Characterization of electrolytic HA/ZrO2 double layers coatings on Ti–6Al–4V implant alloy

Hydroxyapatite (HA) coating was proved having bioactive property and hence improving the bonding strength on bone tissue without inducing the growth of fiber tissue. However, the weak adhesion between HA and metal implants is still the major problem. In this study, a novel method of electrolytic HA/ZrO₂ double layers coating was successfully conducted on F-136 Ti–6Al–4V implant alloy in ZrO₂(NO₃)₂ aqueous solution and subsequently in the mixed solution of Ca(NO₃)₂ and NH₄H₂PO₄. After annealing at 400 °C, 500 °C and 600 °C for 4 h in air, the coated specimens were evaluated by X-ray diffraction analyses, surface morphology observations, scratch tests, dynamic polarization tests, immersion tests and cell culture assays. In addition to corrosion resistance, the adhesion strength of electrolytic deposited HA on Ti alloy was dramatically improved from the critical scratch load 2 N to 32 N by adding the intermediate electrolytic deposition of ZrO₂, which showed the strong bonding effects between Ti alloy substrate and HA coating. Based on the cell morphology and cell proliferation data, HA/ZrO₂ double layers coating revealed the better substrate for the adhesion and proliferation of osteoblasts than the others. It was also found that the crystallization of HA had positive effect on the proliferation of osteoblasts.     

Enhanced biocorrosion resistance and biocompatibility of degradable Mg–Nd–Zn–Zr alloy by brushite coating

To further improve the corrosion resistance and biocompatibility of Mg–Nd–Zn–Zr alloy (JDBM), a biodegradable calcium phosphate coating (Ca–P coating) with high bonding strength was developed using a novel chemical deposition method. The main composition of the Ca–P coating was brushite (CaHPO₄·2H₂O). The bonding strength between the coating and the JDBM substrate was measured to be over 10 MPa, and the thickness of the coating layer was about 10–30 μm. The in vitro corrosion tests indicated that the Ca–P treatment improved the corrosion resistance of JDBM alloy in Hank's solution. Ca–P treatment significantly reduced the hemolysis rate of JDBM alloy from 48% to 0.68%, and induced no toxicity to MC3T3-E1 cells. The in vivo implantation experiment in New Zealand's rabbit tibia showed that the degradation rate was reduced obviously by the Ca–P treatment and less gas was produced from Ca–P treated JDBM bone plates and screws in early stage of the implantation, and at least 10 weeks degradation time can be prolonged by the present coating techniques. Both Ca–P treated and untreated JDBM Mg alloy induced bone growth. The primary results indicate that the present Ca–P treatment is a promising technique for the degradable Mg-based biomaterials for orthopedic applications.     

ZrO2/hydroxyapatite coating on titanium by electrolytic deposition

In this study, hydroxyapatite (HA) was coated on a titanium (Ti) substrate over a ZrO(2) layer by the electrolytic deposition method, this double layer coating was then compared with a single layer coating of HA. The HA layer was used to increase the bioactivity and osteoconductivity of the Ti substrate, and the ZrO(2) layer was intended to improve the bonding strength between the HA layer and Ti substrate, and to prevent the corrosion of the Ti substrate. The electrolytic deposition formed an HA layer with a thicknesses of approximately 20 mum, which adhered tightly to the Ti substrate. The bonding strength of the HA/ZrO(2) double layer coating on Ti was markedly improved when compared to that of the HA single coating on Ti. The improvement in bonding strength with the use of a ZrO(2) base layer was attributed to the resulting increase in chemical affinity of the ZrO(2) to the HA layer and to the Ti substrate. The osteoblast-like cells cultured on the HA/ZrO(2) coating surface, proliferated in a similar manner to those on the HA single coating and on the pure Ti surfaces. At the same time, the corrosion resistance of Ti was improved by the presence of the ZrO(2) coating, as shown by a potentiodynamic polarization test.     

