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。     

阳极电压对钛合金微弧氧化膜性能的影响

摘要：在不同阳极电压下对Ti-6Al-4V合金进行了微弧氧化处理。考察了阳极电压对氧化膜生长速率、表面形貌、相组成及硬度的影响，并对其摩擦学性能进行了表征。研究结果表明，随着阳极电压的升高，氧化膜表面微孔数量减少，表面微孔孔径、粗糙度、氧化膜生长速率均增大，表面硬度先增大后减小。微弧氧化膜主要由Al3TiO5相和金红石TiO2相组成，随着阳极电压的升高，两者相对比例逐渐增大。阳极电压对微弧氧化膜与钢球的摩擦系数影响不大，但对磨损率影响较大，磨损率随阳极电压的升高先减小后增大，氧化膜均具有较好的耐磨性。     

Application of a transmission line model to evaluate the influence of structural defects on the corrosion behavior of arc-PVD CrN coatings

The effect of bias voltages (40 V, 80 V, and 40/60/80 V) on microstructure and electrochemical properties of arc-PVD CrN coatings were evaluated. Increasing the bias voltage produced microstructural changes, from well-defined columns to columnar grains, and increased defect size. The electrochemical response proved susceptible to the defect type. Nano-droplets promoted the formation of oxides, while large pores allowed the migration of the electrolyte to the substrate/CrN interface. An impedance equivalent circuit based on the Bisquert transmission line was proposed to fit the experimentally obtained impedance spectra. The equivalent circuit allowed correlating the coating electrochemical response to the defect densities and sizes. Samples deposited with 40 V showed the lowest corrosion current (0.05 μA/cm² ± 0.01), which was supported by the highest resistances to the transport of ions through the pores (R_p = 1047 ± 88 kΩ?cm²). Films obtained with 80 V reduced R_p values by two magnitude orders compared to CrN 40 V. The increase of pore resistance in CrN 40 V was associated with the oxidation of nano-droplets (proposed auto-protection phenomenon), which blocks open pinholes due to the smallest average size of defects. Tailoring a gradual increase of the bias voltage (40/60/80 V) preserves the auto-protection mechanism of droplets and improves the surface finish of the coating.     

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。     

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.     

Development of hydroxyapatite coatings on laser textured 316 LSS and Ti-6Al-4V and its electrochemical behavior in SBF solution for orthopedic applications

The current work focused on the development of hydroxyapatite (HAP) coating on laser textured metallic implants using electrophoretic deposition. HAP was synthesized by sol-gel technique and its phase purity and surface morphology were confirmed by FT-IR, XRD and SEM analysis. 316 L SS and Ti-6Al-4V metal implants were polished and the surface was modified using Nd-YAG laser operating at a pulse interval of 10 ns at various overlapping rate of 0%, 25% and 50%. The laser treated surface was characterized for its surface roughness using surface profilometry and surface morphology. The surface roughness of the metallic implants was increased by increase in the overlapping rate. The prepared HAP powder was electrophoretically deposited on bare and laser textured Ti-6Al-4V and 316 L stainless steel followed by vacuum sintering at 300 °C for 2 h. Scratch analysis results showed an improvement in adhesion strength for the HAP coatings on laser treated specimens than untreated metal. Corrosion efficiency of the coated samples was studied in SBF solution using EIS and potentiodynamic polarization studies. The result from the corrosion experiments proved increased corrosion resistance property of laser textured coated samples when compared to bare alloy due to higher adhesion of HAP coating on the metal surface.     

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.     

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.     

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.     

Metal Alkoxide Primers in Titanium/Epoxy Bonding

Factors influencing the durability of Ti-6Al-4V/metal alkoxide/epoxy interphases were determined by studying the chemical composition of three metal alkoxides and evaluating the bond durability of Ti-6Al-4V/epoxy bonds primed with these materials. The three alkoxides were sec-butyl aluminum alkoxide, tetra-isopropyl titanate and tetra-n-butyl titanate.

Because adhesive bonds made using phosphate fluoride (P/F) pretreated Ti—6Al—4V substrates were not durable, P/F treated Ti—6Al—4V was chosen as the substrate for testing the possible durability enhancement by the titanium and aluminum alkoxide coatings. Sec-butyl aluminum alkoxide significantly enhanced the bond durability of the P/F pretreated bonds, while the titanium alkoxide primers showed no improvement in durability. The locus of failure and infrared studies indicated the enhancement in durability by the aluminum alkoxide was due to the high concentration of hydroxyl groups on the alkoxide surface available to interact with the epoxy adhesive.     

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.     

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.     

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.     

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.     

Nearly dense Ti–6Al–4V/TiB composites manufactured via hydrogen assisted BEPM

Titanium matrix composites reinforced with in situ formed titanium boride whiskers have long aroused significant interest for advanced applications in fields such as aerospace, biomedicine, and armaments. However, processing approaches dedicated to fabricating these composites have usually been limited by the cost-performance dilemma, thereby limiting commercial success. Blended elemental powder metallurgy (BEPM) has historically been the most economical route to produce titanium-based composites. At the same time, the need to reduce undue sinter porosities has imposed complicated and expensive extra thermomechanical steps in BEPM manufacturing. In the present study, nearly dense Ti–6Al–4V-based composites reinforced with in situ synthesized titanium monoborides (TiB) are prepared by simple press-and-sinter hydrogen-assisted BEPM without hot deformation or hot pressing using TiH₂, TiB₂, and master alloy (Al–V) powder blends as starting material. Vacuum sintering of compacted powder blends results in the formation of a dehydrogenated Ti–6Al–4V matrix with excessive porosity and unevenly distributed partially reacted TiB₂ particles. Such an inappropriate pre-sintered microstructure can be completely transformed into low-porosity uniform Ti–6Al–4V/TiB composites with tailored grains by using hydrogenation and milling of pre-sintered material into hydrogenated pre-alloyed powders and, finally, by using these powders in a second press-and-sinter processing step. The useful influence of hydrogen as a temporary alloying element on microstructure formation is discussed. The densification of hydrogenated powder compacts upon vacuum heating, and the hydrogen emission from the material is studied via dilatometric tests. The evolution of microstructure and phase composition during processing steps was investigated by scanning electron microscopy and x-ray diffraction. Compressive tests were used to evaluate the mechanical properties of materials produced after the first and second sintering. The results show that hydrogen-assisted BEPM can be a cost-effective route for in situ fabrication of Ti–6Al–4V/TiB composites with reliable mechanical properties.