Ternary hydroxyapatite/chitosan/graphene oxide composite coating on AZ91D magnesium alloy by electrophoretic deposition

In this work, ternary HA/chitosan/graphene oxide (GO) coating was applied via electrophoretic deposition on AZ91D magnesium alloy as bone implants, successfully. Subsequently, phase composition, surface morphology, hardness, corrosion behavior, bioactivity and antibacterial of the composite coatings were studied. Hardness and Young's modulus of the composite coatings increased from 40 ± 1.5 MPa and 3.1 ± 0.42 GPa to 60 ± 3.12 MPa and 8 ± 0.53 GPa for composite coatings with 0 and 2 wt% GO, respectively. The results of the SBF solution soaking of the composites after 24 days, indicated the improvement of HA growth due to the increasing of the GO addition in composite coating. New HA grains with leaf-like morphology grew uniformly at higher amounts of GO (1 and 2 %wt) in a perfectly balanced composition. Rate of the substrate corrosion significantly decreased from 4.3 to 0.2 (mpy), when the amount of GO increased from 0 to 2 wt% due to reduction of the surface cracks at the presence of the GO reinforcement. Also, there was no Escherichia coli and Staphylococcus aureus bacteria growth in broth medium after 24 h and OD₆₀₀ results at 24 h post inoculation for the 2%wt GO addition in coating.     

A novel biomedical TiN-embedded TiO2 nanotubes composite coating with remarkable mechanical properties,corrosion, tribocorrosion resistance,and antibacterial activity

Tribocorrosion is a severe problem in dental implants, artificial joints, and other implants, and it will affect the long-term safety of the implants. To improve the deficiencies of titanium alloys, we combined physical vapor deposition technology and anodic oxidation to prepare TiN to embed TiO₂ nanotube composite coatings (NTNTs-TiN). Results show that the hardness of the NTNTs-TiN composite coatings reaches 33.2 ± 0.6 GPa, and the grains of the composite coatings were further refined. The NTNTs-TiN coating has the smallest average coefficient of friction (0.22) during tribocorrosion. The tribocorrosion resistance of NTNTs-TiN coating in SBF is increased by ∼44 and ∼2 times compared with Ti6Al4V alloy and TiN coating, respectively. The capillarity effect of the lower contact angle of NTNTs-TiN can form a continuous water-lubrication film at the interface between the counter-ball and coating and produce a lubrication film composed of Ca, Mg, and P, which reduces the coefficient of friction significantly. The NTNTs/TiN composite coating exhibits the best synergistic effect of wear and corrosion. In addition, the NTNTs-TiN coating also exhibits excellent antimicrobial and corrosion properties, which provides a new solution for the long-term safe use of implants in the human body.     

A sol-gel based bioactive glass coating on laser textured 316L stainless steel substrate for enhanced biocompatability and anti-corrosion properties

In this study, we have synthesized a new family of bioactive glass (BAG) comprising of SiO₂, Na₂O, CaO, K₂O, P₂O₅ and MgO via sol-gel route. The composition of these oxides has been selected in such a way that the BAG has a coefficient of thermal expansion close to the 316L stainless steel (SS). In vitro test by soaking the BAG in simulated body fluid (SBF) showed good bioactivity due to ion exchange between alkali ions from the BAG and the ions present in the SBF. The 316L SS substrates were textured using laser before application of BAG using sol-gel dip coating. Pull off test showed that the adhesion strength in case of textured and non-textured surfaces were 4.2 MPa and 2.46 MPa, respectively. This implies that texturing of the surface is helpful in increasing the adhesion strength of the coating. The bioactive glass-coated textured surface of 316L SS substrate showed better corrosion resistance in SBF than the bare substrate for which the respective corrosion current densities were 35 nA/cm² and 353 nA/cm², thereby indicating that the single layer sol-gel dip coating of bioactive glass improved the corrosion resistance of the 316L SS implants. The analysis of scanning electron microscopy (SEM) images of the coating after immersion in SBF shows the formation and growth of the apatite layer that will further inhibit the corrosion of the substrate. These results demonstrate the potential of the synthesized BAG as a coating material for 316L SS implants.     

