Untreated Ti6Al4V Research Articles

Thermal analyses and weight gain modeling study on Ti–Al – based intermetallic coated Ti6Al4V alloy

Abstract Ti6Al4V alloy is a commonly used α + β alloy among titanium alloys. In this study, in order to improve the oxidation resistance of the Ti6Al4V alloy, Ti–Al – based aluminum coating was deposited to the surface by the pack cementation method. The aluminizing process was carried out in an open atmosphere oven at 700 °C for 4 and 6 h. It has been observed that the coating layer thickness varies between 13 and 17 µm depending on the duration of cementation process. From XRD analysis, it has been detected the TiAl3, TiAl2, and TiAl phases on the coating layer. Aluminum coated and untreated Ti6Al4V alloys were subjected to oxidation tests at 800, 850, and 900 °C for 4, 20, and 40 h. The obtained nonlinear weight gain characteristic has been modeled to determine the coating status of the samples. It was determined that the highest weight gain was in the untreated sample. Using the provided model, samples were classified in terms of coating condition by systematic approach based on weight gain profile versus time. Oxidation tests also supported with DTA and TG analyses.

Mechanically tailored surface of titanium based alloy (Ti6Al4V) by laser surface treatment

In this study, laser surface treatment (LST) of Ti6Al4V carried out by melting within a narrow regime of optimum process parameters for the formation of a surface with improved wear and tribo-corrosion resistance is presented. The effect of applied power and shrouding gas on the microstructure, phase, surface hardness, residual stress, dry wear (against tungsten carbide, WC) and tribocorrosion resistance (against ZrO2 in Hank's solution) is established. LST in argon atmosphere leads to the formation of a composite structure consisting of acicular α’ martensite and α. LST in nitrogen atmosphere causes the formation of titanium nitride (TiN and Ti2N) dispersed in α matrix. Due to LST, there is an increase in surface microhardness both under argon (435–630 VHN) and nitrogen atmosphere (839–1327 VHN) when compared to untreated Ti6Al4V (278 VHN). There is a marginal decrease in wear rate (against WC ball) due to laser surface melting (5.17–5.81 × 10−3 mm3/Nm) under argon and a substantial decrease in wear rate when melting was conducted under nitrogen atmosphere (1.91–4.94 × 10−3 mm3/Nm) as compared to Ti6Al4V (5.93 × 10−3 mm3/Nm). The mechanism of wear is established. On the other hand, the tribo-corrosion rate is found to decrease for laser surface melting (3.5–4.8 × 10−3 mm3/Nm) and nitriding (1.3–3.2 × 10−3 mm3/Nm) as compared to Ti6Al4V (5.7 × 10−3 mm3/Nm). Bioactivity in terms of calcium phosphate deposition followed by dipping in Hank's solution was found to increase due to both melting and nitriding, though nitriding offered a marginally higher bioactivity than only melting.

In vitro long-term antibacterial performance and mechanism of Zn-doped micro-arc oxidation coatings

Micro-arc oxidation (MAO) coatings containing 2.86 wt%, 5.83 wt% and 8.81 wt% Zn (Zn-2.86 wt%, Zn-5.83 wt% and Zn-8.81 wt%) were separately fabricated on Ti6Al4V alloys using EDTA-ZnNa2 electrolytes. In vitro antibacterial examination exhibits that the antibacterial rates of Zn-2.86 wt%, Zn-5.83 wt% and Zn-8.81 wt% against Staphylococcus aureus (S. aureus) are 76.0 %, 100.0 % and 99.2 %, respectively. Reactive oxygen species (ROS) level of MAO samples is significantly higher than that of the untreated Ti6Al4V. Zn-containing coatings especially Zn-5.83 wt% induces the strongest oxidative stress on S. aureus due to relatively high released Zn2+ concentration. Moreover, qPCR analysis shows that MAO samples inhibit the icaADBC transcription and result in the down-regulation of PIA production, thereby mitigating biofilm formation. After immersion in simulated body fluid (SBF) for 3, 8 and 14 d, the antibacterial rate of Zn-5.83 wt% is 84.7 %, 63.2 % and 12.5 % respectively, and ROS level of MAO samples is also significantly higher than that of the untreated Ti6Al4V even after 14 d of immersion, suggesting that the antibacterial performance of MAO samples can last a relatively long immersion period and exhibit large application potential in orthopedic clinic.

