Application of surface response analysis to the optimisation of nitric passivation of cp titanium and Ti6Al4V

Passivation of Ti6Al4V and cp Ti by mean of nitric acid treatment are used to reduce their surface reactivity, and consequently increasing resistance to corrosion, in physiological media.

In this work, the response surface methodology was employed to know the effects of operating parameters of the nitric passivation (HNO₃ content, temperature of solution and passivation period) on the corrosion resistance of commercially pure (cp) titanium and Ti6Al4V alloy in Ringer's solution. The experiment included two 3³ factorial designs. According to the responses from the experimental designs, the effects of each variable were calculated and the interactions between them were determined. The statistical test has revealed that the main effect of the nitric acid content is the most significant factor. The surface response methodology was applied to graphically determine the optimal working conditions.

Different electrochemical techniques (OCP, Rp and cyclic polarisation tests) were used to compare the electrochemical behaviour of cp Ti and Ti6Al4V, with and without passivation.     

Hydroxyapatite coating on titanium substrate by electrophoretic deposition method: Effects of titanium dioxide inner layer on adhesion strength and hydroxyapatite decomposition

Nanosized hydroxyapatite (HA) powders were prepared by a chemical precipitation method and electrophoretically deposited on Ti6Al4V substrates. The powders were calcined before the deposition process in order to obtain crack-free coating surfaces. As an inner layer between Ti6Al4V substrate and HA coating, nanosized titanium dioxide (TiO₂) powders were deposited, using different coating voltages, in order to connect substrate and HA tightly. Moreover, this layer is considered to be acting as a diffusion barrier, reducing the HA decomposition due to ion migration from the metal substrate into the HA. After the sintering stage, adhesion strengths of coatings were measured by shear testing, phase changes were studied by X-ray diffraction, and coating morphology was analyzed through scanning electron microscopy observations. Results showed that usage of the TiO₂ inner layer prevented HA decomposition. Furthermore, decreasing the voltage used in TiO₂ deposition resulted in crack-free surfaces and increased adhesion strength of the overall coating.     

Effects of Micro-Arc Oxidation of Ti6Al4V Alloy on Adhesion Property to Electroless Ni-P-ZrO2 Composite Platings and Their Wear Resistance

在Ti6Al4V合金微弧氧化膜表面制备Ni-P-ZrO2化学复合镀层,微弧氧化处理时间分别为15、30、60、90 min。采用扫描电镜/能谱仪、划痕试验、热震试验、显微硬度计和球盘式摩擦磨损试验机研究了微弧氧化膜结构对Ni-P-ZrO2化学复合镀层的结合性能与摩擦性能的影响。结果表明：随着微弧氧化时间的增加,复合镀层的结合性能显著提高,原因是微弧氧化膜的多孔性结构及其机械锁合效应。与Ti6Al4V合金相比,微弧氧化+化学复合镀处理后的试样硬度和耐磨性显著提高,Ti6Al4V合金表现为是严重的黏着磨损,而Ni-P-ZrO2复合镀层以磨砺磨损为主     

Preparation of titanium oxide and hydroxyapatite on Ti–6Al–4V alloy surface and electrochemical behaviour in bio-simulated fluid solution

In order to improve the bonding strength between hydroxyapatite (HA) coating and Ti–6Al–4V substrate, a uniform titanium oxide film was obtained by controlled anodic oxidation. After that an alkaline treatment with NaOH solution was used to make them more bioactive. Finally hydroxyapatite coating has been prepared on Ti–6Al–4V substrate through electrochemical deposition. Comparative electrochemical behaviour of untreated and surface modified Ti–6Al–4V alloy, in bio-simulated fluid solution was investigated by electrochemical techniques. SEM was used to observe the morphology of modified surfaces and the thicknesses of the oxide films prepared were evaluated on the cross-sections of the samples using SEM–FIB.     

