ZrO2 Composite Coatings Research Articles

Effects of air annealing treatments on the microstructure, components, and mechanical properties of magnetron sputtered Al2O3–Cr2O3–ZrO2 composite coatings

To investigate the effects of air annealing on the microstructure, components, and mechanical properties of ceramic composite coatings, Al2O3–Cr2O3–ZrO2 composite coatings were prepared on silicon substrate using radio frequency magnetron sputtering at room temperature, and then air-annealed in a temperature range of 450–850 °C for 30 min. The results indicated that the phase-structure and superficial characteristics, including morphology and surface roughness, were not visibly altered in the annealed coatings up to 600 °C; the elemental component distributions remained uniform. The improvement in the mechanical properties was attributed to the growth of oxide grains. There were no significant changes in the components of Al, Cr, Zr, and O in the annealed coatings. However, an increase in the Cr component and a decrease in the Zr component occurred on the coating surface; the overall structure of the composite coatings possessed a favorable heat resistance. Upon annealing at 750 °C, the thermally-driven formation of uniform and refined nanoparticles on the coating surface was responsible for the effective enhancement of the mechanical properties. Furthermore, annealing at 850 °C induced the enlargement of the precipitated Cr2O3 nanoparticles and the generation of micro-defects, resulting in a drastic morphological evolution, an evident increase in the surface roughness, and a significant decrease in the mechanical properties. This study provides new perspectives on designing novel thermal barrier coatings and understanding the role of high temperature air annealing on the microstructural transformation.

Microstructure and Properties of Al2O3–ZrO2–Y2O3 Composite Coatings Prepared by Plasma Spraying

Al2O3–ZrO2–Y2O3 composite coatings were prepared by plasma spraying Al2O3–ZrO2 composite powder with varying amounts of Y2O3. The effects of Y2O3 on the microstructure and properties of the plasma-sprayed Al2O3–ZrO2 composite coatings were investigated, and the results showed that the composition of the composite powder had a significant influence on the microstructure and properties of the Al2O3–ZrO2–Y2O3 coatings. The Al2O3–ZrO2 and Al2O3–ZrO2–Y2O3 coatings were composed of yttria-stabilized zirconia (YSZ), α-Al2O3, and γ-Al2O3. The Al2O3–ZrO2–Y2O3 coating had a lower friction coefficient and wear rate compared with the Al2O3–ZrO2 coating. The Al2O3–ZrO2–Y2O3 coating showed the most uniform and compact microstructure, highest microhardness, good toughness, and adhesive strength when 3 wt.%Y2O3 was added. This method of adding rare-earth Y2O3 to improve the overall performance of Al2O3–ZrO2 coatings has potential application value.

Comparative Anticorrosion Performance of Electrochemically Produced Zn–NiO and Zn–NiO–ZrO2 Composite Coatings on Mild Steel

Zinc composite coatings of Zn–NiO and Zn–NiO–ZrO2 were produced by electrodeposition on mild steel using a Zn-sulphate bath. The homogeneous dispersion of the metal oxide nanoparticles for composite coating was achieved by magnetic stirring of the bath solution for about 6 h. The surface characteristics were examined by scanning electron microscopy supported by energy dispersive spectroscopy. The hydrophobic nature of the deposits has been determined by contact angle images of the deposits. The comparative corrosion resistive property of Zn, Zn–NiO and Zn–NiO–ZrO2 deposits was investigated by using a corrosion medium of 3.65% NaCl solution. The corrosion resistance performance of the coatings was analyzed by the Tafel polarization and electrochemical impedance spectroscopy.

Preparation and Properties of an Electroless Triple-Layered Ni-P Based-TiO2/ZrO2 Composite Coating

Preparation and Properties of an Electroless Triple-Layered Ni-P Based-TiO2/ZrO2 Composite Coating

Characterization of Cr–ZrO2 composite coatings electrodeposited from Cr(III) bath

The aim of this work was to incorporate ZrO2 particles into a Cr matrix within the research work aimed at obtaining metal matrix composite coatings (Cr–ZrO2) under direct current and to evaluate their protective properties. A Cr–ZrO2 composite coating was deposited from an electrolyte based on trivalent chromium sulphate with formate-urea as a complexing agent containing various concentrations of ZrO2. Cross-section investigations have revealed that ZrO2 particles incorporated into the Cr coating are uniformly distributed. The results indicate that ZrO2 particles influence the microhardness, morphology and corrosion behaviour of Cr–ZrO2 composite coatings obtained from the Cr(III) bath.