The synergetic effect of micro-blasting and thermal oxidation on the corrosion performance of Ti6Al4V

Ti6Al4V alloy is widely used for orthopaedic applications due to its excellent osteointegration, good biocompatibility, great strength-to-weight ratio, and comparable elasticity with bone. However, when this alloy is exposed for long-term in the body fluid, it releases the corrosion products of metals and metal oxides. The released particles react with the surrounding tissue and cause an adverse local tissue reaction (ALTR) which leads to pseudotumor formation, and osteolysis (bone degradation). Thus, corrosion is a critical parameter for bio-implants and in this study to minimize corrosion, thermal oxidation was performed on micro-blasted Ti6Al4V surfaces for 24 and 48 h. Surface morphology, phase analysis, surface roughness, and wettability of all types of samples were evaluated using FESEM, EDS, XRD, AFM, and Goniometer. The electrochemical performance was studied in 0.9 wt% NaCl. The combined mechanical and thermal process increases surface roughness and improves the hydrophilic nature of the Ti6Al4V surface by 67 %. The formation of metastable Ti2O3 during micro-blasting and further transformation of anatase and rutile TiO2 during thermal oxidation increases the intensity of anatase and rutile TiO2 formed on the surface and enhances corrosion resistance. Overall, micro-blasting with 48 h thermal oxidation showed 2 times higher corrosion resistance and reduced corrosion rate by almost 50 % as compared with the untreated Ti6Al4V.

Effect of potassium fluoride on the structure and corrosion properties of anodic coatings on Ti6Al4V alloy

In this study, KF film was obtained by anodization method on Ti6Al4V material, which ispreferred to be used in many areas such as the defense industry, biomedical field and aviation sector. Theaim of this study is to compare the corrosion resistance of untreated Ti6Al4V, TiO2 coated Ti6Al4V andKF (potassium fluoride) coated Ti6Al4V samples. XRD and SEM were used for the structuralcharacterization of the samples. Corrosion experiments were performed in simulated body fluid (SBF).According to the results, the highest corrosion resistance was obtained in the new morphological structureobtained by KF coating of the volcano-type structures.

Effect of Functional Nanoporous TiO2 Film Obtained on Ti6Al4V Implant Alloy to Improve Resistance in Biological Solution for Inflammatory Conditions.

The metallic titanium-based biomaterials are sensitive to corrosion-induced degradation in biological fluids in the presence of inflammatory conditions containing reactive oxygen species (ROS). Excess ROS induces oxidative modification of cellular macromolecules, inhibits protein function, and promotes cell death. In addition, ROS could promote implant degradation by accelerating the corrosive attack of biological fluids. The functional nanoporous titanium oxide film is obtained on titanium alloy to study the effect on implant reactivity in biological fluid with reactive oxygen species such as hydrogen peroxide, which are present in inflammations. The TiO2 nanoporous film is obtained by electrochemical oxidation at high potential. The untreated Ti6Al4V implant alloy and nanoporous titanium oxide film are comparatively evaluated for corrosion resistance in biological solution by Hank's and Hank's doped with hydrogen peroxide by electrochemical methods. The results showed that the presence of the anodic layer significantly improved the resistance of the titanium alloy to corrosion-induced degradation in biological solutions under inflammatory conditions.

High temperature oxidation behavior of thermal and plasma processed aluminide coated Ti6Al4V alloys

In this study, the high temperature cyclic oxidation behavior of thermal and plasma-treated aluminide coated Ti6Al4V alloy was investigated at 800 °C up to 360 h in 24 h cyclic exposures. The microstructural characteristics, phase analysis, morphological features, and microhardness of resultant oxidized samples were evaluated and compared with those of untreated Ti6Al4V alloy. The weight gain studies conducted from the cyclic oxidation tests revealed very minimal weight gain in plasma treated (PT) aluminide coated samples as compared to the thermal treated (TT) and uncoated (UC) samples. XRD results indicate that the UC samples oxidized at 800 °C exhibits the formation of a thick oxide layer consisting of only the rutile phase (TiO2). The TT and PT samples oxidized at 800 °C revealed presence of both alumina (Al2O3) and rutile (TiO2) phases. However, PT samples revealed stable α-Al2O3 phase whereas the TT samples showed metastable θ-Al2O3 phases in the oxide layer. The surface morphological features reveal that the oxide film formed on the surface of the PT samples had enough stability at 800 °C irrespective of the oxidation time. The PT samples exhibited higher hardness and improved oxidation resistance as compared to TT and UC samples. Increase in thermal stability, mechanical and oxidation properties of PT samples could be attributed to the formation of stable alumina (α-Al2O3) and presence of nanocrystalline aluminide phases (TiAl3 & TiAl2) in the diffusion layers during the oxidation tests. Therefore, a strong emphasis was placed on correlating the interfacial processes to the high temperature oxidation behavior.

