements before, during and after mechanical disruption of the passive film in a tribo-electrochemical cell on commercial pure titanium and Ti6Al4V alloy in inorganic buffer solutions in the pH range from 2.0 to 12.0 and calf bovine serum at pH 4.0 and 7.0 are reported. Additionally, the effect of pH, electrolyte and sample composition on the repassivation rate has been investigated. The potentials achieved during the abrasion of Ti6Al4V are the same as those characterizing pure titanium, which indicates that the corrosion current of both materials in the active state is due to the oxidation of titanium. However, commercial pure titanium displays a tendency to repassivate faster than Ti6Al4V in inorganic buffer solutions thanks to the lower critical current density and the higher catalytic activity towards the hydrogen evolution reaction observed on the pure metal in comparison with the alloy.Proteinaceous solutions like bovine serum, significantly slow down the anodic dissolution and the cathodic reactions both on titanium and the alloy. However, the repassivation rate of the Ti6Al4V is not affected by serum, while that of cp titanium significantly decreases both at pH 4.0 and 7.0.     

Mesh Ti6Al4V Material Manufactured by Selective Laser Melting (SLM) as a Promising Intervertebral Fusion Cage

Intervertebral cages made of Ti6Al4V alloy show excellent osteoconductivity, but also higher stiffness, compared to commonly used polyether-ether-ketone (PEEK) materials, that may lead to a stress-shielding effect and implant subsidence. In this study, a metallic intervertebral fusion cage, with improved mechanical behavior, was manufactured by the introduction of a three-dimensional (3D) mesh structure to Ti6Al4V material, using an additive manufacturing method. Then, the mechanical and biological properties of the following were compared: (1) PEEK, with a solid structure, (2) 3D-printed Ti6Al4V, with a solid structure, and (3) 3D-printed Ti6Al4V, with a mesh structure. A load-induced subsidence test demonstrated that the 3D-printed mesh Ti6Al4V cage had significantly lower tendency (by 15%) to subside compared to the PEEK implant. Biological assessment of the samples proved that all tested materials were biocompatible. However, both titanium samples (solid and mesh) were characterized by significantly higher bioactivity, osteoconductivity, and mineralization ability, compared to PEEK. Moreover, osteoblasts revealed stronger adhesion to the surface of the Ti6Al4V samples compared to PEEK material. Thus, it was clearly shown that the 3D-printed mesh Ti6Al4V cage possesses all the features for optimal spinal implant, since it carries low risk of implant subsidence and provides good osseointegration at the bone-implant interface.     

电流密度对Ti 6Al 4V微弧氧化膜形貌和性能的影响

采用NaAlO2-Na3PO4-NaF溶液体系,研究了电流密度对Ti 6Al 4V合金微弧氧化膜厚度、生长速率、表面形貌、粗糙度、组成相以及氧化膜耐蚀性、耐磨性等影响.结果表明,(1)在试验的电流密度范围内,氧化膜的厚度随电流密度的增大呈线性增大,但氧化膜的粗糙度却几乎呈指数增大,表面质量变差;(2)在质量分数为3.5%的NaCl溶液中显示了比Ti 6Al 4V钛合金更好的耐蚀性;(3)在干摩擦条件下,氧化膜的摩擦系数高于基体的,氧化膜的磨损机制为脆性断裂.     

在非水溶液体系中电泳沉积Ti6Al4V/BG/HA梯度涂层

本工作的目的是探索制备钛合金表面生物活性梯度涂层的新方法 ,提高涂层的结合强度及稳定性 .通过诱导羟基磷灰石 (HA)在生物玻璃 (BG)颗粒表面的结晶 ,改变了生物玻璃表面的带电特性 ;采用电泳沉积 (EPD)法 ,在非水溶液体系中实现了BG和HA在阴极Ti6Al4V基体上的共沉积 ,经烧结获得了生物活性梯度陶瓷涂层 ,得到了一种制备生物活性梯度陶瓷涂层的新工艺 .用XRD对涂层的相组成进行了定性分析 ,结果表明涂层由HA ,榍石和玻璃组成 ;采用粘结拉伸法测定的涂层与基体结合强度大于 18MPa,用SEM观察涂层表面及断面的形貌 ,可见涂层表面较为平整 ,没有明显的裂纹 ;涂层与基体结合紧密 ,且存在一明显的界面梯度区域 .     

