Ti-6Al-4V钛合金脉冲阳极氧化工艺

研究了Ti-6Al-4V钛合金脉冲阳极氧化工艺,并对影响阳极氧化膜厚度的主要因素(如温度、电流密度、时间等)进行了研究,得到了满足膜厚要求的工艺参数。将优化得出的工艺参数应用于零件的仿形试件生产,得到厚度均匀的阳极氧化膜,并对其表面形貌、成分等进行了分析。     

The influence of chloride and sulphate ions on the corrosion behavior of Ti and Ti-6Al-4V alloy in oxalic acid

The electrochemical behavior of pure Ti and Ti-6Al-4V alloy was investigated in oxalic acid solution using various electrochemical techniques, i.e. open circuit potential (OCP), potentiodynamic polarization, electrochemical impedance measurements (EIS) and surface examination via scanning electron microscope (SEM) technique. The influence of concentration and temperature on the electrochemical behavior of TI and its alloy were also studied. The results of polarization measurements showed that corrosion current density (i_corr) increases with increasing either temperature or oxalic acid concentration for both samples. Moreover, the value of i_corr for Ti was found to be lower than that for Ti-6Al-4 V alloy, where the corrosion resistance for titanium was always higher. The effect of additives as SO₄²⁻ and Cl⁻ ions was studied; results indicated that the oxide film resistance (R_ox) value decreases with increasing the concentration of SO₄²⁻ ion. However, for Cl⁻ ion, the value of R_ox decreases with increasing Cl⁻ ion concentration up to 1 mM before it starts to increase at higher concentrations. EIS and polarization results are in good agreement with each other. The obtained results were confirmed by surface examination.     

Corrosion resistance of pulsed laser-treated Ti-6Al-4V implant in simulated biofluids

A commercial Ti-6Al-4V alloy was treated with a pulsed-wave Nd:YAG laser under various process conditions to obtain surface oxide layer for corrosion resistance. The corrosion behaviors of bare and laser-treated Ti-6Al-4V alloy exposed to three different simulated biofluids (SBFs), namely, (1) NaCl solution, (2) Hank's solution, and (3) Cigada solution, were studied by using the electrochemical techniques like open circuit potential (OCP), Tafel analysis, and electrochemical impedance spectroscopy (EIS). The Tafel analysis showed that the laser-treated Ti-6Al-4V specimens were more corrosion resistant than the bare specimens in any of the above SBFs. The various electrical equivalent circuit models were applied to fit the EIS results to further understand corrosion mechanisms due to different surface layers formed on the alloy surface before and after the laser treatment. Optical and AFM imaging techniques were used to evaluate the topographic and morphologic features of the alloy exposed to such SBFs. The corrosion behavior of the laser-treated surfaces was explained by the melting and solid-state oxidation processes, the morphology of the surface oxide, and the underlying alloy microstructure. It is realized during the present investigation that better corrosion resistance and surface stability can be achieved by oxide growth in solid-state, under a pulsed laser condition.     

Structural evaluation,preliminary in vitro stability and electrochemical behavior of apatite coatings on Ti6Al4V substrates

Medical-grade alloys, such as Ti-6Al-4V, have been used for fixation of fractured bone and for the total replacement of defective bone. Their bioactivity could be improved by applying a bone-like apatite layer onto their surfaces. This, in turn, enhances their integration with the surrounding tissues upon implantation. In addition, the presence of a bioactive bone-like coating minimizes the likelihood of corrosion. Various methods are known for the formation of apatite coating onto Ti-6Al-4V, among which sputtering has shown its promise as a simple direct method. In the current work, a sputtering technique was used to develop a 300 nm-thick bone-like apatite layer onto Ti-6Al-4V. Structural composition, integrity and morphology of the as-coated and thermally treated coatings were investigated. Coated substrates were further evaluated after soaking them in a simulated body fluid (SBF) for up to 14 days. Results showed the formation of an amorphous apatite layer onto the alloy, that was further shown to partially crystallize upon heat treatment. As a result of SBF treatment, the apatite layer was found to remodel through a dissolution-precipitation mechanism due to its amorphous and non-stoichiometric nature, forming a smooth layer with better homogeneity and decreased surface roughness. Electrochemical analysis of the coated alloys showed the enhanced corrosion protection of the alloy surfaces by coating them with apatite. In addition, pre-grinding of the alloy surfaces before the formation of the coating was also found to improve the corrosion inhibition of the alloy surfaces in aqueous media.     