Novel Catalytic Ceramic Conversion Treatment of Ti6Al4V for Improved Tribological and Antibacterial Properties for Biomedical Applications.

Titanium oxide layers were produced via a novel catalytic ceramic conversion treatment (CCCT, C3T) on Ti-6Al-4V. This CCCT process is carried out by applying thin catalytic films of silver and palladium onto the substrate before an already established traditional ceramic conversion treatment (CCT, C2T) is carried out. The layers were characterised using scanning electron microscopy, X-ray diffraction, transmission electron microscopy; surface micro-hardness and reciprocating tribological performance was assessed; antibacterial performance was also assessed with S. aureus. This CCCT has been shown to increase the oxide thickness from ~5 to ~100 µm, with the production of an aluminium rich layer and agglomerates of silver and palladium oxide surrounded by vanadium oxide at the surface. The wear factor was significantly reduced from ~393 to ~5 m3/N·m, and a significant reduction in the number of colony-forming units per ml of Staphylococcus aureus on the CCCT surfaces was observed. The potential of the novel C3T treatment has been demonstrated by comparing the performance of C3T treated and untreated Ti6Al4V fixation pins through inserting into simulated bone materials.

Enhancement of the tribological performance and surface wettability of Ti6Al4V biomedical alloy with boric/sulfuric acid anodic film

Titanium and its alloys have many advantages such as acceptable biocompatibility and good corrosion resistance and these advantages make them a widely preferred biomaterial. However, it is also known that they have some disadvantages such as poor wear resistance and insufficient surface wettability. Therefore, to overcome this disadvantages, boric/sulfuric anodic films with different anodization time was formed on the surface of Ti6Al4V. The morphological and structural properties of anodic films were evaluated by XRD, XPS, SEM, Raman spectra, micro-hardness tester, 3D profilometer, and surface tension-meter. Also, the tribological behavior of them was analyzed by a pin-on-disk tribo-tester. The average coefficient of friction (CoF) of the untreated Ti6Al4V alloy is 0.37, while the CoF of boron containing TiO2 anodic films is in the range of 0.04–0.15. Also, the anodic films reduced the wear rate by about 30% compared to the untreated Ti6Al4V. In addition to all these, it was observed that the anodic films changed the surface morphology. It was determined that the produced anodic films were in porous structures and with the increase of the applied anodizing time, the possibility of contacting the liquid with the surface increased.

A Sheep Model for the Osseointegration of PEO-treated Gamma Titanium Aluminide

A sheep model was used to study the osseointegration of gamma titanium aluminide (γTiAl) screws subjected to plasma electrolytic oxidation (PEO). The degree of osseointegration was determined by measuring the maximum torque for screw removal from bone after 3 and 6 months of implant placement in sheep for PEO-treated γTiAl, untreated γTiAl, and untreated Ti6Al4V cortical screws. The amount of bone growth and mineralization were qualitatively observed by von Kossa staining of the bone tissue in the region surrounding the implants. Inductive Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) was carried out to determine trace amounts of metallic elements in blood serum samples obtained from the animals. Generally Al, Cr and V were present in blood serum in comparable quantities in the control and implanted animals, while neither Ti nor Nb was detected. Results from histological analysis and SEM images indicated that de novo bone growth occurred to a greater extent for the PEO treated γTiAl screws. Furthermore, the torque for screw removal from bone was significantly higher (p<0.05) for the PEO-treated γTiAl implants. Taken together, the data supports that the PEO surface treatment enhanced osseointegration to a considerable degree indicating the potential for favorably utilizing PEO-treated γTiAl for dental and orthopedic implant applications.