Synthesis of a novel nanostructured zinc oxide/baghdadite coating on Mg alloy for biomedical application: In-vitro degradation behavior and antibacterial activities

In this research, zinc oxide (ZnO) and zinc oxide/baghdadite (ZnO/Ca₃ZrSi₂O₉) were prepared on the surface of Mg alloy using physical vapor deposition (PVD) coupled with electrophoretic deposition (EPD). For this purpose, the nanostructured ZnO was prepared with a thickness of 900 nm and crystallite sizes of 64 nm as under layer while nanostructured baghdadite with a thickness of 10 µm was deposited on the Mg alloy substrate as an over-layer. Electrochemical measurement exhibited that the ZnO/Ca₃ZrSi₂O₉-coated specimen has a higher corrosion resistance and superior stability in simulated body fluid (SBF) solution in comparison with the ZnO-coated and bare Mg alloy samples. Antibacterial activities of the uncoated and coated specimens were evaluated against various pathogenic species (Escherichia coli, Klebsiella pneumoniae, and Shigella dysenteriae) via disc diffusion method. The obtained results showed that ZnO and ZnO/Ca₃ZrSi₂O₉ coatings have great zones of inhibition (ZOI) against E. coli, Klebsiella, and Shigella. However, less ZOI was found around the bare Mg alloy. Therefore, ZnO/Ca₃ZrSi₂O₉ is a promising coating for orthopedic applications of biodegradable Mg alloys considering its excellent antibacterial activities and high corrosion resistance.     

Corrosion behavior of TiN and TiN/Ti composite films on Ti6Al4V alloy in Hank’s solution

Surface films of TiN and TiN/Ti were deposited on Ti6Al4V alloy by arc ion plating (AIP). Open-circuit potential, potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) were employed to investigate the corrosion performance of TiN and TiN/Ti films in Hank’s simulated body fluid at 37 °C and pH 7.4. Scanning electron microscopy (SEM) was used to study the surface morphology of the corroded samples after the potentiodynamic polarization tests. The results show that the TiN and the TiN/Ti films can provide effective protection for the Ti6Al4V substrate in Hank’s fluid, and the TiN/Ti composite film showed a corrosion resistance superior to that of the TiN film. The outer TiN layer of the composite film mainly acted as an efficient barrier to corrosion during short-term experiments. In contrast to the bare Ti6Al4V, no pitting was observed on the surface of the TiN and TiN/Ti films deposited on the bare alloy after potentiodynamic polarization.     

Biodegradable magnesium alloy coated with TiO2/MgO two-layer composite via magnetic sputtering for orthopedic applications: A study on the surface characterization,corrosion, and biocompatibility

In this study, a coating of thin TiO₂ layer and a TiO₂/MgO double layer were created on the surface of AZ91D alloy by magnetic sputtering method in order to improve the corrosion and biocompatibility properties of this alloy. The microstructural studies by field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) showed that coatings were formed continuously and homogeneously on the alloy surface. In the double-layer coating, MgTiO₃ and Mg₂TiO₄ compounds were formed at the coating/substrate interface in addition to TiO₂ and MgO phases as the main phases in the coating structure. The results of corrosion test showed that in general, coating improves the corrosion of AZ91D alloy in simulated-body fluid (SBF). The double-layer coating showed the best corrosion resistance at a corrosion current of 5.743 × 10^?7 μA/cm² and a corrosion potential of ?1.513 V due to its cathodic protection of the substrate and blockage of the path of the corrosive solution towards the substrate. In vitro tests showed that considering the good match between the used materials as the coating and body, no toxic material exits which results in improvement in biocompatibility, adhesion, and bone-cell multiplication.     