Effect of transition layer on the performance of hydroxyapatite/titanium nitride coating developed on Ti-6Al-4V alloy by magnetron sputtering

A gradient transition multilayer hydroxyapatite/titanium nitride (HA/TiN) coating was prepared on the Ti-6Al-4V alloy by magnetron sputtering. The composition, surface topography, microstructure, adhesion strength and electrochemical properties of the as-deposited coatings were characterized by SEM/EDS, AFM, XRD, FT-IR and electrochemical workstation. The experimental results showed that the single TiN coating deposited at a partial pressure of nitrogen (N₂) of 0.08?Pa had the best internal stress and tribological performance, and its volume loss was only 0.89% of that of Ti-6Al-4V alloy. The introduction of the TiN transition layer greatly improved the wear resistance of the Ti-6Al-4V alloy, and the adhesion strength of the HA layer to the substrate increased from 6.50?±?0.5?N to 11.70?±?1.2?N, an increase of 56%. The HA/TiN coating surface consisted of uniform hemispherical particles with dense structure and invisible defects (micro-cracks and pores). For the HA surface layer, the crystal structure and active hydroxyl (-OH) group was restored after heat treatment. Potentiodynamic polarization experiments indicated that the HA/TiN coating achieved the lowest corrosion current density and the most positive corrosion potential compared to the single TiN layer and Ti-6Al-4V alloy. In summary, it can be conclude that the gradient transition layer can well improve the mechanical properties and electrochemical behavior of the titanium alloy, and largely ensuring the stability of the surface bioactive coating.     

Adhesion Tensile Testing of Environmentally Exposed Ti-6Al-4V Adherends

The structural and bonding properties of Ti-6Al-4V adherends, prepared by chromic acid anodization (CAA), were studied as a function of exposure in high-temperature environments such as vacuum, air, boiling and pressurized water, and steam. Subsequent to the environmental exposure, bonds were produced and the adhesive tensile strengths measured. Long-term exposure to high temperature, dry environments did not cause structural changes to the adherend oxide but did result in poor bond strength. The failure mode in these cases was within the oxide, which was apparently weakened by the exposure. The water-and steam-exposed oxides underwent a transition from amorphous to crystalline TiO₂ (with an accompanying change in oxide morphology); however, bond strength was maintained for moderate exposures at T ≤ 250°C. For exposure at T = 300°C, the bond strength was degraded severely. The latter result can be explained by a lack of porosity in the transformed oxide. SEM and XPS measurements were made on debonded surfaces to determine the loci of failure.     

Factors Affecting the Durability of Ti-6Al-4V/Epoxy Bonds

Factors influencing the durability of Ti-6Al-4V/epoxy interphases were studied by determining chemical and physical properties of Ti-6Al-4V adherend surfaces and by characterizing the strength and durability of Ti-6Al-4V/epoxy bonds.

Ti-6Al-4V adherend surfaces were oxidized either by chemical etch or anodization. Four principal pretreatments were studied: chromic acid anodization (CAA), sodium hydroxide anodization (SHA), phosphate fluoride acid etch (P/F) and TURCO basic etch (TURCO). The oxides were characterized by SEM, STEM, profilometry, contact angles and XPS.

All adhesive bonding was carried out using a structural epoxy, FM-300U. Both lap shear and wedge test samples were tested in hot, wet environments. The results lead to the conclusion that the interfacial area between the adhesive and adherend is the primary factor affecting bond durability.     

TiB2涂层刀具制备及干铣削Ti-6Al-4V磨损行为研究?