Enhanced corrosion and tribocorrosion behavior of Ti6Al4V alloy by auto–sealed micro-arc oxidation layers

Surface modification of titanium alloys are being considered to justify their use as articulating surfaces. This study examined the corrosion and tribocorrosion behavior of Ti6Al4V specimens whose surfaces were modified using micro-arc oxidation (MAO) at −3 o C and + 20 °C. After MAO, the porous oxide layers containing Ca and P that are incorporated from the electrolyte, were fabricated on the surface. Many of the pores were sealed by the deposition of erupted materials on the surface of −3 °C MAO layers, resulted in a reduced surface fraction of open-porosities. Corrosion studies revealed nearly 80 mV positive shifting of corrosion potential and more than 50% decrease in the passive current density of auto-sealed layers. In contrast to the sudden potential drop of the untreated Ti6Al4V alloy, the MAO layers showed no significant decrease during the tribocorrosion. The presence of a relatively smooth surface with some parallel scratches were the main characteristics of mild abrasive wear as the dominant wear mechanism of the −3 °C MAO layers.

Manipulation tribological behavior of Ti6Al4V alloy via a duplex treatment of double glow plasma surface molybdenizing-laser surface texturing (LST)

In this work, Ti6Al4V alloy was treated by a duplex treatment of double glow plasma surface molybdenizing-laser surface texturing (LST) aiming to realize surface strengthening and manipulate its tribological behavior. The double glow plasma surface alloying (DGPSA) with molybdenum (Mo) was firstly conducted on the Ti6Al4V alloy and followed by LST to prepare round dimple-shape texture with a density of 5%, 7%, 11%. The results showed that Mo and Mo/Ti solid solution phases were detected in the Mo-layer by X-ray diffraction (XRD), the received Mo-layer with a thickness of about 13μm was uniform and compact. Double glow plasma surface molybdenizing significantly improved the surface hardness and elastic modulus of Ti6Al4V alloy by nanoindentation test. The gradient distributed Mo-layer was tightly adhered to the Ti6Al4V alloy matrix through scratching and indentation tests. Duplex treated Ti6Al4V alloy with a 5% texture density suggested better wear resistance in comparison to the untreated Ti6Al4V alloy, which was confirmed by a 48.7% lower specific wear rate than that of Ti6Al4V alloy. Taking advantages of DGPSA and LST, duplex treatment of double glow plasma surface molybdenizing-laser surface texturing was established to create on the working surface of Ti6Al4V alloy with promisingly improved tribological behavior.

Nanosecond Laser Surface Patterning of Ti6Al4V Bio-alloy for Improved Biological Performance

Biological performances such as osseointegration and biocompatibility of Ti6Al4V alloy primarily depends on topological and chemical properties of the surface of the bio-material. Here, a nanosecond pulsed Nd:YAG laser has been used to generate microstructures on Ti6Al4V surface by irradiating with 6000 number of laser shots per site. Formation of ripple structure and generation of sub-oxide phases on laser treated titanium surface supported uniform and dense growth of HAP on the sample. In contrast, discrete nucleation of HAP with comparable higher precipitation of calcium occurred on untreated Ti6Al4V sample when subjected to similar in vitro tests by exposing the sample to simulated body fluid. Initial interaction and growth of U2OS cells on untreated and laser treated Ti6Al4V substrates were quantified using MTT assay. More numbers of cell were attached to laser treated sample in comparison to untreated sample as observed in confocal microscope images. Our results suggested that surface patterning of Ti6Al4V alloy using nanosecond pulsed laser promoted bio-integration without compromising its biocompatibility. Copyright © VBRI Press.

