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There are various surface treatments used to modify titanium surfaces to render it bioactive. In this study commercially pure titanium surfaces (cp Ti), grade 2 were modified by acid etching (AE) and anodic oxidation (OA) in order to evaluate the bioactivity in vitro of these surfaces using the simulated body fluid (SBF). The AE was realized using a mixture of acids and AO using 1 mol.L-1 sulfuric acid. The anodic films were obtained under potentiostatic mode, during 60s using as anode a bar of titanium. All the surfaces that means cp Ti, AE and AO were analyzed concerning to morphology, rugosity, structural changes before in vitro bioactivity tests. It was observed by scanning electron microscopy (SEM) that all surfaces presented different morphologies: those with AE showed a surface with peaks and rounded valleys, with Ra = (564±80) nm, the oxidized surfaces with sulfuric acid showed a morphology with small pores uniformly distributed over the surface and Ra = (177±0,02) nm. X-rays diffraction results showed the presence of titanium hydride on the samples with AE and the anatase and rutile phases on the anodic films after heat treatment at 600°C/1h. Bioactivity tests in vitro using SBF at 37°C showed that small aggregates containing Ca and P were observed on surfaces with AE after 30 days soaked in SBF and the surfaces oxidized were fully coated with an apatite layer, identified by SEM.

In recent years, many surface modification processes have been developed in order to induce the osseointegration on titanium surface and thus to improve the implants' biocompatibility. In this work, Ti surface has been modified by shot blasting followed by anodic oxidation process in order to associate the good surface characteristics of both processes to obtain a rough and porous surface able to promote the titanium surface bioactivity. Commercially pure titanium (grade 2) plates were used on the surface treatments that were as follows: Shot blasting (SB) performed using alumina (Al2O3) particles, and anodic oxidation (AO) using NaOH electrolyte. The morphology, structural changes and the open-circuit potentials (OCP) of the surfaces were analyzed. It can be observed that an increase on the roughness of the blasted surface and a rough and porous surface happens after the AO process. The anodic film produced is thin and followed the blasted surface topography. It can be observed that there are small pores with regular shape covering the entire surface. X-ray diffraction results showed the presence of the anatase and rutile phases on the blasted and anodized surface after heat treatment at 600 °C/1 h. Concerning electrochemical measurements, when the different samples were submitted to open-circuit conditions in a physiological electrolyte, the protective effect increases with the oxidation process due to the oxide layer. When the surface was blasted, the OCP was more negative when compared with the Ti surface without surface treatments.

In this work, the resistance to scratch and wear (pin-on-flat) tests of five different porous TiO2 films were compared. Such tribological tests were carried out under dry conditions. The coatings were electrodeposited on commercially pure-Ti by anodic oxidation method in different electrolyte solutions at constant voltages. The scratch tests were conducted by applying increasing normal loads up to 400 mN. The coefficient of friction (COF) varied from 0.2 up to 0.5, and increased at larger penetrations depths. When the electrolyte concentration was changed from 0.5 into 1.0M H2SO4, the COF slightly decreased. Scanning electron microscopy indicated that the coatings produced in H2SO4/150V and Na2SO4/100V did not have their substrates revealed. In addition, the samples anodized in H2SO4/150V had the highest elastic recoveries. Therefore, such coatings seem to be more resistant to scratch tests than the others. The wear tests were carried out with Berkovich tip as counter-face under constant normal loads of 10 mN in 10 forward-backward cycles. The coatings deposited in H2SO4/150V had the lowest wear volume rates. The findings suggest that the porous Ti oxide coatings electrodeposited above their rupture voltages are more suitable to both scratch- and wear-resistance compared to those prepared at the lowest voltage (H2SO4/100V).

Titanium has been used in the production of dental implants and orthopedic prostheses due to the low tendency to corrosion and good biocompatibility. Meanwhile, the surface of titanium is not bioactive. Several surface treatments have been developed to make the surface of such metals bioactive. The aim of this work was to evaluate two of these modification processes in commercially pure titanium grade 2, both of them using NaOH solutions: the anodic oxidation and the alkali treatment. The surface morphology was evaluated by SEM/EDS, the crystal structure by XRD, and the mechanical properties and scratch resistance by instrumented indentation. The anodic oxidation (AO) was carried out using NaOH electrolyte 0.1 mol/L and constant current density of 150 mA/cm² for one minute. The alkaline treatment (AT) was performed by soaking the Ti sample in NaOH 5 mol/L solution at 60 °C for 24 hours; after this, the sample was heat treated at 600 °C for one hour in atmospheric air. The AO produced a TiO2 layer on Ti, whereas a thin sodium titanate layer was obtained by AT. Each surface modification resulted in a specific morphology, but both of them presented the increase in roughness as a common characteristic. The alkali treated Ti surfaces showed the lowest elastic modulus and hardness values. The largest increase in hardness between the treated surfaces was obtained for Ti after anodic oxidation. Scratch test indicates that the TiO2 film from AO has higher strength to tangential loading than the Ti substrate. In addition, for the Ti submitted to AT, the scratch test indicates that the modified surface layer has a poor adhesion with the substrate. Based on these results it is possible to conclude that, using NaOH solutions, Ti surfaces treated by anodic oxidation present improved mechanical properties than the alkali-treated ones.