The investigation of the tribocorrosion properties of DLC coatings deposited on Ti6Al4V alloys by CFUBMS

Various machine components produced from titanium alloys used in various industries are subject to a combination of electrochemical and mechanical effects. The science of surface transformations resulting from the interaction of mechanical loading and chemical reactions that occur between elements of a tribosystem exposed to corrosive environments is described as tribocorrosion. This research focuses on the tribocorrosion behaviour of Ti6Al4V alloys after coated by using closed field unbalance magnetron sputtering (CFUBMS). The structural analyses of the coatings were performed using Raman spectroscopy and scanning electron microscopy (SEM). Tribocorrosion experiments were performed in a pin-on-disc tribotester under electrochemical polarisation in NaCl 1 wt.% solution. This study shows that the Ti-DLC coating is protecting the Ti6Al4V alloy and having good performance in corrosion and tribocorrosion conditions. The OCP values for Ti6Al4V substrate and Ti-DLC protective coatings during tribocorrosion tests were measured as −560 V and −330 V, respectively. These results showed that Ti-DLC protective coating on Ti6Al4V substrates increased the tribocorrosion resistance by acting as a barrier layer.     

Effect of Surface Texture on the Adhesion Performance of Laser Treated Ti6Al4V Alloy

The growing demand in lighter and safer structures generates the requirement of lighter joining strategies, particularly for lightweight metal alloys, composites, and also joining dissimilar materials together. Titanium alloys stand out as the conventional choice for materials for light weight structures. Adhesive bonding of titanium is an appealing route for joint design, also for the possibility of joining it with dissimilar materials. The realization of a strong joint depends not only on the joint design and type of adhesive, but also on the preparation of the adhering surface. Laser texturing presents advantages compared to common surface preparation processes in terms of eco-compatibility, energetic efficiency, ease of manufacturing, and repeatability. This work presents a preliminary investigation on laser texturing of Ti6Al4 V alloy with a pulsed fiber laser source with the aim to increase surface adhesion for bonding. Particularly, different surface textures are proposed, and laser machining strategies are developed. The results showed that laser texturing provided up to eightfold and 30% higher shear strength compared to plain and sand blasted surfaces, respectively. Failure analysis showed that a margin of improvement is still possible by adapting the surface texture for better cavity filling and reducing surface damage caused by the laser treatment.     

Plasma-sprayed coatings as surface treatments of aluminum and titanium adherends

Plasma-sprayed coatings have been evaluated as surface treatments for aluminum and titanium adherends. The best aluminum treatment is found to be a 50-μm thick blend of an aluminum-12% silicon alloy and polyester with 20-40% polyester. For FM-300M film adhesive, this coating gives a wedge test performance equivalent to phosphoric acid anodization (PAA). For FM-123 film adhesive, its performance is between that of the Forest Products Laboratory (FPL) etch and PAA. The aluminum in the composite coating provides structural strength and adhesion to the substrate; the polyester serves to toughen the coating and perhaps supplement the physical bonding (mechanical interlocking) provided by the microscopically rough morphology with chemical bonding to the adhesive. For titanium, a 50-μm plasma-sprayed Ti-6Al-4V coating provides an identical performance to the best chemical treatment with crack propagation entirely within the adhesive. These plasma-sprayed coatings avoid the disposal and environmental costs of conventional chemical treatments using chromates and strong acids or bases. They are also well suited to repair or refurbishment of existing components.     