等离子喷涂制备HA/ZrO2复合涂层

采用等离子喷涂技术,在Ｔｉ－６Ａｌ－４Ｖ基体上成功地制备了羟基磷灰石／氧化锆（ＨＡ／ＺｒＯ２）复合涂层,对涂层的微观结构,相组成和结合强度进行了研究,并以模拟体液试验评估涂层的生物活性,结果表明,复合涂层较有较为微观结构,ＨＡ／ＺｒＯ２复合涂层的结合强度明显高于ＨＡ涂层,ＨＡ／６０ｗｔ％ＺｒＯ２涂层的结合强度高达２８．５ＭＰａ,为ＨＡ涂层的２．２倍,复合涂层在模拟体液中浸泡一段时间后,表面覆盖一层     

Coatings of hydroxyapatite — nanosize alpha alumina composites on Ti-6Al-4V

Composites of hydroxyapatite (HA) and nanosize-alpha-(α)-Al₂O₃ with 5 wt.% CaF₂ were coated on Ti-6Al-4V rods by cold pressing and sintered in air or argon atmosphere at 1100 °C to improve the bonding between the metal and the ceramic. 25 and 40 wt.% α-Al₂O₃-5 wt.% CaF₂-HA composites gave the best results of strong bonding. 25 wt.% α-Al₂O₃-5 wt.% CaF₂-HA and Ti-6Al-4V showed the same thermal expansion coefficients. The thermal expansion coefficient of the 40 wt.% α-Al₂O₃-5 wt.% CaF₂-HA composite was slightly smaller than that of Ti-6Al-4V, which created a compressive stress on the coating, resulting in improved bonding between the metal and the ceramic.     

Effects of hydroxyapatite/Zr and bioglass/Zr coatings on morphology and corrosion behaviour of Rex-734 alloy

To improve corrosion resistance of metallic implant surfaces, Rex-734 alloy was coated with two different bio-ceramics; single-Hydroxyapatite (HA), double-HA/Zirconia(Zr) and double-Bioglass (BG)/Zr by using sol–gel method. Porous surface morphologies at low crack density were obtained after coating and sintering processes. Corrosion characteristics of coatings were determined by Open circuit potential and Potentiodynamic polarization measurements during corrosion tests. Hardness and adhesion strength of coating layers were measured and their surface morphologies before and after corrosion were characterized by scanning electron microscope (SEM), XRD and EDX. Through the SEM analysis, it was observed that corrosion caused degradation and sphere-like formations appeared with dimples on the coated surfaces. The coated substrates that exhibit high crack density, the corrosion was more effective by disturbing and transmitting through the coating layer, produced CrO₃ and Cr₃O₈ oxide formation. It was found that the addition of Zr provided an increase in adhesion strength and corrosion resistance of the coatings. However, BG/Zr coatings had lower adhesion strength than the HA/Zr coatings, but showed higher corrosion resistance.     

Hydroxyapatite coating on the Ti-35Nb-xZr alloy by electron beam-physical vapor deposition

The aim of this study was to investigate the hydroxyapatite coating on the Ti-35Nb-xZr alloy by electron beam-physical vapor deposition. The Ti-35Nb-xZr ternary alloys contained from 3 wt.% to 10 wt.% Zr content were manufactured by arc melting furnace. Hydroxyapatite (HA) coatings were prepared by electron-beam physical vapor deposition (EB-PVD) method, and crystallization treatment was performed in Ar atmosphere at 300 and 500 °C for 1 h. The coated surface morphology of Ti-35Nb-xZr alloy was examined by FE-SEM, EDX and XRD, respectively. In order to evaluate the corrosion behavior, the tests were performed by potentiodynamic, cyclic polarization and AC impedance test. All the electrochemical data were obtained using a potentiostat. The Ti-35Nb-xZr alloys exhibited equiaxed structure with β phase, the peak of β phase increased with Zr contents. The hardness and elastic modulus of Ti-35Nb-xZr alloys decreased as Zr content increased. The HA coated layer was approximately 150 nm and Ca/P ratio of HA coated surface after heat treatment at 500 °C was around 1.67. The HA thin film consisted of small droplets with spherical shape by crystallization. From the anodic polarization curves, HA coated and heat treated Ti-35Nb-10Zr alloy showed higher corrosion potential than other samples. HA coated film on the Ti-35Nb-10Zr alloy can be shown high polarization resistance by crystallization.     