Hydrogen diffusion is a well-known cause of embrittlement in titanium devices, however the use of H-implantation has been investigated to enhance the titanium biocompatibility and bioactivity. In the present study, effects of the hydrogen ion implantation on Ti and nitrided Ti through glow discharge are reported, focusing the surface tribo-mechanical response at nanoscale. The structural and chemical features were also evaluated, before and after the hydrogen implantation, by NRA, XRD, XPS, SEM and EDS. The hydrogen implantation increased the H content on Ti up to two times, promoted the formation of δ-TiH precipitates and changed the Ti oxidation state, without affecting hardness and elastic modulus. Hydrogen implanted after nitriding produced blisters, formed by H accumulation near the surface region of the nitride layer due to its barrier effect. A “denitriding” process at very near surface region was also observed after the hydrogenation. Nitriding increased Ti hardness by 120% and elastic modulus by 18%. Hydrogenation became the nitrided Ti harder and stiffer, increasing the hardness and elastic modulus by 180% and 41%, respectively. In both Ti and nitrided Ti, nanotribological tests pointed out that the surface became brittle after hydrogenation. On the other hand, the H-implantation had negligible effects on the Ti and nitrided Ti tribological behaviors in the tests performed under severe dry conditions.

Although titanium metal has been used intensively in the last years as biomaterial in the medical and dental areas its surface is not bioactive. In this work, titanium metal was submitted to an alkali treatment in order to make the metal surface bioactive. The samples were submitted to alkaline treatment (AT) using NaOH 5M aqueous solution at 60°C for 24 h and after that they were heated thermically to stabilize the layer obtained with AT. The bioactivity of the samples was evaluated soaking them into the simulated body fluid (SBF) at 36,5°C for 28 days. The morphological, structural changes and the electrochemical characterization were analyzed using scanning electron microscopy, x-ray diffraction and electrochemical impedance spectroscopy (EIS), respectively. It was verified that after AT plus heat treatment (HT) a sodium titanate layer was formed on the samples surface and after the bioactivity tests an apatite layer was formed. Impedance analysis show that the resistance of film on Ti is high and this value increases when the sample is soaked in SBF. It means that the apatite (HPA) film is occurring and the value of the capacitance with the presence of the HPA film (Cp) values indicate that the film maintain a compact and uniform characteristics.

Anodic oxidation is a promising technique to become titanium surfaces bioactive, by simultaneously changing the surface morphology, structure and chemical properties. Calcium and phosphorus based electrolytes were used to produce anodic films on c.p. Ti with two different current densities, 150 mA/cm2 and 300 mA/cm2. Morphology and structure were examined by SEM, EDS and XRD, and elastic modulus and hardness of the surfaces by instrumented indentation. Besides rutile and anatase TiO2 phases, hydroxyapatite was also identified on the films, as well as the segregation of very soft Ca and P-rich zones. Low values for the elastic modulus and hardness values close to the Ti corroborate to the applicability of Ca and P based TiO2 anodic films in biomedical titanium implants.

Porous TiO 2 coatings were produced on commercially pure Ti substrates by micro-arc oxidation (MAO) in 1.0 M H 2 SO 4 electrolyte for different anodizing times. Their mechanical properties were assessed by means of instrumented indentation, XRD residual stress measurements and scratch resistance tests. The rutile/anatase ratio increased from ~ 0 up to 84% in the 10–360 s anodizing time range, with further increase of coating thickness, porosity and roughness. Titania coatings produced for 180 and 360 s had poor adhesion and uneven surfaces with spontaneous detachment from the substrate. Coating hardness ranged from 3.5 up to 4.0 GPa (close to Ti), whereas the effective elastic modulus varied from 110 up to 120 GPa (19% lower than Ti), regardless of the substrate effects. Coatings exhibited tensile residual stresses, while the substrate compressive stress increased forming a plateau at about − 110 MPa for anodizing time longer than 60 s. The presence of such hardened layer beneath the interface improved the coating integrity in the scratch tests under the severe tribological condition, thereby increasing about tenfold the detachment critical load for the samples prepared in the 10–60 s MAO time range. Therefore, the 60 s anodizing time can be a useful reference line for producing mechanically resistant porous titania coatings.

