Application of high-frequency magnetron sputtering to deposit thin calcium-phosphate biocompatible coatings on a titanium surface

Thin calcium-phosphate coatings were deposited on titanium substrates by high-frequency magnetron sputtering. The elemental composition of coatings and types of chemical bonds were studied by Rutherford backscattering (RBS) and Fourier transform infrared spectroscopy (FTIR), respectively. An analysis of the IR spectra detected absorption bands caused by vibrations of phosphate PO ₄ ^3? groups and pyrophosphate H₂PO ₄ ^? anions, which are typical of apatites. The RBS results showed that the coating contains elements typical of calcium phosphates, i.e., Ca, P, and O; 45.4 ± 1.1, 3.6 ± 0.5, and 41.1 ± 0.7 at %, respectively. The Ca/P atomic ratio depends on sputtering conditions and varies in the range 1.7–4.0. The physicomechanical characteristics of the coatings and their solubility in a biological liquid were studied. The grown coatings can significantly reduce dissolution of substrates and extraction of dopants into the surrounding solution.     

Surface modification of pure titanium by hydroxyapatite-containing composite coatings

Micro-arc oxidation (MAO) is commonly applied to modify the surface of titanium (Ti)-based medical implants with a bioactive and porous Ti oxide (TiO₂) coating. The study reports a new method of incorporating hydroxyapatite (HA) within the TiO₂ coating by MAO and alkali heat treatment (AHT) in the solution containing Ca ion and P ion. The morphology, composition and phase composition of the coatings were analyzed with scanning electron microscopy with energy-dispersive X-ray spectrometer and X-ray diffraction. Surface topography and roughness of the coatings were investigated by atomic force microscopy operated in the tapping mode. The results showed that TiO₂-based coatings were obtained on pure Ti by MAO with an electrolyte containing Ca ion and P ion; the prepared MAO coatings were mainly composed of Ca, P, O and Ti. AHT transformed Ca and P to HA crystals. In conclusion, the TiO₂/HA composite coatings can be obtained on the surface of pure Ti by MAO and AHT, and the addition of Ca ion and P ion to the AHT solution contributed to the formation of HA.     

Deposition of titanium nitride and hydroxyapatite-based biocompatible composite by reactive plasma spraying

Titanium nitride is a bioceramic material successfully used for covering medical implants due to the high hardness meaning good wear resistance. Hydroxyapatite is a bioactive ceramic that contributes to the restoration of bone tissue, which together with titanium nitride may contribute to obtaining a superior composite in terms of mechanical and bone tissue interaction matters.The paper presents the experimental results in obtaining composite layers of titanium nitride and hydroxyapatite by reactive plasma spraying in ambient atmosphere. X-ray diffraction analysis shows that in both cases of powders mixtures used (10% HA + 90% Ti; 25% HA + 75% Ti), hydroxyapatite decomposition occurred; in variant 1 the decomposition is higher compared with the second variant. Microstructure of the deposited layers was investigated using scanning electron microscope, the surfaces presenting a lamellar morphology without defects such as cracks or microcracks. Surface roughness values obtained vary as function of the spraying distance, presenting higher values at lower thermal spraying distances.     

Formation and study of electrospark coatings based on titanium aluminides

Coatings containing Ti-Al intermetallics are fabricated by the electrospark deposition of titanium on aluminum and aluminum on titanium. The microstructure and composition of the grown coatings is studied by scanning electron microscopy, X-ray diffraction, and S-ray microanalysis. It is found that the surface layer formed in argon mostly contains the α-TiAl₃ intermetallic independent of the duration and frequency of discharge pulses. The γ-TiAl and α₂-Ti₃Al phases can be obtained by aluminum deposition on titanium followed by the subsequent deposition of a second titanium layer. Aluminum oxide and titanium nitride are additionally formed during the deposition of electrospark coatings in air.     