Thermal treatment effect on the surface and in vitro corrosion characteristics of arc deposited TiN coating on Ti alloy for orthopedic applications

The influence of post thermal treatment at (500,600,700, and 800 °C) of cathodic arc physical vapor deposited TiN coated Ti6Al4V (Ti64) alloy was studied for orthopedic uses. The structure, surface characteristics, mechanical properties of coated and treated samples was investigated using XRD, FESEM/EDX, XPS, AFM, and micro indentation. The influence of post heat treatment on the in vitro corrosion-resistant behavior in a physiological medium was assessed by linear polarization, electrochemical frequency modulation, and impedance spectroscopic measurements. The results showed that a TiN layer of 5 ± 0.15 μm was formed over Ti64 alloy with higher microhardness and modulus compared to the bare substrate. The rutile TiO₂ oxide phase begins to form with the TiN at 500 °C, the TiO₂ phase intensity increased with the temperature, and the TiO₂ upper layer over the TiN film was formed at 700 and 800 °C. The microhardness and modulus were increased at 500 °C due to enhanced crystallinity of TiN, then decreased with increasing the temperature due to the internal stress relaxation of TiN and formation of the TiO₂ phase. The treated samples showed higher resistance to plastic deformation compared to the TiN coated and uncoated alloy. The sample treated at 500 °C showed the highest hardness, modulus, and resistance to plastic deformation. The obtained in vitro corrosion results indicated that post thermal treatment improves the corrosion resistance of TiN coated.     

In vitro biocompatibility of a nanocrystalline β-Ta2O5 coating for orthopaedic implants

To improve the durability and bioactivity of Ti–6Al–4V alloy used for medical implants, the β-Ta₂O₅ nano-crystalline coatings were introduced using double cathode glow discharge technique. The coating microstructure was characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The coating exhibits an assembly of near-equiaxed grains, locally aligned normal to the coating surface. The β-Ta₂O₅ coating exhibits strong adhesion to substrate and a strong resistance to deformation and cracking under applied loads. Cells culture tests showed that the coating is more beneficial to the adhesion and proliferation of NIH-3T3 cells as compared to the uncoated alloy. In-vitro bioactivity was evaluated by immersion of the coating in simulated body fluids (SBF) for different periods up to 14 days at 37 °C. The results indicated that bioactivity of Ti–6Al–4V was dramatically improved after the deposition of β-Ta₂O₅, since the coating has a higher apatite forming ability than the Ti–6Al–4V substrate. Finally, the electrochemical behavior of the β-Ta₂O₅ coating after soaking in SBF at 37 °C for 0, 3, 7, and 14 days was studied through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). EIS measurements also confirm that the presence of a hydroxyapatite layer on the coating becomes thicker and denser during soaking in SBF. Moreover, the coating exhibits better corrosion resistance than the bare alloy. Hence, the β-Ta₂O₅ coating is a promising candidate coating for protection of orthopedic implants with enhanced bioactivity and corrosion resistance.     

Tribological behaviour of RF-magnetron sputter deposited hydroxyapatite coatings in physiological solution

The aim of the paper is to explore the tribological performance of hydroxyapatite (HA) coatings deposited by radio frequency (RF) magnetron sputtering on AZ31 magnesium alloy (96% Mg, 3% Al, 0.7% Zn, 0.3% Mn) for biomedical applications. In this study, the position of the samples on a substrate holder, relative to a target erosion zone was taken into consideration in order to elucidate its impact on the coating characteristics, such as composition, morphology, surface topography and tribology. Substrate rotation and arc-movement were foreseen in the experimental set-up to increase the uniformity of thin film properties. The deposited HA thin films were revealed to exhibit an increase of the Ca/P ratio from 1.83 to 1.97, a decrease of (002) texture and thickness, as the samples were shifted towards the target erosion zone. By coatings, the roughness of Mg alloy was decreased (R_{a Mg alloy}=31.3 nm; R_{a coating}=29 nm and 21 nm). The coating placed in the centre of the substrate holder showed high hardness and Young's modulus (H =8.3±0.9 GPa; E=89±10 GPa) than the coating prepared under the target erosion zone (H =6.9±1.1 GPa; E=75±6 GPa). The coating deposited under target erosion zone exhibits superior friction behaviour in simulated body fluid environment, with the friction coefficient (μ) of 0.184, while the sample located in the centre of the substrate holder possesses the friction coefficient (0.306) comparable to the AZ31 substrate (0.307). The low wear rate was determined in the case of coating deposited under target erosion zone (4.83×10⁻⁵ mm³ N⁻¹ m⁻¹) than uncoated AZ31 substrate (0.00518 mm³ N⁻¹ m⁻¹) or than coating placed in the centre of the substrate holder (0.00294 mm³ N⁻¹ m⁻¹).     

