Papers by Keyword: Composite Coating

Abstract: The graphite/CaF₂/TiC/Ni-base alloy composite coating was prepared on the surface of 45 carbon steel by plasma spray. Effects of loads, friction counterparts and lubricants on the tribological properties of the composite coating were investigated. The results show that the wear rate of the GCTN composite coating against Si₃N₄ is 0.67×10^-3mm³/m, which is about 2 times that against GCr15 steel, because Si₃N₄ induces micro-cutting wear of the composite coating. Water and NaCl solution may induce increasing of friction coefficients and wear rates. Especially, wear rate of the GCTN composite coating in NaCl solution is increased by 3.1 times compared with those under dry sliding and water. The GCTN composite coating presents better anti-wear property than Ni-base alloy coating in different environmental mediums.

Abstract: AISI 304 stainless steel powder and Al₂O₃ powder was used to produce laser cladding composite coatings in order to improve the surface wear resistance of 45 steel. Microstructure of the composite coating was examined and analyzed by metallographic microscope. Microhardness and wear resistance of the composite under different scanning velocities were evaluated. The results show that the composite coating is composed of planar crystal, cellular crystal, dendritic crystal and fine equiaxed; the composite coatings under different technological parameters are made of the same phases, ferrite (α) and austenite (γ) phases. Microhardness of the composite is enhanced along with the increase of scanning velocity; effect of scanning velocity on wear loss of the composite coatings is not significant.

Abstract: TiB₂ and Gd₂O₃ were used as codeposited particles for the first time in preparing Ni-TiB₂-Gd₂O₃ composite coatings to improve its performance. Ni-TiB₂-Gd₂O₃ composite coatings were prepared by electrodeposition method from a nickel cetyltrimethylammonium bromide and hexadecylpyridinium bromide solution containing TiB₂ and Gd₂O₃ particles. The content of codeposited TiB₂ and Gd₂O₃ in the composite coatings was controlled by the addition of different TiB₂ and Gd₂O₃ particles concentrations in the solution, respectively. The effects of TiB₂ and Gd₂O₃ content on microhardness, wear weight loss, and friction coefficient of composite coatings were investigated, respectively. Ni-TiB₂-Gd₂O₃ composite coatings shows higher microhardness and lower wear weight loss, friction coefficient than those of the pure Ni coating and Ni-TiB₂ composite coatings. The wear weight loss of Ni-TiB₂-Gd₂O₃ composite coatings is lower 9.13 and 1.59 times than that of the pure Ni coating and Ni-TiB₂ composite coatings, respectively. The friction coefficients of pure Ni coating, Ni-TiB₂ and Ni-TiB₂-Gd₂O₃ composite coatings are 0.723, 0.815 and 0.43, respectively. Ni-TiB₂-Gd₂O₃ composite coatings shows the least friction coefficient among the three coatings. Gd₂O₃ particles in composite coatings serves as solid lubricant between contact surfaces, decreases the friction coefficient, abates the wear and increases the corrosion resistance of the composite coatings. The loading-bearing capacity and the wear-reducing effect of the Gd₂O₃ particles in the composite coatings are closely related to the content of Gd₂O₃ particles in the composite coatings.

Abstract: An arc-sprayed oxidation protective barrier coating system on austenitic stainless steel is composed of an inner Ni-Cr-Ti alloy layer and a pure aluminum outer layer. The high-temperature oxidation behavior of the coatings on 304N substrate was investigated during isothermal exposures in air at 1100°C. Experiments showed that interdiffusion of alloying elements within the protective coatings occurred, and the elements, Cr,Ni and Al, were also diffusing into the substrate metal. As test time proceeded, aluminum nitrides were generated in situ in the substrate, which had a layer-like distribution. The nitrides generated play the roles as element diffusion barriers, and together with the surface alumina they provide a long-term effective anti-oxidant protection to the steel substrate. The coatings on 304N substrate were not deteriorated and the substrate was protected well, being exposed to 1100°C for 350 hours. The analysis results of oxidation kinetics showed that the specific mass changes of the coated specimens were much smaller than those without coatings.

Abstract: Ni-TiB2-Gd2O3 composite coatings were prepared by electrodeposition method from a nickel cetyltrimethylammonium bromide and hexadecylpyridinium bromide solution containing TiB2 and Gd2O3 particles. The composite coatings were characterized with X-ray diffraction (XRD), atomic emission spectrometer (ICP-AES), scanning electron microcopy (SEM) and energy- dispersive analyses of X-ray (EDAX), respectively. That the codesposition of TiB2 and Gd2O3 into the coatings were demonstrated by XRD, EDAX, ICP-AES and SEM. TiB2 and Gd2O3 entered the lattice of Ni. The incorporation of TiB2 and Gd2O3 particles in the matrix can largely reduce the wear of the nickel composite coatings.