Characteristics of grain growth of microarc oxidation coatings on pure titanium

Grainy titania coatings are prepared by microarc oxidation on pure titanium （TA2） substrates in a Na2SiO3NaF electrolytic solution. The coating thickness is measured by an optical microscope with a CCD camera. Scanning electron microscope （SEM） and x-ray diffraction （XRD） are employed to characterize the microstructure and phase composition of coatings. The results show that the coating thickness increases linearly as the treatment time increases. The coatings are mainly composed of anatase and rutile （TiO2）. With the increase of treatment time, the predominant phase composition varies from anatase to rutile, which indicates that phase transformation of anatase into rutile occurs in the oxidizing process. Meanwhile, the size of grains existing on the coating surface increases and thus the surface becomes much coarser.     

Production of carbon-nitrogen coatings modified by titanium nitride

We offer a method of producing composite coatings based on carbon-nitrogen compounds modified by titanium nitride clusters. The structure of the material obtained is studied by transmission electron microscopy. A comparison between electron diffraction patterns from carbon-nitrogen and titanium-nitride modified coatings reveals the presence of a hexagonal syngony in the carbon-nitrogen condensate. The mech-anism of the modification effect on the structure and properties of the obtained coating is discussed.     

Oxidation of vanadium nitride and titanium nitride coatings

The oxidation of vanadium nitride (VN) and titanium nitride (TiN) coatings in ultra-high vacuum has been investigated in situ by X-ray photoelectron spectroscopy. On the VN coatings mixed oxide layers containing V³⁺ and V⁴⁺ species form at elevated temperatures (?600°C) and at high oxygen exposures, which cover completely the VN surface. Under similar oxidation conditions the TiN surface oxidises partially to a mixture of TiO₂ and Ti oxynitride (TiO_xN_y) phases. This oxidation behaviour has been correlated to the tribological properties of the VN and TiN coatings investigated recently.     

SEM and EDX studies of bioactive hydroxyapatite coatings on titanium implants

This work presents a study on an alternative coating method based on biomimetic techniques which are designed to form a crystalline hydroxyapatite layer very similar to the process corresponding to the formation of natural bone. The HA formation on the surface of titanium alloy pretreated with NaOH solution is investigated. Two types of solutions such as supersaturated calcification solution (SCS) and modified SCS (M-SCS) were used to investigate bone-like apatite formation on alkali-treated titanium. The hydroxyapatite deposits are investigated by means of scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The data suggest that the method utilized in this work can be successfully applied to obtain deposition of uniform coatings of crystalline hydroxyapatite on titanium substrates.     

Surface oxidation phenomena of boride coatings grown on iron

Single phase and polyphase boride coatings were grown on iron using B₄C-base powder mixures, oxidized for 1 h in gascous oxygen at temperatures up to 850°C and then studied by means of surface Mössbauer measurements, X-ray diffraction analyses and metallographic observations.     

Comparison of calcium phosphate coatings formed on femtosecond laser-induced and sand-blasted titanium

High energy femtosecond laser process was employed to create regular surface patterning on titanium while sand blasting treatment made a coarse surface. Both laser-induced titanium and blasted titanium could promote the formation of calcium phosphate compounds after the acid and alkali treatment, but little crystallized hydroxyapatite was grown on the laser-induced titanium in 1.5SBF only for 6 h, whereas Ca₄P₆O₁₉ was formed on the sand-blasted titanium. The femtosecond laser process together with common acid and alkali treatment might provide potential choice to enhance the biocompatibility of titanium and its alloys.     

Microhardness and refractive index of titanium dioxide-based binary coatings

Glass composites covered by sol–gel TiO₂–m Me _x O _y (Me _x O _y = ZnO, CdO, SnO, CuO, and Fe₂O₃ and m = 2, or 10 wt %) binary oxide coatings have been studied. The microhardness of the composites and glass substrate has been measured, and the microhardness of the coatings has been determined from these measurements. A correlation between the microhardness of the coatings, their refractive index, and packing density of disperse sol phase particles in the coating has been established.     