钛合金表面GO/HA/MAO复合膜层的制备及其性能

为了改善钛合金种植体在体液中的腐蚀及摩擦腐蚀行为,延长其在人体环境中的服役时间,在微弧氧化 (MAO)膜层上采用溶胶凝胶(Sol-gel)法于羟基磷灰石(HA)和氧化石墨烯(GO)的混合溶胶中浸渍提拉成膜,从而在 Ti6Al4V 合金表面成功地制备了 GO/ HA/ MAO 复合膜层。 结果表明,MAO 膜层表面的微孔及微球被 GO/ HA 薄膜有效的覆盖且较为致密;膜层的物相组成主要为金红石相及锐钛矿相的 TiO₂、HA、SiO₂ 和GO;根据电化学腐蚀和摩擦腐蚀结果分析知,GO/ HA/ MAO 复合膜层在模拟体液(SBF)中的耐蚀性及耐摩擦腐蚀性相比于 MAO 膜层和 Ti6Al4V 基体均得到了显著提高。     

Joining of ZrB2 Ceramics to Ti6Al4V by Ni-Based Interlayers

Pure ZrB₂ and ZrB₂-SiC composites were joined to Ti6Al4V at 1100 °C using B-Ni50 (at.%) as a filler alloy. The brazing medium and the processing parameters were chosen on the basis of specific wetting tests which showed the good adhesion properties of the B-Ni alloy with both the ceramic and the Ti alloy; interfacial reactions were foreseen and interpreted by phase diagram analysis. A multilayer metal-ceramic interfacial structure was observed in the joints and a key role was played by Ti coming from Ti6Al4V: it worked as the active element enhancing the adhesion of the liquid to the ceramic and segregated at the interface forming TiB. A satisfactory mechanical performance was obtained for ZrB₂-SiC/Ti6Al4V joints, which exhibited a room temperature shear strength of 74 MPa.     

Ti- 6Al-4V/hydroxyapatite composite coatings prepared by thermal spray techniques

The poor mechanical properties of hydroxyapatite (HA) can be enhanced by forming a composite with a bioinert and mechanically strong metal alloy such as Ti-6A1-4V. Biomedical composites composed of titanium alloys and HA can offer concomitant bioactive properties as well as good mechanical strength and toughness. This paper describes an attempt to improve coating mechanical properties by forming a composite composed of HA and Ti-6A1-4V. Several compositions (20, 33, and 80 wt % HA) were prepared. Subsequent examination of the plasma-sprayed coatings revealed alternating HA-rich and titanium-rich lamella microstructures. The HA-rich regions appeared porous as a result of poor interparticle adhesion, with the 80 wt% HA coatings having the highest porosity. Mechanical property analysis showed the 20 wt% HA coating to have the highest storage modulus (∼60 GPa). This coating also had the highest bond strength (≥20 MPa max). The coatings tended to exhibit increased bond strength at thicknesses less than or equal to 60 μm. The excellent bond strength of the Ti-6A1-4V/HA composite is caused by the superior interfacial bond between the Ti-6Al-4V-rich splats and the substrate. The encouraging development of this composite raises the possibility of its use as a bond coat for plasma-sprayed HA on titanium-alloy implants.     

The Tribological Performance of Surface Treated Ti6A14V as Sliding Against Si<Subscript>3</Subscript>N<Subscript>4</Subscript> Ball and 316L Stainless Steel Cylinder

Closed field unbalanced magnetron sputtering was used to deposit diamond-like carbon (Ti-C:H) coatings on Ti6Al4V alloy and gas nitrided Ti6Al4V alloy. Four different specimens were prepared, namely untreated Ti6Al4V alloy (Ti6Al4V), gas nitrided Ti6Al4V alloy (N-Ti6Al4V), Ti-C:H-coated Ti6Al4V alloy (Ti-C:H/Ti6Al4V) and Ti-C:H-coated gas nitrided Ti6Al4V alloy (Ti-C:H/N-Ti6Al4V). The tribological properties of the four specimens were evaluated using a reciprocating wear tester sliding against a Si₃N₄ ball (point contact mode) and 316L stainless steel cylinder (line contact mode). The wear tests were performed in a 0.89 wt.% NaCl solution. The results showed that the nitriding treatment increased the surface roughness and hardness of the Ti6Al4V alloy and improved the wear resistance as a result. In addition, the Ti-C:H coating also improved the tribological performance of Ti6Al4V. For example, compared to the untreated Ti6Al4V sample, the Ti-C:H coating reduced the wear depth and friction coefficient by 340 times and 10 times, respectively, in the point contact wear mode, and 151 times and 9 times, respectively, in the line contact wear mode. It is thus inferred that diamond-like carbon coatings are of significant benefit in extending the service life of artificial biomedical implants.     