Performance analysis of grafted poly (2-methacryloyloxyethyl phosphorylcholine) on additively manufactured titanium substrate for hip implant applications

The incidence of total hip arthroplasty (THA) has been evidently growing over the last few decades. Surface modification, such as polymer grafting onto implant surfaces using poly (2-methacryloyloxyethyl phosphorylcholine) (PMPC), has been gaining attention due to its excellent biocompatibility and high lubricity behaviour resulting in reducing surgical recurrence number and increasing implant lifetime. Investigating thermal stability and mechanical properties of the grafted polymer is, therefore, extremely important as these properties define the failure mechanism of implants. This study focuses on optimising monomer concentration to achieve the best physical, thermal and mechanical properties of the grafted additively manufactured titanium (Ti6Al4V) implants. Three different concentration of monomers, 0.4 M, 0.6 M and 0.8 M, were investigated, and grafted implants were characterised. The results from thermal analysis confirmed that the PMPC polymer is thermally stable for implant applications regardless of the monomer concentrations. A significant reduction in Young’s modulus of polymer grafted samples (33.2–42.9%), in comparison with untreated Ti6Al4V samples and consequent improvement of wear resistance and elasticity behaviour, proved the potentiality of polymer films for implant applications. In summary, polymer grafted implant prepared with 0.6 M monomer concentration showed the optimal thermal, physical and wear resistance properties.

Significant Suppression of Staphylococcus aureus Colonization on Intramedullary Ti6Al4V Implants Surface-Grafted with Vancomycin-Bearing Polymer Brushes.

Orthopedic implant-associated bacterial infection presents a major health threat due to tendency for periprosthetic bacterial colonization/biofilm formation that protects bacteria from host immune response and conventional antibiotic treatment. Using surface-initiated atom transfer radical polymerization and copper-catalyzed azide-alkyne cycloaddition (CuAAC), alkynylated vancomycin is conjugated to azido-functionalized side chains of polymethacrylates grafted from Ti6Al4V. High-efficiency CuAAC across the substrate is confirmed by complete surface conversion of azides by X-ray photoelectron spectroscopy (XPS) and elemental mapping of changing characteristic elements. The vancomycin-modified surface (Ti-pVAN) significantly reduces in vitro adhesion and colonization of Staphylococcus aureus (S. aureus), a main bacterial pathogen responsible for periprosthetic infection and osteomyelitis, compared to untreated Ti6Al4V, supporting retained antibacterial properties of the covalently conjugated antibiotics. When the surface-modified intramedullary Ti-pVAN pins are inserted into mouse femoral canals infected by bioluminescent Xen29 S. aureus, significantly reduced local bioluminescence along with mitigated blood markers for infection are detected compared to untreated Ti6Al4V pins over 21 days. Ti-pVAN pins retrieved after 21 days are confirmed with ∼20-fold reduction in adherent bacteria counts compared to untreated control, supporting the ability of surface-conjugated vancomycin in inhibiting periprosthetic S. aureus adhesion and colonization.

Mechanical testing of antimicrobial biocomposite coating on metallic medical implants as drug delivery system.

Post-operative infection often occurs following orthopedic and dental implant placement requiring systemically administered antibiotics. However, this does not provide long-term protection. Over the last few decades, alternative methods involving slow drug delivery systems based on biodegradable poly-lactic acid and antibiotic loaded hydroxyapatite microspheres were developed to prevent post-operative infection. In this study, thermally anodised and untreated Ti6Al4V discs were coated with Poly-Lactic Acid (PLA) containing Gentamicin (Gm) antibiotic-loaded coralline Hydroxyapatite (HAp) are investigated. Following chemical characterization, mechanical properties of the coated samples were measured using nanoindentation and scratch tests to determine the elastic modulus, hardness and bonding adhesion between film and substrate. It was found that PLA biocomposite multilayered films were around 400nm thick and the influence and effect of the substrate were clearly observed during the nanoindentation studies with heavier loads. Scratch tests of PLA coated samples conducted at ~160nm depth showed the minimal difference in the measured friction between Gm and non Gm containing films. It is also observed that the hardness values of PLA film coated anodised samples ranged from 0.45 to 1.9GPa (dependent on the applied loads) against untreated coated samples which ranged from 0.28 to 0.8GPa.