由于切削过程中产生高温、刀具粘结与氧化严重,钛合金切削尤其是干切削,一直是刀具行业的重大挑战之一,而在刀具表面添加涂层是提高钛合金切削刀具寿命的有效途径。利用脉冲磁控溅射技术制备了TiB2涂层刀具,以相同基体的无涂层刀具为对照,干铣削Ti-6Al-4V钛合金,切削速度从30~100 m/min变化,研究TiB2涂层刀具的切削性能与失效机理。所制备的TiB2涂层具有(100)择优取向的六方晶体结构,组织致密。涂层硬度可高达4000 HV。切削实验发现,在30 m/min的低速时,TiB2涂层刀具的切削寿命超过无涂层刀具57%之多,当切削速度加倍到60 m/min时,刀具寿命未见下降。当切削速度增加到100 m/min时,TiB2涂层刀具与无涂层刀具切削寿命相当。TiB2涂层刀具表面氧化所产生的B2O3液化膜,起自润滑作用,可充分减少钛合金的粘结,降低摩擦力。因此,在TiB2或B2O3消失之前,TiB2涂层刀具均有良好表现。在100 m/min时,切削高温造成B2O3强烈挥发,且TiB2被氧化为多孔疏松的TiO2,刀具寿命急剧下降到无涂层刀具的水平。     

Microstructure evolution and bonding mechanism of ZrO2 ceramic and Ti-6Al-4V alloy joints brazed by Bi2O3-B2O3-ZnO glass paste

Ceramics and metal joinings have been widely employed in aerospace, dental implants, and the electronic packaging industry for fabricating multifunctional components. In this study, the 35Bi₂O₃-50B₂O₃-15ZnO (mol.%) glass has been employed for joining the ZrO₂ ceramic and Ti-6Al-4V alloy. The effect of brazing temperature on the microstructure evolution, mechanical properties, and bonding mechanism of brazed joints has been analyzed. The microstructure of the ZrO₂/glass/Ti-6Al-4V joints and the content of Bi₄B₂O₉, Bi₂O₃ and Bi₂₄B₂O₃₉ precipitated crystals in glass were found to be dependent on the brazing temperature. The reaction product of Bi₄Ti₃O₁₂ was identified in the glass/Ti-6Al-4V interface because of the chemical reaction between the oxidized layer of Ti-6Al-4V alloy and glass. A maximum shear strength as high as 48.8 ± 5.2 MPa was obtained. Our work, thus, demonstrates that the 35Bi₂O₃-50B₂O₃-15ZnO glass is an effective bonding material for joining ZrO₂ ceramic and Ti-6Al-4V alloy under low temperature in an ambient atmosphere.     

The Durability of Adhesively-bonded Ti-6Al-4V

The durability of chromic acid-anodized Ti-6Al-4V alloy, adhesively-bonded with FM-5 supported polyimide adhesive has been studied. The performance tests compared titanium samples that had been thermally treated and bonded, and samples that were bonded and thermally treated. Following the thermal treatment, the durability was examined (1) by immersing wedge-type specimens in boiling water and measuring the crack growth and (2) by measuring the lap shear strength for single lap specimens. In the wedge tests, failure occurs within the adhesive for specimens treated at temperatures below 371°C for less than one hour. For treatments at higher temperatures and for longer periods of time, failure occurs within the anodic oxide. From the lap shear tests, the principal finding is that the lap strength decreases with increasing treatment time at constant temperature and with increasing temperature at a fixed time. For the lap specimens, failure occurs to a greater extent within the oxide as the treatment time and temperature increase. Surface analysis results indicate the formation of an aluminum fluoride species. It is reasoned that the formation of fluorine-containing materials weakens the oxide and promotes failure within the anodic oxide.     

Heat-resistant thermoplastic/ chromic acid anodized Ti-6Al-4V single lap bond evaluation

Structural, heat-resistant thermoplastic adhesives were evaluated in single lap bonds. The amorphous thermoplastics tested were polyphenylquinoxaline, glass filled Ultem polyetherimide, unfilled Ultem polyetherimide, and Victerex polyethersulfone. The adherend was chromic acid anodized Ti-6Al-4V, tested unprimed and primed with Lica 44 titanate. Initial bond strengths were similar for all adhesives. In general, Lica 44 titanate primer did not affect bond strength. Bond strength was not influenced by 170°C ageing, but 232°C ageing did decrease bond strength when polyphenylquinoxaline was the adhesive. Failure occurred primarily in the adhesive fillet and propagated into the unprimed or primed anodic oxide/polymer interphase.     