Voltammetric stability of anodic films on the Ti6Al4V alloy in chloride medium

The biocompatibility and mechanical integrity of Ti and Ti6Al4V alloy can be affected by corrosion processes. This paper presents studies on the stability of anodic oxide films on Ti6Al4V and Ti in chloride medium. The oxides were grown potentiodynamically up to 8.0 V in the phosphate buffer saline (PBS) solution (pH 6.8) at 25 and 37 °C. The morphology of the obtained anodic oxides and the type of corrosion that occurred were analyzed by SEM–EDS. The Ti6Al4V alloy presented less corrosion resistance than pure Ti. Elemental analyses showed that the decrease of the alloy corrosion resistance is due mainly to the corrosion of Al.     

Electrochemical and structural evaluation of functionally graded bioglass-apatite composites electrophoretically deposited onto Ti6Al4V alloy

Titanium and its alloys are widely used as materials for implants, owing to their corrosion resistance, mechanical properties and excellent biocompatibility. However, clinical experience has shown that they are susceptible to localised corrosion in the human body causing the release of metal ions into the tissues surrounding the implants. Several incidences of clinical failures of such devices have demanded the application of biocompatible and corrosion resistant coatings and surface modification of the alloys. Coating metallic implants with bioactive materials is necessary to establish good interfacial bonds between the metal substrate and the bone. Hence, this work aimed at developing a bioglass-apatite (BG-HAP) graded coating on Ti6Al4V titanium alloy through electrophoretic deposition (EPD) technique. The coatings were characterized for their properties such as structural, electrochemical and mechanical stability. The electrochemical corrosion parameters such as corrosion potential (E_corr) (open circuit potential) and corrosion current density (I_corr) evaluated in simulated body fluid (SBF) have shown significant shifts towards noble direction for the graded bioglass-apatite coated specimens in comparison with uncoated Ti6Al4V alloy. Electrochemical impedance spectroscopic investigations revealed higher polarisation resistance and lower capacitance values for the coated specimens, evidencing the stable nature of the formed coatings. The results obtained in the present work demonstrate the suitability of the electrophoretic technique for the preparation of graded coating on Ti6Al4V substrates.     

Comparative determination of TiO2 surface free energies for adhesive bonding application

The development of durable bonds using titanium adherens has been investigated from the point of view of surface energy theoretical models measurements. The traditional Chromium Acid Anodization, which provides excellent durability, has to be phased out due to the use of hazardous Cr (VI) in the bath and as a result, special attention is paid to the sodium hydroxide anodizing and other alkaline chemical etchers. There are hardly any references on the surface free energy of adhesive titanium oxide coatings and therefore the objective of this work was to evaluate the surface and interface energy parameters of the various types of alkaline chromate free surface treatments using Neumann, Fowkes and van Oss–Chaudhury–Good methods in order to determine which method provides greatest differentiation between the coatings. Results show that Fowkes method produced the greatest variance in surface energies of the compared surface treatments and hence can be considered as better suited for more accurate discrimination between the oxide surface treatments on Ti–6Al–4V alloy. Although, in the case of model liquids, i.e. water and diiodomethane, the trends obtained for contact angles, surface energies, works of adhesion and solid/liquid interface energies all correlated between each other, a disagreement between the trends of solid/liquid interface energies calculated using Fowkes and van Oss–Chaudhury–Good methods for surface treatment/adhesive resin was obtained. In case of real adhesive systems, the use of work of adhesion appears more adequate in order to discriminate the surface treatments. Based on these findings the anodization in the tested alkaline bath after a previous alkali etching in the same bath is recommended, although adhesion test has to be still performed.     