Two different Ti oxide films produced by anodic oxidation were submitted to in vitro bioactivity and cell culture tests. The oxide films were produced in 1.0M H2SO4/150V and 1.0M Na2SO4/100V. Surfaces were found to be homogeneous and rough, with the presence of pores. Both oxide films presented anatase and rutile phases. Ti oxide film produced in Na2SO4 was rougher than the film grown with H2SO4 and composed of a rutile-rich phase. Both films were constituted by TiO2 and Ti2O3 oxides. Despite the differences observed, after 7 days, a calcium phosphate layer was precipitated on both surfaces. Indeed, these two treatment conditions seem to be efficient to spread and attach osteoblast-like cells within 4h.

Hydrogen embrittlement in austenitic stainless steels is restricted to the surface due to the low hydrogen diffusion in austenitic structures. The effect of three different nitriding processes: ion implantation (II), plasma immersion ion implantation (PI3) and glow discharge (GD), on the mechanical and structural properties of cathodically hydrogenated AISI 304 stainless steel were studied in the present work. Cathodic hydrogenation was made on untreated and nitrided samples. Surface microstructure after nitriding and hydrogenation was investigated by X-ray diffraction. Mechanical properties were measured by instrumented indentation. Surface crack formation and hardness decrease was observed in non-nitrided samples after cathodic hydrogenation. Hardness of nitrided samples decreases after hydrogen degassing but still has values higher than untreated samples. Comparative analysis of nitriding processes and working conditions indicated that glow discharge plasma nitriding process at 400 °C or 450 °C is the most adequate to avoid crack formation in steel surface after cathodic hydrogenation.

(2007). An evaluation of the behaviour of a zinc layer on a galvanised sheet, joined by MIG brazing. Welding International: Vol. 21, No. 4, pp. 271-278.

Osteoblast adhesion on metallic titanium coated with anodic films was evaluated. The anodic oxidation treatment was carried out on commercially pure-titanium (cp-Ti) substrate under the following conditions: 1.0M H2SO4/150V and 1.0M Na2SO4/100V. Osteoblast cells were cultured onto the samples for 4 hours. The morphologies of both Ti anodic films and cells were observed by scanning electron microscopy (SEM). The oxide films are rough with porous structure. Statistical differences in average surface roughness (Ra) values are found among both anodic films and substrate (abraded cp-Ti), measured by contact profilometry. The oxide films prepared in H2SO4 had greater contact angle, whereas there is no statistical significance between the values for the Ti anodic films produced in Na2SO4 and the substrate surface. Despite the some differences in morphology, roughness and contact angle between the treated and non-treated samples, cell morphologies were similar on all surfaces after 4h of culture. Further, was not clearly observed a correlation between the surface characteristics with cell behavior.

Hydrogen (H) embrittlement in austenitic stainless steels is restricted to the surface due to the low diffusion coefficient of H in face-centred cubic (fcc) structures. Depth-sensing indentation is a very important tool to investigate the mechanical properties of hydrogenated steels at near-surface regions. In the present work, the effect of glow discharge nitriding on the mechanical properties of steels submitted to cathodic hydrogenation was analyzed by instrumented indentation. Cracks are present at the surface after outgassing in the untreated sample. Hardness and elastic modulus are related to the nitriding process and charging time. Hardness of nitrided samples is higher at the near surface region. However, after hydrogenation, the hardness still increases, mainly due to the presence of martensitic phases. In nitrided samples, hydrogen and methane bubbles can be formed after hydrogenation, probably due to high hydrogen concentration under the nitrided layer. Load versus displacement curves in the ni...

Hydrogen effects in austenitic steels submitted to fatigue tests have been studied. Superficial H was introduced cathodically at 50 °C using 1N H2SO4 solution, a platinum counter electrode and a current density of 1000 A/m2 during 4 h. Internal H was introduced cathodically using a mixture of the salts KHSO4 and NaHSO4 at 200 °C during 60 h by applying a constant polarization potential of 850 mV with respect to a silver reference electrode. Fatigue tests were carried out by using a alternate flexion fatigue machine with stress ratio R values equal 1 and frequency of 50 Hz. The samples were tested until the fracture of the material was reached or until the stipulated fatigue limit life was reached. Results showed that superficial H introduced surface cracks during outgassing process while internal hydrogenation did not modify the superficial conditions. Mechanical tests showed that H reduced the fatigue life of these steels, and this effect was even more accentuated at lower stresses. Superficial hydrogenation presented inter and transgranular fracture and the morphology of the fracture remained ductile while internal H presented transgranular fracture and some regions with fracture by cleavage process.

