Papers by Keyword: Nanostructured Coating

Abstract: The oxide layers on titanium were formed by plasma electrolytic oxidation technique in acid aqueous electrolytes containing sodium tungstate and copper acetate. The coatings with WO₃-CuO or WO₃-CuWO₄ oxide layers have been formed in the electrolytes with H₂C₂O₄ (pH~6) or H₂SO₄ (pH~4) accordingly. The coatings with WO₃-CuWO₄ have a developed surface architecture. The surface is constructed from coral-like structures with lamellar nanocrystals containing copper tungstate and tungsten oxide. The layers of tungsten oxide nanocrystals occupy the depressions between these structures. The band gap of the mixed WO₃CuWO₄ oxide layers is 2.8 eV.

Abstract: Nanostructured manganese-containing oxide coatings on titanium were formed by method of plasma electrolytic oxidation in tetraborate aqueous electrolyte containing manganese acetate with and without the acetonitrile addition. These oxide layers with high content of manganese and coated by ordered "leaf-like" mesh nanostructures are formed in the electrolyte without acetonitrile addition. The oxide layers are displayed high acitivity towards oxidation CO and photoactivity in the degradation reaction of methylene blue. The addition of acetonitrile into electrolyte results in the change in the morphology of the coating surface, a significant reduction in the manganese content and, as a consequence, practical loss of activity in the oxidation of CO in CO₂ and a reduction in the photocatalytic activity in the decomposition of methylene blue.

Abstract: The development of advanced materials is increasingly leading to integration of functions into materials and components. This drive in technological innovation is strongly felt in many traditional fields, like textiles or ceramics. Over the last twenty years, the so-called "traditional" ceramics industry for tile production has undergone a profound technological reorganization, both in production technologies and automation of the different production phases, but new products and possible new applications are still needed, thereby opening up new markets. In this paper a critical review of the industrial and scientific effort to obtain antibacterial and self-cleaning coating for ceramic tiles is reported. The main patents and scientific papers in the field are reported as well as some final results obtained by the authors on the evaluation of the durability of photocatalytic coating deposited on industrial ceramic tiles.

Abstract: Process parameters of nanostructured ZrO₂-7%Y₂O₃ coating during plasma spraying on the properties of the coating was optimized based on simulated annealing algorithm. BP neural network was applied to compute fitness of simulated annealing algorithm. A BP neural network model was built, four process parameters were input , the parameters included spraying distance, spraying electric current, primary gas pressure and secondary gas pressure, bonding strength of coating was output. Network was trained by orthogonal test data. Process parameters of coating were optimized by simulated annealing algorithm. The results show that maximal bonding strength of coating is 43.0377MPa. Process parameters for plasma spraying nanostructured ZrO₂-7%Y₂O₃ coating are spraying distance of 80mm, spraying electric current of 977.0283A, primary gas pressure of 0.3046MPa and secondary gas pressure 0.9886MPa.

Abstract: Process parameters of plasma spraying nanostructured Al₂O₃-13%TiO₂ (mass fraction) coating were optimized based on particle swarm optimization (PSO) algorithm. BP neural network was applied to compute fitness of PSO algorithm. A BP neural network model was built. Process parameters of coating were optimized based on PSO algorithm. The results shown that maximal bonding strength was 33.08MPa. Process parameters of plasma spraying nanostructured Al₂O₃-13%TiO₂ (mass fraction) coating were obtained. The results were superior to design of orthogonal optimization. It provided definite reference for selecting the best process parameters of plasma spraying nanostructured Al₂O₃-13%TiO₂ (mass fraction) coating.