Development of novel titanium nitride-based decorative coatings by calcium addition

Calcium was added into titanium nitride coatings deposited using a hybrid magnetron sputtering-arc evaporation process. The calcium content in the films was adjusted by the variation of the pulsed DC current applied to the Ca sputtering target. X-ray diffraction analyses suggested that the increase of the calcium content induced the partial substitution of titanium atoms by calcium ones in the TiN lattice and a refinement of the grain size. Optical reflectance investigations showed that the absorption band of TiN was shifted towards higher wavelengths and that (Ti,Ca)N coatings may be suitable for decorative applications. Finally, the decrease of the film reflectivity was interpreted as a consequence of a free electron concentration decrease as confirmed from electrical resistivity measurements.     

A fibre-optic thermometric sensor based on the thermo-optic effect of titanium dioxide coatings

An experimental determination of the thermo-optic effect of titanium dioxide is described in which the test element is a thin film deposited onto the end face of an optical fibre. The film acts as an etalon. The reflectivity of titanium dioxide films was measured as a function of temperature experimentally over the range 20 °C to 500 °C, and modelled theoretically to yield a value of the thermo-optic coefficient of − 1.49 × 10⁻⁴ K⁻¹. The use of the data in the design of a thin-film optical fibre temperature sensor is described.     

Fluorescence correlation spectroscopy of CdSe/ZnS quantum dot optical bioimaging probes with ultra-thin biocompatible coatings

The colloidal stabilities and emission properties of CdSe/ZnS quantum dot (QD) optical probes capped with a variety of thin, hydrophilic surface coatings were studied using confocal fluorescence correlation spectroscopy. These coatings are based on mercaptoethanol, mercaptopropionic acid (with and without conjugated aminoethoxyethanol), lipopolymers (DSPE-PEG2000), cysteine (Cys), and a variety of Xaa-Cys dipeptides. The study shows that QDs with thin hydrophilic coatings can be designed that combine good colloidal stability and excellent emission properties (brightness). Furthermore, there is a general correlation between colloidal stability and brightness. The experiments reported illustrate that QDs with multiple types of thin coatings can be created for optical imaging applications in a biological environment while also maintaining a size below 10 nm.     

Shadow-casted ultrathin surface coatings of titanium and titanium/silicon oxide sol particles via ultrasound-assisted deposition

Ultrasound-assisted deposition (USAD) of sol nanoparticles enables the formation of uniform and inherently stable thin films. However, the technique still suffers in coating hard substrates and the use of fast-reacting sol–gel precursors still remains challenging. Here, we report on the deposition of ultrathin titanium and titanium/silicon hybrid oxide coatings using hydroxylated silicon wafers as a model hard substrate. We use acetic acid as the catalyst which also suppresses the reactivity of titanium tetraisopropoxide while increasing the reactivity of tetraethyl orthosilicate through chemical modifications. Taking the advantage of this peculiar behavior, we successfully prepared titanium and titanium/silicon hybrid oxide coatings by USAD. Varying the amount of acetic acid in the reaction media, we managed to modulate thickness and surface roughness of the coatings in nanoscale. Field-emission scanning electron microscopy and atomic force microscopy studies showed the formation of conformal coatings having nanoroughness. Quantitative chemical state maps obtained by x-ray photoelectron spectroscopy (XPS) suggested the formation of ultrathin (<10 nm) coatings and thickness measurements by rotating analyzer ellipsometry supported this observation. For the first time, XPS chemical maps revealed the transport effect of ultrasonic waves since coatings were directly cast on rectangular substrates as circular shadows of the horn with clear thickness gradient from the center to the edges. In addition to the progress made in coating hard substrates, employing fast-reacting precursors and achieving hybrid coatings; this report provides the first visual evidence on previously suggested “acceleration and smashing” mechanism as the main driving force of USAD.     