The Durability of Adhesively-bonded Ti-6Al-4V

The durability of chromic acid-anodized Ti-6Al-4V alloy, adhesively-bonded with FM-5 supported polyimide adhesive has been studied. The performance tests compared titanium samples that had been thermally treated and bonded, and samples that were bonded and thermally treated. Following the thermal treatment, the durability was examined (1) by immersing wedge-type specimens in boiling water and measuring the crack growth and (2) by measuring the lap shear strength for single lap specimens. In the wedge tests, failure occurs within the adhesive for specimens treated at temperatures below 371°C for less than one hour. For treatments at higher temperatures and for longer periods of time, failure occurs within the anodic oxide. From the lap shear tests, the principal finding is that the lap strength decreases with increasing treatment time at constant temperature and with increasing temperature at a fixed time. For the lap specimens, failure occurs to a greater extent within the oxide as the treatment time and temperature increase. Surface analysis results indicate the formation of an aluminum fluoride species. It is reasoned that the formation of fluorine-containing materials weakens the oxide and promotes failure within the anodic oxide.     

Enhancement of the Ti-6Al-4V alloy corrosion resistance by applying CrN/CrAlN multilayer coating via Arc-PVD method

In this study, the Ti-6Al-4V substrate was coated by CrN-CrN/TiN-TiN and CrN/CrAlN multilayer coatings using the cathodic arc physical vapor deposition (Arc-PVD) method. The results of potentiodynamic polarization (PDP) have shown the lowest and highest corrosion current density belong to the double-layer (0.16 µA/Cm²) and TiN (0.51 µA/Cm²) samples, indicating the higher corrosion resistance of the double-layer coating. The field emission electron microscope (FESEM), X-ray diffraction pattern (XRD), open circuit potential (OCP), PDP, and electrochemical impedance spectroscopy (EIS) analysis were employed in order to characterize the coatings and evaluate their corrosion behavior. Finally, applying the double-layer coating resulted in the significant improvement of the protective behavior of the Ti-6Al-4V alloy, as compared to the sample coated with TiN in corrosive environments.     

Microstructures and mechanical properties of wear-resistant titanium oxide coatings deposited on Ti-6Al-4V alloy using laser cladding

In this work, a freeze-dried TiO₂ nano-sized powder was used as the coating material and single tracks of TiO_x coating were cladded on Ti-6Al-4V substrates using a diode laser. The microstructure, chemical composition, and mechanical properties of the coatings were characterized and their relationships were explored. Coatings with structural and compositional gradients formed under a laser energy density (LED) of 20 kJ/m, while coatings with a relatively homogeneous microstructure were obtained using a LED of 30 kJ/m. The microstructure evolution was controlled by the molten pool lifetime and the intensity of convective flow during laser processing. The elastic modulus of the graded coating showed a decreasing trend from the top coating surface to the interface while that of the homogeneous coating remained constant. Our results also demonstrated that the hardness and wear resistance of the oxide coatings were up to four and ten times higher than that of the substrate.     

Calcium phosphates of biological importance based coatings deposited on Ti-15Mo alloy modified by laser beam irradiation for dental and orthopedic applications

Ti-15Mo alloy samples were irradiated by pulsed Yb:YAG pulsed laser beam under air and atmospheric pressure. Sequentially, calcium phosphate coatings were deposited on the irradiated surfaces by the biomimetic method. The formation of calcium phosphates (CaP) under biological medium and SBF (Synthetic/Simulated Body Fluid) occurs in the presence of Ca²⁺ and PO₄^3- ions, as well as ions such as: Mg^2+, HCO₃^-, K⁺ and Na⁺, which facilitates the mimicking of the biological process. The biomimetic calcium phosphates-based surfaces were submitted to heat treatment conditions at 350?°C and 600?°C. The present study correlates four conditions of fluency (1.91, 3.17, 4.16 and 5.54?J/cm², respectively) as established have a sufficient energy to promote ablation on the laser beam irradiated surfaces. Likewise, it has been demonstrated the processes of fusion and fast solidification from the laser beam irradiation, under ambient atmosphere, inducing the formation of stoichiometric (TiO₂₎ and non-stoichiometric titanium oxides (TiO, Ti₃O, Ti₃O₅ and Ti₆O) with different oxide percentages depending on the fluency applied. Besides that, laser modification has allowed a clean and reproducible process, providing no traces of contamination, an important feature for clinical applications. The morphological and physico-chemical analysis indicated the formation of a multiphase coatings depending on the heat treatment temperature performed to 350?°C (ACP1–2, CDHA, HA phases) and 600?°C (CDHA, HA and β-TCP phases). It is worth noting multiphasic bioceramic systems has been gaining attention for biomedical applications. The laser beam irradiation associated to bioactive coatings of calcium phosphates of biological interest have shown to be promising and economically feasible for use in clinical applications.     