Preparation and characterization of Cu-Zro2 nanocomposite by DC method

Cu-ZrO2 nanocomposite coatings prepared by electrodeposition method. In bath solution containing different amount of ZrO2 were studied. The structure, surface morphology, mechanical and corrosion resistance properties of nanocomposite are characterized by varies techniques. Cu-ZrO2 composite coatings have higher micro hardness, compared to pure copper coating. Surface morphology of both Cu and Cu–ZrO2 composite coatings were examined through Scanning electron microscopy. The results show that more number of zirconia particles incorporated into copper matrix and then smooth surface, finer grain sized. The incorporation of ZrO2 particles reduces the particle size. It shows the closer particle-particle contact leads to pore free deposition. The X-ray diffraction was conformed the crystallite size and structure of the electrodeposited Cu and Cu–ZrO2 composite coatings. The average crystallite size calculated from Scherrer equation was ~105 nm for copper and ~67 nm for Cu-ZrO2 composites. The structure of electrodeposited Cu and Cu–ZrO2 composite coatings were crystalline orthorhombic which was confirmed from the JCPDS standard. The corrosion resistance behavior of Cu–ZrO2 composite is examined through Tafel polarization and impedance measurement studies in 3.5% NaCl. The result shows that the Cu–ZrO2 composite coatings have more corrosion resistance than pure Cu coating.

In-vitro bioassay of electrophoretically deposited hydroxyapatite–zirconia nanocomposite coating on Ti–6Al–7Nb implant

ABSTRACTHydroxyapatite–zirconia (HA–ZrO2) nanocomposite coatings were prepared on Ti–6Al–7Nb implant by electrophoretic deposition at constant voltage of 50 V. The influence of zirconia content on the phase transition, morphological evolution, wettability and in vitro cyto-compatibility, together with the bioactivity of the nanostructured coatings was examined. From the X-ray diffractometer patterns, a tangible increase and decrease in the peak intensity and width of the characteristic peaks were observed after subsequent sintering at 1000°C for 1 h under a constant flow of argon gas. The sintered HA and HA–ZrO2 composite coatings showed higher hydrophilicity than the bare substrate. From the in vitro bioassays, surface treatment of Ti67 implant by HA–ZrO2 nanocomposite coating increased the cell response as well as the apatite formability, in simulated body fluid within 5 days of incubation.

Electrodeposition and characterization of Ni–Mo–ZrO2 composite coatings

Ni–Mo–ZrO2 composite coatings were produced by electrodeposition technique from citrate electrolytes containing dispersed ZrO2 nanopowder. The influence of deposition parameters i.e. concentration of molybdate and ZrO2 nanoparticles in the electrolyte, bath pH and deposition current density on the composition and surface morphology of the coating has been investigated. The structure, microhardness and corrosion properties of Ni–Mo–ZrO2 composites with different molybdenum and ZrO2 content have been also examined. It was found that ZrO2 content in the deposit is increased by rising the nanoparticles concentration in the plating solution up to 20gdm−3. An increase in molybdate concentration in the electrolyte affects negatively the amount of codeposited ZrO2 nanoparticles. The correlation between the deposition current efficiency and ZrO2 content in the composite coating has been also observed. A decrease in deposition current efficiency leads to deposition of Ni–Mo–ZrO2 composite with low nanoparticles content. This may be explained by formation of higher amounts of gas bubbles on the cathode surface, which prevent the adsorption of ZrO2 nanoparticles on the growing deposit. The XRD analysis revealed that all the studied Ni–Mo–ZrO2 coatings were composed of a single, nanocrystalline phase with FCC structure. It was found that the incorporation of ZrO2 nanoparticles into Ni–Mo alloy matrix affects positively the microhardness and also slightly improves the corrosion properties of Ni–Mo alloy coating.

Incorporation of ZrO2 particles in the oxide layer formed on Mg by anodizing: Influence of electrolyte concentration and current modes

HypothesisThe objectives of the present study are to ascertain, particle incorporation during the initial stages of microarc oxidation (MAO), feasibility of increasing the level of particle incorporation through manipulation of process variables and, the use of MgO–ZrO2 composite coatings either as a pre-treatment or as a post-treatment for MAO coated Mg. ExperimentsAnodic oxide coatings were prepared using 0.3M NaOH+15g/l ZrO2 and 3M NaOH+15g/l ZrO2 at 10V under direct current, pulsed current (PC) unipolar and PC bipolar modes. MAO coatings were prepared using 5g/l NaOH+15g/l Na2SiO3 at 250V under direct current mode for 2min. FindingsThe study reveals that it is possible to incorporate ZrO2 particles in the anodic oxide layer, suggesting such a possibility during the initial stages of MAO. When the MgO–ZrO2 composite coating is used as a pre-treatment, it helps to reduce the size and density of the pores of the MAO coatings and increased the corrosion resistance. When it is used as a post-treatment, lamellar shaped Mg(OH)2 with a very high surface area is formed on the surface, which would be beneficial to impart a better bioactivity and to facilitate immobilization of biomolecules.