Abstract: In this study TiC coating was formed on AISI-D2 steel by mechanical milling. In this regard, steel sample, balls and the powder were placed within a milling vial. Ball milling were carried out with annealed and quench-tempered samples using TiC powder having particle sizes of 44 and 200 μm for 5, 10, 15, 20, 50 and 100 h. During milling treatment, sample surface was exposed to high energy collisions and powder particles trapped between balls and sample adhered to the surface through cold welding. It was shown that the thickness and the structure of the coating depended on powder particle size; hardness and milling time. The thickness of the coating increased at first and decreased thereafter with milling time. The results showed that the substrate hardening decreased the thickness of the coating. Scanning Electron Microscopy (SEM) was employed to investigate the structural characteristics of the coatings. X-ray Diffraction (XRD) analysis was also conducted to determine the kind of phases in the coating. SEM investigations showed that the greatest thickness of the coating was reached after 20 h of milling. Furthermore, no new phases were detected in the XRD results after 100 h. It was shown that the thickness and hardness of coatings with coarse particle size were lower than that of the other. It was revealed that lattice parameter of TiC coating increased with milling time.

Abstract: In this study, conventional and nanostructured MCrAlY/ZrO₂-7wt.%Y₂O₃ double-layer thermal barrier coatings (TBCs) were fabricated on TiAl base intermetallic alloy substrates by the plasma spraying technique. The microstructural characterization and thermal insulation capability of the two types of coatings were comparatively researched. The results show that the conventional ceramic coating has a typical lamellar stacking characteristic. However, the nanostructured coating exhibits a bimodal microstructure, which is composed of both fully melted regions and partially melted regions (remained nanoparticles). The nanostructured TBCs has higher thermal barrier effect than the traditional one. The temperature drops of the nanostructured TBCs at 1100 °C increases 53% compared with that of the conventional TBCs.

Abstract: It has attracted very strong interests in enhancing the wear resistance of the TiAl intermetallic alloy. In this paper, both plasma-sprayed conventional and nanostructured ZrO₂-7wt.%Y₂O₃ thermal barrier coatings (TBCs) were prepared on TiAl alloy, and microhardness of coating were investigated. Meanwhile, the dry sliding friction tests on the substrate, the traditional coating, and the nanostructured coating were evaluated by ball-on-disk tribometer at room temperature. The results show that the microhardness of nanostructured coating is higher than that of the conventional one. Lower friction coefficient and higher wear resistance than the original TiAl alloy is achieved in the coatings under wear test conditions. Due to the existence of nanostructured microstructures, the nanostructured coating exhibits the lowest friction coefficient, and the best wear resistance. The wear mechanism of the original TiAl substrate is severe adhesive wear. However, the wear mechanisms of the TBCs are mild ploughing and severe adhesion.

Abstract: Nanostructured Al2O3-13wt.% TiO2 coatings were prepared by plasma spraying using agglomerated nanocrystalline powders via a spray drying method. The as-sprayed coatings and their worn surface were characterized using scanning electron microscope (SEM). The tribological characteristics were evaluated on block-on-ring configuration. It is found that that the nanostructured coating exhibited a unique bimodal microstructure, which has an important influence on the tribological characteristics. The abrasive wear resistance of the nanocoatings are greatly improved compared with the conventional coatings, and the abrasive wear mechanism is also discussed.

Abstract: Abstract. In this work, conventional and nanostructured Al₂O₃-13wt.%TiO₂ coatings were deposited by the plasma spraying technique. The microstructures of the two types of coatings were analyzed, and the solid particle erosion behaviors of the two coatings were comparatively researched in an erosion tester. Meanwhile, the erosion failure mechanisms of the coatings were discussed. The results show that the traditional coating has laminated structure and some pores. However, the nanostructured coating possesses a denser structure and not obviously lamellar-like structure, and exhibits a bimodal microstructure consisted of fully melted regions and partially melted regions. Owing to the compact microstructure and remained nano-particles, the nanostructured coating had a better erosion wear resistance than the conventional coating. Eroded morphology analysis indicates the main erosion mass loss of the coatings is attributed to lamellar spalling of the sprayed splats and fracture of brittle ceramic particles. In addition, the nanostructued coating has some impact craters and plough marks. In terms of the erosion mechanism, the conventional ceramic coating is dominated by brittle erosion, while the nanostructured ceramic coating is dominated by brittle erosion as well as ductile erosion to some extent.