等离子喷涂HA/Ti复合涂层研究 I.结构、组成和力学性能

采用等离子喷涂方法,在Ｔｉ－６Ａｌ－４Ｖ基体上成功地制备了ＨＡ／Ｔｉ复合涂层,并对复合涂层的微观结构、相组成和力学性能进行了研究．结果表明,ＨＡ和Ｔｉ两相均匀地分布于复合涂层中．ＨＡ／Ｔｉ复合涂层的结合强度明显高于纯 ＨＡ涂层,这主要是由于 ＨＡ／Ｔｉ的复合缓和了涂层与基体之间的热膨胀系数失配．ＨＡ／Ｔｉ复合涂层在模拟体液中浸泡一段时间后,结合强度没有明显降低．ＨＡ／Ｔｉ复合涂层的断裂韧性和硬度均高于 ＨＡ涂层．     

Plasma-sprayed zirconia bond coat as an intermediate layer for hydroxyapatite coating on titanium alloy substrate

This study aims to strengthen the bonding at HA coating/Ti–6Al–4V interface by adding an intermediate ZrO₂ bond coat between them. The bonding strength of the HA/ZrO₂ coating was evaluated with the separately prepared HA coating as control. The phase, microstructure and chemistry, and surface roughness of the plasma-sprayed two-layer HA/ZrO₂ coating on Ti–6A1–4V substrate were investigated by X-ray diffractometry, scanning electron microscopy, and surfcorder, respectively. Experimental results indicate that the bonding strength increases from 28.6±3.22 MPa for HA coating to 36.2±3.02 MPa for HA/ZrO₂ composite coating. Elemental analysis employed on the surface of ZrO₂ bond coat, on which the HA top coat was first dissolved completely in HCl acid, reveals the sign of diffusion of calcium ions from HA to ZrO₂ bond coat. In addition, rougher surface morphology provided by ZrO₂ bond coat is also considered to aid in the bonding at HA/ZrO₂ interface. Similar coating system done by other researchers is compared and discussed.     

In situ composite coating of titania-hydroxyapatite on titanium substrate by micro-arc oxidation coupled with electrophoretic deposition processing

In situ composite coating of hydroxyapatite (HA)/TiO₂ were produced on titanium (Ti) substrate by micro-arc oxidation coupled with electrophoretic deposition (MAO&EPD) technique with different concentrations of HA particles in the 0.2 M NaOH electrolyte solution. The surface morphology and chemical composition of the hybrid coating were effected by HA concentration. The amount of HA particles incorporated into coating layer increased with increasing HA concentration used in the electrolyte solution. The corrosion behavior of the coating layer in simulated body fluids (SBF) was evaluated using a potentiodynamic polarization test. The corrosion resistance of the coated sample was increased compared to the untreated Ti sample. The in vitro bioactivity assessment showed that the MAO&EPD treated Ti substrate possessed higher apatite-forming ability than the untreated Ti. Moreover, the apatite-forming ability had a positive correlation with HA concentration. In addition, the cell behavior was also examined using cell proliferation assay and alkaline phosphatase ability. The coating formed at HA concentration of 5 g/L exhibited the highest cell ability.     

Hydroxyapatite-anatase-carbon nanotube nanocomposite coatings fabricated by electrophoretic codeposition for biomedical applications

In order to eliminate micro-cracks in the monolithic hydroxyapatite (HA) and composite hydroxyapatite/carbon nanotube (HA/CNT) coatings, novel HA/TiO₂/CNT nanocomposite coatings on Ti6Al4V were attempted to fabricate by a single-step electrophoretic codeposition process for biomedical applications. The electrophoretically deposited layers with difference contents of HA, TiO₂ (anatase) and CNT nanoparticles were sintered at 800°C for densification with thickness of about 7–10 μm. A dense and crack-free coating was achieved with constituents of 85 wt% HA, 10 wt% TiO₂ and 5 wt% CNT. Open-circuit potential measurements and cyclic potentiodynamic polarization tests were used to investigate the electrochemical corrosion behavior of the coatings in vitro conditions (Hanks’ solution at 37°C). The HA/TiO₂/CNT coatings possess higher corrosion resistance than that of the Ti6Al4V substrate as reflected by nobler open circuit potential and lower corrosion current density. In addition, the surface hardness and adhesion strength of the HA/TiO₂/CNT coatings are higher than that of the monolithic HA and HA/CNT coatings without compromising their apatite forming ability. The enhanced properties were attributed to the nanostructure of the coatings with the appropriate TiO₂ and CNT contents for eliminating micro-cracks and micro-pores.     