Abstract: In the present study, a surface layer of TiC-CNT hybrid compositecoating has been developed on low alloy steel (LAS) by using powder preplacement and tungsten inert gas (TIG) torch melting techniques.The weighed powder mixture with the content of 1.0 mg per millimeter square area and containing TiC-4wt. % CNT particles was preplaced on LAS surfaces using a suitable binder and then melted under the TIG arc with an operating current of 100 A and energy input of 1440 J/mm. The microstructural and microhardness characteristics of the processed composites coating were analyzed using SEM, EDXand Vickers microhardness testers. Under the melting condition used in this investigation, the arc completely dissolved the composite powder mixture that resolidifiedinto a melt track with radial marks and smooth surfaces. Themelt cross sections were hemispherical in shape and produced 1 mm deep hard coating layer which were free from porosity and cracks. SEM micrographs TiC-CNT hybrid coated surface glazed at 100A consists of fineprecipitated TiC in form globular and cubic dendrites and this is the reason for hardness increment to an average of three times greater than that of substrate value. The result obtained indicated that TIG arc melting process is applicable to generate resolidified layer of precipitated TiC microstructure with uniformly distribution in the coating region.

Abstract: Talc, with different particle sizes, was incorporated to improve flame resistance properties of UV-curable talc/acrylate composite flam-retardant coating at different contents via mechanical blending. Hardness, transmittance, haze, cross-cut adhesion and abrasion resistance results showed that the mechanical and thermal properties of the coatings improved effectively with no comprising on optical properties by adding Talc. The flame retardancy of the UV-curable coatings was investigated by thermogravimetric analysis (TGA) and Microscale Combustion Calorimeter (MCC). The results showed that the incorporation of Talc into the organic network led to an improvement in the thermal stability and flame retardancy of the coating materials. When talc content increased from 0 to 30 wt%, the peak heat release rate (PHRR) decreased from 191.1 W/g to 130.6 W/g, and the total heat release(THR) droped from 17.0 kJ/g to 11.1 kJ/g.

Abstract: Composite Ni/Al₂O₃ coatings were electrochemically deposited from a Watts bath modified with the organic additions of dioctyl sulphosuccinate sodium salt C₂₀H₃₇NaO₇S–(DSS) and 2,3-dihydroxy-1,2 benzisothiazol-3-one 1,1-dioxide C₇H₅NO₃–(LSA). The effect of different amount (50 and 100 g/l) of Al₂O₃ powder and organic additions on microstructure, microhardness, corrosion resistance and tribological properties was investigated. The coatings were examined by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) techniques. The electrochemical behaviour of the coatings in corrosive solutions (1 M NaCl and 1 M Na₂SO₄) was investigated by potentiodynamic polarisation. The tribological properties were investigated by the Taber abrasive wear test, a standard test often applied in industrial practice. The results show that Al₂O₃ particles are uniformly distributed in the composite coatings compared with coatings without organic additions. The addition of organic compounds also reduced the size of the forming nickel crystallites and improved the tribological and corrosion properties of coatings containing the dispersed hard particles of Al₂O₃ added in an amount of 50 g/l and the addition of organic LSA and DSS compounds.

Abstract: Plasma sprayed hydroxyapatite (HA) coatings on titanium alloy substrates have been used extensively due to their excellent biocompatibility and osteoconductivity. However, the low bonding strength between HA and Ti substrates is still problematic in the long-term implantation lifespan. In this paper, HA/Ta composite coatings with various Ta contents (20% and 60%) were fabricated by vacuum plasma spraying (VPS). The microstructure, phase composition of the coatings was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results revealed that the coatings had a rough surface and lamellar structure including some pores. ASTM C-633 standard was used for the measurement of bonding strength, which was found increasing with the increase of Ta contents in the composite coatings. The bonding strength of the composite coating containing 60% Ta (H4T6) reached to 37.2 MPa, which is about 1.9 times that of HA coating. In vitro bioactivity evaluated in simulated body fluids (SBF) showed that bonelike apatite layer was formed on the composite coatings surface, which indicated the good bioactivity of the HA/Ta composite coatings.

Abstract: The study involves a special class of composites called interpenetrating phase composites (IPCs). The Ti(Al,O)/Al2O3 composite was produced using high energy mechanical milling of a mixture of TiO2 and Al followed by a high temperature self-propagating reaction. Characteristics of the feedstock powder were improved by treating it with an organic binder. The feedstock powder was thermally sprayed on to a substrate using high velocity oxygen fuel (HVOF) and air plasma spraying methods. The spraying methods resulted in coatings with significantly different microstructures. Compared with plasma sprayed coating, the coating produced by a HVOF spraying method showed a much finer and densely packed microstructure.