Surface characterization of plasma sprayed pure and reinforced hydroxyapatite coating on Ti6Al4V alloy

Hydroxyapatite coatings suffer from poor mechanical properties like fretting fatigue, toughness and abrasive wear resistance. These properties can be enhanced by incorporation of secondary ceramic and metallic reinforcements in HA. An attempt has been made to deposit HA and HA reinforced with 10 wt.% (80Al₂O₃-20TiO₂) by plasma spray process on Ti6Al4V substrate. These coatings have been characterized using SEM/EDAX, XRD and FTIR spectroscopy. Corrosion studies have been done in SBF solution. Bio compatibility study is not included in this work. Reinforcement has enhanced the tensile strength. There is marginal improvement in microhardness and surface roughness with reinforcement. Both pure and reinforced coatings show superior resistance against corrosion in simulated body fluid.     

The effects of spark anodizing treatment of pure titanium metals and titanium alloys on corrosion characteristics

This study evaluated the surface characteristics of oxide films on commercially pure titanium metals (CP-Ti; Grade 2 and Grade 3) and titanium alloy (Ti6Al4V and Ti6Al7Nb) samples formed by an anodic oxidation treatment, and investigated the effects of anodization on the corrosion characteristics. FE-SEM, XRD, and Raman spectroscopy were used to evaluate the micromorphology and crystalline structure of the oxide films. The corrosion resistance of the sample groups was evaluated using open-circuit potential and cyclic polarization tests. After anodic oxidation up to dielectric breakdown with the same electric current, 150-200 nm-sized pores were distributed homogeneously on pure titanium metal samples, partially occluded pores were observed on the Ti6Al4V alloy, and there was an inhomogeneous size and distribution of pores on the Ti6Al7Nb alloy. The titanium dioxide films formed through anodic oxidation contained a phase mixture of anatase and rutile. The cyclic polarization tests showed that all the tested sample groups were not susceptible to localized corrosion. The as-received and anodically oxidized CP-Ti grade 3 groups showed a higher corrosion resistance than the other groups. The mean E_corr values of the anodically oxidized sample groups, except for the anodized Ti6Al7Nb alloy, showed higher values than those of the respective as-received sample groups. In particular, the Ti6AL7Nb alloy showed a statistically higher E_corr value in the anodized group than in the as-received group (p < 0.05).     

The examination of corrosion behaviors of hap coated Ti implant materials and 316L SS by sol-gel method

In this research, hydroxyapatite (HAP) coatings have been produced on Ti, Ti6Al4V alloy and 316L stainless steel substrates by sol-gel method. (NH₄) · H₂PO₄ is taken as P precursor and Ca(NO₃)₂ · 4H₂O is taken as Ca precursor to obtain HAP coating. Additionally, three different pretreatment processes (HNO₃, anodic polarization, base-acide (BA)) have been applied to Ti, Ti6Al4V alloy and 316L stainless steel substrates. The corrosion behaviors of bare and HAP coated samples are examined in Ringer and 0.9% NaCl. HAP coated Ti have showed over 87.85% inhibition. HAP coated Ti6Al4V alloys have showed over 87.33% inhibition. In Ringer solution, 99.24% inhibition has been showed in HAP coated anodic pretreatment for 316L stainless steel. All pretreatment processes are effective on clinging of HAP coating to the surface. It is seen that impedance values have increased in HAP coatings (Ti and Ti6Al4V). HAP coatings have raised the corrosion resistance of Ti and Ti6Al4V. The values of polarization resistance in HAP coated samples have increased for 316L stainless steel in 0.9% NaCl and Ringer solutions. It is seen in SEM images that open pores and attachments among pores have been observed in the coating, which increases osteointegration. It is noted in EDX analyses of the surfaces of the HAP coated samples that there is only Ca, O, and P on the surface. Ca/P ratio varies in 1.84–2.00 ranges. As Ca/P ratio increases, the inhibition increases too. It is seen in XRD images of HAP powder that there are HA ate structures. Additionally, it is seen in FTIR analysis, characteristic HA absorption bands have occurred in sintered powders.     

Composition and processing effects on the electrochemical characteristics of biomedical titanium alloys

The electrochemical behaviour of the Ti–13Nb–13Zr and Ti–6Al–4V ELI alloys with martensitic microstructures was investigated by polarization and electrochemical impedance spectroscopy (EIS) in Ringer’s solution. The impedance spectra were interpreted by a two time-constants equivalent circuit. Both investigated alloys showed high corrosion resistance, but the thin and uniform passive film on the Ti–6Al–4V ELI alloy surface was more protective. The inner barrier and outer porous layer were highly resistant and capacitive. However, thicker and more porous passive film on the Ti–13Nb–13Zr alloy surface may be beneficial for osteointegration. The suitable thermomechanical processing improved the corrosion resistance of Ti–13Nb–13Zr alloy.     