Synthesis and characterization of Ni-W/TiN nanocomposite coating with enhanced wear and corrosion resistance deposited by pulse electrodeposition

To enhance mechanical properties and anti-corrosion capability of Ni-W alloy further, Ni-W/TiN nanocomposite coating has been co-deposited via pulse current co-deposition in this work. The effects of TiN nanoparticles and operating parameters on the structure and properties of the deposited coating were examined. It illustrated that the nanocomposite coatings are uniform, dense and crack-free, exhibiting dome-like or hill-valley like structure. The particles were homogeneously incorporated in the metallic matrix. RTC analysis indicated that the preferred orientation of Ni-W/TiN was (111) texture. The crystallite size was of 10–16 nm, indicating the formation of nanocrystalline structure. TiN concentration, duty cycle and frequency could influence the amount of TiN particle and W element in the coating, then regulating hardness and anti-wear behaviors. The low duty cycle and long deposition time could diminish the roughness of the coating. The inclusion of TiN nanoparticles in the nickel matrix could promote the nucleation of fresh nickel crystals and restrict the growth of already formed nickel grains, favoring the homogeneous growth and grain refinement of Ni-W crystals. The doped TiN particles would favor the preferred orientation (111) plane, enhanced the hardness, wear and corrosion resistance of Ni-W alloy. Electrochemical results illustrated that the best corrosion-resistant properties of the nanocrystalline coating could be obtained at TiN 30 g L⁻¹, duty cycle of 20% and frequency of 60–200 Hz. The enhanced mechanical properties and corrosion resistance of Ni–W/TiN coating benefits its application in harsh corrosive environment.     

Investigation of the tribological and biomechanical properties of CrAlTiN and CrN/NbN coatings on SST 304

This study examines the influence of thin layer coatings of CrAlTiN and CrN/NbN, deposited via physical vapor, on the biocompatibility, mechanical, tribological, and corrosion properties of stainless steel 304. The microstructure and morphology of the thin CrAlTiN and CrN/NbN layers were characterized by scanning electron microscopy (SEM), EDX, and X-ray diffraction. The pin on disc wear test was performed on bare and metal-nitride coated SST 304 under a 15 N load at 60 rpm and showed that the wear rates of the thin CrAlTiN and CrN/NbN film coatings were lower than the bare substrate wear ratio. The coefficients of friction (COFs) attained were 0.64, 0.5, and 0.55 for the bare substrate, CrN/NbN coating, and CrAlTiN coating, respectively. Nano indentation tests were also performed on CrAlTiN-coated and CrN/NbN-coated SST 304. The nanohardnesses and Young's moduli of the coated substrates were 28 GPa and 390 GPa (CrN/NbN-coated) and 33 GPa and 450 GPa (CrA1TiN-coated), respectively. For comparison, the nanohardness and Young's modulus of the uncoated substrate were 4.8 GPa and 185 GPa, respectively. Corrosion tests were conducted, and the behaviors of the bare and metal nitride-deposited substrates were studied in CaCl₂ for seven days. The corrosion Tafel test results showed that the metal-nitride coatings offer proper corrosion resistance and can protect the substrate against penetration of CaCl₂ electrolyte. The CrN/NbN-coated substrates showed better corrosion resistance compared to the CrAlTiN-coated ones. In evaluating the biocompatibility of the CrAlTiN and CrN/NbN coatings, the human cell line MDA-MB-231 was found to attach and proliferate well on the surfaces of the two coatings.     