Mechanical and biological properties of graded porous tantalum coatings deposited on titanium alloy implants by vacuum plasma spraying

Tantalum (Ta) has excellent mechanical properties, biocompatibility and chemical stability, and is more osteoconductive than titanium or cobalt-chromium alloys. However, it has a relatively high cost and is not easily fabricated. Accordingly, in the present study, a vacuum plasma spraying technique was used to deposit Ta powder in three successive layers on Ti6Al4V substrates. In the deposition process, the melting rate of the Ta powder was controlled by regulating the spray power and powder particle size in such a way as to form a coating with a porosity which increased from the inner layer to the outer layer. The Ta-coatings were processed by alkali treatment (AT), AT and heat treatment (AHT), and AHT with ultrasonic cleaning (AHT-UC), respectively. The average bond strength of the as-sprayed coating was approximately 54.5 ± 2.3 MPa. Moreover, the average porosity and roughness Ra of the coating surface were around 13% and 22.2 μm, respectively. The average porosity of the coating (with a thickness of 350–380 μm) increased from 0.6% in the inner layer to 7.6% in the outer layer. The corresponding hardness and elastic modulus (E) values decreased from 240 ± 20 to 167 ± 62 HV0.1 and 148 ± 5 to 123 ± 4 GPa, respectively. Bone-like apatite inducement tests performed in simulated body fluid (SBF) showed a particularly rapid growth of apatite on the AHT-UC Ta-coating due to the formation of amorphous sodium tantalate during AT. Furthermore, the results obtained from initial in vitro biocompatibility tests showed that osteoblast-like osteosarcoma MG-63 cells had a significantly better attachment and spreading on the Ta-coating and AHT-UC coating following culturing for 3 h than on the untreated Ti6Al4V sample. In other words, both coatings provided a better initial biocompatibility than the native Ti6Al4V substrate.

Enhanced Tribological, Electrochemical, and Biocompatibility Properties of Ti6Al4V Alloy Through Gas Nitriding and CN Coating Deposition

The tribological properties, electrochemical corrosion resistance, and biocompatibility performance of Ti6Al4V alloy were improved through a duplex surface treatment process consisting of high-temperature gas nitriding followed by amorphous carbon nitride (CN) coating deposition. The tribological properties of the specimens were evaluated using a reciprocating sliding wear tester, while the electrochemical properties were examined by potentiodynamic polarization tests. Finally, the biocompatibility of the samples was investigated by means of cytotoxicity tests performed using mouse leukemic monocyte macrophage cells (Raw 264.7). The duplex treatment significantly improved the tribological performance of the Ti6Al4V sample. In particular, compared to an untreated Ti6Al4V sample, the duplex surface treatment (CN-NTs) reduced the wear depth by around 55 times when sliding against a 316L counterbody and 16 times when sliding against a Ti6Al4V counterbody. Of the various specimens, the CN-T sample showed the best corrosion resistance, while the CN-NT sample showed the best biocompatibility performance.

Tribological performance, electrochemical behavior and biocompatibility of high-temperature gas-nitrided Ti6Al4V alloy

PurposeThis paper aims to investigate the tribology, corrosion resistance and biocompatibility of high-temperature gas-nitrided Ti6Al4V alloy.Design/methodology/approachThe tribological properties were studied by reciprocating wear tester. The corrosion resistance was evaluated by using potentiodynamic polarization test. The purified mouse leukaemic monocyte macrophage cells are used to investigate the biocompatibility.FindingsThe results show that the nitriding treatment leads to a significant improvement in the hardness and tribological properties of Ti6Al4V alloy. Specifically, compared to untreated Ti6Al4V, the hardness increases from 3.24 to 9.02 GPa, while the wear rate reduces by 12.5 times in sliding against a Ti6Al4V cylinder and 19.6 times in sliding against a Si3N4 ball. Furthermore, the nitriding treatment yields an improved corrosion resistance and a biocompatibility similar to that of untreated Ti6Al4V.Originality/valueThe nitrided Ti6Al4V alloy is an ideal material for the fabrication of load-bearing artificial implants.

Rapid surface nitriding of titanium alloy by a nanosecond fiber laser under atmospheric conditions

A modified surface layer using a Yb nanosecond fiber laser beam under atmospheric conditions was fabricated by applying a surface nitriding process on disc-shaped Ti–6Al–4V samples. On the generated surface, a melt layer comprising a TiN dendrite structure and a heat affected zone containing a needle-like α phase were detected. The modified layer exhibited optimal characteristics with the treatment at a laser output power of 12W, resulting in a hardness of 12GPa. The results of friction wear evaluation tests revealed that the layer exhibited superior abrasion resistance compared with an untreated Ti–6Al–4V substrate.