High temperature oxidation behavior of TiO2 + ZrO2 composite ceramic coatings prepared by microarc oxidation on Ti6Al4V alloy

Microarc oxidation (MAO) was used to prepare TiO2+ZrO2 composite coatings on Ti6Al4V alloy in Zr-containing electrolytes. The high temperature oxidation resistance and oxidation mechanism of MAO coatings were investigated and discussed. The composite ceramic coatings exhibit a porous structure with small pores (0.4–1μm in diameter) on the inner wall of larger pores, and consist of m-ZrO2 and ZrTiO4. In the case of static oxidation at different temperatures, the high temperature oxidation resistance of Ti6Al4V is improved 2–10 times after MAO treatment. The coated samples oxidized at different temperatures present various oxidation behaviors. A porous TiO2 layer forms after exposing oxidation at 500°C for 300h, while a continuous TiO2 layer forms after oxidation at 600°C for 75h. However, when the coated samples oxidized at 700°C and 800°C, a multilayer structure of MAO coating/transitional layer/TiO2 layer/TiN layer forms on Ti6Al4V with the combined effect of interface migration of MAO coating and air diffusion inward, and the diffusion of substrate elements outward. Especially, it is found that a TiN layer with preferential growth towards (111) lattice planes forms in the multilayer structure in coated samples, which is much different from the oxidation behavior of Ti6Al4V at 700°C and 800°C. The presence of multilayer structure can provide an efficient diffusion barrier, which restrains the growth of TiO2 and TiN.

Antibacterial effects of silver-zirconia composite coatings using pulsed laser deposition onto 316L SS for bio implants.

Bacterial invasion on biomedical implants is a challenging task for long-term and permanent implant fixations. Prevention of initial bacterial adherence on metallic implants is an important concern to avoid extracellular matrix (biofilm) secretion from bacteria that is resistant to antibacterial agents. In order to overcome this defect, recently, surface coatings such as zirconia (ZrO2) with higher smoothness have been shown to improve implants durability. In the present study, pulsed laser deposition (PLD) was used to deposit ZrO2 and silver (Ag)-ZrO2 composite coatings onto 316L stainless steel (316L SS). Phase purity, surface roughness and surface morphology, thickness of the coatings and elemental compositions of the coatings were analyzed using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). Total viable count (TVC) and epifluorescence microscopy analysis were studied to evaluate antimicrobial efficiency of ZrO2 and Ag–ZrO2 composite coatings using gram negative (gram −ve) Escherichia coli (E.coli) and gram positive (gram +ve) Staphylococcus aureus (S.aureus). On the basis of the present study, it could be speculated that ZrO2 coatings exhibited antibacterial activity against only E.coli, whereas Ag–ZrO2 composite coatings showed superior activity against E.coli and S.aureus strains.

Tribocorrosion characteristics of laser deposited Ti–Ni–ZrO2 composite coatings on AISI 316 stainless steel

The tribocorrosion characteristics of laser deposited titanium–nickel–zirconia composite coatings onto AISI 316 substrates have been investigated. Feedstock powders were blended at varying compositions and deposited onto AISI 316 using Nd:YAG high power laser beam at varying scan speeds. The relationships between laser speed, structure and tribocorrosion properties of the synthesised composite coatings were studied. The corrosion and tribocorrosion behaviour of the coatings was studied in 1M H2SO4 solution using a potentiodynamic polarisation technique. The coatings displayed fine and slightly porous structures with relatively well dispersed constituent elements. The Ti–Ni coatings deposited under 0.0067m/s had the highest corrosion resistance while addition of 5% zirconia to the Ti–Ni coatings significantly improved its tribocorrosion resistance.