Hydrogenation effects on the nanohardness of 304L/308L austenitic stainless steel joints have been studied. Surface cracks and α′ martensitic phase are nucleated during aging at room temperature (RT) and the nucleation kinetic depends on the hydrogen (H) outgassing time. Since these effects are confined on the superficial layers of the material, nanoindentation test is a powerful tool to analyze the region modified by H. The hydrogenation was performed cathodically at RT, during 4 h, using an electrolyte of 1 N H 2 SO 4 containing 100 mg l −1 of As 2 O 3 . A platinum counter electrode and a current density of 1000 A m −2 were used. In this work nanoindentation tests were performed as soon as the hydrogenation was interrupted and with the outgassing time varying up from hours to some days. It was observed that nanohardness have high values in the base and weld metal (WM) just after the hydrogenation process have been interrupted and that decreases with H outgassing time. After several days of outgassing time it was observed a significant decrease in hardness of base metal (BM) and WM when compared with a material without H.

The combination of shot blasting (SB) and micro-arc oxidation (or anodic oxidation--AO) in titanium surfaces was shown to provide enhanced conditions for cell differentiation and osseointegration than those provided by SB or AO alone. This study associated both methods aiming to attain titania layers on Ti with adequate tribo-mechanical features for bone implants. SB was performed using alumina particles, and titania layers were grown by AO using a CaP-based electrolyte. Mechanical properties and scratch resistance were characterized at nanoscale by instrumented indentation and nanoscratch, and correlated with morphological and microstructural changes (XRD, SEM, EDS, AFM, and profilometry). Analytical methods were employed to correct roughness and substrate effects on the indentation results. CaP-containing TiO2 layers were produced on AO and SB + AO. The latter presented small pore size and inhomogeneous layer thickness and Ca/P ratios, caused by the non-uniform surface straining by SB that affects the oxide growth kinetics in the electrochemical process. Elastic modulus of SB + AO layer (37 GPa) were lower than the AO one (45 GPa); both of them were smaller than bulk Ti (130 GPa) and close to bone values. The hardness profiles of AO and SB + AO were similar to the substrate ones. Because of the improved load bearing capacity and unique layer features, the critical load to remove the SB + AO titania coating in scratch tests was three times as much or higher than in AO. Results indicate improved mechanical biocompatibility and tribological strength of anodic titania layers grown on sand blasted Ti surfaces.

Rough and porous titanium oxide layers, which are important features for improving the osseointegration of Ti implants with bone tissues, are obtained through the technique of anodic oxidation. The thicknesses of such coatings are typically in the order of micrometers, and their mechanical characterization can be assessed by instrumented indentation, provided that the composite nature of the surface is considered. Titania anodic layers were produced on Ti under galvanostatic mode using Ca–P-based electrolytes (a mixture of (CH3COO)2Ca⋅H2O and NaH2PO4⋅2H2O), employing current densities ( J ) of 150 mA/cm2 and 300 mA/cm2. The structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy with electron dispersive X-ray spectroscopy (SEM/EDS), and profilometry, and the chemical features were characterized by X-ray photoelectron spectroscopy (XPS). TiO2 layers presented the crystalline phases rutile and anatase, and incorporation of Ca and P presented as a calcium phosphate compound. The porosity, roughness, and thickness increased with J . Analytical methods were employed to obtain the modified layers’ elastic modulus and hardness from instrumented indentation data, deducting the substrate and roughness effects. The elastic moduli were about 40 GPa for both values of J , which are similar to the values for human bones (10–40 GPa). The hardness decreased with indentation load, varying from 5 GPa at the near surface to 1 GPa at the layer–substrate interface. Such hardness behavior is a consequence of the surface brittleness under normal loading. Additional scratch tests using an acute tip indicated that the layer integrity under shear forces was 220 mN (J=150 mA/cm2) and 280 mN (J=300 mA/cm2). TiO2 layers produced with both current densities presented good results for in vitro bioactivity tests using simulated body fluid (SBF) solution, which can be attributed to a combined effect of the microstructure, layer porosity, and hydroxyl radicals in plenty at the near surface.