Investigation of the microstructure and properties of doped nanocomposite coatings based on titanium nitride

The special features of the elemental composition, structure-phase and elastically stressed states, and properties of coatings based on titanium nitride are investigated for different concentrations of Al, Si, Cu, Ni, Cr, and C doping elements using x-ray fluorescent analysis, x-ray microanalysis, dark-field electronmicroscopic analysis of the crystal lattice bending and torsion, microhardness measurements, and scratch tests. Influence of the structure and concentration of the doping elements on the relative fraction of nonmetallic atoms, crystal size, and phase composition of the coating is established. High values (several hundred degrees per micron) of the lattice bending-torsion with dipole configuration are established for nanocrystals with sizes smaller than 20 nm. Residual stresses in nanocrystals are estimated for the disclination model of the structural state. It is demonstrated that the increased degree of coating doping improves the thermal stability of their structure and properties.     

Study of coatings based on titanium oxides and oxynitrides using a set of methods

A set of methods has been applied to study the properties of titanium oxide and oxynitride coatings on steel. It is established that the coatings consist of two phases with a nanocrystalline and an amorphous structure with a high proportion (～50 %) of grain boundaries; anatase is the dominant crystalline phase. The obtained results can be applied in the development of coatings for stents as well as for manufacturing hydrogen accumulators.     

Microstructure and friction and wear behavior of laser boronizing composite coatings on titanium substrate

Three kinds of laser boronizing composite coatings were in situ synthesized on Ti substrate by using powders of B, BN and B₄C as starting materials. Microstructures of the laser boronizing composite coatings were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM); and their worn surface morphologies were also observed by using SEM. Moreover, the friction and wear behavior of the boronizing composite coatings under dry sliding condition were evaluated using a UMT-2MT friction and wear tester. It was found that all the three types of laser boronizing composite coatings had higher microhardness and better wear resistance than pure Ti substrate; and their microstructure and wear resistance varied with varying pre-placed powders of B, BN, and B₄C. Under the same dry sliding test conditions, the wear resistance of the three kinds of laser boronizing composite coatings, i.e., sample 1 prepared from pre-placed B, sample 2 obtained from pre-placed BN, and sample 3 fabricated from pre-placed B₄C, is ranked in an order of sample 1 > sample 2 > sample 3, which, surprisingly, well conforms to their order of hardness and friction coefficients.     

Interface adhesion properties of functional coatings on titanium alloy formed by microarc oxidation method

Three functional coatings (namely Al-C, Si-P-Al and P-F-Al coating) were fabricated by microarc oxidation method on Ti6Al4V alloy in different aqueous solutions. The microstructure, phase and chemical composition of coatings were investigated using scanning electron microscope, X-ray diffraction and energy dispersive spectroscopy. The interface adhesion failure mode of the coating is revealed by shear, tensile and thermal shock methods. The coatings exhibit high adhesion strength by the quantitative shearing test, registering as 110, 70, and 40 MPa for Al-C, Si-P-Al and P-F-Al coating, respectively. The tensile test of the coated samples shows that microarc oxidation treatment does not significantly deteriorate mechanical properties of substrate titanium alloy. The observations of the coating failure after subjected to the identical tensile elongation of 3.0% are well in agreement with those results of the shear test. The thermal cycle test indicates that all the coatings have good anti-thermal shocking properties.     

Composition and corrosion resistance of coatings on the basis of nitrides of titanium and chromium

Ti-Cr-N coatings were deposited on a low-carbon steel St3 substrate by overlapping of Ti and Cr plasma flows in residual nitrogen atmosphere using ion bombardment. Auger electron spectroscopy and X-ray diffraction were used to analyze the element and phase composition of the deposited coatings. It was established that, under constant deposition conditions (the arc current, gas pressure, bias voltage), coatings possess the fcc structure of a (Ti,Cr)N solid solution with uniform distribution of elements along the depth. The growth of the substrate bias voltage leads to an increase of titanium concentration in the coating due to changes in the interaction processes (condensation and sputtering) of the deposited materials with the substrate. Corrosion tests of the coatings and steel St3 were performed in acid (1 M H₂SO₄) and salt (3% NaCl) media. It was found that the corrosion processes progress less intensely in salt solution than in acid medium.