Effects of manganese nitrate concentration on the performance of an aluminum substrate β-PbO2–MnO2–WC–ZrO2 composite electrode material

An Al/conductive coating/α-PbO2–CeO2–TiO2/β-PbO2–MnO2–WC–ZrO2 composite electrode material was prepared through electrochemical oxidation co-deposition on an Al/conductive coating/α-PbO2–CeO2–TiO2 substrate. The effects of manganese nitrate concentration on the chemical composition, electrocatalytic activity, and stability of the composite anode material were investigated using energy dispersive X-ray spectroscopy, anode polarization curves, quasi-stationary polarization curves, electrochemical impedance spectroscopy, scanning electron microscopy, and X-ray diffraction. Results revealed that the WC and nano-ZrO2 content in the β-PbO2–MnO2–WC–ZrO2 composite coatings increased with increasing manganese nitrate concentration. Moreover, the highest values of 6.61 wt% and 3.51 wt%, respectively, were achieved at 80 g L−1 manganese nitrate. PbO2 content decreased and MnO2 content increased with the increasing manganese nitrate concentration; both the descending and ascending trends were nonlinear. The Al/conductive coating/α-PbO2–CeO2–TiO2/β-PbO2–MnO2–WC–ZrO2 composite electrode obtained at 80 g L−1 manganese nitrate concentration in plating solution exhibited reduced overpotential for oxygen evolution (0.610 V at 500 A m−2), highest electrocatalytic activity, longest service life (360 h at 40 °C in 150 g L−1 H2SO4 solution at 2 A cm−2), and lowest cell voltage (2.75 V at 500 A m−2). Furthermore, the composite coating obtained with 80 g L−1 manganese nitrate had uniform crystal grains. The deposit formed was flat, dense, and crackless.

Ni–ZrO2 Composite Coating by Electro-Co-Deposition

In the present investigation Ni–ZrO2 metal matrix composite coatings were prepared on steel substrate using watt’s type solution through electro-co-deposition process with different weight percentages of zirconia powder dispersed in the bath. In the coating, nickel is present with faceted appearance along with ZrO2. The microhardness and wear resistance of the coatings increase with increasing weight percentage of particles content in the coating. The hardness of the resultant coatings was found to be 325 VHN for pure Ni coating whereas 401VHN for Ni–ZrO2 (15 g/l ZrO2) coating depending on the particle volume in the Ni matrix. The results also showed that the wear resistance of the composite coatings was improved as compared to unreinforced Ni deposited material. Strengthening of the coating was attributed to the ZrO2 dispersion and partially favorable texture.

Investigations on corrosion proceeding path and EIS of Ni–ZrO2 composite coating

Electrochemical impedance spectroscopy of Ni and Ni–ZrO2 composite coatings was studied. Investigation of corroded surfaces showed that the cluster boundaries in pure Ni and weak bonds between Ni matrix and ZrO2 particles in Ni–ZrO2 composite coating are the appropriate paths for corrosion to proceed. An equivalent circuit diagram based on blocked and partially corroded surface characterisations was proposed, and good agreement was observed between theoretical impedance spectra obtained on the basis of the equivalent circuit and spectra recorded during the measurements. Changes of microstructure and corrosion proceeding paths were recognised as the reasons for the higher corrosion resistance of Ni–ZrO2 with respect to pure Ni.

Formation of High Heat Resistant Coatings by Using Gas Tunnel Type Plasma Spraying

Zirconia sprayed coatings are widely used as thermal barrier coatings (TBC) for high temperature protection of metallic structures. However, their use in diesel engine combustion chamber components has the long run durability problems, such as the spallation at the interface between the coating and substrate due to the interface oxidation. Although zirconia coatings have been used in many applications, the interface spallation problem is still waiting to be solved under the critical conditions such as high temperature and high corrosion environment. The gas tunnel type plasma spraying developed by the author can make high quality ceramic coatings such as Al2O3 and ZrO2 coating compared to other plasma spraying method. A high hardness ceramic coating such as Al2O3 coating by the gas tunnel type plasma spraying, were investigated in the previous study. The Vickers hardness of the zirconia (ZrO2) coating increased with decreasing spraying distance, and a higher Vickers hardness of about Hv = 1200 could be obtained at a shorter spraying distance of L = 30 mm. ZrO2 coating formed has a high hardness layer at the surface side, which shows the graded functionality of hardness. In this study, ZrO2 composite coatings (TBCs) with Al2O3 were deposited on SS304 substrates by gas tunnel type plasma spraying. The performance such as the mechanical properties, thermal behavior and high temperature oxidation resistance of the functionally graded TBCs was investigated and discussed. The resultant coating samples with different spraying powders and thickness are compared in their corrosion resistance with coating thickness as variables. Corrosion potential was measured and analyzed corresponding to the microstructure of the coatings. High Heat Resistant Coatings, Gas Tunnel Type Plasma Spraying, Hardness,