Sodium Hydroxide Anodization of Ti-6AI-4V Adherends

The durability of adhesively bonded titanium structures is a topic of concern in a variety of fields today. There appears to be a definite connection between durability and surface pretreatment of the adherend. A variety of pretreatments are reported for Ti-6-4^1-3. For example, the chromic acid anodization (CAA) pretreatment has received a lot of attention in creating surfaces resulting in improved durability of adhesive bonds.     

The Influence of Ti-6AI-4V Chromic Acid Anodization Conditions Upon Anodic Oxide Thickness and Topography

Chromic acid (CA) anodization of Ti-6A1-4V (6% Al, 4% V by weight) produced an anodic oxide on the alloy surface. The influence of specific CA anodization conditions upon anodic oxide thickness was determined. Each CA anodization condition tested was defined by setting five variables: (1) solution composition; (2) anodization time; (3) solution temperature; (4) initial current density; and, (5) anodization potential.

The results confirmed observations by previous workers about oxide thickness and structure. Data indicated an inverse relationship between film thickness and temperature, and that film growth rate decreases with time.     

Corrosion behaviour of Ti-6Al-7Nb and Ti-6Al-4V ELI alloys in the simulated body fluid solution by electrochemical impedance spectroscopy

The corrosion behaviour of Ti-6Al-7Nb and Ti-6Al-4V ELI (extra low interstitial) was investigated as a function of immersion hours in simulated body fluid (SBF) condition, utilizing potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. Polarisation experiments were conducted after 0, 120, 240 and 360 h of immersion in SBF solution. From the polarisation curves, very low current densities were obtained for Ti-6Al-7Nb alloy compared to Ti-6Al-4V ELI, indicating a formation of stable passive layer. Impedance spectra were represented in the form of Bode plots and it was fitted using a non-linear least square (NLLS) fitting procedure, in which it exhibited a two time constant system suggesting the formation of two layers. The surface morphology of the titanium alloys have been characterized by SEM and EDAX measurements.     

Scratch resistance and electrochemical corrosion behavior of hydroxyapatite coatings on Ti6Al4V in simulated physiological media

Using an electrochemical process, needle-like hydroxyapatite crystals with Ca/P ratio of 1.67 were synthesized on Ti₆Al₄V without the formation of any precursor. In vitro dissolution/precipitation process was investigated by immersion of the coated substrate into Hank??s solution up to 14?days. Physical and chemical characterizations were performed by scanning electron microscope coupled with energy dispersive X-ray spectroscopy and by X-ray diffraction. In particular, through a sequence of reactions including dissolution, precipitation, and ions exchange during immersion tests, a precipitated bone-like apatite coating homogenous and less porous was formed. Further, the corrosion behavior of the untreated and HA-coated specimens in simulated body fluid was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that the corrosion rates of the samples with HA layer before and after immersion tests were 72 and 80?% lower than that of the bare titanium alloy. At last, the adhesion of the HA layer was determined through the use of scratch tests. A particular tribological behavior and a strong link to the substrate were revealed.     

Influence of a hard transition layer on the microstructure and properties of diamond-like carbon/hydroxyapatite composite coating prepared by magnetron sputtering

The nanostructured diamond-like carbon/hydroxyapatite composite coating (DLC/HA) was deposited using magnetron sputtering technique with a densely packed columnar cross-sectional structure and a uniform granular surface morphology. After heat treatment, the amorphous structure of the coating was transformed into a crystal structure. Nanohardness and scratch tests results demonstrated the DLC transition layer significantly enhanced the nanohardness of Ti6Al4V substrates from 4.8 GPa to 10.4 GPa, and increased critical load from 16.6 N (pure HA layer) to 26.5 N (DLC layer) without obvious brittle fracture, flaking and delamination. Electrochemical and immersion tests results demonstrated that DLC/HA composite coatings with a dense gradient transition interlayer had better corrosion resistance and could prevent harmful metal ions being released into the SBF solution more effectively than single HA coatings. Furthermore, active Ca²⁺ ions can be rapidly released from the coating surface during initial immersion in the SBF solution, and facilitated the formation of bone-like apatite.