等离子喷涂HA/Ti复合涂层研究 I.结构、组成和力学性能

采用等离子喷涂方法,在Ｔｉ－６Ａｌ－４Ｖ基体上成功地制备了ＨＡ／Ｔｉ复合涂层,并对复合涂层的微观结构,相组成和力学性能进行了研究。结果表明,ＨＡ和Ｔｉ两相均匀地分布于复合涂层中。ＨＡ／Ｔｉ复合涂层的结合强度明显高于纯ＨＡ涂层,这主要是由于ＨＡ／Ｔｉ的复合和了涂层与基体之间的热膨胀系数失配,ＨＡ／Ｔｉ复合涂层在模拟体液中浸泡一段时间后,结合强度没有明显降低,ＨＡ／Ｔｉ复合涂层的断裂韧性和硬度均高于Ｈ     

High emissivity coatings on titanium alloy prepared by micro-arc oxidation for high temperature application

Micro-arc oxidation coatings were prepared on Ti6Al4V alloy in Na₃PO₄-based electrolyte with different additives such as FeSO₄, Co(CH₃COO)₂, Ni(CH₃COO)₂, and K₂ZrF₆. The composition, structure, surface morphology, and chemical state of the coatings were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis system, and X-ray photoelectron spectroscopy, respectively. The spectral emissivity of the coating was measured by Fourier transform spectrometer apparatus. The bonding strength between the ceramic coating and substrate was studied by tensile strength test and shear strength test. The thermal shock resistance of the coatings was evaluated too. The results showed that the thermal emission of the coatings increased significantly with adding additives. The average spectral emissivity value of the coating with adding Co(CH₃COO)₂ is about 0.91 at wavelength of 3–20 μm. All the coatings showed a tensile strength higher than 30 MPa, and a shear strength higher than 10 MPa. In addition, after subjected to severe thermal shocking for 40 cycles, there was no peeling off of the coating occurred, the coatings possessed good thermal shock resistance.     

Corrosion and erosion behavior of iron aluminide (FeAl(Cr)) coating deposited by detonation spray technique

The electrochemical corrosion and erosion behavior of FeAlCr coating was reported in this article. The FeAlCr coatings were deposited by detonation spray coating system (DSC) by utilizing the gas atomized powder with a nominal composition of Fe-12Al-5Cr at two different pulse frequencies on mild steel (MS) substrate. Feedstock and coatings were characterized using XRD, SEM and elemental mapping. Nanoindentation tests using a Berkovich indenter indicate a hardness of 5.5 GPa and 4.9 GPa for the coatings deposited at 3 Hz and 6 Hz respectively as compared to 1.5 GPa of the substrate. Electrochemical corrosion tests were performed on coated samples in 3.5 wt% NaCl and 2 N H₂SO₄ media and are compared with the bulk MS substrate. Detonation pulse frequency significantly influenced the coating microstructure and corrosion performance. The coating deposited at a frequency of 6 Hz exhibited higher resistance against electrochemical corrosion in 3.5 wt% NaCl medium than the coating that was deposited at 3 Hz frequency. Solid particle erosion tests performed at room temperature (25 °C) and an impingement angle of 90° (normal incidence) using Al₂O₃ as the erodent medium demonstrate a higher erosion loss of the coatings than the bulk MS. On the contrary, at a temperature of 400 °C, the coatings exhibited notably better erosion resistance than the MS substrate, illustrating the potential of FeAlCr coatings for high temperature wear-corrosion resistant applications.     

The influence of heat treatment on the microstructural,mechanical and corrosion behaviour of cold sprayed SS 316L coatings

The present study evaluates the response of cold sprayed SS 316L coatings on mild steel substrate to aqueous corrosion in a 0.1 N HNO₃ solution as determined using polarization tests. The corrosion behaviour of the SS 316L coating was studied not only in the as-coated condition, but also after heat treatment at 400, 800 and 1,100 °C. Heat treatment reduced the porosity, improved inter-splat bonding, increased the elastic modulus and more importantly increased the corrosion resistance of the cold sprayed SS 316L coating.     

Alumina coating formed on medical NiTi alloy by micro-arc oxidation

Al₂O₃ coatings were prepared on NiTi alloy by micro-arc oxidation in an aluminate solution. Thin-film X-ray diffraction (TF-XRD) indicated that the coating consisted of only Al₂O₃ crystal phase. Energy dispersive X-ray spectrometer (EDS) showed that there was about 2.53 at.% Ni in the surface layer, which was greatly lower than that of NiTi substrate. Scanning electron microscopy (SEM) showed that the coating exhibited a typical porous surface and excellent adhesive interface between the coating and the substrate. Direct pull-off test showed that the coating had a mean coating-substrate bonding strength of 28 ± 2 MPa. The results of electrochemical impedance spectroscopy (EIS) study and potentiodynamic polarization test indicated that the corrosion resistance of the coated sample was increased by two orders of magnitude compared with uncoated sample.     

