Materials Science Forum Vols. 492-493

Abstract: Homogeneous and FGM environmental barrier coatings (EBC) made of alumina – NiCr on the steel substrates by high-velocity oxygen fuel (HVOF) spraying technique were studied. At room temperature, these coatings were characterized by DC polarization measurements and by electrochemical impedance spectroscopy (EIS) after various exposure times in highly aggressive basic solutions. At high temperatures (400-750°C) corrosion resistance was tested in respect to sulfide – sulfate – chloride – carbonate melts in air, which simulates environments in incinerators, kraft recovery boilers and turbines. After testing, the samples were examined by SEM and EDS and their corrosion resistance was compared.

Abstract: In the present work, iron doped TiO2 films were prepared by sol-gel method. An extensive study by varying the dopant quantity (0, 0.7, 1.4, 5 % wt Fe2O3 related to TiO2), the type of substrate (glass or ITO coated glass) and annealing temperature (300 and 500°C) was performed. The sol-gel process evolution was studied by viscosity measurements and the unsupported gels were analyzed by thermal analysis (DTA/TGA) and IR spectroscopy. The deposited films were characterized by spectroellipsometry (SE). The catalytic activity of the films was determinate by measuring the degradation rate of the salicylic acid used as a model organic substance. A complex influence of the investigated parameters on the photocatalytic properties of the TiO2 based films was established.

Abstract: NaX molecular sieve films on ceramic paper prepared by in-situ hydrothermal method were investigated. The NaX zeolite seed crystals of a uniform size of 5 µm were synthesized by hydrothermal method in a mother solution having a composition of 3.5Na2O : Al2O3 : 2.1SiO2 : 500~1000 H2O. These dip-coated NaX seed crystal on ceramic paper lead to further the thickness (20 ~ 100 µm) of NaX film on the substrate at 90°C for longer 3~7 days in autoclave. Pure zeolite films consisting of a continuous intergrown of 5~ 20 µm NaX crystal have been prepared on the substrates. The zeolite films were characterized by XRD, SEM, BET and XRF.

Abstract: Indium tin oxide (ITO) thin films were deposited on glass substrates via sol-gel spin coating process from a mixed solution of Indium (Ⅲ) acetylacetonate and Tin (Ⅳ) iso-propoxide. Then, ITO thin films were fired at 500°C, and then annealed at 500°C for 30 min with the sequential annealing process; Vacuum
N2
Ar/H2, N2
Ar/H2 and Ar/H2 gas. The effects of the different annealing processes on the surface morphologies and sheet resistance of ITO thin films were investigated. Sheet resistance values of ITO thin films treated under Vacuum
N2
Ar/H2, N2
Ar/H2 and Ar/H2 annealing process were 1.25 kohm/sq., 3.18 kohm/sq. and 4.92 kohm/sq., respectively. Actually, the sequential atmosphere gases and non-oxidizing gas, which were used in annealing process influenced the microstructural features or surface morphologies of ITO thin films: grain size and surface roughness. Thus, it was presumed that the sequential annealing condition influenced the densification behavior in the microstructural evolution of ITO thin films.

Abstract: Well-crystallized and nano-sized indium tin oxide (ITO) powders were prepared by a solvothermal process from a mixed solution consisting of indium nitrate and tin chloride. The characteristics of the solvothermally synthesized ITO powders were studied to investigate the contribution of the processing variables on the physico-chemical properties of powders. The results of this study show that the nano-sized blue ITO powders with a single phase could be directly obtained by changing the medium from water to organic solvent.

Abstract: Observations elsewhere have shown that multilayer structures with layers ~10 nm thick can be harder than monolithic ones. Here we see whether these effects can be observed at high temperatures and investigate the effect of temperature on the manner of deformation. The hardness of an AlN/CrN multilayer structure with a range of wavelengths from 6-200 nm has been measured at temperatures from room temperature to 400 oC. The changes in hardness have been related to the deformation behaviour observed by cross-sectional transmission electron microscopy and atomic force microscopy. These observations suggest that the mechanical properties of the coatings are dominated by the refinement in the columnar microstructure rather than directly by an effect of the layer interfaces on dislocation motion.

Abstract: Graded Al/AlTi and Al/Al-Si coatings are prepared by depositing nanoparticles with supersonic free-jet PVD (SFJ-PVD). The SFJ-PVD has been developed as a new coating method in which a coating film is formed by depositing nanoparticles with very high velocity onto a substrate. The high velocity of nanoparticles is produced by the supersonic gas flow of inert gas. A smooth, compact and defect-free microstructure is formed both at the interface between substrates and coating films and inside the coating films. The microstructures of Al/AlTi and Al/Al-Si coating films have very fine grain size. Mixing Ti and Al nanoparticles by depositing them onto a substrate produces in-situ syntheses of g-TiAl and a2-Ti3Al intermetallic compounds on the substrate. It is confirmed with nano-indentation hardness tester that graded coatings have graded hardness corresponding to the gradation of composition.

Abstract: This paper reflects our R&D results in the field of functionally graded coating processes. For industrial applications a special architecture for coatings is necessary: because the surface has to withstand environmental attacks, specific physical and mechanical functions and characteristics are required. In the interface region to the substrate additional stresses and strains occur due to the different materials combined. Consequently, the coatings have to be chemically and mechanically adjusted to the substrates. For this challenging problem, a concept named Materials Adapter has been developed within the frame of different research programs at MPA. For optimisation of the interface region an ion bombardment-activated inter-diffusion process ("ion mixing") was employed by using ion assisted electron beam PVD (IA EB PVD). Several Cr, Ti, Al and Zr coatings have been produced. An automated precursor inlet has been installed for CVD processes to obtain preset composition profiles for graded systems. Especially multilayer stacks of PyC-SixCy-SiC-Si3N4-Al2O3 have been deposited in a single growth process. The structure and composition of the coatings and interfaces were investigated by XRD, AFM, SEM, EDX, EPMA, ESCA and the micro-Raman spectroscopy. The characterisation confirms the gradual transition between Si and Cr, as well as between Cr and Al deposited by IA EB PVD and between C and Si grown by CVD.

Abstract: At present, milling of titanium based alloys for aerospace applications is mainly carried out with un-coated WC-Co carbide tools. The present work evaluates the chemical interaction of the Ti-6%Al-4%V alloy with these WC-Co commercial hardmetals. Strong decarburation induced by carbon diffusion to the Ti based alloy is observed at temperatures ranging from 750-1000°C. This reaction is responsible for the high adhesion found at the alloy-carbide interface. Different cathodic arc coatings have proved efficient in inhibiting such reaction and the associated adhesion to the Ti-6%Al-4%V alloy. Delamination induced by reaction between the Ti6Al4V alloy and AlTiN and TiAlCN coatings increases with the hot pressing temperature, being more severe for the AlTiN material. A lower bound of 44 J/m2 has been obtained for the interfacial fracture energy of cathodic arc PVD TiAlCN coatings on hardmetal substrates, this value being significantly higher than those previously reported for TiAlN materials.

Abstract: The influence of nanodispersed complex additives (ZrO2, Al2O3, W, WC, WC-Co, NbC, Si3N4) to SHS electrode materials on the mass transfer, structure and properties of electrospark coatings has been considered dependent on variation of the energy regimes of processing. The influence of the pulse discharge energy on the structure, composition, and properties of TRESS coatings has been studied. The optimum energy regimes of depositing high-quality multifunctional graded ESA and TRESS coatings have been found. It has been shown that introduction of nanodispersed complexes into electrode materials promotes improvement of the properties of ESA coatings.