Effect of Spray Distance on Microstructure and Tribological Performance of Suspension Plasma-Sprayed Hydroxyapatite–Titania Composite Coatings

Hydroxyapatite (HA)–titania (TiO₂) composite coatings prepared on Ti6Al4V alloy surface can combine the excellent mechanical property of the alloy substrate and the good biocompatibility of the coating material. In this paper, HA–TiO₂ composite coatings were deposited on Ti6Al4V substrates using suspension plasma spray (SPS). X-ray diffraction, scanning electron microscopy, Fourier infrared absorption spectrometry and friction tests were used to analyze the microstructure and tribological properties of the obtained coatings. The results showed that the spray distance had an important influence on coating microstructure and tribological performance. The amount of decomposition phases decreased as the spray distance increased. The increase in spray distance from 80 to 110 mm improved the crystalline HA content and decreased the wear performance of the SPS coatings. In addition, the spray distance had a big effect on the coating morphology due to different substrate temperature resulting from different spray distance. Furthermore, a significant presence of OH^? and CO₃ ^2? was observed, which was favorable for the biomedical applications.     

电泳沉积法制备HA/Ti0，复合涂层

羟基磷灰石是一种最有发展前途的生物材料之一.采用电泳沉积方法在钛合金基体上制备了HA/TiO2生物陶瓷涂层.将HA和TiO2粉体分散到正丁醇溶液中,再加入三乙醇胺,通过zeta电位确定了稳定的悬浮液中三乙醇胺和HA/TiO2的含量.研究了沉积电压和电泳时间对HA/TiO2涂层形貌和沉积量的影响.制得均匀致密涂层的适宜电压范围为250～350V.研究结果表明:由于电场强度随沉积时间改变,HA/TiO2沉积量随着沉积时间的增加表现出2段沉积速率不同的线性增长.     

Effects of Duplex Nitriding and TiN Coating Treatment on Wear Resistance,Corrosion Resistance and Biocompatibility of Ti6Al4V Alloy

Ti6Al4V alloy substrates were nitrided at 900 °C. TiN coatings were then deposited on the nitrided substrates using a closed-field unbalanced magnetron sputtering system. The microstructure, hardness and adhesion properties of the TiN-N-Ti6Al4V substrates were evaluated and compared with those of an untreated Ti6Al4V sample, a nitrided Ti6Al4V sample and a TiN-coated Ti6Al4V sample, respectively. The tribological properties of the various samples were investigated by means of reciprocating sliding wear tests performed in 0.9 wt.% NaCl solution against 316L, Si₃N₄ and Ti6Al4V balls, respectively. In addition, the corrosion resistance was evaluated using potentiodynamic polarization tests. Finally, the biocompatibility of the samples was investigated by observing the attachment and growth of purified mouse leukemic monocyte/macrophage cells (Raw 264.7) on the sample surface after culturing periods of 24, 72 and 120 h, respectively. Overall, the results showed that the duplex nitriding/TiN coating treatment significantly improved the tribological, anti-corrosion and biocompatibility properties of the original Ti6Al4V alloy.     

Effects of Traverse Scanning Speed of Spray Nozzle on the Microstructure and Mechanical Properties of Cold-Sprayed Ti6Al4V Coatings

Cold spray has the potential to restore damaged aerospace components made from titanium alloy, Ti6Al4V at low temperature (200-400 °C). Traverse scanning speed during deposition is one of the key factors that affect the quality of the Ti6Al4V coatings as it influences the thermal build-up and coating thickness per pass. As there are fewer reported studies on this, this work investigated the effects of different traverse scanning speeds (100, 300 and 500 mm/s) of cold spray nozzle on the microstructure and mechanical properties of cold-sprayed Ti6Al4V coatings. The cross-sectional analysis showed coating porosities reduces with slower traverse speed, from 3.2 to 0.5%. In addition, the microhardness of the coatings increased from about 361-385 HV due to strain hardening. However, the adhesion strength of the coatings to the substrates significantly decreased with reduced traverse speed from about 60 MPa (glue failure) at 500 mm/s to 2.5 MPa (interface failure) at 100 mm/s. Therefore, this study revealed that the control of heat build-up and thickness per pass during the cold spray deposition of the Ti6Al4V coatings is crucial to attain the desirable properties of the coatings.     