Preparation of Strongly Adherent Platinum Coating by Double Glow Plasma Technology

Abstract

Strongly adherent Pt coating was deposited on Ti alloy substrates using double glow plasma technology. The polycrystalline Pt coating exhibited a preferred (220) orientation. The coating strongly adhered to the substrate, and the adhesive forces between the coating and substrate were all greater than 60 N. The hardness and elastic modulus of the coating were about 1.2 and 180 GPa, respectively. Adherent Pt coating had a better corrosion resistance than the bare substrate in terms of polarization curves. The bright Pt coating was still well bonded to the substrate after corrosion testing. This work suggested that strongly adherent Pt coatings on Ti alloy substrates can be used in industrial production processes.     

Wear and corrosion studies of duplex surface-treated AISI-304 steel by a combination of cathodic cage plasma nitriding and PVD-TiN coating

This work aims to improve the surface properties of AISI-304 austenite stainless steel by using duplex treatment of cathodic cage plasma nitriding (CCPN) and PVD-TiN, and the results are compared with individual treated samples. This combination of treatments is used to improve the inherent drawbacks of individual PVD deposited TiN, such as voids, cracks, and detachment of hard layer from steel due to significant differences in the hardness of steel and hard layer. The hardness of steel (1.9 GPa) is improved to 17 GPa, 12 GPa, and 22 GPa by using only TiN, CCPN, and duplex treatment. The only TiN deposited sample shows the formation of layer with intense diffraction peaks along (311) and (400) orientation, and its orientation changed with intense peaks along (111), (200), and (220) by using duplex treatment, which increases the hardness. Furthermore, the wear resistance is improved by all treatments, specifically by using duplex treatment. While using a ball-on-disc wear tester, the TiN layer is not detached from the substrate in the duplex treated sample, in contrast with the only TiN sample. Furthermore, the corrosion rates are reduced by using the duplex treatment and the appliance of plasma nitriding before the TiN fills the voids and cracks in layer, and thus, the duplex layer effectively prevents steel against corrosive environment. This study suggests that combining these treatments improves surface hardness, wear resistance, and corrosion resistance.     

Substrate effect on wear resistant transition metal nitride hard coatings: Microstructure and tribo-mechanical properties

Four types of different hard transition metal nitrides (TMN:ZrN, CrN, WN and TiN) coatings were deposited on Si (100) and 316LN stainless steel substrates using DC magnetron sputtering. A comprehensive study of microstructure and substrate dependent tribo-mechanical properties of TMN coatings was carried out. Higher hardness (H) and elastic modulus (E) were obtained for WN (H=40 GPa and E=440 GPa) and TiN (H=30 GPa and E=399 GPa) coatings. This is related to the formation of (100) and (111) preferred orientations in WN and TiN coatings, respectively. However, the less hardness and elastic modulus were obtained for ZrN and CrN coatings where (200) orientation is preferred. Remarkably, low friction coefficient (0.06–0.57) and higher wear resistance in the coatings deposited on steel substrates are directly associated with the higher resistance to plastic deformation (H³/E²) and the presence of intrinsic compressive stress. Three body wear modes enhanced the friction coefficient (0.15–0.62) and the wear rate in the coatings deposited on Si substrates. This is primarily associated with low fracture toughness of brittle single crystalline Si (100) substrates. Steel-on-steel contact was dominated in ZrN/steel sliding system. This occurs due to the severe adhesive wear mode of steel ball, whereas, the abrasive wear modes were attained for the CrN, WN and TiN coatings sliding against steel balls.     

Composite multilayered coatings on mild steel

A composite multilayered coating which consisted of an electrodeposited Zn–Fe alloy layer, a zinc phosphate conversion layer, and one, two, or three organic layers was deposited on a mild steel substrate. The adhesion between these multilayered coating and the mild steel substrate was studied with the aid of a scratch testing technique. Observation of the worn surface of different multilayered coatings was performed with the aid of metallurgical microscopy. The same multilayered coatings were examined with FTIR spectroscopy and X-ray diffraction techniques. Finally, the corrosion behavior of bare and multilayered coated mild steel in 0.1 M NaCl solution (pH = 5.5, T = 25°C) was studied.     