Effect of vitreous enamel coating on the oxidation behavior of Ti6Al4V and TiAl alloys at high temperatures

Vitreous enamel coating is a promising candidate as a high temperature protective coating for titanium (Ti)-based alloys due to its high thermo-chemical stability, compatibility, and matching thermal expansion coefficient to the substrates. Vitreous enamel coating is economically attractive because of its low cost and easy handling. The oxidation behavior of Ti6Al4V (at 700°C) and Ti–48Al (at 800–900°C), with and without the vitreous enamel coating exposed to air, are investigated in this article. The results show that the vitreous enamel coating could markedly protect the substrate (Ti6Al4V and Ti48Al) from oxidation at elevated temperatures. In comparison, the TiAlCr coating might not provide long-term protection for the Ti6Al4V alloys due to the heavy interfacial interdiffusion at high temperatures, although a protective Al₂O₃ scale could form at the initial oxidation stage. The vitreous enamel coating remains intact, uniform, compact, and adhesive to the substrate, however, with undetectable interfacial reaction after oxidation. It is also worth noting that some new phases form in the coating during oxidation at 900°C, although the protectiveness of the coating seems to be unaffected.     

Synthesis and evaluation of TaC nanocrystalline coating with excellent wear resistance,corrosion resistance,and biocompatibility

To improve the mechanical properties, corrosion resistance, and biocompatibility of implanted titanium alloys, a TaC nanocrystalline coating was deposited on Ti–6Al–4V alloy using a double-cathode glow discharge method. The microstructure of the newly developed coating was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The coating exhibits a dense and uniform structure, composed of equiaxed TaC grains with an average grain size of 15.2 nm. The mechanical properties of the TaC-coated Ti–6Al–4V alloy were evaluated by a scratch tester, a nanoindentation tester, and a ball-on-disc tribometer. The average hardness of the TaC nanocrystalline coating is about 6 times higher than that of uncoated Ti–6Al–4V alloy and the specific wear rate of the coating is two orders of magnitude lower than that for Ti–6Al–4V at applied normal loads of 4.9 N under dry sliding condition. The electrochemical behavior of the TaC nanocrystalline coating after soaking in Ringer's solution for different periods was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Furthermore, in vitro cytocompatibility of the coating was assessed using MC3T3-E1 mouse osteoblastic cells. The results showed that the TaC coating exhibits better corrosion resistance and biocompatibility as compared to uncoated Ti–6Al–4V alloy.     

Understanding the protective role of a gradient titanium oxide ceramic layer on Ti6Al4V against corrosion via analyses of Mott-Schottky curve and electron work function (EWF)

Thermal oxidation (TO) process was employed to generate a gradient titanium oxide ceramic layer for improving corrosion performance and service safety of Ti6Al4V alloy. The semiconductor characteristic of the TO layer was evaluated in CO₂-saturated simulated oilfield brine. The generated TO layer with a thickness of about 20 μm was dense and continuous without cracks or spalling characteristics. The TO layer mainly comprised of an oxide ceramic layer (rutile TiO₂ ceramic phase, minor anatase one, and Al₂O₃) and an oxygen diffusion layer. The conducted electrochemical analysis suggested that the corrosion resistance of Ti6Al4V alloy was improved using TO surface strengthening process. It was demonstrated that the TO layer with semiconductor characteristics showed a transition from n-type (donor) to p-type (acceptor) with the increasing applied electric potential. The electron work function of the TO layer was higher than that of Ti6Al4V alloy with a naturally formed passive film. The improvement in corrosion properties was attributed to the excellent chemical stability and semiconductor properties of the metal oxide ceramic phases (TiO₂, Al₂O₃) in the TO layer.     

金属热还原法制备低氧高钛铁的基础研究

以金红石、钛精矿、Al(或铝镁合金)为原料采用热还原法制备出高钛铁合金. 计算了不同反应体系的绝热温度以及与TiO2-Al,TiO2-Mg体系相关反应的吉布斯自由能变,采用DTA研究了不同体系的反应动力学,采用XRD等对高钛铁合金进行了表征. 结果表明,所有反应体系的绝热温度均大于1800 K,反应能自发进行;采用Al-Mg合金复合还原剂能保证TiO2的有效还原,降低合金中的氧含量以及夹杂物含量;Al还原TiO2反应的表观活化能为164.497 kJ/mol,反应级数为0.414,Mg还原TiO2的表观活化能为383.235 kJ/mol,反应级数为0.591;高钛铁由Al2O3、TiO2、Ti2O、Fe2TiO4 、Ti9Fe3(Ti0.7Fe0.3)O3等复杂相组成,合金中氧含量高达12.20%.     