等离子喷涂制备HA/ZrO2复合涂层

采用等离子喷涂技术,在Ｔｉ－６Ａｌ－４Ｖ基体上成功地制备了羟基磷灰石／氧化锆（ＨＡ／ＺｒＯ_２）复合涂层,对涂层的微观结构、相组成和结合强度进行了研究,并以模拟体液试验评估涂层的生物活性．结果表明,复合涂层具有较为均匀的微观结构．ＨＡ／ＺｒＯ_２复合涂层的结合强度明显高于 ＨＡ涂层, ＨＡ／６０ ｗｔ％ ＺｒＯ_２涂层的结合强度高达 ２８．５ＭＰａ,为 ＨＡ涂层的 ２．２倍．复合涂层在模拟体液中浸泡一段时间后,表面覆盖一层碳酸磷灰石（ｃａｒｂｏｎａｔｅ－ａｐａｔｉｔｅ）,表明涂层具有良好的生物活性．     

A new method for preparation of direct bonding copper substrate on Al2O3

The oxygen content is usually difficult to control in direct bonding copper process. In this study a new method for preparation of direct bonding copper on alumina ceramic substrates was realized. 96% Al₂O₃ ceramic substrates were first oxidized by pasting a thin layer of Cu₂O and firing at 1150 °C in air. Then copper foil was bonded to the substrate by heating to 1070 °C in pure N₂ atmosphere. Microstructure and composition of the interface between the copper and Al₂O₃ ceramic were analyzed. The XRD and EDS results show that an interphase of CuAlO₂ was formed and a eutectic transformation between oxygen and copper took place at the interface of the copper and the ceramic substrate. The interface was much thicker than the traditionally bonded substrates, which resulted in a better bonding strength. The directly bonded copper alumina substrate samples showed no evidence of de-bonding after 50 thermal cycles comprising quenching from 220 °C to room temperature.     

Novel hydroxyapatite/tantalum surface coating for metallic dental implant

The aim of this study was to design and produce a novel surface composite coating on metallic substrate in order to improve the biocompatibility of metallic dental implant and the bone osteointegration simultaneously.Stainless steel 316L (SS) was used as a metallic substrate and a novel double-layer hydroxyapatite/tantalum (HA/Ta) coating was prepared on it. Tantalum coating was made using physical vapor deposition process and HA coating was produced using plasma-spraying technique on it. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were utilized to investigate the coating characterization. Electrochemical polarization tests were performed in two types of physiological solutions at 37 ± 1 °C in order to determine the corrosion behavior of the coated and uncoated specimens as indication of biocompatibility.The results indicated that the decrease in corrosion current density was significant for HA/Ta coated specimens and was much lower than the value obtained for uncoated 316L SS. The novel double-layer HA/Ta composite coating could improve the corrosion resistance and thus the biocompatibility of 316L SS dental implant.     

Nano-structural bioactive gradient coating fabricated by computer controlled plasma-spraying technology

The poor mechanical property of hydroxyapatite was the major problem for load bearing and implant coating in clinical applications. To overcome this weakness, a bioactive gradient coating with a special design composition of hydroxyapatite (HA), ZrO₂, Ti, bioglass was developed. This 120 μm coating with an upper layer of 30–50 μm porous HA produced by computer controlled plasma spraying which maintained energy level of the plasma which ensure proper melting of powder. The crystal size of the coating was 18.6–26.2 nm. Transformation of t-ZrO₂ to m-ZrO₂ reduced the thermal stress that weakened the coating and lowered down interfacial strength of the coating and metal substrate. Thermal stress of sprayed coating was 16.4 MPa which was much smaller than the sample without thermal treatment of 67.1 MPa. Interfacial strength between the coating and metal substrate was 53 MPa which is much higher than conventional Hydroxyapatite coating. Based on XRD analysis crystallinity of HA approached 98%. Therefore, high temperature treatment improved long term stability of the coating through improved crystallinity of hydroxyapatite and reduced other impure calcium phosphate phase.