Microstructure and Selected Properties of Advanced Biomedical n-HA/ZnS/Sulfonated PEEK Coatings Fabricated on Zirconium Alloy by Duplex Treatment

In this work, sulfonated polyetheretherketone (S-PEEK)-based coatings, nanocrystalline ZnS and hydroxyapatite (n-HA) particles were developed on Zr-2.5Nb zirconium alloy substrates by electrophoretic deposition (EPD) combined with subsequent heat treatment. The properties of suspensions and deposition kinetics were studied. Cationic chitosan polyelectrolyte ensured the stabilization of the suspension and allowed for the co-deposition of all coating components on the cathode. The heating of the coated samples at a temperature of 450 °C and slow cooling resulted in sulfonation of the PEEK and the formation of dense coatings. The coatings were characterized by high roughness, hardness, modulus of elasticity and adhesion strength. The coatings revealed mild hydrophilicity, improved the electrochemical corrosion resistance of the alloy and induced the formation of hydroxyapatite with a cauliflower-like morphology on its surface during the Kokubo test. This work explored the great development potential of advanced sulfonated PEEK-based coatings, incorporating antibacterial and bioactive components by EPD combined with heat treatment to stimulate the surface properties of zirconium alloy for prospective dental and orthopedic applications. The antibacterial and osteoconductive properties of the obtained coatings should be further investigated.     

Influence of radio frequency magnetron sputtering parameters on the structure and performance of SiC films

Amorphous SiC films fabricated by Radio frequency (RF) magnetron sputtering have been widely used due to their excellent properties including high strength, good hardness and outstanding abrasion resistance. However, most researches set a lower target-substrate distance, which limits its large-scale coating for practical industrial application. In this work, the distance between the target and substrate was enlarged to 120 mm, and the effective coating area was about four to ten times than other researches. Furthermore, the effects of sputtering power, deposition pressure, substrate temperature and bias voltage on the structure and performance of SiC films were also investigated. Finally, SiC films with high elasticity modulus (310.8 GPa) and hardness (35.6 GPa) are obtained by RF magnetron sputtering.     

Corrosion resistance of poly p-phenylenediamine conducting polymer coated 316L SS bipolar plates for Proton Exchange Membrane Fuel Cells

The usage of conducting polymers as coating materials for bipolar plates to prevent corrosion is the recent trend in Proton Exchange Membrane Fuel Cell (PEMFC) technology. Paraphenylenediamine (pPD) monomer was electropolymerized to poly p-phenylenediamine (PpPD) over 316L SS. The characterization of PpPD, the conducting polymer coating, over 316L SS was done using attenuated total reflectance infra-red (ATR-IR) spectroscopy to confirm the formation of PpPD. The surface morphology and topography were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion protection performance of the coating was evaluated using open circuit potential (OCP) measurement, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies in PEMFC environment. EIS studies revealed that the charge transfer resistance for the coated substrates has increased by one order of magnitude than the bare substrate. Potentiodynamic polarization studies have registered lower corrosion current density by one order magnitude for the 0.06 M pPD coated substrate than the bare substrate and the polarization resistance values for the coated substrates have increased by two and a half time than the bare substrate. These results showed that PpPD coated substrates exhibited enhanced corrosion resistance in PEMFC environment.     

Syntheses of nano-multilayered TiN/TiSiN and CrN/CrSiN hard coatings

Nano-structured superhard coatings represent the state-of-the-art in the rapidly increasing worldwide market for protective coatings. In this study, the combination of nano-composite and nano-multilayered structures into the same coating was attempted. Nano-multilayered coatings of TiN/TiSiN and CrN/CrSiN were deposited on tool steel substrates by closed-magnetic-field unbalanced DC magnetron sputter ion plating. The coating structures were characterized using X-ray diffraction, atomic force microscopy, and scanning electron microscopy. Mechanical characterizations were performed including nano-hardness measurement, progressively-increasing-load scratch test, and wear test. TiN/TiSiN coatings have a nano-hardness of 40.2 GPa, whereas CrN/CrSiN coatings have a hardness of 30.9 GPa. TiN/TiSiN coatings also showed a higher critical failure force and scratch fracture toughness as well as better wear resistance and lower acoustic emission signal, indicating less total damage to the coatings.