Surface modification of Ti64-Alloy with silver silicon nitride thin films

Ti6Al4V (Ti64) alloys is an alpha-beta titanium alloy with good corrosion resistance, high strength-to-weight ratio, excellent physiochemical stability and good biocompatibility. However, Ti64 alloy loses its biocompatibility when it is introduced into human tissues due to possible toxic of Vanadium (V) and Aluminum (Al) ion release. Thus, modification using silver silicon nitride films onto Ti64 via magnetron sputtering technique was proposed. In this study, a set of experimental depositing AgSiN films on Ti64 alloys using different bias voltage (0, ?75, ?150 and ?200?V) were fabricated. The surface characterization and mechanical performance of the thin films with respect to bias voltage were studied using scanning electron microscope (SEM), atomic force microscope (AFM), X-ray diffraction (XRD), nanoindentation and scratch test. Meanwhile, the biological function of the films was tested through wettability and antibacterial tests. According to the results, all thin films showed similar morphology with the highest adhesion strength (596?mN) was obtained for AgSiN thin film deposited at ?75?V. The hardness (5.5?GPa) and elastic modulus (211.0?GPa) of sample deposited at ?150?V showed an improvement for about 50% compared to the Ti64 substrate (H?=?2.75, E?=?113.8). The lowest compressive residual stress 0.06?GPa was noted for samples that have highest adhesion strength and highest thickness. In terms of biological functionality, all films showed hydrophilic property with wetting angle observed were below 90°. An inhibition zone area that observed on Bulkholderia pseudomallei (B.Psudomallei) and Escherichia coli (E.coli) were 7 and 10?mm respectively, which proved the AgSiN films as a promising candidate to be used in antibacterial applications.     

Evaluation of corrosion behavior of surface modified Ti–6Al–4V ELI alloy in hanks solution

The passive film behavior of Ti–6Al–4V ELI (Extra Low Interstitial) alloy after a chemical treatment followed by a thermal treatment was morphologically and electrochemically characterized. The surface morphological studies were carried out using scanning electron microscopy (SEM), electron dispersive X-ray analysis (EDAX), and Fourier Transformed-Infra Red (FT-IR) analysis to investigate the nucleation and growth of apatite on the chemically and thermally treated Ti–6Al–4V ELI alloy immersed for different durations in Hanks solution. Polarization and impedance spectroscopic (EIS) measurements were carried out in Hanks solution and the electrical parameters were obtained for the passive film using a non-linear least square fitting (NLLS) method.     

Effect of sintering on the microstructure and mechanical properties of alloy titanium-wollastonite composite fabricated by powder injection moulding process

Composite biomaterials are in high demand in the medical field of today. The combination of bioactive wollastonite (WA) glass ceramic with the biocompatibility of alloy titanium (Ti6Al4V) could be a good candidate for implant applications. The rheological properties of Ti6Al4V/WA feedstock show a pseudoplastic behaviour with low activation energy. The feedstock was successfully injected as a green part with no defects. The green part was solvent debound for 6?h in heptane and thermal debound in an argon environment for 1?h. The brown part was successfully sintered at 1300?°C for 3?h with 5?°C/min heating and cooling rates. The average sintered density was 4.12?g/cm³; which is 97.5% from the theoretical density. The highest Young's modulus obtained was 18.10?GPa; which is in the range of human bone strength. EDX analysis shows that by increasing sintering temperature, the level of oxygen decreased. Cell viability test shown an absorbance increased with days increasing indicated that the cellular were proliferated on the composite Ti6Al4V/WA composite which also proved that the composite was non-toxic. This indicates that the Ti6Al4V/WA composite is suitable for bone implant applications.