Nanocomposite coatings composed of nanocrystalline grains of titanium carbide embedded in an amorphous carbon matrix, nc-TiC/a-C(:H), are widely studied due to their mechanical properties such as high hardness [1]. One of the main parameters that determines the final mechanical properties of nc-TiC/a-C(:H) coating system is the relative content of nanocrystalline and amorphous phase. Selective doping of this system by a non-carbide forming element such as nickel is a possible tool for influencing this parameter [2]. Hybrid PVD-PECVD process of titanium target sputtering in a mixture of acetylene and argon was used to deposit nc-TiC/a-C(:H) coatings [3]. Titanium-nickel (92.5 % Ti, 7.5 % Ni) target was used for preparation of nickel doped coatings. Varying acetylene flow rate was used in order to prepare coatings with different content of C in coatings. Several sets of Ni-free nc-TiC/a-C(:H) and Ni-dopped nc-TiC/a-C(:H) coatings were prepared and compared. Several different analyses were used for the determination of the influence of nickel doping on the properties of the deposited coatings. Composition of coatings was determined using EDX technique, the size of TiC grains and the lattice parameter was determined by grazing angle of incidence X-ray diffraction (GIXRD). Coatings were furthermore analyzed by X-ray photoelectron spectroscopy and Raman spectroscopy to determine and also to quantify the present bonds. Fischerscope H100 depth sensing indenter equipped with a Berkovich tip was used for evaluation of hardness of the coatings. Optical emission spectroscopy was used for analysis of properties of plasma during deposition process. There are only peaks corresponding to TiC and no peaks corresponding to Ni in the XRD difractograms. This suggests that that nickel atoms are bonded only in the TiC grains forming (Ti,Ni)C grains, as was proposed by Lewin [2]. The sizes of the TiC and (Ti,Ni)C grains as well as the lattice parameters obtained from XRD analysis exhibit almost no dependence on nickel content of the coatings in the studied range, although difference between the hardness of nickel-free and nickel-doped sets of coatings was observed. This research has been supported by the project CZ.1.05/2.1.00/03.0086 funded by European Regional Development Fund, project LO1411 (NPU I) funded by Ministry of Education, Youth and Sports of Czech Republic and GACR P205/12/0407 project.
Two aqueous solution methods have been developed for coating ceramic fibers with a film of yttria. The first utilizes the decomposition of urea in the presence of yttrium nitrate to yield yttrium basic carbonate (YBC). YBC precipitates heterogeneously forming a film. In the second method, a concentrated aqueous solution of yttrium nitrate, polyethylene oxide, and a commercially available wetting agent is prepared. Ceramic fibers are drawn through the solution, wetting the fiber with a film of the solution. The films are converted to yttria by heating in an oxidizing atmosphere. The film morphologies are characterized using scanning electron microscopy. The film constituencies are characterized using thin film x-ray diffraction spectroscopy. Limits to film thickness are explored.
Abstract Mechanical and fatigue properties of cold sprayed (CS) Cu20Sn bell metal were tested in order to assess the potential applicability of the technology to repair impact areas of church bells. The CS bell metal was compared to its traditional cast counterparts, a fine-grained Cu22Sn bell metal seen in small bells, and a coarse-grained Cu20Sn seen in large bells. Similar to other CS metals, it was shown that both the strength as well as the fatigue crack growth rates at low loading are similar to the cast materials. The fracture toughness of the CS material was comparable with the finegrained Cu22Sn bell metal, while both were significantly lower than the coarse-grained Cu20Sn bell metal. The impact damage rate of the CS material determined by a periodic impact test was significantly higher than the (finegrained) cast material. Both materials showed a stabilized, very slow damage rate after the relatively fast initial crater formation. The results presented in this paper identify CS as a feasible restoration technology for church bells, and the introduced methodology presents a characterization method for quantitative description of bell metal impact damage.
Abstract Impact testing appears as a most promising tool for gaining information on coating behavior in load-bearing applications. During dynamic impact test an indenter impacts successively the surface of the coating with constant force and frequency. The deformation of the coated specimen during impact testing is affected by the mechanical properties of both the substrate and the coating. Varying the impact load and the number of impacts, the evolution of coating surface deformation and contact fatigue failures can be observed. In the paper, the influence of dynamic impact load and number of impacts on the resulting impact crater volume and morphology is analysed, and the interpretation of the results in form of Wohler-like dependance is suggested and demonstrated on two types of HVOF sprayed Co-based alloy coatings. The low-number impact craters evolution and subsurface cracks propagation of HVOF sprayed Co-based alloy coatings is analyzed in more detail, by means of 3D optical microscopy and SEM. The results showed, that the higher ability to deform plastically increased the coatings dynamic impact fatigue lifetime. The cracks, responsible for coatings destruction, spread predominantly along the intersplat boundaries in the pile-up area.