Characterization of the Near-Eutectic Al2O3–40 wt% ZrO2 Composite Coating Fabricated by Atmospheric Plasma Spray. Part II: Microstructure and Mechanical Properties of Nanocomposite Coating

Near-eutectic Al2O3–40wt% ZrO2 coating composed of nano-polycrystalline structure with grain size of 20–50 nm and amorphous phase was deposited by atmospheric plasma spray (APS) using nano-sized powders obtained by sol–gel technique as feedstock. The phase composition and microstructure of as-sprayed coating were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), and high resolution transmission electron microscopy (HRTEM). Meanwhile, some mechanical properties such as micro hardness and cohesion of as-sprayed coating were also studied. The results revealed that the as-sprayed coating consisting of α-Al2O3, γ-Al2O3, and metastable t-ZrO2 was obtained with lower porosity about 7% and average microhardness of 726 kg/mm2 with higher Weibull modulus 16 as compared to the recently reported coating with the same composition. Furthermore, the results from a comparative study in scratching test indicated the present coating exhibited a higher cohesion than that of pure Al2O3 coating and Al2O3–40 wt% ZrO2 coating using spray-dried agglomerated powders as feedstock.

Electrodeposition of Ni–ZrO2 composite coatings and evaluation of particle distribution and corrosion resistance

The Ni–ZrO2 composite coatings were prepared by conventional electrodeposition method in Watts bath containing different amounts of ZrO2 to be codeposited. Pure Ni coating was also prepared as a comparison. The distribution and amount of the particles in the coatings were studied using an optical microscope, SEM, EDX, microhardness instrument and XRD. The results showed that with increasing ZrO2 concentration in the bath up to 90 g L−1, particle content in the coating increases. If concentration of ZrO2 surpasses 90 g L−1, ZrO2 content in the coating decreases, and distribution of the particles in the coating becomes non-uniform. Evaluation of corrosion behaviour showed that with increasing ZrO2 content in the coating, the corrosion potential shifted towards noble and positive values, and the corrosion resistance increased. The results revealed that the electroplated sample in the bath containing 90 g L−1 ZrO2 has the maximum particle content and the best corrosion resistance.

Study of Properties of Ni-Base Nano-ZrO<sub>2</sub> Composite Plating Coatings

The surface of copper plate of the mold need to be reinforced to obtain the plating coatings with high hardness and corrosion resistant properties. Nowadays, Ni-base alloy coatings is used widely in the industrial production. In order to raise the service life of mold, the experiments on the property of Ni-base nano ZrO2 composite plating coatings was done in this paper. The experiments were planned with the orthogonal test design method. The effective factors on the property of coatings, bath temperature, cathode current density, the distance between two electrodes and the magnitude of Nano-ZrO2,were experimentally studied. The optimum process parameter were obtained. The results show that the composite plating layer of Ni-base Nano ZrO2 with good properties can be obtained.The optimal conditions are as follows: the bath temperature is 40 °C, cathode current density is 3A/dm2, the distance between two electrodes is 12 cm, the magnitude of Nano-ZrO2 is 12g/L. In addition binding strength of the coatings were measured quantitatively, and the structure of the plating layer were observed with SEM. The layer with good properties can be obtained in this method.

Characterization of the Near-Eutectic Al2O3–40 wt% ZrO2 Composite Coating Fabricated by Atmospheric Plasma Spray. Part I: Preparation and Characterization of Nano Al2O3–ZrO2 Powder Using Sol–Gel Method

Al(NO3)3·9H2O, ZrOCl2·8H2O, and NH4OH solution were used as starting materials to synthesize Al2O3-40 wt% ZrO2 nano composite powder for plasma spraying by sol–gel method. The results showed that δ-Al2O3 and θ-Al2O3 transformed to α-Al2O3 gradually with the heating temperature rising from 900°C to 1200°C, and only α-Al2O3 existed when the temperature reached 1200°C, while m-ZrO2 and t-ZrO2 coexisted in the system. Meanwhile, the content of m-ZrO2 went up dramatically with the rise of heating temperature and holding time. When the xerogel was heated below 1100°C with the holding time lower than 8 h, the grain size of obtained powder was less than 100 nm. In addition, the grain size of composite powder was more than 100 nm and the growth rate of α-Al2O3 was much larger than that of t-ZrO2 when the heating temperature was raised to 1200°C.