Serum effect on the electrochemical behaviour of titanium, Ti6Al4V and Ti6Al7Nb alloys in sulphuric acid and sodium hydroxide

The corrosion behaviour of cp titanium Ti6Al4V and Ti6Al7Nb alloys is investigated in 2 M sulphuric acid and 2 M sodium hydroxide with and without additions of bovine serum in order to get an insight into the effect of a biological electrolyte on the active corrosion of widely used metallic implants. Ti6Al7Nb alloy shows the highest corrosion resistance in 2 M sulphuric acid, whereas it is the least corrosion-resistant in 2 M sodium hydroxide. Bovine serum inhibits the hydrogen evolution as well as the anodic dissolution reactions in both sulphuric acid and sodium hydroxide. However, the cathodic efficiency of serum in sodium hydroxide is significantly higher than in sulphuric acid. Besides, the results suggest that serum forms a 2-D adsorption layer on the implant materials. Additionally, the surface coverage in sodium hydroxide is ca. 90%, while in acidic solutions only ca. 40%.     

钛合金表面离子束增强沉积的Cr和CrMo合金膜层及其性能

利用多功能离子束增强沉积(IBED)设备，在Ti6Al4V钛合金表面制备Cr和CrMo合金膜层，以提高钛合金表面的耐磨性能。利用X射线衍射仪、扫描电子显微镜、辉光放电光谱仪和显微硬度计分析和测试了IBED膜层的结构、形态、成分分布、硬度和膜基结合强度的大小。利用球一盘磨损试验机和电化学综合测试仪研究了IBED膜层的摩擦学性能和电化学腐蚀特性。结果表明，利用IBED方法可以在难镀材料钛合金表面制备膜基结合强度高、结晶致密和晶粒尺寸达纳米级的高硬度Cr膜和CrMo合金膜层，显著提高了钛合金表面的抗磨性能，且膜层本身有很好的耐Cl^-介质环境电化学腐蚀性能，与钛合金基体之间有很好的接触腐蚀相容性。     

厚度和层间界面对Ti6Al4V钛合金抗弹性能的影响

开展了Ti6Al4V钛合金的抗弹性能研究,通过对厚度为10～30 mm的均质Ti6Al4V钛合金靶板和总厚度为30 mm的(15+15)mm双层Ti6Al4V钛合金靶板的终点弹道侵彻实验,研究了厚度和层间界面对Ti6Al4V钛合金抗弹性能的影响规律。结果表明:Ti6Al4V钛合金的抗弹性能随着厚度的增加逐渐提高;在靶板厚度由15 mm增加到20 mm时,其抗弹性能出现了陡增,这与其损伤模式由脆性冲塞破坏转变为塑性扩孔破坏有关;层间界面不利于Ti6Al4V钛合金抗弹性能的提高,厚度为30mm的单层均质Ti6Al4V钛合金靶板的抗弹性能优于总厚度为30mm的(15+15)mm双层Ti6Al4V钛合金靶板,这与双层靶板的层间界面几乎无剪切强度有关。     

钛合金表面反应电火花沉积TiN/Ti复合涂层

利用自制的电火花沉积充气密闭式保护装置和DZ-1400型电火花沉积/堆焊机,以工业纯钛TA2为电极,以工业纯氮为保护气和反应气,在TC4钛合金表面上反应电火花沉积制备了TiN/Ti复合涂层.利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、X射线光电子仪(XPS)分析了涂层的组织、物相和元素组成,利用显微硬度计测定了涂层的显微硬度,利用自制磨损试验装置对比涂层与淬火W18Cr4V高速钢的磨损性能.结果表明,涂层与基体形成良好的冶金结合,涂层主要由钛和反应合成的TiN组成,涂层的平均显微硬度可达1 388 HV0.1,是基体硬度的6倍以上,涂层具有较好的耐磨性.

Abstract：

TiN/Ti composite coating was deposited on TC4 titanium alloy substrate with the self-made special gas-filled-closed electric-spark deposition device and electric-spark deposition machine modeled DZ-1400, the industry pure titanium (TA2) was used as electrode and the industry pure nitrogen gas as shielding and reacting atmosphere. The microstructures, interfacial behavior, phase and element in the coatings were investigated by scanning electronic microscope, X-ray diffraction and X-ray photo spectrum. The microhardness of coatings was tested and its wear-resistance property was tested by the self-made abrasion machine and compared with Wi8Cr4V rapid steel treated by quenching. The results show that an excellent bonding between the coating and substrate is ensured by the strong metallurgical interface. The coatings are mainly composed of Ti and synthesized TiN. The highest microhardness of coating reaches to 1 388 HV0. 1, which is six times higher than that of the substrates. Wear resistance of the coatings is excellent.